Catalytic effects of metals on the formation of silicon nitride from rice husk ash via carbothermal reduction and nitridation process

Abstract

Rice husk was used in silicon nitride synthesis by the carbothermal reduction and nitridation which has been recognized as one of the common methods for producing silicon nitride. In this study, catalytic effects of metals in the carbothermal reduction and nitridation of rice husk as for silicon nitride synthesis were investigated. Rice husk was first pyrolyzed at 600 ํC for 3 h in argon atmospheres to produce rick husk as (RHA) before impregnated with 1-3% by mass of iron, aluminium, magnesium, copper and yttrium. The product obtained could be categorized into two forms, i.e. carbon containing dark gray power at the bottom of sample holder and white fibrous material on the top of dark gray powder. It is found that the fraction of alpha-silicon nitride is generally decreased when a metal is added to RHA. Only yttrium can enhance in the product, the fraction of alpha-phase. Hydrogen pretreatment of RHA at 1450 ํC and various time are also investigated. It is suggested that the condition of the pretreatment is a crucial factor to control the formation of the crystalline phases, i.e. silicon carbide and silicon nitride in the product