Formation of a porous structure of foam silicates based on liquid-glass compositions

Abstract

The influence of various additives on the porization of liquid-glass compositions using new approaches for analyzing experimental data, making it possible to obtain a quantitative assessment of the influence of inorganic additives and salts, is determined. Application of the law of constancy of the volume phase composition of dispersed systems makes it possible to express mathematically the influence of technological parameters (temperature, time) and the form of the types of additives introduced on the porization processes in such compositions.Liquid glass based on soluble silicates of alkali metals is a unique material which when heated up to 150 -500°C is capable of forming solid inorganic foam. Heating partially dried liquid-glass granules or compositions in molds with a closed volume permits obtaining heat-insulation materials with a rigid porous structure, occupying an intermediate position with respect to functional properties between cellular concretes and foam glass. This material can be called, with full justification, a foam silicate based on liquid glass.Liquid glass compositions (LGC) are obtained by mixing liquid sodium glass with specific additives, which can be divided into several groups according to the effect on the liquid glass and the material being fabricated: 1) inert with respect to liquid glass, acting as a framework forming filler in the finished article;2) gel-forming, giving rise to the gel-forming reaction in liquid glass and thereby destroying its polymer structure;3) thermoreactive additives, which do not interact with liquid glass and decompose on heating, releasing gaseous products.The effect of group-I additives depends on the nature of the substance and the dispersity. As the additive enters the LGC composition without destroying the colloidal structure of the liquid glass itself, it will have an ordering effect on the macrostructure of the heat-insulating material and increase the physical -mechanical properties of the article. When the volume content of the additive exceeds the maximum value for a given substance, the liquid glass coagulates with water being released and a silica gel being formed, which has a negative effect on the swelling capacity of LGC. Examples of such additives are finely dispersed quartz sand, tripoli, diatomite, dehydrated limonite (Fe 2 O 3 ), MgO, and CuO.The group-II gel-forming substances are introduced into GLC to increase the viscosity of LGC rapidly and increase process efficiency -it is easier to regulate the gel obtained and to pack it in molds. However, when the gelling agent content is significant, the polymer structure of the liquid glass breaks down and the porization capacity of the glass decreases, and the density of the articles correspondingly increases and their heat-insulation properties decrease. Thus, these additives must be introduced in small, strictly determined, quantities. Examples of well-known gelling agents are sodium silicofluoride, ethyl alcohol, boric acid, and many water soluble salts of alkali-earth and heavy metals. S...

Study into the feasibility of manufacturing liquid glass using resource-saving technology

“…Such materials include foam-silicate plate products, highly porous granular aggregates, and others [10][11][12][13][14].…”

Influence of Co3O4, Fe2O3and SiC on microstructure and properties of glass foam from waste cathode ray tube display panel (CRT)

“…However, the differences in the chemical composition and, accordingly, the different properties of the cullet of black, white and colour of CRT have an effect on the formation of the porosity and pore size distribution in foam glass batches prepared from the particular types of glass. 2,[5][6][7] Foams are a special class of porous materials comprised of large voids (open or closed cells), with linear dimensions approximately ranging from a few micrometres to few millimetres (10 mm-5 mm). 8,9 Glass foams are a porous heat insulating and sound proof materials, with porosity, apparent density and compressive strength values of about 80-95 vol.-%, 0?1-0?3 g cm -3 and 0?4-6 MPa respectively.…”

Control of porization in liquid glass based thermofoam silicate articles

“…Finely dispersed mineral fillers introduced into LGC in amounts above 8 -10%, adsorbing into their surface ions of the liquid glass or binding free-water dipoles, either give rise to gel formation in the liquid glass or thin the mixture [1,2]. The nature, dispersity, and amount of filler introduced have a decisive effect on the development of gel-formation processes, during which the LGC must acquire the solid-like viscoplastic state required for subsequent granulation of the mixture in auger granulators.…”