The solubility of hydrogen in liquid binary Al-Li alloys

The solubility of hydrogen in liquid binary aluminum alloys with 1, 2, and 3 wt pct lithium has been determined for the temperature range of 913 to 1073 K and pressure 5.3 × 10⁴ to 10.7 × 10⁴ Pa, using an appropriate version of Sieverts’ method. The results fit the Van’t Hoff isobar and Sieverts’ isotherm and the solubility,S, is given by: Al-1 pct Li: log(S/S°) − 1/2 log(P/P°) = −2113/T/k + 2.568 Al-1 pct Li: log(S/S°) − 1/2 log(P/P°) = −2797/T/k + 3.329 Al-1 pct Li: log(S/S°) − 1/2 log(P/P°) = −2889/T/k + 3.508 whereS° is a standard value of solubility equal to 1 cm³ of diatomic hydrogen measured at 273 K and 101,325 Pa per 100 g of metal, andP° is a standard pressure equal to 101,325 Pa. Added lithium progressively increases the solubility of hydrogen in liquid aluminum, due more to its effect on the entropy of solution of hydrogen, through its influence on the liquid metal structure than to an increase in the solute hydrogen atom binding enthalpy.     

The solubility of hydrogen in solid binary aluminum-lithium alloys

The solubility of hydrogen in solid binary aluminum alloys with 1,2, and 3 wt pet lithium has been determined for the temperature range of 473 to 873 K and the pressure range of 26,700 to 113,300 Pa (0.26 to 1.12 atm), using an absorption/quench/desorption technique. The results fit the Van't Hoff isobar and Sieverts' isotherm and are given by log (S/S°)- log (p/p°) =-A/T/K +B whereS, S° are, respectively, the solubility and a standard value of solubility equal to 1 cm3 of diatomic hydrogen measured at 273 K and 101,325 Pa/100 g of metal;p, p° are, respectively, the pressure and a standard value of pressure equal to 101,325 Pa (1 atm). The values of the constantsA andB are Al-1 pet Li 473T/K 680:A = 358;B = 0.576 680T/K 873:A = 604;B = 0.620 Al-2 pet Li 473T/K 740:A = 273;B = 0.597 740T/K 873:A = 676;B = 0.767 Al-3 pet Li 523T/K770:A = 615;B = 1.272 770T/K 873:A = 830;B = 1.166 The solubility of hydrogen is one or two orders of magnitude greater in the alloys than in the pure metal and increases with lithium content. The results are consistent with the dissociative dissolution of a diatomic gas. The isobars are discontinuous at critical temperatures which lie within the a-phase field,i.e., 680, 740, and 770 K for Al-1 pet Li, Al-2 pet Li, and Al-3 pet Li, respectively, indicating a change in the character of the solution at lower temperatures due to an increase in the solute binding energy, which is attributed provisionally to an unidentified change in thea matrix. P. N. Anyalebechi, formerly with the Department of Materials Technology at Brunei, The University of West London, United Kingdom     

Experimental studies on hydrogen solubility in liquid ternary iron-nickel-chromium alloys

The hydrogen solubilities in liquid ternary iron-nickel-chromium alloys have been experimentally determined by Sieverts’ method. The experimental data have been evaluated with the help of regression analysis (Gauß-Jordan) and using own published empirical equations (polynomials). With the help of experimentally determined hydrogen solubilities and the coefficients of the polynomials, the concentration dependencies of hydrogen solubilities, interaction coefficients, enthalpies and entropies of hydrogen solution have been determined. The hydrogen solubility increases with increasing temperature and with an increase in the nickel and chromium concentration. The results have been represented as isothermal planes. The hydrogen solubilities in liquid ternary iron-nickel-chromium alloys (x_Cr ≤ 50%) have been predicted with the help of “Central Atoms” model, assuming the concentration dependencies of the “model parameter λ” and selecting the value of the coordination number (Z’ = 10) for each of the “reference elements” iron or nickel. The comparison between the experimentally determined and the predicted hydrogen solubilities in iron-nickel-chromium alloys confirms that the prediction of hydrogen solubilities in liquid system iron-nickel-chromium can be qualitatively made over a wide range of alloy concentrations (x_Cr = 50%) with the aid of “Central Atoms” model and with the assumption of concentration dependencies of the “model parameter λ”.     

The terminal solubility of hydrogen in niobium-tantalum alloys

The terminal solubility of hydrogen (TSH) in equilibrium with hydride in the Nb-Ta system is known to show a large intermediate maximum at temperatures in the region of 250 K. The origin of this “abnormal” behavior has not been successfully explained previously. In the temperature range of the TSH measurements, pseudo-binary (para-equilibrium) behaviour may be expected. Using the thermodynamic data available for the two pure metal-hydrogen systems, together with reasonable assumptions concerning the ternary mixtures, phase diagrams corresponding to complete equilibrium and paraequilibrium have been constructed for this system. It is clear from the phase diagrams that, rather than being anomalous, a large intermediate maximum in the TSH is the expected behaviour. It is suggested that an increase in the TSH on alloying is likely to be fairly general, irrespective of the relative affinity of solute and solvent for hydrogen.     

The solubility of hydrogen in molten aluminum alloys

The solubility of hydrogen in molten aluminum alloys containing copper, lithium, magnesium, and silicon has been calculated from the solubility of hydrogen in pure metals and binary metal-metal interaction parameters. For the aluminum-copper binary system, where experimental data exist, the agreement between calculated and experimental values is excellent. The solubility of hydrogen in liquid silicon was calculated from the solubility data in aluminum-silicon alloys.     

Effect of chromium on the hydrogen solubility in liquid ternary iron-cobalt-chromium alloys

The experimentally determined hydrogen solubilities (Sieverts’ method) in liquid iron–cobalt–chromium melts were described based on own already published empirical equations and applying the regression analysis (Gauß-Jordan). The experimental results are represented as perspective isothermal planes. Addition of chromium increases the hydrogen solubilities. The hydrogen solubility increases with increasing temperature. The concentration dependencies of the interaction coefficients, enthalpies and entropies of hydrogen solution were calculated from the experimentally determined hydrogen solubility. Assuming a concentration dependence of the model parameter “λ” of the “Central Atoms” model the hydrogen solubilities in ternary iron-cobalt-chromium (x_cr ≤ 20%) melts were predicted. These predictions were made using the own experimentally determined hydrogen solubilities of the binary system iron-cobalt (x_Co ≤ 100%) and iron–chromium (x_Cr ≤ 25%) with iron, and referred to the other two binary systems cobalt–iron (x_Fθ ≤ 100%) and cobalt–chromium (x_cr ≤ 20%) with cobalt as “reference element”. The predicted hydrogen solubilities were compared with the own experimentally determined hydrogen solubilities. The deviations between these two results are less than 2%.     

The solubility of the liquid oxysulfide phase in liquid Fe-O-S alloys

The solubility of the liquid oxide phase in liquid Fe-O alloys has been measured for the temperature range of 1378 to 1740 °C. Also the solubility of the liquid oxysulfide phase in liquid Fe-O-S alloys has been determined for the composition range of 0.08 to 0.30 wt pct oxygen and 0 to 0.5 wt pct sulfur. The oxygen content of liquid iron saturated with the liquid oxide phase is log O = ?6358/T + 2.76. The standard free energy for the formation of the oxide phase is: xFe(l) + O(pct) = Fe_xO(l); ΔG° = 242.4 ? 0.0829T + 166,990/T(kJ). The equation for the standard free energy in the temperature range of 1550 to 1650 °C may be written as: ?117.5 + 0.0496T (kJ). The effect of composition on temperature of saturation of liquid Fe-O-S alloys with the oxysulfide phase is:T(K) = ?6358/(log pct O ? 2.76) - (pct S)x [554 + 135.0(log O ? 2.77)]. The relationship applies for the composition range of 0.15 to 0.30 wt pct oxygen and 0.0 to 0.5 wt pct sulfur and temperatures from 1480 to 1680 °C.     

Measurement of hydrogen solubility in liquid iron alloys employing a constant volume technique

The solubility of hydrogen in liquid pure iron and in several liquid binary iron alloys at steelmaking temperatures has been determined by measuring changes in hydrogen pressure in a constant volume system. The solubility of hydrogen corrected to one atmosphere pressure was found to be 27.70 ± 1.28 cc (STP)/100 grams in liquid pure iron at 1600°C with a temperature coefficient of solubility of 2.9 x 10^-2 cc (STP)/°C. This solubility decreases with increasing concentrations of aluminum, boron, or silicon; slightly increases with increasing concentrations of chromium, nickel, and niobium; and is almost independent of the concentrations of copper or sulfur. The data are compared with those of previous investigators who employed the more conventional Sieverts’ or sampling techniques.     

铝锂合金中氢标准物质的研制

介绍了铝锂合金中氢标准物质的研制过程。该合金在大气下熔炼,为防止氧化采用了氩气保护方式对熔体进行保护。熔炼过程中,采用了特殊的精炼工艺使合金中的氢含量维持在1μg/g左右。熔炼完成后,在氩气保护下,用半连铸方法,将合金铸成120mm圆形铸锭。车去表皮均匀化后挤压成10mm圆棒。该标准物质经低倍检查没发现缺陷,化学成分均匀。采用高频加热-热导法、脉冲加热-热导法以及不同型号的定氢仪对氢进行分析,结果准确、可靠。     

Decomposition and dissolution kinetics ofδ′ precipitation in Al-Li binary alloys

Aside from its technological importance, the Al-Li alloy system also exhibits interesting phase transformations involving both equilibrium and metastable states. Recent theoretical studies have shown that a supersaturated solid solution could take different transformation paths when it is quenched into theα +γ′ field. Suggestions were made that a rapidly quenched solution phase should first undergo a congruent ordering transformation before it decomposes into a two-phase mixture by either a secondary spinodal decomposition or the classical nucleation and growth process. Moreover, a metastable miscibility gap was predicted at lower temperatures. The objective of this research is to study the transformation paths and dynamics in Al-Li binary alloys of three compositions (5.2, 7.0, and 12.0 at. pct Li). This investigation emphasizes thein situ small-angle X-ray scattering (SAXS) observations on specimens subjected to various aging conditions. Special attention is paid to the early stages of the transformation in an attempt to characterize the various possible modes of phase separation on one hand and to study the dynamics of the precipitation process on the other. The following results are obtained: the congruent ordering precedes decomposition at low temperatures; the metastableγ′ solvus curve is reconfirmed; but the predicted metastable miscibility gap is not found. Guinier radii measurements of the particles showed Ostwald ripening is quickly reached upon heating to the aging temperatures. Slowing down behavior is seen at aging temperatures close to the solvus boundary. Activation energies for Li diffusion were obtained using the modified Lifshitz, Slyozov, and Wagner (MLSW) model. A test of dynamical scaling behavior is carried out for the Al-12.0 at. pct Li alloy. Formerly Visiting Scientists at the University of Illinois     

The rate of hydrogen solution in liquid alloys

A study has been completed on the rate of hydrogen solution in inductively stirred liquid pure copper, nickel, cobalt, and several binary alloys of copper and of nickel. Results on the hydrogen solution rate in liquid pure iron also were obtained. A constant-volume Sieverts’ apparatus was used. The melts were exposed to hydrogen, and the rate of solution determined by the time change of gas pressure in the system. The rate of hydrogen solution for all pure metals in this study was controlled by transport of atomic hydrogen in the metal phase. This was directly supported by a) an increase in the hydrogen solution rate constant with melt surface area-volume ratio, b) a decrease in the rate constant with reduced melt stirring, and c) adherence of the initial rate of hydrogen solution to a metal-phase mass transport relation. Formerly Graduate Student, The University of Michigan This paper is based on a portion of a thesis submitted by W. M. Small in partial fulfillment of the requirements for the degree Doctor of Philosophy at The University of Michigan, 1971.     

The diffusion of hydrogen in liquid iron alloys

Rates of absorption of hydrogen in stagnant liquid iron and ten (Fe-X) binary iron alloy systems were studied by an unsteady-state gas-liquid metal diffusion cell technique. These rates were found to be controlled by diffusion of hydrogen in the liquid phase. Chemical diffusion coefficients (D _h) were measured in pure iron and Fe-X alloys in the following (at. pct) composition ranges: Mn (0 to 5), Cr (0 to 25), V (0 to 25), Nb (0 to 10), Mo (0 to 25), W (0 to 5), Ni (0 to 75), Co (0 to 75), Sn (0 to 10), and Cu (0 to 25). All measuredD _H values at 1600°C lie between 7 × 10^-4 and 16 × 10^-4 sq cm per sec. The diffusion coefficients found for pure iron can be represented by D_H ^Fe = 4.37 × 10⁻³ exp (−4134 ± 1012)/RT cm²/sec where the uncertainty in the activation energy, Q, in cal per mole, corresponds to the 90 pct confidence level. A linear relationship was found between the logarithm of the hydrogen diffusion coefficient D_H ^Fe-X and the interaction parameter ε_H ^X for low and medium concentrations of alloying elementX, when applied to a fixed concentration ofX(5 or 25 at. pct) and to individual periods in the periodic table. A useful linear correlation also appears to exist between logD_H ^Fe-X and hydrogen solubility for fixed concentration ofX and with respect to the period in whichX is found. Formerly Research Assistant, Department of Mineral Engineering, Stanford University, Stanford, Calif. This paper is based upon a thesis submitted by P. J. DEPUYDT in partial fulfillment of the requirements of the degree of Doctor of Philosophy at Stanford University and part of a presentation made at the 1970 Annual AIME Meeting.     

Decomposition and dissolution kinetics ofδ′ precipitation in Al-Li binary alloys

Aside from its technological importance, the Al-Li alloy system also exhibits interesting phase transformations involving both equilibrium and metastable states. Recent theoretical studies have shown that a supersaturated solid solution could take different transformation paths when it is quenched into theα +γ′ field. Suggestions were made that a rapidly quenched solution phase should first undergo a congruent ordering transformation before it decomposes into a two-phase mixture by either a secondary spinodal decomposition or the classical nucleation and growth process. Moreover, a metastable miscibility gap was predicted at lower temperatures. The objective of this research is to study the transformation paths and dynamics in Al-Li binary alloys of three compositions (5.2, 7.0, and 12.0 at. pct Li). This investigation emphasizes thein situ small-angle X-ray scattering (SAXS) observations on specimens subjected to various aging conditions. Special attention is paid to the early stages of the transformation in an attempt to characterize the various possible modes of phase separation on one hand and to study the dynamics of the precipitation process on the other. The following results are obtained: the congruent ordering precedes decomposition at low temperatures; the metastableγ′ solvus curve is reconfirmed; but the predicted metastable miscibility gap is not found. Guinier radii measurements of the particles showed Ostwald ripening is quickly reached upon heating to the aging temperatures. Slowing down behavior is seen at aging temperatures close to the solvus boundary. Activation energies for Li diffusion were obtained using the modified Lifshitz, Slyozov, and Wagner (MLSW) model. A test of dynamical scaling behavior is carried out for the Al-12.0 at. pct Li alloy. Formerly Visiting Scientists at the University of Illinois     

On the terminal solubility of hydrogen in Nb-V alloys

The terminal solubility of hydrogen (TSH) in Nb-V alloys is extraordinarily high (at 250 K) in comparison to the TSH values in the component pure metals. An explantion is presented which involves using other thermodynamic data for the system and, where these are lacking, estimating them with the aid of physically reasonable assumptions. The hydrogen atoms, but not the metal atoms, are assumed to be in equilibrium between different phases and the hybride phase mixtures are assumed to be quasi-binary. It is shown that the high TSH results from the suppression of the α-α′ phase transition in the alloys, together with the fact thet there are larger deviations from ideal mixing in the hybride phase as compared with the metal phase.     

The activity coefficient of nitrogen in binary liquid metal alloys

Literature data for the limiting thermodynamic properties of nitrogen in liquid Fe, Co, Ni, and Cr, as well as in the six binary alloys consisting of two of the above elements, are critically evaluated. The ternary data are evaluated in terms of the Wagner model for quasi-interstitial liquid alloys and values of the Wagner parameter h are obtained for each system. The correlation formulated by Chiang and Chang between the Wagner parameter h and the relevant binary thermodynamic properties for oxygen in binary alloys has been found to be equally valid for nitrogen in binary alloys. From this correlation, a value of h may be predicted in the absence of any ternary experimantal data. Utilizing the Wagner model and the value of h obtained for each system, values for the first-order and second-order Gibbs energy interaction parameters ∈N(s) and ρsujN(s) are derived.. The parameters are expressed as a linear function of the reciprocal temperature, i.e. ∈^jN(s) =α + β/T and.ρ^jN_(s) = α′ + β′/T. A linear correlation found by Chipman and Corrigan between β and ∈^jN(s) for systems where Fe is the solvent is also valid for systems with non-ferrous solvents. A linear correlation between β′ and ρ^jN_(s) is also found in the present study.     

Nitrogen solubility in liquid Fe-V and Fe-Cr-Ni-V alloys

Nitrogen solubility in liquid Fe, Fe-V, Fe-Cr-V, Fe-Ni-V and Fe-18 pct Cr-8 pet Ni-V alloys has been measured using the Sieverts’ method for vanadium contents up to 15 wt pct and over the temperature range from 1775 to 2040 K. Nitrogen solution obeyed Sieverts’ law for all alloys investigated. Nitride formation was observed in Fe-13 pet V, Fe-15 pet V and Fe-18 pet Cr-8 pet Ni-10 pet V alloys at lower temperatures. The nitrogen solubility increases with increasing vanadium content and for a given composition decreases with increasing temperature. In Fe-V alloys, the nitrogen solubility at 1 atm N₂ pressure is 0.72 wt pet at 1863 K and 15 pct V. The heat and entropy of solution of nitrogen in Fe-V alloys were determined as functions of vanadium content. The first and second order interaction parameters were determined as functions of temperature as: $$e_N^V = \frac{{ - 463.6}}{T} + 0.148 and e_N^{VV} = \frac{{17.72}}{T} - 0.0069$$ The effects of alloying elements on the activity coefficient of nitrogen were measured in Fe-5 pet and 10 pet Cr-V, Fe-5 pet and 10 pet Ni-V and Fe-18 pet Cr-8 pct Ni-V alloys. In Fe-18 pet Cr-8 pet Ni-10 pet V, the nitrogen solubility at 1 atm N₂ pressure is 0.97 wt pet at 1873 K. The second order cross interaction parameters, e _N ^Cr,V and e _N ^Ni,V , were determined at 1873 K as 0.00129 and ? 0.00038 respectively.     

The activity coefficient of oxygen in binary liquid metal alloys

The Wagner model with one energy parameter,h, for describing the effect of alloying elements on the activity coefficients of nonmetallic solutes in liquid metals is extended to have two energy parameters,h ₁andh ₂. The validity of both the Wagner one-parameter equation and the newly derived two-parameter equation is tested using data available in the literature for twelve ternary metal-oxygen systems. In order to have consistent thermodynamic data, all the relevant binary, as well as the twelve ternary metal-oxygen systems are evaluated using the same thermodynamic values for the reference materials which were used in carrying out the experimental measurements. It is found that the twoparameter equation is capable of quantitatively accounting for the compositional dependences of the activity coefficients of oxygen in all twelve ternary systems while the Wagner one-parameter equation is not. A correlation between the Wagner parameter,h, and the thermodynamic properties of the respective binary metal-oxygen and binary metals systems is found, from which the value of this parameter may be predicted without referring to any ternary data. Accordingly, the two-parameter equation is more useful in evaluating ternary experimental data while the Wagner one-parameter equation in connection with the correlation betweenh and binary data is capable of predicting ternary data without any experimental investigation in the ternary region. Based on the one-parameter and the two-parameter equations, theoretical equations for the first-order and second-order free energy interaction parameters,(∈ ₀ ^j )_sand(ρ ₀ ^j )_s, are derived in terms of the model parameters. The values of(∈ ₀ ^j )_s and(ρ ₀ ^j )_s for all the systems are derived and are found to vary linearly with the reciprocal of temperature. Furthermore, linear relationships between these two interaction parameters and their slopes with 1/T are found, from which the temperature dependence of the interaction parameters may be estimated in the absence of experimental data.