Chemical processing and densification characteristics of lithium aluminosilicate (LAS) gels
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Kwang S. Kim and Chang J. Jung Department of Inorganic Materials Engineering, College of Engineering, Chonnam National University, Kwang-Joo, Korea (Received 29 December 1991; accepted 18 March 1992)
Two different chemical processing routes were successfully used for the fabrication of lithium aluminosilicate (LAS) specimens having dense and homogeneous microstructure with an essentially pore-free state. These are (i) sol-gel route using the hydrolysis-condensation reaction of metal alkoxides and (ii) mixed colloidal processing route. Lowering Li content in the sol-gel-derived LAS significantly enhanced densification and retarded the crystallization. The /3-spodumene (—0.8 /xm) seeding in the sol-gel-derived LAS modified the sequence of phase transformations and lowered the crystallization temperature by 120 "C. Therefore, combining the epitaxial seeding with the sol-gel process, one can bring down the crystallization temperature to the sintering temperature range (~800 °C). Similarly, the LAS gel prepared by the mixed colloidal processing route exhibited a noticeable shrinkage over a broad temperature range (600-950 °C) and produced a dense sintered body with an essentially pore-free microstructure. I. INTRODUCTION Since the introduction of the glass-ceramic materials by Stookey in the early 1960s,1 extensive research efforts have been made for the development of glassceramic materials capable of meeting various industrial requirements. The greatest economic importance has been achieved, so far, by transparent and opaque glassceramics based on the Li 2 O-Al 2 O 3 -SiO2 (abbreviated as LAS hereafter) formulation,2 which has an extremely low thermal expansion coefficient. Since the sol-gel route can produce powder or monolithic gel with high chemical purity and homogeneity on a molecular scale, there has naturally been an increasing interest in the sol-gel route for the preparation of LAS glass-ceramics over the past decade. Until now, most of these studies focused on the crystallization and phase transformation characteristics3"6 and on the preparations and characterizations of LAS sols and gel-derived-powders4'7"9 and porous glass-ceramic monoliths.10 However, little study has so far been made on the dense sintering of the sol-gel-derived LAS specimen. In view of this, the main purpose of the present study was to develop sol-gel-based routes for the fabrication of LAS specimens having dense and homogeneous microstructure with an essentially pore-free state. Two different processing routes were attempted for a
'Address correspondence to this author. J. Mater. Res., Vol. 7, No. 8, Aug 1992 http://journals.cambridge.org
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this purpose: (i) conventional sol-gel processing route using the hydrolysis-condensation reaction of relevant metal alkoxides; (ii) mixed colloidal processing route (or multiphasic sol-gel route) using ultrafine silica and boehmite particles. In addition to the fabrication of sintered LAS specimens, we have systematically examined phase formation characteristics of the LAS
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