Heat-resistance Phosphate Material With Low Dielectric Loss

Aluminum phosphate binder has been used in a wide range of hightemperature applications, such as refractories, coatings, and fiberreinforced composites due to its advantages of no pollution, highmechanical strength, heat resistance,aging resistance and multifunction.Meanwhile as a kind of fine low-dielectric material with excellentdielectric properties and simple structural design, it is also used widly inthe field of aerospace.This paper studies heat-resitence phosphate material includingaluminum phosphate binder and aluminum-chromium-phosphate binder.First the paper studies the synthesis conditions of aluminum phosphatesolution, has a comprehensive and systematic research on the thermalcuring and phase transformation and structure evolution of aluminumphosphate at heating, then preparas the phosphate adhesive withheat-resistant property, and studies the effect of its phase and structure evolution on the mechanics performance at high temperature. The resultsshow that the Al/P mole ratio and sythesis temperature affect thecomposition of Al₂O₃-P₂O₅-H₂O solution; at heating process thealuminum phosphate undergoes series of inter-molecular dehydrationreactions, and finally polymerizes into a polymer shell of chains or ringsof aluminum metaphosphate.The corresponding structural units ofphosphate groups convert from Q0finally to entirely Q2; the preparaedadhesive with aluminum phosphate solution as matrix have goodmechanical and heat resistant properties, and the structure evolution atheating process of the binder leads to the variation of mechanicalproperty.Then it also prepares heat-resistant aluminum-chromium-phosphatematerial with low dielectric loss on the basis of the studies on aluminumphosphate. It studies the effects of chromium addition on the thermalcuring and the phase transformation and structure evolution, thendescribes the effect of the phase and structure changes on the dielectricpeoperties of aluminum phosphate systerm at heating. The results showthat the addition of the metal ion Cr³⁺improves the stability of thesolution; slows the crystallization proces，delays the conversion ofAl₂P₆O₁₈to Al₄(P₄O₁₂)₃, promotes the formation of the cristobalite AlPO4phase, and also lowers the temperature of structure evolution ofphosphorus, meanwhile promotes dehydrolytic condensation of the binder at curing; the adequate amount of Cr³⁺can enhance the anti-moistureabsorption and dielectric peoperties, while has little effect on themechanical property; the prepared heat-resistant material with lowdielectric loss has good performance:heat resistant is up to1000℃, itsrelative dielectric constant is3.2～4.6and dielectric dissipation factortg is0.0091～0.0209, the rate of moisture adsorption（7d） is less than0.07%.