BARIUM METAPHOSPHATE

White powder. Slowly soluble in acids; insoluble in water.

Glasses, porcelains, and enamels.

Barium metaphosphate, used in glasses, porcelains, and enamels, as a flame retardant and in phosphors applications.

Barium metaphosphate can be prepared by the solidstate reaction of metaphosphoric acid and the hydroxide, oxide or carbonate of barium:
BaCO3 + HPO3 + heat Ba(PO3)2 +H2O + CO2
The best temperature to use is about 700°C. It has the CAS number of 13762-83-9 and the molecular weight of 295.2709 g/mol. If diammonium phosphate is used instead of solid metaphosphoric acid, the product is not pure. Colored glasses are obtained caused by the reduction of P-atoms in the phosphate anion by hydrogen released from NH3 to form colloidal dispersions of P4 which produce various colors in the glass. b-Ba(PO3)2 is the final product. This compound can also be prepared by the aqueous reactions:
NaPO3 (aq) + BaCl2 (aq) Ba(PO3)2 (solid) + NaCl (aq)
or
Ba(OH)2 (solid) + 2HPO3 (aq) Ba(PO3)2 (solid) + 2H2O
The dissolution and reaction involving HPO3 are slow and should be carried out in a hot solution. Evaporation at a low temperature (<15°C) serves to form the crystals. The product involves several hydrates depending upon the conditions of precipitation. Anhydrous barium metaphosphate is a white porous powder or granular material that is insoluble in water.