Surface Modification Of Carbon Fiber And The Preparation And Performance Of Silica Based Composites

C_f/SiO₂ composite has low thermal conductivity,high temperature resistance,good mechanical properties,high resistance to erosion,as well as desirable mechanical properties,thereby shows great potential for high-temperature applications.It is found that the silica matrix displays a low wettability against the original reinforcing carbon fibers during the sol-gel fabrication of the C_f/SiO₂ composite.This research emplys different ways of surface modification so as to improve the wettability of the carbon fibers,which are then used to prepare a composite of C_f/SiO₂.Firstly,we use air oxidation and liquid oxidation to modify carbon fiber,and analysis the surface structure and properties of both the untreated fiber and oxidized fiber.The results show that oxidation can make carbon fiber infiltrate of water,by means of increasing surface functional group,and completing a good etching on fiber.The fiber subjected to 450? oxidation treatment shows violent oxidation.As a result The reactive surface area increases,the microcrystals turn into fine grains,and the wetting angle dropsSecondly,heat treatment is applied to the above oxidized fiber.Experimental fiber morphology composition,specific surface area,wettability after heat treatment are investigated.Carbon fiber would remove its surface functional groups during heat treatment,Carbon atom would rearrange to an aromatic ring strcuture,all of these result in a non-infiltration problem.Removing functional group also leaves holes at the same time,which cause a decrease on tensile strength.Thirdly,the C_f/SiO₂ composites are prepared through sol-gel method,using both the untreated fiber and oxidized fiber.The phase,structure,mechanical and high temperature reactions are evaluated.Ultimately,the effects of different preparation parameters on the properties of the C_f/SiO₂ composites are studied.High-temperature heat treatment degrades the flexural strength of the composite since it increase the material defect.A high fiber volume fraction can result in an optimized strength.The composite is not resistant to oxidation and needed to be further improved.The oxided fiber plays a reinforcing effect in improving the flexural strength and elastic modulus of the composites..