Fabrication And Properties Of High Temperature Resistant Composites Based On Ceramic Precursors

Ceramic matrix composite is a new multifunctional material,which has the advantages of high temperature resistance,corrosion resistance,high strength and low density.It can be used in high temperature resistant parts such as antenna hood and engine of spacecraft.In order to improve the high temperature mechanical properties of ceramic matrix composites,ceramic matrix was modified and toughened by continuous fibers in this paper.High temperature resistant composites based on ceramic precursors were prepared,and the effects of hot pressing strength,slurry-to-fiber ratio and powder content on their mechanical properties were investigated.Firstly,Benzoxazine Resin was hybridized by siloxane,and high temperature resistant composites of quartz fiber reinforced benzoxazine were prepared by hot pressing with slurry impregnation.Their molecular structure,curing behavior,heat resistance and mechanical properties were characterized.The results show that the siloxane hybrid benzoxazine has a similar gel temperature and gel time with bisphenol A benzoxazine,but its viscosity is lower,which is conducive to the processing of composite materials.Compared with quartz fiber reinforced bisphenol A benzoxazine composites(5.7%),the flexural strength retention of quartz fiber reinforced siloxane hybrid benzoxazine composites is 37.2%at 300?,exhibited good high temperature resistance.Secondly,aluminium dihydrogen phosphate was introduced into Si3N4 matrix as adhesive,and quartz fiber reinforced Si3N4 ceramic matrix composites were prepared by hot pressing with slurry impregnation.The effects of drying time,powder content and slurry-to-fiber ratio on the properties of the composites were investigated.The results show that the mechanical properties of ceramic matrix composites are the best when dried at room temperature(16?)for 4 hours,the size of Si3N4 powder is 1-3?m,Al(H2PO4)3:Si3N4=1:1,slurry/fiber=2:1 and hot pressing pressure is 2MPa(The bending strength of ceramic matrix composites is 75.64MPa at 300?and 67.91MPa at 500?).And the experimental results show that Aluminum hydroxide can promote low temperature curing of aluminium dihydrogen phosphate;the pretreatment of quartz fiber with tetrabutyl titanate-ethanol solution can reduce the damage of acidic slurry to the fiber.Finally,aluminium dihydrogen phosphate,resorcinol and hexamethylenetetramine were added to SiC matrix as adhesives.Carbon fiber reinforced SiC ceramic matrix composites were prepared by hot pressing with slurry impregnation.The effects of powder content,slurry-to-fiber ratio,hot pressing strength and powder size on the mechanical properties of the composites were investigated.DSC,TGA of the slurry and the flexural strength of the composites were tested.the experimental results show that the dehydration and curing of aluminium dihydrogen phosphate can be effectively promoted by adding resorcinol and hexamethylenetetramine to the slurry,which is conducive to the formation of network structure.And the results show that when the powder content is Al(H2P04)3:SiC=1:1,slurry/fibe=1.5/1,hot pressing pressure is 2MPa and powder size is 5?m,the mechanical properties of the composites are relatively best(bending strength is 222.14MPa at 300? and 165.59MPa at 500?).In this paper,three kinds of ceramic matrix composites were prepared by matrix modification.The flexural strength of quartz fiber reinforced siloxane hybrid benzoxazine composites is 191 MPa at 300? and the bending retention rate is 37.2%.It can be used in the temperature range of 300?.The strength of quartz fiber reinforced Si3N4 ceramic matrix composites at 500? is 67.91MPa,which is not as good as that of the former,but its bending retention at 500? is 89.78%,and its mechanical properties decay slowly,which can meet the requirements of low strength and high temperature resistant composites,and can be applied in the temperature range of 500?.The strength of carbon fiber reinforced SiC ceramic matrix composites at 500? is 165.59MPa,which can meet the requirements of high strength and high temperature resistant composites.This study provides a reference for improving the heat resistance and strength of ceramic matrix composites.