PREPARATION OF ZINC-SODIUM PHOSPHATE-GLASS PRECURSORS BY COACERVATION

Condensed phosphates of (50 - x)Na2O-xZnO-50P(2)O(5), 36.7 less than o r equal to x less than or equal to 46.7 are isolated by separation of coacervates from aqueous colloidal solutions. The relation between the occurrence of coacervation and the presence of complexes in zinc-sodi um polyphosphate solutions has been investigated by P-31 nuclear magne tic resonance and viscosity measurements. Zinc complexes with (PO3-) l igands occur whatever the concentrations, Zn/P ratios, counter-ion nat ure and pH. The coacervation does not coincide with a definite complex nature, but rather on electrostatic-stability-related criteria of the polyphosphate anions. These electrostatic criteria explain the depend ence of the zinc-sodium polyphosphate coacervation on the pH and natur e of the counter-ion. A method of preparation of powdered glass precur sors from coacervates and their formulations are described.