Hydrogen Permeation Resistance Research Articles

Characteristic and behavior of an electrodeposited chromium (III) oxide/silicon carbide composite coating under hydrogen plasma environment

Hydrogen permeation barriers play a crucial role in reducing the risk of hydrogen permeation and radioactive leakage during the service of a fusion reactor. In this work, a chromium (III) oxide/silicon carbide (Cr2O3/SiC) composite coating was proposed to improve the hydrogen permeation resistance of ferronickel alloy. At first, the Cr/SiC composite coating was prepared by pulse electrodeposition in a trivalent chromium plating bath containing suspended SiC nanoparticles, and then oxidized it under 500 °C at a pressure of 100 Pa. The surface morphology, phase structure, surface chemical states, thickness, and the integrity of the composite coating were analyzed and compared. In particular, the effects of hydrogen permeation of the composite coatings were investigated. As a result, the composite coating showed huge potential in improving hydrogen permeation resistance, which provides a promising application for fusion reactors.

Preparation of Al2O3/Cr2O3 tritium permeation barrier with combination of pack cementation and sol–gel methods

In this paper, a layered Al2O3/Cr2O3 composite coating was prepared on the surface of super-clean reduced activation martensitic (SCRAM) steel by the combination of pack cementation and sol-gel methods as a tritium permeation barrier. First, the pack cementation processes was conducted at 980 °C for 30 min to form a chromed layer and then the sample was oxidized to form Cr2O3 layer at 760 °C for 2 h. Subsequently, the sol-gel method was conducted on the as-prepared Cr2O3 coating and Al2O3/Cr2O3 composite coating was finally prepared with subsequent thermochemical treatment. The results showed the first forming Cr2O3 coating was consisted of a 6 μm thick Cr2O3 exterior layer and a 2 μm thick interior diffusion layer due to inter-diffusion of Cr and Fe. The Al2O3/Cr2O3 composite coating was a three-layered structure with a total thickness of 10.5 μm. The outer layer was Al2O3, the middle layer was a mixing layer consisting of Al2O3 and Cr2O3, and the inner layer was a diffusion Cr,Fe layer. Well- crystallized α-Al2O3 formed in the coating at 960 °C which is below the formation temperature of α-Al2O3 resulting from the templet effect of isostructural Cr2O3. The hydrogen permeation test results revealed Al2O3/Cr2O3 composite coating exhibited a good barrier property against hydrogen penetration, thus the composite coating maybe a good choice to increase the hydrogen permeation resistance of SCRAM steel.

Influence of the selective layer morphology on the permeation properties for Pd-PSS composite membranes prepared by electroless pore-plating: Experimental and modeling study

Abstract This work analyzes the relationship between hydrogen permeation behavior and palladium layer morphology, particularly taking into account the palladium introduction into the pores for composite membranes prepared by Electroless Pore-Plating (ELP-PP) over porous stainless steel supports. Fully dense membranes have been achieved with hydrogen permeances in the range 7 - 18 · 10 - 5 mol / m 2 s Pa 0.5 by varying the hydrazine concentration used for the palladium plating. Permeation measurements for pure gases and mixtures have been carried out at different conditions: pressure driving force, temperature and feed composition. Both morphology and permeation properties are clearly influenced by the concentration of hydrazine, used as reducing agent during the ELP-PP process. In this manner, higher hydrazine concentrations provoke the formation of thicker external palladium films and, consequently, the reduction of both external porosity and roughness. On the other side, lower hydrazine concentrations reduce the required amount of palladium to obtain a fully dense membrane. In the last case, however, part of palladium is introduced into the pores of the support in a huger extension. This fact, in turns, generates an additional hydrogen permeation resistance, which diminishes the permeation flux and introduces a threshold in the minimum trans-membrane pressure value required for a hydrogen permeate flux. A new mathematical model, based on the classical Sieverts’ law, is proposed to predict this particular behavior by including a new fitting parameter defined as the ratio of the gas-palladium surface in both retentate and permeate sides of the membrane. This new parameter has been denoted as η , achieving good accuracy between both predicted and experimental data when considering the gap in the trans-membrane pressure. Therefore, the presented model can be used in multiple cases to design and optimize membranes modules, whereas the retentate and permeate gas-palladium surface ratio will be different, as for instance in case of palladium is introduced partially into the pores of supports.

Effect of Hydrogen Exposure on Mechanical and Tribological Behavior of CrxN Coatings Deposited at Different Pressures on IN718.

In the current study, the properties of the CrxN coatings deposited on the Inconel 718 superalloy using direct current reactive magnetron sputtering are investigated. The influence of working pressure on the microstructure, mechanical, and tribological properties of the CrxN coatings before and after high-temperature hydrogen exposure is studied. The cross-sectional scanning electron micrographs indicate the columnar structure of the coatings, which changes from dense and compact columns to large columns with increasing working pressure. The Cr/N ratio increases from 1.4 to 1.9 with increasing working pressure from 300 to 900 mPa, respectively. X-ray diffraction analysis reveals a change from mixed hcp-Cr2N and fcc-CrN structure to approximately stoichiometric Cr2N phase. After gas-phase hydrogenation, the coating deposited at 300 mPa exhibits the lowest hydrogen absorption at 600 °C of all investigated coatings. The results indicate that the dense mixed cubic and hexagonal structure is preferential for hydrogen permeation resistance due to the presence of cubic phase with higher packing density in comparison to the hexagonal structure. After hydrogenation, no changes in phase composition were observed; however, a small amount of hydrogen is accumulated in the coatings. An increase of coating hardness and elastic modulus was observed after hydrogen exposure. Tribological tests reveal that hydrogenation leads to a decrease of the friction coefficient up to 20%–30%. The best value of 0.25 was reached for hydrogen exposed CrxN coating deposited at 300 mPa.

Hydrogen permeation behavior and mechanism of Cr2O3/Al2O3 bipolar oxide film under plasma discharging environment

To improve the thermal stability between aluminide and stainless steel substrate and obtain thermodynamically stable phase of alpha-Al2O3, a new Cr2O3/Al2O3 bipolar oxide barrier was proposed, in which metallic Al was sputtered on the preoxidation coating of electroplated chromium and then oxidizing by oxygen plasma. It was found that Cr2O3 film exhibits P-type semiconducting properties while Al2O3 acts as N-type. Hydrogen discharging plasma was used to simulate the in-pile hydrogen permeation. Raman spectra and atomic force microscopy (AFM) were employed to analyze phase structure and surface morphology. Electrochemical impedance spectroscopy and Mott–Schottky were utilized to qualitatively evaluate effective thickness and the integrity for the oxide film. The depth profile and surface chemical states of involving elements were analyzed by auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS), respectively. The result shows that Cr2O3/Al2O3 bipolar oxides have improved hydrogen permeation resistance and would be a potential candidate for barrier application.

Communication—Hydrogen Permeation Resistance of Nickel Coating Enhanced by Adding the Rare Earth Element Ce

Due to the concentration of high density of trapping sites such as dislocations and vacancies, special grain boundaries (GBs) can be considered as the potential zone for trapping hydrogen, resulting into the slowdown of hydrogen diffusion in materials. A new approach was proposed that the rare earth element Ce was added into the electrodeposition of Ni to enhance the resistance of coating against hydrogen diffusion, which could be attributed to the decrease of grain size and the increased fraction of special boundaries in deposits.

Preparation of tritium permeation barrier consisting of titanium by the pack cementation method

Abstract In this work, tritium permeation barriers were prepared on the surface of super-clean reduced activation martensitic (SCRAM) steel by the pack cementation method. The pack cementation process was conducted by packing samples in a powder mixture consisting of titanium, ammonium chloride and alumina powder at 1000 °C for 30 min to form a titanized coating. Subsequently, the samples were nitrided in an ammonium atmosphere and then oxidized in air at 760 °C for 1 h to obtain a multilayered structure. The results showed that the as-prepared titanized coatings consisted of two layers. The exterior layer was made of TiN and the interior layer was a diffusion layer resulting from titanium atoms diffusing into the substrate. After being nitrided and then oxidized, the coatings were discovered to have transformed into a three-layered structure. The outer layer was rutile TiO2, the middle layer was Ti-N and the inner layer was Ti-C. Hydrogen permeation tests were performed on the coatings and pure matrix steels at room temperature. The results revealed that the three-layered structure coatings exhibited good barrier properties against hydrogen penetration. This three-layered structure coating may be a good material to increase the hydrogen permeation resistance of SCRAM steel.

Hydrogen permeation resistance and characterization of Si–Al and Si–Zr composite sol oxide coating on surface of zirconium hydride

The hydrogen permeation resistance of Si–Zr (SZ) and Si–Al (SA) composite sol oxide coating on zirconium hydride blocks (ZrH1.8) was studied. SZ and SA composite sol were prepared by sol–gel method. SZ and SA composite oxide coatings were prepared on the surface of ZrH1.8 (in situ oxidized or not) in turns by dip-coating and heat treatment. Hydrogen permeation of ZrH1.8 with and without composite oxide coating was compared. Hydrogen desorption experiments in thermal vacuum show that hydrogen permeation resistance of SA composite oxide coating is better than that of SZ, to a certain extent, which could decrease hydrogen thermal loss. Experimental results in the working condition show that the SA composite oxide coating can not only prevent hydrogen permeation, but also retard contact and reaction between CO2 and ZrH1.8 matrix, which could mitigate excessive oxidation of in situ oxide film. Differential scanning calorimetry and thermogravimetry (DSC–TG) analysis was performed to investigate the decomposition behavior of SA and SZ liquid sol in heat treatment process. X-ray diffraction (XRD) and scanning electron microscopy (SEM) analysis were employed to characterize the phase composition, surface and cross-section morphology of the coatings.

Development of Enameling Steel Sheet Used for Heat-Exchanger

The chemical composition and production process of a new kind of enameling steel sheet used for heat-exchanger were introduced. The microstructure, mechanical property and hydrogen permeation resistance of the steel sheet were studied. The enameling adherence and pin-hole ratio of the enameled steel sheet were measured. The results show that the microstructure is ferrite with the grain size of grade 11 and quantities of linear MnS inclusions, grainy manganese-niobium composite oxides and small NbC precipitates are formed in the steel. The average value of hydrogen permeation resistance of the steel is 33 min·mm-2, the enameling adherence is evaluated as level A1and the number of the pin-hole defects in the enameled steel is less than 10 per square meter. Both mechanical property and enameling quality of the steel sheet meet the technical demand of heat-exchanger.

Study of <EM>α</EM>-Al<SUB>2</SUB>O<SUB>3</SUB> about Hydrogen Permeation Resistance and Micromechanism

Study of <EM>α</EM>-Al<SUB>2</SUB>O<SUB>3</SUB> about Hydrogen Permeation Resistance and Micromechanism

Characterization of Coatings for Hydrogen Permeation Resistance

Extended abstract of a paper presented at Microscopy and Microanalysis 2004 in Savannah, Georgia, USA, August 1–5, 2004.

Comparison of Mechanical, Corrosion, and Hydrogen Permeation Properties of Electroless Ni-Zn-P Alloys with Electrolytic Zn-Ni and Cd Coatings

Abstract Novel Ni-Zn-P alloys containing 74 wt% Ni was prepared from a sulfate electrolyte using an electroless process. The mechanical, corrosion, and hydrogen permeation resistance characteristics of the developed Ni-Zn-P alloys were studied and compared with those of electrodeposited Cd and Zn-Ni coatings. Comparison of the mechanical properties shows that the developed alloy possesses engineering attributes comparable to those of Cd coatings. Corrosion studies in a 0.5-M sodium sulfate (Na2SO4) + 0.5-M boric acid (H3BO3) solution at pH 7.0 reveals that the dissolution rate of Ni-Zn-P alloys is five times lower than that of Zn-Ni and Cd coatings. In addition to the corrosion and engineering properties, comparison of the hydrogen permeation characteristics of the developed coating was made with that of Cd and Zn-Ni coatings. The exchange current density, i0; thickness dependent adsorption-absorption rate constant, k″; recombination rate constant, k3; and the surface hydrogen coverage, θs, that character...

Hydrogen permeation resistance of plasma-sprayed Al 2O 3 and Al 2O 3–13wt.% TiO 2 ceramic coatings on austenitic stainless steel

Al 2O 3 and Al 2O 3–13wt.% TiO 2 ceramic coatings were prepared on 21Cr–6Ni–9Mn austenitic stainless steel substrates by plasma spraying. The phase contents and microstructures of the plasma-sprayed coatings were investigated by means of X-ray diffraction (XRD), electron probe microanalysis (EPMA) and scanning electron microscopy (SEM). Also, the hydrogen permeation resistance was measured by thermal hydrogen charging. The results showed that plasma-sprayed Al 2O 3 and Al 2O 3–13wt.% TiO 2 ceramic coatings can improve the hydrogen permeation resistance of 21Cr–6Ni–9Mn austenitic stainless steel effectively, and the hydrogen resistance efficiency of Al 2O 3 coating was higher than that of Al 2O 3–13wt.% TiO 2 coating. Al 2O 3 coating displayed a denser structure than Al 2O 3–13wt.% TiO 2 coating. The phase contents analysis revealed that the presence of the Ni(Cr, Fe, Ti) 2O 4 phase in the Al 2O 3–13wt.% TiO 2 coating in addition to γ-Al 2O 3 and α-Al 2O 3. It was found that the bonding between the plasma-sprayed ceramic coatings and austenitic stainless steel substrates was mechanical rather than metallurgical.

Effects of laser surface remelting on hydrogen permeation resistance of thermally-sprayed pure aluminum coatings

The effects of laser surface remelting on the microstructure and hydrogen permeation resistance of thermally-sprayed aluminum coatings on the surface of austenitic stainless steel have been investigated by means of XRD, SEM and thermal hydrogen charging. The results show that the residual porosity is eliminated and the phases are mainly AlFe(Ni, Cr) and CrFeNi. A metallurgical bond between the coatings and the base metal was formed after laser surface remelting. Also, laser surface remelting can improve the hydrogen permeation resistance of thermally-sprayed pure aluminum coatings to a certain extent.

A study of hydrogen permeation in aluminum alloy treated by various oxidation processes

A set of oxide coatings was formed on the surface of an Al alloy (wt%: Fe, 0.24; Si, 1.16; Cu, 0.05–0.2; Zn, 0.1; Al, residual) by means of various oxidation processes. The hydrogen permeability through the aluminum alloy and its coating materials was determined by a vapor phase permeation technique at temperatures ranging from 400 to 500°C using high-purity H 2 (99.9999%) gas with an upstream hydrogen pressure of 10 4−10 5 Pa. The experimental results show that the hydrogen permeability through aluminum oxide coating is 100–2000 times lower than that through the aluminum alloy substrate. This means that the aluminum oxide is a significant hydrogen permeation barrier. A high hydrogen permeation resistance was observed in an oxide layer prefilmed in 200°C water, while an anodized aluminum oxide film had a less obstructive effect, possibly caused by the porous structure of the anodic oxide. The hydrogen permeability through films of aluminum oxide was not a simple function of the aluminum-oxide phase configuration.