An aluminum deposit oriented to a specific face is obtained from Lewis acidic aluminum chloride (AlCl3) 1-ethyl-3-methylimidazolium chloride (EMIC) ambient-temperature molten salt. We tried to stably produce the oriented deposit with a flat and smooth surface from the AlCl3-EMIC melt with xylene isomers added. Study of aluminum deposition from the xylene-added bath made it possible to investigate the mechanism of the oriented deposition. Aluminum oriented to (110) was electrodeposited from the acidic melt with o-, p-xylene added. On the other hand, aluminum oriented to (100), which has never been obtained, was deposited from the melt with 50mol% m-xylene added after being aged four hours from the bath preparation. Moreover, the deposit had metallic luster. Using SEM, tried to find out the relation between the orientation and the metallic luster. The deposit with metallic luster had a very flat surface. The deposit without metallic luster had a textural structure. Furthermore, we observed the initial state of the deposit by the AFM technique. Prior nucleation took place in the case of the metallic deposit oriented to (100). Prior crystal grain growth took place in the case of the nonmetallic deposit oriented to (110).
The electroless plating method has a particular advantage in that it accepts non-conductive substrates as its substrate materials. The catalyzation pretreatment process is essential for initiating electroless deposition. The most common two-step pretreatment process prior to electroless nickel plating was studied here, which includes the sensitizing step and the activating step. The objective of this study is to investigate the morphological changes of the adsorbate produced on the non-conductive substrates during the period before and after the deposition is initiated. The results obtained are as follows : By using an ICP for the nickel precipitate weight gain measurement when the glass substrate which conducted the catalyzation process was immersed in an electroless Ni-P plating bath, the results show that deposition is already initiated with a low deposition rate even before the deposition can be confirmed with a visual inspection. The observations of the catalyzed surfaces using SEM detect the aggregates of adparticles with sizes grown to reach several microns. The incidence of the grown aggregates has a tendency to be higher as the solubility of Sn in the activating solution is increases. Comparing the results of the morphological observation before and after the initiation of the deposition, it should be concluded that the aggregates produced during the activation step play the starting point of the massive nodular grains that exist on the surface of deposits.
The effects of halide anions on the crystal growth, deposition mechanism and internal stress in copper deposits during electroplating from an acid copper sulfate bath were investigated. The cross-section morphology of deposits was observed using a scanning electron microscope, and the internal stress was in-situ measured using a copper electrode with a resistance-wire type strain gauge setup on its reverse side. The strength of internal tensile stress in a copper deposit of 5μm thick was in the order of F− > no additive > Cl− > Br− > I− in the additive concentration of 50ppm. This order was compared with solubility products of cuprous halide in the plating solution. In particular, chloride ions added in a concentration range of 0 to 200ppm were inclined to make the copper deposits promote epitaxial growth to the crystal orientation of copper substrate, and the internal tensile stress decreased along with an increase in the concentration of chloride ions. Howerver, addition of chloride ions in excess of the solubility products of cuprous chloride always resulted in the precipitation of cuprous chloride onto the copper electrode. Cuprous chloride might bring about the remarkable suppression of cathodic current for copper deposition.
Electrodeposition of Fe-Ni alloys was conducted galvanostatically in sulfate baths of pH 1-3 at 40ºC to investigate their codeposition mechanism. The results obtained are described as follows : (1) The electrodeposition behavior of Fe-Ni alloy showed a typical feature of anomalous codepostion, in which electrochemically less noble Fe deposits preferentially under most plating conditions. This anomalous codepostion was caused by the suppression of Ni deposition due to codeposition of Fe. (2) The anomalous codeposition was evidently dependent on the pH buffer capacity of the baths, which can be explained in terms of the preferential adsorption of FeOH on the deposition sites due to different dissociation constants between FeOH+ and NiOH+ in the multi-step reduction process of hydrated iron-group metal ions. (3) The degree of the preferential deposition of less noble Fe was decreased under the plating conditions to decrease the adsorption of FeOH on the cathode. (4) The pH titration curves were measured in an Fe2+ single bath using NaOH solution. The Fe2+ -single bath showed pH buffering action around pH 6.3, which corresponds to FeOH+ formation in the titration curve calculated from the dissociation constant of FeOH+.
The present study was carried out to fix the silane coupling agent on Zn-Ni-SiO2 composite coatings for the purpose of the development of an alternative process for chromating. The corrosion resistance of Zn-Ni-SiO2 composite coatings was remarkably improved in terms of the silica nanoparticles which uniformly dispersed in the film. Furthermore, silane coupling agents will form chemical bonds with inorganic silica particles by silane coupling treatment for these composite coatings, and suppress the formation of white corrosion products as well as the chromating in salt spray tests.