メチルイソブチルケトン抽出によるダーククロムメッキ液中の亜鉛定量法

概要

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The process of dark chromium plating (nonlustrous chromium plating) caused the dissolution of undercoating of zinc into the electrolyte and an increase of the amount of zinc in electrolyte is unavoidable. An increase of zinc content above a certain amount causes a poor electrodeposition of chromium and the plating becomes uneven. Accordingly, it is necessary to regulate the amount by a frequent determination of zinc. This report deals with a simple and rapid determination by the following procedure: A suitable amount of chromium plating solution is taken in a separatory funnel, 5ml of 10% ammonium thiocyanate is added and Zn(NCS)2 is extracted with 20ml methyl isobutyl ketone. The solvent layer is washed 3 times with ammonium thiocyanate solution for removing of a small amount of chromic acid, the zinc is extracted with ammonia-ammonium chloride buffer solution of pH 10 and determined by titration with EDTAusing EBT as an indicator. The disturbing effect of iron in this case was prevented by adding ammonium fluoride before the extraction and washing of zinc. Also, the disturbing influence of copper was removed by adding potassium cyanide and formalin during the titration. In this method, 56g zinc/l in chromic acid 250g/l can be determined in 15 minutes.
社団法人日本分析化学会の論文