Preparation Of Novel Porous Silica Composites Via Freeze Drying

Freeze-drying, as a method for porous materials, could be used to prepare special morphology of porous materials with high porosity. The sample frozen below the water freezing-point, and sublimating directly ice to gas under high vacuum conditions. During the process, the material microstructure is remained and the technology has a wide usage. The produced porous materials exhibit special characters, such as aligned channels, droplet-shape pores and exhibit corrosion resistance thermal shock resistance and high porosity, and these advantages indicate novel porous materials have a wide applications in heat, electromagnetic and other new type porous composite materials.In this paper, porous silicon oxide ceramic was prepared via freeze drying, and then loaded with rare earth Y2O3: Eu3+particles and Fe(0) particles by impregnation, to produce the new rare earth luminescent materials and porous magnetic materials respectively. The pore structure was determined by adjusting emulsion ratio, the content of dispersion liquid and calcination temperature. And then the content of rare earth Y2O3: Eu3+particles and Fe(0) particles were adjusted by dipping times and dipping solution concentration. And the luminescence properties of porous rare earth luminescence materials and magnetic properties of porous magnetic materials were analyzed carefully.The results show that porous silica were prepared via freeze drying, the size of directional channels is5-20μm, and with increase of oil phase cyclohexane, the droplet shape pores (the size is10-15μm) are produced. The size of pore structure was controlled by the calcination temperature, emulsion ratio and the solution concentration. The nano-particles become tight as the higher calcination temperature.In porous rare earth luminescence materials, Y2O3:Eu3+particles that the size is less1μm loading on the wall of pores, and the content Y2o3:Eu3+particles was increased with the dipping times and the concentration of dipping solution, making the pores smaller. The samples presented red light under ultraviolet light. Finally, luminescence properties of the Y2O3:Eu3+-coated silica were examined and they gave a strong emission peak of612nm attributed to the5Doâ†'7F2transition of Eu3+. And the the fluorescence lifetime of samples is much longer than fluorescent powder(0.664ms), and the longest is1.830ms.In porous magnetic materials, magnetic particles could be reduced in two ways, includes NaBH4solution reduction and H2reduction. The reduction process played an important role on morphologies of the formed iron particles. Iron networks composed of sheet structure with thickness of20nm were obtained from NaBH4, while iron particles from1to3μm were formed in H2atmosphere. The loading amount of iron particles could be controlled by the FeCl3concentration and silica monolith microstructures. Magnetic properties of the porous magnetic materials at room temperature were also investigated. All porous magnetic materials gave s-type hysteresis loops and exhibited soft magnetic properties. Saturated magnetization of the porous magnetic materials was from1.02to116.11emu/g, those in H2reduction was higher than those from NaBH4, and this was attributed to much better crystalline structures.