Porous glass ceramics from siliceous rocks with high operating temperature
Porous glass-ceramic materials although light weighted have relatively high strength, low thermal and sound conductivity, high corrosion resistance, and are non-combustible, etc. They can be obtained from siliceous rocks, the reserves of which are huge. The article considers the obtaining of porous glass ceramic materials with an operating temperature exceeding 900 °C. The materials are obtained from siliceous rocks, Na2CO3, Al2O3 and KCl. Mechanochemical activation of raw materials was carried out in a planetary ball mill. The resulting charge mixture was annealed at a temperature of 850 °C. Experimental results were obtained by using X-ray diffraction (XRD) and thermal (TA) analysis, scanning electron microscopy (SEM), X-ray microtomography (Micro-CT). Physical-mechanical, thermophysical properties and chemical stability of obtained materials were examined. The main crystalline phase of glass ceramics from the calcite-free charge mixture is anorthoclase and quartz. Apart from that samples with calcite charge mixture contain wollastonite and devitrite. The increased content of Al2O3 in the charge mixture displays nepheline in glass ceramics. Calcite in the charge mixture has a significant effect on the microstructure of porous glass ceramics. The number of open pores in the material increases from ≈ 5 % to > 50 %. The compressive strength of porous glass-ceramic materials derived from siliceous rocks reaches 5.1 MPa. In terms of strength, they are significantly superior to foam glass. The minimum thermal conductivity of glass ceramics is 0.065 W/(m∙°С) at a sample density of 244 kg/m3. Samples withstand temperature drops by 230 °C. The material has a high chemical stability and can be operated at temperatures reaching 920 °C inclusively. The obtained materials can be used as thermal insulation of boiler equipment, melting furnaces, etc.