EFFECT OF TRAPS ON DIFFUSIVITY OF HYDROGEN IN 20g CLEAN STEEL

Abstract

Electrochemical permeation experiment is the most common method used in measuring hydrogen diffusivity.Because the effect of hydrogen traps has been ignored,there is a larger deviation between diffusion coefficients of hydrogen given by many investigators,especially at low temperatures.In order to study the effect of hydrogen traps on diffusion coefficient of hydrogen,the permeation current transients were measured by Devanathan-Stachurski cell for the three hydrogen trap states in 20g clean steel in this paper.The first trap state contains the inreversible and reversible hydrogen traps and exists in an original state of the sample.The second trap state contains only the reversible hydrogen traps and exists in the sample treated at 80℃for 3 h after electrochemical permeation experiment.However,the third trap state may not contain any hydrogen traps and exists in the untreated sample after the electrochemical permeation experiment.The electrochemical permeation experiment has been carried out at a constant charging current density(10mA/cm~2)in 0.2 mol/L NaOH solution at 30℃.The experimental results show that the diffusion of hydrogen in electrochemical hydrogen permeation can be described by a modified equation of diffusion flux versus time in ideal crystal.The modified equation proposed in this paper is(J_t)/(J_∞)=(?). The diffusion coefficient and penetration time of hydrogen during electrochemical hydrogen permeation can be obtained directly by using the modified equation to fit the experimental data with a least square method.The experimental results reveal that inreversible hydrogen traps have no effect on the diffusion coefficient of hydrogen,but extend its penetration time.It is also shown that reversible hydrogen traps reduce the diffusion coefficient of hydrogen in 20g clean steel.