Hydrogen Absorption during Electrodeposition and Hydrogen Charging of Sn and Cd Coatings on Iron

The effectiveness of deposits for decreasing hydrogen absorption by the substrate is discussed in terms of a surface or "catalytic" effect and the well‐known barrier effect. Data are presented on the extent of hydrogen absorption during electrodeposition of Sn or Cd onto an Fe substrate, and, subsequently during electrolytic hydrogen charging of the Sn or Cd‐coated Fe membrane. They show that the catalytic effect is in the unfavorable direction of increasing absorption; on the other hand, this behavior favors a decrease in corrosion of any exposed iron at the base of pores and cracks. Hydrogen absorption is significantly reduced due to the barrier effect by both Sn and Cd in proportion to their thickness at ⪞ 1 μm, with Sn being more effective than Cd. Thus, both coatings can be expected to be effective in reducing hydrogen embrittlement of steels. The effective diffusivity of hydrogen at 298 K (25°C) in both the Sn and Cd electrodeposits is ⪝ 10 −10 cm 2 sec −1 . The bilayer, rather than single, membrane technique is needed to measure the diffusivity of hydrogen in these and other metals for which the permeability is very low in order to reduce the time of the measurement.