Hydrolysis of aluminium metal, synthesis of nano alumina and sol-gel processing of monoliths
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Hydrolysis of aluminium metal, synthesis of nano alumina and sol-gel processing of monoliths M. Thiruchitrambalam # Indian Institute of Technology, Mumbai - 400 076 , India. V.R.Palkar * * Dept. of Condensed Matter Physics and Materials Science Group, Tata Institute of Fundamental Research , Mumbai - 400 005, India . Abstract High purity alumina is usually prepared using various intermediate aluminium compounds such as aluminium nitrate, aluminium alkoxides etc., as precursors. In fact the above mentioned intermediate aluminium compounds themselves are produced from aluminium metal. The present investigation is concerned with examining the feasibility of using aluminium hydroxides prepared by hydrolyzing aluminium metal, for sol gel processing. The study assumes added significance in view of the claims of Alcoa that it is possible to produce high purity aluminium metal in large quantities economically. During the present investigation sols were prepared by using various hydroxides, ie., bayerite, gibbsite and boehmite. Sol gel transition was observed only in the case of boehmite sol and this was gelated by either forced gelation method to prepare powder or controlled gelation method to prepare monoliths. Transparent Xerogels (boehmite) could be prepared by controlled gelation method but the presence of a thin layer of bayerite often resulted in translucency. Crack free monoliths could be prepared by heating the xerogels at a low heating rate(< 1 0C/min). It was found that sol gel processed boehmite transformed to alpha alumina at a relatively lower temperature (~ 1080 0C ) than the as prepared boehmite which transformed at about 1200 0C . Key words : alumina, boehmite, ceramics, nano materials, sol-gel preparation, monoliths # Author to whom all the correspondence should be addressed, [email protected] ( M. Thiruchitrambalam ) at present he works with the Department of Mechanical Engineering, Mahalingam College of Engineering, Pollachi, Tamil Nadu ,India Introduction Boehmite or pseudo boehmite [AlO(OH)]is usually prepared by using various intermediate aluminium compounds such as, aluminium alkoxides [1] or inorganic aluminium salts [ 2,3,4 ] etc., and the boehmite thus prepared can be used for sol-gel processing. However there are some disadvantages in using aluminium salts or alkoxides for the preparation of alumina [5]. It is interesting to note that syntheses of aluminium alkoxides require aluminium metal as starting material [7] . It is also known that hydrolysis of aluminium metal in water at room temperature leads to the formation of bayerite[Al(OH)3] and at ~ 100 oC leads to the formation of boehmite [8, 9] . If this boehmite can be used for sol-gel processing, it may become advantageous compared to the use of aluminium salts or aluminium alkoxides for the synthesis of boehmite . The present investigation is primarily concerned about the feasibility of using aluminium metal as a precursor for the the synthesis of boehmite and then using the same for sol-gel processing. The study assumes added sig
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