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Corrosion resistance and porosity of electroplated bright tin coating on steel substrate were evaluated by salt spray test and modified ferricyanide test, and the results were compared with those of other tin coatings.Effects of diffusion of brass substrate in the electrodeposited coating were studied by sulfur dioxide test, microsection observation, and X-ray diffraction method. The results were as follows:1. Porosity of bright tin plating was lower and its corrosion resistance was higher as compared with other tin coatings.2. At places, where steel was exposed in pores of electrodeposited tin, oxygen was expelled from the corrosive solution and electrochemical behavior might be reverse. It was considered that the dissolution of tin was very little; because it was anodic to steel which was made unattached.3. Tin salts such as SnCl2 were converted to precipitated stannous oxychloride by absorbing liquor. Stannous oxychloride was insoluble in water and inhibited exposed steel from corrosion by sealing up capillary tin pores.4. Diffusion rate of zinc from brass substrate into tin coating was very higher than that of copper. The both diffusion rates were higher as compared with other tin coatings. The reason of higher diffusion rates in electrodeposited bright tin would be due to its fine crystals and richness in grain boundary.

Effect of the organic addition agent to acid stannous sulfate bath was studied by Hull cell test and cathode polarisation measurement. Crystal structure of the deposit from the bath was analysed by X-ray diffraction method.Addition of organic compounds, such as wood tar, styrenated phenol, product of amin and aldehyde, that of amin and ketones, etc., to the acid stannous sulfate bath with surface activating agent (sodium n-octyl sulfate) made the polarisation potentials of tin, higher up to 130-400mV at 1.5A/dm2.Brighting agents, lyophobic and weakbasic materials, gave good results in Hull cell test, and showed anionic action in diluted sulfuric acid solution.These addition agents seem to form stable micelles as activating agent and complexes with tin ions in the solution.Acting as carriers micelles and complexes would advantageously convey the brighting agent to the cathode.In the solution over cathode surface of higher pH, micelles would probably lose their balance, and free lyophobic brightner adheres to the growing deposit.Bright tin deposit has fine crystals, however, the brightness is mostly due to the orientation of crystals.As to the full bright deposit, only one face (112, 330) was observed by X-ray diffraction.

Tin-zinc alloys of low zinc content are believed to have high corrosion resistance when they are used for protective films on steel surface. This paper describes the following studies: an optimum composition for protective films was selected by electrochemical measurements of the cast alloys; and, zincate-stannate baths and gluconate baths were investigated to obtain such alloy deposits from baths free from cyanides and fluorides. The following results were obtained: (1) The static potential of tinzinc alloys was base enough to act as a sacrificial film for steel, and the potential of an alloy containin more than about 10% of zinc showed almost the same value as that of single zinc. (2) The anodic dissolution in NaCl solution and the formation of white precipitate on the alloy surface in a salt spray test more readily occurred with the increase in zinc content of the alloy. (3) It was difficult to obtain alloy deposits of lower zinc content from zincate-stannate baths under normal plating conditions. (4) A semi-bright zinc alloy deposit of lower zinc content was obtained from the bath containing 0.25mol/l of metal and 0.50mol/l of Na-gluconate with an additive such as 0.25mol/l of triethanolamine, 2.5-5g/l of polyethyleneglycolnonylphenylether (PEGNPE), 0.2-1g/l of peptone, and 0.04-0.06g/l of o-vanillin at pH=5. It was observed that a deposit of fine luster was apt to be obtained at a composition of nearly equi-molecular ratio between tin and zinc. (5) It was further observed that a deposit of highest zinc content was obtained from gluconate baths containing 20 and 35% of zinc at pH=5, and the zinc content of deposit was almost equal to that of the bath when the plating was conducted at a current density of 1-2Amp/dm2.

Inhibition effects and mechanism of benzotriazole (B.T.A.) on corrosion of Cu in NaCl, NaClO4, and HClO4 solutions were studied by potentiostatic polarization curves, electrical double layer (e.d.l.), and capacity-electrode potential curves; and by the relation between inhibition efficiency (P) determined by immersion test and degree of surface coverage (Q) obtained from e.d.l. capacity in Cu-NaCl-B.T.A. system. Each of the values of P and Q were measured as functions of B.T.A. concentration (m). The results obtained were as follows: (1) The inhibition effect of B.T.A. in Cu-NaCl system depended on its concentration and electrode potential. In anodic potential region, it was found that B.T.A. had little effects in low concentration, but a good inhibition effect was obtained in high concentration, because B.T.A. -Cu complex was formed and adsorbed on the surface. Whereas, in cathodic potential region, inhibition effects were found in both of low and high concentrations, owing to chemisorption of B.T.A. on the surface with a lone electron-pair of N-atom. (2) However, in Cu-NaClO4 system, it was observed that B.T.A. in low concentration had good inhibition effects in anodic and cathodic potential regions. (3) It was also found that B.T.A. had little inhibition effects in acid solutions such as of HClO4, but it had maximum effects in neutral solutions such as of NaCl and NaClO4. (4) The P-m and Q-m curves obtained in Cu-NaCl-B.T.A. system were typical Langmuir's adsorption isotherms. Proper linear correlation was observed between P and Q, but the correlation coefficient varied according to the range of B.T.A. concentration.

Each component in the lead-tin fluoborate plating bath would be quantitatively analyzed by the following procedures simply and correctly.Pb: After the excess of EDTA being added to the bath, Sn++ was oxidized with H2O2. Then, the solution was masked with triethanolamine and back titrated with Zn++ at pH=10 using BT as indicator.Sn++: After Pb was precipitated with H2SO4, titrated by iodometry.Free HBF4 and Free H3BO3: After Pb was precipitated with Na2SO4, free HBF4 was determined by alkaline titration with pH-meter to pH=3.5 as the end point. Then, pH was made to 7.0, mannite was added to it, and free H3BO3 was determined by alkaline titration to pH=8.0 as the end point.Hydroquinone: Precipitate was filtered off from the solution after the determination of HBF4 and H3BO3 and titrated with Ce+4 using ferroin as indicator after made acidic with H2SO4.Lead and tin in the deposit could be determined by the following procedures.Pb: Lead-tin plated layer was dissolved by a remover such as Enstrip TL and the excess of EDTA was added to the solution. Then, tin was masked with triethonolamine and back titrated with Zn at pH=10.Sn: The above solution wa made acidic with HCl and back titrated with Zn at pH=5 in the warm state using PV as indicator to determine Sn+Pb. Then, Sn was calculated.

Polarization behavior of tin anodes in H2SO4 of various concentrations and stannous sulfate plating baths was investigated by potentiostatic method.The anodes with various lead contents were prepared by a conventional melting process.The results obtained were as follows:(1) An oxide film was formed on the surface of tin anodes at potentials above passivation. The film was stable at potentials up to -0.4V(vs. S.C.E.), but it was dissolved when the potential was lowered to the spontaneous electrode potential of tin.(2) The polarization for tin anodes depended upon the concentration of H2SO4, which made the passivity prominent at 3N.(3) The effect of passivity increased with the decrease in purity of anode and lead was the most toxic among impurities.(4) Organic addition agents to the plating bath inhibited the anodic dissolution.(5) It was found that the measurement of anode potential-current density curve was used for selecting an excellent anode for each of various plating baths.