2001 Volume 2001 Issue 7 Pages 387-391
Ni-PTFE (PolyTetraFluoroEthylene) composite film was formed on hydrogen storage alloy (MH alloy) powder particles by means of electroplating method. MH alloy powder (mean diameter, 50 μm) with the composition of MmNi3.65Co0.75Al0.25Mn0.35 (Mm denotes Misch metal) was used. The electroplating apparatus equipped with rotating bath was designed to electroplate the Ni-PTFE composite film on the MH alloy powder particles. The bath was rotated at high speed (350 rpm) to make electrical contact between the particles and the belt-ring cathode made of titanium placed on the inside wall of the bath. The electrolyte solution added MH alloy powder and PTFE powder was agitated by intermittent rotation. PTFE powder particle (mean diameter, 5 μm) was suspended in the electrolyte solution with a cationic surfactant.
The electroplating efficiency on the MH alloy powder was calculated to be 60%. The Ni-PTFE composite film was uniformly deposited on the individual particle, and was observed to be a little bit porous. The surface area after plating was 3.5 times larger than that of the original alloy powder. As the results of PCT) (Pressure Composition Temperature) measurement, characteristics of hydrogen gas absorption-desorption such as the equilibrium pressure, the absorption amount and the hysteresis were found to be maintained. The corrosion resistivity in a strong alkaline solution was extremely enhanced. Even after immersing in 6 mol dm−3 KOH at 70 °C for 72 h, no formation of Mm(OH)3 on the surface of Ni-PTFE plated MH alloy was detected, and especially, the dissolving Mn decreased to less than one twentieth amount of original MH alloy.
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