Study On The Prepartion And Properties Of Silicone Modified ZrB₂ Based Porous Ceramics

In recent years,new aircrafts with various types represented by hypersonic vehicles have been rapidly developed.ZrB₂-based ultra-high temperature ceramics are often used as thermal protection materials for aircraft due to their excellent temperature resistance and high strength.However,its high density and thermal conductivity limit its large-scale application.In the non-structural part of the aircraft,more attention has been paid to the processing,density,heat insulation and other properties of the thermal protection material,of which the requirement of thermal protection strength is used to be low.The combination of organic silicone resin and ZrB₂-based ceramics,which has good processability,temperature resistance,low thermal conductivity and low density,is of great significance for the wide application of ZrB₂-based ultra-high temperature ceramics.In this paper,ZrB₂ with high temperature stability was slected as matrix,togrther with Si,SiO₂,B₄C and chopped carbon fiber were used.ZrB₂-based porous ceramic material was prepared by heating treatment at temperature of 1500?for 1 h.The prepared porous ceramic sample had good dimensional capability,the density was1.926 g/cm³.The components react synergistically at the high temperature to form a dense oxide outer layer and a porous inner structure.The thermal conductivity of the sample is 1.670 W·m^-1·K^-1 at 25?,and it is 2.572 W·m^-1·K^-1 at 1000?.After the static heat test at 1500?,the compressive strength enhanced up to 13.23%compared with that before oxidation.Three kinds of loading methods were designed to load the ferrocene catalyst on the surface of carbon fiber,and CNTs were grown in situ to construct the binary phase structure of chopped carbon fiber-CNTs to improve the mechanical properties of the material.The solid silicone resin with good processability and high ceramization yield was selected as the modifier,and the resin can be transformed to SiO₂ and SiC under the high temperature.This silicon resin can be modified as ZrB₂-based porous ceramics.The results of scanning electron microscopy?SEM?and compressive strength test showed that the suitable content of silicone resin was 10%,the short carbon fiber content was 12.5% and the hollow microsphere content was 10%,which can reduce the density and reduce the volume shrinkage.The density,thermal conductivity,room temperature compressive strength and compressive strength after the static heat test at 1500?of silicone modified porous ZrB₂ ceramics were 1.763g/cm³,1.046 W.m^-1.K^-1,18.181 MPa and 22.397 MPa respectively.Silicone resin was converted to a less crystallized Si-O-C ceramic at high temperatures,the free residual carbon reduces the mechanical properties of the material.The ferrocene catalyst and the FeCl₃ used as structure conversion promoter of silicone resin at high temperature were introduced to strengthen and toughen the silicone modified ZrB₂ based porous ceramic.The ferrocene catalyzed the construction of the binary phase structure of CF-CNTs effectively.At the same time,the carbon-thermal reduction reaction of Fe³⁺consumed the free residual carbon under the high temperature conditions,as a result,the material was strengthened and toughened.The room temperature compressive strength of the toughened sample reached up to 23.296 MPa,and the density was 1.591 g/cm³,the thermal conductivity of the sample was 1.086 W·m^-1·K^-1 at 25°C,and 1.571 W·m^-1·K^-1 at 1000°C;and the compressive strength after the static heat test at 1500°C is 27.187 MPa.The results showed that the samples prepared in this paper have better thermal-insulation properties.