摘要:

AbstractRecent developments of experimental techniques for the measurement of thermodynamic quantities of metals and alloys are reviewed. Special emphasis is placed on calorimetry of reacting and non‐reacting systems, emf methods with liquid and solid electrolytes, and the various Knudsen effusion method

ISSN:0005-9021    

DOI:10.1002/bbpc.19830870902

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1983

数据来源: WILEY

摘要:

AbstractPredictions of the enthalpies of solution in the solid state will be presented for arbitrary combinations of 4d and 5d transition metals. The approach is similar to the one used in a previous paper on combinations of two 4d metals. In addition to the contribution stemming from the chemical interaction, which is equal to the enthalpy of solution in the liquid state, the enthalpy of solution in the solid state contains two other terms. The first of these accounts for the elastic energy arising from the atomic size mismatch, where this size mismatch has been corrected for volume changes that accompany the alloy formation. The second term takes into account the variation of the structure dependent energy in relation to the number of d‐electrons per atom. – The predictions are generally in good agreement with the solubilities found in the respective phase diagrams. For two systems, Zr in Pt and Pt in Nb, that on first sight present exceptions, preliminary experiments indicate that parts of the respective phase diagrams have to be revised. The structure‐dependent contribution manifests itself not only in the limiting solubilities in the main crystal structures of the pure metals, but also in the existence of disordered intermediate phases and may also be responsible for the anomalously large entropy of fusion recently observed for some transition m

ISSN:0005-9021    

DOI:10.1002/bbpc.19830870903

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1983

数据来源: WILEY

摘要:

AbstractThermodynamic functions of compounds with narrow ranges of homogeneity are calculated with the aid of the concept of defect thermodynamics. In doing so, the irregular structural elements of a crystal are formally treated as quasi‐particles in dilute solution on their respective sublattices. This concept is illustrated with binary and ternary ionic crystals (for example Fe3‐δO4; Ag2+δS; Co1‐δ; (Co,Mg)1‐δO; (Fe,Mg)2‐δSiO4). The nonstoichiometry δ of these compounds is calculated as a function of the independent thermodynamic variables and compared with exper

ISSN:0005-9021    

DOI:10.1002/bbpc.19830870904

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1983

数据来源: WILEY

摘要:

AbstractPalladium and platinum alloys have turned out to be a useful subject for relating thermodynamic properties with electronic and elastic quantities of the components. The mixing behavior of a number of interstitial and substitutional alloys exhibits analogous characteristics and may be interpreted by means of the same model. – Two effects are discussed to account for nonideal properties. An “electronic” effect is based on the observation that a number of alloy components behave as electron donors with respect to Pd and Pt. The charge transfer gives rise to a bonding contribution which is determined by the Fermi levels of the components and the valency of the solute. Extremely negative deviations from ideal mixing behavior have been predicted and observed upon adding unnoble components such as Al, Zr, Th or rare earth metals. For a number of Pd alloys the rise of the Fermi energy can be described as a function of the valence electron concentration only, irrespective of the particular donor. – An “elastic” effect is associated with the lattice distortion brought about by the dissolved particles. Models based on continuum elastic considerations are discussed in order to estimate the strain energy at infinite dilution. This quantity is correlated to the pair interaction energy in the quasichemical approach, which was used to calculate the concentration dependence of the elastic contribution. – Based on the underlying assumptions, the thermodynamic excess quantities can be separated in an electronic and an elastic part. These ideas are quite general and should be useful in a number of other metal

ISSN:0005-9021    

DOI:10.1002/bbpc.19830870905

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1983

数据来源: WILEY

摘要:

AbstractThe solutions of hydrogen in palladium and its alloys are classical examples of interstitial metallic solutions. Although these alloys have been studied for a very long time, a good deal of new information has become available in recent years, partly as a result of the application of the combined calorimetric‐equilibrium approach. This experimental method, which was developed in our laboratory about 10 years ago, allows essentially simultaneous determinations of the Gibbs energies, the enthalpies and the entropies of solution. This approach has been particularly useful in throwing new light on the temperature dependence of the thermodynamic properties, and also on their dependence on the alloying constituents. Special interest is attached to the new information on the partial entropies of hydrogen, which points strongly toward a temperature dependent, non‐random distribution of the hydrogen atoms among the available interstitial si

ISSN:0005-9021    

DOI:10.1002/bbpc.19830870906

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1983

数据来源: WILEY

摘要:

AbstractUsing homogeneous equilibria reactions for the description of chemical short range order tendencies in liquid alloys with compound forming tendency it is possible, with the association model, to describe different kinds of asymmetrical concentration dependences, to calculate the temperature dependences of the thermodynamic mixing functions as well as to extrapolate for multicomponent systems. Some exemplary results are shown. The existence of a chemical short range order is an important factor of influence on the glass formation ability obtained by rapid quenching from the liquid phase. On the one hand, it causes small chemical driving forces for a crystallization and, hereby, a thermodynamic promotion of glass formation. On the other hand, glass formation is additionally kinetically favoured, if the stoichiometric compositions of the associates in the liquid alloys are not in accordance with those of the crystalline equilibrium phases in the glass formation range.

ISSN:0005-9021    

DOI:10.1002/bbpc.19830870907

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1983

数据来源: WILEY

摘要:

AbstractThere are many instances in practice of phase changes in which the initial phase e.g. a homogeneous melt is not replaced by one or more thermodynamic stable phases but rather by metastable phases. Knowledge of systems in which metastable phases can form has increased considerably in recent years. Rapid quenching increases the tendency to form metastable phases including ultimately for appropriate compositions the amorphous metallic glasses. In any discussion about metastable phases there arises the question of the conditions under which they form and their stability which depends on temperature, pressure and composition. In the present work some attempts to describe the thermal stability of metallic glasses and the experimental means of measuring it are discussed.

ISSN:0005-9021    

DOI:10.1002/bbpc.19830870908

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1983

数据来源: WILEY

摘要:

AbstractBy the use of examples which mainly concern the configurational entropy of alloy systems an attempt is made to illustrate the application of physical and mathematical models to the assessment of alloy systems. It is emphasized that methods, which are often regarded as independent of models, depend very strongly on some hidden choice of a model. It is shown that different physical models can give the same mathematical model. For further developments it may be essential to test what physical model gives the most realistic description of the situation in the real system. It is also shown that different mathematical models can represent the data very well even when the properties of the system are very specific.

ISSN:0005-9021    

DOI:10.1002/bbpc.19830870909

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1983

数据来源: WILEY

摘要:

AbstractThe general features of thermodynamic calculation of phase equilibria are reviewed. This includes analytical description of the thermodynamic functions by approximations or models, determination of the resulting adjustable coefficients from experimental data, calculation of phase equilibria based on the Gibbs free energy functions of individual phases and graphical representation of the results. Special emphasis is given to different types of two‐dimensional representations only containing partial information about the multidimensional higher order system

ISSN:0005-9021    

DOI:10.1002/bbpc.19830870910

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1983

数据来源: WILEY

摘要:

AbstractThe phase diagrams of the ZrO2–CaO, ZrO2–Y2O3, ThO2–Y2O3and ThO2–La2O3systems are discussed in view of the use of the electrolytes in emf measurements. It is shown that thermodynamic studies on metallic A‐B systems using solid galvanic cells with oxygen and fluorine ion conducting electrolytes require the knowledge of the phase diagrams of the corresponding ternary A‐B‐O and A‐B‐F systems for the cell arrangements. Examples for misleading emf measurements by use of incompatible electrodes are given. Asymmetric cells, side reactions between the electrodes and the electrical leads, and impurities in the cover gas as sources for erroneous emf measurements are demonstrated. The characteristics of reference electrodes for oxide electrolytes in environments with different oxygen partial pressures are outlined. The role of oxygen as an impurity in the electrodes for CaF2electrolyte

ISSN:0005-9021    

DOI:10.1002/bbpc.19830870911

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1983

数据来源: WILEY