Study On Synthesis And Properties Of High Temperature Resistant Fumed Alumina-based Thermal Insulation Composites

The new high-speed aircraft presents an urgent need for high-performance insulation materials that can be quickly prepared.In this paper,the high temperature resistant fumed alumina-based thermal insulation composites were prepared by casting and ambient pressure drying,which consists of fumed alumina powder as nano-matrix,mullite fiber as reinforcement,aluminate cement as binder,?-SiC powder as opacifier,Pluronic P84 as surfactant and deionized water as solvent.The relationship between the preparation process,structure and properties of the materials was systematically studied,and the properties of the materials were tested and characterized.The main research work is as follows:Through the material system design and preparation process design,the raw materials,molding process and drying process were determined,and the fumed alumina-based thermal insulation composites were preliminarily prepared.The effects of drying temperature on the density,drying shrinkage and thermal conductivity of composites were studied.When the drying temperature was 50°C,the composites had good comprehensive performance,and the preparation period was only 36 h.The temperature resistance of the composites at different temperatures was studied.The high temperature resistance was good at 1200°C,and the thermal conductivity at 1100°C was 0.102 W/m·K.The influence of raw material ratio on the performance of thermal insulation composites were studied.The four-factor and three-level orthogonal experiments and univariate experiments were used to determine the raw material ratio of thermal insulation composites with better comprehensive performance.As the amount of deionized water increases,the micron-sized pores in the composites increase,the drying and high-temperature shrinkage increase,the density,the thermal conductivity and compressive strength decrease.Increasing the amount of aluminate cement can improve the internal adhesion of the composites.It can effectively improve the compressive strength of the composites,inhibit the drying and high temperature shrinkage,but at the same time increase the density and thermal conductivity of the composites.Mullite fiber mainly plays the role of skeleton support in the composites.Comprehensive performance index of composites,and finally obtained optimized mass ratio(m _Fumedalumina powder:m?-SiC:m Mullite fiber:m Aluminate cement:m Deionized water:m50%Pluronic_P84=22.5:3.75:27.5:8.75:77.5:1),the composite prepared by this ratio has superior comprehensive performance,the density is 0.630 g/cm³,and the thermal conductivity is0.115 W/m·K at room temperature and ambient pressure,the compressive strengths corresponding to 3%and 10%are 0.23 MPa and 0.63 MPa,respectively.The thermal insulation properties and mechanical properties of fumed alumina-based thermal insulation composites were further optimized.The effect of?-SiC content on the thermal insulation properties of composites was studied.With the increase of the amount of?-SiC,the thermal conductivity of the composites decreases first and then increases.When the content of?-SiC is 2.66 wt%,the thermal conductivity of the composite at room temperature and high temperature is the lowest.The thermal conductivity at room temperature and 1100°C is 0.078 W/m·K and 0.114W/m·K,respectively.The effect of fiber length on the properties of composites was studied.Long fibers(10 mm)can form a better support skeleton than short fibers(50-1000?m).The prepared composites have a density reduction of 15.2%,and the thermal conductivity at 1100°C is reduced by 23.7%to only 0.087 W/m·K,the bending strength is increased by 55.6%.The influence of the forming method on the properties of the composites were studied.After the composite was pressurized,the density increased,and the thermal conductivity at room temperature and high temperature increased.After the composite aerogel,the thermal conductivity at room temperature and high temperature decreased.