Properties of porous glass ceramics based on siliceous rocks
Porous glass ceramic materials are widely used in the construction industry. Foam glass ceramics are obtained from industrial wastes, rocks of various chemical and mineralogical composition and other raw materials. Samples of foam glass ceramic materials obtained by burning the mechanically activated charge were studied. Siliceous rocks from six deposits were ground together with thermonatrite (Na2CO3·H2O). The resulting charge was burned at a temperature of 850 °C. The following properties were determined experimentally: bulk density, compressive strength, water absorption, sorption humidity, thermal conductivity, application limit temperature, thermal and chemical stability of samples. In order to obtain glass ceramic materials with a uniform porous structure, the total amount of cristobalite and the amorphous phase in the composition of siliceous rock has to be more than 44.5 %. The amount of quartz, calcite and muscovite in the rock should not exceed 12 %. The bulk density of the samples decreases with an increase of heilandite share in the charge composition. The maximum compressive strength of the developed materials is 6 MPa with a bulk density of samples equal to 290 kg/m3. The water absorption of samples decreases to 2.5 % (by volume) with an increase of diatomite share in the charge composition for more than 39.5 %. The minimum thermal conductivity of glass ceramics (0.0583 W/m °С) was revealed at a sample density of 180 kg/m3. Insufficiently high values of thermal stability index (167–183 °C) are associated with the presence of both amorphous phase and crystalline minerals in the material, which have different thermal expansion coefficients. The application limit temperature of the material reaches 850 °C. The developed materials demonstrated high chemical stability after boiling in water, an aqueous HCl solution, as well as in an alkaline solution. Regarding a number of indicators, porous glass ceramic materials based on siliceous rocks are superior to foam glass and can be used as thermal insulation of pipelines, industrial plants (melting furnaces, boiler equipment), etc.