Carbothermal synthesis of low-z β'-sialon from silica or elemental silicon in the presence and absence of Y2O3 : An XRD and MAS NMR perspective

• Published in: Journal of materials chemistry 1997, Vol.7 (6), p.1057-1061
• Main Authors: MACKENZIE, K. J. D, EKSTRÖM, T. C, WHITE, G. V, HARTMAN, J. S
• Format: Article
• Language: English
• Subjects: Chemistry; Exact sciences and technology; Inorganic chemistry and origins of life; Miscellaneous; Preparations and properties
• ISSN: 0959-9428; 1364-5501
• DOI: 10.1039/a607677g

Carbothermal formation of low-z beta'-sialon (z = 0.5) from halloysite clay was carried out using two different forms of the necessary additional silicon, namely, finely divided SiO2 (quartz) and elemental Si. XRD and solid-state 29Si and 27Al MAS NMR studies of the early stages of the reaction at 1000-1400 C show that the SiO2 forms both Si3N4, via a series of oxynitrides, and SiC. These then react with the mullite produced by thermal decomposition of the clay, to form beta-sialon. The addition of 3 wt% Y2O3 to the mix does not change the reaction sequence, but facilitates the formation of both mullite and beta'-sialon, in which it also promotes the formation of Al-N units. Using elemental Si, some SiC is formed, which reacts with the mullite and remaining Si to form O'-sialon, which may then react further with mullite to produce beta'-sialon. The addition of Y2O3 forms transient Y2Si2O7 at lower temperatures, but in the later stages facilitates the formation of beta'-sialon with respect to O'-sialon. 7 refs.