Abstract
Plumbogummite-group phosphates [MAl3(PO4)2(OH)5·H2O (M=Pb, Ba, Sr or Ca)] were synthesized by precipitation from the mixed solution of M-salt, Al-salt and orthophosphoric acid at 90°C and pH=B. Synthesized plumbogummite-group phosphates are spherulitic cry-stals with a fibrous structure. The hexagonal unit cell has a=7.027±0.004, c=16.75±0.01Å(M=Pb, plumbogummite), a=7.074±0.006, c=16.84±0.05Å(M=Ba, georceixite), a=7.02±0.01, c=16.60±0.05Å(M=Sr, goyazite) or a=7.015±0.003, c=16.180±0.007Å(M=Ca, crandallite). When heated in air, the synthesized plumbogummite, georceixite, goyazite and crandallite became amorphous at temperatures around 500°C because of the loss of H2O (100-200°C) and (OH)-groups (300-450°C). The amorphous phosphate obtained from geo-rceixite was stable untill 1000°C, while those obtained from plumbogummite, goyazite or crandallite were unstable producing M3(PO4)2 and AlPO4 at temperatures over 700°C (M= Pb) or 950°C (M=Sr or Ca). Florencite [CeAl3(PO4)2(OH)6] could not be synthesized by precipitation from the mixed solution of Ce (NO3)3·6H2O and orthophosphoric acid at pH 2 to 8 even if kept at 90°C for 4 weeks.
