GB642944A - Improvements relating to glassy phosphate powder compositions and process of making the same - Google Patents

Abstract

<PICT:0642944/III/1> <PICT:0642944/III/2> Phosphate glasses for domestic water softening, produced for example by heating dihydrogen mono-sodium orthophosphate and chilling to form a glass, having an alkali metal oxide to phosphorus pentoxide ratio of at least nine to ten, are rendered more easily soluble in water by forming as a coating on the surface of the finely-ground glass particles, the acid reversion product, viz. dihydrogen disodium pyrophosphate, by humidifying and heating, and incorporating in the coating, or mixing with the coated particles, a salt which in water will react with the acid reversion product to generate a gas, thereby dissociating the particles and speeding solution. Such salts are sodium carbonate, bicarbonate, sulphite or bisulphite. In a preferred embodiment the glass particles, ground to pass an 80-mesh sieve, mixed with about 5 parts of sodium carbonate and 5 of sodium bicarbonate, per 100 parts of phosphate, are fed into a rotating drum, the inner surface of which forms a frustrum of a cone. The walls are formed by a series of louvres 9 (Fig. 2) through which at the inlet end of the drum through flue 25 air at a temperature of about 60 DEG C. with a humidity of 90 per cent, hydrates and renders sticky the surface of the phosphate particles, which then pass to a drying zone where air at a temperature of 150 DEG C. enters via flue 26, thereby partially removing the added moisture and reacting the remaining moisture with the glass to form the acid reversion product as a coating which also contains the adhering sodium carbonate and bicarbonate, on the surface of the particles. Alternatively the surface hydration may be effected by means of a hydrated salt or a 10 per cent solution of water in acetone, followed by heating to effect reversion. Specification 642,945 is referred to.ALSO:Phosphate glasses for domestic water softening are rendered more easily soluble by forming a coating on the surface of the finely ground particles of the acid reversion product of the glass, viz. dihydrogen disodium pyrophosphate, by humidifying and heating, and incorporating in the coating, or mixing with the coated particles, a substance which in water will react with the acid reversion product to generate a gas, thereby dissociating the particles and speeding solution. The added substance may be sodium carbonate, bicarbonate sulphite or bisulphite. The final product may be formed into flakes or agglomerates. Specification 642,945 is referred to.