Preparation And Performance Of Oxide Fibrous Porous Ceramics Insulation

With the development of aerospace technology and the speed improvements of aircraft,the higher requirements of thermal protection system materials have been put forward.During the flight,which different parts of aircraft are faced with different thermal environments.For instance,the aerodynamic heating temperature of nose cone,wing leading edge,etc.are relatively high,the thermal shock effects are strong but the proportion of them are small.In comparison,the aerodynamic thermal temperature of aircraft fuselage,wing,etc.are lower while the distribution area is wider.Therefore,light and efficient heat insulation large-area thermal protection materials play an important role in the field of aircraft thermal protection system.Fibrous porous ceramics are composed of chopped ceramic fibers and inorganic binders.Owing to the high porosity,low density and thermal conductivity,these fibrous porous ceramics are widely used to be thermal protection system for space shuttles.In order to obtain fiber porous ceramics with higher strength and lower thermal conductivity,the preparation and properties of fiber porous ceramics are studied in this paper.Ultra-fine quartz fiber are used to being the fiber skeleton,and silica sol and aluminum sol being the binder,respectively.The fiber porous ceramics were prepared by the gel casting method.It was discovered that alumina sol could effectively improve the strength of fibrous porous ceramics.The fibrous porous ceramics prepared by squeeze method with aluminum sol as the binder,when the compressive percentage is20%,the fibrous porous ceramics exhibited a low density(0.38g/cm~3),relativity low thermal conductivity(0.1210W/(m K)),and high compressive strength(0.87MPa).The fibrous porous ceramics with ultrasonic vibration process for 10 mins,presented a density of 0.6g/cm~3,thermal conductivity of 0.1457W/(m·K),and a high compressive strength of 1.87MPa.In order to further improve the mechanical properties of fibrous porous ceramics,the aluminosilicate fibers were added.The results show that the fibrous porous ceramics with the addition of 20%aluminosilicate fibers have better performance after being sintered at 1100℃.The density of the material is 0.45g/cm~3,the thermal conductivity is0.1407W/(m·K),and the compressive strength is 1.80MPa.When the sintering temperature was increased to 1200℃,the thermal conductivity of the material increased significantly to 0.2170W/(m·K)due to the change of fiber crystal structure,while the compressive strength decreased by 1.42 MPa.The effect of aspect ratio on the properties of fibrous porous ceramics was studied,and it was found that when the fiber length was 100μm,the connection index of fibrous porous ceramics was high,the distance between fiber nodes was short.So that the density of the material was 0.55g/cm~3,and the thermal conductivity was0.1425W/(m·K),the fiber strength is as high as 1.7MPa.When the fiber length is600μm,the density of the material is only 0.27g/cm~3,but the compressive strength of the material is 0.46MPa.The reusability of porous fiber ceramics was studied,and it was found that the shrinkage rate of porous fiber ceramics after 20 thermal shock tests was less than 2%,and no delamination and obvious cracks appeared.The compressive strength of the material increased from 0.69MPa to 0.72MPa,showing a small increase,and the thermal conductivity increased from 0.1192W/(m·K)to 0.1258W/(m·K),indicating that the material has good reusability.