The Study On The Preparation Of Large Size Porous Glass Plate With Controlled Pore Size And No Cracks

This paper reported on a detailed study on the preparation of large size porous glass (CPG) with controlled pore size and no cracks. The fabrication of CPG is based on the phase separation phenomenon in sodium borosilicate glass after controlled heat treatment. Sodium-boron-rich phase and silica-rich phase will be formed after the heat treatment, and the first one shows a characteristic of selective dissolution in hot mineral acids, water or alcohols. The dissolution of the sodium-boron-rich phase results in the formation of CPG with a three-dimensional interconnected porous SiO2skeleton structure from the initial two-phase glass. The pore size and pore volume of CPG depend substantially on the structure of the initial two-phase glass, which cloud be controlled by the processes and parameters of the preparation. Because of its unique characteristics such as good biological compatibility, high chemical stability, and surface modifiability, CPG shows potential application in bio-medicine, catalyst chemistry, and medical diagnosis.In this study,7.5Na2O-26.5B2O3-66.0SiO2(in mol%) was chosen as the chemical composition of the initial glass. The effects of glass composition, the temperature and holding time of the heat treatment, the concentration and leaching time of the acid solution and alkali leaching, respectively, on the structure and property of CPG were investigated by using scanning electron microscopy and mercury intrusion porosimetry. The effect of buffer solution for acid leaching on the mechanical strength of CPG plate was also investigated. The processes and parameters of the preparation of CPG plate with controlled pore size were optimized.The results of this study showed that additional1mol%of TiO2could accelerate the phase separation process and increase the pore size and volume in the final products. The acid leaching could be baffled by unconnected network of the separated phases in the initial glass. In order to avoid that, the temperature of heat treatment should not be too high or too low, and the holding time should not be too long or too short. The optimized condition of the heat treatment is620°C,24h. The concentration of acid solution and leaching time played as key roles in the complete dissolution of sodium-boron-rich phase. After leaching in0.5mol/L HCl at95°C for24h, CPG plate with pore diameter between80and100nm was obtained. Saturated Na2B4O7solution was found to be an efficient buffer solution for acid leaching, which was helpful for reduce the heterogeneity of the residual stress between leached and unleached region. Based on that, CPG plates without cracks could be prepared without varying the leaching rate and changing pore structure and property. Alkali leaching(0.5mol/L NaOH,2h,25°C) was found to be efficient for removing the silica colloids remained inside porous networks of silica, but do not etch the interconnected pore channels. The CPG plate consisted with SiO2of more than96wt%. It showed a clean and interconnected porous network with homogeneous distribution. The CPG plate should be a promising material as bio-carrier.