Preparation of copper compounds of different compositions and particle morphologies
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One of the fundamental unresolved problems in the precipitation of uniform solids from homogeneous solutions is the inability to predict the particle morphology. In recent years a large number of the so-called "monodispersed" colloids has been synthesized,1"4 which has provided numerous examples of the effects of the experimental conditions on the shape of the resulting solids. Using the same reactants, in some cases, the morphology is associated with the chemical composition, while in some other instances, the same material may appear in a variety of geometries, often produced by a small change in the experimental parameters (concentration, temperature). The most pronounced effects have been noted when metal salts of the same cation but of different anions were employed. Again, the resulting solids could be of different chemical composition (and consequently morphology) or of the same composition, but different particle shape.1'5'6 The sensitivity of a system to these parameters depends very much on the metal cation in question, i.e., its ability to form different complexes in solution.7 The latter act as precursors to the solid phase formation and as such affect the nature of the resulting precipitates. In this respect, copper(n) solutions are rather convenient media for the investigation of the precipitation processes since, depending on the conditions, a large number of solids of various compositions and shapes can be achieved. This work describes a number of dispersions of copper compounds, obtained by aging dif766 http://journals.cambridge.org
J. Mater. Res., Vol. 6, No. 4, Apr 1991 Downloaded: 11 Mar 2015
ferent Cu(n)-salt solutions at elevated temperature in the presence of urea. II. EXPERIMENTAL
The effects of the concentration of urea and Cu(n) salt solutions, and of the nature of accompanying anions (nitrate, chloride, or sulfate) on the properties of the resulting solids, obtained by aging at 90 °C for different times, were investigated in some detail. All solutions were prepared using reagent grade chemicals and doubly distilled water. Stock solutions were filtered through Nuclepore membranes of 0.20 /im pore size and were freshly prepared after a month of storage. The reaction solutions contained in capped Pyrex tubes (10 cm3 or 50 cm3) or bottles (250 cm3 and 500 cm3) were aged in a forced-air convection oven or in a water bath. After desired periods of time, the tubes were removed and quenched to room temperature in cold water. The precipitates were separated from the mother liquor by filtration, rinsed repeatedly with distilled water, and dried at room temperature in a desiccator. The pH was recorded of the initial solutions and of the liquid after filtration. The weight change on heating of the powders was followed by thermal gravimetric analysis (TGA). Calcination of larger samples was conducted at 400 °C and 800 °C in a tube furnace. The solids, as prepared or calcined, were inspected by scanning electron microscopy. The composition and the structure were evaluated by x-ray diffractio
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