Obtaining of SiAlON Composite via Metal-Thermal and Nitrogen Processes in the SiC-Si-Al-Geopolymer System

Abstract

Goal: obtaining of composite in the SiC-SiAlON system with the metal thermal method in the nitrogen medium. Method: SiALON-s are solid metal oxide solutions in nitrides. Area of their presence is considered in four-component system-Si 3 N 4 -ALN-AL 2 O 3 -SiO 2 . In the present paper SiALON-containing composite was obtained through alum-thermal process in the nitrogen medium on the base of Geopolymer (kaolin and pologycley-Ukraine), SiC, aluminum nano-powder and Si powder with small additives of perlite (Aragatz, Armenia) by the reactive baking method. The advantage of this method is that compounds, which are newly formed thanks to interaction going on at thermal treatment: Si 3 N 4 , Si, AlN are active, which contributes to SiALON formation at relatively low temperature, at 1250 ° C - 1300 ° C. Results - β -SiAlON was formed at the sintering of SiC-aluminium and silicium powder, geopolymer at 1450 ° C. Porosity of carbide SiAlON composite obtained by reactive sintering, according to water absorption, equals to 13% - 15%. The samples were fragmented in a jaw-crusher and were powdered in attrition mill till micro-powder dispersion was obtained. Then samples were hot-pressed at 1620 ° C under 30 MPa pressure. Hold-time at the final temperature was 8 min. Sample water absorption, according to porosity, was less than 0.4%. Further studies were continued on these samples. Conclusion : the paper offers processes of formation of SiC-SiAlON composites and their physical and technical properties. Phase composition of the composites was studied by X-ray diffraction method, while the structure was studied by the use of optic and electron microscope. Electric properties showed that the specimen A obtained by hot-compression is characterized by 2 signs lower resistance than the porous material B, which was used to receive this specimen. Probably this should be connected with transition of the reactively baked structure of the hot-compressed material into compact structure. Obtained materials are used in protecting jackets of thermo couples used for melted metal temperature measuring (18 - 20 measuring) and for constructions used for placing objects in factory furnaces.