Reductive Nitridation of Cristobalite with Carbon in N2 Atmosphere

• Published in: Journal of the Ceramic Association, Japan Vol. 92; no. 1064; pp. 179 - 187
• Main Authors: FUKUSHIGE, Yasuo, NAGAE, Takaharu, SHIMADA, Kinji, KATO, Akio
• Format: Journal Article
• Language: Japanese
• Published: The Ceramic Society of Japan 01.04.1984
• Subjects: Reaction scheme; Reductive nitridation of cristobalite; SiO2-C-N2-Fe2O3 system; α-Si3N4; β-Si3N4
• ISSN: 0009-0255; 1884-2127
• DOI: 10.2109/jcersj1950.92.1064_179

The formation of Si3N4 from cristobalite-carbon-nitrogen was studied at 1360°-1475°C. The results are as follows: (1) Reaction products were α-Si3N4, β-Si3N4 and a small amount of SiC. The fraction of α-form in Si3N4 was ca. 0.90 and increased to ca. 0.95 by the addition of Fe2O3 (0.18wt%). (2) The products consisted of spherical particles with diameter of ca. 1μm. Small amounts of prismatic and needle-shaped particles were also formed. The latter increased slightly by the addition of Fe2O3. (3) The activation energy calculated from the initial reaction rate was ≈150kcal/mol and lowered to ≈135kcal/mol by the addition of Fe2O3. (4) The formation of Si3N4 was considered to occur by the following reaction schemes: I. Reduction of SiO2(s) with C(s) into Si(s, l) and nitridation of Si(s, l) into Si3N4(s) by N2(g). II. Reduction of SiO2(s) with C(s) into SiO(g), disproportionation of SiO(g) into Si(s, l) and SiO2(s), and nitridation of Si(s, l) into Si3N4(s) by N2(g). III. Si3N4(s) is formed by reaction between SiC(s) and N2(g). The reaction scheme of III is not important under the present reaction conditions. (5) In the SiO2-C-N2-Fe2O3 system, the nitridation is considered to occur through the melt of the Fe-Si system.