Preparation of dense shell hollow alumina microspheres with low density, high isostatic strength, low thermal conductivity, and high-temperature thermal stability via spray drying with heat treatment

With the development of high-speed spacecraft, the equipment faces the threat of high temperatures brought about by the high speed. Hollow microspheres commonly applied in equipment may lose efficacy in extremely high-temperature circumstances. Fortunately, the thermal stability of hollow alumina microspheres (HAMs) could solve the drawbacks. However, HAMs prepared by conventional strategies encounter problems of high cost, time-consuming, and low yield. The spray drying can rapidly make soft and agglomerate-free granules on a large scale, which makes HAMs feasible in practical applications. Nonetheless, in previous work, HAMs prepared by spray drying suffer from poor mechanical performance. In this research, Al(NO 3 ) 3 was selected as the alumina source, using spray drying with heat treatment to prepare HAMs, which present low density, high isostatic strength, low thermal conductivity, and high-temperature thermal stability. Furthermore, the relationship between the preparation parameters with the morphology and properties of HAMs was explored. Based on explorations, the formation mechanism of HAMs and the factors influencing their morphology and structure were speculated. These explorations will serve as a paradigm for inspiring and guiding the development of high-performance HAMs, ultimately addressing the lightweight and high-strength demands of composite materials for aircraft under high-temperature conditions.