クエン酸アンモニウム-ヨウ化カリウム浴からのSn-Ag合金めっきにおけるアノードの挙動

概要

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Anodic current density-potential curves of Sn, Ag, Pt, and graphite were measured to obtain informations on the selection of anode materials in ammonium citrate-potassium iodide baths for Sn-Ag alloy plating. The Sn anode was dissolved at small overpotentials in ammonium citrate solutions containing iodide and showed a very smooth electrode surface. However, a displacement deposition of rough Ag was observed when solutions contained Ag+. The Ag anode also dissolved at small overpotentials. Nevertheless, AgI was precipitated at the anode and therefore the limiting current densities were smaller than 10mA/cm2. The main electrode reaction at the Pt and graphite anode was oxidation of iodide to form I3-. This reaction also occurred at the Sn and Ag anode at high overpotentials. Sn2+ species was chemically oxidized by I3- formed at the anode, accumulating Sn4+ species in baths. To prevent both Ag displacement deposition and anodic oxidation of iodide, the electrode potential of the anode in Sn-Ag alloy plating baths must be maintained between -0.2V and 0.4V vs. NHE.
1998-12-01