Estimation of the surface tensions of binary liquid alloys

A simple method to estimate the surface tensions of binary alloys has been developed by assuming that the partial molar excess free energies are proportional to the number of nearest neighbors in both the bulk solution and in the surface itself. In order to estimate the surface tension of the alloys, excess free energies of the alloys and the surface tensions of the pure components are required. This method has been applied to ten alloys exhibiting positive, positive as well as negative, and negative deviations from ideal solution behavior. The method depends upon the reliability of the thermodynamic data for the bulk solutions, and, further, it is important to use an interpolation scheme that is consistent with the Gibbs-Duhem requirement, when the thermodynamic data are presented in tabular form as a function of composition. To accomplish this interpolation, a special calculation technique is presented.     

Surface tension measurements on pure liquid iron and nickel by an oscillating drop technique

A novel experimental technique for the measurement of surface tension of molten metals has been developed. It is based on the Rayleigh equation which relates frequency and surface tension for an oscillating drop. A systematic study has shown this equation to be valid for a liquid metal droplet levitated electromagnetically in an inert flowing gas with no prior calibration required. It is, therefore, an absolute method. The frequencies of oscillation of droplets of pure iron and nickel in a 6 pct H₂-He gas mixture were measured by high speed cinematography. Surface tensions were obtained for temperatures of 1550° to 1780°C for iron and 1475° to 1650°C for nickel. M. E. FRAZER, Formerly Graduate Student, Department of Metallurgy and Materials Science, McMaster University, Hamilton, Ontario, Canada.     

Deposition of iron,nickel and iron-nickel layers from carbonyl vapors

The rate of deposition of iron, nickel and iron-nickel layers from carbonyl vapors is shown to be controlled by diffusion across the gas phase boundary layer in contact with the heated substrate. At a constant flow rate the rate of deposition is shown to increase with increase in temperature up to a critical value above which the rate of deposition either remains constant (for high flow rates) or decreases (for low flow rates). This behavior is explained in terms of the thermal convection contribution to mass transfer in the reaction system. It is shown that the composition of alloy films produced from carbonyl mixtures at temperatures greater than 200°C (473 K) can be predicted to be approximately equal to the molar ratios of iron and nickel in the vapor phase when the carbonyls alone constitute the vapor phase. These predictions cannot be extended to situations where high dilution of the carbonyls in another gas is used, or to deposition temperatures of less than 200°C (473 K).     

The surface tensions of Pb,Sn, and Pb-Sn alloys

The surface tensions of 99.9999 pct Pb and Sn and of alloys made from lead and tin of the same purity have been measured by the sessile-drop method. The surface tension of lead was determined from the melting point, the surface tension of tin from 200°C (32°C of supercooling) and the surface tensions of the Pb−Sn alloys from the respective liquidus temperatures, all, up to a temperature of about 560°C. Within the limits of experimental error, data for both pure metals plot in a rectilinear fashion with negative slopes, thus: γ_lead=472.7−0.085t(±5) dyne/cm γ_tin=569.0−0.080t((±5) dyne/cm The surface tensions of Pb−Sn alloys are not straight-line functions of temperature and the evidence indicates that the temperature coefficients of surface tension are slightly positive at the liquidus temperature.     

Measurements of nitrogen solubility in iron and iron-nickel alloys,using a new temperature gradient method

Usually gas solubility measurements in metals are done isothermally and separately for the solid and liquid states. The knowledge of gas solubility at phase changes, especially in the melting range, is of a predominant interest e.g. for foundrymen or for welders, as defects (segregation, gas pores, inclusions) may occur due to the change of solubility. Therefore, a method has been developed, in which a finely grained sample is exposed to a temperature gradient in a long ceramic tube, until equilibrium with the gas phase with regard to local temperature is reached in all locations. The chilled sample is subdivided into small samples which can be analysed for gas content. The method is demonstrated for the determination of nitrogen solubility in iron and some iron-nickel alloys, where results for the austenite and δ-ferrite phases are presented.     

Enthalpies of formation of liquid binary (copper + iron, cobalt, and nickel) alloys

The enthalpies of formation of liquid binary (Cu+Fe, Co, Ni) alloys are studied by direct reaction calorimetry in the whole range of compositions at 1873, 1823, and 1753 K, respectively. The integral molar enthalpies of mixing are found to be positive in all three systems with the maximum values approaching 10.8±0.7 kJ/mol⁻¹ at x _Fe=0.43, 7.1±0.9 kJ/mol⁻¹ at x _Co=0.55, and 3.7±0.5 kJ/mol⁻¹ at x _N1=0.53. Partial molar enthalpies at infinite dilution constitute 59.4±3.3 kJ/mol⁻¹ for iron, 44.3±4.1 kJ/mol⁻¹ for cobalt, and 14.9±2.2 kJ/mol⁻¹ for nickel in liquid copper. Similar values for copper in liquid iron, cobalt, and nickel are 36.6±3.9, 45.3±6.0, and 17.7±4.4 kJ/mol⁻¹, respectively. The results are compared with the thermodynamic data available in literature and discussed in connection to the equilibrium-phase diagrams. In particular, decreasing from Cu-Fe to Cu-Ni liquid alloys positive values of the excess thermodynamic functions of mixing are fully in accord with the growing stability of phases in these systems. The excess entropies of mixing are estimated by combining the established enthalpies with carefully selected literature data for the excess Gibbs functions. Analysis of possible contributions to the enthalpies of mixing indicates that the experimentally established regularity in ΔH values along the 3d series is likely to arise from the difference in d-band width and d-electron binding energy of the alloy constituents.     

Nitrogen solubility and aluminum nitride precipitation in liquid iron alloys containing nickel and aluminum

The solubility of nitrogen in liquid iron-base Fe-Ni-Al alloys has been measured up to the solubility limit for formation of aluminum nitride using the Sieverts’ method. Measurements were conducted over the temperature range from 1843 to 2023 K and aluminum concentration range from 1.5 to 3.0 wt pct Al. The effect of nickel additions was determined at 2, 5 and 10 wt pct Ni. The cross interaction parameter describing the effect of nickel and aluminum on the activity coefficient of nitrogen in iron was determined. The first and second order effects of nickel on the activity coefficient of aluminum also were determined. The solubility product of aluminum nitride increases with increasing aluminum content and increasing temperature. Addition of nickel decreases the solubility products of aluminum nitride in lower aluminum content alloys. However, the effect of the cross interaction terme _Al ^NiAl becomes significant with increasing aluminum content and compensates for the effects of the first and second order nickel-nitrogen and nickelaluminum interaction terms. Therefore the effect of nickel additions show little effect on the solubility products of aluminum nitride in higher aluminum alloys.     

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.     

The surface tension of liquid nickel-silicon alloys

Summary A study was made of the effect of composition on the surface tension of nickel-silicon alloys with up to 50 at.% Si. An inflection was observed on the isotherm at 28 at.% Si. The unusual shape of the surface tension versus composition curve is ascribed to a microheterogeneous structure of the melt and the presence in the latter of short-range order.     

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.     

The density and surface tension of dilute liquid Na-In alloys and comparison with liquid Na-Cd alloys

The density and surface tension of five liquid Na-ln alloys, containing between 0.5 and 7 at. pct In, have been measured in the temperature range 170° to 400°C using a maximum bubble pressure technique which incorporates an automatic pressure measuring and recording device. The results are compared with corresponding data reported previously for Na-Cd alloys. The gram-atomic volumes of the Na-ln alloys, calculated from the densities, indicate a substantial contraction on alloying which is, on average, about double that for the Na-Cd alloys and qualitatively consistent with thermodynamic data for the two systems. The surface tension of liquid sodium is increased slightly on adding indium, indicating a lower indium concentration in the surface than in the bulk, in contrast to the marked surface active behavior of cadmium. The surface excess concentrations of indium and cadmium are calculated using Gibbs’ adsorption equation. The surface excess entropy, estimated from the temperature dependence of the surface tension, is compared and briefly discussed for the two systems.     

Measurement of the surface tensions of Fe-saturated iron silicate and Fe-saturated calcium ferrite melts by Padday’s cone technique

Padday’s cone technique allows determination of the surface tension of a liquid from measurement of the maximum excess force exerted on a cone during its immersion in, or withdrawal from, the liquid and knowledge of the density of the liquid. As the technique does not require rupture of the meniscus, an equilibrium measurement is obtained. The surface tensions of Fe-saturated iron silicate melts and Fe-saturated calcium ferrites, measured at 1410 °C using iron cones, are in good agreement with values in the literature obtained using the hollow cylinder technique. The maximum excess forces exerted on Pt-Rh cones immersed in liquid iron oxides at 1460 °C in the composition range from saturation with iron toX _Fe2_O3 = 0.205 have been measured. The surface tensions of these melts cannot be determined unambiguously from the experimental measurements because of an uncertainty in the densities of the melts. However, it is shown that the literature values for the surface tension of liquid iron oxide are incorrect because of an error in the experimental procedures used.     

Absorption of gaseous oxygen by liquid cobalt,copper, iron and nickel

An experimental investigation of the rates of oxygen solution in molten cobalt, copper, iron and nickel was carried out using pure oxygen and a constant-volume Sieverts’ method. It was found that the volume of gaseous oxygen which initially reacted with the inductively stirred metals was strongly dependent on the physical nature of the oxide film which formed during the first stage of reaction. The initial temperature of the molten iron, cobalt, and nickel was 1600°C, and for copper was 1250°C. For initial oxygen pressures above the melt of about one atmosphere both molten iron and copper, which formed liquid surface oxides, initially absorbed nearly 20 cm³ (STP) O₂/cm² of melt surface area, while molten cobalt and nickel, which formed solid oxides, absorbed about 6 cm³ (STP) O₂/cm² under the same experimental conditions. For approximately 30 s after the initial reaction between these liquid metals and gaseous oxygen, the oxygen absorption rate was proportional to the square root of the oxygen pressure above the melt, and proportional to the melt surface area, but independent of melt volume. The rate-limiting step for oxygen absorption by liquid iron, cobalt and copper can be described by dissociative adsorption of oxygen molecules at the gas/oxide interface. After 30 s of reaction, the rate of oxygen absorption became less dependent on the oxygen pressure above the melt. This indicated that the rate-controlling step was changing from a surface reaction to growth of the oxide layer by cationic diffusion in the bulk oxide. The oxidation rate of liquid nickel appears to be too complex to be described by models for dissociative adsorption of oxygen molecules at the gas/oxide interface and parabolic growth of the oxide layer. The formation of a thin layer of nickel oxide which allows oxygen to migrate through cracks or grain boundaries may be responsible for the relatively high oxygen absorption rate compared to that of liquid cobalt. R. H. RADZILOWSKI, formerly a Graduate Studient at The University of Michigan     

Absorption of gaseous oxygen by liquid cobalt, copper, iron and nickel

An experimental investigation of the rates of oxygen solution in molten cobalt, copper, iron and nickel was carried out using pure oxygen and a constant-volume Sieverts' method. It was found that the volume of gaseous oxygen which initially reacted with the inductively stirred metals was strongly dependent on the physical nature of the oxide film which formed during the first stage of reaction. The initial temperature of the molten iron, cobalt, and nickel was 1600‡C, and for copper was 1250‡C. For initial oxygen pres-sures above the melt of about one atmosphere both molten iron and copper, which formed liquid surface oxides, initially absorbed nearly 20 cm³ (STP) O₂/cm² of melt surface area, while molten cobalt and nickel, which formed solid oxides, absorbed about 6 cm³ (STP) 0₂/cm² under the same experimental conditions. For approximately 30 s after the initial reaction between these liquid metals and gaseous oxygen, the oxygen absorption rate was proportional to the square root of the oxygen pressure above the melt, and pro-portional to the melt surface area, but independent of melt volume. The rate-limiting step for oxygen absorption by liquid iron, cobalt and copper can be described by dissocia-tive adsorption of oxygen molecules at the gasJoxide interface. After 30 s of reaction, the rate of oxygen absorption became less dependent on the oxygen pressure above the melt. This indicated that the rate-controlling step was changing from a surface reaction to growth of the oxide layer by cationic diffusion in the bulk oxide. The oxidation rate of liquid nickel appears to be too complex to be described by models for dissociative ad-sorption of oxygen molecules at the gasJoxide interface and parabolic growth of the oxide layer. The formation of a thin layer of nickel oxide which allows oxygen to migrate through cracks or grain boundaries may be responsible for the relatively high oxygen ab-sorption rate compared to that of liquid cobalt. Formerly a Graduate Student at The University of Michigan     

Nature of the strength of tungsten - nickel - iron alloys

Conclusions A study was made of the structural changes taking place in W - Ni - Fe alloys during slow cooling from the sintering temperature. It is shown that aging occurs in the binder phase and in a layer of the refractory tungsten-base phase adjoining the low-melting-point constituent.A W - Ni - Fe alloy sintered in the presence of a liquid phase and slowly cooled from the sintering temperature has a complex multiphase structure of a dispersed-aggregate type. The results of the present investigation provide a foundation for subsequent research into the behavior of the phase constituents of these alloys during plastic deformation and into the nature of their strength.Translated from Poroshkovaya Metallurgiya, No. 5(65), pp. 73–78, May, 1968.     

The surface tensions of indium and cadmium

The surface tensions of 99.9999 pct In and Cd have been measured by the sessile drop method. The surface tension/temperature behavior of liquid indium is nonlinear and within a certainty of 99.5 pct, can be represented by the following quadratic equation:γ _In = 568.0 − 0.04t − 7.08 × 10⁻⁵ t ² ± 5 dyne per cm At its melting point, the surface tension of liquid indium is 560 ± 5 dyne per cm. The slope of the temperature coefficient of the surface tension of liquid cadmium is strongly positive at the melting point, becomes zero about 100°C above the melting temperature (at which point the surface tension is a maximum), and is negative at higher temperatures. At the melting point, the surface tension of cadmium is 590 ± 5 dyne per cm. The surface tension of cadmium is not as readily affected by nonequilibrium thermal conditions as is the surface tension of zinc. The form of the surface tension/temperature curve of indium and cadmium together with similar data for Zn, Cu, Pb, and Sn support a theoretical scheme which generalizes liquid metal surface tension behavior and which, on the basis of calculations, lists liquid metals according to their propensity for surface ordering.     

Thermodynamic properties of solid alloys of chromium with nickel and iron

The thermodynamic properties of chromium have been determined in the Ni-Cr and Fe-Cr binary systems and in the Fe-corner of the Fe-Ni-Cr system. These properties are based on experimental measurements using solid oxide electrolyte cells of the type: Cr, Cr₂O₃ I ThO₂-Y₂O₃Cr (alloy), Cr₂O₃. In the Ni-Cr system, between 900 and 1300°, the activity of chromium exhibits negative deviation from ideality up to about 25 at. pct chromium. For alloys higher in chromium content, the activity of chromium exhibits positive deviation from ideality. In the Fe-Cr system, between 900 and 1200°, and 0 and 63 at. pct Cr, the chromium activity when referred to solid pure chromium exhibits positive deviation from ideality in both the γ and α phases, approaching ideality with increasing temperature. The nickel and iron activities in these two respective binary systems were calculated by a Gibbs-Duhem integration. The activity of chromium, referred to solid pure chromium, was measured between 900 and 1200° in solid Fe-Ni-Cr alloys with chromium concentrations of 9, 20, and 30 at. pct and Ni concentrations of 8, 18, and 30 at. pct. Additions of nickel to Fe-Cr alloys in the above concentration range are found to increase the chromium activity. The effect of nickel in increasing the chromium activity is greater at both greater chromium contents and lower temperatures. Formerly Graduate Student at The University of Michigan, is Staff Associate, Gulf Energy and Environmental Systems, LaJolla, California. This paper is based on a portion of a thesis submitted by F. N. MAZANDARANY in partial fulfillment of the requirements for the degree Doctor of Philosophy at The University of Michigan.