Ikram Ul Haq

Preparation and characterization of uniformly coated particles by homogeneous precipitation (cobalt compounds on nickel compounds)

Abstract Nickel basic carbonate [NiCO 3 · Ni(OH) 2 · H 2 O] particles were coated with crystalline cobalt carbonate (CoCO 3 ) by heating their suspension in an aqueous solution of cobalt nitrate and urea at elevated temperatures. In the absence of core particles, the same reactant mixture produced a dispersion of amorphous cobalt basic carbonate [2CoCO 3 · Co(OH) 2 · H 2 O] particles. On calcination at 700°C, the shell and core materials of the coated particles transformed, respectively, into Co 2 O 3 , and NiO, while producing a third phase (NiCo 2 O 4 ) at the core/coating interface. No sintering was observed during calcination and the particles retained their morphological features to a significant extent.

Preparation and characterization of uniform coated particles (Cobalt compounds on cadmium compounds)

Uniformly dispersed particles of CdCO3 were prepared by homogeneous precipitation from aqueous solutions of cadmium sulphate and urea at the elevated temperatures. These particles were then employed as cores for coating with 2CoCO3·Co(OH)2·H2O from cobalt nitrate and urea solutions at 85°C. In the absence of cores, when heated under similar conditions, the coating solutions produced nearly uniform particles of 2CoCO3·Co(OH)2·H2O. On calcination at 700°C, the core [CdCO3], coated [CdCO3/2CoCO3·3Co(OH)2], and coating precursor [2CoCO3·Co(OH)2·H2O] particles transformed into CdO, CdO/Co3O4, and Co3O4, respectively. No sintering occurred during calcination and the particles preserved their morphological features to a significant extent.

Chemical modulation of crystalline state of calcium oxalate with nickel ions.

BACKGROUND We explored that the presence of nickel ions in the precipitation medium affected size, shape and crystalline phase of the precipitated particles of calcium oxalate, whereas the applied synthesis conditions strongly influenced their uniformity. METHODS Aqueous solutions of oxalic acid and calcium chloride, containing varying amounts of nickel sulfate, were mixed at room temperature and allowed to sonicate for various periods of time. The obtained particles were characterized by SEM, XRD, TG/DTA, and FTIR. RESULTS Results revealed that particle morphology of calcium oxalate and their hydration states were dependent upon the chemical composition of the reactant solutions. For instance, the particles precipitated out in the form of dihydrate and having prismatic, and discs shaped particle morphology, when nickel ions were introduced in the starting reactant solution in different amounts. In contrast, the calcium oxalate particles precipitated under identical conditions in the absence of nickel ions were in the form of flakes with corrugated edges. Obvious variations were also found in the XRD patterns and crystallite size of these three solids. Heat treatment produced changes in the surface morphology of these particles due to loss of material and converted them calcium oxide. CONCLUSIONS Gentle mixing of aqueous solutions of calcium chloride and oxalic acid in the absence and presence of nickel ions produced precipitated particles of calcium oxalate. Chemical composition of the reactant solutions and their order of mixing were found to be the key parameters in controlling the particle morphology and their hydration/crystalline state. Heat treatment at the elevated temperature transformed the as-prepared calcium oxalate to calcium oxide with visible changes in surface features of the particles.

Characterization of Monodispersed γ-Al2O3 Particles, Synthesized by Homogeneous Precipitation under Reflux Boiling

Abstract In this study, micron size uniform particles of aluminum compounds were synthesized by the homogeneous precipitation method under reflux boiling, using aluminum nitrate, urea and potassium sulfate as starting materials. In this method, varying amounts of the reactants were heated in a Pyrex glass round bottom flask at the boiling temperature for various periods of time, which led to the production of precipitated particles in the reactant mixtures. Scanning electron microscopic (SEM) examination of the precipitated particles revealed that uniformity in particle morphology of the precipitated particles was dependent on the applied experimental conditions. As such, the latter were extensively optimized for obtaining particles of uniform morphology and size. Some of the batches of the precipitated particles were calcined at the elevated temperature (800 and 1000 °C) for transformation into crystalline solids. Similarly, the as prepared and calcined particles were characterized by SEM, XRD, TGA/DTA and FTIR. XRD results revealed that at 1000 °C of calcinations, the as prepared amorphous alumina transformed in to crystalline state, while below this temperature, i.e. at 800 °C calcination, the powder was amorphous in nature. The point of zero charge (PZC) of the desired sample was estimated by the salt addition method.

Synthesis and Characterization of Uniform Zirconia Particles by Homogeneous Precipitation Method

Abstract Colloidal spherical particles (micrometer size) of zirconia were synthesized at 50°C by homogeneous precipitation method from aqueous solutions, containing appropriate amounts of zirconium chloride, hydrochloric acid, potassium sulphate and urea. Results revealed that reactants concentration significantly affected characteristics of the precipitated solids, which ranged from gel to dispersion of discrete particles. Size uniformity in the resulted particles was obtained only under limited conditions. SEM images revealed that particles of zirconia obtained under the described experimental conditions have spherical morphology, which maintained their original shape after calcination at 700°C. Selected powders were also characterized with XRD, TGA/DTA, and FT-IR techniques. XRD results showed that as-prepared and calcined powders were crystalline. We believe that our method is simple and has the potential for further tailoring of the particles characteristics. Work is in progress in our laboratory in developing Cu-ZrO2 metal matrix composite coating on steel substrate with better resistant properties than simple Cu electroplating.

Effect of calcination temperature on the morphological and dielectric properties of phase-pure MnCrFeO4 nanoparticles

ABSTRACT Phase-pure MnCrFeO4 particles were synthesized by the controlled precipitation and the effect of calcination on different properties were investigated. XRD results showed intermediate phases in the particles calcined at 800 °C, while complete transformation into spinel phase at 1000 °C. The particle size increased linearly with calcination temperature. The increase in AC conductance with frequency showed the involvement of small polarons in the conduction mechanism. The dielectric constant and loss tangent steeply decreased while remained constant over the high frequency range. The phase-pure MnCrFeO4 particles showed lowest dielectric losses that make them a promising candidate for application in high-frequency devices.