Preparation And Properties Of Graphene Oxide Grafted Carbon Fibers Reinforced SiBOC Composites

Continuous fiber reinforced ceramic matrix composite（FRCMC） is one of the most future materials that are used in high temperature and structure, which is mainly due to their excellent properties, such as super lightweight, high toughness and high stability. Polymer precursor derived ceramic, which is known as Polymer-Infiltration-Pyrolysis and simple named PIP, is a new method of preparing CFRCMC. However, the untreated carbon fiber has the disadvantages of the poor infiltration, low reactivity and large inertia, which caused the poor interfacial properties between the substrate and carbon fiber. In order to improve the interfacial properties of the composites, we need to modify the surface of carbon fiber firstly.In this research, we firstly studied the synthesis mechanism and characterization of graphene oxide（GO） modified CFs hierachical reinforcement firstly. The hierachical reinforcement was prepared by a chemical method- “Grafting-to” in the aquatic medium with PEI as coupling agent, EDC and NHS as activating agent. However, the GO aqueous solution can be easily affected by the p H values and the electric charges. After the addition of the activator EDC, the water solution of graphene oxide appeared serious aggregation, which mainly because of the changes of zeta potential. In order to solve this problem, a little amount of NH₃?H₂O was added to the solution to promote the dispersion of GO by adjusting the p H and the electric charges. It was the first time that the GO was grafted onto the surface of carbon fiber in the aquatic medium. The interfacial strength of the composites was evaluated through micro-bond tests, and the results showed that the interfacial shear strength increased 86.2% for GO-grafted CF composites than the untreated carbon fiber.Secondly, a new SiBOC ceramic precursor polymer was synthesized by using Tetrahydroxydiboron（B₂（OH）₄） as the B source, and the polymerization mechanism was discussed in detail. Four different SiBOC ceramic precursor dry gel with different B/Si molar ratio were prepared by a sol-gel method, in between which Poly（methylhydrosiloxane）（PMHS） as a raw material and Tetrahydroxydiboron（B₂（OH）₄） provided element boron. The results show that the B element did improve the ceramic yield and thermal stability of the ceramic precursor by thermogravimetric analysis technique. When the B/Si molar ratio is 0.3, the yield of SiBOC ceramic precursor is 80.8%. And with the gradual increase in the pyrolysis temperature, the graphitization degree of free carbon and high temperature stability of SiBOC ceramic increased gradually, respectively.Finally, the graphene oxide grafted carbon fibers reinforced SiBOC ceramic matrix composites with four different density were prepared by different cycle using polymer infiltration and pyrolysis（PIP） process, and the obtained densities of composites are 0.39g/cm³, 0.62g/cm³, 0.84g/cm³ and 1.03g/cm³, respectively. The mechanical properties, thermal physical properties and high temperature stability of the composites were investigated. The results show that with the increase of the number of PIP, the density of composites increases, the porosity of composites decreases, the compressive mechanical properties of composites increases exponentially, the thermal conductivity increases linearly and the composites have good high temperature stability in the oxidation atmosphere. When the density of composites is 1.03g/cm³, the mechanical properties is the highest among these composites. The value of compressive strength is 19.27 and 12.40 MPa, modulus of compression is 836.52 MPa and 533.38 MPa in the z and x/y direction, respectively; the value of bending strength is 12.85 MPa and 7.06 MPa in the z and x/y direction, respectively; and the thermal conductivity at room temperature is 0.671W?m^-1?k^-1 and 0.661W?m^-1?k^-1 in the z and x/y direction, respectively.