Porous glass-ceramics cation exchangers: Cation exchange properties of porous glass-ceramics with skeleton of fast Li io
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Masunobu Maeda Department of Applied Chemistry, Nagoya Institute of Technology, Gokiso-cho, Showa-ku, Nagoya 466, Japan (Received 26 May 1993; accepted 5 October 1993)
Lithium titanium orthophosphate LiTi 2 (PO 4 ) 3 (LTP) has attracted attention as a chemically stable fast Li+-conductor in ambient atmosphere. It was reported in our previous paper7 that monolithic microporous glass-ceramics with a skeleton of this crystal were successfully prepared from glasses in the pseudobinary system of LTP and Ca 3 (PO 4 ) 2 . Here we report that these porous glass-ceramics (mean pore diameter: —40 nm; total specific surface area: ~ 3 0 m 2 ; porosity: —45 vol. %) show excellent cation exchange properties. Approximately 50% of Li+ ions in the materials are exchanged with monovalent ions with ionic radii smaller than 130 ppm in 1 h at room temperature. In particular, Li+ ions are selectively exchanged with Ag+ ions even in the presence of Na+ ions. The exchange rate in the porous glass-ceramics is larger by two orders of magnitude than that of sintered LTP. The ratio of these exchange rates is close to that of the total surface areas, indicating that most of the pores in porous LTP glass-ceramics are available for ion exchange reactions. These are the first porous glass-ceramics having excellent cation exchange properties.
I. INTRODUCTION Microporous glass-ceramics utilizing spinodal-type phase separation in glass have some outstanding advantages over porous ceramics prepared by conventional sintering processes of powdery materials.1 They have well-controlled continuous pores and may be obtained in a desired shape and dimension. However, research and development have been mainly focused on silica-based systems following the invention of porous SiO2 glass,2 which is obtained from Na 2 O-B 2 O3-SiO 2 glasses. If porous glass-ceramics with a skeleton of crystals having a special function can be realized, they should have combined advantages of porous bodies (pores and large surface area), glass-ceramics (ease of shaping and better fabrication process), and crystal skeletons (functionality). In 1989, we reported3 that porous glassceramics with a skeleton of CaTi 4 (PO 4 ) 6 were fabricated from glasses in the pseudobinary system of CaTi4(PO4)6 and Ca 3 (PO 4 ) 2 by controlled crystallization and subsequent leaching of Ca 3 (PO 4 ) 2 with acids. This was the first porous glass-ceramics based on phosphates4 to our knowledge. Since then, we have fabricated porous glassa
)Present address: Research Laboratory of Engineering Materials, Tokyo Institute of Technology, Nagatsuda, Midori-ku, Yokohama 227, Japan. J. Mater. Res., Vol. 9, No. 3, Mar 1994
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ceramics with a skeleton of various functional crystals, TiO 2 , 5 NASICON-type crystals with a 3-dimensional (3D) network structure,6"8 and zirconium phosphate-type structure with a 2D-layered structure,9 and integrated these two types of crystals10 along with their applications to supporting materials11 for enzymes and humidity senso
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