Study And Preparation Of High Performance Aluminum Phosphates Wave-transparent Materials

The present study developed a process of aluminum phosphates ceramics for radomeapplication. The composite for high-speed guided weapon and radome have been studied. Itwas based on the superior dielectric properties and mechanical performance of aluminumphosphates（AlPO₄）, aluminum borate whisker materials （9Al₂O₃·2B₂O₃）, zirconiumanhydride （ZrO2） and silicon nitride（CSi₃N₄）.The phosphates composites used in wave-transparent material is with thermostability, highstrength, excellent dielectric property, inoxidizability, low thermal expansion coefficient, andwell structure of design etc. It is the ideal material that is well thermal stability and lowdielectric loss, and it can satisfy many kinds of special environment and be widely used onvarious rockets, guided weapon and space shuttle. The aluminum borate whisker has highmodulus of elasticity, well mechanical properties, heat resistance, corrosion resistance,insulating property and neutron absorptivity, as well as its dielectric constant is low. ZrO2haschemical resistance， inoxidizability， thermostability and thermal shock resistance. CSi₃N₄also has excellent performance as well as ZrO2. So they adapt to reinforce the wave-transparentmaterial. Therefore, ZrO2and CSi₃N₄reinforced9Al₂O₃·2B₂O₃-AlPO₄ceramic composites areprepared by using ZrO2and CSi₃N₄as reinforced materials in order to improving dielectricproperty and the toughness of9Al₂O₃·2B₂O₃-AlPO₄ceramic composites, and making thealuminum phosphates wave-transparent material widespread availability in aerospace field.CSi₃N₄-9Al₂O₃·2B₂O₃-AlPO₄composite and ZrO2-9Al₂O₃·2B₂O₃-AlPO₄composite areprepared by conventional sintering technology at ordinary pressure, after chose confirmed finewhisker content and sinter system. The mechanical properties and dielectric properties ofcomposites were tested. The toughen mechanism and wave-transparent principle of compositeswere discussed.The mechanical properties and dielectric properties of CSi₃N₄-9Al₂O₃·2B₂O₃-AlPO₄composites was studied. The results showed the relative density, flexural strength, Vickershardness of composites were increased firstly and then decreased with the sinteringtemperature and CSi₃N₄content raised. When the sintering temperature and CSi₃N₄content were1050℃and5wt%respectively, flexural strength, the Vickers hardness dielectric propertie and dielectric loss get maximum value, they were167.29MPa,381.15MPa，3.15and0.0089respectively; But the apparent porosity is decreasing firstly and then increasing with sinteringtemperature and CSi₃N₄content raised. The residual strength still kept80%after thermal shockat1000℃.Apparent porosity, relative density, flexural strength, Vickers hardness, dielectricproperties of ZrO2-9Al₂O₃·2B₂O₃-AlPO₄were studied. The results showed that the relativedensity, flexural strength, Vickers hardness of composites increase firstly and then decreasewith ZrO2content and sintering temperature raised. When the sintering temperature and ZrO2content were850℃and3wt%respectively, the relative density, flexural strength, the Vickershardness and dielectric propertie get maximum value, they were2.01g/cm3,230.58MPa,506.68MPa and5.19respectively; But the apparent porosity was decreasing firstly and thenincreasing with sintering temperature and ZrO2content raised.The toughen mechanism and wave-transparent principle of composites were analyzed.Residual stress resulted in microcrack， because different grains have different coefficients ofthermal expansion, the microcrack can release remanent strain. It was the first reason. Whiskerextraction, cracks deflection, and whisker bridging were the second reason to increase thestrength and toughness of composites.