Vacuum Hot Extraction Research Articles

The determination of hydrogen and deuterium in Zr–2.5Nb material by hot vacuum extraction mass spectrometry

An analysis method for the determination of H and D concentrations in Zr–2.5Nb material has been established based on hot vacuum extraction and isotope dilution mass spectrometry. Hot vacuum extraction enables complete removal of the hydrogen isotopes from the sample. The isotope dilution technique is used to determine quantitatively the amount of hydrogen isotopes in the extracted gas. Methods for preparing standards of H, D or H and D in Zr–2.5Nb have also been established. These ‘in-house’ standards are used to assess the performance of the analysis method. The analysis uncertainty, based on the determined content relative to the dosed H or D isotope content of each standard, is 1% (at a level of confidence of 95%) for samples containing greater than ∼5 μmoles H or D. The uncertainty increases to 5% as the sample content decreases to 0.5 μmoles H or D. The uncertainty of this analysis method is well within the requirements for surveillance examinations of CANDU ® reactors and post-irradiation examinations of reactor components.

Solubility and partitioning of hydrogen in metastable Zr-based alloys used in the nuclear industry

Abstract Terminal solubility and partitioning of hydrogen in Zr–Nb alloys with different niobium concentrations were examined using differential scanning calorimetry and hot vacuum extraction mass spectrometry. Specimens were charged to different concentrations of hydrogen and annealed at 1123 K to generate a two-phase structure consisting of α-Zr (Zr–0.6 wt.% Nb) and metastable β-Zr (Zr–20 wt.% Nb) within the alloy. Specimens were aged at 673 and 773 K for up to 1000 h to evaluate the effect of the decomposition of the metastable β-Zr to α-Zr+β-Nb on the solubility limit. The results show that the solubility limit for hydrogen in the annealed Zr–Nb alloys is higher than in unalloyed Zr and that the solubility limit increases with the niobium concentration of the alloy. They also show that the hydrogen solubility limits of the completely aged Zr–Nb alloys are similar and approach the values for pure α-Zr. The solubility ratio of hydrogen in β-Zr (Zr–20 wt.% Nb) to that in α-Zr (Zr–0.6 wt.% Nb) was found to range from 9 to 7 within the temperature range 520–580 K.

Determination of H2 and D2 content in metals and alloys using hot vacuum extraction

A hot vacuum extraction technique for the determination of hydrogen in metal and alloy samples has been standardised. After measuring the total pressure of the evolved gases, individual hydrogen and deuterium intensities are measured using an on-line quadrupole mass spectrometer. Synthetic mixtures of H2 and D2, in known concentrations, have been analysed by QMS and an analytical expression correlating the measured [D2]/[HD] intensity ratio with the mole fraction of deuterium in the synthetic mixture has been arrived at. The precision and accuracy in the measurement of hydrogen is about 10% at 50 ppmw level.

Hydrogen solubility limits in α- and β-zirconium

Specimens of pure zirconium and Zr–20Nb alloy were charged to different hydrogen concentrations from the gas phase at 673 K. Before and after charging with hydrogen, the Zr–20Nb specimens were annealed in vacuum at 1123 K for 1 h and cooled to room temperature within about 30 min to produce a β-Zr structure. Some of these specimens were annealed further at 773 K for about 500 h to completely transform them to ( α-Zr+ β-Nb) phase. The specimens were analyzed for hydride transition temperatures using differential scanning calorimetry and for hydrogen concentration using hot vacuum extraction mass spectrometry. The hydrogen solubility limits found for pure Zr are in good agreement with the previously reported values. The solubility limits found in β-Zr are about two orders of magnitude higher than the solubility limits in α-Zr and the solubility limits found in the aged Zr–20Nb alloy are very close to those in α-Zr.

Vacuum fusion-mass spectrometric determination of H, N and O in U 3Si fuel using the standard addition technique

A vacuum fusion-mass spectrometric method is described for the determination of H, N and O in uranium suicide fuels. Samples are fused with an 85% Pt/15% Sn flux in a graphite crucible heated to 1300 °C to release nitrogen and oxygen as N 2 and CO, respectively. Hydrogen evolves more readily and is determined without the flux, to minimize the H 2 blank. The H + 2 , C + and N + signals are used to determine the partial pressures of the extracted H 2, CO and N 2, after calibration with known gas mixtures. The precision and accuracy of gas analysis is ca. 2% (1 s). The N and O determinations in fuel samples are quantitated by the standard addition technique, which shows recoveries of 91 and 99% for N and O, respectively. The hydrogen results showed good agreement with those obtained by an independent hot vacuum extraction method. The overall uncertainty of fuel analyses is large because of fuel heterogeneity. Detection limits are: H, 1; N, 9; O, 30 μg g .

Hydrogen solubility limits in Excel, an experimental zirconium-based alloy

Specimens of Excel alloy were charged to different hydrogen concentration levels from the gas phase. Two different techniques were used to determine the hydride dissolution and precipitation/nucleation temperatures on heatup and cooldown of the specimens. These were the differential scanning calorimetry (DSC) and dynamic elastic modulus (DEM) techniques. Hydrogen concentration in the specimens was measured using hot vacuum extraction methods. The hydrogen solubility limit in Excel is found to be higher than for Zircaloy-2 or Zr-2.5wt.% Nb. Similar to other zirconium alloys, a strong hysteresis is observed. The hydride dissolution temperatures measured by both DSC and DEM techniques are in good agreement and do not depend on the experimental conditions. However, the precipitation temperatures are very sensitive to Tmax (the highest temperature reached in the heating/cooling cycle). The reason for the difference in solubility between Excel and, particularly, Zr-2.5wt.% Nb is explored.

Diffusivity and Solubility of Hydrogen in Grain-Refined Aluminum

Diffusion coefficients and solubilities of hydrogen in grain-refined aluminum have been measured by a vacuum hot extraction method. Four samples with different grain sizes are prepared by melting, addition of Ti and B, casting, remelting and unidirectional solidification. Grain-refined samples contain some small particles in the matrix. The hydrogen diffusivity follows an Arrhenius type linearity on an inverse temperature dependence at 573 to 873 K. The diffusivity is not influenced by the small particles in the matrix, and depends only on the grain size. We have confirmed a propriety of the «Grain Boundary Cross Effect » relating to both of a fast diffusion along grain boundaries and of a suppressed diffusion by a hydrogen trapping at nodes or junctions of grain boundaries

一方向凝固させたＡｌ‐Ｓｉ合金鋳塊中の水素拡散

Hydrogen diffusivity in Al-(2-14mass%) Si alloy ingots melted in nitrogen gas flow and solidified unidirectionally were measured by a vacuum hot extraction method. The diffusivity of D1 for as-cast samples decreased to D2 for hydrogen-charged and extracted samples, under an influence of the heating effects. The differences between D1 and D2 increased at the lower temperatures and with amounts of eutectics. The heating effects attended with the decreasing of diffusivity were due to two phenomena. The first was a loss of a long-range enhanced diffusion paths along the surfaces on the thin plate-like particles of eutectic silicon in as-cast samples, and the second was a grow-up of hydrogen trapping at the large granular silicon particles precipitated in α-aluminum at around 673K. The hydrogen solubilities in Al-Si alloys increased with the concentration of silicon.

Effect of retained austenite on the hydrogen content and effective diffusivity of martensitic structure

In this work, the effects of retained austenite on the hydrogen content and the effective hydrogen diffusivity of an otherwise fully martensitic structure have been studied. In the electrochemical permeation experiment, the results on the first permeation transient indicate that high-carbon as-quenched specimens have a lower effective diffusivity than those with an additional subzero treatment. This was due to the presence of retained austenite in the former specimens, which afforded more sites for hydrogen trapping throughout the specimen membrane, hence lowering the hydrogen diffusion during the first transient. As the hydrogen traps were filled up, however, the second permeation transients gave similar effective diffusivity for both as-quenched and quenched + subzero-treated specimens. After hydrogen charging in hydrogen sulfide solution, the hydrogen contents of the specimens were determined using the vacuum hot extraction method. The results show that the hydrogen contents of as-quenched specimens were higher than those of the specimens subjected to quenched + subzero treatment. This again was due to the existence of retained austenite in as-quenched martensitic matrix, where the interfaces between the retained austenite and martensitic plates provided extra sites for hydrogen trapping. The hydrogen content of the presenting retained austenite in the martensite was independent of the carbon content of the specimen, but only depended on the hydrogen-charging period.

Methods for the determination of lithium and impurities in Pb17Li

Analytical methods for the determination of the main compounds and impurities in Pb17Li eutectic alloy which are used in our laboratory are summarized. Metallic impurities and the lithium content are analysed by means of atomic absorption spectrometry or optical emission spectrometry with inductive plasma excitation after decomposition of the samples in nitric acid. The determination of carbon is performed by combustion in oxygen and IR-absorption of CO2. Nitrogen is distilled as NH3 by means of the micro-Kjeldahl method and photometrically determined because of its small quantity. The most important non-metallic impurity is oxygen. The analysis for oxygen is performed using vacuum hot extraction. The samples have to be carefully protected against contamination by air and moisture.The estimation of oxygen contents resp. chemical activities is successfully performed using electrochemical meters. Thoria-yttria, zirconia-yttria or -calcia are suitable as solid electrolyte materials, indium-indium oxide serves as oxygen reference potential electrode. The advantage of the oxygen meters is that they detect the oxygen contents in solution in the liquid alloy. The meters can also be used to roughly measure the chemical activity of lithium in the liquid alloy. The temperature range to apply the meters is 350 to 500°C.Analytical techniques are also necessary to detect corrosion phenomena in suurface areas of materials. The glow discharge optical spectrometry is a method which determines elemental concentrations of up to 35 elements in relation to the distance from the surface. Measurements are performed up to 50 μm depth, from the adherent layer of Pb17Li into the material matrix. This technique has the capacity to measure quantitatively and sensitively lithium concentration profiles in the adherent layer and the corroded material.

Technical Note:Electrochemical Behavior of Ti-30Mo in a Gamma Radiolysis Environment

The amounts of hydrogen take-up by Ti-30Mo alloy were measured by hot vacuum extraction. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were applied to investigate the oxide layers and morphology of the surfaces after free immersion in the brine solution at 108 C, both with and without radiation. In situ measurements of the open circuit potential (OCP) and polarization behavior were conducted to study the corrosion properties of Ti-30Mo in brine at 25 C, both with and without radiation. Furthermore, hydrogen peroxide was added to brine to discover what effects are produced by H/sub 2/O/sub 2/ without radiation. These results are compared with the effects of ..gamma...

Electromigration of hydrogen and deuterium in tantalum: Isotope effect

Electromigration experiments at steady-state were conducted to determine the effective valence of hydrogen isotopes in tantalum specimens at room temperature (25 °C). Varying solute concentrations were obtained by gas-phase and electrolytic charging of the specimens. The transient concentration profiles of several specimens were monitored by a resistance technique allowing a controlled current through the samples. Steady-state concentration profiles were obtained by direct hot-vacuum extraction measurements. The results indicate a strong concentration dependence for the effective valence and evidence of a possible reversal in the direction of solute migration. While the reversal in the case of deuterium migration is not certain, an isotope effect on the effective valence as a whole is substantial. Deuterium has a 30 pct higher effective valence. The hypothesis that solute segregation at lattice defects and differing electronic structure of the defects and the perfect lattice are responsible for the concentration dependence of effective valence is found invalid as both cold-worked and annealed specimens did not indicate any microstructure effect on Z*. The concentration dependence of diffusion coefficient does not justify the strong dependence of Z* on concentration observed experimentally.

真空抽出法によるアルミニウム中の分子状水素の挙動と抽出過程

The vacuum hot extraction (VHE) and the vacuum fusion extraction (VFE) methods were tried. Molecular hydrogen in aluminum having gas pores is extractive by the VHE method. The extraction proceeds through the dissociation, dissolution, diffusion and evolution processes. The molecular hydrogen requires time for extraction so longer than the diffusive hydrogen as 4hrs or more. In the VFE method, molecular hydrogen is completely extracted within 1hr. Hydrogen in aluminum having gas pores is extracted by the VHE method in the following three steps in accordance with elevated temperatures: (i) When the pores 10-2cm or more in radius in the surface layer up to 13μ in depth attain the internal gas pressure 16.5 atm or more at 250°to 480°C, they grow as blisters and evolves molecular hydrogen. Hydrogen extracted from the blisters is less than 0.04cc/100g. (ii) Hydrogen 0.61cc/100g in solution diffused in aluminum cast in a green sand mold is extracted at 480°to 660°C, Hydrogen over this value forms pores and remains in molecular state. And (iii) The residual molecular hydrogen is extracted at above 660°C.

粉末タンタル中窒素の高温真空加熱定量法における黒鉛の効果

粉末タンタル中窒素の高温真空加熱定量法における黒鉛の効果

Ein verfahren zur bestimmung kleinster stickstoffgehalte in Niob durch vakuumheissextraktion

]A method for the vacuum hot extraction of gases without the use of crucibles and fluxes is described and applied to the determination of gas contents of high-melting-point metals at low atomic ppm. The Nb-N system is quoted as an example. The reaction vessel (after baking at 150 °C) was evacuated by means of a turbomolecular pump at a effective rate of 240 ls −1. Degassing was carried out in ultra-high vacuum employing a residual nitrogen partial pressure of 2 × 10 −10 Torr and liquid and/or solid samples were melted by the lévitation method in a radiofrequency field. The evolved gases were detected using a quadrupole mass filter and the quantity of nitrogen evolved calculated by integrating the partial pressure over the time period at a given pumping rate independent of pressure. In addition to giving a chemical analysis of the gas-metal system at low atomic ppm, this method also enables the thermodynamic and kinetic parameters to be determined. The minimum detectable concentration of nitrogen dissolved in niobium was ca. 0.5 at. ppm, the distribution coefficient between solid and liquid niobium 0.76 with the solubility of nitrogen being unaffected by additions of carbon up to 4.5 at.%. The contamination of high purity niobium during sample preparation has also been investigated.

Helium Charging of Metals by Tritium Decay

The results of a study on the use of the decay of tritium to helium as a method of charging metals with helium were presented. Tritium was dissolved into vanadium and niobium specimens at elevated temperatures, allowed to decay to helium at room temperature, and then removed from the given specimen by hot vacuum extraction. Post-high-temperature test /sup 3/He concentrations up to 500 appm were achieved and were found to agree within +-7 percent with tritium decay concentration calculations. Substantial ductility decreases were found in niobium specimens tested at 1020/sup 0/C and containing greater than 130 appm helium. The ductility losses appeared to correlate with the appearance of helium on the grain boundaries. A niobium specimen containing 170 appm helium and subjected to an 1800/sup 0/C anneal exhibited a substantial loss of load-carrying grain-boundary area due to grain-boundary helium bubble formation.

New methods for the determination of hydrogen content of aluminum and its alloys: Part I. Improvements in the vacuum extraction method

The vacuum hot extraction method, first proposed by Ransley for the determination of hydrogen content of aluminum and its alloys, was systematically investigated to check if it could be considered as a reference procedure for the development of other methods directly applicable in routine work. For that, the use of an improved apparatus involving a mass spectrometer as gas detector and specimens intentionally charged with deuterium —a tracer whose properties are similar to those of hydrogen—permits the following conclusions: 1) The method is correct for any alloy, even for all the alloys with a high magnesium or zinc content, 2) The “getter effect” which could lead to inaccurate results does not occur, provided the pumping speed of the transfer pump exceeds the rate of outgassing from the sample, 3) The extraction from the solid phase seems to be complete, since results obtained in this condition are not significantly different from those obtained from melted samples. 4) The time required for an analytical determination (several hours) due essentially to the preliminary operations, cannot be practically reduced by extraction at higher temperature in the liquid state. The Ransley method can thus be considered as a reference method for checking other more practical methods.

New methods for the determination of hydrogen content of aluminum and its alloys: Part II. Rapid determination by the nitrogen carrier fusion method

A method for determining hydrogen in steel by melting with nitrogen as a carrier gas was adapted for aluminum and its alloys. Dehydrogenationvs temperature was investigated in order to define an optimal sequence of operating conditions. The results obtained by the method were systematically compared to those given by the reference vacuum hot extraction method. The essential characteristics of this new method can be summarized as follows: 1) The detection limit is 0.02 ml/100 g (0.02 ppm H2). 2) The method is valid for any alloy, even for those with high volatile constituent content such as Zn or Mg. 3) The bulk hydrogen content is not significantly different from that given by the vacuum hot extraction method. 4) “Surface” hydrogen could be eliminated by a thermal treatment at 400°C prior to melting. 5) Correlations appeared between changes in thermal and dehydrogenation curves, the last one representing a characteristic spectrum of the alloy studied. 6) A complete analysis requires 15 min instead of several hours for the hot extraction method. It is thus applicable in routine industrial work.

Effect of gas extraction temperature on determination of hydrogen in titanium by vacuum hot extraction

Effect of gas extraction temperature on determination of hydrogen in titanium by vacuum hot extraction

The preparation and purification of americium metal by evaporation

In order to redetermine some physical and chemical properties of americium metal, several grams of 241Am have been prepared by two independent methods: lanthanum reduction of the oxide and thermal dissociation of the intermetallic compound Pt 5Am. After its separation from excess lanthanum or alloy constituent by evaporation, americium metal was further purified by sublimation at 1100 C and 10 −6 Torr. Irrespective of the method of preparation, the temperatures of evaporation or condensation and the material of the condenser, the americium samples displayed the same d.h.c.p. crystal structure. As determined by vacuum hot extraction, the oxygen, nitrogen and hydrogen contents are equal or smaller than 250, 50 and 20 ppm, respectively.