1111216-A is referenced by 3 patents.
Alkali metal hemiphosphates, MH2PO4.H3 PO4, and mixtures with a mono alkali metal orthophosphate MH2PO4 having an M: P ratio in the mixture of between 0.5:1 and 0.75:1, are prepared by mixing anhydrous MH2PO4 with anhydrous H3PO4 in a molar proportion of MH2PO4:H3PO4 of from 1:1 to 3:1. The MH2PO4 is preferably the sodium salt, though the potassium and lithium salts may be used. The acid which has a phosphorus pentoxide content of from 70 to 76% by weight is preferably added to the phosphate which may be in the form of a spray dried powder, and the reaction may be carried out in the presence of a heel of previously prepared hemiphosphate. The temperature of the reaction mixture is preferably below 40 DEG C., but the mixture may be heated to a temperature within the range 50-70 DEG C. and then cast, by cooling the slurry.