Preparation And Properties Of Porous Y₂SiO₅Ceramics By Gel-casting

In this paper, porous Y2SiO5ceramics have been prepared by gel-casting andreaction sintering from yttrium and silica particles. The preparation process andproperties are the main points of this paper. To be specific, the research includes thefactors which influence the rheological properties of Y2O3/SiO2slurry, gelation behaviorand its influencing factors, drying parameters and binder burnout process of the greenbodies and the temperature of reaction sintering. Finally, the microstructure, machanicalproperties, themal properties and dielectric properties of porous Y2SiO5ceramics whickwere preparationed by gel-casting and foaming-gel methods were investigated.In the process of preparation of Y2O3/SiO2slurry, the influence of dispersantdosage and pH on slurry viscosity were studied by using LVDV-II+PRO rotationalviscometer. The influence of monomer, initiator and catalyst on gelation behavior werealso studied by controlling variables method. The results prove that while adding1wt.%dispersants and pH is2, the Y2O3/SiO2slurry reach a minimum viscosity. While adding1wt.%initiator and3mL/L catalyst, the gelation rate and the effect is the most suitablefor gel-casting. Through contrast test, the drying process of wet billet is optimized.Through the TG/DSC analysis of green, optimization and obtained good degreasingprocess. Through the study the temperature of Y2O3and SiO2synthesized and gain pureY2SiO5to determine the reaction sintering temperature.Porous Y2SiO5ceramics prepared by gel-casting and foaming-gel preparationprocess were researched. By XRD analysis, the results show that two processes bothgenerated porous Y2SiO5ceramic, but there was Y2O3residue in which were preparedby gel-casting. In the aspect of microstructure, porous ceramics prepared by twoprocesses had a uniform three-dimensional innerconnectivity fine pore structure. Thepore size was between2.1-3.2?m. The pore size of which were prepared by gel-castingis smaller, and the porosity of foaming-gel with a small amount of large pores werehigher. The highest porosity measure by drainage reached68.9%, while the impact onthe porosity in the process of preparing a low solid content of porous ceramics was verysmall. In the mechanical properties, porous Y2SiO5ceramics prepared by two processeswere similarity. The highest flexural strength in room temperature was8.7MPa, and theelastic moduli were between0.4-0.7GPa. The compressive strength at room temperaturewas up to13.6MPa, and the highest compressive strength in1000oC was12.3MPa. Theporous ceramic prepared by gel-casting presented better in mechanical properties. In thethermal performance, the thermal expansion coefficients of the porous ceramic Y2SiO5were low, about6.0×10-6K-1. The porous Y2SiO5ceramics prepared in this study exhibited good high temperature stability. The sample size, material quality, and phasecomposition were not changed after heat treatment. The thermal conductivity of porousY2SiO5ceramics which were prepared by foaming-gel were low in1200oC, the lowestthermal conductivity reached0.23W/(m·K). In the dielectric properties, the dielectricconstants of porous Y2SiO5ceramic with different solid content were relatively small,and the porous ceramic prepared by foaming gel was better in the dielectric properties.