The diffusion of antimony in alpha iron

Diffusion coefficients of antimony in α-iron were determined in the temperature range 700 to 900°C using the residual activity method. Specimens were large-grained polycrystals for the higher temperature measurements and single crystals for the low temperature measurements. Above 800°C the data may be represented by the equationD _sb(cm²/s) = (440 ± 200) exp [- (270,000 ± 7000)/RT]. The activation energy (reported in J/mole) is approximately equal to that measured for iron self-diffusion in this same temperature range, although the antimony diffusion coefficients are a factor of ten larger than the iron self diffusion coefficients. The potential for strongly coupled vacancy-antimony motions is demonstrated, based on the observed enhancement of iron self diffusion in dilute iron-antimony alloys. Finally molybdenum is shown to have a negligible effect on the diffusion of antimony in α-iron. These results are discussed in relation to the phenomenon of temper brittleness in steels. Embrittlement kinetics in iron-antimony alloys are shown to be consistent with an antimony diffusion controlled segregation mechanism.     

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.     

Activity coefficient of antimony and arsenic in molten iron and carbon saturated iron

In connection with removal of tramp elements from molten iron and steel, activity coefficients of arsenic and antimony in carbon saturated iron and in pure iron were determined between 1473 to 1923 K and between 1823 to 1923 K, respectively, by measuring the distribution of those elements between the metals and silver. The following activity coefficients are observed: for carbon saturated iron: log γ_As = 3560/T + 1.14, log γ_Sb = 6890/T + 5.06; and for molten iron: log γ°_As = - 198/T - 1.41, log γ°_Sb = - 7030/T + 4.38, respectively. The possibility of the removal of arsenic and antimony from molten iron by using a BaO-BaF₂ flux is discussed.     

Irregular growth of AlSb in solid aluminum-solid antimony diffusion couples

An investigation was made of the growth of the intermediate phase aluminum antimonide (AlSb) in solid aluminum-solid antimony diffusion couples, AlSb being the only intermediate phase present in the equilibrum phase diagram. Most diffusion couples were assembled from polycrystalline aluminum and antimony, but a few were made from single crystals; the diffusion couple surfaces were prepared in a variety of ways and the couples were isothermally annealed at temperatures between 450° and 615°C. It was found in all cases that AlSb nucleates at the original interface and after sufficient time coalesces into a highly irregular layer, irrespective of the details of the surface treatment. In several cases in which limited nucleation of AlSb took place, the morphology of the crystals was such as to suggest that the observed anisotropic growth was related to the zinc-blende crystal structure of the AlSb. Formerly Graduate Student, Department of Physical and Engineering Metallurgy, Polytechnic Institute of Brooklyn, Brooklyn, N. Y. Formerly Graduate Student, Department of Physical and Engineering Metallurgy, Polytechnic Institute of Brooklyn.     

Growth of aluminum antimonide in solid aluminum-liquid antimony diffusion couples

An investigation was made of the isothermal growth of the intermediate alloy phase aluminum antimonide AlSb, at the interfaces of diffusion couples consisting either of solid aluminum and liquid antimony or of solid aluminum and of an Sb−Al alloy slightly supersaturated in AlSb. The diffusion anneals were carried out in the temperature range 635° to 655°C and for times up to 48 hr. In the solid aluminum vs liquid antimony couples, it was found that considerable dissolution of solid aluminum occurred at the solid-liquid interface before the first crystals of AlSb appeared. Subsequently, a two-phase region, consisting of AlSb crystals of greatly varying sizes interspersed throughout the liquid antimony developed between the instantaneous solid-liquid interface and the original solid-liquid interface. The results suggest that the dominant mechanism influencing the growth of AlSb in these diffusion couples is diffusional mass transport of aluminum in liquid antimony. The rapid diffusion of aluminum leads first to the dissolution of solid aluminum and saturation of the liquid antimony, and next to the growth of large discrete crystals of AlSb presumably via an Ostwald-ripening mechanism. N. GRADO, formerly Graduate Student, Department of Physical and Engineering Metallurgy, Polytechnic Institute of Brooklyn, Brooklyn, N.Y.     

The alpha ⇆ gamma transformation in iron powders

The alpha ⇆ gamma transformation in various size fractions of three different types of iron powder was studied by differential thermal analysis. The alpha-to-gamma transformation temperature increases considerably with decreasing particle size and with the number of thermal cycles through the transformation for a given particle size. The gamma-to-alpha transformation temperature decreases with decreasing particle size and remains about constant during thermal cycling through the transformation.     

Grain boundary segregation of sulfur and antimony in iron alloys

A correlation between sulfur and antimony grain boundary segregation has been observed on inter-granular surfaces of iron by Auger electron spectroscopy (AES). The slope of a plot of S/Sb indicated a ratio of two antimony atoms per sulfur atom arriving at the grain boundary, while the ratio for the total S/Sb at the grain boundary was about 1.2. These results were obtained with Fe, Fe + 0.07Mn, Fe + 0.03Sb, Fe + 0.1Mn + 0.02Sb, and Fe + 0.1Mn + 0.05Sb (at. pct) alloys. Possible expla-nations for this correlated segregation, such as cosegregation of sulfur and antimony, precipitation of a thin layer of antimony sulfide, and compctitive segregation with carbon and nitrogen, were evalu-ated using AES, X-ray photoelectron spectroscopy (XPS), and scanning transmission electron mi-croscopy with energy-dispersive X-ray (STEM-EDS). The results of these analyses indicated that there was no resolvable antimony sulfide phase in the grain boundary and that S and Sb were not chemically bound at the grain boundary in a two-dimensional phase. The S was shown to be strongly bound to the iron in a chemical state close to that of an iron sulfide, but the Sb was in the elemental state. Nor could this correlated segregation be satisfactorily explained by a cosegregation process nor by compctitive segregation with other elements. The most plausible explanation appears to involve the effect of sulfur on the activity/solubility of antimony or antimony on the activity/solubility of sul-fur, as explained by an increase in the ratioX _c /X _Co in the Brunauer-Emmett-Teller (BET) adsorption isotherm adapted for equilibrium segregation in solids.     

Improvement of Kryukov and Zhukhovitskii method for measurement of diffusion. Application to self-diffusion in alpha iron

Abstract

The method developed by Kryukov and Zhukhovitskii for the measurement of diffusion coefficients has been improved by deriving the exact relation between the measured activities and the diffusion time. The new equation is similar to that of Kryukov and Zhukhovitskii except for an additional term and is linear for all values of time. The method has been used to measure the self-diffusion coefficient of alpha iron between 809 and 889°C. The self-diffusion coefficient (in cm²/sec) is given by

D _a = 5.4 exp (?60.3/RT)

The extrapolation of this result to the delta phase is in good agreement with the value determined experimentally in that phase.

Résumé

Les auteurs ont amélioré la méthode de Kryukov et Zhukhovitskii pour la mesure des coefficients de diffusion en dérivant la relation exacte entre les activités mesurées et le temps de diffusion. La nouvelle relation est semblable à celie de Kryukov et Zhukhovitskii sauf pour un terme additionnel; elie est lineaire pour toute valeur du temps. La methode a ete utilisee pour mesurer le coefficient d'autodiffusion du fer en phase alpha entre 809 et 889°C. Le coefficient d'autodiffusion, exprime en cm²/sec, est donne par

D _a = 5.4 exp (?60.3/RT)

L'extrapolation de ce resultat à la phase delta est en bon accord avec les résultats expérimentaux obtenus dans cette phase.     

Distribution of antimony between carbon-saturated iron and synthetic slags

Author A.F. Kalcioglu is performing national service with the Turkish army.     

The alpha ⇄ gamma transformation mechanisms in iron particles

Metallurgical and Materials Transactions A -     

Interaction of exogenous refractory nanophases with antimony dissolved in liquid iron

The heterophase interaction of Al₂O₃ refractory nanoparticles with a surfactant impurity (antimony) in the Fe–Sb (0.095 wt %)–O (0.008 wt %) system is studied. It is shown that the introduction of 0.06–0.18 wt % Al₂O₃ nanoparticles (25–83 nm) into a melt during isothermal holding for up to 1200 s leads to a decrease in the antimony content: the maximum degree of antimony removal is 26 rel %. The sessile drop method is used to investigate the surface tension and the density of Fe, Fe–Sb, and Fe–Sb–Al₂O₃ melts. The polytherms of the surface tension of these melts have a linear character, the removal of antimony from the Fe–Sb–Al₂O₃ melts depends on the time of melting in a vacuum induction furnace, and the experimental results obtained reveal the kinetic laws of the structure formation in the surface layers of the melts. The determined melt densities demonstrate that the introduction of antimony into the Fe–O melt causes an increase in its compression by 47 rel %. The structure of the Fe–Sb–O melt after the introduction of Al₂O₃ nanoparticles depends on the time of melting in a vacuum induction furnace.     

Thermodynamic activity of antimony at dilute solutions in carbon-saturated liquid iron

Activity measurements of Sb are made by equilibrating antimony containing liquid metal,e.g., Pb, Cu, or Ag, with carbon-saturated liquid iron. At low Sb concentrations in Fe-C_sat., γ _° ^sb = 3.2 at 1200 °C increasing to 23.3 at 1550 °C. Previous work onγ _° ^sb in Pb, Cu, Ag, and Fe-C_sat. are reviewed and reassessed in the light of the present work. Formerly a Senior Research Engineer.     

粗锑氧化除铁的研究

介绍了一种粗锑火法精炼深度除铁的方法,在氧化性气氛下用磷酸盐作为除铁剂,精锑含铁可降至50×10-6以下。     

原子荧光光谱法测定铁矿石中砷和锑

通过对灯电流、硼氢化钠浓度等参数的实验,确立了铁矿石中砷、锑的分析方法.样品经过氧化钠高温融解,盐酸酸化后,采用氢化物发生原子荧光光谱法进行测定.     

Permeation of hydrogen through alpha iron

The permeation rate of hydrogen through two alpha iron specimens was measured by means of a low pressure steady-state permeation technique under conditions such that diffusion was the rate controlling process for permeation. The observed permeation rate in these samples can be described by the equation: J=5.55 ±.52 × 10^-9 p ^1/2 exp - 8095 ± 88/RT mole s^-1 cm^-1 torr^-1/2 over a range of hydrogen pressures from 21 torr to 766 torr and over a temperature range of 342 to 619 K. Variation of permeation rate with the square root of hydrogen pressure was used as evidence that the permeation process was diffusion rather than surface reaction controlled. The permeation data were used in conjunction with the solubility expression of Gonzalez¹ to determine the diffusivity of hydrogen through alpha iron as:D = 1.01 × 10^-3 exp - 1595/RT cm²/s     

Copper diffusion in iron during high-temperature tensile creep

The diffusion of liquid copper in iron from a notched surface has been studied by metallographic, microanalysis, and sessile drop techniques. The diffusivity of copper was found to be 0.59×10^?6 sq cm per sec at 1100°C and 0.97×10^?6 sq cm per sec at 1130°C. The diffusion factor,D ₀ was 0.78×10^?3 sq cm per sec and the activation energy 19.0 kcal per mole. The predominant mode of copper penetration was along grain boundaries, but when larger volumes of copper at the iron surface were used, surface diffusion increased and grain boundary penetration remained constant. The most frequently occurring dihedral angle for liquid copper was 34 deg at 1100° and 1130°C. The liquid copper/austenite interfacial energy was found to be 444 ergs per sq cm between 1100 and 1130°C. From sessile drop measurements, the contact angle was determined as 35 deg at 1100°C and 28 deg at 1130°C, from which values the respective interfacial energies were calculated to be 387 ergs per sq cm and 301 ergs per sq cm.