Hydrothermal growth of millimeter-sized aluminosilicate sodalite single crystals in noble metal capsules
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Hydrothermal growth of millimeter-sized aluminosilicate sodalite single crystals in noble metal capsules Tomohiro Hayashi, Hidemoto Shiga, Masayoshi Sadakata, and Tatsuya Okuboa) Department of Chemical System Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan
Masahiro Yoshimura Materials and Structures Laboratory, Tokyo Institute of Technology, 4259 Nagatsuta, Midori, Yokohama 226-8503, Japan (Received 17 September 1997; accepted 16 December 1997)
Aluminosilicate sodalite Na8 [SiAlO4 ]6 Cl2 single crystals are synthesized by hydrothermal processing at 873–973 K and 100–150 MPa in noble metal capsules to avoid contamination. The starting material is aluminosilicate gel, and spontaneous nucleation followed by its growth takes place. The largest size of the single crystals obtained is 1 mm across. Longer aging and heating result in larger single crystals. It is also found that the aluminum source in the synthesis gel and the element used in the noble metal capsules influence the single crystal growth. Judging from x-ray diffraction (XRD) (powder and single-crystal), optical microscopy, and thermogravimetry and differential thermal analysis (TG-DTA), the sodalite single crystals grown have good quality compared with the conventional powder.
I. INTRODUCTION
Sodalite is one of the zeolites that comprise sodalite cages. Its entrance windows are too small for most molecules to enter. Accordingly, sodalite has not been used for catalysis or gas separation, while much attention has been paid to its use as container (host) for encapsulation of a variety of guests. By encapsulating silver halides within sodalite cages in the course of the sodalite synthesis, a new concept of optical memory devices is proposed.1,2 Cadmium sulfide within zeolite A, X, or Y with larger windows might be useful as an optical transistor,2,3 which would work as a switch for lasers. In order to materialize these devices, it is indispensable to synthesize zeolite single crystals and thin film with controlled structure as the container. So far zeolites had been used as catalysts, adsorbents, and ion exchangers, however, which promoted no motivation to grow giant single crystals. The single crystals were grown for singlecrystal x-ray diffraction. Thus, limited works have been carried out. Bye and White4 hydrothermally synthesized and grew aluminosilicate sodalite single crystals by seeded growth. The crystal products (up to 1.2 cm across) comprised only the (100) dodecahedral faces, and were perfectly transparent in the smaller specimens, although some of the larger specimens contained veils. The synthesis condition by spontaneous nucleation to supply the a)
Author to whom all correspondence should be addressed. e-mail: [email protected] J. Mater. Res., Vol. 13, No. 4, Apr 1998
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seeds was not described. Mel’nikov and Litvin5,6 also hydrothermally synthesized and grew the single crystals by seeded growth. D
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