Synthesis of alumina/nickel composite by electrodeposition of nickel
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Ni 2+ ions in aqueous solutions were electrochemically deposited within pores of alumina compacts attached to carbon or Pt electrode at room temperature. The deposition behavior of Ni metal in the pores of alumina compacts was expressed by an empirical power law equation of W = kt", where W is the weight of Ni deposited, k the deposition rate constant, t the deposition time, and n the experimental constant (0.52-0.56). The shape of Ni deposited was dependent on the geometry of positive electrode.
Many metal/ceramic composites have been developed to give high fracture toughness and high electrical conductivity to ceramic materials and to give high strength, high hardness, and high corrosion resistance to metal materials. Frequently used processes for the synthesis of composites are sintering of mixed powders of metal and ceramics, infiltration of molten metal into the spaces of porous ceramic compacts, oxidation of molten metal, or tape casting and hot-pressing of metal/ceramic laminates.'" 6 In this study, we have investigated a processing for metal/ceramic composites by depositing metal electrochemically in the pores of porous ceramic materials at room temperature. The features of this processing are summarized as follows: (i) The final microstructures of composites depend on the starting pore structures of ceramic materials; (ii) The metal ions present in aqueous or nonaqueous solutions are electrochemically deposited at low or room temperature, leading to possibilities of no control of processing atmosphere and no restriction of the melting points of metals; (iii) Little reaction at the interfaces of metal/ceramics is expected; (iv) The fraction of metal in the composite is controlled by the electric charge passed; and (v) The metal deposited itself acts as a following electrode. Based on the above concept, the basic experiment was carried out with porous alumina compacts and aqueous nickel solutions to synthesize electrochemically metal/ceramic composites. A high purity submicrometer-sized a-alumina powder (>99.99 wt. %, Sumitomo Chemical Co. Ltd., Tokyo, Japan) with a specific surface area of 10.0 m 2 /g (equivalent spherical diameter 0.15 /xm) was dispersed at 12-15 vol% solids in aqueous solutions at pH 7.0-7.3 and consolidated to thick films (0.81-1.06 mm thick, synthesis I) by the doctor blade method or to a columnar
a) Address
all correspondence to this author. J. Mater. Res., Vol. 10, No. 11, Nov 1995
http://journals.cambridge.org
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rod (diameter 1.2 cm, length 2.0-3.5 cm, synthesis II) by filtration through gypsum molds. In the center of the alumina rod, a Pt wire of diameter 300 /xm was set as an electrode. These green compacts were heated at 1100 °C for 1 h to give enough strength for the handling in the electrochemical experiment. The densities of calcined alumina compacts were 54-62% of theoretical density. Carbon cloth 410 yttm thick (specific resistivity 150 /iflcm, Kureha Chemical Industry Co. Ltd., Tokyo, Japan) was attached to one side of the calcined alumina sheet.
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