| abstract |
Calcium, magnesium barium, zinc, iron and aluminium orthophosphates are prepared by treating salts or oxides of these metals with phosphoric acid (which may be formed in situ) first at a temperature below 30 DEG C. and pH 1.5-2.5, then at above 60 DEG C. and pH 2.5-3.5, separating the crystals by hot filtration and then heating to dehydrate said crystals. The crystals obtained before dehydration are flat plate-like crystals of the respective tetrahydrated orthophosphates, the final dehydrated product may be used as a dental setting compound. |