Preparation And Properties Of Silicon Carbide Fiber Containing Aluminum

Due to its high tensile strength,high elastic modulus,high temperature resistance,and remarkable oxidation and corrosion resistance,the continue SiC fiber is one of the most promising reinforcement for ceramic matrix composites?CMCs?,which have been widely applied for aerospace,nuclear energy engineering and high-temperature insulation.Aluminum-containing SiC fiber prepared by Polymer-Derived method has attracted more attention owing to its excellent thermal stability.However,the process of polymer-derived aluminum-containing SiC fibers is complicated and influenced by many factors.So far,performance of aluminum-containing SiC fibers prepared by domestic researchers has been inferior than that by foreign.Therefore,it is of great significance to further research high performance aluminum-containing SiC fibers.In this work,polyaluminocarbosilane?PACS?precursor with a theoretical aluminum content of 0.37 wt%was synthesized by the reaction of low softening point polycarbosilane?PCS?and 8-hydroxyquinoline aluminum?Alq₃?.Fourier transformed infrared spectroscopy analysis?FT-IR?,X-ray photoelectron spectroscopy analysis?XPS?and energy spectrum analysis?EDS?were used to analyze the composition and structure of the PACS precursors.SiC?OAl?fibers was prepared by melt spinning,air curing and pyrolysis.Scanning electron microscope?SEM?and transmission electron microscope?TEM?with attached energy spectrum analysis?EDS?and X-ray diffraction?XRD?were used to analyze the fiber morphology,composition and microstructure.Tensile strength and high temperature oxidation resistance were also investigated.The main conclusions are as follows:?1?The as-prepared precursor was just like a light yellow transparent resin with the synthesis temperatures of about 250? and a holding period of 1h.An effective chemical combination between Alq₃ and PCS was formed and the Al atom was mainly existed in the Si-O-Al band.The continuous fiber length reached up to 4335m after the spinning time lasted for15min when the spinning process contains a spinning temperature of about 335?,spinning pressure of 0.5MPa and spinning speed of 1000r/min.?2?The green fibers were treated at the temperature of about 200? with a hold period of8h.The oxygen introduced during air curing was about 4.8 wt%.The pyrolysis temperature was1000?,and heating rate was lower than 3?/min.The diameter of as-prepared SiC?OAl?fibers was about 9¹1?m,and the average tensile strength was 1.9².2GPa.The fibers had a very smooth and dense surface without obvious surface defects such as micropores and microcracks.The fibers which contained 0.46 wt%aluminum and 9¹2 wt%oxygen were mainly composed of SiC_xO_y amorphous phase,a small amount of?-SiC crystallite and amorphous carbon.?3?After treated at 1000? in air for 30h,SiC?OAl?fibers maintained 89%of the initial strength about 1.90GPa.the tensile strength of SiC?OAl?fibers oxidized at 1100? and 1200? in air for 0.5h were no less than 1.85GPa.The surface morphology of fibers oxidized at high temperature was smooth and dense.The oxidized fibers have a skin-core structure,and oxide layer is composed of amorphous SiO₂.