PREPARATION AND PARTICLE-SIZE CONTROL OF AMMONIUM POLYPHOSPHATE FORM II BY THE PHASE TRANSITION OF AMMONIUM POLYPHOSPHATE FORM I-II

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In the preparation of ammonium polyphosphate form II according to the phase transition of ammonium polyphosphate form I under alternate flow of wet ammonia and dry air, particle size of ammonium polyphosphate form II was controlled by changing flow time of alternate flow-gases of wet ammonia and dry air. To obtain a small crystalof ammonium polyphosphate form II, the phase transition from form I to II on ammonium polyphosphate under a short flow time of wet ammonia was required. Under the reaction conditions, APP form-II crystals with average particle sizes smaller than 2.6μm were produced and the APP crystals with particle sizes larger than 4μm were not included in the products.