Strengthening mechanism of mechanical properties of lightweight mullite fiber thermal insulation materials with different types of binders

Mullite fiber thermal insulation materials (MFMs) were constructed by combining mullite fibers (MFs) with three different high-temperature binders via freeze-casting method. Silica sol (SS), aluminum dihydrogen phosphate (ADP), and borosilicate sol (BS) were chosen as high-temperature binds to improve their mechanical properties. The analysis of the microstructures, phase, and organization indicated that the MFMs presented different enhancement effects derived from different binders. The “wing-like” enhancement was generated by the SS binder, but obvious cracks appear in the solid-phase traces. There were many tiny “insect-nest-like” cavities on the surfaces of the fibers due to the release of P 2 O 5 gas during the chemical reaction of ADP. The “ductile” enhancement was characterized by the formation of borosilicate glass phase for the BS binder. Combining the density, mechanical property, thermal conductivity, and microstructure of the samples, C4-1200 has the optimal comprehensive property and shows excellent thermal insulation and cold insulation performances.