Convection-Dependent Hydrogen Permeation into a Carbon Steel Sheet

Experimental A carbon steel sheet of 0.015 wt% and thickness of 1 mm was used as a specimen. Both sides of each specimen sheet were ground and flattened until 0.05-0.80 mm by mechanical polishing finally using colloidal silica particles of 0.05 μm. The thickness variation of speci- men sheet was controlled within 5%. The back side was electroplated with a nickel layer of 0.5 μm in thickness by cathodic polarization at 0.1 A cm −2 in a Watt's bath (1 mol dm −3 NiSO4 + 0.2 mol dm −3 NiCl2 + 0.6 mol dm −3 H3BO3) at 323 K. Fig.1is a schematic diagram of a Devanathan-Stachurski cell used in this study. The specimen sheet was sandwiched between the two electrochemical cells made from acrylic glass with two O-rings and connected with two potentiostats as working electrodes. The front and back sides of the sample sheet served as hydrogen entry and exit electrodes, respectively. Each cell had a platinum counter electrode and an Ag/AgCl/saturated KCl reference electrode with a Luggin- Haber capillary. The electrolyte in both cells was pH 8.4 boric-borate buffer solution deaerated by bubbling pure Ar gas. The electrolyte in the hydrogen entry side cell was flowed by using a bimorph pump at a constant or sinusoidally pertubated volume flow rate in the range of 0.145-1.50 cm 3 s −1 , while the electrolyte in the cell for the hydrogen exit side was stagnant. During the potentiostatic polarization of entry and exit electrodes, currents flowing through both electrodes were recorded with the electrolyte flow rate using a PC controlled by a LabVIEW (National Instruments) program.