Surface vs diffusion in TDS of hydrogen

Abstract

The paper addresses the numerical simulation of conditions in which the measurement of thermal desorption spectra of hydrogen (TDS) is carried out. Plane steel samples of 10 mm thickness were used as the specimens for simulation. The skin effect which is observed with standard hydrogen charging of samples was accounted for the initial conditions. The standard diffusion of hydrogen was simulated according to Fick’s law. Solution of the Fick’s equation is obtained by finite element methods using the developed code. The resulting solutions show that standard hydrogen charging can lead to the appearance of an additional TDS peak, even without taking into account the traps. New interpretation of the TDS method for hydrogen dissolved in a solid was suggested.

Application of micropolar theory to the description of the skin effect due to hydrogen saturation

“…Consider a long circular cylindrical specimen of radius r 0 and length L in a cylindrical coordinate system (r, ϕ, z). Assume that distributed couples n • M| r=r 0 = M 0 (10) or microrotations θ| r=r 0 = θ 0 (11) are prescribed on the boundary. Here, n is the outward normal to the lateral surface.…”

“…It gives correct results only inside the body, while in the vicinity of the border the given solution should be clarified by a boundary-layer type solution. A zero classical boundary condition (equation ( 12)) leads to zero classical solution, whereas nonclassical boundary conditions (equations (10) or ( 11)) lead to displacements and microrotations in the vicinity of the border.…”

“…One of the remaining boundary conditions (equation (10) or equation (11)) must be used to find the integration constants K and A. In the case of a static boundary condition, the solution takes the form…”

“…A uniform distribution of hydrogen can be obtained only after 500 h, which is several times larger than the standard average duration of the experiment. Standard hydrogen saturation of specimens in an electrolyte also results in an extremely nonuniform distribution of hydrogen across the specimen [5, 9, 10]. In fact, what is saturated, in both methods, is only a thin layer in the vicinity of the surface.…”

Physical Modeling of Steel Resistance to Hydrogen Embrittlement

“…Mainly aqueous solutions of salts, hydrochloric, sulfuric, and other acids with or without various stimulants are used as charging media. A distinctive feature of this method is the «skin effect» of surface layers [2][3][4]. The greatest efficiency is shown by the change in the electric current and duration of the experiment, as well as the use of notched samples, as any angle of the cathode accelerated absorbs hydrogen due to the increased concentration of the electric field in it [5,6].…”