Numerical modeling of thermal desorption mass spectroscopy (TDS) for the study of hydrogen diffusion and trapping interactions in metals

Abstract

International audienceDeriving the kinetic reaction constants associated with hydrogen diffusion and trapping in metals from thermal desorption mass spectroscopy (TDS) spectra proves to be complicated and the existing analysis methods are subject to debate. This article will provide a brief background of several commonly employed analysis techniques and discuss the necessity of a more complex and rigorous analysis method for the determination of the kinetic constants associated with hydrogen trapping interactions. Furthermore, a numerical simulation method will be proposed using the McNabb & Foster equations to fit experimental TDS spectra in order to derive both diffusion and trapping/detrapping parameters, including the respective pre-exponential constants and activation energies associated with these interactions in metals

A generalised model of hydrogen diffusion in metals with multiple trap types

“…[13][14][15]33,37,42,44,50,52,[57][58][59][60][61]). Thermal desorption analyses and permeation measurements have been the usual sources of experimental data used to identify the required characteristics [13][14][15]33,44,52,57,58]. In general, simulation of the performed experiments with the definite diffusion-trapping model and adjusting the predictions to the measurements has been the way of obtaining diffusion and trapping parameters from experimental data.…”

“…In general, simulation of the performed experiments with the definite diffusion-trapping model and adjusting the predictions to the measurements has been the way of obtaining diffusion and trapping parameters from experimental data. Following this route, a series of simplifications have frequently been adopted to bypass or reduce the difficulty of the direct solution of particular diffusion-trapping equations, thereby downgrading the original modelling frameworks to different degrees [33,44,57,58]. Among the available approaches, the simpler ones are limited to applying the thermal analysis techniques, relying only on the kinetics of the diffuser escape from traps during specimen heating and neglecting diffusion through a specimen [33,44].…”

“…Among the available approaches, the simpler ones are limited to applying the thermal analysis techniques, relying only on the kinetics of the diffuser escape from traps during specimen heating and neglecting diffusion through a specimen [33,44]. On the other side, more or less sophisticated procedures [14,15,42,52,57,58] have been designed that consist in fitting the theoretical predictions of a definite diffusion-trapping model with the results of specialised (de)hydrogenation or permeation experiments by means of optimising a set of model parameters using different methods such as the classical least squares fit or heuristics. In these methodologies, the process of solving the governing diffusion-trapping equation(s) is the only model-specific element, and these procedures can straightforwardly be adopted to evaluate the set of parameters for any given model.…”

“…In addition, this approach can produce inconsistent or inconclusive results because of lack of solution uniqueness proofs. Consequently, such procedures require validation processes [57,58] combining a sensitivity assessment, complementary tests and their simulations using an obtained set of candidate parameter values. Regardless, caution should be used when performing experiments and data treatment to comply with specific validity requirements of a particular model that will be used to extract the desired parameters from raw data.…”

Role of grain boundaries in the diffusion of hydrogen in nickel base alloy 600: Study coupling thermal desorption mass spectroscopy with numerical simulation

“…These results will then be analyzed using the numerical simulation of Fick's second law of diffusion, Eq. 1, and spectral fitting approach described in a previous article [29]. Using this coupled experimental and numerical approach the deuterium diffusion coefficient in A600 was determined and the role grain boundaries may play in the H diffusion phenomenon in this specific material is addressed.…”