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

采用两种喷雾热解方法，一种是采用双流体喷嘴雾化器，另一种是采用超声振动器雾化器，将细小的碳化硅颗粒悬浮在硝酸铝溶液中，制备碳化硅颗粒增强Al_2O_3复合材料的细粉。采用SEM、TEM、XRD、DTA-TG、粒度分析仪、BET比表面积仪和万能试验机等多种实验工具对热压法制备的粉末及其复合材料进行了表征。在870℃的温度下，用双流体喷嘴雾化制备的粉末呈空心球形，比表面积为30m^2/g。它由无定形氧化铝和结晶碳化硅组成。该方法成功地合成了含碳化硅的氧化铝粉体，合成速率高，回收率高。所合成的粉末为2 ~ 10 μ m直径的次级颗粒，主要由非常细小的颗粒组成，直径为50 μ m。合成粉体中SiC含量为悬浮液掺量的60 ~ 70%。用超声振动器制备的粉末在900℃下加热后，呈致密球形，直径接近1 μ m。虽然合成率有限，但回收率高达70-80%。粉末主要由无定形氧化铝和结晶碳化硅组成。喷雾态粉末中SiC含量约为初始悬浮液混合量的40%。然后将两种粉末在30MPa的压力下，在1700℃的氩气中热压2h。SiC含量高达22vol%的复合材料比用相同工艺制备的纯氧化铝具有更高的抗弯强度。在同样的情况下，达到了两倍以上的强度。SiC颗粒的分散限制了基体晶粒的生长。通过透射电镜观察两种粉末烧结后的复合材料，发现氧化铝颗粒中含有纳米尺寸的碳化硅晶粒。从而证实了纳米分散复合材料的形成。少

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