Thermal stability of the waylandite-structured nanocrystalline BiAl3(PO4)2(OH)6

A nanocrystalline powder of the waylandite-structured bismuth hydroaluminophosphate was ob-tained under hydrothermal conditions at 200 degrees C, 7 MPa and pH 7, and characterized by X-ray diffractometry, scanning electron microscopy (SEM), and energy dispersive microanalysis (EDAX). The simultaneous thermal analysis and high-temperature X-ray diffractometry have shown that the crystal-chemical formula of this com-pound can be represented as BiAl3(PO4)2O(OH)4 center dot(H2O). This compound retains its structure and crystallite size (similar to 65 nm) up to about 500 degrees C. It has been determined that the decomposition of this compound in the 540-800 degrees C range results in the formation of Bi2O3, Bi2Al4O9 and AlPO4 phases. At temperatures above 800 degrees C, a complete thermal decomposition of Bi2Al4O9 and the formation of crystalline alpha-Al2O3 occur in this system, while Bi2O3 keeps evaporating during the isothermal exposure.

Automated summary

A nanocrystalline powder of waylandite-structured bismuth hydroaluminophosphate was successfully synthesized under hydrothermal conditions, and it was found to remain stable below 500 degrees C. Decomposition occurred in the range of 540-800 degrees C, resulting in the formation of multiple phases, while complete thermal decomposition and the formation of crystalline alpha-Al2O3 occurred above 800 degrees C.