A Kinetic Study of Nickel Deposition on Spherical Silica Particles and Viscose Fibers by Chemical Plating
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TRODUCTION
MICROSILICA particles coated with nickel or nickel alloy are found to be an attractive composite material for a thermal barrier coating (TBC) and abradable sealing.[1–3] This composite could be used even above 1273 K. For example, nickel-coated spherical silica particles are successfully employed to obtain a thermal barrier and abradable sealing layer in plasma or oxygen-acetylene flame thermal spray processes.[4,5] Compared with nickel carbonyl decomposition[6,7] and hydrothermal reduction processes,[8,9] chemical plating process is an easier practice. To the knowledge of the present authors, most of the current chemical plating baths would not be able to produce a nickel layer free from P and B. The presence of P or B is proved to be detrimental to the mechanical properties and corrosion resistance of the final product at approximately 973 K and above.[10,11] The solution, nickel sulfate-ammonium sulfateammonia-hydrazine hydrate, has been reported to be a promising alternative for coating pure nickel on BN particles.[12] It has even been applied in the preparation of composites of nickel-coated viscose fibers.[13] To the knowledge of the present authors, no attempt has been made to coat a nickel layer on silica microparticles using this system. FAN LI, Associate Professor, formerly with the Department of Material Science and Engineering, Royal Institute of Technology, is with the Department of Chemistry and Chemical Engineering, College of Environment and Energy Engineering, Beijing University of Technology, Beijing 100124, P.R. China. DU SICHEN, Professor, is with the Department of Material Science and Engineering, Royal Institute of Technology, Stockholm SE-10044, Sweden. Contact email: [email protected] DENGJUN ZHANG, Professor, is with the Institute of Process Engineering, Chinese Academy of Sciences, Beijing 100080, P.R. China. Manuscript submitted June 26, 2007. Article published online June 9, 2009. METALLURGICAL AND MATERIALS TRANSACTIONS B
It has been found in the case of nickel coating on BN particles that Ni or Pd acts as an active center for catching Ni from the solution through the reaction Ni2+ + 2H*ad fi Ni + 2H+.[14,15] A mathematical model has been developed for describing this mechanism by taking account of the surface area change. It would be interesting to examine whether this mechanism would also apply to the coating processes of viscose fibers and silica particles. The aim of the present work is threefold, as follows: (1) examining the possibility of producing nickel-coated silica particles using the solution system, nickel sulfateammonium sulfate-ammonia-hydrazine hydrate, and finding out the optimum process parameters; (2) studying the mechanism of the coating process; and (3) generally applying a kinetic model to describe the nickel coating processes, in which the rate is controlled by the reaction at the growing interface.
II.
EXPERIMENTAL
The materials used in the present study, along with their purities and suppliers, are listed in Table I. The silica particles supplied by ZhongKe*
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