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.