Polyfunctional Carboxylic Acids as Coprecipitating Agents For Barium, Yttrium, and Copper
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POLYFUNCTIONAL CARBOXYLIC ACIDS AS COPRECIPITATING AGENTS FOR BARIUM, YTTRIUM, AND COPPER Robert B. Hallock, P.O. Rexer, M.S. Jolly, W.E. Rhine, and M.J. Cima Ceramics Processing Research Laboratory, Massachusetts Institute of Technology, Cambridge, MA 02139 ABSTRACT The suitability of several polyfunctional carboxylic acids as coprecipitating agents for Ba, Y, and Cu was investigated. Essentially complete precipitation from alcoholic solutions was achieved for all three metals when tartaric acid was employed as the precipitating agent. The amorphous precipitate formed under these conditions was composed of uniform particles about 50 nm in diameter, and was converted readily to high purity Ba2YCu 3O.x. INTRODUCTION The formation of Ba 2 YCu3 OTix from coprecipitated oxalate salts has been claimed to offer several advantages over solid state reaction between the oxides, including improved homogeneity, lower temperature synthesis, better superconducting properties, and sintering to nearly theoretical density [1-4]. The main disadvantage encountered in oxalate coprecipitation is the incomplete precipitation of one or more of the metals, resulting in loss of control over the stoichiometry of the precipitate [1-4]. We have investigated the use of several polyfunctional carboxylic acids as precipitating agents for Ba, Y, and Cu. The extent of precipitation of all three metals was monitored by inductively coupled plasma emission spectroscopy (ICP) analyses of the filtrates from the coprecipitation reactions. None of the acids investigated gave complete precipitation of all three metals from aqueous solution. However, in a mixed solvent system (ethanol/water), the use of tartaric acid allowed the isolation of a highly reactive amorphous precursor to Ba 2YCu 3O7.-. EXPERIMENTAL PROCEDURE Solubility Studies The carboxylic acids were dissolved in a minimum amount of water and added to aliquots of a stock aqueous solution of Ba, Y, and Cu acetates (0.1175 M Ba, 0.0578 M Y, 0.1762 M Cu) such that the mole ratio of reagents was 2Ba: lY : 3Cu : 7acid. The resulting precipitates were isolated by filtration and their morphologies examined by scanning electron microscopy (SEM). The filtrates were diluted 1:100 and analyzed for Ba, Y, and Cu by ICP (Laboratory for Special Analysis, Randolph, MA). In several cases, crystals formed from the filtrate over a period of days or weeks. These crystalline products were isolated and characterized.
Mat. Res. Soc. Symp. Proc. Vol. 180. 01990 Materials Research Society
878
Tartaric Acid Coprecipitation from Ethanol/Water Mixtures Barium acetate (7.67 romol), yttrium acetate (3.83 romol), and copper acetate (11.50 romol) were dissolved at room temperature in a mixture of 400 mL ethanol and 200 mL water. The acetate solution was added over a period of about 30 s to a solution of the tartaric acid in 600 mL ethanol. A blue gelatinous precipitate formed upon mixing. The precipitate was isolated by filtration and dried overnight at 45°C. Formation of Ba'7YCu30 7 .xfrom Coprecipitated Tartrate Prec
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