Low-cost high-yield synthesis of nanosize powders of Si-based nitrides and carbides by CO 2 laser induced gas phase reactions

Abstract

Amorphous Si 3N 4, Si/N/C and crystalline SiC nano-powders, 5–50 nm in mean diameter, with yields of 40–120 g/h were synthesized via laser induced gas phase reactions of low cost hexamethyldisilazane (HMDS) and NH 3 (or H 2). Reaction flame temperatures, which were controlled by the total gas flow rate, greatly influenced powder composition and crystallinity. Amorphous Si 3N 4 powders (96 wt%) were obtained at 1000 °C from HMDS+NH 3; β-SiC (93 wt%) was formed at 1600 °C with H 2. Amorphous Si/N/C powders with various N C ratios (0.1–6) were synthesized at various temperatures. The main impurities in the powders were the organo-ligands such as NH x and CH x ( x = 1–3) whose existence also resulted in a strong surface absorption of oxygen.