INDIUM PLATING

摘要

Indium is the only trivalent metal that can readily be electrodeposited from a cyanide solution. Solution make-up and operational parameters are summarized in Table I. Indium hydroxide [In(OH)_3] is first prepared by the precipitation of indium chloride (InCl_3) using ammonium hydroxide or sodium hydroxide. The purified and dried In(OH)_3 is then dissolved in an alkaline cyanide solution stabilized with a sugar such as D-glucose, dextrose, or sorbitol. The cyanide bath is used in applications demanding extremely high throwing power and adhesion. Deposits are uniform and bright matte in appearance. Since this a high pH bath, it had the disadvantage of requiring the use of insoluble anodes, necessitating replenishment in the form of an indium cyanide concentrate. Its cathode efficiency is initially 90%, but upon bath aging decreases from this value to 50-75%. Periodic determination of the plating rate is thus required.