The Powder Preparation of Blue Cobalt Aluminate at 210^°C Using the Malonate Method

Abstract

A powder, containing 80 percent of blue cobalt aluminate (CoAl2O4) crystallites, was synthesized at 210 o C using a (metal nitrate-malonic acid-ammonium hydroxide-ammonium nitrate) system. The optimal amount of concentrated ammonia water and initial decomposition temperature were determined for the blue CoAl2O4 crystallites preparation. Three CoAl2O4 precursor pastes, corresponding to the various amounts of concentrated ammonia water, were prepared by evaporating the initial solutions in an electric furnace fixed at 80 o C under a vacuum of 25 torr. The initial solution was used to dissolve the starting materials. The powder with the maximum content (80%) of blue CoAl2O4 crystallites was prepared when the prepared precursor was decomposed at 210 o C. The blue CoAl2O4 crystallite content in the prepared sample decreased with increasing initial decomposition temperature. For 0.2 mole of the Al 3+ ion, the chemical compositions of the precursor corresponded to molar ratios of 0.4, 1.40, 2.56 and 2.00 for the Co 2+ ion, malonic acid, ammonia and ammonium nitrate per mole of the Al 3+ ion, respectively. The blue CoAl2O4 crystallite content in the sample decreased with the amount of ammonia deviated from the optimal value. The characteristics of the powders were examined using X-ray diffraction, optical microscopy, Fourier transformation infrared spectroscopy and the BrunauerEmmett-Teller technique.