Conditions for carbothermal synthesis of a-Si3N4 are presented with special emphasis on the reaction temperature, C: SiOz ratio, and precursor mixing. With pure precursors, the conversion temperature is 1500" to 1550°C. An excess of C is necessary for complete conversion, and a simple sol-gelmixing technique provides excellent intermixing of the precursors. Copious flow of Nz gas throughout the reactor bed is essential if pure Si3N4 is to be produced; small concentrations of CO and Oz promote Sic and Si2Nz0, respectively.
In this work, the carbothermal reduction of AI203 to AIN was studied.boehmite (AIOOH) were examined in order to observe the diffcrences in reaction behaviour and powder characteristics obtained from each type of precursor. Cane sugar (sucrose) and carbon black were used as carbon sources. Reaction conditions studied were carbon to alumina ratio, temperature and reaction time. Sucrosp. resulted in a close-to-stoichiometric ratio of AI 2 0 3 : C (l : 3.2) achicving full conversion to AIN and produced a regular powder morphology, whiist carbon black required higher ratio (> 1 : 4) to reach full conversion with agglomeration of the AIN powder. The optimal reaction temperature was 1600 oC with the reaction time being dependent on the Al 2 0 3 source. The results of the thermodynamic study for the AI-N-O-C system suggest a solid-state reaction process which is consistent with the experimental observations. Moreover, flowing N 2 gas flushes out the product CO gas and thus forces the equilibrium in favour of AIN formation. Reaction mechanisms are proposed for the two forms of carbon precursor.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.