Hydrogen permeation in plastically deformed steel membranes

We study the influence of plastic deformation on the electrochemical permeability of hydrogen. For this purpose, membrane specimens of FeE690T steel were deformed in the cold state by rolling or tension, and the diffusion of hydrogen in these specimens was measured by the classical Devanathan-Stachursky technique. The effective diffusion coefficients are determined according to the time dependences of the intensity of hydrogen flow from the back side of the membrane. They are characterized by the well-pronounced dependence on the level of strain. Moreover, the diffusion of hydrogen is simulated by taking into account the phenomenon of seizure of hydrogen atoms by traps formed in the presence of plastic strains. The linear diffusion equation is used to compute the time dependence of permeation of hydrogen for various densities of the traps. The effective coefficients of hydrogen diffusion are determined from the permeation curves. The accumulated results are in good agreement with the experimental data. Published in Fizyko-Khimichna Mekhanika Materialiv, Vol. 42, No. 1, pp. 77–81, January–February, 2006.     

氢化镁放氢动力学的研究

无烟煤经碱熔-酸洗-碳化处理后制得了微晶碳,以微晶碳及肥煤作助磨剂,在氢气气氛下机械球磨金属镁3h,制得储氢材料氢化镁。在等温条件下用体积法进行放氢测试,根据放氢数据用Arrhenius方程计算出的放氢活化能为104.85kJ/mol。在变温条件下用程序升温脱附法测得材料的TPD曲线,用Kissinger方程和Sharp方程分别对材料的活化能进行计算。Kissinger方程求得的活化能为105.87kJ/mol;当升温速率为5,10和15℃/min时,Sharp方程求得的活化能分别为108.33,98.70和113.19kJ/mol。等温法和非等温法均可用于放氢活化能的计算,由于公式、原理、采用数据等方面的不同,求得的活化能有差异。     

Hydrogen absorption and desorption characteristics of ferro-titanium alloys

Hydrogen absorption and desorption characteristics of commercially supplied ferrotitaniums with 41 to 51 at% Ti have been studied. The characteristics are similar to those of high purity FeTi although the ferro-titaniums include some impurities. The activation temperatures of the ferro-titaniums are slightly higher than that of the high purity FeTi. Plateaus in the hydrogen absorption and desorption curves are not obvious compared with those of high purity FeTi. It is concluded that the ferro-titaniums are good, low-cost hydrogen storage materials.     

Hydrogen transport by group 5 metals: Achieving the maximal flux density through a vanadium membrane

Hydrogen transport by 100-μm-thick vanadium and palladium membranes was studied in the pressure range from 1 × 10^?8 to 4.5 × 10^?1 MPa at a temperature of 400°C. Both sides of the vanadium membrane were covered by 2 μm of palladium (Pd-V-Pd) for facilitating the dissociative absorption and associative desorption of H₂ molecules. At low pressures, hydrogen flux densities through vanadium and palladium membranes are nearly the same; at high pressures, the flux through the vanadium membrane becomes 16 times larger than the flux through the palladium membrane and attains a value of 2.4 scc cm^?2 s^?1. This flux of permeating hydrogen is larger than all values ever observed earlier for membranes made of group 5 metals or any other unsupported metal membranes.     

Hydrogen permeation through deformed and heat-treated Armco pure iron

ABSTRACT

The goal of this study is to obtain a deeper insight in the relation between hydrogen diffusion and hydrogen traps present in Armco pure iron. Cold deformation was applied to this material, which initially contained a limited amount of traps. The cold deformation was applied to increase the dislocation density and modify grain boundary characteristics. In this way, the hydrogen diffusivity decreased as the hydrogen trapping ability of the microstructure increased. A subsequent heat treatment allowed changing the density of microstructural defects again and consequently increased the hydrogen diffusion coefficient. In addition, studying blister formation showed that a higher degree of deformation caused more surface blisters, while recovery lowered the number of blisters. Electron backscatter diffraction characterisation provided the necessary input on the microstructural features and their evolution. Analysis of these samples allowed evaluating the correlation between hydrogen diffusion, blister formation and microstructural defects.

This paper is part of a thematic issue on Hydrogen in Metallic Alloys     

Hydrogen accumulation in graphite and etching of graphite on hydrogen desorption

Studies of Atomic Hydrogen accumulation in highly oriented pyrolytical graphite (HOPG) have been performed using scanning tunnelling microscope (STM) and atomic force microscope (AFM). It is found that after intercalation atomic hydrogen is stored among graphene layers in H₂ gas form, captured inside graphene blisters. On desorption of hydrogen, some lateral etching of upper graphene layers takes place. Significant information about intake, retention and possibility of manifold accumulation of hydrogen in HOPG has been found.     

Hydrogen trapping in helium damaged metals: a theoretical approach

A model which explains the trapping of hydrogen around or near helium bubbles is presented. According to this model, hydrogen atoms are attracted toward the bubbles due to positive stresses created by the very high pressure (350 kbar) existing inside the bubbles. The extreme trapping energy of hydrogen atoms around helium bubbles has been theoretically calculated and found to be 0.71 eV atom^–1. It is shown that most of the hydrogen atoms are trapped in a very small volume located very close to the bubble surface. The total hydrogen quantity was found to be in the range of 45–76 atoms per bubble for a wide range of hydrogen atom concentration, C. The good agreement between the theoretical results and data based on many experimental measurements reinforces the assumptions underlying the very basis of the suggested mechanism. The model proposed in this study can lead to better understanding of failure mechanisms.     

Unified and generalized treatment of thermal desorption data

A unified treatment of formal mathematical relationships for thermal desorption from an energetically homogeneous surface is given for a wide class of heating regimes. The processing of experimental data is discussed.     

Hydrogen permeation behaviour and associated phase transformations in annealed AISI304 stainless steels

The effective diffusion coefficient and subsurface concentration of hydrogen in annealed AISI304 austenitic stainless steels have been measured by the electrochemical permeation method. The effects of different cathodic current densities on the effective diffusion coefficient, hydrogen concentration beneath the cathodic surface and steady state permeation current density have been studied. The value of the effective diffusion coefficient for the permeated specimens increases with increasing charging current density. The hydrogen subsurface concentration and steady state permeation current density first increase with increasing charging current density, then decrease with increasing current density. X-ray diffraction analyses were used to investigate the phase transformation during hydrogen charging. The results revealed that cathodic charging resulted in the formation of a considerable amount of ε and α′ martensites, which will increase with charging time.     

Self-oscillatory effects accompanying the field-induced desorption of alkali metals

Self-oscillatory effects were observed during continuous field-induced desorption of alkali metals (K, Cs) from a gold-coated tungsten surface. The substrate surface images in alkali metal ions, reflecting various stages of the desorption process, were obtained using a field-ion microscope.     

Hydrogen detection in metals: a review and introduction of a Kelvin probe approach

Abstract

Hydrogen in materials is an important topic for many research fields in materials science. Hence in the past quite a number of different techniques for determining the amount of hydrogen in materials and for measuring hydrogen permeation through them have been developed. Some of these methods have found widespread application. But for many problems the achievable sensitivity is usually not high enough and ready-to-use techniques providing also good spatial resolution, especially in the submicron range, are very limited, and mostly not suitable for widespread application. In this work this situation will be briefly reviewed and a novel scanning probe technique based method introduced.     

Competitive sorption and desorption of heavy metals by individual soil components

Knowledge of sorption and desorption of heavy metals by individual soil components should be useful for modelling the behaviour of soils of arbitrary composition when contaminated by heavy metals, and for designing amendments increasing the fixation of heavy metals by soils polluted by these species. In this study the competitive sorption and desorption of Cd, Cr, Cu, Ni, Pb and Zn by humified organic matter, Fe and Mn oxides, kaolinite, vermiculite and mica were investigated. Due to the homogeneity of the sorbents, between-metal competition for binding sites led to their preferences for one or another metal being much more manifest than in the case of whole soils. On the basis of k(d100) values (distribution coefficients calculated in sorption-desorption experiments in which the initial sorption solution contained 100mgL(-1) of each metal), kaolinite and mica preferentially sorbed and retained chromium; vermiculite, copper and zinc; HOM, Fe oxide and Mn oxide, lead (HOM and Mn oxide also sorbed and retained considerable amounts of copper). Mica only retained sorbed chromium, Fe oxide sorbed cadmium and lead, and kaolinite did not retain sorbed copper. The sorbents retaining the greatest proportions of sorbed metals were vermiculite and Mn oxide, but the ratios of k(d100) values for retention and sorption suggest that cations were least reversibly bound by Mn oxide, and most reversibly by vermiculite.