Synthesis of Nano-Dispersed Powders for Non-Oxide Composites by Spray Pyrolysis Method

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Fine powders for SiC particle reinforced Al_2O_3 composite were prepared by two kind of spray pyrolysis methods, one was using a two-fluid nozzle atomizer and the other was using an ultrasonic vibrator for atomizer, from a suspension of fine SiC particles into aluminum nitrate solution. Characteristics of each powders and the composites prepared from these powders by a hot-press technique were observed using various kinds of experimental tools, such as SEM,TEM,XRD,DTA-TG,a particle size analyzer, a BET surface area meter and an universal testing machine.Powders prepared using a two-fluid nozzle atomizer and pyrolized at 870ﾟC were hollow sphere in shape and having 30m^2/g specific surface areas. It consisted of amorphous alumina and crystalline SiC.SiC containing alumina powders were successfully synthesized by this method in a high synthesis rate and a high retrieval ratio. The as-synthesized powders were secondary particle in 2 to 10 mum in diameter consisted of very fine primarily p … More articles in 50 nm in diameter. SiC contents in the as-synthesized powders were 60 to 70% of the mixing amount in the suspension.Powders prepared using an ultrasonic vibrator for atomizer and pyrolized at 900ﾟC were dense sphere in shape and nearly 1mum in diameter. Whereas synthesis rate was very limited, high retrieval ratio of 70-80% was attained. The powders consisted of mostly amorphous alumina and crystalline SiC.SiC contents in as-sprayd powders were about 40% of the mixing amount in the starting suspension.Both powders were then hot-pressed at 1700ﾟC for 2h in Ar under a 30MPa applied pressure. Composites containing up to 22vol%SiC showed higher bending strength than that of pure alumina prepared by the same technique. In same case, more than twice in strength were achieved. Dispersion of SiC particles restricted grain growth of the matrix grains. From TEM observation of the composites sintered from both powders, it was clarified that nanometer size SiC grains were included into an alumina grains. Thus formation of nano-dispersed composites was confirmed. Less