L. V. Goncharuk

Thermodynamics of Interaction of Rare-Earth Metals with d-Metals. The Scandium ― Iron System

Gibbs free energies, enthalpies, and entropies of formation of the compounds ScFe2 and Sc29Fe6 are found by measuring the emf of galvanic cells in the range 720-1030 K. The nature of interaction in Fe ― REM binary systems is analyzed. Scandium is shown to behave like a 3d-metal during interaction with iron.

Thermodynamic parameters of scandium-iridium compounds and ScIr2

EMF measurement for galvanic cells has been used in the range 813–1023 K to determine the Gibbs energies, enthalpies, and entropies of formation for the phases ScIr3 within its region of homogeneous existence and also ScIr2.

Microstructure, Growth Kinetics, and Abrasive Wear Resistance of Boride Layers on Fe–30% Cr Alloy

Two boride layers are found to form at the interface between reacting phases in the course of boriding a Fe–30% Cr alloy in boron powder with KBF4 (activator) in the temperature range of 850–950°C and reaction times 3600–43200 sec (1–12 h). Each of these layers is single-phase structurally (crystallographically) and two-phase compositionally (chemically). The outer boride layer bordering boron consists of the crystals of the (Fe, Cr)B and (Cr, Fe)B compounds, while the inner layer adjacent to the alloy base comprises the crystals of the (Fe, Cr)2B and (Cr, Fe)2B compounds. The characteristic feature of both layers is a profound texture. Diffusional layer-growth kinetics are close to parabolic and can alternatively be described by a system of two non-linear differential equations dx/dt = (kB/x) – (rgkFe/py), dy/dt = (kFe/y) – (qkB/sgx), where x is the outer FeB layer thickness (m), y is the inner Fe2B layer thickness (m), kB is the FeB layer growth-rate constant (m2⋅sec–1), kFe is the Fe2B layer growth-rate constant (m2⋅sec–1), g is the ratio of the FeB and Fe2B molar volumes, p = q = r = 1, and s = 2 (factors from the chemical formulae of FeB and Fe2B). The temperature dependence of the layer growth-rate constants obeys a relation of the Arrhenius type K = Aexp (–E/RT), where K stands for any constant, A is the frequency factor, E is the activation energy, R is the gas constant, and T is the absolute temperature. Application of the least-squares fit method yielded the following equations: kB = 3.42⋅10–8⋅exp(–175.4 kJ × × mol–1/RT) m+⋅sec–1, kFe = 7.45⋅10–9 exp(–144.6 kJ⋅mol–1/RT) m2⋅sec–1. Microhardness values are 18.1 GPa for the outer boride layer, 15.2 GPa for the inner layer, and 1.75 GPa for the alloy base. The dry abrasive wear resistance of the outer boride layer, found from mass loss measurements, is more than 300 times greater than that of the Fe–30% Cr alloy base. Such a huge increase in wear resistance is due to the microstructure of boride layers having a peculiar regular arrangement of enhanced rigidity.

Thermodynamic Properties of Holmium Germanides

The Gibbs free energy, enthalpy, and entropy of forming holmium germanides HoGe3–x (HoGe2,7), HoGe2–y (HoGe1,8), HoGe2–a (HoGe1,7), HoGe2–b (HoGe1,5), Ho3Ge4, HoGe, Ho11Ge10, Ho5Ge4, and Ho5Ge3 are determined by measuring electromotive forces in the temperature range 770–970 K. The negative values of the Gibbs free energy and enthalpy of formation increase with holmium content in a compound and reach extreme values for Ho5Ge3, which has the highest melting point and is the only congruently melting compound in the Ho–Ge system. The thermodynamic properties of forming solid and liquid alloys of holmium with germanium are compared. Like the solid alloys, the highest enthalpy of mixing is in the range of Ho-rich compositions. The standard enthalpy and entropy of formation of HoGe1.5, HoGe, and Ho5Ge3 are calculated.

Phase composition and thermodynamic properties of alloys of the Te—PbTe—Sb2Te3 system

The phase composition and thermodynamic properties of Te−PbTe−Sb2Te3 alloys are determined by means of X-ray phase analysis and measurements of electromotive forces in the temperature range 540–660 K. The formation of the Pb2Sb6Te11 ternary compound in this temperature range has not been confirmed. The results of the electrochemical measurements confirm the mutual solubility of the components of the quasibinary PbTe−Sb2Te3 system. The activities of PbTe are determined in the (PbTe+Sb2Te3) phase field.

Thermodynamics of formation of HoGe3–x and HoGe2–y higher holmium germanides

The Gibbs energy, enthalpy, and entropy of formation of HoGe3–x (HoGe2.7) and HoGe2–y (HoGe1.8) from solid compounds are determined by emf measurement in the temperature range 770–965 K. The formation enthalpy of the higher holmium germanide is in good agreement with ∆fH° (HoGe2.7) calculated from the limiting mixing enthalpy of Ho in liquid germanium on the assumption that

Thermodynamics of rare earth metal interaction with copper

\varDelta {\bar{H}_{Ho}}

Interaction of 25% chromium steel with boron powder

for solid alloys in the [HoGe2.7 + Ge] region remains the same as

Thermodynamic properties of holmium bismuthide

\varDelta \bar{H}_{Ho}^\infty

Thermodynamic properties of silicon-rich holmium silicides

for liquid alloys.