Synthesis of Sialon from Kaolinite and Carbon Black Nanopowder

Ceramics of the Si–Al–O–N system has a great technological interest because of their good thermomechanical properties at high temperatures. It is possible to obtain phases such as β-SiC, Si3N4, β-sialons, AlN or mixtures of these phases by means of carbonitriding reactions starting from minerals such as quartz, diatomite and other aluminosilicate minerals [1, 2].In this work a clay-based mixture from carbon black and kaolinite was prepared by saponified with sodium hydroxide solution.Sialon was synthesized from kaolinite-carbon black nanopowder mixture by carbothermal reduction and nitridation (CRN) processing at 1500°C as follow [3, 4]:With increasing the reactive temperature about 1300 oC, kaolinite can be mullited:3(Al2O3. 2SiO2) → (3Al2O3. 2SiO2) (mullite) + 4SiO2 (colloid)Above 1300 oC, the mullite product was reduced and nitrided to β-sialon. The reaction can be written as:3Al2O3. 2SiO2+ 10SiO2+ 27C+ 9N2 → 3Si4Al2O2N6 (z =2) + 27COor2(3Al2O3. 2SiO2) + 9C+ 3N2 → Si4Al2O2N6 (z=2)+ 5Al2O3+ 9COThe z value may depend mainly on the starting mixtures and their reaction conditions [5].SEM, and XRD were used to characterize the phases, structure and morphology of products. In the CRN product from this mixture, β-sialon is the main phase