Crystalline-layered sodium disilicate

Manufacturing Process of Crystalline Layered Sodium Disilicates. 403... 

Crystalline layered sodium disilicate powder sodium phyllosilicate... 

The manufacturing process sequence to crystalline layered sodium disilicate may start with the production of sodium silicate solution of a Si02 Na20 ratio of 2 by the hydrothermal process (see Table 22.1 and Figure 22.11). Quartz sand is reacted at temperatures of 180-240 C with sodium hydroxide solution of 50 wt% strength. The reaction can be performed in a nickel-clad autoclave, which is equipped with a stirring device and heated by injection of steam. The reaction solution is filtrated after addition of perlite as the filter aid. The 45 wt% solids content of the final liquor was realized by dilution with water [21,49,51,95],... 

The crystallization of amorphous, water-containing sodium silicate to anhydrous crystalline layered sodium disilicate is crucial. It is effected in a further step. The formation of delta-crystal phase is an exothermic process at 685°C [89],... 

FIGURE 22.11 Production of crystalline layered sodium disilicates. 

Sodium disilicate, Na2SijO, may be converted to hydrated silica. Thus by treating the silicate with concentrated cold acid, washing out salts with water and water with acetone, and drying in vacuum at 40°C, a crystalline disilicic acid is obtained (76, 77). Such layerlike structures arc termed lepidoidal (scalelike) or phylloidal (leaflike). Liebau distinguished two types of layer structures. They are internally hydrogen bonded and exhibit only weak acidity (78). 

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