Natural additive agents in the electrodeposition process have long been used to improve deposition flatness and help prevent impurities from precipitating during deposition. The effective molecular weight and elements of these natural additives during deposition, however, have not been clarified sufficiently to understand the mechanism behind their effectiveness. In this research, we used gelatin having an average molecular weight of 18000, determined by HPLC, as a natural additive. We also used polyethylene glycol (PEG) having average molecular weights of 20000, 6000, and 2000 as a synthetic additive. Mass deposit changes were monitored by QCM. We obtained the following results: 1) Mass change during deposition depended on the molecular weight of the additive. 2) The deposition rate in the presence of gelatin was lower than that in the presence of PEG. 3) Anomalous mass change was detected during deposition in the presence of gelatin and PEG additives. This corresponded to the change in the surface morphology of deposits.
SCM 435 was plasma-sulfnitrided at 823K for 3.6-18ks in a 30% N2-70% H2 mixing gas atmosphere at 665Pa by hybrid-treating ion-nitriding and sputtering of MoS2. MoS2 was positioned 20mm above the specimen and applied discharge voltages of 300-600V. Sulfnitriding layers formed on the specimen's surface were evaluated by EPMA, X-ray diffraction, microscopic observations and microhardness changes. A 4-μm nitride (γ'-Fe4N) layer and a 400-μm nitrogen diffusion layer formed on specimens ion-nitrided without applying an electric potential. A 12-μm compound layer of sulfide (FeS) and nitride (ε-Fe2-3N and γ'-Fe4N) formed beneath the sulfide, and a 400-μm nitrogen diffusion layer formed on the surface of specimens plasma-sulfnitrided by applying an electric potential of 500V. The compound layer formed in plasma-sulfnitriding was thicker than in ion-nitriding. The compound layer thickness and surface hardness depend on specimen temperature, treatment time and the electric potential applied to MoS2. Mo and S were included in plasma-sulfnitrided compound layers. Surface hardness after plasma-sulfnitriding is higher than after conventional sulfnitriding. This may be due to Mo sputtered from the MoS2 target.
We studied corrosion by Zn-Co alloys electroplated from sulfate solutions onto iron substrate in a salt spray test (SST) by using scanning electron, X-ray diffraction, and X-ray photoelectron spectroscopy (XPS). We found Zn-Co alloy surfaces corroded by SST to be covered by corrosion products (white rust) consisting of Zn(OH)2, ZnO, Zn5(CO3)2(OH)6, and ZnCl2·4Zn(OH)2 due to the dissolution of Zn. For γ-phase alloys consisting of 10∼20wt%Co, a corrosion product with low electrical conductivity (ZnCl2·4Zn(OH)2) formed mainly with the corrosion product apparently effective subsequently as a barrier against further corrosion. The good corrosion resistance of γ-phase films can be attributed to conversion to a more noble-metal site due to Co concentrating on the corroded surface as corrosion advanced.
We studied the mechanism behind the double-zincate process, used for pretreating aluminum alloy, through SEM observation, electrode potential tracing, and weight changes determined during each zincate process. Zinc particles grew during the first zincate process, with a thin, uniform Zn layer forming during the second zincate process. We found that the difference in zinc particle nucleation between the first and second processes is related to surface morphology and in thickness nonuniformities in the preexisting oxide film air-formed on the alloy.
We studied corrosion wear of alloy tool steel (SKD 11) coated with VC and precipitation-hardened stainless steel (SUS 630) in NaCl aqueous solution. SUS 630 lost more weight than SKD 11 coated with VC, except where SUS 630 was used as a rotor at a load region below 9.8×10-1MPa. VC film appeared externally sound overall. Sample edges revealed galvanic corrosion of the substrate and partial disappearance of the VC film, and SUS 630 was plastically deformed under high load. The polarization curve indicated that VC film and SUS 630 form a galvanic couple with SKD 11 in NaCl solution, and that VC film and SUS 630 behave cathodic and SKD 11 anodic. Pinhole defects were detected in VC-coated SKD 11 using optical and scanning electron microscopy by anodic polarization in deaerated 0.5kmol·m-3 H2SO4 solution. Pinhole defects averaged 2∼4 per cm2
We studied the ZrB2 content in Cu-ZrB2 composite layers produced by dispersion plating. The current density, stirrer rotation rate, and direction of substrate setup was changed to determine the conditions required to maximize ZrB2 content in the matrix. The ZrB2 particle codeposition rate reportedly depends on the plating current density and on the stirring rate of the plating solution. The optimum plating condition maximizing ZrB2 content was at 5A·dm-2 and 900rpm. Substrate setup in the direction of the plating solution stream is an important factors. A linear relationship exists between ZrB2 content and the amount of Cu-ZrB2 composite deposited in the region exceeding 10mg·cm-2 of Cu-ZrB2 composite.