Sol-gel derived porous aluminum oxide cryogel – Fiber composite systems

•A low cost- and energy-consumption synthesis was newly developed for Al2O3 cryogel-fiber composites.•A transparent spinnable mixture can be obtained by hydrolysis degree of 1.8 and 10 m/m% Al(III) concentration.•The cryogel-fiber composites have an excellent thermal conductivity value, 0.040 W/(m⋅K).•The porous composites can be applied up to 1500 °C in contrast with the generally application temperature of 1000 °C.•Al2O3 cryogel-fiber composites demonstrate their excellent applicability in the space satellite test. The main aim of present research was to develop a new low-cost synthesis route to produce ultralight Al2O3 cryogel – fiber composite materials for high temperature insulation. The Al2O3 fibers give the matrix in these composites, instead of the typical reinforcement phase. The synthesis of precursor systems of fiber drawing and freeze drying is based on sol–gel chemistry. The starting materials (inorganic Al salts, organic solvents, and additives) were the same for both type of porous Al2O3 systems. The length of fibers (5–10 cm) is sufficient to form a matrix in the composites. The average diameter of fibers is 10 µm; the size of cryogel particles is generally 20–30 µm in the composites. The composite systems were characterised by 2D and 3D SEM, N2 sorption analysis, FTIR spectroscopy, thermal conductivity measurements, thermo-vacuum, vibration, and satellite tests.