To expand the utilization of iron tailings, four kinds of porous ceramics were prepared by foam gel-casting with pressureless sintering, foam gel-casting with reactive sintering, and mold forming with reactive sintering using fine-grained high-silicon iron tailings, iron tailings + graphite, and iron tailings + graphite + silicon carbide as raw materials, respectively. DSC-TG and XRD analysis was applied to investigate the sintering process of iron tailings and the carbothermal-reduction reaction between iron tailings and graphite. The four porous ceramics’ porosities, compressive strengths, and thermal conductivities were further analyzed. The results show that the porous ceramics made only from iron tailings possesses high porosity (87.2%), compressive strength (1.37 MPa), and low thermal conductivity (0.036 W/(m·K)), meeting the requirement of thermal insulation material. Silicon carbide porous ceramics with improved thermal conductivity but a slight sacrifice of strength can be fabricated through carbothermal reduction between iron tailings and graphite. Moreover, the compressive strength of silicon carbide porous ceramics can be significantly increased by adding some silicon carbide to the raw materials. The silicon carbide porous ceramics achieved high porosity of 91.6%, high compressive strength of 1.19 MPa and thermal conductivity of 0.31 W/(m·K), which can be a guarantee of a carrier for composite phase change materials or light thermal conductive materials. Compared with foam gel-casting, the mold-forming process can significantly improve the thermal conductivity (1.15 W/(m·K)) of silicon carbide porous ceramics and greatly reduce the cost of raw materials and manufacturing, which is profitable for industrialization.

Ceramic fibers are the vital high-temperature thermal insulating materials due to their excellent mechanical property, high-temperature stability and thermal shock resistance. However, practical application of traditional ceramic fiber membranes in the field of thermal insulation are greatly limited by their high thermal conductivities at high-temperatures. In this work, SiZrOC nanofiber membranes with high infrared shielding performance were prepared by electrospinning technique. The SiZrOC nanofibers were composed of SiO₂, ZrO₂, SiOC, and free carbon phase with average diameter of (511±108) nm. The SiZrOC nanofiber membranes exhibited possess excellent high-temperature thermal insulation performance. Thermal conductivity of SiZrOC nanofiber membranes at 1000 ℃ reached 0.127 W·m^-1·K^-1, obviously lower than that of other traditional ceramic fibers. In addition, the as-prepared SiZrOC nanofiber membranes exhibited high strength, good flexibility and excellent high-temperature stability, so they had great potential for high-temperature thermal insulation. Therefore, preparation strategy of SiZrOC nanofiber membranes also provides a new route for designing other high-performance thermal insulators.

Silica aerogels have wide application prospect in high temperature heat insulation due to their low density and high porosity. However, the brittleness and high cost of supercritical drying restrict their application. In this study, spongy silicone aerogels with high flexibility were prepared via Sol-Gel polymerization and atmospheric pressure drying using vinyltrimethoxysilane (VTMS) and vinylmethyldimethoxysilane (VMDMS) as precursors. The effects of precursor molar ratio on the microstructure and compressive resilience of aerogels, as well as the inorganic transformation process of aerogels in high temperature aerobic and anaerobic environments were studied. The results show that with the increase of VTMS/VMDMS ratio in the precursor, the aerogel particles become smaller and more tightly packed, and the compression resilience of aerogels also decreased. In air at 800 ℃, aerogels were transformed into inorganic SiO₂ by oxidation of organic side groups, fracture and rearrangement of main chain Si-O-Si. In N₂ at 800 ℃, aerogels were transformed into the mixture of inorganic SiO₂ and free carbon by pyrolysis reaction, and after further treatment at 1000-1400 ℃, SiO₂ and free carbon were subjected to carbothermal reduction reaction to form amorphous Si-O-C structures such as SiO₄, SiCO₃, SiC₂O₂, and SiC₃O, and a small amount of β-SiC nanowires. The Si-O-C structure formed by carbothermal reduction reaction at 1200 ℃ has optimal high temperature oxidation resistance, which can provide reference for the preparation of pyro-oxidation resistant Si-O-C aerogels.