A study of the effect of quartz-to-cristobalite transformation on SiC generation in metallurgical-grade silicon production

A study of the effect of quartz-to-cristobalite transformation on SiC generation in metallurgical-grade silicon production | 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 A study of the effect of quartz-to-cristobalite transformation on SiC generation in metallurgical-grade silicon production 嘉禾 田, Kuixian Wei, Xiaocong Deng, Wenhui Ma This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-3831130/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 20 Feb, 2024 Read the published version in Silicon → Version 1 posted 7 You are reading this latest preprint version Abstract Silicon carbide (SiC) is an essential intermediate product formed during the smelting process of metallurgical-grade silicon (MG-Si), and its production efficiency is a key factor in determining the overall efficiency of MG-Si production. In this study, we investigated the effect of quartz-to-cristobalite transformation on SiC generation in industrial silicon production and elucidated the differences in the reaction characteristics of quartz and cristobalite when they interacted with carbonaceous reductants. The experimental results indicated that the rate of direct carbothermal reduction of cristobalite was 1.45 times that of quartz. Moreover, the indirectly formed SiC layer in the cristobalite/C diffusion couple exhibited a thickness of 920.87 µm, which was 1.55 times that in the quartz/C diffusion couple. Both the reaction thermodynamic calculations and crystal transformation theory analysis revealed that the changes in the chemical energy and crystal structure of SiO 2 during the phase transformation process reduced the stability of cristobalite compared with quartz at high temperatures. Consequently, cristobalite reacted more easily with C at high temperatures to form SiC and SiO. The results of the study are highly significant for improving the reaction mechanism in the smelting process of MG-Si and enhancing the production efficiency of MG-Si. metallurgical-grade silicon carbothermal reduction crystalline transformation diffusion couples Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 1. Introduction Metallurgical-grade silicon (MG-Si) is a vital industrial raw material widely used in photovoltaic, semiconductor, and organosilicon industries [ 1 – 3 ]. MG-Si is mainly produced through a carbothermal reduction method, which involves smelting silicon dioxide and a carbonaceous reductant within a submerged arc furnace (SAF) [ 4 – 6 ]. Years of industrial practice and scientific research have revealed that silicon carbide (SiC) and silicon monoxide (SiO) are the primary intermediate products generated within SAF. Both the generation of SiC and the stabilisation of SiO are vital factors influencing the efficiency of MG-Si production [ 7 , 8 ]. Currently, improving the efficiency of SiC generation has been a primary focus for both enterprises and scholars in this field [ 9 , 10 ]. To optimise the MG-Si production process, Hutchison and Abolpour et al. [ 11 , 12 ] investigated the thermodynamics of the production process and developed a thermodynamic diagram for the Si–C–O system. Moreover, Siri et al. [ 13 ] verified the reaction system in SAF by excavating a halted mineral heat furnace and sketched a schematic of the reactions occurring within the furnace by analysing the compositions at various furnace locations. Extensive theoretical studies and production practices have revealed that a low-temperature reaction zone in the furnace, where SiO 2 remains in a solid-phase state, was the main region for SiC generation. In this region, SiC formation mainly depended on reactions (1)–(3) [ 14 ]. Initially, during the contact reaction between SiO 2 and carbonaceous reductant, the direct SiC generation reaction (1) mainly occurred at the interface. Subsequently, as most of the C on the surface of the carbonaceous reductant was consumed in the SiC generation reaction, reaction (1) was less likely to occur at the reaction interface, thereby facilitating the SiO generation reaction (2). In this phase, a part of SiO and a large amount of SiO generated in the high-temperature region was trapped by the carbonaceous reductant in this reaction zone, and then reaction (3) occurred to produce SiC [ 15 – 17 ]. Alan et al. [ 18 ] investigated the kinetics of the carbothermal reduction of SiO 2 and C for SiC synthesis in a temperature range of 1567–2000°C. The result revealed that reaction (3) served as the reaction rate-controlling step and could be described by the shrinkage nucleation model. \(Si{O_2}+3C=SiC+2CO\) [ 1 ] \(Si{O_{2(g)}}+C=Si{\text{O}}+C{O_{(g)}}\) [ 2 ] \(Si{O_{(g)}}+2C=SiC+2C{O_{(g)}}\) [ 3 ] In the process of SiC formation, not only the reaction between different substances occurs, but also the characteristics of the reaction raw materials change with the increase of temperature. In this stage, the carbonaceous reductant mainly undergoes dehydration reactions, which involve the removal of water and volatile components, and feature an increase in graphitisation [ 19 – 21 ]. Moreover, SiO 2 continuously undergoes a more significant crystalline transformation reaction at high temperatures. In the process of solid phase crystal transformation of SiO 2 , the transformation from quartz crystal to cristobalite crystal mainly occurs. [ 22 – 24 ]. Li et al. [ 25 ] formulated a reactivity equation for carbonaceous reductants. The calculation results revealed that coal and charcoal exhibited higher reactivity, petroleum coke featured a greater degree of graphitisation, and carbon black displayed a lower reactivity. This suggests that the significant changes that occurred in the carbonaceous reductant with increasing reaction temperature were not conducive to the optimisation of the smelting reaction. Wiik et al [ 26 ] conducted thermogravimetric experiments using quartz and cristobalite powders mixed with carbon powders, respectively. The results revealed a greater weight loss in the experiments involving the mixture of cristobalite powder and C powder, indicating that cristobalite exhibited a larger specific surface area, which affected the reaction rate. Additionally, Folstad et al. [ 27 , 28 ] investigated the characteristic reactions of SiO2 and SiC with different crystalline shapes via thermogravimetric analysis. The results indicated that despite the theoretical expectation of increased porosity and reactivity in the cristobalite crystalline shape, no significant practical difference was observed. Therefore, further practical exploration is required to analyse the effect of transforming the crystalline form of SiO 2 into cristobalite on the SiC generation reaction. Although existing studies have investigated the in-furnace reactions of MG-Si from various perspectives, these studies have mainly focused on the generation, reaction, and kinetics of intermediates such as SiC and SiO. However, the effect of the transformation of quartz crystal types on in-furnace reactions in SAF has not been systematically investigated. This study aimed to explore the differences in reactivity among different crystal types of quartz through thermogravimetric and diffusion couple experiments and to elucidate the reasons for these differences. These findings are highly significant for improving the reaction system and enhancing the production efficiency and quality of MG-Si. 2. Experimental 2.1Materials In this study, we used silica and charcoal as raw materials. Table 1 shows the chemical composition of silica and the industrial analysis of charcoal. Table 1 The composition analysis of the raw materials Silica Charcoal Composition Fe 2 O 3 Al 2 O 3 CaO SiO 2 FC ad A ad V ad M ad Content % 0.022 0.018 0.002 99.8% 74.06 0.9 21.03 4.01 2.2Experimental Procedure SiO 2 was cut into sheets of 20 mm thickness using a diamond wire cutter and polished on a polishing machine using 500, 800, and 1600 mesh water-abrasive sandpaper in sequence. Charcoal was crushed into 100–200 mesh powder and used as a carbon source. Then, the charcoal powder was pressed into disc-shaped pellets with a diameter of 20 mm and a thickness of 2 cm using a mould under a pressure of 8 t, and an appropriate amount of water was added as a binder. Afterward, the pellets were dried in a blower drying oven at 90 ℃ for 8 h to remove moisture and then prepared for use. Finally, the charcoal pellets were placed on top of the polished silica sheet to obtain the required diffusion couples. The preparation process of the diffusion couple is shown in Fig. 1 . Cristobalite, a high-temperature crystalline silica, was formed from β-quartz through the breaking and remodelling of Si–O bonds at high temperatures. In this experiment, cristobalite was produced by heating the silica to 1600°C, and the temperature was maintained for 2 h. Subsequently, cristobalite was characterised via X-ray diffraction (XRD) (Fig. 6 b). To investigate the effect of quartz and cristobalite on SiC generation through reaction (1), experiments were performed via thermogravimetry. Before conducting the experiment, quartz and prepared cristobalite were individually ground into 180–200 mesh powders and thoroughly mixed with charcoal powder at a molar ratio of 1:3. During the experiment, the furnace chamber was purged with 99.99% argon gas for 30 min to create an oxygen-free environment. The furnace maintained a pressure of 1 bar. Approximately 10 mg of the raw material was used in the experiment, and the temperature increased at a rate of 10 K/min and was held at a temperature of 1673 K for 180 min. Weight loss data were recorded using a computer. To investigate the effect of quartz and square quartz on SiC generation through reaction (3), experiments on the thermal reduction reaction of diffusion-coupled carbon were performed using a box-type resistance furnace. The experimental conditions were maintained at 1873 K for 2 h. The quartz-phase diffusion couple pellet was denoted as C1, and the square quartz-phase diffusion couple pellet was labelled as C2. Before conducting the experiment, the prepared diffusion couple was placed in a corundum boat and loaded into the box-type resistance furnace. Subsequently, the air inside the furnace was evacuated using a mechanical pump, and 99.99% argon was introduced as the protective gas. A continuous flow of argon (50 ml/min) and a constant pressure (1 atm) were maintained throughout the experiment. The chamber resistance furnace was heated, and the temperature was controlled according to a preset programme. Circulating water was used to cool the furnace during the heating process. As the target temperature was reached, the holding time began. At the end of the holding time, the furnace was naturally cooled to room temperature, and the samples were removed. Owing to the loose nature of pellets, epoxy resin was used to secure them in position. After the epoxy resin was completely solidified, it was longitudinally cut using a hand saw, and the cut surface was polished with a polishing machine to facilitate subsequent detection and analysis. The operation flow chart is shown in Fig. 2 . In the chart, ‘A’ represented the contact surface of the diffusion couple, and ‘B’ denoted the reaction cross section. 2.3Analysis and Characterization The chemical composition of the raw materials was examined using an X-ray fluorescence spectrometer (XRF, ZKS100e, Japan) and an X-ray diffractometer (XRD, X’Pert3 Powder, PANalytical, Cu Kα radiation) to investigate the final phase composition of the flake silica. Elemental distributions in the sample cross section were observed via electron probe microanalysis/wavelength dispersive spectroscopy (EPMA-WDS, JXA8230, JEOL, Japan). Weight losses during the reaction of quartz crystallites were examined using a thermogravimetric–differential thermal analyser (TG-DTA,HTG-4,HENVEN, China). The thermodynamics of the carbothermic reduction reaction of silica were calculated using the reaction module of the FactSage 8.1 thermodynamic software. 3. Results and Discussion 3.1Theoretical implications of the quartz-to-cubic quartz transition for carbothermal reduction reactions To visually illustrate the relationship between the three main reactions of SiC generation in the low-temperature region, the standard Gibbs free energy change for reactions (1)– (3) in a temperature range from 1273 to 2273 K was calculated using FactSage 8.1. Figure 3 (a) illustrates the Gibbs free energy change versus temperature for reactions (1)-(3). The calculations revealed that under standard atmospheric pressure, the theoretical initial temperatures for the formation of SiC and SiO from SiO 2 and C were 1517 and 1749°C, respectively. However, in practice, SiC and SiO can reactively form at temperatures lower than theoretical initial reaction temperatures [ 29 – 31 ]. The main reason for the discrepancy between theoretical predictions and practical observations was that the physical phase data collected in the thermodynamic database were primarily based on the stable physical phase structures in the standard state. For example, the thermodynamic parameters of reactant C in reactions (1)–(3) were derived from graphite, which was more stable compared with carbonaceous reductants that are only locally graphitised [ 6 , 32 , 33 ]. Consequently, the theoretical reaction (1) and reaction (2) required a larger energy input, which explains the higher theoretical initial reaction temperature compared with the actual reaction occurrence temperature. Moreover, despite the thermodynamic advantage of reaction (1) over reaction (2), reaction (1) mainly produced solid SiC, while reaction (2) primarily generated gaseous SiO. The kinetic advantage of reaction (2) played a vital role in SiO formation when the carbon source was insufficient [ 14 ]. A comparison of reaction (1) with reaction (3) indicated that the Gibbs free energy of reaction (3) was more negative than that of reaction (1) at temperatures below the SiO production temperature of 1749°C. At this point, reaction (3) gained a thermodynamic advantage over reaction (1). Additionally, because reaction (3) was a gas–solid reaction and reaction (1) was a solid–solid reaction, reaction (3) exhibited better kinetic advantages. The combined thermodynamic and kinetic advantages of reaction (3) made it the predominant reaction for SiC generation. In summary, theoretically, lowering the initial reaction temperature of either reaction (1) or reaction (2) can directly or indirectly promote SiC generation. Regarding the unique effect of SiO2 crystallographic transition on the reaction results [ 26 – 28 ], Fig. 3 (b) shows the theoretical Gibbs free energy differences between pure phase quartz and cristobalite reacting with C at 1573 and 2273°C to produce SiC and SiO. Thermodynamic calculations revealed that quartz and cristobalite reacted with C at standard atmospheric pressure. The theoretical initial reaction temperatures for the formation of SiC were 1712 K and 1640 K, while the theoretical initial reaction temperatures for the SiO formation were 1995 K and 1885 K. Despite the similar molecular formula of quartz and cristobalite, they featured significant differences in the Gibbs free energy variations during the standard reaction. These calculations indicated that the theoretical use of cristobalite instead of quartz in the MG-Si smelting process promoted both reactions (1) and (2). Consequently, this facilitated the direct generation of SiC and SiO, which further facilitated the occurrence of reaction (3) and the large-scale generation of SiC. 3.2Effect of substitution of quartz by cristobalite on SiC generation 3.2.1Crystalline phase transition of quartz Similar to the heating process during the descent of charges in an electric furnace, the quartz raw material was roasted to observe the transformation of its crystal shape during the heating process. XRD patterns (Fig. 4(a)–(b) revealed significant changes in the quartz crystal shape after roasting at 1600°C for 2 h. Figure 4(a) shows that the crystal type of the quartz raw material used for smelting at room temperature mainly consisted of α-quartz. Figure 4(b) shows the crystalline state of quartz raw materials after roasting and holding at 1600°C for 2 h. Almost all the quartz phases transitioned to cristobalite, and the holding time at 1600°C provided the energy required for phase transition nucleation and growth. The formation of another high-temperature crystalline form of silica (i.e., phosphor quartz) was not observed during the process possibly because the formation of phosphor quartz required certain impurity doping [ 34 – 36 ]. Therefore, only the effect of silica transformation from quartz to square quartz on SiC generation needs to be considered during the smelting process. The red line in the figure represented the raw XRD diffraction data, the blue line was obtained from the Rietveld refinement calculations, and the purple line indicated the error between the raw data and refinement calculations. The curve calculated through Rietveld refinement significantly corresponded to the experimentally obtained diffraction curve, indicating that the roasted quartz was completely transformed into square quartz. Figures 4(c)–(d) show the morphology of the quartz samples before and after roasting. Notably, the heat-treated and non-heat-treated samples featured significant morphological differences. The non-heat-treated sample exhibited a smooth and flat surface and displayed a hard texture that was not easily broken. In contrast, the surface of the heat-treated sample featured cracks and a significantly large size, making it susceptible to breakage upon the application of a slight external force. This result was consistent with Wiik's [ 8 ] explanation that the density of the quartz phase decreased during its transformation to square quartz, resulting in tensions that made the samples fragile. 3.2.2 Changes in SiC formation To effectively visualise the difference in reactivity between quartz and cristobalite, the direct carbothermal reduction reaction (reaction 1) was analysed via thermogravimetry (Fig. 5 ). The entire reaction process was classified into three stages. Stage ① occurred at temperatures below 1400 ℃. Although the carbothermal reduction reaction temperature was not reached at this time, a decrease in mass was observed at this stage. This reduction was attributable to the presence of a certain amount of volatile matter and moisture in the charcoal. As the temperature increased, the volatile matter and moisture gradually volatilised, resulting in a decrease in mass. During the heating process, the charcoal underwent cracking [ 19 – 21 ]. Stage ② began at 1400 ℃ as the volatile matter in the charcoal was significantly volatilised. According to the description of reaction (1), the charcoal and silica reacted and produced CO gas, and the rate of mass reduction in the cristobalite phase exceeded that in the quartz phase. The weight loss rate of cristobalite, as calculated, was 1.45 times that of quartz. In stage ③, as the holding time reached 250 min, the slope of the cristobalite mass reduction curve slope approached 0, while at this time, the mass reduction of the quartz carbonaceous reductant continuously decreased. This observation confirmed that cristobalite exhibited a higher reactivity from an alternative perspective. The elemental distribution of cross-section B after diffusion couple reaction was characterised via EPMA, and the results are shown in Fig. 6 . Figures 6 (a)–(d) illustrate the elemental distribution of C1 under a temperature condition maintained at 1600°C for 2 h. Figures 6 (a)-(b) represent the electron micrographs of the C1 reaction cross section. It can be seen that there are obvious contrast differences between the two phases.A large greyish-white area was visible near the contact surface, while the region farther from the contact surface was dominated by grey areas. The grey-white region featured a measured depth of 593.75 µm. The EPMA map (Fig. 6 c) indicated that the grey-white region represented the diffusion of Si elements into the charcoal interior. This was due to the inward reaction of SiO gas, an intermediate product of the carbothermal reduction, through the pores inside the charcoal, which generated SiC in the interior of the charcoal [ 37 , 38 ]. Figure 6 (d) shows A gradual inward decrease in elemental C within the contact region, which occurred due to the escape of elemental C in the form of CO according to reaction (3). Figures 6 (e)–(h) show the electron micrographs of the C2 reaction cross section. Figures 6 (e)–(f) illustrate a similar diffusion pattern in grey-white and quartz diffusion couples. However, the grey-white region of the C2 reaction cross section exhibited a larger size than the C1 region, which extended to 920.87 µm. The Si element in C2 exhibited a larger diffusion depth than the C2 Si element (Fig. 6 g). Figure 6 (h) shows the EPMA plot of elemental C for the square quartz diffusion couple. This observation confirmed that the escape of CO was significantly higher within square quartz compared with quartz. Thus, the square quartz featured a stronger capacity to produce SiO through reaction (2) with C compared with quartz. This increased SiO production, leading to the generation of SiC through reaction (3), consistent with the thermodynamic calculations. 3.3 The mechanism of the transformation of quartz to cristobalite to promote the formation of SiC The crystalline transition of quartz into cristobalite involved high-temperature structural changes, including the fracture and remodelling of silica–oxygen tetrahedra in the silica crystals. A schematic of the crystal structure of SiO 2 refined after Rietveld refinement for both crystal types is shown in Fig. 7 . The α-quartz was characterised by a hexagonal crystal system, with a P622 space group and cell parameters a = b = 5.01Å, c = 5.47Å, α = β = 90°, γ = 120°, low symmetry, and compactness (Fig. 7 a). As the temperature exceeded 1400°C, the β-quartz was further transformed into cristobalite. The α-cristobalite was characterised by a cubic crystal system with a space group Fd \(\stackrel{-}{3}\) m and cell parameters a = b = c = 5.405 Å, α = β = γ = 90° (Fig. 7 b). This transformation was irreversible; thus, cristobalite did not revert to β-quartz or α-quartz at lower temperatures. According to the previous experimental results, the difference in reactivity between cristobalite and quartz was analysed from the microscopic perspective of the crystal structure. Cristobalite, a high-temperature crystalline silica, was formed from β-quartz through the breaking and remodelling of Si–O bonds above 1400°C. Because the phase transition process was endothermic, cristobalite exhibited high internal energy and chemical potential energy. Additionally, the Si–O bond length was altered during the process of Si–O bond reconstruction. Particularly, β-quartz featured a Si–O bond length of 1.58 Å, while square quartz exhibited a Si–O bond length of 1.62 Å. A longer bond length indicates a lower energy required for breaking. Cristobalite featured a more porous and loose structure compared with β-quartz, characterised by three main changes. First, the connection between the Si–O tetrahedra shifted from bridge bonds to double bonds. Second, the angle between the Si–O tetrahedra changed from 120° to 90°. Third, the bond length of the Si–O bond changed from 1.58 Å for the β-quartz Si–O bond to 1.62 Å for the square quartz Si–O bond. Furthermore, square quartz, a high-temperature crystalline silica, exhibited high internal and chemical potential energy but low stability at high temperatures compared with β-quartz, making square quartz more reactive with other compounds [ 39 – 41 ]. 4. Conclusion The carbothermal reduction reaction between silica and charcoal during industrial silicon smelting was simulated via thermogravimetric and diffusion couple methods. Additionally, the effects of different crystalline types of silica (i.e., quartz and quartzite) on the generation of silicon carbide and their reaction mechanisms were investigated through thermodynamic calculations and theoretical analyses. This study presents the following key conclusions: Cristobalite contributed to the production of SiC both directly through reaction (1) and indirectly through reaction (2). Cristobalite reacted more easily with carbon than quartz due to two main reasons: ① The phase transition of silica from quartz to cristobalite was an endothermic process, therefore, cristobalite exhibited a higher internal energy and chemical potential. At high temperatures, cristobalite was prone to decomposition or reduction. ② β-quartz exhibited a Si–O bond length of 1.58 Å, while the cristobalite featured a Si–O bond length of 1.62 Å. Longer bond lengths required less energy for breaking, making cristobalite more likely to undergo carbothermal reduction at the same temperature. Declarations Ethics Approval The data of our submission requires ethics approval and compliance with ethical standards. Consent to Participate Not applicable. Consent for Publication Not applicable.Informed Consent All authors and associated personnel are aware of and agree to the content of this submission. Conflict of Interest The authors declare that we have no financial and personal relationships with other people or organizations that can inappropriately influence our work, there is no professional or other personal interest of any nature or kind in any product, service and/or company that could be construed as influencing the position presented in, or the review of, the manuscript entitled, “A study of the effect of quartz-to-cristobalite transformation on SiC generation in metallurgical-grade silicon production”. Competing Interests The authors declare no competing interests. Acknowledgments We gratefully acknowledge that this study was supported by the Yunnan Outstanding Youth Fund (No. 202101AV070007), and the Major Science and Technology Projects in Yunnan Province (No. 202202AG050012). Authors’ Contribution Jiahe Tian: Conceptualization, Methodology, Writing-original draft. Data curation Xiaocong Deng: Writing-review. Data curation. Kuixian Wei: Writing-review & editing, Super-vision, Funding acquisition. Wenhui Ma: Supervision, Funding acquisition. References Yuelong Yu X, Bai S, Li J, Shi L, Wang F, Xi W, Ma R, Deng (2023) Review of silicon recovery in the photovoltaic industry. Curr Opin Green Sustainable Chem 44:100870. https://doi.org/10.1016/j.cogsc.2023.100870 Ma L, Yu Z, Ma W, Qing S, Wu J (2019) Assessment and study on the impact on environment by multi-crystalline silicon preparation by metallurgical route. Silicon 11:1383–1391. https://doi.org/10.1007/s12633-018-9937-6 Lei Y, Ma W, Wu J, Wei K, Li S, Morita K (2018) Impurity phases and their removal in Si purification with Al–Si alloy using transition metals as additives. J Alloys Compd 734:250–257. https://doi.org/10.1016/j.jallcom.2017.10.292 Ringdalen E, Tangstad M (2012) Reaction mechanisms in carbothermic production of silicon, study of selected reactions. The Minerals, Metals & Materials Society (TMS), pp 195–203 Chen Z, Ma W, Wu J, Wei K, Yang X, Lv G, Yu J (2016) Influence of carbothermic reduction on submerged arc furnace energy effic-iency during silicon production. Energy 116:687–693. https://doi.org/10.1016/j.energy.2016.09.034 Schei A, Tuset JK, Tveit H (1998) Production of high silicon alloy. Tapir Tangstad M, Ksiazek M, Andersen V, Ringdalen E (2010), June Small scale laboratory experiments simulating an industrial silicon furnace. In Proceedings of the Twelfth International Ferroalloys Congress, Sustainable Future, Helsinki, Finland (pp. 6–9) Wiik K, Motzfeldt K (1995) Kinetics of reactions between silica and carbon and the formation of silicon carbide. MRS Online Proceedings Library (OPL), 410, 435. https://doi.org/10.1557/PROC-410-435 Van Dijen FK, Metselaar R (1991) The chemistry of the carbothermal synthesis of β-SiC: Reaction mechanism, reaction rate and grain growth. J Eur Ceram Soc 7(3):177–184. https://doi.org/10.1016/0955-2219(91)90035-X Li X, Zhang G, Ostrovski O, Tronstad R (2016) Effect of gas atmosphere on the formation of silicon by reaction of SiC and SiO 2 . J Mater Sci 51:876–884. https://doi.org/10.1007/s10853-015-9413-2 Hutchison SG, Richardson LS, Wai CM (1988) Carbothermic reduction of silicon dioxide—A thermodynamic investigation. Metall Trans B 19:249–253. https://doi.org/10.1007/BF02654209 Abolpour B, Shamsoddini R (2020) Mechanism of reaction of silica and carbon for producing silicon carbide. Prog React Kinet Mech 45:1468678319891416. https://doi.org/10.1177/1468678319891416 Bø SM (2016) Phases and zones in the silicon process (Master's thesis, NTNU). http://hdl.handle.net/11250/2407000 Liu D, Deng X, ai J, Yang S, Wei K, ,&Ma W (2022) Formation mechanism of sic in the diffusion couple interface during the mg-si pro-duction process. Silicon 14(17):11371–11380. https://doi.org/10.1007/s12633-022-01876-4 Li X, Zhang G, Tang K, Ostrovski O, Tronstad R (2015) Carbothermal reduction of quartz in different gas atmospheres. Metall Mater Trans B 46:1343–1352. https://doi.org/10.1007/s11663-015-0293-2 Vangskåsen J (2012) Metal-producing mechanisms in the carbothermic sili-con process (Master's thesis, Institutt for materialteknologi). http://hdl.handle.net/11250/249099 Agarwal A, Pad U (1999) Influence of pellet composition and structure on carbothermic reduction of silica. Metall Mater Trans B 30:295–306. https://doi.org/10.1007/s11663-999-0059-9 Weimer AW, Nilsen KJ, Cochran GA, Roach RP (1993) Kinetics of carbothermal reduction synthesis of beta silicon carbide. AIChE J 39(3). https://doi.org/10.1002/aic.690390311 Várhegyi G, Szabó P, Till F, Zelei B, Antal MJ, Dai X (1998) TG, TG-MS, and FTIR characterization of high-yield biomass charcoals. Energy Fuels 12(5):969–974. https://doi.org/10.1021/ef9800359 Jayaraman K, Kok MV, Gokalp I (2017) Thermogravimetric and mass spectrometric (TG-MS) analysis and kinetics of coal-biomass blends. Renewable Energy 101:293–300. https://doi.org/10.1016/j.renene.2016.08.072 Surup GR, Nielsen HK, Heidelmann M, Trubetskaya A (2019) Characterization and reactivity of charcoal from high temperature pyrolysis (800–1600 ℃). Fuel 235:1544–1554. https://doi.org/10.1016/j.fuel.2018.08.092 Kjelstadli ME (2016) Kinetics and mechanism of phase transformations from quartz to cristobalite (Master's thesis, NTNU). http://hdl.handle.net/11250/2406964 Ringdalen E (2015) Changes in quartz during heating and the possible effects on Si production. Jom 67:484–492. https://doi.org/10.1007/s11837-014-1149-y Feya OD, Wang Q, Lepeshkin SV, Baturin VS, Uspenskii YA, Oganov AR (2018) Tetrahedral honeycomb surface reconstructions of quartz, cristobalite and stishovite. Sci Rep 8(1):11947. https://doi.org/10.1038/s41598-018-29853-1 Li F, Tangstad M, Ringdalen E (2018) Carbothermal reduction of quartz and carbon pellets at elevated temperatures. Metall Mater Trans B 49:1078–1088. https://doi.org/10.1007/s11663-018-1195-x Wiik K (1990) Kinetics of reactions between silica and carbon. Norges tekniske høgskole. Institutt for uorganisk kjemi. http://hdl.handle.net/11250/2396774 Folstad MB, Ringdalen E, Tveit H, Tangstad M (2021) Effect of different SiO 2 polymorphs on the reaction between SiO 2 and SiC in Si pr-oduction. Metall Mater Trans B 52:792–803. https://doi.org/10.1007/s11663-020-02053-x Folstad MB (2017) Effect of different polymorphs of SiO 2 on the reaction between SiO 2 and SiC in Si production(Master's thesis, NTNU). http://hdl.handle.net/11250/2453816 Jayakumari S, Tangstad M (2020) Transformation of β-SiC from cha-rcoal, coal, and petroleum coke to α-SiC at higher temperatures. Metall Mater Trans B 51:2673–2688. https://doi.org/10.1007/s11663-020-01970-1 Andresen B (1995) Process model for carbothermic production of silicon metal Pavelko RG, Sevast’yanov VG, Ezhov YS, Kuznetsov NT (2007) Silicon carbide transport during carbothermic reduction of SiO 2 : Ther-modynamic evaluation and experimental study. Inorg Mater 43:700–703. https://doi.org/10.1134/S0020168507070059 : Myrvågnes. Analyses and characterization of fossil carbonaceous materials for silicon production, 2008[J]. NTNU, Trondheim http://hdl.handle.net/11250/248717 Seo WS, Koumoto K (1996) Stacking faults in β-SiC formed during carbothermal reduction of SiO 2 . J Am Ceram Soc 79(7):1777–1782. https://doi.org/10.1111/j.1151-2916.1996.tb07995.x Stevens SJ, Hand RJ, Sharp JH (1997) Polymorphism of silica. J Mater Sci 32:2929–2935. https://doi.org/10.1023/A:1018636920023 Buerger MJ (1954) The stuffed derivatives of the silica structures. American Mineralogist: Journal of Earth and Planetary Materials, 39(7–8), 600–614 Buerger MJ (1936) The general rôle of composition in polymorphism. Proc-eedings of the National Academy of Sciences 22(12):685–689. https://doi.org/10.1073/pnas.22.12.685 Nordbø EA (2019) Interaction of SiO-gas and Charcoal and the Formation of SiC and Si (Master's thesis, NTNU). http://hdl.handle.net/11250/2623366 Myrhaug EH (2005) Non-fossil reduction materials in the silicon process: Properties and behaviour Wu Z, Hao X, Liu X, Meng J (2007) Structures and elastic properties of OsN 2 investigated via first-principles density functional calculations. Phys Rev B 75(5):054115. https://doi.org/10.1103/PhysRevB.75.054115 Buerger ΜJ (1935) The silica framework crystals and their stability- fields. Z für Kristallographie-Crystalline Mater 90(1–6):186–192. https://doi.org/10.1524/zkri.1935.90.1.186 Sun T (1989) Effects of solid solution on the high-low inversion of cristobalite and the stabilization of high cristobalite (Doctoral dissertation, Virginia Polytechnic Institute and State University). http://hdl.handle.net/10919/54793 Additional Declarations No competing interests reported. Cite Share Download PDF Status: Published Journal Publication published 20 Feb, 2024 Read the published version in Silicon → Version 1 posted Editorial decision: Revision requested 20 Jan, 2024 Reviews received at journal 19 Jan, 2024 Reviewers agreed at journal 16 Jan, 2024 Reviewers invited by journal 16 Jan, 2024 Editor assigned by journal 16 Jan, 2024 Submission checks completed at journal 16 Jan, 2024 First submitted to journal 03 Jan, 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. We do this by developing innovative software and high quality services for the global research community. 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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-3831130","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":267522359,"identity":"55eb4c4f-761d-4d75-8dc1-5471e6a9043a","order_by":0,"name":"嘉禾 田","email":"","orcid":"","institution":"Kunming University of Science and Technology","correspondingAuthor":false,"prefix":"","firstName":"嘉禾","middleName":"","lastName":"田","suffix":""},{"id":267522360,"identity":"b83ecc13-140b-4282-ae64-767ae43f7224","order_by":1,"name":"Kuixian Wei","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA5UlEQVRIiWNgGAWjYBACCRCRUCHBw8/eAxbg4SNOyxkbOcmeMwwMB4Ba2IjSwtiWZmxwIweshYGgFskZOYYPHrAdTpw58+3Bxx9z7GTYGJgfPrqBR4s0zxljgwSew4n90nnJBge3JQMdxmZsnINHixx77zaJBAmgLbNzzCQObmMGauFhk8arhZl3+48Eg8OJG26eAWmpJ6xFGmgLQ0ICyPs8IC2HCWuR7Dn/WSLhACiQc4wNzm47zsPGTMAvEjfSEj/+/AeKyjOGDyq3Vdvzszc/fIxPCxbATJryUTAKRsEoGAVYAAB+90fnnWU9eQAAAABJRU5ErkJggg==","orcid":"","institution":"Kunming University of Science and Technology","correspondingAuthor":true,"prefix":"","firstName":"Kuixian","middleName":"","lastName":"Wei","suffix":""},{"id":267522361,"identity":"69052df6-ce86-4075-9a71-ed785003277b","order_by":2,"name":"Xiaocong Deng","email":"","orcid":"","institution":"Kunming University of Science and Technology","correspondingAuthor":false,"prefix":"","firstName":"Xiaocong","middleName":"","lastName":"Deng","suffix":""},{"id":267522362,"identity":"1e62d1f8-244d-4fca-9764-a4fc45bacd3f","order_by":3,"name":"Wenhui Ma","email":"","orcid":"","institution":"Kunming University of Science and Technology","correspondingAuthor":false,"prefix":"","firstName":"Wenhui","middleName":"","lastName":"Ma","suffix":""}],"badges":[],"createdAt":"2024-01-03 06:04:46","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-3831130/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-3831130/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1007/s12633-024-02908-x","type":"published","date":"2024-02-20T15:01:28+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":49797368,"identity":"1aba73d5-36a8-489e-9423-ff9b08ca08c2","added_by":"auto","created_at":"2024-01-18 07:40:55","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":4501752,"visible":true,"origin":"","legend":"\u003cp\u003eThe flowchart of thepreparation of the diffusion coup\u003c/p\u003e","description":"","filename":"Fig.1.png","url":"https://assets-eu.researchsquare.com/files/rs-3831130/v1/b9fefa21dd7eee367dc819fe.png"},{"id":49797371,"identity":"5ea2b8e7-55d3-4072-ba5f-e458bdd3a137","added_by":"auto","created_at":"2024-01-18 07:40:55","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":104499,"visible":true,"origin":"","legend":"\u003cp\u003eSchematic diagram of diffusion couple sample processing\u003c/p\u003e","description":"","filename":"Fig.2.png","url":"https://assets-eu.researchsquare.com/files/rs-3831130/v1/1e4d9ea547b8200ac364343b.png"},{"id":49797876,"identity":"fcc9c530-d38c-4ae1-bdb2-0e3c58f86aff","added_by":"auto","created_at":"2024-01-18 07:48:55","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":1217111,"visible":true,"origin":"","legend":"\u003cp\u003e(\u003cstrong\u003ea\u003c/strong\u003e) Thermodynamics of carbothermal reduction reactions (\u003cstrong\u003eb\u003c/strong\u003e) Gibbs free energies of quartz and cubic quartz reactions with C\u003c/p\u003e","description":"","filename":"Fig.3.png","url":"https://assets-eu.researchsquare.com/files/rs-3831130/v1/21803d26feb25e07e375d945.png"},{"id":49797372,"identity":"189a120d-4bce-4b06-beda-7365bb7d590b","added_by":"auto","created_at":"2024-01-18 07:40:55","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":7858632,"visible":true,"origin":"","legend":"\u003cp\u003eSamples before and after roasting and their XRD patterns (\u003cstrong\u003ea\u003c/strong\u003e). Raw quartz XRD (\u003cstrong\u003eb\u003c/strong\u003e). Raw square quartz XRD (\u003cstrong\u003ec\u003c/strong\u003e).Raw quartz (\u003cstrong\u003ed\u003c/strong\u003e). Cristobalite\u003c/p\u003e","description":"","filename":"Fig.4.png","url":"https://assets-eu.researchsquare.com/files/rs-3831130/v1/e52ae81e9ac752491b4b0c62.png"},{"id":49797369,"identity":"0bcf23ca-38fb-4c31-aafd-7a846d7bf7df","added_by":"auto","created_at":"2024-01-18 07:40:55","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":1519120,"visible":true,"origin":"","legend":"\u003cp\u003eThermogravimetric analysis of the reaction (1) of quartz and cristobalite\u003c/p\u003e","description":"","filename":"Fig.5.png","url":"https://assets-eu.researchsquare.com/files/rs-3831130/v1/0ad8628554e50ca3f8f8f869.png"},{"id":49797373,"identity":"d6b11708-8912-49d6-b2a7-e7fdfc2a6fb4","added_by":"auto","created_at":"2024-01-18 07:40:55","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":8502280,"visible":true,"origin":"","legend":"\u003cp\u003eEPMA analysis of diffusion coupled reductant reaction cross sections. \u003cstrong\u003e(a)-(d) \u003c/strong\u003eElectron microscopy and elemental distribution of the C1 reaction cross section\u003cstrong\u003e (e)-(h) \u003c/strong\u003eElectron microscopy and elemental distribution of the C2 reaction cross section\u003c/p\u003e","description":"","filename":"Fig.6.png","url":"https://assets-eu.researchsquare.com/files/rs-3831130/v1/d01991ceea9e758ad4571aec.png"},{"id":49797374,"identity":"ecac6b1f-8950-431a-858d-d7e0799e48b6","added_by":"auto","created_at":"2024-01-18 07:40:55","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":9823902,"visible":true,"origin":"","legend":"\u003cp\u003eQuartz phase transformation crystal structure transformation (\u003cstrong\u003ea\u003c/strong\u003e) α-quartz ;(\u003cstrong\u003eb)\u003c/strong\u003e α-cristobalite\u003c/p\u003e","description":"","filename":"Fig.7.png","url":"https://assets-eu.researchsquare.com/files/rs-3831130/v1/f097f26fce9a7d23de73d995.png"},{"id":51648353,"identity":"8c1e33c4-25ae-4c0b-acd8-ab0a39d155ed","added_by":"auto","created_at":"2024-02-26 15:12:38","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":3347901,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-3831130/v1/f60eab68-2dac-403c-95f6-4d5b872d9b26.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"A study of the effect of quartz-to-cristobalite transformation on SiC generation in metallurgical-grade silicon production","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eMetallurgical-grade silicon (MG-Si) is a vital industrial raw material widely used in photovoltaic, semiconductor, and organosilicon industries [\u003cspan additionalcitationids=\"CR2\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. MG-Si is mainly produced through a carbothermal reduction method, which involves smelting silicon dioxide and a carbonaceous reductant within a submerged arc furnace (SAF) [\u003cspan additionalcitationids=\"CR5\" citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]. Years of industrial practice and scientific research have revealed that silicon carbide (SiC) and silicon monoxide (SiO) are the primary intermediate products generated within SAF. Both the generation of SiC and the stabilisation of SiO are vital factors influencing the efficiency of MG-Si production [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. Currently, improving the efficiency of SiC generation has been a primary focus for both enterprises and scholars in this field [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e, \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eTo optimise the MG-Si production process, Hutchison and Abolpour et al. [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e, \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e] investigated the thermodynamics of the production process and developed a thermodynamic diagram for the Si\u0026ndash;C\u0026ndash;O system. Moreover, Siri et al. [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e] verified the reaction system in SAF by excavating a halted mineral heat furnace and sketched a schematic of the reactions occurring within the furnace by analysing the compositions at various furnace locations. Extensive theoretical studies and production practices have revealed that a low-temperature reaction zone in the furnace, where SiO\u003csub\u003e2\u003c/sub\u003e remains in a solid-phase state, was the main region for SiC generation. In this region, SiC formation mainly depended on reactions (1)\u0026ndash;(3) [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e]. Initially, during the contact reaction between SiO\u003csub\u003e2\u003c/sub\u003e and carbonaceous reductant, the direct SiC generation reaction (1) mainly occurred at the interface. Subsequently, as most of the C on the surface of the carbonaceous reductant was consumed in the SiC generation reaction, reaction (1) was less likely to occur at the reaction interface, thereby facilitating the SiO generation reaction (2). In this phase, a part of SiO and a large amount of SiO generated in the high-temperature region was trapped by the carbonaceous reductant in this reaction zone, and then reaction (3) occurred to produce SiC [\u003cspan additionalcitationids=\"CR16\" citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e]. Alan et al. [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e] investigated the kinetics of the carbothermal reduction of SiO\u003csub\u003e2\u003c/sub\u003e and C for SiC synthesis in a temperature range of 1567\u0026ndash;2000\u0026deg;C. The result revealed that reaction (3) served as the reaction rate-controlling step and could be described by the shrinkage nucleation model.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"No\" id=\"Taba\" border=\"1\"\u003e \u003ccolgroup cols=\"2\"\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 \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(Si{O_2}+3C=SiC+2CO\\)\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003e[\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(Si{O_{2(g)}}+C=Si{\\text{O}}+C{O_{(g)}}\\)\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e[\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(Si{O_{(g)}}+2C=SiC+2C{O_{(g)}}\\)\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e[\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]\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\u003eIn the process of SiC formation, not only the reaction between different substances occurs, but also the characteristics of the reaction raw materials change with the increase of temperature. In this stage, the carbonaceous reductant mainly undergoes dehydration reactions, which involve the removal of water and volatile components, and feature an increase in graphitisation [\u003cspan additionalcitationids=\"CR20\" citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e]. Moreover, SiO\u003csub\u003e2\u003c/sub\u003e continuously undergoes a more significant crystalline transformation reaction at high temperatures. In the process of solid phase crystal transformation of SiO\u003csub\u003e2\u003c/sub\u003e, the transformation from quartz crystal to cristobalite crystal mainly occurs. [\u003cspan additionalcitationids=\"CR23\" citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e]. Li et al. [\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e] formulated a reactivity equation for carbonaceous reductants. The calculation results revealed that coal and charcoal exhibited higher reactivity, petroleum coke featured a greater degree of graphitisation, and carbon black displayed a lower reactivity. This suggests that the significant changes that occurred in the carbonaceous reductant with increasing reaction temperature were not conducive to the optimisation of the smelting reaction. Wiik et al [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e] conducted thermogravimetric experiments using quartz and cristobalite powders mixed with carbon powders, respectively. The results revealed a greater weight loss in the experiments involving the mixture of cristobalite powder and C powder, indicating that cristobalite exhibited a larger specific surface area, which affected the reaction rate. Additionally, Folstad et al. [\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e, \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e] investigated the characteristic reactions of SiO2 and SiC with different crystalline shapes via thermogravimetric analysis. The results indicated that despite the theoretical expectation of increased porosity and reactivity in the cristobalite crystalline shape, no significant practical difference was observed. Therefore, further practical exploration is required to analyse the effect of transforming the crystalline form of SiO\u003csub\u003e2\u003c/sub\u003e into cristobalite on the SiC generation reaction.\u003c/p\u003e \u003cp\u003eAlthough existing studies have investigated the in-furnace reactions of MG-Si from various perspectives, these studies have mainly focused on the generation, reaction, and kinetics of intermediates such as SiC and SiO. However, the effect of the transformation of quartz crystal types on in-furnace reactions in SAF has not been systematically investigated. This study aimed to explore the differences in reactivity among different crystal types of quartz through thermogravimetric and diffusion couple experiments and to elucidate the reasons for these differences. These findings are highly significant for improving the reaction system and enhancing the production efficiency and quality of MG-Si.\u003c/p\u003e"},{"header":"2. Experimental","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1Materials\u003c/h2\u003e \u003cp\u003eIn this study, we used silica and charcoal as raw materials. Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e shows the chemical composition of silica and the industrial analysis of charcoal.\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\u003eThe composition analysis of the raw materials\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"9\"\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 \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c9\" colnum=\"9\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/th\u003e \u003cth align=\"left\" colspan=\"4\" nameend=\"c5\" namest=\"c2\"\u003e \u003cp\u003eSilica\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"4\" nameend=\"c9\" namest=\"c6\"\u003e \u003cp\u003eCharcoal\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eComposition\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eAl\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eCaO\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eSiO\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eFC\u003csub\u003ead\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003eA\u003csub\u003ead\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003eV\u003csub\u003ead\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003eM\u003csub\u003ead\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eContent %\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.022\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.018\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.002\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e99.8%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e74.06\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e0.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e21.03\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e4.01\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=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2Experimental Procedure\u003c/h2\u003e \u003cp\u003eSiO\u003csub\u003e2\u003c/sub\u003e was cut into sheets of 20 mm thickness using a diamond wire cutter and polished on a polishing machine using 500, 800, and 1600 mesh water-abrasive sandpaper in sequence. Charcoal was crushed into 100\u0026ndash;200 mesh powder and used as a carbon source. Then, the charcoal powder was pressed into disc-shaped pellets with a diameter of 20 mm and a thickness of 2 cm using a mould under a pressure of 8 t, and an appropriate amount of water was added as a binder. Afterward, the pellets were dried in a blower drying oven at 90 ℃ for 8 h to remove moisture and then prepared for use. Finally, the charcoal pellets were placed on top of the polished silica sheet to obtain the required diffusion couples. The preparation process of the diffusion couple is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eCristobalite, a high-temperature crystalline silica, was formed from β-quartz through the breaking and remodelling of Si\u0026ndash;O bonds at high temperatures. In this experiment, cristobalite was produced by heating the silica to 1600\u0026deg;C, and the temperature was maintained for 2 h. Subsequently, cristobalite was characterised via X-ray diffraction (XRD) (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e6\u003c/span\u003eb).\u003c/p\u003e \u003cp\u003eTo investigate the effect of quartz and cristobalite on SiC generation through reaction (1), experiments were performed via thermogravimetry. Before conducting the experiment, quartz and prepared cristobalite were individually ground into 180\u0026ndash;200 mesh powders and thoroughly mixed with charcoal powder at a molar ratio of 1:3. During the experiment, the furnace chamber was purged with 99.99% argon gas for 30 min to create an oxygen-free environment. The furnace maintained a pressure of 1 bar. Approximately 10 mg of the raw material was used in the experiment, and the temperature increased at a rate of 10 K/min and was held at a temperature of 1673 K for 180 min. Weight loss data were recorded using a computer. To investigate the effect of quartz and square quartz on SiC generation through reaction (3), experiments on the thermal reduction reaction of diffusion-coupled carbon were performed using a box-type resistance furnace. The experimental conditions were maintained at 1873 K for 2 h. The quartz-phase diffusion couple pellet was denoted as C1, and the square quartz-phase diffusion couple pellet was labelled as C2. Before conducting the experiment, the prepared diffusion couple was placed in a corundum boat and loaded into the box-type resistance furnace. Subsequently, the air inside the furnace was evacuated using a mechanical pump, and 99.99% argon was introduced as the protective gas. A continuous flow of argon (50 ml/min) and a constant pressure (1 atm) were maintained throughout the experiment. The chamber resistance furnace was heated, and the temperature was controlled according to a preset programme. Circulating water was used to cool the furnace during the heating process. As the target temperature was reached, the holding time began. At the end of the holding time, the furnace was naturally cooled to room temperature, and the samples were removed. Owing to the loose nature of pellets, epoxy resin was used to secure them in position. After the epoxy resin was completely solidified, it was longitudinally cut using a hand saw, and the cut surface was polished with a polishing machine to facilitate subsequent detection and analysis. The operation flow chart is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e. In the chart, \u0026lsquo;A\u0026rsquo; represented the contact surface of the diffusion couple, and \u0026lsquo;B\u0026rsquo; denoted the reaction cross section.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e2.3Analysis and Characterization\u003c/h2\u003e \u003cp\u003eThe chemical composition of the raw materials was examined using an X-ray fluorescence spectrometer (XRF, ZKS100e, Japan) and an X-ray diffractometer (XRD, X\u0026rsquo;Pert3 Powder, PANalytical, Cu Kα radiation) to investigate the final phase composition of the flake silica. Elemental distributions in the sample cross section were observed via electron probe microanalysis/wavelength dispersive spectroscopy (EPMA-WDS, JXA8230, JEOL, Japan). Weight losses during the reaction of quartz crystallites were examined using a thermogravimetric\u0026ndash;differential thermal analyser (TG-DTA,HTG-4,HENVEN, China). The thermodynamics of the carbothermic reduction reaction of silica were calculated using the reaction module of the FactSage 8.1 thermodynamic software.\u003c/p\u003e \u003c/div\u003e"},{"header":"3. Results and Discussion","content":"\u003cdiv id=\"Sec7\" class=\"Section2\"\u003e\n \u003ch2\u003e3.1Theoretical implications of the quartz-to-cubic quartz transition for carbothermal reduction reactions\u003c/h2\u003e\n \u003cp\u003eTo visually illustrate the relationship between the three main reactions of SiC generation in the low-temperature region, the standard Gibbs free energy change for reactions (1)\u0026ndash; (3) in a temperature range from 1273 to 2273 K was calculated using FactSage 8.1. Figure \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e(a) illustrates the Gibbs free energy change versus temperature for reactions (1)-(3). The calculations revealed that under standard atmospheric pressure, the theoretical initial temperatures for the formation of SiC and SiO from SiO\u003csub\u003e2\u003c/sub\u003e and C were 1517 and 1749\u0026deg;C, respectively. However, in practice, SiC and SiO can reactively form at temperatures lower than theoretical initial reaction temperatures [\u003cspan class=\"CitationRef\"\u003e29\u003c/span\u003e\u0026ndash;\u003cspan class=\"CitationRef\"\u003e31\u003c/span\u003e]. The main reason for the discrepancy between theoretical predictions and practical observations was that the physical phase data collected in the thermodynamic database were primarily based on the stable physical phase structures in the standard state. For example, the thermodynamic parameters of reactant C in reactions (1)\u0026ndash;(3) were derived from graphite, which was more stable compared with carbonaceous reductants that are only locally graphitised [\u003cspan class=\"CitationRef\"\u003e6\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e32\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e33\u003c/span\u003e]. Consequently, the theoretical reaction (1) and reaction (2) required a larger energy input, which explains the higher theoretical initial reaction temperature compared with the actual reaction occurrence temperature. Moreover, despite the thermodynamic advantage of reaction (1) over reaction (2), reaction (1) mainly produced solid SiC, while reaction (2) primarily generated gaseous SiO. The kinetic advantage of reaction (2) played a vital role in SiO formation when the carbon source was insufficient [\u003cspan class=\"CitationRef\"\u003e14\u003c/span\u003e]. A comparison of reaction (1) with reaction (3) indicated that the Gibbs free energy of reaction (3) was more negative than that of reaction (1) at temperatures below the SiO production temperature of 1749\u0026deg;C. At this point, reaction (3) gained a thermodynamic advantage over reaction (1). Additionally, because reaction (3) was a gas\u0026ndash;solid reaction and reaction (1) was a solid\u0026ndash;solid reaction, reaction (3) exhibited better kinetic advantages. The combined thermodynamic and kinetic advantages of reaction (3) made it the predominant reaction for SiC generation. In summary, theoretically, lowering the initial reaction temperature of either reaction (1) or reaction (2) can directly or indirectly promote SiC generation.\u003c/p\u003e\n \u003cp\u003eRegarding the unique effect of SiO2 crystallographic transition on the reaction results [\u003cspan class=\"CitationRef\"\u003e26\u003c/span\u003e\u0026ndash;\u003cspan class=\"CitationRef\"\u003e28\u003c/span\u003e], Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e(b) shows the theoretical Gibbs free energy differences between pure phase quartz and cristobalite reacting with C at 1573 and 2273\u0026deg;C to produce SiC and SiO. Thermodynamic calculations revealed that quartz and cristobalite reacted with C at standard atmospheric pressure. The theoretical initial reaction temperatures for the formation of SiC were 1712 K and 1640 K, while the theoretical initial reaction temperatures for the SiO formation were 1995 K and 1885 K. Despite the similar molecular formula of quartz and cristobalite, they featured significant differences in the Gibbs free energy variations during the standard reaction.\u003c/p\u003e\n \u003cp\u003eThese calculations indicated that the theoretical use of cristobalite instead of quartz in the MG-Si smelting process promoted both reactions (1) and (2). Consequently, this facilitated the direct generation of SiC and SiO, which further facilitated the occurrence of reaction (3) and the large-scale generation of SiC.\u003c/p\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec8\" class=\"Section2\"\u003e\n \u003ch2\u003e3.2Effect of substitution of quartz by cristobalite on SiC generation\u003c/h2\u003e\n \u003cdiv id=\"Sec9\" class=\"Section3\"\u003e\n \u003ch2\u003e3.2.1Crystalline phase transition of quartz\u003c/h2\u003e\n \u003cp\u003eSimilar to the heating process during the descent of charges in an electric furnace, the quartz raw material was roasted to observe the transformation of its crystal shape during the heating process. XRD patterns (Fig.\u0026nbsp;4(a)\u0026ndash;(b) revealed significant changes in the quartz crystal shape after roasting at 1600\u0026deg;C for 2 h. Figure\u0026nbsp;4(a) shows that the crystal type of the quartz raw material used for smelting at room temperature mainly consisted of \u0026alpha;-quartz. Figure\u0026nbsp;4(b) shows the crystalline state of quartz raw materials after roasting and holding at 1600\u0026deg;C for 2 h. Almost all the quartz phases transitioned to cristobalite, and the holding time at 1600\u0026deg;C provided the energy required for phase transition nucleation and growth. The formation of another high-temperature crystalline form of silica (i.e., phosphor quartz) was not observed during the process possibly because the formation of phosphor quartz required certain impurity doping [\u003cspan class=\"CitationRef\"\u003e34\u003c/span\u003e\u0026ndash;\u003cspan class=\"CitationRef\"\u003e36\u003c/span\u003e]. Therefore, only the effect of silica transformation from quartz to square quartz on SiC generation needs to be considered during the smelting process. The red line in the figure represented the raw XRD diffraction data, the blue line was obtained from the Rietveld refinement calculations, and the purple line indicated the error between the raw data and refinement calculations. The curve calculated through Rietveld refinement significantly corresponded to the experimentally obtained diffraction curve, indicating that the roasted quartz was completely transformed into square quartz. Figures\u0026nbsp;4(c)\u0026ndash;(d) show the morphology of the quartz samples before and after roasting. Notably, the heat-treated and non-heat-treated samples featured significant morphological differences. The non-heat-treated sample exhibited a smooth and flat surface and displayed a hard texture that was not easily broken. In contrast, the surface of the heat-treated sample featured cracks and a significantly large size, making it susceptible to breakage upon the application of a slight external force. This result was consistent with Wiik\u0026apos;s [\u003cspan class=\"CitationRef\"\u003e8\u003c/span\u003e] explanation that the density of the quartz phase decreased during its transformation to square quartz, resulting in tensions that made the samples fragile.\u003c/p\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/div\u003e\n \u003cdiv id=\"Sec10\" class=\"Section3\"\u003e\n \u003ch2\u003e3.2.2 Changes in SiC formation\u003c/h2\u003e\n \u003cp\u003eTo effectively visualise the difference in reactivity between quartz and cristobalite, the direct carbothermal reduction reaction (reaction 1) was analysed via thermogravimetry (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003e). The entire reaction process was classified into three stages. Stage ① occurred at temperatures below 1400 ℃. Although the carbothermal reduction reaction temperature was not reached at this time, a decrease in mass was observed at this stage. This reduction was attributable to the presence of a certain amount of volatile matter and moisture in the charcoal. As the temperature increased, the volatile matter and moisture gradually volatilised, resulting in a decrease in mass. During the heating process, the charcoal underwent cracking [\u003cspan class=\"CitationRef\"\u003e19\u003c/span\u003e\u0026ndash;\u003cspan class=\"CitationRef\"\u003e21\u003c/span\u003e]. Stage ② began at 1400 ℃ as the volatile matter in the charcoal was significantly volatilised. According to the description of reaction (1), the charcoal and silica reacted and produced CO gas, and the rate of mass reduction in the cristobalite phase exceeded that in the quartz phase. The weight loss rate of cristobalite, as calculated, was 1.45 times that of quartz. In stage ③, as the holding time reached 250 min, the slope of the cristobalite mass reduction curve slope approached 0, while at this time, the mass reduction of the quartz carbonaceous reductant continuously decreased. This observation confirmed that cristobalite exhibited a higher reactivity from an alternative perspective.\u003c/p\u003e\n \u003cp\u003eThe elemental distribution of cross-section B after diffusion couple reaction was characterised via EPMA, and the results are shown in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003e. Figures\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003e(a)\u0026ndash;(d) illustrate the elemental distribution of C1 under a temperature condition maintained at 1600\u0026deg;C for 2 h. Figures\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003e(a)-(b) represent the electron micrographs of the C1 reaction cross section. It can be seen that there are obvious contrast differences between the two phases.A large greyish-white area was visible near the contact surface, while the region farther from the contact surface was dominated by grey areas. The grey-white region featured a measured depth of 593.75 \u0026micro;m. The EPMA map (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003ec) indicated that the grey-white region represented the diffusion of Si elements into the charcoal interior. This was due to the inward reaction of SiO gas, an intermediate product of the carbothermal reduction, through the pores inside the charcoal, which generated SiC in the interior of the charcoal [\u003cspan class=\"CitationRef\"\u003e37\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e38\u003c/span\u003e]. Figure\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003e(d) shows A gradual inward decrease in elemental C within the contact region, which occurred due to the escape of elemental C in the form of CO according to reaction (3). Figures\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003e(e)\u0026ndash;(h) show the electron micrographs of the C2 reaction cross section. Figures\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003e(e)\u0026ndash;(f) illustrate a similar diffusion pattern in grey-white and quartz diffusion couples. However, the grey-white region of the C2 reaction cross section exhibited a larger size than the C1 region, which extended to 920.87 \u0026micro;m. The Si element in C2 exhibited a larger diffusion depth than the C2 Si element (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003eg). Figure\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003e(h) shows the EPMA plot of elemental C for the square quartz diffusion couple. This observation confirmed that the escape of CO was significantly higher within square quartz compared with quartz. Thus, the square quartz featured a stronger capacity to produce SiO through reaction (2) with C compared with quartz. This increased SiO production, leading to the generation of SiC through reaction (3), consistent with the thermodynamic calculations.\u003c/p\u003e\n \u003c/div\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec11\" class=\"Section2\"\u003e\n \u003ch2\u003e3.3 The mechanism of the transformation of quartz to cristobalite to promote the formation of SiC\u003c/h2\u003e\n \u003cp\u003eThe crystalline transition of quartz into cristobalite involved high-temperature structural changes, including the fracture and remodelling of silica\u0026ndash;oxygen tetrahedra in the silica crystals. A schematic of the crystal structure of SiO\u003csub\u003e2\u003c/sub\u003e refined after Rietveld refinement for both crystal types is shown in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003e. The \u0026alpha;-quartz was characterised by a hexagonal crystal system, with a P622 space group and cell parameters a\u0026thinsp;=\u0026thinsp;b\u0026thinsp;=\u0026thinsp;5.01\u0026Aring;, c\u0026thinsp;=\u0026thinsp;5.47\u0026Aring;, \u0026alpha;\u0026thinsp;=\u0026thinsp;\u0026beta;\u0026thinsp;=\u0026thinsp;90\u0026deg;, \u0026gamma;\u0026thinsp;=\u0026thinsp;120\u0026deg;, low symmetry, and compactness (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003ea). As the temperature exceeded 1400\u0026deg;C, the \u0026beta;-quartz was further transformed into cristobalite. The \u0026alpha;-cristobalite was characterised by a cubic crystal system with a space group Fd\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\stackrel{-}{3}\\)\u003c/span\u003e\u003c/span\u003em and cell parameters a\u0026thinsp;=\u0026thinsp;b\u0026thinsp;=\u0026thinsp;c\u0026thinsp;=\u0026thinsp;5.405 \u0026Aring;, \u0026alpha;\u0026thinsp;=\u0026thinsp;\u0026beta;\u0026thinsp;=\u0026thinsp;\u0026gamma;\u0026thinsp;=\u0026thinsp;90\u0026deg; (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003eb). This transformation was irreversible; thus, cristobalite did not revert to \u0026beta;-quartz or \u0026alpha;-quartz at lower temperatures.\u003c/p\u003e\n \u003cp\u003eAccording to the previous experimental results, the difference in reactivity between cristobalite and quartz was analysed from the microscopic perspective of the crystal structure. Cristobalite, a high-temperature crystalline silica, was formed from \u0026beta;-quartz through the breaking and remodelling of Si\u0026ndash;O bonds above 1400\u0026deg;C. Because the phase transition process was endothermic, cristobalite exhibited high internal energy and chemical potential energy. Additionally, the Si\u0026ndash;O bond length was altered during the process of Si\u0026ndash;O bond reconstruction. Particularly, \u0026beta;-quartz featured a Si\u0026ndash;O bond length of 1.58 \u0026Aring;, while square quartz exhibited a Si\u0026ndash;O bond length of 1.62 \u0026Aring;. A longer bond length indicates a lower energy required for breaking. Cristobalite featured a more porous and loose structure compared with \u0026beta;-quartz, characterised by three main changes. First, the connection between the Si\u0026ndash;O tetrahedra shifted from bridge bonds to double bonds. Second, the angle between the Si\u0026ndash;O tetrahedra changed from 120\u0026deg; to 90\u0026deg;. Third, the bond length of the Si\u0026ndash;O bond changed from 1.58 \u0026Aring; for the \u0026beta;-quartz Si\u0026ndash;O bond to 1.62 \u0026Aring; for the square quartz Si\u0026ndash;O bond. Furthermore, square quartz, a high-temperature crystalline silica, exhibited high internal and chemical potential energy but low stability at high temperatures compared with \u0026beta;-quartz, making square quartz more reactive with other compounds [\u003cspan class=\"CitationRef\"\u003e39\u003c/span\u003e\u0026ndash;\u003cspan class=\"CitationRef\"\u003e41\u003c/span\u003e].\u003c/p\u003e\n\u003c/div\u003e"},{"header":"4. Conclusion","content":"\u003cp\u003eThe carbothermal reduction reaction between silica and charcoal during industrial silicon smelting was simulated via thermogravimetric and diffusion couple methods. Additionally, the effects of different crystalline types of silica (i.e., quartz and quartzite) on the generation of silicon carbide and their reaction mechanisms were investigated through thermodynamic calculations and theoretical analyses. This study presents the following key conclusions:\u003c/p\u003e \u003cp\u003e \u003col\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003e Cristobalite contributed to the production of SiC both directly through reaction (1) and indirectly through reaction (2).\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003eCristobalite reacted more easily with carbon than quartz due to two main reasons: ① The phase transition of silica from quartz to cristobalite was an endothermic process, therefore, cristobalite exhibited a higher internal energy and chemical potential. At high temperatures, cristobalite was prone to decomposition or reduction. ② β-quartz exhibited a Si\u0026ndash;O bond length of 1.58 \u0026Aring;, while the cristobalite featured a Si\u0026ndash;O bond length of 1.62 \u0026Aring;. Longer bond lengths required less energy for breaking, making cristobalite more likely to undergo carbothermal reduction at the same temperature.\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003c/ol\u003e \u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eEthics Approval\u003c/strong\u003e The data of our submission requires ethics approval\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eand compliance with ethical standards.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent to Participate\u003c/strong\u003e Not applicable.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent for Publication\u003c/strong\u003e Not applicable.Informed Consent All authors and associated personnel are aware of and agree to the content of this submission.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConflict of Interest\u003c/strong\u003e The authors declare that we have no financial and personal relationships with other people or organizations that can inappropriately influence our work, there is no professional or other personal interest of any nature or kind in any product, service and/or company that could be construed as influencing the position presented in, or the review of, the manuscript entitled, \u0026ldquo;A study of the effect of quartz-to-cristobalite transformation on SiC generation in metallurgical-grade silicon production\u0026rdquo;.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting Interests\u003c/strong\u003e The authors declare no competing interests.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAcknowledgments\u003c/strong\u003eWe gratefully acknowledge that this study was supported by the Yunnan Outstanding Youth Fund (No. 202101AV070007), and the Major Science and Technology Projects in Yunnan Province (No. 202202AG050012).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthors\u0026rsquo; Contribution\u003c/strong\u003e Jiahe Tian: Conceptualization, Methodology, Writing-original draft. Data curation\u003c/p\u003e\n\u003cp\u003eXiaocong Deng: Writing-review. Data curation.\u003c/p\u003e\n\u003cp\u003eKuixian Wei: Writing-review \u0026amp; editing, Super-vision, Funding acquisition.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eWenhui Ma: Supervision, Funding acquisition.\u0026nbsp;\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eYuelong Yu X, Bai S, Li J, Shi L, Wang F, Xi W, Ma R, Deng (2023) Review of silicon recovery in the photovoltaic industry. Curr Opin Green Sustainable Chem 44:100870. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.cogsc.2023.100870\u003c/span\u003e\u003cspan address=\"10.1016/j.cogsc.2023.100870\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMa L, Yu Z, Ma W, Qing S, Wu J (2019) Assessment and study on the impact on environment by multi-crystalline silicon preparation by metallurgical route. Silicon 11:1383\u0026ndash;1391. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1007/s12633-018-9937-6\u003c/span\u003e\u003cspan address=\"10.1007/s12633-018-9937-6\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLei Y, Ma W, Wu J, Wei K, Li S, Morita K (2018) Impurity phases and their removal in Si purification with Al\u0026ndash;Si alloy using transition metals as additives. J Alloys Compd 734:250\u0026ndash;257. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.jallcom.2017.10.292\u003c/span\u003e\u003cspan address=\"10.1016/j.jallcom.2017.10.292\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eRingdalen E, Tangstad M (2012) Reaction mechanisms in carbothermic production of silicon, study of selected reactions. The Minerals, Metals \u0026amp; Materials Society (TMS), pp 195\u0026ndash;203\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eChen Z, Ma W, Wu J, Wei K, Yang X, Lv G, Yu J (2016) Influence of carbothermic reduction on submerged arc furnace energy effic-iency during silicon production. Energy 116:687\u0026ndash;693. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.energy.2016.09.034\u003c/span\u003e\u003cspan address=\"10.1016/j.energy.2016.09.034\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSchei A, Tuset JK, Tveit H (1998) Production of high silicon alloy. Tapir\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eTangstad M, Ksiazek M, Andersen V, Ringdalen E (2010), June Small scale laboratory experiments simulating an industrial silicon furnace. In Proceedings of the Twelfth International Ferroalloys Congress, Sustainable Future, Helsinki, Finland (pp.\u0026nbsp;6\u0026ndash;9)\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWiik K, Motzfeldt K (1995) Kinetics of reactions between silica and carbon and the formation of silicon carbide. MRS Online Proceedings Library (OPL), 410, 435. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1557/PROC-410-435\u003c/span\u003e\u003cspan address=\"10.1557/PROC-410-435\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eVan Dijen FK, Metselaar R (1991) The chemistry of the carbothermal synthesis of β-SiC: Reaction mechanism, reaction rate and grain growth. J Eur Ceram Soc 7(3):177\u0026ndash;184. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/0955-2219(91)90035-X\u003c/span\u003e\u003cspan address=\"10.1016/0955-2219(91)90035-X\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLi X, Zhang G, Ostrovski O, Tronstad R (2016) Effect of gas atmosphere on the formation of silicon by reaction of SiC and SiO\u003csub\u003e2\u003c/sub\u003e. J Mater Sci 51:876\u0026ndash;884. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1007/s10853-015-9413-2\u003c/span\u003e\u003cspan address=\"10.1007/s10853-015-9413-2\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eHutchison SG, Richardson LS, Wai CM (1988) Carbothermic reduction of silicon dioxide\u0026mdash;A thermodynamic investigation. Metall Trans B 19:249\u0026ndash;253. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1007/BF02654209\u003c/span\u003e\u003cspan address=\"10.1007/BF02654209\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAbolpour B, Shamsoddini R (2020) Mechanism of reaction of silica and carbon for producing silicon carbide. Prog React Kinet Mech 45:1468678319891416. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1177/1468678319891416\u003c/span\u003e\u003cspan address=\"10.1177/1468678319891416\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eB\u0026oslash; SM (2016) Phases and zones in the silicon process (Master's thesis, NTNU). \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttp://hdl.handle.net/11250/2407000\u003c/span\u003e\u003cspan address=\"http://hdl.handle.net/11250/2407000\" targettype=\"URL\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLiu D, Deng X, ai J, Yang S, Wei K, ,\u0026amp;Ma W (2022) Formation mechanism of sic in the diffusion couple interface during the mg-si pro-duction process. Silicon 14(17):11371\u0026ndash;11380. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1007/s12633-022-01876-4\u003c/span\u003e\u003cspan address=\"10.1007/s12633-022-01876-4\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLi X, Zhang G, Tang K, Ostrovski O, Tronstad R (2015) Carbothermal reduction of quartz in different gas atmospheres. Metall Mater Trans B 46:1343\u0026ndash;1352. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1007/s11663-015-0293-2\u003c/span\u003e\u003cspan address=\"10.1007/s11663-015-0293-2\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eVangsk\u0026aring;sen J (2012) Metal-producing mechanisms in the carbothermic sili-con process (Master's thesis, Institutt for materialteknologi). \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttp://hdl.handle.net/11250/249099\u003c/span\u003e\u003cspan address=\"http://hdl.handle.net/11250/249099\" targettype=\"URL\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAgarwal A, Pad U (1999) Influence of pellet composition and structure on carbothermic reduction of silica. Metall Mater Trans B 30:295\u0026ndash;306. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1007/s11663-999-0059-9\u003c/span\u003e\u003cspan address=\"10.1007/s11663-999-0059-9\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWeimer AW, Nilsen KJ, Cochran GA, Roach RP (1993) Kinetics of carbothermal reduction synthesis of beta silicon carbide. AIChE J 39(3). \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1002/aic.690390311\u003c/span\u003e\u003cspan address=\"10.1002/aic.690390311\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eV\u0026aacute;rhegyi G, Szab\u0026oacute; P, Till F, Zelei B, Antal MJ, Dai X (1998) TG, TG-MS, and FTIR characterization of high-yield biomass charcoals. Energy Fuels 12(5):969\u0026ndash;974. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1021/ef9800359\u003c/span\u003e\u003cspan address=\"10.1021/ef9800359\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eJayaraman K, Kok MV, Gokalp I (2017) Thermogravimetric and mass spectrometric (TG-MS) analysis and kinetics of coal-biomass blends. Renewable Energy 101:293\u0026ndash;300. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.renene.2016.08.072\u003c/span\u003e\u003cspan address=\"10.1016/j.renene.2016.08.072\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSurup GR, Nielsen HK, Heidelmann M, Trubetskaya A (2019) Characterization and reactivity of charcoal from high temperature pyrolysis (800\u0026ndash;1600 ℃). Fuel 235:1544\u0026ndash;1554. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.fuel.2018.08.092\u003c/span\u003e\u003cspan address=\"10.1016/j.fuel.2018.08.092\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKjelstadli ME (2016) Kinetics and mechanism of phase transformations from quartz to cristobalite (Master's thesis, NTNU). \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttp://hdl.handle.net/11250/2406964\u003c/span\u003e\u003cspan address=\"http://hdl.handle.net/11250/2406964\" targettype=\"URL\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eRingdalen E (2015) Changes in quartz during heating and the possible effects on Si production. Jom 67:484\u0026ndash;492. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1007/s11837-014-1149-y\u003c/span\u003e\u003cspan address=\"10.1007/s11837-014-1149-y\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eFeya OD, Wang Q, Lepeshkin SV, Baturin VS, Uspenskii YA, Oganov AR (2018) Tetrahedral honeycomb surface reconstructions of quartz, cristobalite and stishovite. Sci Rep 8(1):11947. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1038/s41598-018-29853-1\u003c/span\u003e\u003cspan address=\"10.1038/s41598-018-29853-1\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLi F, Tangstad M, Ringdalen E (2018) Carbothermal reduction of quartz and carbon pellets at elevated temperatures. Metall Mater Trans B 49:1078\u0026ndash;1088. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1007/s11663-018-1195-x\u003c/span\u003e\u003cspan address=\"10.1007/s11663-018-1195-x\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWiik K (1990) Kinetics of reactions between silica and carbon. Norges tekniske h\u0026oslash;gskole. Institutt for uorganisk kjemi. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttp://hdl.handle.net/11250/2396774\u003c/span\u003e\u003cspan address=\"http://hdl.handle.net/11250/2396774\" targettype=\"URL\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eFolstad MB, Ringdalen E, Tveit H, Tangstad M (2021) Effect of different SiO\u003csub\u003e2\u003c/sub\u003e polymorphs on the reaction between SiO\u003csub\u003e2\u003c/sub\u003e and SiC in Si pr-oduction. Metall Mater Trans B 52:792\u0026ndash;803. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1007/s11663-020-02053-x\u003c/span\u003e\u003cspan address=\"10.1007/s11663-020-02053-x\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eFolstad MB (2017) Effect of different polymorphs of SiO\u003csub\u003e2\u003c/sub\u003e on the reaction between SiO\u003csub\u003e2\u003c/sub\u003e and SiC in Si production(Master's thesis, NTNU). \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttp://hdl.handle.net/11250/2453816\u003c/span\u003e\u003cspan address=\"http://hdl.handle.net/11250/2453816\" targettype=\"URL\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eJayakumari S, Tangstad M (2020) Transformation of β-SiC from cha-rcoal, coal, and petroleum coke to α-SiC at higher temperatures. Metall Mater Trans B 51:2673\u0026ndash;2688. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1007/s11663-020-01970-1\u003c/span\u003e\u003cspan address=\"10.1007/s11663-020-01970-1\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAndresen B (1995) Process model for carbothermic production of silicon metal\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003ePavelko RG, Sevast\u0026rsquo;yanov VG, Ezhov YS, Kuznetsov NT (2007) Silicon carbide transport during carbothermic reduction of SiO\u003csub\u003e2\u003c/sub\u003e: Ther-modynamic evaluation and experimental study. Inorg Mater 43:700\u0026ndash;703. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1134/S0020168507070059\u003c/span\u003e\u003cspan address=\"10.1134/S0020168507070059\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003e: Myrv\u0026aring;gnes. Analyses and characterization of fossil carbonaceous materials for silicon production, 2008[J]. NTNU, Trondheim \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttp://hdl.handle.net/11250/248717\u003c/span\u003e\u003cspan address=\"http://hdl.handle.net/11250/248717\" targettype=\"URL\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSeo WS, Koumoto K (1996) Stacking faults in β-SiC formed during carbothermal reduction of SiO\u003csub\u003e2\u003c/sub\u003e. J Am Ceram Soc 79(7):1777\u0026ndash;1782. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1111/j.1151-2916.1996.tb07995.x\u003c/span\u003e\u003cspan address=\"10.1111/j.1151-2916.1996.tb07995.x\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eStevens SJ, Hand RJ, Sharp JH (1997) Polymorphism of silica. J Mater Sci 32:2929\u0026ndash;2935. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1023/A:1018636920023\u003c/span\u003e\u003cspan address=\"10.1023/A:1018636920023\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBuerger MJ (1954) The stuffed derivatives of the silica structures. American Mineralogist: Journal of Earth and Planetary Materials, 39(7\u0026ndash;8), 600\u0026ndash;614\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBuerger MJ (1936) The general r\u0026ocirc;le of composition in polymorphism. Proc-eedings of the National Academy of Sciences 22(12):685\u0026ndash;689. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1073/pnas.22.12.685\u003c/span\u003e\u003cspan address=\"10.1073/pnas.22.12.685\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eNordb\u0026oslash; EA (2019) Interaction of SiO-gas and Charcoal and the Formation of SiC and Si (Master's thesis, NTNU). \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttp://hdl.handle.net/11250/2623366\u003c/span\u003e\u003cspan address=\"http://hdl.handle.net/11250/2623366\" targettype=\"URL\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMyrhaug EH (2005) Non-fossil reduction materials in the silicon process: Properties and behaviour\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWu Z, Hao X, Liu X, Meng J (2007) Structures and elastic properties of OsN\u003csub\u003e2\u003c/sub\u003e investigated via first-principles density functional calculations. Phys Rev B 75(5):054115. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1103/PhysRevB.75.054115\u003c/span\u003e\u003cspan address=\"10.1103/PhysRevB.75.054115\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBuerger ΜJ (1935) The silica framework crystals and their stability- fields. Z f\u0026uuml;r Kristallographie-Crystalline Mater 90(1\u0026ndash;6):186\u0026ndash;192. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1524/zkri.1935.90.1.186\u003c/span\u003e\u003cspan address=\"10.1524/zkri.1935.90.1.186\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSun T (1989) Effects of solid solution on the high-low inversion of cristobalite and the stabilization of high cristobalite (Doctoral dissertation, Virginia Polytechnic Institute and State University). \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttp://hdl.handle.net/10919/54793\u003c/span\u003e\u003cspan address=\"http://hdl.handle.net/10919/54793\" targettype=\"URL\" 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":"silicon","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"scon","sideBox":"Learn more about [Silicon](https://www.springer.com/journal/12633)","snPcode":"12633","submissionUrl":"https://submission.nature.com/new-submission/12633/3","title":"Silicon","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"metallurgical-grade silicon, carbothermal reduction, crystalline transformation, diffusion couples","lastPublishedDoi":"10.21203/rs.3.rs-3831130/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-3831130/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eSilicon carbide (SiC) is an essential intermediate product formed during the smelting process of metallurgical-grade silicon (MG-Si), and its production efficiency is a key factor in determining the overall efficiency of MG-Si production. In this study, we investigated the effect of quartz-to-cristobalite transformation on SiC generation in industrial silicon production and elucidated the differences in the reaction characteristics of quartz and cristobalite when they interacted with carbonaceous reductants. The experimental results indicated that the rate of direct carbothermal reduction of cristobalite was 1.45 times that of quartz. Moreover, the indirectly formed SiC layer in the cristobalite/C diffusion couple exhibited a thickness of 920.87 \u0026micro;m, which was 1.55 times that in the quartz/C diffusion couple. Both the reaction thermodynamic calculations and crystal transformation theory analysis revealed that the changes in the chemical energy and crystal structure of SiO\u003csub\u003e2\u003c/sub\u003e during the phase transformation process reduced the stability of cristobalite compared with quartz at high temperatures. Consequently, cristobalite reacted more easily with C at high temperatures to form SiC and SiO. The results of the study are highly significant for improving the reaction mechanism in the smelting process of MG-Si and enhancing the production efficiency of MG-Si.\u003c/p\u003e","manuscriptTitle":"A study of the effect of quartz-to-cristobalite transformation on SiC generation in metallurgical-grade silicon production","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-01-18 07:40:50","doi":"10.21203/rs.3.rs-3831130/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2024-01-20T16:52:19+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-01-20T01:16:02+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"7b40e27f-3ad4-482e-897e-f30e5b7483a9","date":"2024-01-17T00:51:33+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2024-01-16T17:59:22+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2024-01-16T13:06:26+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2024-01-16T13:06:25+00:00","index":"","fulltext":""},{"type":"submitted","content":"Silicon","date":"2024-01-03T06:02:11+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"silicon","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"scon","sideBox":"Learn more about [Silicon](https://www.springer.com/journal/12633)","snPcode":"12633","submissionUrl":"https://submission.nature.com/new-submission/12633/3","title":"Silicon","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"d2e3201c-10dc-4238-ab74-b136aba7c20a","owner":[],"postedDate":"January 18th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2024-02-26T15:05:49+00:00","versionOfRecord":{"articleIdentity":"rs-3831130","link":"https://doi.org/10.1007/s12633-024-02908-x","journal":{"identity":"silicon","isVorOnly":false,"title":"Silicon"},"publishedOn":"2024-02-20 15:01:28","publishedOnDateReadable":"February 20th, 2024"},"versionCreatedAt":"2024-01-18 07:40:50","video":"","vorDoi":"10.1007/s12633-024-02908-x","vorDoiUrl":"https://doi.org/10.1007/s12633-024-02908-x","workflowStages":[]},"version":"v1","identity":"rs-3831130","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-3831130","identity":"rs-3831130","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}