Isothermal hydrogen absorption process of Pd-capped Mg films traced by ion beam techniques and optical methods

Pd-capped nanocrystalline Mg films were prepared by electron beam evaporation and hydrogenated under isothermal conditions to inves-tigate the hydrogen absorption process via ion beam techniques and in situ optical methods.Films were characterized by different techniques such as X-ray diffraction(XRD)and scanning electron microscopy(SEM).Rutherford backscattering spectrometry(RBS)and elastic recoil detection analysis(ERDA)provided a detailed compositional depth profile of the films during hydrogenation.Gas-solid reaction kinetics theory applied to ERDA data revealed a H absorption mechanism controlled by H diffusion.This rate-limiting step was also confirmed by XRD measurements.The diffusion coefficient(D)was also determined via RBS and ERDA,with a value of(1.1±0.1)·10^(−13)cm^(2)/s at 140℃.Results confirm the validity of IBA to monitor the hydrogenation process and to extract the control mechanism of the process.The H kinetic information given by optical methods is strongly influenced by the optical absorption of the magnesium layer,revealing that thinner films are needed to extract further and reliable information from that technique.

Study on the hydrogen absorption properties of a YGdTbDyHo rare-earth high-entropy alloy

This study investigated the microstructure and hydrogen absorption properties of a rare-earth high-entropy alloy(HEA),YGdTbDyHo.Results indicated that the YGdTbDyHo alloy had a microstructure of equiaxed grains,with the alloy elements distributed homogeneously.Upon hydrogen absorption,the phase structure of the HEA changed from a solid solution with an hexagonal-close-packed(HCP)structure to a high-entropy hydride with an faced-centered-cubic(FCC)structure without any secondary phase precipitated.The alloy demonstrated a maximum hydrogen storage capacity of 2.33 H/M(hydrogen atom/metal atom)at 723 K,with an enthalpy change(ΔH)of-141.09 kJ·mol^(-1)and an entropy change(ΔS)of-119.14 J·mol^(-1)·K^(-1).The kinetic mechanism of hydrogen absorption was hydride nucleation and growth,with an apparent activation energy(E_(a))of 20.90 kJ·mol^(-1).Without any activation,the YGdTbDyHo alloy could absorb hydrogen quickly(180 s at 923 K)with nearly no incubation period observed.The reason for the obtained value of 2.33 H/M was that the hydrogen atoms occupied both tetrahedral and octahedral interstices.These results demonstrate the potential application of HEAs as a high-capacity hydrogen storage material with a large H/M ratio,which can be used in the deuterium storage field.

Hydrogen absorption characteristics and microstructural evolution of TC21 titanium alloy

The hydrogen absorption characteristics and microstructural evolution of TC21 titanium alloy were investigated by kinetic model analysis, optical microscopy （OM） and X-ray diffraction （XRD）. The results show that the hydrogen absorption reaction occurred during the hydrogen absorption process of TC21 titanium alloy can be divided into two different stages according to the hydrogen absorption kinetics. After hydrogenation, the microstructure of TC21 titanium alloy changes obviously. Just a little hydrogen will change the contrast of transformedβphase. The contrast ofα phase darkens when the hydrogen content in TC21 titanium alloy exceeds 0.5% （mass fraction）. The phase/grain boundaries become ambiguous or even vanished, andβ phase becomes the main phase instead ofα phase when the hydrogen content reaches 0.625%. Moreover,α phase disappears when the hydrogen content reaches 1.065%. Additionally, the XRD analysis shows that α＇ martensite and FCCδ hydride appear in the hydrogenated alloy. According to the microstructures and XRD analysis, the schematic diagrams of hydrogen diffusion process in TC21 titanium alloy were established.

Kinetics of the hydrogen absorption and desorption processes of hydrogen storage alloys: A review

High hydrogen absorption and desorption rates are two significant index parameters for the applications of hydrogen storage tanks.The analysis of the hydrogen absorption and desorption behavior using the isothermal kinetic models is an efficient way to investigate the kinetic mechanism.Multitudinous kinetic models have been developed to describe the kinetic process.However,these kinetic models were de-duced based on some assumptions and only appropriate for specific kinetic measurement methods and rate-controlling steps(RCSs),which sometimes lead to confusion during application.The kinetic analysis procedures using these kinetic models,as well as the key kinetic parameters,are unclear for many researchers who are unfamiliar with this field.These problems will prevent the kinetic models and their analysis methods from revealing the kinetic mechanism of hydrogen storage alloys.Thus,this review mainly focuses on the summarization of kinetic models based on different kinetic measurement methods and RCSs for the chemisorption,surface penetration,diffusion of hydrogen,nucleation and growth,and chemical reaction processes.The analysis procedures of kinetic experimental data are expounded,as well as the effects of temperature,hydrogen pressure,and particle radius.The applications of the kinetic models for different hydrogen storage alloys are also introduced.

Structure of Liquid Aluminum and Hydrogen Absorption

The hydrogen content in aluminum melts at different temperature was detected. The structure in aluminum melts was investigated by molecular dynamics simulation. The first peak position of pair correlation function, atomic coordination number and viscosity of aluminum melts were calculated and they changed abnormally in the same temperature range. The mechanism of hydrogen absorption has been discussed. From molecular dynamics calculations, the interdependence between melt structural properties and hydrogen absorption were obtained.

Hydrogen absorption of NdDyFeCoNbCuB sintered magnets

Hydrogen absorption and desorption characteristics for high coercivity NdDyFeCoNbCuB sintered bulk magnets were studied, by differential scanning calorimetry （DSC） measurement and hydrogenation kinetics measurement. The DSC measurements showed that hydrogenation of Nd-rich phase occurred in the temperature range of 40-185 ℃, hydrogenation of the tetragonal （Ф） phase in the temperature range of 185-220 ℃, as well as the disproportionation of the Ф phase that occurred in a broad temperature range from around 500 to 800 ℃. The hydrogenation kinetics measurements indicated that hydrogen absorption of the bulk magnets at 50 ℃ absorbed more hydrogen than at 150 ℃, although this procedure was slower at 50 ℃ than at 150℃. This phenomenon was discussed by means of pressure-concentration-temperature （p-c-T） diagrams.

Hydrogen absorption of LaFe_(11.5)Si_(1.5) compound under low hydrogen gas pressure

Hydrogen absorptions of LaFe11.sSi1.5 compound in 1-atm hydrogen gas at different temperatures are investigated. The hydrogen content in the hydrogenated sample does not increase with the increase of temperature of hydrogen absorption but changes complicatedly. The characteristic of first-order transition in LaFe11.sSil.5 compound is weakened after hydrogen absorption. It leads the peaks of magnetic entropy to become wider and the hysteresis loss to reduce significantly, but relative cooling power （RCP） is not changed considerably.

HYDROGEN ABSORPTION OF FeTi+x wt-% La ALLOYS WITH ALTERNATE LAYER STRUCTURE

Superior hydrogen absorbability of the alloys fo FeTi-La with alternate layer structure was found firstly.It would be available at 30℃ under 6 MPaH_2 without any prior treatment.

THIN FILM PREPARATION OF AMORPHOUS Ti-Ni ALLOY AND THEIR HYDROGEN ABSORPTION PROPERTIES

Amorphous Ti_(0.88)Ni_(1.00) and Ti_(1.69)Ni_(1.00) alloy films are prepared by means of ion beam sputtering using TiNi and Ti_2Ni alloy targets, respectively. Their hydrogen absorption properties are investigated by a galvanostatic method. The results show th the discharge capacity of the Ti_(1.69)Ni_(1.00) sample is higher than that of the Ti_(0.88)Ni_(1.00) sample. And the film electrodes have high durability and long cycle life.

Microstructure and Hydrogen Absorption/Desorption Behavior of Mg23-xLaxNi10 Alloy

Induction melting was used as a routine method to synthesize Mg_（23）Ni_（10）, Mg_（22）LaNi_（10） and Mg_（21）La_2Ni_（10） alloys, and followed by a detailed microstructural characterization which included X-ray diffraction（XRD）, scanning electron microscopy（SEM） with energy dispersive spectrometer（EDS）, high resolution transmission electron microscope（HRTEM） and hydrogen absorption/desorption measurements. XRD analysis results showed that Mg_2Ni and Mg phases were detected in the XRD pattern of the Mg_（23）Ni_（10） alloy, however, the La addition results in conversion from Mg to LaMg_3 and La_2Mg_（17） phases and appearance of crystal defects included dislocations, twin grain boundary and vacancy in the Mg_（22）LaNi_（10） and Mg_（21）La_2Ni_（10） alloy textures. The total maximum hydrogen absorption capacity was 4.45 wt% for the Mg_（23）Ni_（10） alloy, however, the Mg_（22）LaNi_（10） and Mg_（21）La_2Ni_（10） alloys with vacancy, dislocations and twin grain boundary, absorbed 3.66 wt% and 3.60 wt%, respectively, indicating that the La addition led to decreasing of the maximum hydrogen absorption capacity. Besides, hydrogen absorption/desorption of 90% of saturated state expended for about 456 and 990 s for pristine Mg_（23）Ni_（10） alloy, by contrast, the time decreased owing to improvement of hydrogen absorption and desorption kinetics in the alloy with La element, with which the uptake time for hydrogen content to 90% of saturated state was 150 and 78 s, and 90% hydrogen can be released in 930 and 804 s for Mg_（22）LaNi_（10） and Mg_（21）La_2Ni_（10） alloys in the experimental condition.

Hydrogen Absorption Thermodynamic Properties of Rare Earth Based Hydrogen Storage Alloy in Benzene

The hydriding/dehydriding thermodynamic properties of the slurry system formed by suspending La rich mischmetal nickel hydrogen storage alloy (MlNi 5) in Benzene (C 6H 6) were investigated. The pressure composition isotherms for both the alloy powder and the slurry suspended with MlNi 5 were measured at several temperatures(10, 20, 30, 40 ℃). The standard enthalpy of formation Δ H ° and standard entropy of formation Δ S ° for the alloy powder with and without benzene were determined respectively. The experimental results show that the values of Δ H ° and Δ S ° for the hydriding reaction of hydrogen storage alloy (MlNi 5) of the slurry system and the gas solid system are all very close.

Thermodynamics of hydrogen absorption and desorption in TC21 alloy

In this paper,it was addressed a hydrogen absorbing and desorbing thermodynamics inα+βtype TC21 titanium alloy with high strength and toughness based on thermodynamic experiments and calculation.The relationship between concentration(C),temperature(T),and pressure(P)of TC21 alloy is shown by P-C-T curves during hydrogen absorption and desorption process,which were measured by multistep hydrogenation/dehydrogenation methods from 625 to 750℃.The P-C-T isotherms at a given temperature were separated into three regions.The partial thermodynamic functions of hydrogen reaction were evaluated by a modified form of Sievert’s law and P-CoTrelation of different regions was expressed by the modified Sievert’s law.The results show that the enthalpy of hydrogen reaction in the first and third region relies on hydrogen content.According to Vant’s Hoff law,enthalpy and entropy of hydrogenation platform in TC21 alloys are-53.58 kJ·mol^(-1)and-127.41 J·K·mol^(-1),respectively.Compared with P-C-T curves of hydrogen absorption,that of hydrogen desorption exists hysteresis.

Hydrogen Absorption and Desorption during Heat Treatment of AISI 4140 Steel

Hydrogen plays an important role in the formation of quench cracks of structural steels. To clarify hydrogen ab- sorption and desorption during heat treatment of AISI 4140 steel, thermal desorption spectrometry （TDS） analysis was carried out for the specimens in the as-rolled, as quenched, and quenched and tempered conditions. Results show that hydrogen content increased from 0. 127 ×10 6 in the as-rolled specimen to 0. 316 × 10-6 in the as-oil-quenched specimen. After tempering at 200 ℃, the hydrogen content in the oil-quenched specimen decreased to 0. 155 × 10-6 , and the peak temperature of hydrogen desorption increased from 200 to 360 ℃. From the dependence of hydrogen content in the as-quenched specimens on austenitizing time, it can be deduced that hydrogen absorption occurs during austenitizing. The simulation of hydrogen absorption contributes to a better understanding on the distribution of hy- drogen during the heat treatment in structural steels.

Flow hydrogen absorption of LaFe_(10.9)Co_(0.8)Si_(1.3) compound under constant low hydrogen gas pressure

The hydrogen absorption of the LaFe（10.9）-Co（0.8）Si（1.3） compound under constant 1.01 × 10-5 Pa H2 gas in a flow hydrogen atmosphere was studied. The effects of hydrogen absorption on structure, Curie temperature, phase transition and magnetic property were investigated by X-ray diffraction（XRD）, differential scanning calorimeter（DSC） and superconducting quantum interference device,respectively. The hydrides of LaFe（10.9）Co（0.8）Si（1.3） crystallize into NaZn（13）-type structural phase after hydrogen absorption at temperature from 548 to 623 K. Lower hydrogen absorption temperature is of no advantage for pure 1：13 phase formation in a flow H2 atmosphere. The Curie temperature（TC） of LaFe（10.9）Co（0.8）Si（1.3） compound increases by70 K or more after hydrogen absorption. For LaFe（10.9）-Co（0.8）Si（1.3）H（1.8） compound, the maximum magnetic entropy change and the relative cooling power under a magnetic field change of 0-2 T are 6.1 J·kg^-1·K^-1 and 170 J·kg^-1,respectively. Large refrigerant capacity, low hysteresis loss and wide temperature span of magnetic entropy change peak make it a competitive practical candidate for magnetic refrigerant.

ELECTROCHEMICAL PROPERTIES OF THE HYDROGEN ABSORPTION OF AMORPHOUS Ml－Ni ALLOY FILMS

The amorphous Ml-Ni films were prepared by means of ion beam sputtering the electrochemical hydrogen storage,discharge ability and durability of amorphous film electrodes are investigated,The results show that the maximum capacities of the amorphous MlNi_(1.79),MlNi_(2.52),and MlNi_(3.44) samples are 90,100 and 142 mAh/g,respectively,and the MlNi_(3.44) amorphous film does not off and disintegrate into fine particles a fier more than 580 cycles.

Study on Hydrogen Storage Properties,Anti-Oxide Ability and Rate Limiting Step of ZrCr-Based Alloy after Introducing Cobalt as Additive

In this work,the microstructure,hydrogen storage properties,anti-oxide ability and rate limiting step of Zr(Cr_(1−x)Co_(x))_(2)(x=0,0.2,0.4 and 0.6)alloys have been investigated.After studying the crystal structure,we found that all alloy samples could show C14-type phase but the alloy sample x=0 could also show a small amount of Cr phase.Rietveld fitting showed that lattice parameter and unit cell volume of C14-type phase decreased with increasing x.After further research,it was clear that the first hydrogen absorption capacity decreased with increasing x.But introducing more Co content had a positive influence on the effective hydrogen storage capacity and cyclic hydrogen absorption and desorption properties of the alloy sample.We also found that adding Co to ZrCr_(2)alloy could improve its anti-oxide ability.In addition to this,the rate limiting step model was also studied.

Hydrogen and nitrogen absorption properties of Ce-added Zr_(2)(Fe_(1-x)Ni_(x)) alloys

To improve the nitriding resistance of Zr_(2)Fe alloy,the Ce-added Zr_(2)(Fe_(1-x)Ni_(x))(x=0,0.15,0.3,0.5)alloys were prepared by magnetic levitation melting method.The effects of Ni substitution for Fe on the phase structure,hydrogen and nitrogen absorption properties of the alloys were investigated by X-ray diffraction,scanning electron microscopy and p-c isotherm measurements.The experimental results show that Ni substitution can effectively inhibit the formation of both α-Zr and ZrFe_(2) phases and promote the formation of C16 structure Zr_(2)(Fe,Ni)phase,causing Ni-substituted alloys to exhibit low nitrogen absorption rate and capacity.At 623 K under 0.5 MPa nitrogen pressure,the nitrogen absorption capacity of Ce-added Zr_(2)(Fe_(0.5)Ni_(0.5))alloy reaches to 0.8 mL/g,much lower than that of Zr_(2)Fe alloy(1.5 mL/g).Ni substitution decreases the crystal cell volume of the C_(16)Zr_(2)(Fe,Ni)phase,resulting in an increase in the hydrogen absorption equilibrium pressure.At 623 K under 0.05 MPa hydrogen pressure,the hydrogen absorption capacity decreases from 1.46 wt%of Zr_(2)Fe alloy to 1.41 wt%of Ce-added Zr_(2)(Fe_(0.5)Ni_(0.5))alloy.

Kinetics of Liquid-Phase Hydrogenation of Benzene in a Metai Hydride Slurry System Formed by MlNi_5 and Benzene

The kinetics of liquid-phase hydrogenation of benzene in misch metai nickel-five (MINi5) and benzene slurry system was studied by investigating the influences of the reaction temperature, pressure, alloy concentration and stirring speed on the mass transfer-reaction processes inside the slurry. The results show that the whole process is controlled by the reaction at the surface of the catalyst. The mass transfer resistance at gas-liquid interface and that from the bulk liquid phase to the surface of the catalyst particles are negligible. The apparent reaction rate is zero order for benzene concentration and first order for hydrogen concentration in the liquid phase. The kinetic modei obtained fits the experimental data very well. The apparent activation energy of the hydrogen absorption reaction of MINi5-C6H6 slurry system is 42.16kJ·mol-1.

Magnetic entropy change and magnetic properties of LaFe_(11.5)Si_(1.5) after controlling the Curie temperature by partial substitution of Mn and hydrogenation

Magnetic properties and magnetic entropy changes of La（Fe_（1-x）Mn_x）_（11.5）Si_（1.5）H_y compounds are investigated. Their Curie temperatures are adjusted to room temperature by partial Mn substitution for Fe and hydrogen absorption in 1-atm（1 atm = 1.01325×10~5Pa） hydrogen gas. Under a field change from 0 T to 2 T, the maximum magnetic entropy change for La（Fe_（0.99）Mn_（0.01））_（11.5）Si_（1.5）H_（1.61）is-11.5 J/kg. The suitable Curie temperature and large value of ？S_m make it an attractive potential candidate for the room temperature magnetic refrigeration application.

Boundary Element Method (BEM) Analysis for Galvanic Corrosion of Hot Dip Galvanized Steel Immersed in Seawater

A numerical analysis of galvanic corrosion of hot-dip galvanized steel immersed in seawater was presented. The analysis was based on the boundary element methods （BEMs） coupled with Newton-Raphson iterative technique to treat the nonlinear boundary conditions, which were determined by the experimental polarization curves. Results showed that galvanic current density concentrates on the boundary of steel substrate and zinc coating, and the sacrificial protection of zinc coating to steel substrate results in overprotection of steel cathode. Not only oxygen reduction but also hydrogen reduction could occur as cathode reactions, which probably led up to the adsorption and absorption of hydrogen atoms. Flat galvanized steel tensile sample shows a brittle behavior similar to hydrogen embrittlement according to the SSRT （show strain rate test） in seawater.