Basic Research On The Occurrence State And Regulation Of Key Impurities In Industrial Silicon For Organosilicon Monomer Synthesi

Organosilicone plays a vital role in the chemical industry due to its exceptional performance and wide range of applications.It is commonly known as the"industrial vitamin"and"technological catalyst".Within this technology-intensive sector,the synthesis of organosilicon monomer holds a crucial position in the industrial chain.Improving the technical indicators of organosilicon monomer synthesis,such as reaction activity and selectivity,is an urgent requirement for achieving high-end and high-quality development in the organosilicon industry.Production research has shown that optimizing the technical indicators of organosilicone monomer synthesis requires specific considerations regarding the presence of impurities in Metallurgical Grade Silicon（MG-Si）.The primary impurity phase,Si₈Al₆Fe₄Ca,enhances reaction selectivity,while appropriate amounts of CaSi₂,CaAl₂Si₂,and Al₈Fe₅Si₇improve reaction activity.Maintaining low concentration of FeSi₂,FeTiSi₂,Al（Si）,and P is crucial to prevent the degradation of technical indicators.However,previous studies on regulating the presence of impurity in MG-Sihave mainly focused on achieving high levels of purity,which does not meet the requirements of organosilicone monomer synthesis.Therefore,this study systematically investigates the presence and regulation of key impurities in MG-Siused for organosilicone applications.It examines the current formation status of essential impurities in MG-Siand conducts optimization research on the solidification and refining process of MG-Simelt based on this analysis.The study establishes a regulatory framework for the presence of impurities that is suitable for organosilicone applications.The specific research results are outlined as follows:（1）The study provides insights into the influence of oxidation ladle refining on the presence of impurities in MG-Si.In Simelt,the separation behavior of impurities is determined by the thermodynamic stability of their oxides.Oxidative ladle refining demonstrates effectiveness in separating Caand Al from Crude Metallurgical Grade Silicon（C-MG-Si）.However,the removal of Fe,Ti,and P poses challenges.The refining process induces changes in the composition of the melt,leading to modifications in the existence state of impurities.Specifically,the disappearance of CaSi₂and CaAl₂Si₂is observed,while the precipitation of FeSi₂increases.The precipitation of Si₈Al₆Fe₄Cadecreases,whereas Ti and P accumulate.Ti consistently precipitates in the form of FeTiSi₂.Consequently,oxidation ladle refining falls short in meeting the requirements for the existence state of impurities in organosilicon monomer synthesis.（2）The study provides insights into the influence of mold casting solidification on the existence states of impurities in MG-Si.Variations in the solidification and diffusion behaviors of impurities result in a gradual decrease in the enrichment levels of of Ca,Al,Fe,Ti,and P towards the center of the ingot.The uneven distribution of impurities leads to the changes in their existence states,with a higher relative concentration of Feobserved at the periphery the ingot,predominantly precipitating as FeSi₂,while Si₈Al₆Fe₄Cashows increased precipitation towards the center of the ingot.As a result,MG-Siproducts obtained from the periphery of mold casting solidification are not suitable for the synthesis of organosilicon monomers.（3）The study aimed to optimize the solidification method of MG-Simelt for organosilicon applications.Various cooling treatments,such as furnace slow cooling（5K/min）,air cooling,crucible water quenching,and melt water quenching,were employed.It was observed that increasing the cooling rate resulted in higher concentration of Al,Ca,and Ti being trapped in the primary Siand the high-temperature precipitate phase（i.e.,Fe₃Si₇）.Meanwhile,the transition of the high-temperature precipitate phase and the formation of low-temperature precipitate phase were impeded.The impact of increasing solidification rate on the existence state of impurities can be summarized as follows:a reduction in the formation of FeTiSi₂and Si₈Al₆Fe₄Ca,and an increase in the formation of FeSi₂.Controlled and gradual solidification can promote the concentration of Caand Al in the liquid phase,enhance the precipitation of Si₈Al₆Fe₄Ca,and achieve the optimization of the impurity existence state of organosilicon applications.（4）The study established a regulation mechanism for controlling the existence state of Si-Fe-Al-Caquaternary impurities.Through the utilization of phase diagram analysis and thermodynamic equilibrium calculations,Si-Fe-Al-Caalloys with different compositions were prepared in experimental settings.The regulation of Fe,Ca,and Al concentration ratios has the following effects on the impurity existence state:an increase in Feconcentration primarily leads to a higher precipitation of FeSi₂phase.A moderate increase in Caconcentration facilitates the transformation of Si₇Al₈Fe₅into CaAl₂Si₂and Si₈Al₆Fe₄Caphases.Increasing Al concentration primarily promotes the conversion of CaSi₂into CaAl₂Si₂,while the presence of residual liquid-phase Al encourages the transformation of CaAl₂Si₂and FeSi₂into Si₈Al₆Fe₄Caphase.However,an excessive increase in Al concentration results in the precipitation of Al（Si）.By controlling Al and Caconcentrations while considering Feconcentration,it becomes possible to achieve the desired impurity existence states for monomer synthesis.（5）The study has developed a control scheme for regulating the concentrations of Ti and P in C-MG-Simelt.By analyzing the smelting products and raw materials of the electric furnace and combining them with thermodynamic calculations,the behavior patterns of Ti and P have been elucidated.It has been observed that as Ti approaches the high-temperature area near the electric arc,it undergoes reduction by Siand subsequently becomes enriched in C-MG-Simelt.On the other hand,P exhibits easy reducibility and valatility,causing it to migrate with the furnace gas and accumulate in microsilica powder.A portion of P is retained in Simelt due to gas-liquid two-phase equilibrium.During the reduction process,Feis preferentially incorporated into Simelt,and the strong affinity between Feand P promotes the enrichment of P in Simelt.Therefore,reducing the presence of impurities in the raw materials can effectively decrease the concentration of Ti and P in the resulting product.Additionally,lowering Feconcentration in the system can also contribute to reducing the concentration of P in the final product.（6）Enhanced separation of Ti and P was successfully achieved during the secondary refining process conducted Simelt.At temperature above 1823K,C exhibits a stronger affinity for Ti compared to Si,resulting in the capturing effect of Ti by C.The utilization of characteristic slag composed of SiO₂-CaO-Al₂O₃combined with C capturing enables the enhanced separation of Ti,the concentration of Ti decreased from 0.0429wt.%to 0.0350wt.%,leading to an increased removal efficiency of Ti of up to 18.41%.Furthermore,direct vacuum refining of C-MG-Siat1723K and a vacuum level ranging from 3×10^-3to 5×10^-3Pa for a duration of 2.5hours achieved a remarkable removal efficiency of P,reaching 79.17%.The concentration of P decreased from 0.0072wt.%to 0.0015wt.%,while the separation efficiency of Ca,Al,O and C is not satisfactory.By subjecting C-MG-Sito a two-step treatment involving oxidation ladle refining and vacuum refining,the enhanced separation of Al,Ca,P,C,and O was successfully realized.Moreover,the introduction of a slightly negative pressure environment during the oxidation ladle refining process resulted in an average removal efficiency of P surpassing zero and increasing to 21.76%.