ES211027A1 - New crystalline sodium borate - Google Patents

Abstract

<PICT:0737925/III/1> Sodium borate monohydrate is produced by heating a sodium borate or mixture of sodium borates having a molar ratio Na2O : B2O3 between 0.4 and 0.7 and a water content as hereinafter defined, in a closed vessel until equilibrium is attained or until a sufficient quantity of monohydrate crystals have deposited from solution, and to a working temperature which is dependent as hereinafter defined on the molar ratio and water content, filtering and washing the product. Fig. 1 is an isothermal diagram of the relevant part of the system Na2O-B2O3-H2O at 150 DEG C.: B represents pure sodium borate monohydrate, C a borate produced by Augers ("Augers sodium borate") and A the ternary point at which the solubility curves AD and AE of Augers sodium borate and the monohydrate, respectively, meet. The water content of the starting materials is so chosen that it lies within the area marked "1 : 2 : 1 + soln" on Fig. 1, or within the corresponding portions of similar isothermal diagrams. Below 115 DEG C., however, sodium diborate monohydrate is not formed. By adjusting the operating temperature and the water content, any ratio Na2O : B2O3 from 0.4-0.7 may be used. This ratio may be adjusted by adding sodium metaborate, boric acid, or caustic soda. Water in addition to that present in the crystalline material employed may be added. Preferred starting materials are mixtures of borax deca- or pentahydrate and crystalline sodium metaborate or caustic soda. The preferred process uses a molar ratio of 0.52, a total water content of 35 per cent by weight of the starting materials and a temperature of 170 DEG C. Other advantageous proportions and temperatures, and examples, are given.