Research On Synthesis Of High Temperature-Resistant Materials With Al-CrO₃ System By SHS

This paper is about the reaction of SHS with the powders of A1 and CrO₃ to synthesis a new kind of insulating materials.Al₂O₃ is used as a dilution agent to control the thermal value of the reaction.NaF is used as an addition agent to remove the oxide films on the surface of the aluminous powder.With the studies of the particle size of the materials,the quantity of the dilution agent and the plastering agent,the initial temperature,the pressure and so on, it can reach the conclusion of what are the influencing factors to the productions and observe the effect of the combustion.The XRD and SEM and some other detection methods are used to detect the productions and made the test of capabilities.The combustion synthesis mechanism of the Al-CrO₃ system adiabatic materials is that the instant high temperature is caused by the ignescent; CrO₃ melts at 187℃and reacts with Al to form Cr₂O₃ and Al₂O₃.Unreacted liquid CrO₃ completely with Al can be decomposed into Cr₂O₃ and oxygen at 250℃.Al particles begin to melt down from the exterior at 659℃and react with Cr₂O₃ to form into Al₂O₃ and Cr.Liquid A1 also reacts with oxygen source from both the air and the decomposed CrO₃ to form into liquid Al₂O₃ and reacts with nitrogen in the air to form into AlN.Additionally,liquid Cr reacts with N₂ to form into Cr₂N,and the elements Cr,Al and O can also be formed into(Cr,Al)₂O₃ solid solutions at high temperature when they are reacted.These reactions cause the temperature in the reacted region to reach 2600 K.With Al₂O₃ powder in the raw materials acted as the crystal nucleus in liquid resultants,some whiskers and the crust-like Al₂O₃ and(Cr,Al)₂O₃ solid solutions are formed during this process,and a small amount of AlN and Cr₂N can also be produced.Research shows that,the Al-CrO₃ system of the insulating material synthesized by the SHS with heat-resistant and high-intensity has characteristics with high refractoriness over 1800℃,cold crushing strength 19MPa,thermal conductivity 0.80 W·m^-1·K^-1at 600℃.All the above characteristics are better than the insulating material synthesized by the traditional method.In a word,the insulating material of this study has good capabilities such as high-intensity,heat-resistant and heat insulation.It can be generalized to the industrial production with the environment of high temperature.