Influence of additives on the properties of spherical nickel particles prepared by ultrasonic spray pyrolysis
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Influence of additives on the properties of spherical nickel particles prepared by ultrasonic spray pyrolysis S. Stopic´ Faculty of Technology and Metallurgy, Belgrade, Yugoslavia
J. Nedeljkovic´ and Z. Rakocˇevic´ Vincˇa Institute of Nuclear Sciences, Belgrade, Yugoslavia
D. Uskokovic´ Institute of Technical Sciences, Serbian Academy of Sciences and Arts, Belgrade, Yugoslavia (Received 6 January 1997; accepted 5 April 1999)
Ideal spherical nonagglomerated Ni particles (mean diameter 0.62–1.12 m) were prepared by ultrasonic spray pyrolysis of NiCl2 aqueous solution in the presence of 0.1 mass% of Pd, Cu, or Ni in an H2–N2 atmosphere at 900 °C. Incomplete reduction of the NiCl2 aqueous solution in the absence of additives was observed under the same conditions. Differential thermal and thermal-gravimetric analyses revealed a decrease in initial reduction temperature of NiCl2 from 375 to 275 °C by the addition of Pd, Cu, or Ni. The morphology of Ni particles was analyzed using scanning tunneling microscopy. The surface roughness of Ni particles was found to be controllable by addition of appropriate additives.
I. INTRODUCTION
Thick-film technology has a significant role in hybrid integrated circuit and multicomponent ceramic capacitor production where, ideal, spherical, nonagglomerated submicronic Ni particles, due to their good conductivity, are indispensable. Being cheaper, Ni substitutes noble metals (Pt, Pd, Au, and Ag) wherever possible.1 The morphology of the particles can be controlled by careful selection of initial precursor, method of preparation, and adjustment of the reaction parameters: temperature, solution concentration, and hydrogen partial pressure in an H2–N2 gaseous mixture.1,2 The use of additives to accelerate the reduction of NiCl2 by hydrogen and to control the morphology of particles is of great importance but has not been investigated thoroughly. Production of multicomponent Ni-based catalysts of strictly controlled compositions is often based on temperature-programmed NiCl2 reduction by hydrogen with the addition of noble metals. Yentis et al.3 have shown that the addition of Pt to NiCl2, under isothermal conditions, accelerates the reduction process and lowers the reduction temperature from 350 to 300 °C. As shown by these authors, dissociation of H2 molecules in the presence of Pt into a reactive atomic form promotes the reduction process. The interest in obtaining Ni from NiCl2 aqueous solution has been growing recently due to its good solubility in water and applications in lowtemperature chlorination processes.4 Also, reduction of chlorine solution is widely used for the recovery of Ni J. Mater. Res., Vol. 14, No. 7, Jul 1999
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from spent catalysts,5 while the addition of < 0.1 mass% of Pd to the polycrystalline Ni powder, a poor H2 absorbent at low pressures, significantly improves its absorption properties.6 Metal powders, used in thick-film technology, are usually prepared by che
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