Influencing mechanism and interaction of muscovite on thermal decomposition of ammonium polyphosphate

The interaction mechanism and phase evolution of ammonium polyphosphate (APP) mixed with muscovite (APP/muscovite) were studied by TG, XRD and SEM, respectively, during heating. When the temperature is not higher than 300 °C, muscovite has no effect on the thermal decomposition of APP, and the initial decomposition temperature of APP/muscovite at 283 °C is basically the same as the APP at 295 °C, and the main thermal decomposition products are polyphosphoric acid and NH₄H₂PO₄ at 300 °C. The polyphosphoric acid, the decomposition products of APP, can enable K and Si out of muscovite and interact with muscovite chemically to generate Al₂O₃·2SiO₂, α-SiO₂ and phosphates (AlPO₄ and K₅P₃O₁₀) compounds during 400 °C-800 °C, which own obvious adhesive phenomenon and porous structure with the apparent porosity of 58.4%. Further reactions between phosphates other than reactions among Al₂O₃·2SiO₂ and α-SiO₂ can generate KAlP₂O₇ at 1 000 °C and the density of residual product is improved by low melting point phosphate filling pore to form relatively dense structure and decrease the apparent porosity to 44.4%. The flame resistant and self-supported ceramic materials are expected to enhance the fire-retarding synergistic effect between APP and muscovite.