R. Boom

Model predictions for the enthalpy of formation of transition metal alloys II

Abstract We present a computer program in Algol 60 by means of which enthalpy effects can be calculated for binary alloys in which at least one transition metal is involved. Predictions can be made by means of this program for seven fixed ordered compositions in the solid phase and for the two limiting heats of solution and the heat of mixing at the equlatomic composition in the liquid phase. For solid alloys the predictions are representative for equilibrium compounds. As an example, we Include the output for combinations of iron and cobalt with all other metals. In addition, we include a complete table of heats of solution in liquid alloy systems. A discussion is given of both the accuracy of the predictions and the differences between predictions and the experimentally observed quantities that vary systematically with the position of the elements in the periodic table.

On the heat of formation of solid alloys

Abstract We demonstrated recently that the available experimental data on the heat of formation of solid alloys of transition metals can be accounted for by means of a cellular model. The energy effect is derived from two contributions; a negative one, arising from the difference in chemical potential, ϑ∗, for electrons at the two types of atomic cells, and a second term, which reflects the discontinuity in the density of electrons, n ws , at the boundary between dissimilar atomic cells. Expressed as a formula, ΔH ~ [-Pe(Δϑ∗) 2 + Q(Δn ws ) 2 ] . In this paper we demonstrate that the second term is preferably to be written as Q 0 (Δn 1 3 ws ) 2 . Values for P and Q 0 can be derived from basic arguments. The advantage of this alteration is that the values for P and Q 0 are now nearly the same for widely different alloy systems (i.e., as different as intermetallic compounds of two transition metals, and liquid alloys of two non-transition metals). It is demonstrated that the description (and hence the predictions) for heats of formation of alloys of transition metals is sufficiently accurate to be of practical interest. The present model conflicts strongly with descriptions of heats of formation of transition metal alloys in terms of the Engel-Brewer theory.

On the heat of mixing of liquid alloyS—II

Abstract In a previous paper, the authors demonstrated that the alloying behaviour of liquid metals can be described, in a qualitative way, by a simple cellular model. In the present paper, a quantitative analysis of heats of mixing and solution is given for liquid alloys; all parameters used in the calculations are tabulated. The values calculated from the model generally agree with available experimental data. Discrepancies between model and experiment mainly occur for systems with large negative heats of mixing and can be attributed to ordering effects in the liquid alloy. A complete list of calculated values of heats of solution of metals in liquid iron, uranium, and tin is presented. A comparison is made between the present model and existing models.

Enthalpies of formation of liquid and solid binary alloys based on 3d metals: IV. Alloys of cobalt

Abstract Continuing the papers on alloys of Sc, Ti, V, Cr, Mn and Fe we review in the present paper, on the basis of the model developed by Miedema and co-workers, experimental and predicted enthalpies of formation of ordered binary intermetallic compounds of Co with arbitrary metal partners. The enthalpy effects are also reviewed for liquid Co alloys. The predicted values agree quite satisfactorily with the available experimental data for binary systems of Co with a transition metal. In the binary systems where Co is alloyed with a non-transition metal larger differences are sometimes observed. Since Co with other transition metals may often form solid solutions the enthalpy of forming solid solutions is dealt with in a concise way distinguishing between magnetic and non-magnetic matrix metals.

Enthalpies of formation of liquid and solid binary alloys based on 3d metals

Abstract Model predictions are presented for heats of formation of binary intermetallic compounds of Sc, Ti or V with arbitrary metal partners, and for heats of mixing and solution of the corresponding liquid alloy systems. Predicted values are compared with the existing experimental data as well as with qualitative information derived from phase diagram information. A complete set of binary phase diagrams based on Sc, Ti or V is presented in schematic form. Differences between experimental and calculated enthalpy values are discussed.

Predicting heat effects in alloys

Abstract We have previously demonstrated that the enthalpy of alloy formation can be described in terms of a cellular atomic model. Energy effects are expressed as contact interactions that take place at the interface shared by pieces of dissimilar metals having the size of atoms. In this paper the consequences of the contact interaction approach are discussed at osme length. Examples are: (i) the regular solution approach for the heat of liquid alloys and the pair interaction model for treating ordering in metallic solid solutions are basically inadequate if the two types of atoms differ appreciably in size: and (ii) an important quantity is ƒ A B , the degree to which A atoms are surrounded by B-type neighbours. This quantity determines the concentration dependence of the formation enthalpies of ordered phases in a binary system and makes it possible to rationalize their occurrence.

Enthalpies of formation of liquid and solid binary alloys based on 3d metals: II alloys of chromium and manganese

Abstract As has been done in a previous paper [4] on alloys of Sc, Ti and V, we present in this paper model predictions for heats of formation of binary intermetallic compounds of Cr and Mn with arbitrary metal partners. Enthalpies of liquid alloys are also predicted. Calculated values are compared with experimental data as with the qualitative information that can be derived from the phase diagrams. The available binary phase diagrams based on Cr and Mn are presented. The effect of the magnetic properties on the enthalpies of formation is included in the discussion.

Thermodynamic properties of compounds in the indium-bismuth system

Abstract Heats of formation at 273°K of the compounds InBi, In5Bi3 and In2Bi have been determined to be −711 ± 60 cal/g-atom, −405 ± 54 cal/g-atom and −109 ± 55 cal/g-atom, respectively, by means of liquid tin solution calorimetry. Comparison with earlier measurements and evaluations is made and some conclusions about the relative stability of the compounds are formulated. Heats of solution at infinite dilution of indium, bismuth and silver in tin at 587°K are presented (−124 ± 21 cal/g-atom, 130 ± 47 cal/g-atom and 3637 ± 24 cal/g-atom, respectively).

Energy Effects in Bulk Metals

For many processes in bulk metallic systems it is of importance to be able to predict the energy effects involved. Very often information is available from experiments but in a large number of cases information is lacking. In these cases, theoretical calculations, for instance band-structure calculations, are needed which require special expertise and therefore cannot easily be done by anybody who needs information on particular energy effects. In order to solve this problem, in the 1980s, an empirical model has been developed by Miedema that predicts a number of energy effects that are essential in metals.