Microstructures and mechanisms of phosphorous incorporation into electrodeposited Ni-P thin films are studied using X-ray diffraction ͑XRD͒ and electron probe microanalyzer ͑EPMA͒. An atomic pair distribution function calculated from the XRD pattern exhibits the nearest neighbor distance of 2.5 Å 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.

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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 ͑AFM͒. The growth exhibits scaling behaviors characterized by the roughness exponent ␣ and growth exponent ␤. The analysis of the AFM images of the nickel thin films reveals that ͑i͒ for direct current electrodeposition: ␣ ϭ 0.96 and ␤ ϭ 0.78, and ͑ii͒ for pulse current electrodeposition: ␣ ϭ 0.92 and ␤ ϭ 0.65. Each value of ␣ 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 ␤ Ͼ 1/2.

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Electrochemical hydrogen permeation tests of pure Fe sheets rusted by cyclic corrosion test (CCT) and atmospheric exposure were carried out under controlled temperature and humidity to investigate the influence of atmospheric corrosion on the hydrogen entry behavior. The hydrogen entry into the Fe specimens rusted by CCT increased under wet condition, and the hydrogen entry was increased with the CCT cycle number. During drying process after the wetting, hydrogen entry was further enhanced and a peak of hydrogen current was observed. The peak hydrogen permeation current tended to increase with the growth of rust layer, and the peak value of the hydrogen permeation current became remarkably higher than that at the highest humidity when the rust layer was relatively thick. Similar enhancement of hydrogen entry into an outdoor-exposed specimen was also observed during drying. Drying process after CCT resulted in an increase in hydrogen content of 5 mm-thick steel specimens measured by means of thermal desorption analysis, indicating the enhancement of hydrogen entry during drying process and showing a good agreement with the electrochemical hydrogen permeation test results. It is required to take into consideration the enhanced hydrogen entry to estimate concentration of hydrogen from the environment.