Occurrence of Bimodal Pore Structure and Leaching Process in the Preparation of Porous Glass from Fluorine Containing Sodium Borosilicate Glass

  • KAWAMURA Hirotoshi
    Department of Chemistry and Material Engineering, Faculty of Engineering, Shinshu University
  • TAKUSAGAWA Nobuo
    Department of Chemistry and Material Engineering, Faculty of Engineering, Shinshu University
  • TARUTA Seiichi
    Department of Chemistry and Material Engineering, Faculty of Engineering, Shinshu University
  • KITAJIMA Kunio
    Department of Chemistry and Material Engineering, Faculty of Engineering, Shinshu University

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  • 含フッ素ソーダホウケイ酸塩ガラスの多孔質化過程と二元型細孔構造の生成
  • Occurrence of Bimodal Pore Structure an

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Abstract

Leaching process in the preparation of porous glass from fluorine containing sodium borosilicate glass was intensively investigated under different conditions of phase-separation temperature, the thickness of specimens and the amount of acid leaching solution. Techniques employed are pore size distribution measurements and SEM observation with focusing on the leaching of SiO2 component from the B2O3-rich phase. The pores formed in the inner part of specimens, after being treated with 0.5mol/l sulfuric acid solution of 200ml/(g-specimen) at 92±1°C for 0.5h, had a smaller size than those formed in the surface layer of specimens. Those smaller pores contained a larger amount of silica-gel which precipitated from the B2O3-rich phase in the leaching process. This is the cause why a bimodal pore structure was inevitably obtained through the course of leaching: the silica-gel was removable by leaching with a larger amount of acid solution for a prolonged time. In the early stage of leaching process, the dissolution of the B2O3-rich phase proceeds, forming smaller pores with residual silica-gel, and the silica-gel is subsequently removed from the smaller pores resulting in enlargement. This diffusion-controlled process proceeds from the surface of the specimen to its inner part, indicating that a thin specimen is effective to accomplish the complete removal of the silica-gel with a minimum amount of the leaching solution.

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