Preparation And Properties Characterization Of Silicon-containing Oxide Continuous Fibers

With the rapid development of materials science and technology,the sol-gel method for fabricating oxide continuous fibers has been widely employed.The sol-gel method is a wet chemical method with the advantages of the low temperature of fabrication process,high chemical composition uniformity,high product purity,and so on.Al2O3-SiO2 composite continuous ceramic fibers and SiO2 continuous fibers were performed by sol-gel method,and the preparation of spinnable precursor sol,the spinning process,gel fiber ceramization,ceramic fiber microstructure and the mechanical properties of the fiber were studied in detail.Oxide continuous fibers have been widely applied in various fields like aerospace,due to its unique properties.However,domestic research on oxide fibers is still in very initial stage,and there is still a large gap in product performance compared with other countries.Therefore,the research and preparation of oxide continuous fibers is urgent and of great importance.1.Preparation and characterization of Al2O3-SiO2 ceramic continuous fibersIn this experiment,the aluminium-containing sol was prepared through two different methods.One is prepared using the aluminum hydroxide suspension arising from the reaction of inorganic aluminium salt solution and alkali solution as an aluminium source,followed by addition of a certain proportion of acetic acid to prepare the spinnable aluminium carboxylate sol.The other is the Al13 sol prepared by adding aluminium chloride hexahydrate solution.After mixing with silica sol or spinning auxiliaries,the spinnable sol possessing suitable viscosity was obtained when the solution was evaporated,then,the gel fibers were obtained by dry spinning technology.After pyrolysis in air,two kinds of alumina-silica composite continuous ceramic fibers were obtained.They were characterized by TG-DSC-MS,XRD,FT-IR,TEM and SEM,and so on.The effects of properties of fabricated ceramic fibers resulted from the precursor sol were systematically researched.The results show that the spinnability of aluminium carboxylate sol comes from the formation of aluminium dimer or trimer and aluminium polymer.The spinnability of Al13 sol comes from the condensation of Al13 particles.During the ceramization process,the compact ceramic continuous fibers can be obtained by using slow heating rate and long holding time at the low temperature,and by performing fastly heating rate and short holding time at high sintering temperature.2.Preparation and characterization of SiO2 continuous fibersIn the present work,the precursor sol was firstly prepared using tetraethyl orthosilicate as the silicon source,ethanol as the solvent,nitric acid as the catalyst,and ethyl cellulose as the spinning auxiliaries.The combined mixture was stirred and concentrated,the spinnable sol possessing the proper viscosity was obtained,followed by dry spinning and pyrolysis technology at high temperature to form continuous silica fibers,successively.The precursor sol and ceramization process how to affect the fiber properties were respectively studied by TG-DSC,XRD.FT-IR,SEM,and so on.The results indicate that the hydrolysis process can be dominated by alcohol polymerization by controlling the ratios of water combined with silicon and the ratios of acid combined with silicon.Both the gelation time of the sol can be prolonged and the stability of the sol can be obviously improved by addition of ethyl cellulose.It provides a new thought about fabricating silica fibers at low temperature.When the water/silicon ratio is about 2.0 and the ratio of acid/silicon is about 0.03,the sol shows long-term stability along with with good spinnability to form fine gel fibers.The SiO2 fiber prepared by the sol-gel method has a diameter of about 8.6 μm and a maximum tensile strength of 0.88 GPa.