Study On Dry-Spinning, Gel-Drying And Sintering Of Precursor For Al₂O₃/SiO₂ Filaments

Al₂O₃/SiO₂ filaments,one kind of aluminum based monocrystal or multicrystal fibers of which major content is Al₂O₃（small amount of ZrO₂, SiO₂ and B₂O₃）,attracting much attention in these years.Aluminum based fiber has many outstanding advantages such as good thermomechanical properties,good chemical and oxidation resistance,excellent creep resistance and high used temperature.It has better oxidation resistance and high strength at higher temperature compared with carbon fiber and SiC fiber which belong to non-oxidation fiber;it can be used in aerospace, military,civilian fields.So,many researchers are interested in the field of preparing Al₂O₃/SiO₂ filaments with good performance.In this paper,Al/Si precursor was prepared by sol-gel method, conscious gel fiber was attained by dry-spinning which was dried and sintered under certain conditions to become Al₂O₃/SiO₂ filaments. The properties of Al/Si spinning sol affect process of dry-spinning. Transparent sol was prepared by adding aluminium nitrate（AN）, aluminium-tri-isopropoxide（AIP）and tetraethylorthosilicate（TEOS）into pure water one by one.There exited two steps:hydrolysis and polymerization.In the first step,the PH was different after adding AIP or TEOS,AIP particles turned smaller with hydrolysis time and couldn’t be seen after 24 hours;in the second step,colloid particles became larger after adding spinning assist,viscosity of sol raised with environmental temperature,the FTIR spectrum of dried gel showed that there exited Al-O tetrahedral.Al-O octahedral and Si-O tetrahedral.The spinnability of Al/Si sol was best between 50℃-60℃.the temperature of spinning chimney should be relative lower,especially the last section.The surface of gel fiber appeared crack at high temperature, and property of gel fiber could be improved at low temperature.Gels with different drying control chemical additives（DCCAs）and polyvinylpyrrolidone（PVP）as spinning assistant were dried at several temperatures.The influences of temperatures,DCCAs and PVP in the drying process were investigated by drying kinetics.On the one hand DCCA reduce solvent volatilization speed largely,on the other hand it displaced the water from the surface of the gel to form new hydrogen bonds and decreased the surface tension largely.The gel with DMF showed crack-free at temperature 70℃. Mullite crystallization phase presented in the Al₂O₃/SiO₂ fiber sintered at 985℃and the key sintered temperature scale was from 985℃to 1002℃.The FTIR spectrum of gel fiber sintered at different temperatures showed that characteristic peaks of organic disappeared above 600℃.The XRD spectrum of gel fiber sintered at different temperatures indicated that there exited crystallization phase at 900℃and crystallized completely at 1100℃.The crystallization kinetic parameters were determined by a non-isothermal method by which the apparent activation energy(E_c=797.79kJ·mol^-1),the Avrami exponent（n=2.04）and the rate constant(k₀=8.447×10³³s^-1)were calculated.Sintering assistant decreased crystallization temperature obviously.Fiber doped with sintering assistant had no crack or micropore and compacted at 1000℃...