Synthesis of Silicon Sulfide by Using CS2 Gas

Abstract

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.

Synthesis and Growth Mechanism of SiS2 Rods

“…The main reaction to synthesize SiS 2 (s) ( eq 5 ) proceeds below 1993 K and the side reaction to SiS(g) ( eq 6 ) starts to proceed when T > 628 K. 33 The former dominates because it has a larger Gibbs free-energy (absolute value) than the latter. Besides, the forward reactions in eqs 7 and 8 would be very difficult to happen below 1993 K (also in this work), while the partial pressures of SiS(g) are 10 –3 atm in eq 7 ( 3 , 37 ) and 10 –5 atm in eq 8 , respectively. 3 , 37 This means, if the SiS(g) was generated via eq 6 , it would tend to produce SiS 2 (s) and Si(s) as in the backward reaction of eq 7 or react with S 2 (g) to form SiS 2 (s) as in the backward reaction of eq 8 .…”

“…The preferred orientation of orthorhombic SiS 2 has been reported before, such as SiS 2 with a fibrous, a needle-shaped, or a pillar-shaped morphology/structure. 3 , 13 , 16 However, so far, there is little explanation for the growth mechanism. Some orthorhombic materials with preferred orientation have also been investigated, such as Bi 2 S 3 nanorods 41 − 43 or nanotubes, 43 Sb 2 S 3 nanorods, 44 BiSCl polygonal tubes, BiSI bundle-rods, 45 and so on.…”

“…Therefore, the contribution of SiS(g) in the “elemental method” (as in this work) to synthesize SiS 2 (s) can be neglected, which is different from that in a “compound method”. 3 , 13 , 16 − 20…”

“…Silicon disulfide (SiS 2 ) is an important synthetic compound used in fundamental and applied research. It is one of the important raw materials for sulfide-based solid electrolytes. − There are five polymorphs of SiS 2 . One is the ambient-pressure (NP) phase (≤3.83 MPa, 973–1570 K) ,,− with an orthorhombic structure ( Ibam , Space Group no.…”

“…Synthesis methods for NP-SiS 2 have been summarized and classified into two groups: compound ,,− and elemental ,,,− methods. As for the latter, both silicon (Si) and sulfur (S) sources are elementary substances.…”