Preparation And Properties Of Alumina Based Ceramic Porous Insulation Materials

With the rapid development of aerospace science and technology,the exploration of the outer space and the earth's atmosphere has become an important research direction in the field of aerospace.Aircrafts face a harsh aerodynamic heating environment when flying,so the thermal protection system of the aircrafts is drawing more and more attention.As a thermal protection system for hypersonic vehicles,we need a material with the characters of high efficiency,light weight,heat resistance,low thermal conductivity and low coefficient of expansion.This paper used Al2O3 Fiber as matrix and SiO2 as binder,prepared two kinds of ceramic fiber porous thermal insulation materials by vacuum filtration.The density,porosity,thermal conductivity,compressive strength,rebound characteristics and microstructure of the materials were tested and studied.The experimental results showed that in the preparation of thermal insulation tile,using a sieve with 20 mesh,adding 1g PAM aqueous solution(the concentration of polyacrylamide aqueous solution is 0.33%)as dispersion agent and the sintering schedule is as following: the heating rate is 2?/min from room temperature to 700?,and 5?/min from 700? to 1500?,then keeping temperature for 2 hours,could prepare samples with low thermal conductivity coefficient,density and high mechanical strength.Silicon sol can be used as high temperature bonding agent,with the concentration increasing from 7.5% to 30%,the density of samples increased from 0.37g/cm3 to 0.57g/cm3,the porosity decreased from 88.86% to 77.28%,the thermal conductivity increased from 0.20W/m·K to 0.27W/m·K,and the compressive strength increased from 0.56 MPa to 1.54 MPa.With the ratio of SiO2 fiber to Al2O3 fiber increased from 1:4 to 1:1,the density of the samples increased from 0.27g/cm3 to 0.30g/cm3,the porosity decreased from 90.60% to 88.30%,The thermal conductivity is about 0.12W/m·K to 0.13W/m·K,and the compressive strength decreased from 0.49 MPa to 0.20 MPa.When tested the compressive strength of the samples which used silicon sol as high temperature bonding agent,they would fracture obviously,the compressive strength and strain curves of the samples could be divided into four parts: linear stage,fracture stage,stress recovery stage and platform stage.In the compression rebound test,the rebound rate is very high even after the fracture,so they can be considered as rigid samples.When tested the compressive strength of the samples which used silicon fiber as high temperature bonding agent,they would not fracture but would experience an obvious yield stage,the compressive strength and strain curves of the samples could be divided into three parts: linear stage,platform stage and compaction stage.In the compression rebound test,the rebound rate would be very low after yield,so they can be considered as plastic samples.