Silicon sulfide (SiS2) was synthesized from Si, SiC, Si3N4, and a eutectic Al-Si liquid. An Ar-CS2 gas mixture, after bubbling through liquid CS2, was passed over pulverized Si, SiC, Si3N4, or a eutectic Al-Si alloy liquid. White, needle-shaped SiS2 was precipitated as a single phase on the colder downstream surface when Si powder in a SiO2 liner was heated over 1273 K. This deposition mechanism involves a reaction between Si and CS2 to form SiS2, with the vaporization of SiS(g) and deposition as SiS2(s) from SiS(g) and S2(g). Quartz was unaffected by the reaction gases. Notably, Si, SiC, Si3N4, and the eutectic Al-Si liquid were found to be suitable sources for SiS2 synthesis, although this was suppressed owing to Al2S3 formation on the latter.

Metallic sulfides with layered morphologies, such as SiS2, are employed in all-solid rechargeable battery electrolytes. The two-dimensional polymeric chain structure of SiS2 makes it suitable for Li intercalation.[2,3,4,5] Unlike some sulfides, SiS2 is not a naturally occurring mineral and must be synthesized. This study focuses on SiS2 synthesis from powdered Si, SiC, and Si2N3, as well as eutectic Al-Si liquid. The objectives of the study were as follows: (1) to determine which of the Si sources, if any, would form SiS2; (2) to determine the reaction processing conditions for SiS2 formation; and (3) to characterize the SiS2 and associated products. The proposed process offers the benefit of providing a means for recycling common Si waste. This sulfide synthesis approach is applicable to catalyst formation or laterite upgrading.

The standard synthesis process for SiS2 employs the reaction of Al2S3 with SiO2 at temperatures above 1523 K. Direct reaction between S and Si is difficult because of the high melting point of Si, the high vapor pressure of S, and easy sublimation of SiS2. Although some sulfides can be formed by slow heating of encapsulated metal and S powder followed by a high-temperature soak lasting weeks or months, this is too slow for commercial production. In this study, the potentially faster and lower-temperature reaction of the selected Si sources with CS2 vapor entrained in Ar was investigated.