Wataru Oshikawa

Amorphous Structures and Kinetics of Phosphorous Incorporation in Electrodeposited Ni-P Thin Films

Microstructures and mechanisms of phosphorous incorporation into electrodeposited Ni-P thin films are studied using X-ray diffraction (XRD) and electron probe microanalyzer (EPMA). An atomic pair distribution function calculated from the XRD pattern exhibits the nearest neighbor distance of 2.5 A and a split double peak at the second neighbor distance that is observed in amorphous structures. The electrodeposited Ni-P alloy is found to have an amorphous structure similar to rapid-quenched Ni-P alloys. The phosphorous concentrations in the Ni-P deposits measured by EPMA decrease with an increase in current densities. The dependence of the phosphorous concentration on the current density is analyzed with respect to the kinetics of chemical reactions in Ni-P electrodeposition. The experimental result agrees well with a solution of rate equations that describe the indirect incorporation of phosphorous.

Surface Roughening in the Growth of Direct Current or Pulse Current Electrodeposited Nickel Thin Films

The surface roughening in the growth of direct current or pulse current electrodeposited nickel thin films at a low current density is investigated using atomic force microscopy (AFM). The growth exhibits scaling behaviors characterized by the roughness exponent a and growth exponent β. The analysis of the AFM images of the nickel thin films reveals that (i) for direct current electrodeposition: α = 0.96 and β = 0.78, and (ii) for pulse current electrodeposition: α = 0.92 and β = 0.65. Each value of α for the two techniques is almost in agreement with that predicted by a statistical model of linear diffusion dynamics. X-ray diffraction of the nickel thin films indicates the presence of preferred growth orientations that are related to the growth exponent β > 1/2.

Characterization of electrodeposited nickel film surfaces using atomic force microscopy

Abstract Microstructures of nickel surfaces electrodeposited on indium tin oxides coated glasses are investigated using atomic force microscopy. The fractal dimension D and Hurst exponent H of the nickel surface images are determined from a frequency analysis method proposed by Aguilar et al. [J. Microsc. 172 (1993) 233] and from Hurst rescaled range analysis. The two methods are found to give the same value of the fractal dimension D ∼2.0. The roughness exponent α and growth exponent β that characterize scaling behaviors of the surface growth in electrodeposition are calculated using the height-difference correlation function and interface width in Fourier space. The exponents of α ∼1.0 and β ∼0.8 show that the surface growth does not belong to the universality classes theoretically predicted by statistical growth models.

Evaluation of Corrosivity in Atmospheric Environment by ACM (Atmospheric Corrosion Monitor) Type Corrosion Sensor

An ACM (Atmospheric Corrosion Monitor) type corrosion sensor, consisting of a Fe-Ag galvanic couple was developed and applied for the evaluation of corrosivity of atmospheric environments. The sensor was designed considering mass-production and good reproducibility of results, making it convenient for long-term corrosion data acquisition. Besides the sensor output, I, temperature, relative humidity (RH) were also recorded by a microcomputer. By analyzing the magnitude and time variation of I, the occurrence and duration of rain, dew and dry periods, Train, Tdew and Tdry, respectively, could be distinguished and determined. And by referencing to the empirical I-RH calibrating curve, the amount of deposited sea salt, Ws, could also be estimated. It was also found that the corrosion loss could be estimated in both indoor and outdoor sites by analyzing sensor output. Corrosivities of some kinds of exposure sites, not only outdoor environments but also indoor environments, were evaluated by using the ACM sensor.

Novel process for electrodeposition of Bi2S3 thin films

Abstract A novel method for electrochemical deposition of Bi 2 S 3 from an aqueous acid bath comprising Na 2 S 2 O 3 and Bi(NO 3 ) 3 complexed with disodium salt of ethylene diamine tetraacetic acid (Na 2 EDTA) is proposed using SO 3 −2 ions as a sulfur source. For stoichiometric deposition, the initial concentrations of Na 2 S 2 O 3 and Bi(NO 3 ) 3 in the solution are determined from the experimental current–potential relations based on a current model under diffusion control. X-ray diffraction reveals that the deposits have no single substance and compound other than Bi 2 S 3 within experimental uncertainties. This indicates that the system in this study obeys the current model under diffusion control.

Surface Growth of Ni Thin Films Electrodeposited on Ni(100) Surfaces

Surface growth of Ni thin films electrodeposited on Ni(100) substrates has been investigated using atomic force microscopy. In the early stage of growth, islands nucleated on the Ni(100) substrates, which appear to be rectangular in cross section, grow laterally in the same crystallographic orientation. Growth surfaces display a normal scaling behavior characterized by the linear surface diffusion universality class. Along the time evolution, instability in growth occurs and a transition from two- to three-dimensional growth is observed. In this stage, surface growth obeys anomalous scaling characterized by a local roughness exponent ζ loc = 1.0, global scaling exponent ζ = 2.1, and dynamic exponent z = 1.0.

Anomalous dimension in pitting corrosion of SUS304 in a NaCl solution

The current–potential relations of SUS304 for a NaCl solution in water ranging from 0.01 to 2 mol/dm3 over a 298–333 K temperature range were investigated in order to exhibit the presence of anomalous dimensions that characterize the phase transition such as pitting corrosion. Using the anomalous dimension, all the experimental current points can be represented by a single curve in a reduced variable.

Fractal behavior of galvanic current of dual electrode type of atmospheric corrosion monitor

Eleven-month series of the galvanic current of dual electrode type devices exposed to the atmosphere are analyzed to make clear the fractal behavior of corrosion. The result indicates that a relation predicted by the scaling theory is strictly consistent with the experimental result and the fractal behavior of corrosion is insensitive to the local details.

Effect of Thickness of Water Film on Atmospheric Corrosion Behavior of Carbon Steel

Atmospheric corrosion for carbon steel was discussed with taking notice of the relation between the corrosion rate, CR, and the thickness of adsorbed water film, d, onto deposited sea salt. Amount of water adsorbed onto sea salt was measured under various conditions of amount of deposited sea salt, Ws, and relative humidity, RH. Derived concentration of the solution film was compared with that calculated thermodynamically. Corrosion amount of carbon steel specimens exposed for a month under various Ws and RH was measured and CR along with d were obtained for each condition. The relations of CR to d had the same tendency as is found on “moist corrosion” and “wet corrosion” in Tomashov’s model; However, it showed a maximum CR = 0.29mm/y at d = 56µm, thicker than that reported by Tomashov.