Dissolution of Calcium Silicates in Molten CaCl(2)

Electrodeposition of silicon in molten CaCl(2) has been drawing increasing attention. Soluble silicate anions in the melt can be reduced and tailored into functional materials. To ensure a precise control of the electrochemical processes, a comprehensive knowledge on the soluble silicate anions in the melt is indispensable. Here, we clarify the formation behavior of soluble silicate anions by dissolving solid CaSiO(3) and Ca(2)SiO(4) in molten CaCl(2) at temperatures from 1047 K to 1233 K (774 °C to 960 °C). It is found that Ca(2)SiO(4) dissolves more and faster. The formation of Ca(2)SiO(3)Cl(2) or Ca(3)SiO(4)Cl(2) as an intermediate product is observed. Metasilicate (SiO(3)(2−)) and orthosilicate (SiO(4)(4−)) are detected as soluble anions in the melt when dissolving CaSiO(3) and Ca(2)SiO(4), respectively. Mass transfer of these ions plays an important role in determining the overall dissolution rate. The polymeric chain-like structure of SiO(3)(2−) is the reason for the slower dissolution of CaSiO(3) compared with that of Ca(2)SiO(4), which dissolves as SiO(4)(4−) with a completely isolated tetrahedral structure in the melt. Phase relationships in the CaCl(2)–CaSiO(3) and CaCl(2)–Ca(2)SiO(4) binary systems at the CaCl(2)-rich side are clarified. These results should be useful for manipulating the electrochemical reactions of Si (IV) anions on purposes. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s11663-022-02679-z.