Deuterium permeation and isotope effects in nickel in an elevated temperature range of 450–850 °C

A series of deuterium permeation experiments were carried out using a nickel membrane in an elevated temperature range of 450–850 °C for application to nuclear fusion and nuclear hydrogen technologies. A complete set of permeability, diffusivity, and solubility data for deuterium in nickel was successfully determined. The results of this study were compared with results previously reported by other authors. The results for deuterium were also compared with the results for hydrogen to estimate the isotope effect. The results for and a discussion of deuterium permeation and the isotope effects in nickel are presented.     

Thermal management of high temperature polymer electrolyte membrane fuel cell stacks in the power range of 1–10 kWe

Maintaining optimal temperature of the stack is critical for efficient operation of high temperature polymer electrolyte membrane fuel cells. While a number of possibilities of thermal management exist for small stacks, the problem becomes more complicated for larger stacks. In the present study, the thermal management of stacks in the power range of 1–10 kWe is considered through computational fluid dynamics simulations. It is shown that large stacks need to have dedicated cooling plates through which a coolant is circulated. Further, stacks of the size of 10 kWe can have reasonably low cell temperature variations (∼20 K) only by passing pre-heated liquid coolant through the coolant plates. Estimates show that the concomitant increase in the coolant flow rate induces large pressure drops, of the order of 30 bar, if a four-parallel serpentine is used on an active cell area of 30 cm × 30 cm. It is therefore necessary to use parallel channel flow fields with carefully designed feeder manifolds to maintain optimal cell temperatures and reasonably low coolant pressure drops in large stacks.     

Influence of Au ions irradiation on the deuterium permeation behavior in the oxidized Fe–Cr–Al ferritic steel

Our previous study has shown that an effective tritium permeation barrier (TPB) with Al₂O₃ layer found could be obtained by oxidization of a Fe–Cr–Al ferritic steel. In this study, irradiation effects on deuterium permeation behavior through oxidized Fe–Cr–Al ferritic steel (OFFS) have been investigated by Au ions irradiation followed by deuterium gas driven permeation (GDP) experiments. The deuterium permeability of the irradiated and original OFFS samples has been obtained and compared. Oxide layer has been characterized by X-ray photoelectron spectroscopy (XPS) experiment and scanning electron microscopy (SEM) experiment. The defects in the oxide layer with and without Au ions irradiation have been characterized by Doppler broadening spectrometry of positron annihilation (DBS-PA) experiments. The deuterium permeation behavior of OFFS changed owing to the Au ions irradiation, which could be attributed to the increased density of vacancy-type defects.     

Influence of water vapor on hydrogen permeation through 2.5 μm Pd-Ag membranes

Hydrogen permeation experiments were performed to evaluate the influence of water vapor on hydrogen permeability in 80-20% by weight Pd-Ag membranes of 2.5 μm thickness. In particular, hydrogen flux was measured in pure hydrogen permeation tests as well as in experiments with binary mixtures containing also nitrogen or water vapor, that were performed at temperatures ranging from 473 to 723 K and at a transmembrane pressure differences up to about 3 bar. The membranes, supplied by NGK Insulator Ltd., Japan, showed a very high hydrogen permeance and lifetime, as well as virtually infinite selectivity (exceeding 10000 for H₂-N₂ mixtures). The experiments in hydrogen-nitrogen mixtures were carried out at different temperatures, hydrogen concentrations and feed flow rates and confirmed the existence of a non-negligible concentration polarization phenomenon in the experimental module. The gas phase mass transport and the module fluid dynamics were thus analyzed and the dimensionless numbers characterizing these processes were evaluated at the different operative conditions; a linear correlation was found to hold between Sherwood and Péclet numbers. Interestingly, the hydrogen permeate fluxes measured with feeds containing H₂-H₂O mixtures resulted always lower than those obtained for the nitrogen-hydrogen mixtures performed at the same hydrogen mole fraction and operative conditions: in particular, the hydrogen flux depletion increased with decreasing temperature and/or increasing the concentration of water vapor. All the experimental evidences suggest a clear interaction between water vapor and metallic layer, causing a lower hydrogen adsorption capacity of the membrane surface. That phenomenon is reversible, since the original permeance of the membrane was restored once the water vapor was removed from the feed, and is apparently due to a competitive H₂-H₂O adsorption on the Pd-Ag surface. The hydrogen flux depletion was then modeled by considering the simultaneous effects of gas phase resistance and competitive adsorption on the surface, obtaining a rather good agreement between experimental data and calculated results.     

High-purity hydrogen gas from the reaction between BOF steel slag and water in the 473–673 K range

A novel method for producing hydrogen with water and BOF steel slag was developed. The steel slag was reacted with water during 2–57 days at 50 MPa for temperatures ranging from 473 to 673 K. The quantitative evolution of the slag and gas compositions indicated that the main H₂ producing reaction is:     

The thermal conductivity of sodium in the temperature range 90–850°C

This work describes an experiment which was carried out in order to determine the effect of temperature on the thermal conductivity of sodium, in the temperature range 90–850°C. The experimental method is based on a mathematical model which is briefly examined in the first section. The apparatus and the test procedure are described in the second section, with reference to the major features of the measurement device. In the last section the experimental results are compared with previously published data.     

Absolute rate measurements for the reaction of the OH radical with diacetylene over the temperature range of 296–688K

Absolute rate constants have been measured for the reaction of the OH radical with diacetylene over the temperature range of 296–688K using a flash photolysis-resonance fluorescence technique. The best fit to the data is given by the following Arrhenius expression:

$\text{k=1.11×10}{}^{\mathrm{?11}}\text{exp{}\text{410±300(cal/mole)}\text{RT}\text{} cm}{}^3\text{molecule}{}^{\mathrm{?1}}\text{s}{}^{\mathrm{?1}}\text{.}$

Thermodynamic calculations based on group additivity methods are used to infer probable product channels for the reaction. Since the reaction between the OH radical and diacetylene is thought to be a critical pathway for hydrocarbon oxidation in fuel rich flames, the present results have implications for models of such flames. These implications are discussed.     

In-situ studies of gas phase composition and anode surface temperature through a model DIR-SOFC steam–methane reformer at 973.15 K

A comparative study into the effects of total volume flow rate, methane ‘residency time’, methane volume flow rate, and steam-to-carbon ratio on the steam–methane reforming process was performed in a model Direct Internal Reforming SOFC (DIR-SOFC) reformer operating in steady state at a nominal temperature of 973 K. The spatial distributions of major gas species (CH₄, H₂O, CO, CO₂, and H₂) over the reformer surface were measured in-situ using Vibrational Raman Spectroscopy. Surface temperature measurements were recorded using IR thermometry. The effects of varying the intake mole fractions of methane and water were considered. The results of this work have demonstrated a strong positive correlation between the intake mole fraction of methane and the rate of the steam–methane reformation reaction. A weak negative correlation between the intake mole fraction of water and the rate of the reformation reaction was also shown.     

Hydrogen permeation in a Cr–Mo–V medium-carbon steel: Effect of the quenching medium and tempering temperature

Hydrogen permeation tests are carried out to evaluate the effect of the quenching medium and tempering temperature on the permeation parameters and density of hydrogen traps, of a Cr–Mo–V low-alloy medium-carbon steel. Three types of steel membranes are tested: 1) in the as-quenched condition, 2) tempered at 235 °C and 3) tempered at 530 °C; each one quenched in two different media: oil or brine. From the as-quenched condition, the apparent concentration of hydrogen and hydrogen flux, tend to decrease as the tempering temperature increases. The membranes in the as-quenched condition and tempered at 530 °C, show lower hydrogen diffusivity and higher density of hydrogen traps than membranes tempered at 235 °C. It is concluded that tempering at 235 °C, promotes hydrogen induced cracking, which is contrary to what has been previously determined. The cracking is related to a higher hydrogen diffusivity and lower density of hydrogen traps.     

Hot deformation behaviour of niobium in temperature range 700–1500°C

Abstract

Niobium was hot deformed in vacuum in uniaxial compression to a true strain of 0·6 in the temperature range of 700–1500°C and the strain rate range of 10^?3–10 s^?1. Strain rate sensitivity was calculated from the compression tests data and mapped out in contour plots with the aim to optimise the hot workability of niobium. The domain of hot workability was identified in the temperature range of 1200–1500°C and strain rate range of 10^?2–1 s^?1. In this domain the strain rate sensitivity was ～0·15, the stress exponent 7·5 and the activation energy 246 kJ mol^?1. Microstructure of the deformed samples showed features of dynamic recrystallisation within the high strain rate sensitivity domain and features of flow instability in the regime of low strain rate sensitivity. Compared to a previous study on Nb–1Zr–0·1C alloy, Nb showed a lower flow stress and an optimum hot working domain at lower temperatures.     

New results on the visco-elastic behaviour of ionomer membranes and relations between T–RH plots and proton conductivity decay of Nafion 117 in the range 50–140 °C

The colligative properties of acidic solution inside Nafion^® 117 membranes have been investigated, in a large temperature range, by two different methods.     

Performance of copper–ceria catalysts for water gas shift reaction in medium temperature range

A series of copper–ceria catalysts with copper loading in the range of 20–90 at% Cu (=100 × Cu/(Cu + Ce)) were prepared by the method of coprecipitation, and their performance was tested for water gas shift (WGS) reaction in medium temperature condition (150–360 °C). Both fresh and used catalysts were characterized using XRD, H₂-TPR and BET surface area measurements. After the first run, the catalysts stabilized in terms of activity and BET surface area. XRD results of used catalysts confirmed the formation of metallic Cu species during WGS reaction. The WGS activity of ceria catalysts increased with copper loading, and the synergy of copper and ceria was confirmed. Results showed 80 at% copper–ceria had the best performance. The catalysts showed stable activities at 360 °C.     

Study on the performance of hydrogen isotopes permeation sensor in liquid Li–Pb

Liquid Li–Pb alloy is served as neutron multiplier, tritium breeder, and coolant in Dual Coolant Lithium–Lead (DCLL) breeding blankets. In order to monitor the tritium transport continuously and measure the tritium production rate accurately, the concentration of hydrogen isotopes in liquid breeder is an essential factor for tritium measurement. The hydrogen isotopes permeation-based capsule seems to be the most reliable sensor and is simple from the fabrication point of view. To verify the stability and repeatability of hydrogen isotopes concentration measured by permeation capsule in Li–Pb, a system based on a Nb-capsule and a quadrupole mass spectrometry was devised. The sensor would be applied to determine the variation rate of total pressure while a quadrupole mass spectrometry to measure partial pressure values of different hydrogen isotopes. The response time of the sensor is less than 100 s in liquid Li–Pb alloy and the growth rate of pressure has good repeatability in dynamic mode. Besides, calculations based on numerical simulation of the hydrogen isotopes sensor are presented.     

Kinetics of hydrogen abstraction O(3P) + alkane → OH + alkyl reaction class: An application of the reaction class transition state theory

This paper presents an application of the reaction class transition state theory (RC-TST) for prediction of thermal rate constants of the O(³P) + alkane → OH + alkyl reaction class. Parameters of the RC-TST were derived from first principles from a set of 19 reactions representing hydrogen abstractions from primary, secondary, and tertiary carbon atoms so that rate constants of any reaction in this class can be estimated without any further information or with its reaction energy calculated either at the density functional theory BH&HLYP/cc-pVDZ level or the semiempirical AM1 level. Detailed error analyses show that when compared to explicit theoretical calculations, the systematic errors in the calculated rate constants arising from the use of analytical expressions to approximate different reaction class factors in the RC-TST method are less than 40% on the average over the temperature range from 300 to 3000 K. In addition, we found that the rate constants estimated using either approach are in good agreement with available data in the literature.     

Kinetics of the hydrogen-induced diffusive phase transformation in Nd–Fe–B industrial alloy

The kinetics of the hydrogen-induced diffusive phase transformation in industrial alloy Nd–Fe–B has been investigated. The isothermal kinetic curves were received for temperatures from 750 to 620°C at the hydrogen pressure 0.1 MPa. An isothermal kinetics diagram was obtained. This diagram is similar to the ones of the transformations in steels during heating. It is shown that the investigated phase transformation is a diffusion-controlled one with the mechanism of nucleation and growth.     

Bottom-up cost evaluation of SOEC systems in the range of 10–100 MW

A detailed bottom-up cost evaluation of SOEC systems in the range of 10–100 MW was carried out based on recent experimental results in the SOEC field. Capital costs of installed SOEC systems were evaluated starting from raw SOEC materials. Two scenarios were defined, assuming different capacities of SOEC units, yearly production capacities of SOEC cells and stacks as well as operating conditions of manufacturing lines. It resulted in installed capital costs of 309–395 €/kW for SOEC units integrated into power-to-methane plants (reference case) and of 380–494 €/kW for stand-alone SOEC units. This highlights the cost reduction potential of the SOEC technology when thermally coupled with a steam source. These costs were compared with previous capital cost estimates for future SOEC, proton exchange membrane (PEM) and alkaline electrolysis systems available in the literature. A sensitivity analysis allowed to identify which parameters have the highest impact on installed system costs. In the least favorable conditions, it was estimated that they could raise up to 494–618 €/kW for SOEC units in the reference case and up to 573–727 €/kW for stand-alone SOEC units.     

Study of the NaBH4–NaBr system and the behaviour of its low temperature phase transition

A mechano-chemical method was used to synthesize solid solution Na(BH₄)_1-xBr_x with 0 ≤ x ≤ 1. Samples with compositions of x ≤ 0.333 were annealed, in order to form a single phase material. Bromide substitution leads to smaller unit cell size and lower temperature and enthalpy of the order-disorder phase transition of NaBH₄. There is a linear relation between the amount of substitution, the temperature, the enthalpy and the kinetics of the phase transition. This linear relation between enthalpy and amount of substitution can be expressed by the function ΔH = ?6.268x + 1.206 where x is the amount of substitution and ΔH is the enthalpy.     

Point defect diagrams for pure and doped titanium (IV) oxide TiO2−δ in temperature range of 1073–1573 K

Abstract

The point defect diagrams in non-stoichiometric titanium (IV) oxide TiO_2?δ, pure and doped with M³⁺ and M⁵⁺ metal ions, are presented in this work. A new method was used for the calculations of the diagrams. This method is based on derived relations between standard Gibbs energy of formation of oxygen vacancies and interstitial cations, intrinsic ionic and electronic defects and oxygen pressure at which the oxide has stoichiometric composition, and it uses experimental values of deviation from the stoichiometry. The calculations were performed using the results of studies obtained by many authors in the temperature range of 1073–1573 K.