Novel High-Temperature-Resistant Phosphates: Thermal Ablation Behavior of La-Al System Phosphates at 2000 °C

The saturation-free and directionless cross-linking and interpenetration processes between La³⁺ and [(H₂PO₄)2Al(HPO₄)]-plasma in La-Al phosphate by mixing Al(OH)₃, CrO₃, and H₂O₂ dissolved in H₃PO₄ and La₂O₃ as a curing accelerator, as well as the thermal stability of the La-Al phosphate bulk materials and the evolutions of the phase composition and morphology at different temperatures were studied using thermogravimetric/differential scanning calorimetry under different temperatures in a muffle furnace. The La-Al phosphates showed good thermal stability, and the thermal weight loss rate of the materials decreased from 18% before heat treatment to ∼2% after heat treatment. In addition, the La-Al phosphate bulk material showed excellent resistance to ablation when subjected to ablation by an oxyacetylene flame at 2000 °C for 30 s. It evolved into a dense LaPO₄ and AlPO₄ high-temperature phase layer on the sample surface, which prevented further ablation damage to the sample and significantly improved the temperature resistance of the La-Al phosphate bulk material.