Preparation And Properties Of Silicon Carbide Fiber Containing Aluminum

As a high strength material with low density and superior chemical stability,SiC fibers,particularly aluminum-containing ones,have excellent high temperature resistance and are promising for wide applications in many industries such as aerospace,nuclear and chemical engineering.However,domestic and foreign researches on aluminum sources are mainly limited to aluminum acetylacetonate,aluminum tri-sec-butoxide and so on,volatilizing easily when heated,so it is difficult to control the aluminum content.It is,therefore,necessary to study the two news aluminum sources-aluminum tristearate and 8-Hydroxyquinoline aluminum salt(Alq3).In this thesis,synthesis of polyaluminocarbosilane(PACS)was carried out by using polycarbosilane and aluminum tristearate or 8-Hydroxyquinoline aluminum salt as start materials at high temperature under argon atmosphere.The solvents for Alq3 are xylene,benzyl alcohol or N,N-Dimethylformamide(DMF);The two types of PACS were melt-spun into green fibers,then cured in ambient air and pyrolysed to ceramic fibers,respectively.For aluminum tristearate,corresponding fibers,1-SiC(Al)-1 and 1-SiC(Al)-2,containing theoretically 0.1 Owt%and 0.28wt%aluminum respectively,were fabricated.And also,for Alq3,ceramic fibers,2-SiC(Al)-1,2-SiC(Al)-2 and 2-SiC(Al)-3,containing theoretically 0.06wt%,0.37%wt%and 0.84wt%aluminum respectively,were fabricated;This two PACS were analysied by Fourier Transform Infrared Spectroscopy analysis(FT-IR)and X-ray Photoelectron Spectroscopy analysis(XPS);Also investigations including the effects of contents of aluminum and the type of aluminum source on fiber tensile strength were carried out;Fiber morphology,microstructure and chemical composition were characterized by Scanning Electron Microscope(SEM)and Tunnelling Electron Microscope(TEM)with attached Energy Spectrum Analysis(EDX);X-ray Diffraction(XRD)was used for identifying phase compositions;In order to analysis the effect of aluminum,SiC(0)fiber,without aluminum,and 2-SiC(Al)-2 were exposed to high-temperature oxidation conditions,the changes of the fibers were identified by the surface structure and phase compositons.The main results are summarized as follows.(1)FT-IR test results show that the chemical reaction takes place between PCS and aluminum tristearate or Alq3.XPS tests show that aluminum element exists in the form of Al-O bond in the precursor of 2-SiC(AI)-3.(2)When xylene is chosen as the solvent for Alq3,the diameter of 2-SiC(AI)-I is 12?m,average strength is 1.6GPa.When benzyl alcohol is chosen as the solvent for Alq3.:the diameters of 2-SiC(Al)-2 and 2-SiC(Al)-3 are 25?m,average strength are less than 1.0GPa.When DMF is chosen as the solvent for AIq3,the precursor of 2-SiC(Al)-2 can spinning 2 minute every time,about 440m.The diameter of 2-SiC(Al)-2 is 13?m,average strength is 1.2GPa.(3)The diameter of 1-SiC(Al)-1 is 12?m,average strength is 1.2GPa.The diameter of 1-SiC(AI)-2 is 25?m,average strength is less than 1.0GPa.(4)After the high-temperature oxidation conditions,the surface of 2-SiC(Al)-2 is smoother than SiC(0),After the heat treatment:1000?,50h,in the XRD pattern,SiC(0)has a weak SiO2 peak,while there is almost no SiO2 peak for 2-SiC(Al)-2,demonstrating the oxidation resistance of aluminum element.