Electrodeposited tin-zinc alloys are considered promising as lead-free alternatives to solder coatings. Eutectic tin-zinc alloy film was deposited at 2∼3A/dm2, 25°C, and pH 4 using the following bath composition. 0.18M SnSO4, 002M ZnSO4, 05M sulfosuccinic acid, and 1g/L polyoxyethylenenonylohenol ether (POENPE). The presence of POENPE increased tin deposition polarization markedly over a wide potentials range, and an appreciable amount of zinc was codeposited. Tin and zinc ions in the elluent were separated in the form of hydroxide, and the residual concentration of tin and zinc ions were lowered to less than 0.1mg/L. On a copper substrate, zinc in the alloy film migrated rapidly to the copper substrate at below eutentic point. Plated nickel films were effective to preventing thermal zinc migration.
Reactions between Fe-Zn alloy layer coatings formed on the Fe specimen surface hot-dipped in Zn melt (primary melt) and Zn-Al melt (secondary melt) were investigated. In order to determine the formation mechanism of alloy layer coatings, as dipped coatings containing Zn melt and annealed coatings without Zn melt were dipped into secondary melt, and their microstructures and solute concentration distributions in coatings were compared. Coatings containing Zn melt and Zn-Al melt reacted rapidly because the reactionis controlled by rapid Al and Zn diffusion in Zn melt. Annealed coatings and Zn-Al melt reacted relatively slow because the reaction is controlled by solid diffusion in Fe-Zn alloys in coatings.
Surface pretreatment effects of Al and Al-Mg alloy on Zn deposition in the zincate process were evaluated using SEM and XPS. Al surface dissolution in a concentrated NaOH solution followed by zincate treatment produced rapid Zn particles nucleation with uniform size due to Al surface oxide film thinning. The anodic oxidation pretreatment of Al used jointly with electropolishing followed by zincate treatment also resulted in deposition of uniform Zn particles. Anodic oxidation pretreatment without electropolishing, however, resulted in nonuniform Zn deposition indicating that defects in the oxide film could be active sites for Zn nucleation. Al-Mg alloys require both alkaline and acid cleaning in surface pretreatment because Al dissolves in concentrated alkaline solution, and Mg dissolves in acid solution. Magnesium or its enriched compounds on the surface during zincate process in an alkaline zincate solution inhibits Al dissolution and Zn deposition. XPS showed that Zn2+ remains in the Al oxide layer, which partially charged after Zn stripping in a HNO3 solution. The role of the first zincate process in double zincate treatment is discussed based on these results.
Environmental protection requires that lead be recycled. The oxidation behavior of recycled lead containing 100-200ppm of impurities was examined using the quartz crystal microbalance technique, and compared to that of virgin lead having 99.99 and 99.9999 mass% purity. Although early-stage oxidation obeyed the cubic rate law for all lead films, the rates of recycled leads far exceeded those of virgin leads in a dry atmosphere at 303K. Both Bi and Cu impurities increased the oxidation rate, but the addition of∼100ppm of Sn affected oxidation behavior only negligibly. XPS and AES revealed that the oxidation product of high-purity Pb film consisted mostly of PbO2-x. Bi, Cu, and Sn film products were Bi2O3, Cu2O, and SnO respectively. Where the PbO2-x is an n-conductor, the increased oxidation rate of high-purity Pb film by adding trace amounts of Bi or Cu is interpreted by the controlled valence principle.
Life tests for titanium electrodes plated in an alkaline platinum electroforming bath or acid platinum plating bath were conducted in a sulfuric acid solution. After 1, 025h of electrolysis on an electrode plated in the alkaline platinum electroforming bath, twice the platinum remained compared to that on an electrode plated in the acid platinum plating solution. Two types of platinum consumption thus appear to occur one by dissolving and the other by peeling. Platinum plated in an alkaline electroforming bath was more resistant to peeling.