Electrochemical Hydrogen Charging Research Articles

Zirconium hydrides and their effect on the circumferential mechanical properties of Zr–Sn–Fe–Nb tubes

The characteristics of zirconium hydrides formed by the electrochemical hydrogen charging method and their effect on the mechanical properties of Zr–Sn–Fe–Nb tubes were investigated. The hydrides were observed to be mostly circumferentially oriented and were identified as ϵ-ZrH2 and γ-ZrH phases by X-ray diffraction. The distribution of hydrides was found to become more homogeneous when the cooling rate was higher from 400°C. The room temperature strength of Zr–Sn–Fe–Nb tubes increased slightly and the ductility decreased with the formation of the hydrides. The mechanical properties were slightly modified by the size and distribution of hydrides. Secondary cracks along the platelets of hydrides were observed on the fracture surfaces of tubes. The slight loss of ductility in the presence of circumferential hydrides is thought to be associated with the secondary cracking during the final process of the fracture.

Effects of electrochemical hydrogen charging on lead-based relaxor ferroelectric multilayer ceramic capacitors

Lead-based relaxor ferroelectric multilayer ceramic capacitors (MLC's) were placed in 0.05 M NaOH solution to evolve hydrogen on their silver termination electrode by electrolysis of water. After this treatment, the MLC's failed as their insulation resistance was greatly decreased, their dielectric loss was considerably increased, and their capacitance was obviously decreased. By annealing in air at 650 °C for 30 min, the properties of the MLC's were restored. It is proposed that electrochemically generated hydrogen atoms can diffuse into the ceramic body of MLC's and undergo reduction to it, which may be one of the reasons for the negative influence of electroplating on lead-based relaxor ferroelectric MLC's.

Effect of Hydrogen on Surface of Niobium

ABSTRACTNiobium single crystals are used as substrate material for constructing superconducting quantum interference device or SQUID. The use of niobium is prompted by the fact that it is a low Tc metallic superconductor. In order to fabricate the device the surface of the crystal has to be polished flat. This is achieved by combination of mechanical polishing and electrochemical polishing. It has been reported that during electrochemical polishing hydrogen can enter the material forming Niobium hydrides. These can result in surface roughening of a magnitude greater than the thickness of the films subsequently deposited. This leads to failure of the films. The problem can be solved by annealing the material at 300° C to remove any hydrogen that might be present. However it is phenomenologically interesting to study the effect of electrochemical hydrogen charging on the surface of Niobium.

Effect of cathodic hydrogen charging on the surface of duplex stainless steel

The effect of cathodic hydrogen charging on the mechanical properties of steels has been extensively investigated. There is a general agreement, that cathodic charging during a tensile test leads to reduction in ductility, and embrittlement. The effects of cathodic charging on the surface of metals also have been reported in the literature. Electrochemical hydrogen charging of austenitic stainless steels has been shown to result in surface cracks even without externally applied strain/stress. So far no quantitative analysis of the surface strains has been reported. The aim of this investigation is to study the effect of cathodic charging on the surface of duplex stainless steel and to estimate the plastic deformation of the surface layer using computer simulation.

Acoustic emission from a palladium electrode during hydrogen charging and its release in a LiOH electrolyte

Acoustic emission (EA) from a palladium electrode dipped in a 0.1 M LiOH electrolyte was measured during electrochemical hydrogen charging and its release. Large AE signals were observed for a few minutes in the first stage of the hydrogen charging in contrast with the small random AE signals caused by the evolution of hydrogen and oxygen gas. These signals appear to reflect the deformation of the Pd lattice by hydrogen charging. Various types of periodic AE signals were also observed during hydrogen charging and hydrogen release after charging for long periods. It is believed that these phenomena are associated with the hydrogen-transfer mechanism through defects existing in the palladium.

The influence of palladium on the hydrogen-assisted cracking resistance of PH 13-8 Mo stainless steel

We compare the hydrogen-assisted cracking resistance of wrought PH 13-8 Mo stainless steel alloyed with 0.4 to 1.0 wt pct palladium to the conventional alloy when aged to yield strengths of 1170 to 1250 MPa. Intergranular hydrogen cracking is suppressed with Pd in both static load and constant extension rate tests conducted with electrochemical hydrogen charging. These results are analyzed to elucidate the role of Pd in suppressing intergranular cracking. Palladium is found both in substitutional solid solution in the martensitic phase and also in the form of randomly distributed PdAl precipitates in all Pd-modified alloys. Interfacial segregation of Pd to grain boundaries and lath boundaries is not observed at any levels above a detection limit of approximately 0.5 monolayers. Hydrogen permeation analyses indicate that hydrogen ingress is not inhibited by Pd but that apparent diffusion coefficients are lowered relative to the conventional alloy. Lower diffusion coefficients are consistent with the creation of a strong but reversible hydrogen trap, identified as the uniformly distributed PdAl phase. We hypothesize that PdAl trap sites force a redistribution of trapped hydrogen, which lowers the amount of interfacially segregated hydrogen at prior austenite grain boundaries for the electrochemical conditions applied. These assertions are supported by a simplistic trapping model for PH 13-8 Mo which shows that both the hydrogen trap binding energy and the trap density for the PdAl trapping site are greater than the hydrogen trap binding energy and density for prior austenite grain boundaries.

Colouration of oxidized niobium surfaces by electrochemical hydrogen charging

The colouration of oxidized niobium surfaces by electrochemical hydrogen charging was studied. Oxide films were formed on niobium sheet specimens by two different methods: anodic oxidation in an NaF-H2SO4 solution and oxidation in air at 773 K. Nb2O5 was formed with monoclinic and pseudohexagonal structures for anodic and air oxidation respectively. Both oxide films showed a colour change from white to dark blue on cathodic polarization in an H2SO4 solution. To complete the colouration by cathodic charging, a constant amount of electrical charge was needed irrespective of the current density. The response of the colour change was faster for the anodically oxidized surface than for the air oxidized surface. Charging with deuterium produced a similar colour change as for hydrogen charging, but the response was slower than for hydrogen.

Colouration of oxidized niobium surfaces by electrochemical hydrogen charging

The colouration of oxidized niobium surfaces by electrochemical hydrogen charging was studied. Oxide films were formed on niobium sheet specimens by two different methods: anodic oxidation in an NaF-H 2 SO 4 solution and oxidation in air at 773 K. Nb 2 O 5 was formed with monoclinic and pseudohexagonal structures for anodic and air oxidation respectively. Both oxide films showed a colour change from white to dark blue on cathodic polarization in an H 2 SO 4 solution. To complete the colouration by cathodic charging, a constant amount of electrical charge was needed irrespective of the current density. The response of the colour change was faster for the anodically oxidized surface than for the air oxidized surface. Charging with deuterium produced a similar colour change as for hydrogen charging, but the response was slower than for hydrogen.

Hydrogen permeation into aluminum alloy 1060 as a result of corrosion in alkaline medium. Basic features of the process

Unlike the usual electrochemical hydrogen charging, chemical evolution of hydrogen is described herein for the assessment of hydrogen permeation into a thin metal membrane during the chemical corrosion of aluminum alloy 1060 in alkaline medium. With appropriate surface treatment of the ionization side of the membrane, the results show that the hydrogen permeation rate attains a limiting value with increasing alkaline concentration, and varies with the reciprocal of the thickness of the membrane. The permeation constant, D(cm 2 s −1) has been evaluated and compared with available data. A mechanism for hydrogen permeation is proposed while the basic characteristics of the process are presented and discussed.

Hydrogen-induced microtwinning in ferritic stainless steels

Electrochemical hydrogen charging of thin foil specimens of ferritic stainless steels resulted in extensive microtwinning. Microtwins were plate- or needle-like on {110}-planes with a common 〈111〉 growth direction. Hydrogen-induced microtwinning was similar in both steels. Hydrogen embrittlement is expected to be related to hydrogen-induced microtwinning of the ferritic stainless steels.