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Unformatted text preview: ORIGINAL PAPER S. Heinemann á R. Wirth á G. Dresen Synthesis of feldspar bicrystals by direct bonding Received: 19 February 2001 /Accepted: 16 May 2001 Abstract We have produced synthetic feldspar bicrystals using a direct bonding technique. A gem-quality ortho- clase crystal from Itrongay, Madagascar, was used for the bonding experiments. Microprobe analysis shows only minor concentrations of iron and sodium. Ortho- clase single crystal plates oriented parallel 0 0 1) were cut and chemomechanically polished with silica slurry. From interferometry, ®nal roughness of the square crystal plates was about 0.34 nm. Specimens were wet- chemically cleaned using deionised water. The bonding procedure produced an orthoclase bicrystal with an optically straight grain boundary-oriented parallel 0 0 1), which was investigated by HREM. Along the interface no amorphous layer was observed between lattice fringes of both crystals. We suggest that the bicrystals formed by initial hydrogen bonding and sub- sequent water loss and polymerisation of silanol and aluminol groups at elevated temperatures. Key words Bicrystal synthesis á Feldspar á Direct bonding á Grain boundary Introduction A grain boundary may be de®ned as the zone separating two crystals diering in crystallographic orientation, composition or dimension of the crystal lattice McLean 1957). In polycrystalline, multiphase materials grain boundaries or phase boundaries are present in a large number of con®gurations. The interfaces form three- dimensional networks very much like the networks of liquid ®lms that constitute foams. The physical proper- ties of grain boundaries, like their energy, resistivity and diusivity, control the bulk physical properties of rocks. Most of our present knowledge on grain boundaries comes from studies of metals and alloys e.g. Gleiter and Chalmers 1972; Sutton and Ballu 1995). Likewise, the structure and properties of grain or phase boundaries in ceramics consisting of complex ionic and covalent com- pounds are also well investigated e.g. Yan and Heuer 1983; Pask and Evans 1987; Wolf and Yip 1992; Tomsia and Glaeser 1998). Compared to metals and ceramics, however, the chemical and mineralogical composition of silicate rocks is much more complex. Still relatively few studies exist that investigate the structure of grain boundaries in natural or synthetic rocks. The importance of grain or phase boundaries for rocks has been pointed out in several papers covering topics like the structure of grain boundaries White and White 1981; Lee et al. 1984; Wirth 1986; Hay and Evans 1988; Bons et al. 1990; Renard and Ortoleva 1997; Hiraga et al. 1999), diusion in grain boundaries Nagy and Giletti 1986; Joesten 1991; Eiler et al. 1992; Fisler et al. 1997), impurity seg- regation Byerly and Vogel 1973), chemically induced grain boundary migration Evans et al. 1986) and meta- morphism Wada et al. 1998). Melt ®lms along grain or phase boundaries indicating a possible amorphous structure of the grain or phase boundaries have been...
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This note was uploaded on 04/23/2010 for the course ME 524 taught by Professor Hsia during the Spring '10 term at University of Illinois at Urbana–Champaign.
- Spring '10