Thermochemical Properties of Liquid Alloys in Fe ― O and Fe ― O ― Metal Systems

An isoperibolic calorimeter has been used to determine the partial and integral enthalpies of mixing for liquid alloys in the binary Fe ― O system and ternary Fe ― O ― M ones at 1915 K. The enthalpies of mixing in these systems are high exothermic quantities, which agree with published data. It is found that the first partial enthalpy of mixing for oxygen is _280 kJ/mole. The enthalpies of mixing have been calculated from the standard enthalpies of formation Δ_f H ^º ₂₉₈ for iron oxides throughout the concentration range. The enthalpies of mixing have been calculated and measured for binary alloys in the Fe ― O system, which are correlated one with the other.     

Enthalpies of Solution and Mixing for Graphite in Molten Silicon at 2000 K

Partial and integral enthalpies of mixing have been determined in an isoperibolic calorimeter for liquid alloys in the silicon – carbon binary system at 2000 K. These enthalpies of mixing are small exothermic quantities which agree with published data. The enthalpy of mixing _f Hº₂₉₈ has been calculated for silicon carbide.     

Thermodynamics of Liquid Alloys and Metastable Phase Transformations in the Copper - Titanium System

We have used solution calorimetry at temperatures of 1573 K and 1873 K over broad concentration ranges to study the mixing enthalpy of Cu - Ti liquid alloys. The molar mixing enthalpies of the system are significant negative values. We have established the temperature dependence of the molar mixing enthalpies of the system: there is an increase in their exothermicity as the temperature is lowered. The significant negative mixing enthalpies of the system allow us to conclude that the chemical bonds are localized in the studied melts and consequently associates form. We tested this conclusion within ideal associated solution theory, which describes well the results obtained with a set of CuTi and CuTi₂ associates. Using the model obtained, we have calculated the excess thermodynamic functions of mixing (enthalpy, Gibbs free energy, heat capacity) for the liquid alloys. We estimated the Gibbs energies of fcc, bcc, and hcp solutions in the system by the CALPHAD method, using data from the initial sections of the phase diagrams and from the corresponding thermodynamic data. We have calculated the metastable phase equilibria between the limiting solid solutions and the liquid or supercooled liquid phase. It was shown that for the supercooled liquid and the amorphous phase, a broad concentration range of relative thermodynamic stability can be obtained. The concentration range of amorphization of Cu - Ti melts corresponds to the position of the metastable liquidus line and the T₀ line at temperatures close to the temperature range of amorphous solidification. __________ Translated from Poroshkovaya Metallurgiya, Nos. 5–6(443), pp. 67–80, May–June, 2005.     

Mixing enthalpy and heat content measurements of liquid binary iron-niobium alloys

The mixing enthalpy of the system iron-niobium has been determined at 1935 and 2035 K for alloys having Nb mass contents of up to 51.5 % by the levitation alloying calorimetry (LAC). Moreover, by means of the combination of an electromagnetic levitation unit with a drop calorimeter the temperature functions of the enthalpies of the eutectic alloys Fe_89.4Nb_10.6 and Fe₄₁Nb₅₉ and the congruent melting compound Fe₂Nb have been measured in the liquid state and below their melting points. From these values the melting enthalpies and entropies are calculated. The experimental results are compared with literature data. In consideration of the standard formation enthalpy of the alloys their enthalpy values could be connected with the mixing enthalpy.     

Thermochemistry of alloys of transition metals: Part III. Copper-Silver, -Titanium,Zirconium, and -Hafnium at 1373 K

The enthalpies of mixing of liquid copper with liquid silver and with solid titanium, zirconium, and hafnium have been measured by high temperature reaction calorimetry at 1371 to 1373 K. A least squares treatment of the data for copper-silver alloys yields the following expression for the molar enthalpy of mixing: ΔH_mix = ϰ_Agϰ_Cu(17.66 − 5.46 ϰ_Ag) kJ mol⁻¹. The enthalpies of solution of solid titanium, zirconium, and hafnium in dilute solutions in liquid copper are all exothermic; the following values were found: -2.0 kJ mol⁻¹ for Ti, -52.5 kJ mol⁻¹ for Zr, and -46.3 kJ mol⁻¹ for Hf. These values are all significantly less exothermic than predicted by the semiempirical theory of Miedema. The enthalpies of formation of congruent melting intermetallic phases in the systems Cu-Ti, Cu-Zr, and Cu-Hf were measured by drop calorimetry or by solution calorimetry in liquid copper. The enthalpies of formation of the solid alloys have been compared with corresponding data for the liquid alloys.     

Enthalpy of mixing of liquid Cu-Ni-Ti alloys at 1873 K

The enthalpy of formation of ternary Cu-Ni-Ti alloys at 1873 K is studied at x _Ti = 0?0.6 along sections characterized by fixed ratios: x _Ni: x _Cu = 1: 3, 1: 1, and 3: 1. For investigations, a high-temperature isoperibolic calorimeter is used. The isotherm of the integral enthalpy of mixing of liquid Cu-Ni-Ti alloys at 1873 K is described using the Redlich-Kister polynomials for binary systems and the Maggianu model for ternary interaction. The contribution of ternary interaction to the heat of formation of the alloys in the concentration range x _Ti < 0.45 is exothermic; in the other fields of the concentrational triangle, this contribution is endothermic. The first partial enthalpies of mixing of Al, Sn, Si, Y, Zr, Hf, or Fe with Cu-Ni-Ti melts are exothermic, which indicates an increase in the thermodynamic stability of the liquid phase as a result of the dissolution of additions of these metals.     

Enthalpy of mixing of liquid Cu-Ti-Zr alloys

The enthalpy of mixing of liquid Cu-Ti-Zr ternary alloys is studied by high-temperature isoperibolic calorimetry at 1873 K along three ray sections characterized by the ratios x _Zr: x _Cu = 3: 7, x _Ti: x _Cu = 3: 7, and x _Zr: x _Ti = 1 at x _Cu = 1?0.4. The isotherm of the integral enthalpy of mixing of these melts is described in terms of the Redlich-Kister-Muggianu model. Along with the substantial contributions of binary copper-titanium and copper-zirconium interactions, the contribution of a ternary interaction to the enthalpy of mixing of liquid Cu-Ti-Zr alloys also exists. The first partial enthalpies of mixing of Ni, Al, Si, Sn, and Y with the melts are studied to determine the character of the interaction between the ternary Cu-Ti-Zr melts and metal additions that facilitate amorphization upon melt quenching. The introduction of these metals into the ternary melts is shown to increase their thermodynamic stability.     

Mixing enthalpies and calorimetric investigations of liquid iron-vanadium alloys

By means of a special levitation alloying calorimeter (LAC) the mixing enthalpies of liquid Fe-V alloys were determined in the iron rich range, up to 35 at.% V at a mean temperature of 1990 K; in the vanadium rich range, up to 32 at.% Fe at a mean temperature of 2320 K. The results were verified by a drop calorimetric experiment, where the enthalpy of an Fe-V alloy with 69 at.% Fe was measured. The total systematic error of the LAC was calculated to be within ± 10 %. Different thermodynamic models were applied to describe the results. By the quasi-chemical model the experimental results for the mixing enthalpies in kJ/mol are expressed by the equation ΔH^m=x_Fex_V(?28.61–80.58x_Fex_V).     

Experimental study and modeling of the thermodynamic properties of Cu-Fe-Ni melts

The partial mixing enthalpy of nickel in ternary liquid Cu-Fe-Ni alloys is studied at 1873 K along sections characterized by ratios x _Cu: x _Fe = 3, 1, and 1/3 at x _Ni = 0–0.55. The investigations are undertaken using a high-temperature isoperibolic calorimeter. The temperature and composition dependence of the excess mixing Gibbs energy of liquid Cu-Fe-Ni alloys are described in terms of the Muggianu-Redlich-Kister model using the data obtained, the literature data on the activities of liquid alloy components, and the thermodynamic properties of melts of the boundary binary systems. This model is used to calculate isotherms of the thermodynamic properties of the liquid alloys over the entire composition range. The contribution of a ternary interaction to the integral mixing enthalpy of liquid Cu-Fe-Ni alloys is found to be mainly positive.     

Enthalpies of mixing of rare-earth metal-aluminum alloys: Model calculations

Integral enthalpies of mixing Δ_mix H for binary rare-earth metal (REM)-aluminum systems are calculated using the following three semiempirical approaches: an ideal solution model for interaction products, the Miedema model, and a specific calculation algorithm developed by us. Possible qualitative and, for a number of alloys, quantitative agreement of the calculation results with each other and the experimental data is demonstrated. The model parameters that allow the enthalpies of mixing to be calculated using simple relations are reported. The values of Δ_mix H are calculated for Al-REM alloys over the entire composition range.     

Thermochemistry of binary liquid gold alloys: The systems gold-copper and gold-silver at 1379 K

The enthalpies of mixing of the binary liquid alloys of gold with copper and silver have been measured by high temperature reaction calorimetry. The experimental results are described by the following analytical expressions which were derived by a least squares treatment of the data: Au-Cu: ΔH_mix = X_AuX_Cu(-28,821 - 2,468 X^Au + 9,541 X_Au ²) J mol^-1 Au-Ag: ΔH_mix = X_AuX_Ag(-15,820 - 529 X_Au @#@) J mol^-1 The results are compared with excess Gibbs energy data from the published literature to yield approximate excess entropies of mixing. For the gold-copper system the observed parabolic dependence of the enthalpy interaction parameter on composition is well accounted for by the quasi-chemical theory.     

Volume effects and associations in liquid alloys

The regular associated solution model for binary systems has been modified by incorporating the size of the complex as an explicit variable. The thermodynamic properties of the liquid alloy and the interactions between theA _μB type of complex and the unassociated atoms in anA-B binary have been evaluated as a function of relative size of the complex using the activity coefficients at infinite dilution and activity data at one other composition in the binary. The computational procedure adopted for determining the concentration of clusters and interaction energies in the associated liquid is similar to that proposed by Lele and Rao. The analysis has been applied to the thermodynamic mixing functions of liquid Al-Ca alloys believed to contain Al₂Ca associates. It is found that the size of the cluster significantly affects the interaction energies between the complex and the unassociated atoms, while the equilibrium constant and enthalpy change for the association reaction exhibit only minor variation, when the equations are fitted to experimental data. The interaction energy between unassociated free atoms remains virtually unaltered as the size of the complex is varied between extreme values. Accurate data on free energy, enthalpy, and volume of mixing at the same temperature on alloy systems with compound forming tendency would permit a rigorous test of the proposed model.     

Phase relations associated with the aluminum blast furnace: Aluminum oxycarbide melts and Al-C-X (X=Fe,Si) liquid alloys

The thermodynamic properties and the phase relations were evaluated and estimated for the Al-O-C, Al-Si-C, and Al-Fe-C systems which are important to understand the chemical behavior in an aluminum blast furnace. The mixing properties of binary liquid alloys, including metal-carbon systems, were represented by the Redlich-Kister equation. The properties of liquid Al−C and Si−C alloys were estimated so as to be consistent with their phase diagrams. The coefficients of Al−Fe and Fe−C liquids were evaluated from reported values for activity and enthalpy. The extrapolation to the higher order systems was made by Maggianu's method. The aluminum oxycarbide melt was represented by a subregular solution model. In the Al-O-C system, liquid alloy/oxycarbide melt equilibria were calculated and compared with earlier experimental results and estimates. Attempts were made to clarify the volatilization of aluminum oxycarbide melts, and also the carbidation of liquid aluminum alloys. An empirical correlation between the first terms of the Redlich-Kister equation for the enthalpies and the excess entropies was discussed.     

Thermal chemistry and short-range order in Co-Sb melts

The enthalpies of mixing for the liquid Co-Sb alloys are measured by isoperibolic calorimetry at 1600 K over the whole concentration range relative to liquid Sb and undercooled liquid Co. The minimal integral enthalpy of mixing is −6.3 ± 0.6 kJ/ mole at x_Co = 0.50. Activity of components, Gibbs energy, and the entropy of mixing are calculated using a short-range ordering model considering CoSb associates formed in molten Co-Sb alloys. __________ Translated from Poroshkovaya Metallurgiya, Vol. 46, No. 5–6 (455), pp. 96–101, 2007.     

Interactions in Molten Aluminum (Silicon) ― Boron Alloys

Isoperibolic calorimetry has been used to determine the partial and integral enthalpies of mixing for liquid alloys in the binary systems aluminum (silicon) boron at 1873 K. Those enthalpies are small exothermic quantities, which agree with published data. The enthalpies of mixing have also been calculated from the _f H ₂₉₈ of the metal borides. The concentration dependence has been determined for these enthalpies in binary alloys in the nontransition metal boron systems.     

Thermodynamic properties of liquid alloys of the Ni-Hf system

By the method of calorimetry in isoperibolic conditions are determined integral and partial mixing enthalpies of liquid alloys of the Ni-Hf system at 1770 ± 5 K. Defined that liquid Ni-Hf alloys are formed with allocated large quantity of heat. The analysis of own and literary data has allowed to establish for mixing enthalpies of binary Ni-Hf liquid alloys dependence on temperature. With use of the Schröder equation are calculated the activities of studied alloys components from co-ordinates of liquidus line of the phase diagram of this system. Between calculated and experimentally established values of melts components activities of the Ni-Hf system is observed only qualitative consent. Are also calculated ΔG and ΔS of liquid Ni-Hf alloys.     

Thermochemical properties of ternary Si-Ni-Al liquid alloys

Partial (for aluminum) and integral mixing enthalpies of ternary Si-Ni-Al liquid alloys are examined by high-temperature calorimetry under isoperibolic conditions at 1770 ± 5 K. Alloys of five radial sections with a constant ratio of silicon-to-nickel mole fractions (x_Si/x_Ni = 0.85/0.15; 0.7/0.3; 0.5/0.5; 0.3/0.7, and 0.15/0.85) within the interval compositions to aluminum mole fraction x_Al ∼ 0.6 are studied. The mixing enthalpies of Si-Ni-Al alloys are characterized by great exothermal values. Exothermal partial enthalpies of aluminum mixing increase at infinite dilution with increasing nickel concentration in starting binary alloys ( reaches −17.0 ± 3.3 kJ/mole for section with x_Si/x_Ni = 0.85/0.15 and −119.0 ± 11.2 kJ/mole for x_Si/x_Ni = 0.15/0.85). An analysis of alloy-formation energy parameters in the ternary Si-Ni-Al system indicates that the interaction of the components in the bounded binary Si-Ni and Ni-Al systems greatly contributes to Δ_mH, the effect of the former prevailing. The thermochemical properties of ternary alloys and of Ge-Ni-Al melts and simulated mixing enthalpies of ternary Sn (C)-Ni-Al liquid alloys are compared. __________ Translated from Poroshkovaya Metallurgiya, Vol. 46, No. 3–4 (454), pp. 79–85, 2007.