Tribologically-driven steady-state hydrogen evolution from mild steel by electrochemical extraction technique

Abstract

tlydrogen in material can give rise to many detrimental effects such as hydrogen embrittlement in service, tq Therefore, the study of reducing hydrogen content in material to less than a safe limit is of great importance in technology. Recently, accelerated hydrogen evolution from bearing steel during the wear process and tribologically-driven hydrogen uptake were reported by using a mass spectrometric method, t21 Baek et al. [31 have also shown wear-enhanced hydrogen evolution by an electrochemical extraction technique using a potentiostat and proposed a model for wear-enhanced hydrogen evolution. However, the proposed model t31 is still in the dark to be fully applicable to hydrogen evolution after the initial period of wear process. Considering this aspect, there is a need for additional work on a more reliable analysis. Therefore, it seems appropriate in the present work (1) to investigate the effects of lattice defects generated due to wear process on tribologically-driven hydrogen evolution from the transient analysis of the hydrogen permeation; (2) to distinguish the model governing the tribologically-driven hydrogen evolution in the later stage of wear process from that in the early stage. The chemical composition and the hardness value of pin and disc specimens used in the wear experiments are given in Table I. The pin specimens in the wear test were cylindrical rods of 3 cm length, 0.8 cm diameter with flat ends of 0.50 cm 2 area. The disc specimens for both hydrogen extraction and permeation were cylindricalshaped of 0.08 cm thickness and 2.4 cm diameter. Before the wear tests, the surface of both specimens was polished using 1000 grit emery paper and then ultrasonically cleaned in acetone for 10 minutes. Hydrogen was introduced into the disc specimens for extraction runs by cathodic charging at a current density of 5 m A / c m z in a 4 vol pet H z S O 4 aqueous solution containing 100 mg mszO3/1 as a hydrogen recombination son [41 ,,-,_ poi. . ~ ne hydrogen charging time was 4 hours, which yielded an initial hydrogen concentration, Co, of 2.49 • 10 -.5 m o l / c m 3 Fe in the specimen. The wear experiments were conducted at room temperature (298 K) in dry air using a pin-on-disc wear machine. The sliding time was taken as a wear test variable under an applied load of 9.8 N and a sliding velocity of 0.193 m/s . The increase of surface temperature due to the wear process was measured with a chromel-alumel