Hydrogen In Aluminum Research Articles

Behavior of hydrogen in aluminum exposed in different atmospheres

Hydrogen in aluminum alloys frequently causes degradation of mechanical properties and surface quality of the products. Thus, the behavior of hydrogen in aluminum has been extensively studied. However, there has been an appreciable controversy in whether hydrogen intrudes the aluminum when exposed to air with moisture. In this study, hydrogen behavior in a pure aluminum foil that had been dehydrogenated and subsequently exposed to mainly air at temperatures ranging from room temperature to 550°C was analyzed by means of TDS, thermal desorption spectroscopy. In the specimens exposed to air and water at room temperature, hydrogen evolution was clearly observed at temperatures above about 450°C in the TDS spectra. This means that moisture at the specimen surface was converted to atomic hydrogen through the reaction with aluminum which subsequently diffuses into the specimen and is trapped by certain sites. Additionally, the specimens were annealed at several temperatures and humidities for 1 h. In the specimens exposed to air at different temperatures and humidity, the amount of hydrogen contained in the specimens was increased as the humidity and the temperature. Two peaks were seen at about 450 and 550°C in the spectra of the specimens containing large amount of hydrogen, and were found to correspond to the hydrogen trapped by dislocations and micro pores, respectively.

Nanostructures from Hydrogen and Helium Implantation of Aluminum

AbstractThis study investigates a pathway to nanoporous structures created by hydrogen and helium implantation in aluminum. Previous experiments for fusion applications have indicated that hydrogen and helium ion implantations are capable of producing bicontinuous nanoporous structures in a variety of metals. This study focuses specifically on implantations of hydrogen and helium ions at 25 keV in aluminum. The hydrogen and helium systems result in remarkably different nanostructures of aluminum at the surface. Scanning electron microscopy, focused ion beam, and transmission electron microscopy show that both implantations result in porosity that persists approximately 200 nm deep. However, hydrogen implantations tend to produce larger and more irregular voids that preferentially reside at defects. Implantations of helium at a fluence of 1018 cm-2 produce much smaller porosity on the order of 10 nm that is regular and creates a bicontinuous structure in the porous region. The primary difference driving the formation of the contrasting structures is likely the relatively high mobility of hydrogen and the ability of hydrogen to form alanes that are capable of desorbing and etching Al (111) faces.

21202 水素マイクロプリント法によるアルミニウム中の水素の可視化 : 検出効率に及ぼす試料表面イオンプレーティング処理の影響(材料の特性と組織(1),OS.6 材料の特性と組織)

21202 水素マイクロプリント法によるアルミニウム中の水素の可視化 : 検出効率に及ぼす試料表面イオンプレーティング処理の影響(材料の特性と組織(1),OS.6 材料の特性と組織)

Al合金溶湯鍛造材の疲労特性に及ぼす溶存水素および大気湿度の影響

Al合金溶湯鍛造材の疲労特性に及ぼす溶存水素および大気湿度の影響

ＳＯ２雰囲気中で暴露したＡｌ‐Ｍｇ合金の焼なまし時の水素吸収挙動

Hydrogen in aluminum and its alloys has a great influence on the occurrence of blisters. It is known that hydrogen may be absorbed during heat treatment process. In this study, the effect of exposure to SO2-bearing atmosphere on the hydrogen absorption into Al–Mg alloys during annealing was investigated. The exposure treatment was confirmed to cause absorption of sulfur on the specimen surface, and was found to increase the hydrogen content during annealing in a wet atmosphere due to promotion of hydrogen absorption. In contrast, without the exposure treatment, the hydrogen content decreased during the annealing due to release of hydrogen. The amount of absorbed hydrogen increased with increasing annealing temperature, time and humidity in the atmosphere. The morphology of oxide film formed during annealing was affected by the sulfur adsorption on the surface and was presumed to influence the hydrogen absorption/release behavior in Al–Mg alloys. In pure aluminum, however, there was no significant influence of the exposure on the inner hydrogen content after annealing, while the number of blisters that occurred on the surface after annealing increased by the sulfur adsorption on the surface prior to annealing.

Analysis of polydisperse bubbles in the aluminium–hydrogen system using a size-dependent contrast

The characterization of hydrogen defects in an aluminium–hydrogen system was performed previously [Buckleyet al.(2001).J. Appl. Cryst.34, 119–129] using small-angle scattering, inelastic neutron scattering and electron microscopy techniques. This analysis resulted in the determination of the relative change in lattice parameter as a result of hydrogen introduction into the Al matrix. However, this method relied on the average volume of the bubbles of hydrogen and also the pressure in a bubble of average volume. The characterization of the Al–H system has been improved by considering the size polydispersity of the hydrogen bubbles. The determination of a volume-fraction size distribution of the bubbles from small-angle scattering data has allowed a polydispersity analysis to be undertaken. A size-dependent contrast has been utilized in the modification of the volume-fraction size distribution into a more accurate form that accounts for varying concentrations of hydrogen within bubbles of different sizes. The determination of the size-dependent contrast is based upon an equation of state for molecular hydrogen which incorporates the compressibility of hydrogen under high pressures. The formation of alane (AlH3) is also investigated, as it can be formed by the chemisorption of hydrogen in aluminium under high pressures. The polydispersity analysis has allowed a more accurate description of the Al–H system and can be applied to similar scattering systems where the scattering length density is not constant over the whole scattering size regime.

3613 Al合金溶湯鍛造材の疲労特性に及ぼす溶存水素の影響(S13-3 環境効果,S13 実用構造材料の疲労問題と健全性評価)

Rotating bending fatigue tests were carried out for a squeeze cast Al alloy AC4CH-T6, in order to investigate the effect of hydrogen in molten aluminum on fatigue properties. The hydrogen contents were 0.22 and 0.38cc/100gAl. Voids were increased with increase in hydrogen content. However, static strength, ductility and fatigue strength were hardly influenced by hydrogen content. Most fatigue life was occupied by the growth life of a small crack which was evaluated by the small crack growth law.

SIMS study of deuterium distribution in chemically charged aluminum containing oxide layer defects and trapping sites

Hydrogen (deuterium) distribution that occurred during electrochemical and chemical charging in a high purity single aluminum crystal (grown in [1 1 0] direction) was studied, using Secondary Ion Mass Spectrometry (SIMS). Deuterium distribution was measured for specimens that were electrochemically charged in H 2SO 4 solutions or chemically charged in NaOH solutions, for various charging times at room and higher temperatures. The effect of “aging” related defect formation in aluminum was determined. In the hydrogenation of aluminum under high fugacity conditions (such as electrochemical and chemical charging), non-steady state diffusion produces concentration–distance profiles that may not be calculated by assuming simple diffusion behavior. Moreover, the hydrogen–vacancy interactions and microstructural changes (defect formations) must be taken into account in the process of the characterizing the state of hydrogen in aluminum. Interstitially hydrogen enters the aluminum lattice poorly. Hydrogen penetrates the aluminum matrix accompanied by vacancies formed at the surface during conditions of high fugacity. Aluminum hydroxide and hydrogen interactions form hydrogen–vacancy complex at the surface, which diffuses into the volume and then clusters to form H 2 interior bubbles in the aluminum. The SIMS technique was used to characterize hydrogen (deuterium) distributions in chemically charged aluminum in the order to obtain concentrations–depth profiles. The advantages of this method are that the actual concentrations–depth profiles are obtained and they include microstructural changes, such as defects (vacancies, voids, bubbles, micro-cracks, dislocations and surface oxides) formed during the electrochemical and chemical reactions in aluminum with aqueous solutions.

Characterization of hydrogen defects forming during chemical charging in the aluminum

The behavior of hydrogen and deuterium in high-purity aluminum introduced by high-fugacity chemical techniques has been studied. The aims were to establish: (a) the presence of the hydrogen–vacancies clusters and bubbles formations, (b) their size and size distributions, (c) the symmetry of the clusters and the dependence of these parameters on the hydrogen charging conditions and on subsequent annealing procedures and (d) the kinetics of hydrogen release from these clusters and the structure of the remaining defects produced when the hydrogen is removed. The study was combined with a parallel series of experiments, which utilized secondary ion mass spectrometry (SIMS), X-ray techniques (Laue, small-angle X-ray scattering (SAXS), diffractometer measurements), transmission electron microscopy (TEM) and scanning electron microscope (SEM). The experiments revealed the existence of a large size distribution of hydrogen voids and bubbles on the surface and under the surface obtained during electrochemical and chemical charging. The depth of these defects was controlled by electrochemical and chemical charging conditions and depended on the charging time. Hydrogen nearly entered the aluminum lattice interstitially. A TEM technique revealed the existence of surface bubble from the interactions between the aluminum hydroxide with hydrogen and formed a hydrogen–vacancy complex at the surface, which diffused into the volume and then clustered to form H 2 interior bubbles. A large size (some micrometers in the diameter) to very small sizes (nanometers in the diameter) in the distribution and variety in the density of the surface bubbles was obtained. Between the densely packed surface bubbles, formation of the dense dislocations could be seen. Internal bubble with symmetrical bend contours of the height and dense distributions of dislocations was observed.

Hydrogen in aluminum: First-principles calculations of structure and thermodynamics

Despite decades of study, several key aspects of the Al-H system remain the subject of considerable debate. In an effort to elucidate some of these unknowns, we perform a systematic study of this system using first-principles density-functional calculations. We show that generalized gradient approximation (GGA) calculations provide an accurate picture of energetics, phase stability and structure, diffusion, and defect binding in the Al-H system. A series of calculations for hydrides in the M-H systems (M=Al, Ba, Ca, K, Mg, La, Li, Na, Ni, Pd, Sc, Sr, Ti, V, and Y) also shows that the GGA calculations are a quantitatively accurate predictor of hydride formation energies. For Al-H, we find: (i) In agreement with experiment, the observed metastable hydride, ${\mathrm{AlH}}_{3}$ is found to have a small, negative formation enthalpy at ambient conditions, but a strongly positive formation free energy. (ii) Linear response calculations of ${\mathrm{AlH}}_{3}$ yield vibrational frequencies, phonon densities of states (DOS), and heat capacities in excellent agreement with experimental measurements, and suggest the need for a reinterpretation of measured phonon DOS. (iii) Atomic relaxation and anharmonic vibrational effects both play an important role in the tetrahedral versus octahedral interstitial site preference of H in Al. (iv) The calculated heat of solution of H in the preferred tetrahedral site is large and positive (+0.71 eV), consistent with experimental solubility data and with Al as an endothermic hydrogen absorber. (v) Interstitial H interacts strongly with Al vacancies $(\ensuremath{\square}),$ with a calculated H-$\ensuremath{\square}$ binding energy of 0.33 eV. (vi) In the absence of vacancies, the calculated migration energy of H between the tetrahedral and octahedral interstitial sites is 0.18 eV, but for H migrating away from an Al vacancy, the migration energy increases to 0.54 eV. Vacancy trapping of H can therefore provide an explanation for observed disparate H migration barriers.

Behaviour of hydrogen impurity in aluminium alloys during anodizing

The present study examines the behaviour of hydrogen impurity in an Al–6.5 at.% W alloy during anodizing, using elastic recoil detection and nuclear reaction analyses. Increased concentrations of hydrogen are found near the alloy/anodic film interface, amounting to ∼2×10 15 H atoms cm −2 for the particular alloy, containing 0.1–0.3 at.% hydrogen in the bulk regions, and conditions of anodizing. The enrichment arises from hydrogen in the alloy (i) diffusing to the interface, which acts as a trap, or (ii) accumulating at the interface, due to the growth of the anodic film, or a combination of both processes. Diffusion is consistent with the known mobility of hydrogen in aluminium near ambient temperature. Further, accumulation, and subsequent oxidation, of hydrogen are expected based on the general behaviour of alloying elements in anodized aluminium. The anodic films contained ∼0.1–0.3 at.% hydrogen, originating from either the electrolyte or the alloy.

The detection of hydrogen in molten aluminium

The presence of hydrogen in aluminium poses problems to the foundry and casting industries, because high residual hydrogen contents in molten aluminium cause significant porosity in the solid aluminium after casting. This usually renders the product useless as it may fail mechanically. Therefore, fast, accurate and reliable techniques are required for monitoring the dissolved hydrogen content in molten aluminium, but this particularly harsh environment places considerable restrictions on the equipment that can be used. Several methods are available for the determination of hydrogen in aluminium melts, but they either suffer problems of accuracy, reliability and longevity or are not applicable to industrial environments. It is considered that the most appropriate device for the hydrogen analysis in aluminium melts should be an electrochemical sensor, which employs a proton conducting solid electrolyte in conjunction with a measuring electrode and a suitable reference electrode. The electromotive force of such a cell allows direct calculation of the hydrogen concentration in the melt. However, all the electrochemical sensors reported in the literature thus far exhibit distinct drawbacks. This article discusses the various techniques for the determination of hydrogen in molten aluminium with particular emphasis on the benefits and shortcomings of the existing electrochemical sensors.

Characterization of the charging techniques used to introduce hydrogen in aluminum

Aluminum foils and single crystals of varying thickness and purity were charged with hydrogen using gas plasma, electrochemical and chemical methods. The concentrations of hydrogen introduced were monitored by gas extraction and prompt γ-activation analysis measurements. X-ray diffraction measurements indicated that within experimental error there was either a small lattice contraction or a zero change in lattice parameter after charging. It was found that during cathodic and chemical charging an Al(OH) 3 layer formed on the surface. Extensive experiments revealed that unless the surface layer formed during the charging process was removed, the concentration of H measured with either analysis method was erroneously high. The plasma charged samples do not form an Al(OH) 3 layer on the surface, but instead form H–vacancy complexes at the surface which diffuse into the volume and then cluster to form H 2 bubbles. The structure of the hydrogen solutes introduced by the charging methods is discussed and the diffusivity of a hydrogen–vacancy complex at 300 K is estimated.

The interaction between lattice vacancies and hydrogen in aluminum

The thermodynamic properties of aluminum–hydrogen solid solutions containing lattice vacancies have been calculated using a canonical ensemble approach and a Fermi–Dirac distribution to describe the distribution of H atoms between vacancy-generated sites and ‘normal’ interstitial sites. The equilibrium vacancy concentration has been calculated as a function of temperature and hydrogen concentration.

Behavior of Hydrogen in Superheated Aluminum and its Alloys Melt

The quantitative relationship between the hydrogen content and the superheated temperature of the aluminum and its alloys melt has been investigated by using HYSCAN II. It is found that the hydrogen content in aluminum and its alloys melt can be controlled by thermal-rate treatment technology. The experiment results indicated that the hydrogen content in aluminum and its alloys melt increases with increasing temperature and decreases with decreasing temperature under certain superheated temperature. The hydrogen in different existences in aluminum melt has different reversibility. The hydrogen content can be greatly reduced in superheated aluminum and its alloys melt by thermal-rate treatment technology.

Hydrogen sensing in molten aluminium using a commercial electrochemical sensor

A commercial electrochemical sensor for the determination of hydrogen in molten aluminium was critically assessed under laboratory conditions. The probes make use of a proton conducting solid electrolyte and were found to measure correct emfs for several hours. The applicability of the recently developed current reversal technique on this type of sensor was demonstrated. The long-term behaviour of the device was investigated and found to be critical.

The identification of hydrogen trapping states in an Al-Li-Cu-Zr alloy using thermal desorption spectroscopy

Thermal desorption spectroscopy (TDS) was utilized to identify several metallurgical states in an Al -2Li - 2Cu-0.1Zr (wt pct) alloy, which trap absorbed hydrogen. Six distinct metallurgical desorption states for hydrogen were observed for tempers varying from the T3 to peakaged condition. Lower energy thermal desorption states were correlated with interstitial sites, lithium in solid solution, and δ′ (Al3Li) precipitates. These states have trap-binding energies ≤25.2 kJ/mol. Under the charging conditions utilized, approximately 4 pct of the total (e.g., trapped and lattice) hydrogen content was associated with interstitial sites, consistent with the view that the intrinsic lattice solubility of hydrogen in aluminum is very low. In contrast, dislocations, grain boundaries, and T1 (Al2CuLi) particles were found to be higher energy-trap states with trap-binding energies ≥31.7 kJ/mol. Approximately 78 pct of all absorbed hydrogen occupied these states. Moreover, greater than 13 pct of the available trap sites at grain boundaries were occupied. Such a high hydrogen coverage at grain-boundary sites supports the notion that hydrogen contributes to grain-boundary environmental cracking in Al-Li-Cu-Zr alloys. Also, it points out the error in assuming that hydrogen cannot play a major role in cracking of Al-based alloys due to the low lattice solubility.

アルミニウム中の水素の検出とその可視化

アルミニウム中の水素の検出とその可視化

The diffusion and trapping of hydrogen in high purity aluminum

The diffusion and trapping of hydrogen in high purity (99.999 wt%), polycrystalline aluminum was investigated using both isothermal and constant heating rate desorption techniques. Constant heating rate desorption was used to elucidate the effects of microstructural trap states on the apparent diffusivity of hydrogen in aluminum. Isothermal desorption of hydrogen from annealed, uniformly charged, cylindrical specimens was bulk diffusion controlled. Diffusion data exhibited simple Arrhenius behavior between 30 and 600°C and is described with 95% confidence by D=1.75±0.15×10 −8( m 2/s ) exp{−16.2±1.5( kJ/mol)/RT}. Constant heating rate desorption spectra revealed three distinct trapping states with desorption energies 15.3±4.8, 43.5±17.5, and 84.8±32.2 kJ/mol. These trapping states are associated with interstitial lattice sites, dislocations, and vacancies, respectively. Identification, quantification, and understanding the role of these trap states in permeation and desorption experiments helps explain the large scatter in reported values of the diffusivity of hydrogen in aluminum.

The dose effect of silicon implantation on hydrogen trapping in aluminum

We have studied the dose effect of silicon as an added element on the trapping of hydrogen in aluminum. For this purpose, we implanted 78 or 150 keV silicon ions into aluminum specimens with doses of 3 × 10 15–3 × 10 17Si/cm 2 and successively 30 keV hydrogen ions with a dose of 3 × 10 16H/cm 2 at 300 K. After the hydrogen implantation, the depth profiles and thermal behaviors of hydrogen in the samples were measured by means of an elastic recoil detection (ERD) method. It was found that the silicon element implanted into aluminum is supersaturated even at 5 at.% and drastically affects the thermal behavior of hydrogen, depending on the dose.