Pyrolytic Conversion of Spherical Organo‐silica Powder to Silicon Nitride under Nitrogen

Abstract

Monodisperse, spherical Si 3 N 4 powder composed of fine particulates was synthesized by pyrolyzing spherical organo-silica powder under nitrogen. The organo-silica powder was prepared by hydrolyzing a mixture of phenyltrimethoxysilane (PTMS) and tetraethoxysilane (TEOS) in a methanol solution of water and ammonia. The organo-silica powder consisted of 81.3 at.% silicon units derived from PTMS and 18.7 at.% silicon units derived from TEOS. During the pyrolysis under nitrogen, the organo-silica powder decomposed to a mixture of free carbon and silica, with an increase of the surface area, at 500°-600°C, followed by the formation of ␣-Si 3 N 4 , with ␤-Si 3 N 4 as a minor phase, at 1450°and 1500°C and ␤-SiC at 1550°C. The pyrolyzed powders, which retained the spherical shape and monodispersity of the organo-silica powders, with a reduction in mean particle diameter, were composed of fine particulates that were ∼40 nm in size.

Carbothermal Reaction of Silica–Phenol Resin Hybrid Gels to Produce Silicon Nitride/Silicon Carbide Nanocomposite Powders

“…However, due to the kinetic factors, the boundary temperature observed varied from 14001C to above 15001C. 16,30,42 Also due to the kinetic factors, Si 3 N 4 /SiC composite powders could be produced slightly above the boundary temperature in our study. This can be explained as follows: in the carbothermal synthesis, gaseous SiO was first formed via the following reactions 38,43 : The data in the parentheses present the phase compositions in mol%.…”

“…The equilibrium phases below and above the boundary temperature are Si 3 N 4 and SiC, respectively. However, due to the kinetic factors, the boundary temperature observed varied from 1400°C to above 1500°C 16,30,42 . Also due to the kinetic factors, Si 3 N 4 /SiC composite powders could be produced slightly above the boundary temperature in our study.…”

“…Micrometer‐sized Si 3 N 4 crystals were not observed by Choi et al 30 . in their products from monodisperse spherical organo‐silica powders.…”

“…This process has been used to obtain inorganic-organic hybrid gels, in which the organic compound acts as a carbon source. Carbothermal reactions of the hybrid gels containing silica have led to SiC powders, [20][21][22][23][24][25][26][27][28][29] Si 3 N 4 powders, 30 SiC and Si 3 N 4 fibers, [31][32][33] and Si-Ti-C and Si-Zr-C fibers. [34][35][36] We have developed a two-step sol-gel process for the preparation of silica-phenol resin hybrid gels.…”

Additive‐Assisted Nitridation to Synthesize Si3N4 Nanomaterials at a Low Temperature

“…Traditionally, silicon nitride powders were prepared in high temperature (1100°–1700°C), and various methods have been used such as the direct nitridation of silicon, 6 the carbothermic reduction of silicon oxide, 7 self‐propagating synthesis, 8 and laser‐ or plasma‐assisted vapor phase reaction 9 . Also, silicon nitride nanomaterial could be prepared by the thermal decomposition method, such as the thermal decomposition of polymeric precursors, 10 Na 2 SiF 6 11 in a nitrogen atmosphere, and a carbonaceous silica xerogel 12 …”