No.10（2015）5.Acting mechanisms of citric acid on the properties of nickel citrate electroplated film

Tadashi Doi

  For coping with the strict effluent regulations on boron discharge established for environmental protection in Japan, the authors have developed a new nickel electroplating bath (hereinafter simply referred to as a "Citrate bath") using citric acid instead of boric acid in a Watts bath. The citrate bath offers an excellent, practical, and more environmentally friendly plating method for bright nickel decoration and protection. The hard deposit obtained from the citrate bath has the crystal structure of fine and random orientation not achievable with the conventional methods. In order for clarifying the coating mechanism the citrate bath, an investigation was made on the relation between the properties of the film and the presence status of chemical species of the complexes with nickel ion using the citric acid and acetic acid and succinic acid. Based on the results, it assumed that abundant free nickel ions are present in a citrate bath and the nickel is electrodeposited from the chelate of nickel citrate complexes. I concluded that the finely-grained hard deposit of randomly-oriented structure is produced through the electrodeposition of nickel from the specific structure of the nickel citrate complexes forming the chelate of the nickel ion with two carboxyl groups of citrates among three.

Keywords
Citric acid, Electroplating, Nickel citrate electroplating bath, Properties of the film, Carboxyl groups, Chelate

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