Function Of Hydrogen Concentration Research Articles

Equation of State, Structure, and Transport Properties of Iron Hydride Melts at Planetary Interior Conditions

AbstractIron hydrides are a potentially dominant component of the metallic cores of planets, primarily because of hydrogen's ubiquity in the universe and affinity for iron. Using ab initio molecular dynamics, we examine iron hydrides with 0.1, 0.33, 0.5, and 0.6 mol fraction hydrogen up to 100 GPa between 3,000 and 5,000 K to describe how hydrogen content affects the melt structure, hydrogen speciation, equation of state (EOS), atomic diffusivity, and melt viscosity. We find that the addition of hydrogen decreases the average Fe–Fe coordination number and lengthens Fe–Fe bonds, while Fe–H coordination number increases. The pair distribution function of hydrogen at low pressure indicates the presence of molecular hydrogen. By tracking chemical speciation, we show that the amount of molecular hydrogen increases and the number of iron in Hx≥1Fey≥0 clusters decreases as the hydrogen concentration increases. We parameterize a pressure, volume, temperature, and composition EOS and show that the molar volume and Grüneisen parameter of the melts decrease while the compressibility and thermal expansivity increase as a function of hydrogen concentration. We find that hydrogen acts as a lubricant in the melts as the iron and hydrogen become more diffusive and the melts become more inviscid as the hydrogen concentration increases. We estimate 2.7 wt% hydrogen in the Martian core and 0.49–1.1 wt% hydrogen in Earth's outer core based on comparisons to seismic models, with the assumption that the cores are pure liquid iron‐hydrogen alloy, and we compare the small exoplanet population with mass‐radius curves of iron hydride planets.

Influence of temperature and hydrogen content on the transverse mechanical properties of Zircaloy-4 fuel cladding

This paper presents the results of the investigation on the influence of hydrogen on the transverse mechanical properties of the Zircaloy-4 fuel cladding at various temperatures ranging from room temperature to 600οC. Data pertaining to the mechanical properties of the fuel cladding in the hoop direction are required for the analysis of high burn-up fuel behaviour under loss of coolant accident (LOCA) and reactivity initiated accident (RIA) conditions. Using the ring tension test method, the mechanical properties of the Zircaloy-4 fuel cladding in the transverse direction were evaluated as functions of hydrogen concentration and test temperature. The effect of hydrogen on the mechanical properties was observed to be marginal but the effect of temperature was significant in the investigated hydrogen concentration range (47–475 ppmw).

Analysis of Hydrogen-Assisted Brittle Fracture Using Phase-Field Damage Modelling Considering Hydrogen Enhanced Decohesion Mechanism

This study proposes a hydrogen-assisted fracture analysis methodology considering associated deformation and hydrogen transport inside a phase-field-based formulation. First, the hydrogen transport around a crack tip is calculated, and then the effect of hydrogen enhanced decohesion (HEDE) is modeled by defining the critical energy release rate as a function of hydrogen concentration. The proposed method is based on a coupled hydrogen mechanical damage under phase-field and implemented through a user subroutine in ABAQUS software. The test using compact tension (CT) sample is investigated numerically to study the hydrogen embrittlement on 45CrNiMoVA steel. Experimentally, the microstructural fracture presents a mixed brittle fracture mode, consisting of quasi-cleavage (QC) and intergranular (IG) fracture with hydrogen. This fracture mode is consistent with the suggested HEDE mechanism in the model. The simulation results show that hydrogen accumulates at the crack tip where positive hydrostatic stress is located. Moreover, the model estimates the initial hydrogen concentration through iterations. The simulated load-line displacement curves show good agreement with the experimental plots, demonstrating the predictive capabilities of the presented scheme.

Tracer diffusion in proton-exchanged congruent LiNbO3 crystals as a function of hydrogen content.

The proton-exchange process is an effective method of fabricating low-loss waveguides based on LiNbO3 crystals. During proton-exchange, lithium is replaced by hydrogen and Li1-xHxNbO3 is formed. Currently, mechanisms and kinetics of the proton-exchange process are unclear, primarily due to a lack in reliable tracer diffusion data. We studied lithium and hydrogen tracer diffusion in proton-exchanged congruent LiNbO3 single crystals in the temperature range between 130-230 °C. Proton-exchange was done in benzoic acid with 0, 1, 2, or 3.6 mol% lithium benzoate added, resulting in micrometre thick surface layers where Li is substituted by H with relative fractions between x = 0.45 and 0.85 as determined by Nuclear Reaction Analysis. For the diffusion experiments, ion-beam sputtered isotope enriched 6LiNbO3 was used as a Li tracer source and deuterated benzoic acid as a H tracer source. Isotope depth profile analysis was carried out by secondary ion mass spectrometry. From the experimental results, effective diffusivities governing the lithium/hydrogen exchange as well as individual hydrogen and lithium tracer diffusivities are extracted. All three types of diffusivities can be described by the Arrhenius law with an activation enthalpy of about 1.0-1.2 eV and increase as a function of hydrogen content nearly independent of temperature. The effective diffusivities and the lithium tracer diffusivities are identical within a factor of two to five, while the hydrogen diffusivities are higher by three orders of magnitude. The results show that the diffusion of Li is the rate determining step governing the proton-exchange process. Exponential dependencies between diffusivities and hydrogen concentrations are determined. The observed increase of Li tracer diffusivities and effective diffusivities as a function of hydrogen concentration is attributed to a continuous reduction of the migration enthalpy of diffusion by a maximum factor of about 0.2 eV. Simulations based on the determined diffusivities can reproduce the step-like profile of hydrogen penetration during proton-exchange.

Innovative method to estimate state of charge of the hydride hydrogen tank: application of fuel cell electric vehicles

ABSTRACT Significant attention has been paid to metal hydrides (MH) as an environmentally friendly and safe way to store hydrogen. This technology has considerable potential for the application of embedded hydrogen storage in fuel cell electric vehicles, but its widespread application faces a major problem in terms of estimating the remaining hydrogen amount in the tank. In this work, a new method is proposed for estimating the state of charge (SoC) of the hydrogen hydride tank (HHT) by application of piezoelectric material. The idea is to cover the entire inner wall of the metal-hydride tank with a layer of piezoelectric material. During the process of hydrogen absorption, the pressure inside the tank increases, resulting in an increase in the mechanical stress applied to the piezoelectric layer, thus generating a voltage. This effect can therefore be used as an effective means of estimating the amount of hydrogen absorbed. The COMSOL Multiphysics software was used to implement the model and solve the differential equation of energy, mass, and moment. The simulation results showed that the voltage evolution as a function of hydrogen concentration follows the same behavior as the variation of the Pressure Concentration Isotherm (PCI).

Examination of the Hydrogen Incorporation into Radio Frequency-Sputtered Hydrogenated SiNx Thin Films

In this work, amorphous hydrogen-free silicon nitride (a-SiNx) and amorphous hydrogenated silicon nitride (a-SiNx:H) films were deposited by radio frequency (RF) sputtering applying various amounts of hydrogen gas. Structural and optical properties were investigated as a function of hydrogen concentration. The refractive index of 1.96 was characteristic for hydrogen-free SiNx thin film and with increasing H2 flow it decreased to 1.89. The hydrogenation during the sputtering process affected the porosity of the thin film compared with hydrogen-free SiNx. A higher porosity is consistent with a lower refractive index. Fourier-transform infrared spectroscopy (FTIR) confirmed the presence of 4 at.% of bounded hydrogen, while elastic recoil detection analysis (ERDA) confirmed that 6 at.% hydrogen was incorporated during the growing mechanism. The molecular form of hydrogen was released at a temperature of ~65 °C from the film after annealing, while the blisters with 100 nm diameter were created on the thin film surface. The low activation energy deduced from the Arrhenius method indicated the diffusion of hydrogen molecules.

Potentiometric Hydrogen Sensing of Ordered SnO2 Porous Thin Films

Introduction The sensing performance of mixed-potential gas sensors is highly dependent on the electrode microstructure. Recently, much effort has been made to improve the sensor performance by engineering of the electrode microstructure [1, 2]. Nevertheless, the different microstructure parameters, such as thickness, porosity, and three phase boundary (TPB), contribute jointly to the sensing response, and their respective contributions are usually difficult to identify. Thus, deviation of the apparent sensor behavior from the reality is usually unable to judge due to the uncertain effect of electrode catalytic reaction. In order to unravel the true response behavior, it would be necessary to reduce or minimize impact of the electrode diffusion-reaction process and control the microstructure, which could be achieved by using a very thin electrode with well-defined and controllable morphology. Herein, we fabricated thin ordered SnO2 sensing electrodes on YSZ substrate by employing a Polystyrene (PS) sphere-template method [3]. By varying the PS sphere diameter, three sensors of different electrode thickness and electrode/electrolyte interface were obtained. The gas sensing characteristics of the sensors were systematically studied. The sensing behavior was discussed in relation to variation of the electrode process and TPB density. Sensor fabrication and characterization As depicted in Figure 1, highly-ordered porous thin film sensors were prepared by using PS sphere templates in 200 nm, 500 nm and 1000 nm diameters. SEM, TEM and AFM images of SnO2 porous film electrodes were presented in Figure 2. Periodically ordered films of inverse opal structure were observed, with uniform circular pore openings and interconnected walls as the skeleton. Each film was porous and a homogenous assembly of 10-20 nm sized particles. The wall height was roughly half of the PS sphere size, which increased from 121 nm to 248 nm and 448 nm for the three PF films. Sensing performance Figure 3a and b show the response values and response time of the three PF sensors as a function of hydrogen concentration at 500 °C. Obviously, the response significantly increased, i.e., became more negative, with decreasing template diameters, while the response time of the three sensors was short and generally rather close to each other, with a value of 4.5 s-6 s for 500 ppm H2 at 500 °C. Figure 3c displays the cross-sensitivities of the PF sensors to 100 ppm various gases at 450 °C. The PF sensors exhibited much poorer H2 selectivity than regular thick film sensors [4].The small film thickness and porous nature of the PF SE are highly favorable for the gas transport from the gas phase to the TPB, which are beneficial to the response kinetics. That the three PF sensors exhibited very close response time despite their minor difference in the film thickness, suggesting absence of significant electrode process and large H2 concentration reduction. This may allow us to study the effect of the TPB density on the sensing response. The TPB length was thus estimated for the PF sensors (Figure 4a). Clearly, the TPB density increased from 56.8 μm-1 to 89.7 μm-1 with the decreasing template diameters. It can also be seen that for each H2 concentration, the response increased (became more negative) monotonically with increasing TPB density (Figure 4b-c). It should be noted that thin film favors fast response kinetics and large response but may be disadvantageous to the selectivity. To achieve good overall sensing performance, e.g., fast response kinetics, large response, and high selectivity, careful tuning of the film thickness and TPB density would be demanded.

Detection of Hydrogen Embrittlement in Plated High-Strength Steels with Eddy Currents: Is the Sensitivity Sufficient?

Hydrogen embrittlement (HE) of high-strength steels has been a long-standing issue in the aerospace industry. Detecting the presence of hydrogen in steel with a low-cost and fast non-destructive method would be useful to avoid wasting parts. In this paper, we evaluate the feasibility of using eddy currents to achieve this goal. At first, we evaluate HE and hydrogen content in a series of chromium-plated 4340 steel notched bar samples (extremely embrittled) using sustained-load tests and thermal desorption spectroscopy. The failure of the notched bars at only 20% of their maximum mechanical load is coherent with the high hydrogen concentration in the samples, which can be as high as 1400 ppm atomic ( $$\sim \,30\%$$ in steel, $$\sim \,70\%$$ in the coating). However, a baking at $$190\,{^{\circ }}\hbox {C}$$ for 23 h can desorb most embrittling hydrogen in the 4340 steel and relieve HE. Therefore, successive bakings are used to progressively desorb hydrogen from the samples and produce various hydrogen concentrations. By using eddy currents after each baking, coupled with a finite element model implemented in COMSOL, we can deduce the electric and magnetic properties of steel and chromium as a function of hydrogen concentration. Unfortunately, no significant variation of these properties can be observed, even for concentration variations as large as $$\sim \,900\,\hbox {ppma}$$ . The only observable changes happen after performing bakings at high temperature, which induce microstructural changes in the samples. However, eddy currents remain a good approach to detect small changes in electromagnetic materials properties resulting from other causes than hydrogen.

Failure analysis of structural steel subjected to long term exposure of hydrogen

Embrittlement of steel due to its exposure to hydrogen is a well-established phenomenon, which diminishes its ductility and toughness. However, there is limited research on how hydrogen, which evolves from the corrosion process, affects the yield strength of mild steel in the long-term. This paper presents the results obtained from a long-term investigation on hydrogen evolving from a corrosion reaction, which causes embrittlement of mild steel. Both mechanical tests and microstructural analyses on corroded steel specimens are performed at three different intervals for one year. Time-dependent relations for predicting the corrosion rate and its subsequent hydrogen release were derived by analysing the test results. Moreover, relations for predicting the change in yield strength as a function of hydrogen content, corrosion rate and compositional element change were developed, along with one single equation considering all these factors. Furthermore, fractography analysis was performed to observe HE effect and reasons for the decline in yield strength. The analysis revealed hydrogen induced micro cracks, micro pores, intergranular cracks, grains deformation and hydrogen blisters.

Potentiometric Hydrogen Sensing of Ultrathin Highly-Ordered SnO2 Films

Introduction The sensing performance of mixed-potential gas sensors is highly dependent on the electrode microstructure. Recently, much effort has been made to improve the sensor performance by engineering of the electrode microstructure [1, 2]. Nevertheless, the different microstructure parameters, such as thickness, porosity, and three phase boundary (TPB), contribute jointly to the sensing response, and their respective contributions are usually difficult to identify. In order to shed light on the role of TPB, it is crucial to minimize the influence of the diffusion-reaction process occurring inside the electrode, which could be achieved by using a very thin electrode. Moreover, a highly-ordered electrode morphology may help obtain well-defined TPB. Herein, we fabricated sub-micron thick ordered SnO2 sensing electrodes on YSZ substrate by employing a Polystyrene (PS) sphere-template method [3]. Three sensors were obtained by using PS spheres of different diameters in order to vary the TPB density. The gas sensing characteristics of the sensors were systematically studied. The sensing behavior was discussed in relation to the electrode microstructure. Sensor fabrication and characterization As depicted in Figure 1, ultrathin highly-ordered porous film sensors were prepared by using PS sphere templates in 200 nm, 500 nm and 1000 nm diameters. SEM, TEM and AFM images of SnO2 porous film electrodes were presented in Figure 2. Periodically ordered films of inverse opal structure were observed, with uniform circular pore openings and interconnected walls as the skeleton. Each film was porous and a homogenous assembly of 10-20 nm sized particles. The wall height was roughly half of the PS sphere size, which increased from 121 nm to 248 nm and 448 nm for the three PF film electrodes. Sensing performance Figure 3a and b show the response values and response time of the three PF sensors as a function of hydrogen concentration at 500°C. Obviously, the response significantly increased, i.e., became more negative, with decreasing template diameters, while the response time of the three sensors was generally rather close to each other, with a value of 4.5 s-6 s for 500 ppm H2 at 500°C. Figure 3c displays the cross-sensitivities of the PF sensors to 100 ppm various gases at 450°C. The PF sensors exhibited much poorer H2 selectivity than regular thick film sensors [4].The ultra-small film thickness and porous nature of the PF SE are highly favorable for the gas transport from the gas phase to the TPB. The three PF sensors exhibited very close response time despite their minor difference in the film thickness (in the order of hundreds of nanometer), suggesting absence of significant electrode process and of large H2 concentration reduction. This may allow us to study the effect of the TPB density on the sensing response. The TPB length was thus estimated for the PF sensors. Clearly, the TPB density values increased with the decrease of the PS template diameter. It can also be seen that for each H2 concentration, the response indeed increased (became more negative) monotonically with increasing TPB density (Figure 4). It should be noted, however, that the ultra-thin film electrode was disadvantageous to the selectivity. To achieve good overall sensing performance, e.g., fast response kinetics, large response, and high selectivity, careful tuning of the film thickness and TPB density would be demanded.

Operando NAP-HT-XPS and Impedance Spectroscopy Study of Pulsed Laser Deposited Ni-Ce0.9Gd0.1O2-δ Solid Oxide Fuel Cell Electrode

Detailed chemical information from electrode surfaces at operating conditions is essential for rational development of solid oxide cell (SOC) electrodes but so far, because of harsh operating conditions very little is known about mechanistic aspects of surface reactions as well as surface thermodynamics at SOC electrodes under electrochemical reaction conditions (1,2). Spectroelectrochemistry, i.e. spectroscopic (X-ray absorption, X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy) characterization of operating electrode at electrochemically controlled conditions is promising approaches for characterization of surface properties like oxidation states, surface polarization, surface coverage with adsorbate, etc. at real or almost real working conditions.This study present results of operando high temperature (HT)-NAP-XPS spectroelectrochemical measurements of pulsed lased deposited thin film Ni-Ce0.9Gd0.1O2-δ electrode using novel dual-chamber spectroelectrochemical cell at H2, at different cell polarizations at 650 °C. Change on redox state of surface Ni and Ce atoms has been observed as a function of hydrogen concentration.

Comparison of methods for determining insulin resistance indexes of obese patients with coronary artery disease and chronic pancreatitis

The influence of the circuit’s electric modes on the radiation sensitivity of hydrogen sensors based on the metal-insulator-semiconductor field-effect transistor with structure Pd-Ta2O5-SiO2-Si (MISFET) was researched. There were measured the hydrogen responses of output voltages V of the MISFET-based circuits at different gate voltages before and after electron irradiations. The voltages V as functions of hydrogen concentration C were determined for different ionizing doses D. Models of influence of the electric modes on the radiation sensitivity of sensors were based on experimental dependencies of V(C, D). The recommendations for the optimal choice of MISFET-based circuit’s electric modes were formulated.

Duodenum-preserving pancreatic head resection for paraduodenal (groove) pancreatitis treatment

The influence of the circuit’s electric modes on the radiation sensitivity of hydrogen sensors based on the metal-insulator-semiconductor field-effect transistor with structure Pd-Ta2O5-SiO2-Si (MISFET) was researched. There were measured the hydrogen responses of output voltages V of the MISFET-based circuits at different gate voltages before and after electron irradiations. The voltages V as functions of hydrogen concentration C were determined for different ionizing doses D. Models of influence of the electric modes on the radiation sensitivity of sensors were based on experimental dependencies of V(C, D). The recommendations for the optimal choice of MISFET-based circuit’s electric modes were formulated.

Decohesion Energy of $$\Sigma 5(012)$$ Grain Boundaries in Ni as Function of Hydrogen Content

Degradation due to hydrogen embrittlement (HE) is initiated at the nanoscale, and the development of a predictive understanding of HE will have to consider the range all the way from atomic to macro scale. Density functional theory (DFT) can be used to calculate the effect of hydrogen in metals on the atomic scale. It is, however, limited to small models consisting of $$\sim 1000$$ atoms, which puts the relevance for real-life scenarios into question. In the current study, the effect of model size is explored for two grain boundary (GB) systems, $$\Sigma 3[110](111)$$ and $$\Sigma 5[100](012)$$ . For the latter, the preferred sites for H occupation and the sequence in which sites are filled upon increasing H contents are investigated, and decohesion energies are calculated as function of H content. Emphasis is laid on identifying the most physical model for these studies, by evaluating effects of model size and structural relaxation procedures. It is found that the decohesion energy does not decrease linearly with H content and has to be calculated explicitly for full H coverage to find out how much H absorption weakens the GB.

Influence of electrical modes on radiation sensitivity of hydrogen sensors based on Pd-Ta2O5-SiO2-Si structures

The influence of the circuit’s electric modes on the radiation sensitivity of hydrogen sensors based on the metal-insulator-semiconductor field-effect transistor with structure Pd-Ta2O5-SiO2-Si (MISFET) was researched. There were measured the hydrogen responses of output voltages V of the MISFET-based circuits at different gate voltages before and after electron irradiations. The voltages V as functions of hydrogen concentration C were determined for different ionizing doses D. Models of influence of the electric modes on the radiation sensitivity of sensors were based on experimental dependencies of V(C, D). The recommendations for the optimal choice of MISFET-based circuit’s electric modes were formulated.

Impact of obesity on the prognosis of an acute pancreatitis

The influence of the circuit’s electric modes on the radiation sensitivity of hydrogen sensors based on the metal-insulator-semiconductor field-effect transistor with structure Pd-Ta2O5-SiO2-Si (MISFET) was researched. There were measured the hydrogen responses of output voltages V of the MISFET-based circuits at different gate voltages before and after electron irradiations. The voltages V as functions of hydrogen concentration C were determined for different ionizing doses D. Models of influence of the electric modes on the radiation sensitivity of sensors were based on experimental dependencies of V(C, D). The recommendations for the optimal choice of MISFET-based circuit’s electric modes were formulated.

Monitoring of hydrogen concentration using capacitive nanosensor in a 1% H 2 –N 2 mixture

In this work, a hydrogen capacitor nanosensor with palladium nanoparticles (PdNPs) electrode based on metal–oxide–semiconductor structure has been fabricated. The capacitor sensor has been fabricated on the n-type silicon substrate with an oxide film thickness of 50 nm. PdNPs are synthesised and then deposited on the oxide surface using spin coating. PdNPs are characterised using by transmission electron microscope and UV spectrum. Also, the morphology of the oxide surface is characterised using by atomic force microscope. The response time and recovery time of nanosensor have been explained at the room temperature. The time interval to 90% of the signal value for 1% H2–N2 mixture was 1.4 s and recovery time was 14 s. The curve of pressure as a function of hydrogen concentration (H/Pd) in the PdNPs and the mechanism of the nanosensor are reported. The capacitor nanosensor based on nanoparticles shows sensitive and fast response.

Electronic properties and bonding in ZrHx thin films investigated by valence-band x-ray photoelectron spectroscopy

The electronic structure and chemical bonding in reactively magnetron sputtered ZrHx (x=0.15, 0.30, 1.16) thin films with oxygen content as low as 0.2 at% are investigated by 4d valence band, shallow 4p core-level and 3d core-level X-ray photoelectron spectroscopy. With increasing hydrogen content, we observe significant reduction of the 4d valence states close to the Fermi level as a result of redistribution of intensity towards the H 1s - Zr 4d hybridization region at about 6 eV below the Fermi level. For low hydrogen content (x=0.15, 0.30), the films consist of a superposition of hexagonal closest packed metal (alpha-phase)and understoichiometric delta-ZrHx (CaF2-type structure) phases, while for x=1.16, the film form single phase ZrHx that largely resembles that of stoichiometric delta-ZrH2 phase. We show that the cubic delta-ZrHx phase is metastable as thin film up to x=1.16 while for higher H-contents, the structure is predicted to be tetragonally distorted. For the investigated ZrH1.16 film, we find chemical shifts of 0.68 and 0.51 eV towards higher binding energies for the Zr 4p3/2 and 3d5/2 peak positions, respectively. Compared to the Zr metal binding energies of 27.26 and 178.87 eV, this signifies a charge-transfer from Zr to H atoms. The change in the electronic structure, spectral line shapes, and chemical shifts as function of hydrogen content is discussed in relation to the charge-transfer from Zr to H that affects the conductivity by charge redistribution in the valence band.

Chip temperature influence on characteristics of MISFET hydrogen sensors

The influence of chip temperature on the hydrogen sensitivity of the metal-insulator-semiconductor field-effect transistor (MISFET) with structure Pd-Ta2O5-SiO2-Si was investigated. MISFET sensing elements were fabricated on silicon chip together with (p–n)-junction temperature sensor and heater-resistor. There were measured the hydrogen responses of the MISFET threshold voltage at room and higher chip temperatures (up to 180°C). The threshold voltage as a function of hydrogen concentration was determined at different temperatures. The models of temperature sensitivity of the threshold voltage based on the experimental data approximations are presented in this work.

Realization of palladium-based optomechanical cantilever hydrogen sensor

Hydrogen has attracted attention as an alternative fuel source and as an energy storage medium. However, the flammability of hydrogen at low concentrations makes it a safety concern. Thus, gas concentration measurements are a vital safety issue. Here we present the experimental realization of a palladium thin film cantilever optomechanical hydrogen gas sensor. We measured the instantaneous shape of the cantilever to nanometer-level accuracy using diffraction phase microscopy. Thus, we were able to quantify changes in the curvature of the cantilever as a function of hydrogen concentration and observed that the sensor’s minimum detection limit was well below the 250 p.p.m. limit of our test equipment. Using the change in curvature versus the hydrogen curve for calibration, we accurately determined the hydrogen concentrations for a random sequence of exposures. In addition, we calculated the change in film stress as a function of hydrogen concentration and observed a greater sensitivity at lower concentrations.