Small-polaron models for the hydrogen-concentration dependence of hydrogen diffusion in Nb

1982 ◽  
Vol 26 (12) ◽  
pp. 6455-6469 ◽  
Author(s):  
D. L. Tonks ◽  
R. N. Silver
Keyword(s):  
Concentration Dependence ◽  
Hydrogen Concentration ◽  
Hydrogen Diffusion ◽  
Small Polaron

Concentration Dependence of Hydrogen Diffusion in Hydrogenated Silicon

1998 ◽  
Vol 507 ◽  
Author(s):  
W. Beyer ◽  
U. Zastrow
Keyword(s):  
Diffusion Coefficient ◽  
Amorphous Silicon ◽  
Concentration Dependence ◽  
Hydrogen Concentration ◽  
Hydrogen Diffusion ◽  
Band Model ◽  
Hydrogenated Silicon ◽  
Trapping Model ◽  
Hydrogen Implantation ◽  
Amorphous Si

ABSTRACTThe concentration dependence of hydrogen diffusion was studied in hydrogenated crystalline and amorphous silicon prepared by hydrogen implantation into crystalline Si wafers and into amorphous silicon of low hydrogen concentration. The results are compared with data for plasma-grown a-Si:H and µc-Si:H films. The increase of the diffusion coefficient with rising hydrogen concentration in a-Si:H is explained by an (equilibrium) energy band model of hydrogen diffusion whereas the decrease of the diffusion coefficient in c-Si:H is explained by a trapping model. The different behavior is attributed to a greater flexibility of the amorphous Si network compared to the crystalline Si lattice which is also visible in a difference in hydrogen-related microstructure formation.

The Concentration Dependence of Hydrogen Diffusion in fcc TiHx, TiDxand YHx*

1992 ◽  
Vol 1 (1) ◽  
pp. 631-635
Author(s):  
U. Stuhr ◽  
D. Steinbinder ◽  
H. Wipf ◽  
B. Frick
Keyword(s):  
Concentration Dependence ◽  
Hydrogen Diffusion

Investigation of Hydrogen Diffusion Characteristics of the Heat Affected Zone of 2.25Cr-1Mo-0.25V Steel by an Electrochemical Permeation Method

2019 ◽  
Author(s):  
Xin Song ◽  
Zelin Han ◽  
Bin Liu ◽  
Mu Qin ◽  
Yuancai Duo ◽  
...  
Keyword(s):  
Grain Boundaries ◽  
Hydrogen Concentration ◽  
Heat Affected Zone ◽  
Hydrogen Diffusion ◽  
Trap Density ◽  
Hydrogen Diffusivity ◽  
Hydrogen Flux ◽  
Hydrogen Trap ◽  
Diffusion Characteristics ◽  
Effective Hydrogen

Abstract The heat affected zone (HAZ) of 2.25Cr-1Mo-0.25V welded joint is a critical part for the safety of hydrogenation reactors. Hydrogen has a significant effect on the HAZ, studying hydrogen diffusion characteristics, such as: hydrogen flux and the effective hydrogen diffusivity has a remarkable value in investigating the hydrogen-induced material degradation mechanisms. In this work, an electrochemical permeation method was applied to study the hydrogen diffusion characteristics of HAZ. Then, the metallographic microscope and a software “Image J” were used to analyze the density of grain boundaries of HAZ. The effect of the post–weld heat treatment (PWHT, i.e. annealing) on the hydrogen diffusion characteristics of HAZ was also been investigated. The results show that after PWHT, the effective hydrogen diffusivity of HAZ increases from 1.63 × 10−7cm2·s−1 to 3.68 × 10−7cm2·s−1, the hydrogen concentration decreases from 1.92 × 10−4mol·cm−3 to 1.09 × 10−4mol·cm−3, and the hydrogen trap density decreases from 3.00 × 1026m−3 to 0.76 × 1026m−3. Thus, PWHT can significantly reduce density of grain boundaries, thereby reducing the hydrogen trap density, enhancing the hydrogen diffusivity and reducing the hydrogen concentration.

Hydrogen Concentration Dependence of Bragg Wavelength of UV-Written Fiber Grating

1998 ◽  
Vol 15 (12) ◽  
pp. 886-888 ◽  
Author(s):  
Li-bin Fu ◽  
Gu Tan ◽  
Wan-jin Xu ◽  
Xiang-zhi Lin ◽  
Hong-du Liu
Keyword(s):  
Concentration Dependence ◽  
Hydrogen Concentration ◽  
Fiber Grating ◽  
Bragg Wavelength

Electron small polarons and their transport in bismuth vanadate: a first principles study

2015 ◽  
Vol 17 (1) ◽  
pp. 256-260 ◽  
Author(s):  
Kyoung E. Kweon ◽  
Gyeong S. Hwang ◽  
Jinhan Kim ◽  
Sungjin Kim ◽  
SeongMin Kim
Keyword(s):  
Concentration Dependence ◽  
Electron Mobility ◽  
First Principles ◽  
Density Functional Calculations ◽  
Density Functional ◽  
Small Polaron ◽  
Polaron Hopping ◽  
Polaron Formation ◽  
Hybrid Density Functional ◽  
Small Polarons

Hybrid density functional calculations demonstrate small polaron formation in electron-doped BiVO4, and predict the polaron hopping barrier to increase with lattice constant and also the possible concentration-dependence of electron mobility.

Electromagnetic Induction Post Heating to Reduce NDE Delay Times of Welding In-Service Repairs

2020 ◽  
Author(s):  
Liam Hagel ◽  
Jonathan Prescott ◽  
Alireza Kohandehghan ◽  
Stuart Guest ◽  
Sean Lepine
Keyword(s):  
Stress Concentration ◽  
Hydrogen Concentration ◽  
Induction Heating ◽  
Thermal Convection ◽  
Heat Affected Zone ◽  
Hydrogen Diffusion ◽  
Heat Removal ◽  
High Energy ◽  
Fillet Weld ◽  
Delay Times

Abstract When a pipeline requires a repair, a pressure-containing steel sleeve or an emergency repair fitting is often fillet welded to the in-service pipe to return the pipeline to normal service conditions. During welding, the flowing product rapidly quenches the fillet weld, promoting the formation of high hardness and low ductility microstructures in the heat-affected zone. The rapid cooling rates also limit the mobility of diffusible hydrogen introduced from the welding electrodes. The hydrogen can be trapped in the weld metal and heat-affected zone and concentrated in specific locations throughout the weld based on the welding deposition sequence. Fillet welds also contain inherent locations of geometric stress concentration at the weld toes and root locations. The elevated hydrogen concentration in the in-service weld, combined with the geometrical stress concentrations at the location of crack-susceptible microstructures, can increase the likelihood of forming a hydrogen-induced crack. Delayed non-destructive examination (NDE) is often employed to wait a sufficient time for any cracks to form so they can be detected. To reduce hydrogen concentration at the locations of stress concentration and NDE delay times, post-heating can be applied to the in-service weld. Elevating the temperature within the weld can enable hydrogen diffusion and reducing the cracking propensity. The rapid heat removal due to flowing product requires post-heating techniques with high energy outputs that will not overheat the steel surfaces. Electromagnetic induced current (induction heating) methods can produce sufficient thermal energy in the electrically conductive steel pipe and sleeve. Coupled numerical finite element analysis (FEA) models were utilized to simulate various induction cable arrangements and thermal convection coefficients, representative of various pipeline products. The analysis of the induction heating arrangements for the studied thermal convection coefficient was conducted to achieve a minimum temperature of 120 °C in the fillet weld root and toes to enable sufficient thermal driving force for hydrogen diffusion while ensuring the pipe and sleeve surface temperature does not exceed 200 °C. An optimal induction heating procedure was found to which could achieve the target temperatures within a reasonable heating time such that NDE delay times of in-service welds can be reduced by 5–6 times.

Diffusion of Hydrogen in Titanium-Vanadium Alloys

2005 ◽  
Vol 237-240 ◽  
pp. 340-345 ◽  
Author(s):  
Hans Jürgen Christ ◽  
S. Schroers ◽  
F.H.S. dos Santos
Keyword(s):  
Diffusion Coefficient ◽  
Titanium Alloys ◽  
Hydrogen Concentration ◽  
Hydrogen Diffusion ◽  
High Strength ◽  
Vanadium Concentration ◽  
Vanadium Alloys ◽  
High Hydrogen ◽  
Hydrogen Diffusion Coefficient ◽  
Diffusion Of Hydrogen

β–titanium alloys are very attractive materials for many applications because they combine low density, high strength and excellent corrosion resistance. The available data indicate a much higher hydrogen diffusion coefficient in β–titanium alloys as compared to α and α + β alloys. In order to predict the range of applicability of β–titanium alloys in environments, which release hydrogen, the hydrogen diffusion coefficient (DH) needs to be known quantitatively. In the framework of this study the value of DH was determinated on samples, which were electrochemically hydrogen charged. Long thin rods were used as samples and charged in such a way that high hydrogen concentrations were obtained in one half of the length of the specimens, while the other half was kept virtually unaffected. After charging, the rods were annealed enabling hydrogen to diffuse. Hydrogen concentration profiles were experimentally determined and evaluated on the basis of the Matano technique, in order to reveal any effect of concentration on DH. The experiments were carried out on β–titanium alloys of the binary Ti–V system. The concentration range of vanadium in the alloys studied was selected in such a way that it represents the compositions commonly found in commercial alloys. The results show that the effect of hydrogen concentration on DH is negligible and that DH increases with the vanadium concentration.

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