Alumina powders via a controlled precipitation of aluminum acetate
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J. C. Droguet Baikowski-Chimie BP22 74001, Annecy Cedex, France (Received 23 November 1988; accepted 12 April 1989) A new method of producing alumina powder is described. Aluminum basic acetate is first synthesized from alkoxide precursor. The chemical reactions which control the precipitation of this salt are followed, using IR spectroscopy. Alumina powder is obtained by further thermal decomposition, and the thermal evolution of the precipitate is studied.
I. INTRODUCTION High purity submicron monodisperse ceramic powders have recently received increasing interest. The advantages of such powders have been previously described.1 The usual way to produce such oxide particles from alkoxides is the hydrolysis of the alkoxide into an organic solvent. For silica the process is very flexible,2"4 but the synthesis conditions are more drastic for other oxides.5"11 Aluminum alkoxides undergo a very rapid hydrolysis reaction, and an uncontrolled precipitation of aluminum hydroxide often occurs. Alumina having suitable properties is not yet obtained from hydrolysis of an organic alkoxide solution.12 Thus we have looked for another chemical way of allowing controlled precipitation of an aluminum salt. This salt must meet the following requirements. It must be easily thermally decomposed to give rise to alumina, without important morphological change for the precipitated particles. Otherwise it is of great interest to use a solvent in which water is not soluble to preserve the alkoxide from hydrolysis. Using these concepts we propose in this paper a new way to synthesize alumina particles.
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v) ( c m " 1 ) FIG. 1. IR spectra: (a) Et2O; (b) Et2O-ASB mixture (molar ratio: 23.5); (c) Et2O-sBuOH mixture (molar ratio: 18); (d) Et2O-AcOH mixture (molar ratio: 18).
II. SYNTHESIS OF BASIC ALUMINUM ACETATE The selected starting material is aluminum sec-butoxide (ASB), a very common alkoxide compound. The solvent is diethyl ether. An acetic acid solution is rapidly added to the alkoxide solution while stirring. In the mixture the concentrations are in the range 0.2-0.3 M and 2-3 M for the alkoxide and the acetic acid, respectively. After an induction time of a few minutes, the precipitation occurs. The transparent solution becomes milky, and the stirring is maintained for a few hours. The reactions that occur in the mixture are studied by IR spectroscopy. Cells with NaCl windows are used. Figure 1 shows the spectra of the solvent and reactant solutions. The spectra are recorded at concentrations which are those of the reaction media for a given addition of acetic acid (acetic acid/ASB molar ratio equal to 1.3). Spectra a J. Mater. Res., Vol. 4, No. 4, Jul/Aug 1989
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and b correspond to that of Et2O and that of the Et2O-ASB mixture, respectively. This latter spectrum is a simple superposition of that of Et2O and ASB. In this figure we have included the spectrum [Fig. l(c)] of a sec-butyl alcohol solution because this compound is expected to be a byprodu
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