Exploring Graphite-Based Thermal Greases For Optimal Microelectronic Device Cooling

Exploring Graphite-Based Thermal Greases For Optimal Microelectronic Device Cooling | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Exploring Graphite-Based Thermal Greases For Optimal Microelectronic Device Cooling Roman Shishkin, Vicktoria Arkhipova, Nina Zhirenkina, Zillara Fattakhova, and 1 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4690353/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 26 Sep, 2024 Read the published version in International Journal of Thermophysics → Version 1 posted 4 You are reading this latest preprint version Abstract The quest for effective thermal management solutions for microelectronic devices, catering to the escalating heat flows, necessitates innovative strategies. The significance of thermal interface materials, especially thermal greases, in minimizing thermal resistance within the "microelectronic device – heat-dissipating element" interface, has been widely acknowledged across industries such as microelectronics, aviation, and space engineering. Despite the promising reported values, a crucial consideration entails the method of ascertaining thermal conductivity, necessitating measurements in bulk samples to ensure accurate representations. Graphite, owing to its commercial accessibility and commendable thermal conductivity, emerges as a standout candidate for composite material development, as demonstrated in recent research. We observed that the use of graphite-based fillers, particularly in the form of well-crystallized graphite particles, effectively reduced processor temperatures and enhanced thermal conductivity, outperforming industrially utilized thermal pastes. Our findings accentuate the potential of these materials in contributing to the development of cutting-edge composite materials for microelectronics, highlighting their high prospects for future applications in high-performance devices. thermal interface materials thermal grease graphite carbon thermal conductivity Raman spectroscopy Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 1. Introduction The escalating heat dissipation demands of modern microelectronic devices necessitate the development of effective thermal management solutions. A critical factor influencing the overall thermal resistance of the "device-heat sink" system lies in the thermal interface between the components. Air gaps formed at the interface due to micro-roughness significantly impede heat transfer. Thermal interface materials (TIMs), such as thermal greases, are employed to fill these voids and improve thermal contact [ 1 ]. While TIMs are widely used across various industries, including microelectronics, aerospace, and space engineering [ 2 ], conventional thermal greases often fall short in meeting the stringent requirements of advanced microelectronic devices. Computational modeling studies have shown that thinner TIM layers require lower thermal conductivity values to achieve optimal operating temperatures under natural convection conditions [ 3 ]. However, commercially available thermal greases such as KPT-8, possessing a thermal conductivity of 0.8 W·m − 1 ·K − 1 , are insufficient for effective heat dissipation in microelectronic devices. This necessitates the exploration of novel materials and approaches for developing polymer-matrix composites with enhanced thermophysical properties [ 4 , 5 ]. Numerous materials are being investigated as potential TIM fillers, including AlN, Al 2 O 3 , BN, and various forms of carbon [ 1 , 4 – 6 ]. However, achieving high thermal conductivity often requires the use of hybrid fillers, incorporating materials with diverse morphologies, sizes, or chemical compositions [ 7 ]. Examples include composites containing 82.76 vol.% of Galinstan-coated (alloy of Ga 78.3 at. %, In 14.9 at. %, Sn 6.8 at. %) aluminum oxide particles in a polymer matrix, reaching a thermal conductivity of 6.23 W·m − 1 ·K − 1 [ 8 ], and epoxy-based composites with structured boron nitride flakes, demonstrating thermal conductivity values exceeding 10 W·m − 1 ·K − 1 along the particle alignment axis [ 9 , 10 ]. Additionally, composites incorporating metallic silver and boron nitride nanofibers on aramid nanofibers have achieved a thermal conductivity of 9.44 W·m − 1 ·K − 1 [ 11 ]. Carbon materials, including graphite, diamond, nanotubes, and graphene, have garnered significant attention due to their exceptional thermal conductivity and low density [ 12 , 13 ]. For instance, silicone rubber filled with structured and pre-vulcanized graphite, achieved through hot pressing, exhibits a thermal conductivity of up to 13.93 W·m − 1 ·K − 1 along the graphite particle alignment axis [ 14 ]. Furthermore, infiltration of a pre-built array of carbon nanotubes with polydimethylsiloxane has resulted in thermal conductivities exceeding 4.0 W·m − 1 ·K − 1 along the nanotube axis [ 15 ]. The melt stirring method has been employed to produce carbon fiber/olefin block copolymer composites with thermal conductivities reaching 15.06 W·m − 1 ·K − 1 [ 16 ]. Despite the high thermal conductivity values reported in literature, it is crucial to note that these measurements are typically conducted on thin-film materials. Direct determination of thermal conductivity relies on measuring the temperature gradient across a sample at a known heat flux [ 3 , 17 ]. With thin samples and high thermal conductivity, the temperature gradient can approach zero, leading to overestimated thermal conductivity values. Therefore, accurate thermal conductivity measurement necessitates using bulk samples of composite materials with a sufficient thickness to establish a plateau where the temperature gradient remains consistent regardless of sample thickness [ 3 ]. Given its widespread commercial availability and respectable thermal conductivity, graphite emerges as a promising candidate for use as a filler in composite materials for thermal interface applications. Previous research [ 18 ] has demonstrated that the incorporation of ground, low-ash graphite powder (GMZ) into thermal greases can achieve a thermal conductivity of up to 2.85 W·m − 1 ·K − 1 , surpassing the values reported for diamond, copper, aluminum, aluminum oxide, and nitride. Furthermore, a mixture of graphite and aluminum nitride has achieved a thermal conductivity coefficient exceeding 3.02 W·m − 1 ·K − 1 [ 3 ], indicating its potential for further investigation. Despite the extensive variety of commercially available graphite and technical carbon materials, the optimal selection for the production of highly efficient thermal greases remains elusive. This work aims to systematically investigate the structural and morphological characteristics of various carbon and graphite powders, with varying production methods, particle sizes, and phase compositions, and assess their impact on the thermal conductivity of graphite-polydimethylsiloxane composite materials. This comparative study seeks to establish a comprehensive understanding of the relationship between the properties of different carbon materials and their performance as fillers in thermal interface applications. 2. Materials and Methods 2.1 Raw materials and composites production: The graphite and carbon powders investigated in this study are summarized in Table 1 . Approximately 2 grams of polydimethylsiloxane (PDMS-1000) was carefully weighed and placed in a porcelain mortar. Graphite or carbon powder, selected from one of the trademarks listed in Table 1 , was then gradually added to the binder in small portions. Thorough mixing was performed until a homogeneous grease-like consistency was achieved. The mass of the graphite or carbon powder used was meticulously recorded to enable subsequent calculations of the mass and volume fractions. The resulting compositions are presented in Table 2 . 2.2 Methods Phase composition and structural analysis of the powders were conducted using a Shimadzu XRD 7000 diffractometer (Shimadzu, Japan). CuKα radiation (λ = 1.5418 Å) was employed to obtain diffraction patterns in the angular range of 10° to 80°, with a step size of 0.03° and a scanning rate of 5 seconds per point. Crystalline size was determined from the XRD data using the modified Scherrer equation as described in [ 19 ]. The morphology of the powder particles was investigated using a JEOL JSM 6390LA scanning electron microscope. Particle size measurements were performed based on the SEM images, analyzed using ImageJ software. Low-temperature nitrogen adsorption-desorption isotherms were obtained at -195°C using a Gemini VII automatic analyzer, adhering to the ASTM C1274-10 standard. The measurements were conducted with an error tolerance of no more than 10%. The specific surface area was calculated automatically based on the Brunauer-Emmett-Teller (BET) theory. Raman scattering of light was performed on a Renishaw inVia-Reflex system equipped with an Ar⁺ laser (532 nm). Spectra were acquired using 1% laser power, an exposure time of 15 seconds, and a 5-fold repetition of measurements. The spectral resolution was 1 cm − 1 . Thermal conductivity measurements were conducted using a custom-built setup based on the IT-lambda-400 device, previously described in [ 3 ]. To facilitate plane-parallel measurements, the thermal grease was placed in a thermazote ring with a height of 4 mm, a diameter of 16 mm, and a wall thickness of 1 mm. The obtained thermal conductivity values were compared with those of commercially available thermal greases: KPT-8, Arctic MX-4, and Geek RG-5. A detailed description of the methodology used for comparative testing on a personal computer processor can be found in [ 3 ]. Table 1 Graphite and carbon starting materials properties Powder Chemical purity, % Ash content, % Manufacturer Carbon black ( CB ) 95.0 2.0 Tuimazytehocarbon Technical carbon 95.0 2.0 Thermal carbon obtained by pyrolysis of gas without air access Т-900 95.0 0.15 Channel carbon obtained by incomplete combustion of gas in a diffusion flame K-354 98.5 0.05 Furnace carbon obtained by incomplete combustion of gas with forced air supply to the reactor P-701 99.6 0.48 Graphite ( Ozersk ) 99.6 0.1 SilKaM Enriched crystal pencil graphite GK-1 99.0 1.0 Rosgraphite Enriched crystalline electrode graphite GE-1 98.0 10.0 Colloidal carbon S-1 93.5 1 Ecotec Biocarbon, obtained from orange peel ( Biocarbon O ) Synthesized in [ 20 ] Biocarbon, obtained from tires ( Biocarbon S ) Table 2 Graphite and carbon-based thermal greases composition Powder Mass fraction of powder ± 0.1, % PDMS mass fraction ± 0.1, % Carbon black 48.0 52.0 Technical carbon 48.1 51.9 Т-900 49.6 50.4 Ozersk 50.0 50.0 K-354 28.2 71.8 P-701 43.4 56.6 GK-1 56.7 43.3 GE-1 57.5 42.5 S-1 60.8 39.2 Biocarbon O 33.3 66.7 Biocarbon S 43.0 57.0 3. Results and discussion 3.1. XRD of graphite and carbon materials X-ray diffraction (XRD) analysis was performed to investigate the phase composition and structural characteristics of the various graphite and carbon powders. The results are presented and discussed below, categorized based on the observed XRD patterns. Group 1: Technical Carbon and Graphite Powders (K-354, P-701, T-900). The XRD patterns for technical carbon and graphite powders, namely trademarks K-354, P-701, and T-900, exhibited similar diffraction features (Fig. 1a). The observed peaks corresponded to graphite (COD 96-110-0004), with a hexagonal space group of R-3m (166) and lattice parameters of a = 2.456 Å and c = 10.041 Å. The degree of crystallinity for these samples was approximately 69.5%. Group 2: Graphite from Ozersk, Trademarks GE-1, GK-1, and Colloidal Carbon S-1. This group of samples exhibited distinct XRD patterns. The graphite from Ozersk was identified as a single-phase material, corresponding to graphite with a hexagonal space group of P63/mmc (194) and lattice parameters of a = 2.464 Å and c = 6.711 Å (COD 96-901-1578). The GK-1 sample displayed a mixture of the two graphite phases mentioned above, R-3m and P63/mmc. Samples GE-1 and S-1 shared a common feature: an oxidized surface, evidenced by the presence of carbon oxides in their XRD patterns (Fig. 1b). The degree of crystallinity for these samples was approximately 100%. Group 3: Carbon Black and Biocarbon. The biocarbon produced from orange peel exhibited an almost amorphous structure with weak graphite peaks (Fig. 1c). The XRD pattern of carbon black was difficult to interpret definitively, with peaks potentially attributable to monoclinic silicon oxide (coesite) or calcium carbonate (calcite) within an amorphous carbon matrix. However, the absence of characteristic Raman shifts at 525 cm⁻¹ and 1085 cm⁻¹, corresponding to these impurities, suggests that these peaks likely arise from carbon. Moreover, similar but sharper peaks were observed in the biocarbon S XRD pattern (Fig. 1c). Consequently, the XRD pattern was attributed to carbon (ICDD 00-46-0943). The biocarbon S sample was identified as a two-phase material: the first phase, as described above, was carbon as in carbon black, and the second was an orthorhombic carbon with a space group of Cmc21 (36) and lattice parameters of a = 2.460 Å, b = 4.260 Å, and c = 28.960 Å. All samples within this group displayed low crystallinity. The Scherrer equation was employed to calculate the crystallite size of the graphite and carbon samples (Table 3 ). The results indicated that partially amorphous carbons exhibited very small crystallite sizes, ranging from 1 to 1.74 nm. In contrast, graphite materials exhibited significantly larger crystallite sizes, ranging from 18.13 to 45.33 nm. Considering the potential applications, the roughness of coupling surfaces can vary from 12.5 to 0.4 µm. Therefore, the primary particles of all materials under investigation could effectively fill these gaps. However, it is important to note that primary particles rarely exist as isolated and well-distributed entities in powders. They commonly form aggregates or agglomerates from nanoparticles, and their size and morphology will be examined in detail in subsequent sections. Table 3 Graphite and carbon materials crystallite size Powder 2 Theta ± 0.03, deg. Crystallite size, nm Carbon black 29.35 1.74 Technical carbon 25.24 1.52 Т-900 27.97 1.60 Ozersk 26.44 34.00 K-354 24.19 1.15 P-701 24.49 1.35 GK-1 26.53 34.01 GE-1 24.88 5.42 S-1 26.44 18.13 Biocarbon O (Carbon 2H) 26.32 45.33 Biocarbon O (Carbon O) 24.16 1.0 Biocarbon S (Carbon O) 24.97 1.48 Biocarbon S (Carbon C) 28.57 8.28 From the perspective of XRD phase analysis, samples with a high degree of crystallinity are considered more promising due to their higher thermal conductivity compared to partially amorphous materials. 3.2. Raman spectra of graphite and carbon Raman spectroscopy was employed to investigate the structural characteristics and graphitization degree of the graphite and carbon powders. The Raman spectra were obtained by irradiating the samples with a 532 nm laser, and the spectral range analyzed was from 1000 to 3400 cm − 1 (Fig. 2a). The Raman spectra of all carbon samples exhibited the characteristic G and D modes of graphite, as reported in previous studies [ 21 – 25 ]. The G mode, located around 1580 cm⁻¹, originates from the in-plane bond-stretching motion of pairs of sp² hybridized carbon atoms. The D mode, typically located around 1350 cm⁻¹, represents a breathing mode of A1g symmetry involving phonons near the K zone boundary, indicative of the presence of sp³ hybridized carbon. The D mode is negligible for ideal graphite and becomes more pronounced with increasing disorder [ 26 ]. The ratio of the intensities of the G and D modes (IG/ID) is commonly used to characterize the degree of graphitization in carbon materials. A higher IG/ID value signifies a higher degree of graphitization. As observed in the presented Raman data (Fig. 2), the D peak intensity for well-crystallized graphite was significantly lower than that of the G peak. Figure 3 depicts the ratio of band intensities and their full width at half maximum (FWHM). Notably, the GK-1 graphite sample exhibited a peak area ratio[ 27 ] of 4.87, while other samples ranged from 0.3 to 1.94. Raman spectroscopy reveals a correlation between peak shifts and molecular bond length. A decrease in bond length results in a shift of the Raman peak towards higher wavenumbers (characteristic of graphite containing materials), while an increase in bond length corresponds to a shift towards lower wavenumbers (typical of carbon-based materials). The presence of a 2D band in the Raman spectrum indicates the presence of graphene layers [ 27 ]. The second-order Raman spectrum exhibited weak bands at 2452 cm⁻¹ and 3244 cm⁻¹, corresponding to the D + D” and 2D’ harmonics, respectively. The D” band is attributed to an in-plane longitudinal acoustic (LA) branch near the K point, while the D’ band corresponds to a phonon of the in-plane longitudinal optical (LO) branch near the zone center (Γ point) [ 28 ]. In the Raman spectra of almost all samples (Fig. 2b), peaks were detected at approximately 250 cm⁻¹ and 360 cm⁻¹, likely associated with a high density of states of disorder-activated acoustic phonons (DAAP) [ 29 , 30 ]. Upon Lorentzian decomposition, a gentle peak around 2000 cm⁻¹ was observed in the biocarbon O sample, potentially corresponding to the vibrational symmetric mode of CH₂ [ 31 ] or the presence of adsorbed CO [ 32 ]. The spectra of biocarbon, carbon black, and technical carbons exhibited a broad D-band (Fig. 3) in the range from 1350 to 1379 cm⁻¹. In contrast, samples with high crystallinity displayed a narrower D and G band FWHM (6.7–40 cm⁻¹). The smallest D-band shift was observed for carbon K-354 and P-702 (1350–1354 cm⁻¹), while the largest shift occurred for biocarbon (1379 cm⁻¹). Additionally, a prominent peak in the range of 2800–3000 cm⁻¹ was observed for the biocarbon O sample, a common mode attributed to ν(CH₂) as a surface impurity after synthesis. Based on their Raman spectra (Fig. 4), the carbon samples could be broadly classified into two groups: Graphite (G peak position ~ 1580 cm⁻¹, I D /I G ratio ~ 0.5) Nanocrystalline Graphite (G peak shifted to ~ 1600 cm⁻¹, I D /I G ratio increased to 2.0) [ 26 ]. 3.3. Morphology of graphite and carbon Scanning electron microscopy (SEM) was employed to investigate the morphology and particle size distribution of the different graphite and carbon powders. The SEM images and resulting observations are discussed below, categorized by sample type: Biocarbon and Colloidal Carbon: samples of biocarbon and colloidal carbons (Fig. 5 a-c) exhibited a well-developed surface morphology characterized by large agglomerates surrounded by smaller, irregularly shaped particles. Well-Crystallized Graphite: powders of well-crystallized graphite (GE-1, GK-1, graphite from Ozersk) were observed as large agglomerates of irregular shapes (Fig. 5 d-f). Carbon Black and Technical Carbons: samples of carbon black and technical carbons were represented by small, spherical graphite particles (Fig. 5 g-k). From a morphological perspective, technical carbons appear most promising for achieving densely packed structures. Particle size measurements were obtained from SEM images and calculated from surface area data using Eq. 1, assuming spherical particle morphology. These results are presented in Table 4 . Due to the complex morphology of biocarbon O particles, size measurements for this sample were inconclusive. Several samples, including carbon black, T-900, and P-701, exhibited similar particle sizes according to both SEM analysis and calculations from surface area data (Eq. 1), indicating a well-distributed particle distribution as observed in the SEM images (Fig. 5 ). In contrast, other samples displayed an aggregate structure. While particle size could be calculated from surface area data, the SEM images revealed aggregates, and the measured size corresponded to the aggregate rather than the individual particles. $$\:\begin{array}{c}a=\:\sqrt{\frac{{S}_{a}}{4\pi\:}}\#\left(1\right)\end{array}$$ Where a – calculated spherical particle size, S a – surface area. Combining particle size data with the presence of agglomerates and aggregates suggests that well-distributed particles are the most promising fillers for thermal interface materials. Table 4 Graphite and carbon powder surface area and particle size Powder Surface area, m 2 /g Calc. particle size, µm Particle size (SEM), µm Carbon black 10 0.89 0.57 Technical carbon 10 0.89 24.8 Т-900 15 1.09 0.66 Ozersk 5 0.63 23.9 K-354 112 2.99 12.0 P-701 24 1.38 0.59 GK-1 63 2.24 19.9 GE-1 28 1.49 118.4 S-1 110 2.96 10.5 3.4 Thermal conductivity and operational bench test The thermal conductivity of the prepared thermal greases was investigated, and the results are discussed below, focusing on the correlation between material characteristics and thermal performance. Influence of Crystallinity and Particle Size: the highest thermal conductivity values were obtained for thermal greases containing trademarks GE-1, GC-1, and graphite from Ozersk. These materials share the common characteristics of high crystallinity (Fig. 1) and large particle size or agglomerates (Table 4 ). The high crystallinity preserves the inherently high thermal conductivity of crystalline graphite, while the larger particles/agglomerates reduce the number of thermally resistive interfaces between the graphite and the liquid polydimethylsiloxane (PDMS) matrix along the height of the test sample. This combination contributes to the observed high thermal conductivity values (Fig. 6 ). Impact of Amorphization and Particle Size: despite having comparable particle sizes to GK-1 graphite, carbon black and biocarbon S, due to their high amorphization, their thermal conductivity values did not exceed 0.65 W·m⁻¹·K⁻¹. Technical carbons, with their smaller particle sizes and lower degree of crystallinity, also exhibited lower thermal conductivity values. Correlation with Mass Fraction and Surface Area: similar mass fractions of graphite were observed for technical carbons (T-900, P-701) and carbon black (Table 2 ). This similarity can be attributed to their comparable particle size (Fig. 5 , Table 4 ) and specific surface area (Table 4 ). K-354 carbon, which possesses a higher specific surface area (Table 4 ), demonstrated a lower mass fraction. This observation is explained by the need for a larger amount of polymer to effectively bind the particles with a more developed surface in order to maintain the desired viscous consistency of the thermal grease. While commercially available thermal greases such as Arctic MX-4 (declared thermal conductivity of 8.5 W·m⁻¹·K⁻¹) and RGeek RG-5 (declared thermal conductivity of 15.7 W·m⁻¹·K⁻¹) claim high thermal conductivity values, the experimentally obtained results (Fig. 6 ) indicate a significant overestimation. This discrepancy is likely attributed to the measurement techniques employed by the manufacturers. Specifically, the thermal conductivity is typically determined by examining a thin layer of the composite material. This methodology allows for a wide range of possible thermal conductivity values to correspond to the same temperature gradient at the sample ends, considering the measurement error. This observation aligns with previously reported calculated data [ 3 ], suggesting that the declared values might be overestimated due to the limitations of the measurement technique. This study investigated the potential of graphite and carbon-based thermal greases for enhancing heat dissipation in microelectronics devices. The performance of the developed materials was compared to commercially available thermal pastes, utilizing both benchtop thermal conductivity measurements and operational bench testing on a CPU. A wide range of thermal greases with high thermal conductivity are commercially available for high-performance devices. Comparative evaluation of the developed materials against these existing solutions provides insights into their potential applications. Operational bench testing, which simulates real-world operating conditions, is a critical approach for assessing thermal interface materials (TIMs). This study confirmed the significant influence of TIM layer thickness on heat dissipation from microelectronic devices [ 3 ]. Thinner TIM layers require lower thermal conductivity to achieve optimal device temperature control. An operational bench test was conducted on a CPU, comparing the developed thermal greases with the commercially available KPT-8 thermal paste under 100% CPU load. The resulting temperature profiles of the processor cores (Fig. 7 ) revealed varying performance across the tested samples. Sample P-701: This sample demonstrated the poorest performance, attributed to a lower mass fraction of graphite (43.4 wt%) compared to T-900 (49.6 wt%). This discrepancy likely arises from a greater tendency of P-701 particles to agglomerate during mechanical mixing, leading to non-uniform particle distribution within the polymer matrix. While this effect is minimized in bulk thermal conductivity measurements due to sample thickness, it becomes significant when applying a thin layer to the CPU. Samples GK-1 and S-1: These well-crystallized samples reduced the maximum CPU temperature from 54°C to 49°C. This improvement is attributed to their small, well-crystallized graphite particles, enabling the application of a thin TIM layer with higher thermal conductivity (1.85 and 1.21 W·m⁻¹·K⁻¹, respectively) compared to KPT-8. Samples GE-1 and T-900: Both samples achieved the lowest CPU temperature (47°C), demonstrating the effectiveness of contrasting approaches. GE-1's large graphite grains resulted in high thermal conductivity (2.19 W·m⁻¹·K⁻¹), surpassing KPT-8. Conversely, T-900's fine carbon particles allowed for a thin TIM layer, minimizing thermal resistance at the CPU-radiator interface despite lower thermal conductivity (0.6 W·m⁻¹·K⁻¹). The thermal conductivity values achieved with the developed graphite-based thermal greases and their promising performance in the CPU operational bench test highlight their potential for developing new, highly efficient composite materials for microelectronics applications. 4. Conclusions Samples with high crystallinity, such as well-crystallized graphite and colloidal carbon S-1, displayed larger crystallite sizes ranging from 18.13 to 45.33 nm, while partially amorphous carbons exhibited significantly smaller crystallite sizes (1 to 1.74 nm). The high crystallinity of these materials is a promising factor for their application as fillers in thermal interface materials, as it is directly correlated with higher thermal conductivity. However, the presence of agglomerates and aggregates, which are not accounted for by XRD analysis, must be considered in subsequent morphological studies to ensure effective performance in real-world applications. The presence of characteristic G and D bands in the Raman spectra confirmed the graphitic nature of all samples. Samples with higher crystallinity, such as GK-1, exhibited a significantly lower D peak intensity compared to the G peak, indicating a greater degree of graphitization. The observed shift in the G peak position, along with the ID/IG ratio, provided further insights into the graphitization degree, allowing for the classification of samples into graphite and nanocrystalline graphite groups. The presence of disorder-activated acoustic phonons (DAAP) in most samples indicated structural defects and disorder, while the presence of a 2D band suggested the presence of graphene layers in some materials. Biocarbon and colloidal carbons exhibited large agglomerates with smaller, irregularly shaped particles, while well-crystallized graphite powders displayed large agglomerates of irregular shapes. Carbon black and technical carbons exhibited small, spherical particles, with technical carbons showing the most promising morphology for achieving densely packed structures. Particle size measurements, obtained from SEM images and surface area data, indicated a well-distributed particle size for some samples, while others displayed an aggregate structure. The presence of agglomerates and aggregates highlights the importance of considering particle distribution and morphology in addition to particle size when designing effective thermal interface materials. Well-distributed particles, as observed in technical carbons and certain other samples, are likely to offer the most effective filling capabilities, leading to enhanced thermal conductivity and overall performance. Thermal greases containing well-crystallized graphite with large particle sizes or agglomerates, such as GE-1, GK-1, and graphite from Ozersk, exhibited the highest thermal conductivity values. This is attributed to the combination of high inherent thermal conductivity of crystalline graphite and reduced thermal resistance at the interfaces between graphite particles and the PDMS matrix due to fewer interfaces. Conversely, amorphous carbons, such as carbon black and biocarbon S, despite comparable particle sizes to GK-1, showed significantly lower thermal conductivity due to their amorphous structure. Technical carbons, with smaller particle sizes and lower crystallinity, also exhibited lower thermal conductivity. The study also revealed a correlation between mass fraction, surface area, and thermal performance. Materials with higher specific surface area, such as K-354 carbon, required a larger amount of polymer to maintain the desired viscosity, leading to a lower mass fraction of filler material. Furthermore, the study highlighted the potential overestimation of thermal conductivity values reported by manufacturers of commercial thermal greases. The discrepancy between declared and experimentally measured values is likely due to the measurement techniques employed, which often involve thin layers of the composite material, potentially leading to inaccurate estimations. The observed results align with previous research suggesting a need for more accurate and standardized measurement techniques for thermal conductivity evaluation of thermal interface materials. In conclusion, this study investigated the potential of graphite and carbon-based thermal greases for enhancing heat dissipation in microelectronics devices. The developed materials were compared to commercially available thermal pastes using both benchtop thermal conductivity measurements and operational bench testing on a CPU. The study confirmed the significant influence of TIM layer thickness on heat dissipation from microelectronic devices. The results suggest that the developed graphite-based thermal greases have promising potential for developing new, highly efficient composite materials for microelectronics applications. Further research is needed to optimize the performance of these materials and explore their potential for other applications. Declarations Author Contributions: Conceptualization: R.A. Shishkin. Data curation: R. A. Shishkin, A. V. Leschok. Formal analysis: R. A. Shishkin. Methodology: R. A. Shishkin, Z. A. Fattakhova, N. V. Zhirenkina, V. G. Arkhipova. Project administration: R. A. Shishkin. Investigation: R. A. Shishkin, Z. A. Fattakhova, N. V. Zhirenkina, V. G. Arkhipova. Supervision: R. A. Shishkin, A. V. Leshok. Validation: R. A. Shishkin. Writing-original draft: R. A. Shishkin. Writing-review and editing: R. A. Shishkin, A. V. Leshok. Funding: This research was funded by state assignment, grant number 124020600004-7 Data Availability Statement: Data available on request. Conflicts of Interest: The authors declare no conflicts of interest References Y. Yang, L. Kui, S. Yulin et al., Review of thermal interface materials for microelectronic packaging. Microelectron. Comput. 40 , 64–74 (2023). https://doi.org/10.19304/J.ISSN1000-7180.2022.0684 Z.Y. Jiang, J.Y. Li, Z.G. Qu et al., Theoretical analysis on thermal grease dry-out degradation in space environment. Int. J. Therm. Sci. 179 , 107694 (2022). https://doi.org/10.1016/J.IJTHERMALSCI.2022.107694 R.A. Shishkin, Investigation of thermal greases with hybrid fillers and its operational bench test. J. Electron. Mater. 51 , 1189–1201 (2022). https://doi.org/10.1007/s11664-021-09385-7 K. Ruan, X. Shi, Y. Guo, J. 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Chung, Performance of Thermal Interface Materials. Small. 18 , 2200693 (2022). https://doi.org/10.1002/SMLL.202200693 A.P. Zemlyanskaya, R.A. Shishkin, V.S. Kudyakova et al., The study of TIM polymer composite materials thermal conductivity. AIP Conf. Proc. 2174 (2019). https://doi.org/10.1063/1.5134342 N. Sapna, Budhiraja, V. Kumar, S.K. Singh, X-ray Analysis of NiFe 2 O 4 Nanoparticles by Williamson-Hall and Size-Strain Plot Method. J. Adv. Phys. 6 , 492–495 (2018). https://doi.org/10.1166/JAP.2017.1363 A.P. Ilyushchanka, A.V. Liashok, L.N. Dyachkova, S.A. Yankovsky, The Influence of Biocarbon Powder Produced from a Pine Nutshell on Tribotechnical Properties of Copper Based Friction Material Running Under Conditions of Boundary Friction. J. Frict. Wear. 43 , 305–311 (2022). https://doi.org/10.3103/S106836662205004X/FIGURES/7 J. Wu, M.L. Bin, Lin, X. Cong et al., Raman spectroscopy of graphene-based materials and its applications in related devices. Chem. Soc. Rev. 47 , 1822–1873 (2018). https://doi.org/10.1039/c6cs00915h A.C. Ferrari, Raman spectroscopy of graphene and graphite: Disorder, electron-phonon coupling, doping and nonadiabatic effects. Solid State Commun. 143 , 47–57 (2007). https://doi.org/10.1016/j.ssc.2007.03.052 K.N. Kudin, B. Ozbas, H.C. Schniepp et al., Raman spectra of graphite oxide and functionalized graphene sheets. Nano Lett. 8 , 36–41 (2008). https://doi.org/10.1021/nl071822y H. Wang, Y. Wu, C. Kai et al., (2006) Disorder induced bands in first order Raman spectra of carbon nanowalls. In: 2006 Sixth IEEE Conference on Nanotechnology S. Reich, C. Thomsen, Raman spectroscopy of graphite. Philosophical Trans. Royal Soc. A: Math. Phys. Eng. Sci. 362 , 2271–2288 (2004). https://doi.org/10.1098/rsta.2004.1454 A.C. Ferrari, J. Robertson, Interpretation of Raman spectra of disordered and amorphous carbon. Phys. Rev. B 61 , 14095–14107 (2000) F. Destyorini, Y. Irmawati, A. Hardiansyah et al., Formation of nanostructured graphitic carbon from coconut waste via low-temperature catalytic graphitisation. Eng. Sci. Technol. Int. J. 24 , 514–523 (2021). https://doi.org/10.1016/j.jestch.2020.06.011 L. Bokobza, J.-L. Bruneel, M. Couzi, Raman Spectra of Carbon-Based Materials (from Graphite to Carbon Black) and of Some Silicone Composites. C —. J. Carbon Res. 1 , 77–94 (2015). https://doi.org/10.3390/c1010077 R. Lazzari, N. Vast, J.M. Besson et al., Atomic Structure and Vibrational Properties of Icosahedral B 4 C Boron Carbide. Phys. Rev. Lett. 83 , 3230–3233 (1999) K.Y. Xie, V. Domnich, L. Farbaniec et al., Microstructural characterization of boron-rich boron carbide. Acta Mater. 136 , 202–214 (2017). https://doi.org/10.1016/j.actamat.2017.06.063 J. Chen, J. Li, L. Xu et al., The glass-transition temperature of supported PMMA thin films with hydrogen bond/plasmonic interface. Polym. (Basel). 11 (2019). https://doi.org/10.3390/polym11040601 S. Garimella, V. Drozd, A. Durygin, J. Chen, High pressure Raman and x-ray diffraction studies on the decomposition of tungsten carbonyl. J. Appl. Phys. 111 , 112606 (2012). https://doi.org/10.1063/1.4726196 Additional Declarations No competing interests reported. Cite Share Download PDF Status: Published Journal Publication published 26 Sep, 2024 Read the published version in International Journal of Thermophysics → Version 1 posted Editorial decision: Revision requested 09 Jul, 2024 Editor assigned by journal 06 Jul, 2024 Submission checks completed at journal 06 Jul, 2024 First submitted to journal 05 Jul, 2024 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-4690353","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":324533157,"identity":"d862a8ae-0f5e-4e47-9589-98944c75a2e1","order_by":0,"name":"Roman Shishkin","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA2ElEQVRIie3OMQrCMBTG8VcCTlHXSMFe4Ykgipfpw6GLqODiJIVA166FeghBcK4GdOkBMri5Ogi5gFScRGLdHPIfMuXH+wBcrn9MeDGDQkCbcSh+Ix1ZnwCw6i8WvOauIJfSLMrhrH9uHo4a1Lydxw1j43g5JH6mxXKgWqGaghpll4LlViIoYfwuaK84VgRBh4zZSJCRNBXZyRcJvhHQFPtcC9qyF8FvBDUlPi8FZc9hGGFPk/Q21mHR1fDTmtK07JvpaoxdPVFwsw17O1o9XlwfuFwul+tjD97dS+pkApnZAAAAAElFTkSuQmCC","orcid":"","institution":"Institute of Solid State Chemistry Ural branch of Russian Academy of Science","correspondingAuthor":true,"prefix":"","firstName":"Roman","middleName":"","lastName":"Shishkin","suffix":""},{"id":324533158,"identity":"ddd81b0d-7ec1-4966-bc74-433dbe744a90","order_by":1,"name":"Vicktoria Arkhipova","email":"","orcid":"","institution":"Institute of Solid State Chemistry Ural branch of Russian Academy of Science","correspondingAuthor":false,"prefix":"","firstName":"Vicktoria","middleName":"","lastName":"Arkhipova","suffix":""},{"id":324533162,"identity":"f1221cb1-9b2b-4b1b-97cc-52fb1edf6115","order_by":2,"name":"Nina Zhirenkina","email":"","orcid":"","institution":"Ural Federal University named after the first President of Russia B.N. Yeltsin","correspondingAuthor":false,"prefix":"","firstName":"Nina","middleName":"","lastName":"Zhirenkina","suffix":""},{"id":324533165,"identity":"90e0c59d-4c7e-4a2e-9813-5da947c1cae6","order_by":3,"name":"Zillara Fattakhova","email":"","orcid":"","institution":"Institute of Solid State Chemistry Ural branch of Russian Academy of Science","correspondingAuthor":false,"prefix":"","firstName":"Zillara","middleName":"","lastName":"Fattakhova","suffix":""},{"id":324533166,"identity":"93951d85-5b1b-4ba5-a48e-52ff344bedbd","order_by":4,"name":"Andrey Leshok","email":"","orcid":"","institution":"Institute of powder metallurgy named after the academic O.V. Romanov","correspondingAuthor":false,"prefix":"","firstName":"Andrey","middleName":"","lastName":"Leshok","suffix":""}],"badges":[],"createdAt":"2024-07-05 07:23:23","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-4690353/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-4690353/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1007/s10765-024-03437-w","type":"published","date":"2024-09-26T15:57:43+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":61393923,"identity":"bf2ecb66-8c31-4a75-bc09-4ba512858db5","added_by":"auto","created_at":"2024-07-30 08:34:19","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":128863,"visible":true,"origin":"","legend":"\u003cp\u003eXRD patterns of (a) technical carbon; (b) graphite; (c) biocarbon and carbon black\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-4690353/v1/82afc56c61fcfb391ae13a6e.png"},{"id":61393408,"identity":"d905227d-8c54-4183-bad8-1d346594d95d","added_by":"auto","created_at":"2024-07-30 08:26:19","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":163468,"visible":true,"origin":"","legend":"\u003cp\u003e(а) Raman spectra of graphite and carbon; (b) Example of Raman spectra decomposition into Lorentzian\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-4690353/v1/9da687af87959311ef434a58.png"},{"id":61393922,"identity":"8f3b172b-9645-4794-80f1-a45242679610","added_by":"auto","created_at":"2024-07-30 08:34:19","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":35080,"visible":true,"origin":"","legend":"\u003cp\u003eDependence of (a) FWHM and (b) I\u003csub\u003eG\u003c/sub\u003e/I\u003csub\u003eD\u003c/sub\u003e ratio from graphite and carbon trademark\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-4690353/v1/785f4c178ca29fbab04426a3.png"},{"id":61393405,"identity":"4e166537-3efd-4147-b84d-d0251b2dc38b","added_by":"auto","created_at":"2024-07-30 08:26:19","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":46349,"visible":true,"origin":"","legend":"\u003cp\u003eDependence of (a) G-band peak position and (b) corresponding FWHM as a function from I\u003csub\u003eG\u003c/sub\u003e/I\u003csub\u003eD\u003c/sub\u003e ratio\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-4690353/v1/faa61b298de08892bd1c3c01.png"},{"id":61393412,"identity":"5e3aa063-e965-462d-83c1-014198509317","added_by":"auto","created_at":"2024-07-30 08:26:20","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":302800,"visible":true,"origin":"","legend":"\u003cp\u003eSEM images of graphite and carbons: (а) biocarbon O, (b) biocarbon S, (с) colloidal carbon S-1, (d) graphite GE-1, (e) GK-1, (f) Ozersk, (g) K-354, (h) P-701, (j) T-900, (k) carbon black, (l) technical carbon\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-4690353/v1/9f424a7d44ba3fdf3b4a0e5d.png"},{"id":61393924,"identity":"c8bcf6f5-e469-41f0-baf9-cabcaad4a7ab","added_by":"auto","created_at":"2024-07-30 08:34:19","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":108019,"visible":true,"origin":"","legend":"\u003cp\u003eThermal conductivity of produced and commercially available thermal greases\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-4690353/v1/af73343a9f29dc2121d802eb.png"},{"id":61393410,"identity":"bc6d51ac-c423-48ca-bbfc-cf872cd6200a","added_by":"auto","created_at":"2024-07-30 08:26:19","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":57162,"visible":true,"origin":"","legend":"\u003cp\u003eResults of operational bench test of thermal greases\u003c/p\u003e","description":"","filename":"7.png","url":"https://assets-eu.researchsquare.com/files/rs-4690353/v1/e5adb3d1b2a2084606ed3dba.png"},{"id":65627246,"identity":"5349513c-8463-44a7-9214-7cf85c65e075","added_by":"auto","created_at":"2024-09-30 16:13:50","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1480199,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4690353/v1/67f98133-691a-449a-9242-b8cce467f1c6.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Exploring Graphite-Based Thermal Greases For Optimal Microelectronic Device Cooling","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eThe escalating heat dissipation demands of modern microelectronic devices necessitate the development of effective thermal management solutions. A critical factor influencing the overall thermal resistance of the \"device-heat sink\" system lies in the thermal interface between the components. Air gaps formed at the interface due to micro-roughness significantly impede heat transfer. Thermal interface materials (TIMs), such as thermal greases, are employed to fill these voids and improve thermal contact [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]. While TIMs are widely used across various industries, including microelectronics, aerospace, and space engineering [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e], conventional thermal greases often fall short in meeting the stringent requirements of advanced microelectronic devices.\u003c/p\u003e \u003cp\u003eComputational modeling studies have shown that thinner TIM layers require lower thermal conductivity values to achieve optimal operating temperatures under natural convection conditions [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. However, commercially available thermal greases such as KPT-8, possessing a thermal conductivity of 0.8 W\u0026middot;m\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e\u0026middot;K\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, are insufficient for effective heat dissipation in microelectronic devices. This necessitates the exploration of novel materials and approaches for developing polymer-matrix composites with enhanced thermophysical properties [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e, \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eNumerous materials are being investigated as potential TIM fillers, including AlN, Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e, BN, and various forms of carbon [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan additionalcitationids=\"CR5\" citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]. However, achieving high thermal conductivity often requires the use of hybrid fillers, incorporating materials with diverse morphologies, sizes, or chemical compositions [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]. Examples include composites containing 82.76 vol.% of Galinstan-coated (alloy of Ga 78.3 at. %, In 14.9 at. %, Sn 6.8 at. %) aluminum oxide particles in a polymer matrix, reaching a thermal conductivity of 6.23 W\u0026middot;m\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e\u0026middot;K\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e], and epoxy-based composites with structured boron nitride flakes, demonstrating thermal conductivity values exceeding 10 W\u0026middot;m\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e\u0026middot;K\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e along the particle alignment axis [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e, \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]. Additionally, composites incorporating metallic silver and boron nitride nanofibers on aramid nanofibers have achieved a thermal conductivity of 9.44 W\u0026middot;m\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e\u0026middot;K\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eCarbon materials, including graphite, diamond, nanotubes, and graphene, have garnered significant attention due to their exceptional thermal conductivity and low density [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e, \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]. For instance, silicone rubber filled with structured and pre-vulcanized graphite, achieved through hot pressing, exhibits a thermal conductivity of up to 13.93 W\u0026middot;m\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e\u0026middot;K\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e along the graphite particle alignment axis [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e]. Furthermore, infiltration of a pre-built array of carbon nanotubes with polydimethylsiloxane has resulted in thermal conductivities exceeding 4.0 W\u0026middot;m\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e\u0026middot;K\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e along the nanotube axis [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]. The melt stirring method has been employed to produce carbon fiber/olefin block copolymer composites with thermal conductivities reaching 15.06 W\u0026middot;m\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e\u0026middot;K\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eDespite the high thermal conductivity values reported in literature, it is crucial to note that these measurements are typically conducted on thin-film materials. Direct determination of thermal conductivity relies on measuring the temperature gradient across a sample at a known heat flux [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e, \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e]. With thin samples and high thermal conductivity, the temperature gradient can approach zero, leading to overestimated thermal conductivity values. Therefore, accurate thermal conductivity measurement necessitates using bulk samples of composite materials with a sufficient thickness to establish a plateau where the temperature gradient remains consistent regardless of sample thickness [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eGiven its widespread commercial availability and respectable thermal conductivity, graphite emerges as a promising candidate for use as a filler in composite materials for thermal interface applications. Previous research [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e] has demonstrated that the incorporation of ground, low-ash graphite powder (GMZ) into thermal greases can achieve a thermal conductivity of up to 2.85 W\u0026middot;m\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e\u0026middot;K\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, surpassing the values reported for diamond, copper, aluminum, aluminum oxide, and nitride. Furthermore, a mixture of graphite and aluminum nitride has achieved a thermal conductivity coefficient exceeding 3.02 W\u0026middot;m\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e\u0026middot;K\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e], indicating its potential for further investigation.\u003c/p\u003e \u003cp\u003eDespite the extensive variety of commercially available graphite and technical carbon materials, the optimal selection for the production of highly efficient thermal greases remains elusive. This work aims to systematically investigate the structural and morphological characteristics of various carbon and graphite powders, with varying production methods, particle sizes, and phase compositions, and assess their impact on the thermal conductivity of graphite-polydimethylsiloxane composite materials. This comparative study seeks to establish a comprehensive understanding of the relationship between the properties of different carbon materials and their performance as fillers in thermal interface applications.\u003c/p\u003e"},{"header":"2. Materials and Methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1 Raw materials and composites production:\u003c/h2\u003e \u003cp\u003eThe graphite and carbon powders investigated in this study are summarized in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e.\u003c/p\u003e \u003cp\u003eApproximately 2 grams of polydimethylsiloxane (PDMS-1000) was carefully weighed and placed in a porcelain mortar. Graphite or carbon powder, selected from one of the trademarks listed in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e, was then gradually added to the binder in small portions. Thorough mixing was performed until a homogeneous grease-like consistency was achieved. The mass of the graphite or carbon powder used was meticulously recorded to enable subsequent calculations of the mass and volume fractions. The resulting compositions are presented in Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2 Methods\u003c/h2\u003e \u003cp\u003ePhase composition and structural analysis of the powders were conducted using a Shimadzu XRD 7000 diffractometer (Shimadzu, Japan). CuKα radiation (λ\u0026thinsp;=\u0026thinsp;1.5418 \u0026Aring;) was employed to obtain diffraction patterns in the angular range of 10\u0026deg; to 80\u0026deg;, with a step size of 0.03\u0026deg; and a scanning rate of 5 seconds per point. Crystalline size was determined from the XRD data using the modified Scherrer equation as described in [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThe morphology of the powder particles was investigated using a JEOL JSM 6390LA scanning electron microscope. Particle size measurements were performed based on the SEM images, analyzed using ImageJ software.\u003c/p\u003e \u003cp\u003eLow-temperature nitrogen adsorption-desorption isotherms were obtained at -195\u0026deg;C using a Gemini VII automatic analyzer, adhering to the ASTM C1274-10 standard. The measurements were conducted with an error tolerance of no more than 10%. The specific surface area was calculated automatically based on the Brunauer-Emmett-Teller (BET) theory.\u003c/p\u003e \u003cp\u003eRaman scattering of light was performed on a Renishaw inVia-Reflex system equipped with an Ar⁺ laser (532 nm). Spectra were acquired using 1% laser power, an exposure time of 15 seconds, and a 5-fold repetition of measurements. The spectral resolution was 1 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eThermal conductivity measurements were conducted using a custom-built setup based on the IT-lambda-400 device, previously described in [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. To facilitate plane-parallel measurements, the thermal grease was placed in a thermazote ring with a height of 4 mm, a diameter of 16 mm, and a wall thickness of 1 mm. The obtained thermal conductivity values were compared with those of commercially available thermal greases: KPT-8, Arctic MX-4, and Geek RG-5. A detailed description of the methodology used for comparative testing on a personal computer processor can be found in [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e].\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eGraphite and carbon starting materials properties\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"4\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePowder\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eChemical purity, %\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eAsh content, %\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eManufacturer\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCarbon black (\u003cb\u003eCB\u003c/b\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e95.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e2.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\" morerows=\"4\" rowspan=\"5\"\u003e \u003cp\u003eTuimazytehocarbon\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eTechnical carbon\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e95.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e2.0\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eThermal carbon obtained by pyrolysis of gas without air access \u003cb\u003eТ-900\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e95.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.15\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eChannel carbon obtained by incomplete combustion of gas in a diffusion flame \u003cb\u003eK-354\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e98.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.05\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eFurnace carbon obtained by incomplete combustion of gas with forced air supply to the reactor \u003c/p\u003e \u003cp\u003e\u003cb\u003eP-701\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e99.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.48\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eGraphite (\u003cb\u003eOzersk\u003c/b\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e99.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eSilKaM\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eEnriched crystal pencil graphite \u003cb\u003eGK-1\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e99.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eRosgraphite\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eEnriched crystalline electrode graphite \u003cb\u003eGE-1\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e98.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e10.0\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eColloidal carbon \u003cb\u003eS-1\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e93.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eEcotec\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eBiocarbon, obtained from orange peel (\u003cb\u003eBiocarbon O\u003c/b\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eSynthesized in [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e]\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eBiocarbon, obtained from tires (\u003cb\u003eBiocarbon S\u003c/b\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eGraphite and carbon-based thermal greases composition\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"3\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePowder\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eMass fraction of powder\u0026thinsp;\u0026plusmn;\u0026thinsp;0.1, %\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003ePDMS mass fraction\u0026thinsp;\u0026plusmn;\u0026thinsp;0.1, %\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCarbon black\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e48.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e52.0\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTechnical carbon\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e48.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e51.9\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eТ-900\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e49.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e50.4\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eOzersk\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e50.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e50.0\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eK-354\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e28.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e71.8\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eP-701\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e43.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e56.6\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eGK-1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e56.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e43.3\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eGE-1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e57.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e42.5\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eS-1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e60.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e39.2\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eBiocarbon O\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e33.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e66.7\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eBiocarbon S\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e43.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e57.0\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"3. Results and discussion","content":"\u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003e3.1. XRD of graphite and carbon materials\u003c/h2\u003e \u003cp\u003eX-ray diffraction (XRD) analysis was performed to investigate the phase composition and structural characteristics of the various graphite and carbon powders. The results are presented and discussed below, categorized based on the observed XRD patterns.\u003c/p\u003e \u003cp\u003eGroup 1: Technical Carbon and Graphite Powders (K-354, P-701, T-900). The XRD patterns for technical carbon and graphite powders, namely trademarks K-354, P-701, and T-900, exhibited similar diffraction features (Fig.\u0026nbsp;1a). The observed peaks corresponded to graphite (COD 96-110-0004), with a hexagonal space group of \u003cem\u003eR-3m\u003c/em\u003e (166) and lattice parameters of a\u0026thinsp;=\u0026thinsp;2.456 \u0026Aring; and c\u0026thinsp;=\u0026thinsp;10.041 \u0026Aring;. The degree of crystallinity for these samples was approximately 69.5%.\u003c/p\u003e \u003cp\u003eGroup 2: Graphite from Ozersk, Trademarks GE-1, GK-1, and Colloidal Carbon S-1.\u003c/p\u003e \u003cp\u003eThis group of samples exhibited distinct XRD patterns. The graphite from Ozersk was identified as a single-phase material, corresponding to graphite with a hexagonal space group of \u003cem\u003eP63/mmc\u003c/em\u003e (194) and lattice parameters of a\u0026thinsp;=\u0026thinsp;2.464 \u0026Aring; and c\u0026thinsp;=\u0026thinsp;6.711 \u0026Aring; (COD 96-901-1578). The GK-1 sample displayed a mixture of the two graphite phases mentioned above, R-3m and P63/mmc. Samples GE-1 and S-1 shared a common feature: an oxidized surface, evidenced by the presence of carbon oxides in their XRD patterns (Fig.\u0026nbsp;1b). The degree of crystallinity for these samples was approximately 100%.\u003c/p\u003e \u003cp\u003eGroup 3: Carbon Black and Biocarbon. The biocarbon produced from orange peel exhibited an almost amorphous structure with weak graphite peaks (Fig.\u0026nbsp;1c). The XRD pattern of carbon black was difficult to interpret definitively, with peaks potentially attributable to monoclinic silicon oxide (coesite) or calcium carbonate (calcite) within an amorphous carbon matrix. However, the absence of characteristic Raman shifts at 525 cm⁻\u0026sup1; and 1085 cm⁻\u0026sup1;, corresponding to these impurities, suggests that these peaks likely arise from carbon. Moreover, similar but sharper peaks were observed in the biocarbon S XRD pattern (Fig.\u0026nbsp;1c). Consequently, the XRD pattern was attributed to carbon (ICDD 00-46-0943). The biocarbon S sample was identified as a two-phase material: the first phase, as described above, was carbon as in carbon black, and the second was an orthorhombic carbon with a space group of \u003cem\u003eCmc21\u003c/em\u003e (36) and lattice parameters of a\u0026thinsp;=\u0026thinsp;2.460 \u0026Aring;, b\u0026thinsp;=\u0026thinsp;4.260 \u0026Aring;, and c\u0026thinsp;=\u0026thinsp;28.960 \u0026Aring;. All samples within this group displayed low crystallinity.\u003c/p\u003e \u003cp\u003eThe Scherrer equation was employed to calculate the crystallite size of the graphite and carbon samples (Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). The results indicated that partially amorphous carbons exhibited very small crystallite sizes, ranging from 1 to 1.74 nm. In contrast, graphite materials exhibited significantly larger crystallite sizes, ranging from 18.13 to 45.33 nm. Considering the potential applications, the roughness of coupling surfaces can vary from 12.5 to 0.4 \u0026micro;m. Therefore, the primary particles of all materials under investigation could effectively fill these gaps. However, it is important to note that primary particles rarely exist as isolated and well-distributed entities in powders. They commonly form aggregates or agglomerates from nanoparticles, and their size and morphology will be examined in detail in subsequent sections.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eGraphite and carbon materials crystallite size\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"3\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePowder\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003e2 Theta\u0026thinsp;\u0026plusmn;\u0026thinsp;0.03, deg.\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eCrystallite size, nm\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCarbon black\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e29.35\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e1.74\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTechnical carbon\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e25.24\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e1.52\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eТ-900\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e27.97\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e1.60\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eOzersk\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e26.44\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e34.00\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eK-354\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e24.19\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e1.15\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eP-701\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e24.49\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e1.35\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eGK-1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e26.53\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e34.01\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eGE-1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e24.88\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e5.42\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eS-1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e26.44\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e18.13\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eBiocarbon O (Carbon 2H)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e26.32\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e45.33\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eBiocarbon O (Carbon O)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e24.16\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e1.0\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eBiocarbon S (Carbon O)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e24.97\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e1.48\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eBiocarbon S (Carbon C)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e28.57\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e8.28\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e\u003cp\u003eFrom the perspective of XRD phase analysis, samples with a high degree of crystallinity are considered more promising due to their higher thermal conductivity compared to partially amorphous materials.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003e3.2. Raman spectra of graphite and carbon\u003c/h2\u003e \u003cp\u003eRaman spectroscopy was employed to investigate the structural characteristics and graphitization degree of the graphite and carbon powders. The Raman spectra were obtained by irradiating the samples with a 532 nm laser, and the spectral range analyzed was from 1000 to 3400 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (Fig.\u0026nbsp;2a).\u003c/p\u003e \u003cp\u003eThe Raman spectra of all carbon samples exhibited the characteristic G and D modes of graphite, as reported in previous studies [\u003cspan additionalcitationids=\"CR22 CR23 CR24\" citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e]. The G mode, located around 1580 cm⁻\u0026sup1;, originates from the in-plane bond-stretching motion of pairs of sp\u0026sup2; hybridized carbon atoms. The D mode, typically located around 1350 cm⁻\u0026sup1;, represents a breathing mode of A1g symmetry involving phonons near the K zone boundary, indicative of the presence of sp\u0026sup3; hybridized carbon. The D mode is negligible for ideal graphite and becomes more pronounced with increasing disorder [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThe ratio of the intensities of the G and D modes (IG/ID) is commonly used to characterize the degree of graphitization in carbon materials. A higher IG/ID value signifies a higher degree of graphitization. As observed in the presented Raman data (Fig.\u0026nbsp;2), the D peak intensity for well-crystallized graphite was significantly lower than that of the G peak. Figure\u0026nbsp;3 depicts the ratio of band intensities and their full width at half maximum (FWHM). Notably, the GK-1 graphite sample exhibited a peak area ratio[\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e] of 4.87, while other samples ranged from 0.3 to 1.94.\u003c/p\u003e \u003cp\u003eRaman spectroscopy reveals a correlation between peak shifts and molecular bond length. A decrease in bond length results in a shift of the Raman peak towards higher wavenumbers (characteristic of graphite containing materials), while an increase in bond length corresponds to a shift towards lower wavenumbers (typical of carbon-based materials).\u003c/p\u003e \u003cp\u003eThe presence of a 2D band in the Raman spectrum indicates the presence of graphene layers [\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e]. The second-order Raman spectrum exhibited weak bands at 2452 cm⁻\u0026sup1; and 3244 cm⁻\u0026sup1;, corresponding to the D\u0026thinsp;+\u0026thinsp;D\u0026rdquo; and 2D\u0026rsquo; harmonics, respectively. The D\u0026rdquo; band is attributed to an in-plane longitudinal acoustic (LA) branch near the K point, while the D\u0026rsquo; band corresponds to a phonon of the in-plane longitudinal optical (LO) branch near the zone center (Γ point) [\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eIn the Raman spectra of almost all samples (Fig.\u0026nbsp;2b), peaks were detected at approximately 250 cm⁻\u0026sup1; and 360 cm⁻\u0026sup1;, likely associated with a high density of states of disorder-activated acoustic phonons (DAAP) [\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e, \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e]. Upon Lorentzian decomposition, a gentle peak around 2000 cm⁻\u0026sup1; was observed in the biocarbon O sample, potentially corresponding to the vibrational symmetric mode of CH₂ [\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e] or the presence of adsorbed CO [\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThe spectra of biocarbon, carbon black, and technical carbons exhibited a broad D-band (Fig.\u0026nbsp;3) in the range from 1350 to 1379 cm⁻\u0026sup1;. In contrast, samples with high crystallinity displayed a narrower D and G band FWHM (6.7\u0026ndash;40 cm⁻\u0026sup1;). The smallest D-band shift was observed for carbon K-354 and P-702 (1350\u0026ndash;1354 cm⁻\u0026sup1;), while the largest shift occurred for biocarbon (1379 cm⁻\u0026sup1;). Additionally, a prominent peak in the range of 2800\u0026ndash;3000 cm⁻\u0026sup1; was observed for the biocarbon O sample, a common mode attributed to ν(CH₂) as a surface impurity after synthesis.\u003c/p\u003e \u003cp\u003eBased on their Raman spectra (Fig.\u0026nbsp;4), the carbon samples could be broadly classified into two groups:\u003c/p\u003e \u003cp\u003e \u003cul\u003e \u003cli\u003e \u003cp\u003eGraphite (G peak position\u0026thinsp;~\u0026thinsp;1580 cm⁻\u0026sup1;, I\u003csub\u003eD\u003c/sub\u003e/I\u003csub\u003eG\u003c/sub\u003e ratio\u0026thinsp;~\u0026thinsp;0.5)\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003eNanocrystalline Graphite (G peak shifted to ~\u0026thinsp;1600 cm⁻\u0026sup1;, I\u003csub\u003eD\u003c/sub\u003e/I\u003csub\u003eG\u003c/sub\u003e ratio increased to 2.0) [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e].\u003c/p\u003e \u003c/li\u003e \u003c/ul\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003e3.3. Morphology of graphite and carbon\u003c/h2\u003e \u003cp\u003eScanning electron microscopy (SEM) was employed to investigate the morphology and particle size distribution of the different graphite and carbon powders. The SEM images and resulting observations are discussed below, categorized by sample type:\u003c/p\u003e \u003cp\u003eBiocarbon and Colloidal Carbon: samples of biocarbon and colloidal carbons (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e5\u003c/span\u003ea-c) exhibited a well-developed surface morphology characterized by large agglomerates surrounded by smaller, irregularly shaped particles.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eWell-Crystallized Graphite: powders of well-crystallized graphite (GE-1, GK-1, graphite from Ozersk) were observed as large agglomerates of irregular shapes (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e5\u003c/span\u003ed-f).\u003c/p\u003e \u003cp\u003eCarbon Black and Technical Carbons: samples of carbon black and technical carbons were represented by small, spherical graphite particles (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e5\u003c/span\u003eg-k). From a morphological perspective, technical carbons appear most promising for achieving densely packed structures.\u003c/p\u003e \u003cp\u003eParticle size measurements were obtained from SEM images and calculated from surface area data using Eq.\u0026nbsp;1, assuming spherical particle morphology. These results are presented in Table\u0026nbsp;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e. Due to the complex morphology of biocarbon O particles, size measurements for this sample were inconclusive.\u003c/p\u003e \u003cp\u003eSeveral samples, including carbon black, T-900, and P-701, exhibited similar particle sizes according to both SEM analysis and calculations from surface area data (Eq.\u0026nbsp;1), indicating a well-distributed particle distribution as observed in the SEM images (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e5\u003c/span\u003e). In contrast, other samples displayed an aggregate structure. While particle size could be calculated from surface area data, the SEM images revealed aggregates, and the measured size corresponded to the aggregate rather than the individual particles.\u003cdiv id=\"Equa\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equa\" name=\"EquationSource\"\u003e\n$$\\:\\begin{array}{c}a=\\:\\sqrt{\\frac{{S}_{a}}{4\\pi\\:}}\\#\\left(1\\right)\\end{array}$$\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eWhere a \u0026ndash; calculated spherical particle size, S\u003csub\u003ea\u003c/sub\u003e \u0026ndash; surface area.\u003c/p\u003e \u003cp\u003eCombining particle size data with the presence of agglomerates and aggregates suggests that well-distributed particles are the most promising fillers for thermal interface materials.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab4\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 4\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eGraphite and carbon powder surface area and particle size\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"4\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePowder\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSurface area, m\u003csup\u003e2\u003c/sup\u003e/g\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eCalc. particle size, \u0026micro;m\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eParticle size (SEM), \u0026micro;m\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCarbon black\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.89\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.57\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTechnical carbon\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.89\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e24.8\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eТ-900\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e15\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1.09\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.66\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eOzersk\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.63\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e23.9\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eK-354\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e112\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e2.99\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e12.0\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eP-701\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e24\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1.38\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.59\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eGK-1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e63\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e2.24\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e19.9\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eGE-1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e28\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1.49\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e118.4\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eS-1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e110\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e2.96\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e10.5\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec9\" class=\"Section2\"\u003e \u003ch2\u003e3.4 Thermal conductivity and operational bench test\u003c/h2\u003e \u003cp\u003eThe thermal conductivity of the prepared thermal greases was investigated, and the results are discussed below, focusing on the correlation between material characteristics and thermal performance.\u003c/p\u003e \u003cp\u003eInfluence of Crystallinity and Particle Size: the highest thermal conductivity values were obtained for thermal greases containing trademarks GE-1, GC-1, and graphite from Ozersk. These materials share the common characteristics of high crystallinity (Fig.\u0026nbsp;1) and large particle size or agglomerates (Table\u0026nbsp;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e). The high crystallinity preserves the inherently high thermal conductivity of crystalline graphite, while the larger particles/agglomerates reduce the number of thermally resistive interfaces between the graphite and the liquid polydimethylsiloxane (PDMS) matrix along the height of the test sample. This combination contributes to the observed high thermal conductivity values (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e6\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eImpact of Amorphization and Particle Size: despite having comparable particle sizes to GK-1 graphite, carbon black and biocarbon S, due to their high amorphization, their thermal conductivity values did not exceed 0.65 W\u0026middot;m⁻\u0026sup1;\u0026middot;K⁻\u0026sup1;. Technical carbons, with their smaller particle sizes and lower degree of crystallinity, also exhibited lower thermal conductivity values.\u003c/p\u003e \u003cp\u003eCorrelation with Mass Fraction and Surface Area: similar mass fractions of graphite were observed for technical carbons (T-900, P-701) and carbon black (Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). This similarity can be attributed to their comparable particle size (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e5\u003c/span\u003e, Table\u0026nbsp;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e) and specific surface area (Table\u0026nbsp;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e). K-354 carbon, which possesses a higher specific surface area (Table\u0026nbsp;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e), demonstrated a lower mass fraction. This observation is explained by the need for a larger amount of polymer to effectively bind the particles with a more developed surface in order to maintain the desired viscous consistency of the thermal grease.\u003c/p\u003e \u003cp\u003eWhile commercially available thermal greases such as Arctic MX-4 (declared thermal conductivity of 8.5 W\u0026middot;m⁻\u0026sup1;\u0026middot;K⁻\u0026sup1;) and RGeek RG-5 (declared thermal conductivity of 15.7 W\u0026middot;m⁻\u0026sup1;\u0026middot;K⁻\u0026sup1;) claim high thermal conductivity values, the experimentally obtained results (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e6\u003c/span\u003e) indicate a significant overestimation. This discrepancy is likely attributed to the measurement techniques employed by the manufacturers. Specifically, the thermal conductivity is typically determined by examining a thin layer of the composite material. This methodology allows for a wide range of possible thermal conductivity values to correspond to the same temperature gradient at the sample ends, considering the measurement error. This observation aligns with previously reported calculated data [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e], suggesting that the declared values might be overestimated due to the limitations of the measurement technique.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThis study investigated the potential of graphite and carbon-based thermal greases for enhancing heat dissipation in microelectronics devices. The performance of the developed materials was compared to commercially available thermal pastes, utilizing both benchtop thermal conductivity measurements and operational bench testing on a CPU.\u003c/p\u003e \u003cp\u003eA wide range of thermal greases with high thermal conductivity are commercially available for high-performance devices. Comparative evaluation of the developed materials against these existing solutions provides insights into their potential applications.\u003c/p\u003e \u003cp\u003eOperational bench testing, which simulates real-world operating conditions, is a critical approach for assessing thermal interface materials (TIMs). This study confirmed the significant influence of TIM layer thickness on heat dissipation from microelectronic devices [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. Thinner TIM layers require lower thermal conductivity to achieve optimal device temperature control.\u003c/p\u003e \u003cp\u003eAn operational bench test was conducted on a CPU, comparing the developed thermal greases with the commercially available KPT-8 thermal paste under 100% CPU load. The resulting temperature profiles of the processor cores (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e7\u003c/span\u003e) revealed varying performance across the tested samples.\u003c/p\u003e \u003cp\u003eSample P-701: This sample demonstrated the poorest performance, attributed to a lower mass fraction of graphite (43.4 wt%) compared to T-900 (49.6 wt%). This discrepancy likely arises from a greater tendency of P-701 particles to agglomerate during mechanical mixing, leading to non-uniform particle distribution within the polymer matrix. While this effect is minimized in bulk thermal conductivity measurements due to sample thickness, it becomes significant when applying a thin layer to the CPU.\u003c/p\u003e \u003cp\u003eSamples GK-1 and S-1: These well-crystallized samples reduced the maximum CPU temperature from 54\u0026deg;C to 49\u0026deg;C. This improvement is attributed to their small, well-crystallized graphite particles, enabling the application of a thin TIM layer with higher thermal conductivity (1.85 and 1.21 W\u0026middot;m⁻\u0026sup1;\u0026middot;K⁻\u0026sup1;, respectively) compared to KPT-8.\u003c/p\u003e \u003cp\u003eSamples GE-1 and T-900: Both samples achieved the lowest CPU temperature (47\u0026deg;C), demonstrating the effectiveness of contrasting approaches. GE-1's large graphite grains resulted in high thermal conductivity (2.19 W\u0026middot;m⁻\u0026sup1;\u0026middot;K⁻\u0026sup1;), surpassing KPT-8. Conversely, T-900's fine carbon particles allowed for a thin TIM layer, minimizing thermal resistance at the CPU-radiator interface despite lower thermal conductivity (0.6 W\u0026middot;m⁻\u0026sup1;\u0026middot;K⁻\u0026sup1;).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe thermal conductivity values achieved with the developed graphite-based thermal greases and their promising performance in the CPU operational bench test highlight their potential for developing new, highly efficient composite materials for microelectronics applications.\u003c/p\u003e \u003c/div\u003e"},{"header":"4. Conclusions","content":"\u003cp\u003eSamples with high crystallinity, such as well-crystallized graphite and colloidal carbon S-1, displayed larger crystallite sizes ranging from 18.13 to 45.33 nm, while partially amorphous carbons exhibited significantly smaller crystallite sizes (1 to 1.74 nm). The high crystallinity of these materials is a promising factor for their application as fillers in thermal interface materials, as it is directly correlated with higher thermal conductivity. However, the presence of agglomerates and aggregates, which are not accounted for by XRD analysis, must be considered in subsequent morphological studies to ensure effective performance in real-world applications.\u003c/p\u003e \u003cp\u003eThe presence of characteristic G and D bands in the Raman spectra confirmed the graphitic nature of all samples. Samples with higher crystallinity, such as GK-1, exhibited a significantly lower D peak intensity compared to the G peak, indicating a greater degree of graphitization. The observed shift in the G peak position, along with the ID/IG ratio, provided further insights into the graphitization degree, allowing for the classification of samples into graphite and nanocrystalline graphite groups. The presence of disorder-activated acoustic phonons (DAAP) in most samples indicated structural defects and disorder, while the presence of a 2D band suggested the presence of graphene layers in some materials.\u003c/p\u003e \u003cp\u003eBiocarbon and colloidal carbons exhibited large agglomerates with smaller, irregularly shaped particles, while well-crystallized graphite powders displayed large agglomerates of irregular shapes. Carbon black and technical carbons exhibited small, spherical particles, with technical carbons showing the most promising morphology for achieving densely packed structures. Particle size measurements, obtained from SEM images and surface area data, indicated a well-distributed particle size for some samples, while others displayed an aggregate structure. The presence of agglomerates and aggregates highlights the importance of considering particle distribution and morphology in addition to particle size when designing effective thermal interface materials. Well-distributed particles, as observed in technical carbons and certain other samples, are likely to offer the most effective filling capabilities, leading to enhanced thermal conductivity and overall performance.\u003c/p\u003e \u003cp\u003eThermal greases containing well-crystallized graphite with large particle sizes or agglomerates, such as GE-1, GK-1, and graphite from Ozersk, exhibited the highest thermal conductivity values. This is attributed to the combination of high inherent thermal conductivity of crystalline graphite and reduced thermal resistance at the interfaces between graphite particles and the PDMS matrix due to fewer interfaces. Conversely, amorphous carbons, such as carbon black and biocarbon S, despite comparable particle sizes to GK-1, showed significantly lower thermal conductivity due to their amorphous structure. Technical carbons, with smaller particle sizes and lower crystallinity, also exhibited lower thermal conductivity. The study also revealed a correlation between mass fraction, surface area, and thermal performance. Materials with higher specific surface area, such as K-354 carbon, required a larger amount of polymer to maintain the desired viscosity, leading to a lower mass fraction of filler material.\u003c/p\u003e \u003cp\u003eFurthermore, the study highlighted the potential overestimation of thermal conductivity values reported by manufacturers of commercial thermal greases. The discrepancy between declared and experimentally measured values is likely due to the measurement techniques employed, which often involve thin layers of the composite material, potentially leading to inaccurate estimations. The observed results align with previous research suggesting a need for more accurate and standardized measurement techniques for thermal conductivity evaluation of thermal interface materials.\u003c/p\u003e \u003cp\u003eIn conclusion, this study investigated the potential of graphite and carbon-based thermal greases for enhancing heat dissipation in microelectronics devices. The developed materials were compared to commercially available thermal pastes using both benchtop thermal conductivity measurements and operational bench testing on a CPU. The study confirmed the significant influence of TIM layer thickness on heat dissipation from microelectronic devices. The results suggest that the developed graphite-based thermal greases have promising potential for developing new, highly efficient composite materials for microelectronics applications. Further research is needed to optimize the performance of these materials and explore their potential for other applications.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAuthor Contributions:\u003c/strong\u003e \u003cem\u003eConceptualization:\u003c/em\u003e R.A. Shishkin. \u003cem\u003eData curation:\u003c/em\u003e R. A. Shishkin, A. V. Leschok. \u003cem\u003eFormal analysis:\u003c/em\u003e R. A. Shishkin. \u003cem\u003eMethodology:\u003c/em\u003e R. A. Shishkin, Z. A. Fattakhova, N. V. Zhirenkina, V. G. Arkhipova. \u003cem\u003eProject administration:\u003c/em\u003e R. A. Shishkin. \u003cem\u003eInvestigation:\u003c/em\u003e R. A. Shishkin, Z. A. Fattakhova, N. V. Zhirenkina, V. G. Arkhipova. \u003cem\u003eSupervision:\u003c/em\u003e R. A. Shishkin, A. V. Leshok. \u003cem\u003eValidation:\u003c/em\u003e R. A. Shishkin. \u003cem\u003eWriting-original draft:\u003c/em\u003e R. A. Shishkin. \u003cem\u003eWriting-review and editing:\u003c/em\u003e R. A. Shishkin, A. V. Leshok.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding:\u003c/strong\u003e This research was funded by state assignment, grant number 124020600004-7\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData Availability Statement:\u003c/strong\u003e Data available on request.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConflicts of Interest:\u003c/strong\u003e The authors declare no conflicts of interest\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eY. Yang, L. Kui, S. Yulin et al., Review of thermal interface materials for microelectronic packaging. Microelectron. 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Phys. \u003cb\u003e111\u003c/b\u003e, 112606 (2012). \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1063/1.4726196\u003c/span\u003e\u003cspan address=\"10.1063/1.4726196\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"international-journal-of-thermophysics","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"ijot","sideBox":"Learn more about [International Journal of Thermophysics](http://link.springer.com/journal/10765)","snPcode":"10765","submissionUrl":"https://submission.nature.com/new-submission/10765/3","title":"International Journal of Thermophysics","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"thermal interface materials, thermal grease, graphite, carbon, thermal conductivity, Raman spectroscopy","lastPublishedDoi":"10.21203/rs.3.rs-4690353/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4690353/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"The quest for effective thermal management solutions for microelectronic devices, catering to the escalating heat flows, necessitates innovative strategies. The significance of thermal interface materials, especially thermal greases, in minimizing thermal resistance within the \"microelectronic device – heat-dissipating element\" interface, has been widely acknowledged across industries such as microelectronics, aviation, and space engineering. Despite the promising reported values, a crucial consideration entails the method of ascertaining thermal conductivity, necessitating measurements in bulk samples to ensure accurate representations. Graphite, owing to its commercial accessibility and commendable thermal conductivity, emerges as a standout candidate for composite material development, as demonstrated in recent research. We observed that the use of graphite-based fillers, particularly in the form of well-crystallized graphite particles, effectively reduced processor temperatures and enhanced thermal conductivity, outperforming industrially utilized thermal pastes. Our findings accentuate the potential of these materials in contributing to the development of cutting-edge composite materials for microelectronics, highlighting their high prospects for future applications in high-performance devices.","manuscriptTitle":"Exploring Graphite-Based Thermal Greases For Optimal Microelectronic Device Cooling","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-07-30 08:26:14","doi":"10.21203/rs.3.rs-4690353/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2024-07-09T06:46:33+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2024-07-06T04:16:40+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2024-07-06T04:16:30+00:00","index":"","fulltext":""},{"type":"submitted","content":"International Journal of Thermophysics","date":"2024-07-05T07:15:10+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"international-journal-of-thermophysics","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"ijot","sideBox":"Learn more about [International Journal of Thermophysics](http://link.springer.com/journal/10765)","snPcode":"10765","submissionUrl":"https://submission.nature.com/new-submission/10765/3","title":"International Journal of Thermophysics","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"864187f8-444b-4335-88f1-fd88ba05b5f4","owner":[],"postedDate":"July 30th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2024-09-30T16:04:11+00:00","versionOfRecord":{"articleIdentity":"rs-4690353","link":"https://doi.org/10.1007/s10765-024-03437-w","journal":{"identity":"international-journal-of-thermophysics","isVorOnly":false,"title":"International Journal of Thermophysics"},"publishedOn":"2024-09-26 15:57:43","publishedOnDateReadable":"September 26th, 2024"},"versionCreatedAt":"2024-07-30 08:26:14","video":"","vorDoi":"10.1007/s10765-024-03437-w","vorDoiUrl":"https://doi.org/10.1007/s10765-024-03437-w","workflowStages":[]},"version":"v1","identity":"rs-4690353","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4690353","identity":"rs-4690353","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}