Investigation of parameters relating to silicon nitride (Si3N4) powder production from sepiolite by carbo-thermal reduction and nitridation

INVESTIGATION OF PARAMETERS RELATING TO SILICON NITRIDE (Sİ3N4) POWDER PRODUCTION FROM SEPIOLITE BY CARBO-THERMAL REDUCTION AND NITRIDATION Ph. D Thesis Halil ARIK GAZİ UNIVERSITY INSTITUTE OF SCIENCE AND TECHNOLOGY May 1996 ABSTRACT In this work, investigation of parameters relating to silicon nitride (Si3N4) powder production from sepiolite by carbo-thermal reduction and nitridation was investigated. About 70% of World reserves for sepiolite is in Turkey. It is a magnesium hydro-silicate clay mineral with half unit cell ideal formula of Mga Sİ12 O30 (OH)4 (OH2)4 8H20. Sepiolite from Ankara - Polatlı - Türktaciri area was concentrated using hydro-metallurgical leach method. In this way about 10 % dolomite present in the brown sepiolite was disolved and 100% pure sepiolite was obtained. Minus 100 mesh sepiolite was mixed with minus 325 mesh carbon black with C/Si02 molar ratios of 1.5, 3.0, 4.0, 5.0 and 7.5. Mixing was carried out by milling for 5 hours in a ball mill with alumina balls. 5 grams of these mixtures were placed in graphite boats and then located at the centre of controlled atmosphere tube furnace with alumina tube. Carbo- thermal reduction and nitridation was carried out under 4.5 cm3/min N2 gas flow. Treatment temperatures were 1200-1300-1400 and 1450 °C and times were 2-4-8-16 hours. All reaction products were analysed by XRD and SEM- EDX; morphologies and chemical compositions were determined. Results showed that after 16 hours of treatment at 1400 °C with C/Si02 molar ratio of 4, transformation to Si3N4 formation was nearly 1 00%. Science Code : 225.01.00.225.01.01 Key Words : Sepiolite, Nitride Ceramics, Si3N4, Carbo-Termal Reduction Number of Pages : 143 Supervisor : Prof. Dr. Süleyman S ARITAŞ V