The chemical changes during the drying of monocalcium phosphates can be
represented as follows, temperature 200° for one hour:
8[CaH₄(PO₄)₂·H₂O] = 4CaH₄(PO₄)₂ + Ca(PO₃)₂ + Ca₂P₂O₇
+ CaH₂P₂O₇ + 2H₃PO₄ + 12H₂O.
The further drying at 200° produces the following decomposition:
4CaH₄(PO₄)₂ + Ca(PO₃)₂ + Ca₂P₂O₇ + CaH₂P₂O₇ + 2H₃PO₄
= 2Ca(PO₃)₂ + 4CaH₂P₂O₇ + Ca₂P₂O₇ + 2H₃PO₄ + 5H₂O.
2Ca(PO₃)₂ + 4CaH₂P₂O₇ + Ca₂PO₇ + 2H₃PO₄
= 6Ca(PO₃)₂ + 2CaH₂P₂O₇ + 5H₂O.
Finally, pyrophosphate at 210° is completely decomposed into
metaphosphate and water according to the following formula:
6Ca(PO₃)₂ + 2CaH₂P₂O₇ = 8Ca(PO₃)₂ + 2H₂O.
Provided the drying is made at once at 210° the sum of the changes
produced as indicated above, can be represented by the following
formula:
8[CaH₄(PO₄)₂·H₂O] = 8Ca(PO₃)₂ + 24H₂O.