Thermodynamic behaviour of zinc in Fe‐C and CaO‐FeO‐CaF2 slag at high temperatures

The distribution ratio of zinc between Ag‐Zn and Fe‐Zn alloys was measured to clarify the thermodynamic behaviour of zinc in Fe‐C melt at high temperatures. Also, the distribution ratio between Ag‐Zn alloy and CaO‐FeO‐CaF₂ slag was measured to understand the dissolution mechanism of zinc in molten slags. The activity coefficient of zinc in Ag‐Zn alloy was preliminarily measured as a fundamental thermodynamic data for the activity of zinc in Fe‐C melt. From the dependence of the activity coefficient of zinc in Fe‐C melts on temperature and carbon content, the following equation could be obtained at 1473 ‐ 1623 K: The distribution ratio of zinc between Ag‐Zn alloy and CaO‐FeO‐CaF₂ slag increased by increasing both the oxygen potential and slag basicity. The stoichiometric coefficients of the dissolution reaction were obtained by considering the relationship between zinc distribution ratio and slag basicity or oxygen partial pressure, when one of these two independent variables was fixed. The dissolution reaction of zinc into the slags could be described as follows:      

Thermodynamic measurements in molten Pb-Sn alloys

The reversible galvanic cell: Sn(l), SnO₂(s)/CaO-ZrO₂/Pb-Sn(l), SnO₂(s) (electrolyte) was employed to determine the thermodynamic properties of liquid Pb-Sn alloys in the composition range ofX _sn from 0.1 to 0.9 and in the temperature range of 875 to 1100 K. The activities of both tin and lead exhibit only moderate positive deviations from the respective Raoult’s law lines and do not agree with the values reported in the literature.S ^E , as calculated by combiningH ^E values of Kleppa andF ^E values determined in this investigation, are positive and range from 0 to 0.139 eu. S. K. DAS, formerly M. Tech. Student, Department of Metallurgical Engineering, Indian Institute of Technology, Kanpur, India This paper is based on a portion of a thesis submitted by S. K. DAS in partial fulfillment of the requirements of the M. Tech. degree at the Indian Institute of Technology, Kanpur.     

The Thermodynamic Properties of Fe‐Mn‐C Melt at Reduced Pressure

The solubility of carbon in the Fe‐Mn‐C system was measured under reduced pressure of 1 Pa at 1573 K and 1673 K, respectively. The carbon solubility in terms of mole fraction in the iron based solution was found varying with manganese mole fraction in the solution and with temperature, as x_C= 0.1819 + 0.2531 x_Mn at 1573 K and x_C = 0.1981 + 0.2515x_Mn at 1673K. Manganese has a stronger influence on the carbon solubility at lower pressure than it has at higher pressure. The pressure was found to have an insignificant effect on the carbon solubility when manganese in the melt was absent. The activity interaction parameters between manganese and carbon in the alloy were determined from carbon solubilities at 1573 and 1673 K. Analysis of the experimental results showed that under vacuum conditions, the activity interaction parameter of manganese with carbon is higher than that at atmospheric pressure.     

Thermodynamic properties of lanthanum silicides at high temperatures

The enthalpies of five lanthanum silicides were determined over the temperature range 380–2225 K by the method of mixtures. Values of the basic thermodynamic functions of the materials were calculated and tabulated, as well as the temperatures, enthalpies, and entropies of fusion. The temperatures and enthalpies of fusion were related to the relative concentrations of silicon in the compounds.Institute of Materials Science Problems, Ukrainian National Academy of Sciences, Kiev. Translated from Poroshkovaya Metallurgiya, Nos. 3–4, pp. 48–53, April–May, 1994.     

Phosphorus segregation in austenite in Fe–P–C,Fe–P–B and Fe–P–C–B alloys

The equilibrium grain boundary segregation of phosphorus was investigated in Fe–P–C, Fe–P–B and Fe–P–C–B alloys after austenitising at temperatures ranging from 825–1100 °C. The grain boundary concentrations were determined by Auger electron spectroscopy on intergranular fracture surfaces. Phosphorus, carbon and boron segregate to the austenite grain boundaries. The segregation of P in austenite occurs mainly in equilibrium, but some additional segregation takes place during quenching. Boron and, in a lesser degree, carbon were found to decrease the grain boundary concentration of phosphorus. The results can be explained by assuming equilibrium segregation and mutual displacement of these elements in austenite.     

Thermodynamic properties of liquid tin-tellurium alloys at high temperature

Electromotive force measurements on galvanic cells have been performed in order to obtain the tin activity in liquid tin-tellurium alloys in the composition range 0.200 <x _Te < 0.750 and between 673 and 1123 K. The position of some liquidus points, determined by emf measurements, was verified by differential thermal analysis. Moreover calorimetric measurements were made at 873 K. By graphical integration of the Gibbs-Duhem relationship, partial molar Gibbs energy and enthalpy changes, ΔG _Te and ΔH _Te were obtained. The integral thermodynamic properties ΔH _M,TΔS _M and ΔG _M were also calculated at 1100 K. From these thermodynamic values and the variations of viscosity and electrical resistivity given in the literature and according to the essentially covalent nature of the bonding in the solid SnTe, we have qualitatively investigated the dependence of the nature and the evolution of the interactions with the temperature in the neighborhood of the compositionx _Te = 0.500. J. Rakotomavo, who is preparing his thesis     

Thermodynamic study on phase equilibria in the liquid Fe‐S‐O system

The phase equilibria and thermodynamic properties of the Fe‐S‐O melt at 1273 – 1573 K were investigated by employing thermochemical equilibration technique. The γ‐Fe+liquid region was extended to higher sulphur content region than that of literature. The solubility of FeS in slags decreased with increasing the activity of FeO and the solubility slightly decreased with increasing temperature. The activity of FeO exhibited a negative deviation from ideality in the composition with a molar mass fraction of less than about 60 % FeO, while a positive deviation was observed at X_FeO > 0.6. However, the activity of FeS exhibited a positive deviation from ideality at 1273 K, and a nearly ideal behaviour at 1573 K, respectively. The enthalpy changes of mixing were calculated to be some positive value. The sulfur content in reduced solid iron decreased from about 110 to 70 ppm at 1273 K as the ratio FeO/FeS in slag increased up to the composition doubly saturated by Fe/FeO, while the sulfur content decreased from about 400 to 150 ppm at 1573 K. The oxygen content in reduced solid iron increased to about 3 ppm at 1273 K with increasing FeO/FeS ratio up to the composition saturated by FeO.     

Toward a probe for velocity measurement in molten metals at high temperatures

The electromagnetic probe of Ricou and Vives for measurement of velocity in liquid metals is well known. This probe incorporates a permanent magnet. Consequently, the use of the probe at temperatures approaching the Curie temperature of the magnet is difficult. Above that temperature, the probe is inoperable. This article describes a modification of the probe; the permanent magnet was replaced by an electromagnet. The article treats the theory of using an electromagnet and gives an account of experiments in which the principle of the probe was demonstrated by velocity measurements in an alloy with a low melting point. Circuits for measurements with the electromagnet driven by both alternating and direct current are described; better results were obtained with the latter. Two types of probes were examined, one intended for complete submersion in the melt and the other for measurements near the surface of the melt. An air-cooled version was found to withstand external temperatures of 970 K, while the internal temperature remained below 390 K.     

The oxidation behavior of some Ni-Cr-Al alloys at high temperatures

Oxidation of ternary Ni-Cr-Al alloys containing different Cr/Al ratios has been studied in the temperature range 800° to 1300°C. Most of the studies were performed in 1 atm oxygen or air, but the oxygen pressure dependence for one of the alloys was also investigated. The experimental methods included thermogravimetric measurements of oxidation rates and studies on reacted specimens by means of X-ray diffraction, metallographic techniques, electron microprobe analysis, and electron microscopy. In general, the oxidation rates decrease faster with time than that for an ideal parabolic behavior. The major reaction products were NiO, Cr₂O₃,α-Al₂O₃, and Ni(Cr,Al)₂O₄. The relative amounts of these were a function of composition, temperature, oxygen pressure, and reaction time. The Ni-9Cr-6Al alloy has the best oxidation resistance due to the formation ofα-Al₂O₃ at all temperatures investigated. The oxidation mechanism of the alloy is discussed.     

Oxygen and carbon sensing in Fe—O—C and Fe—O—C—Xn melts at elevated carbon contents

In the present study on solid electrolyte probes, the attempt was made to measure accurate and reproducible EMF values representing the extremely low oxygen activities in Fe—O—C melts at varying C contents. Various types of sensors were designed and successfully tested in laboratory experiments. Reliable oxygen activities were measured in Fe—O—C melts up to 4 wt. % C under pure CO gas, and f_o and f_c values were derived as a function of C content at 1 400 to 1 600°C. Further measurements were made in Fe—O—4 wt. % C—X_n melts at various contents of X_n (S_n = Si, Mn, Cr). Moreover, a solid oxide electrolyte probe with a CO gas channel to measure oxygen and carbon activities was developed and successfully tested in high-carbon iron melts.     

Thermography of the phase transformations in nickel-based eutectic alloys at high pressures and temperatures

The phase transformations in STEMET 1301A and STEMET 1311 nickel solder alloys are studied by differential barothermal analysis and metallography at temperatures up to 1100°C and pressures up to 120MPa. When the pressure increases, the temperature of the onset of crystallization of the initial amorphous STEMET 1301A alloy decreases and that of the STEMET 1311 alloy increases. At high pressures, the solidus temperatures of the alloys changes insignificantly and the liquidus temperature of the STEMET 1301A alloy increases by 30°C. The solidification ranges of both alloys at 120 MPa are found to broaden substantially.