Studies of the Preparation and Physical Properties of Multivalent Metal Condensed Phosphates. Part XI. The Preparation of Various Aluminum Phosphates and Their Thermal Transformation

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In the reaction of Al2O3 or Al(OH)3 with phosphoric acid, the conditions of the formation of the I and II types of aluminum dihydrogen tripolyphosphate, AlH2P3O10, and the A and B types of aluminum tetrametaphosphate, Al4(P4O12)3, were established. The I and II types of AlH2P3O10 were chiefly obtained at 300 °C; the formation of the I type predominated when the water content of the primary product was 15–30%, while the II type was more readily formed at a water content of 10–15%. Also, the I and II types were easily formed at vapor pressures of 1–5 atm. Al4(P4O12)3 was produced when the water content was less than 10% or more than 30%. On the other hand, the A and B types of Al4(P4O12)3 were easily formed at 500 °C; the A type was chiefly formed when the water content was below 10% or above 25%, while the B type was produced at the water content of 10–25%. The water content of the primary product is presumably due to the dehydration caused by the condensation of the P–OH. Thus water, effective for the formation of aluminum phosphates, is the structural water (P–OH). Further, the B type was liable to be formed on rapid dehydration, while the A type was more readily produced on slow dehydration. Accordingly, the formation of aluminum phosphate has been confirmed to be greatly dependent on the water content of the primary product and on the vapor pressure in the secondary heat treatment.
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