Search Results for thermodynamics

This article introduces the fundamental concepts of chemical thermodynamics and chemical kinetics in describing presolidification phenomena. For metallurgical systems, the most important thermodynamic variables are enthalpy and Gibbs free energy. A qualitative demonstration of the interrelationship between phase diagrams and thermodynamics is presented. The article discusses processes that generally limit the rates of chemical processes. These include nucleation of the product phase and interphase mass transport. The article provides a discussion on the dissolution of alloy with melting point lower than bath temperature and dissolution of alloy that is solid at bath temperatures.

This article discusses the application of thermodynamic in the form of phase diagrams for visually representing the state of a material and for understanding the solidification of alloys. It presents the derivation of the relationship between the Gibbs energy functions and phase diagrams, which forms the basis for the calculation of phase diagrams (CALPHAD) method. The article also discusses the calculation of phase diagrams and solidification by using the Scheil-Gulliver equation.

Thermodynamic descriptions have become available for a large number of alloy systems and allow the calculation of the phase diagrams of multicomponent alloys. This article begins with a discussion on three laws of thermodynamics: the Law of Conservation of Energy, the Second Law of Thermodynamics, and the Third Law of Thermodynamics. It informs that for transformations that occur at a constant temperature and pressure, the relative stability of the system is determined by its Gibbs free energy. The article describes the Gibbs free energy of a single-component unary system and the Gibbs free energy of a binary solution. It schematically illustrates the structure of a binary solid solution with interatomic bonds and shows how the equilibrium state of an alloy can be obtained from the free-energy curves at a given temperature. The article concludes with information on the construction of eutectic and binary phase diagrams from Gibbs free-energy curves.

Metals can react chemically with oxygen when exposed to air. Essential to an understanding of the gaseous corrosion of a metal are the crystal structure and the molar volume of the metal on which the oxide builds, both of which may affect growth stresses in the oxide. This article presents crystal structures and thermal properties of pure metals and oxides in a tabular form. The free energy of reaction, which describes the oxidation process of a pure divalent metal, is presented. The article illustrates the Richardson-Jeffes diagram, which is used in the determination of the standard Gibbs energy change of formation of oxides and the corresponding dissociation pressures of the oxides as a function of temperature. It demonstrates the Kellogg diagram which shows stability range in more complicated multioxidant systems. The article explains the determination of partial pressures of gas mixtures and partial pressures of volatile oxidation products.

Molten salts, in contrast to aqueous solutions in which an electrolyte (acid, base, salt) is dissolved in a molecular solvent, are essentially completely ionic. This article begins with an overview of the thermodynamics of cells and classification of electrodes for molten salts: reference electrodes and indicator electrodes. It explains that corrosion in molten salts can be caused by the solubility of the metal in the salt, particularly if the metal dissolves in its own chloride. The article describes the factors that affect the corrosion of titanium, namely, the titanium chloride content of the magnesium chloride melt, magnesium or sodium content, and oxygen content of the product. It concludes with a discussion on the oxygen activity in the titanium metal product.

This article provides a discussion on the fundamentals of corrosion thermodynamics. The discussion focuses on electrochemical reactions, molten salt corrosion thermodynamics, and geochemical modeling.

This article is a comprehensive collection of the thermodynamic equations and property relations of the first and second laws of thermodynamics that are applicable to closed-system consisting of several homogeneous and heterogeneous phases.

The control of the solidification process of cast iron requires understanding and control of the thermodynamics of the liquid and solid phases and of the kinetics of their solidification, including nucleation and growth. This article addresses issues that allow for the determination of probability of formation and relative stability of various phases. These include the influence of temperature and composition on solubility of various elements in iron-base alloys; calculation of solubility lines, relevant to the construction of phase diagrams; and calculation of activity of various components. It discusses the role of alloying elements in terms of their influence on the activity of carbon, which provides information on the stability of the main carbon-rich phases of iron-carbon alloys, that is, graphite and cementite. The article reviews the carbon solubility in multicomponent systems, along with saturation degree and carbon equivalent.

This article addresses two issues on thermodynamics, namely, the calculation of solubility lines and the calculation of the activity of various components. It discusses alloying elements in terms of their influence on the activity of carbon. The article describes the desulfurization and deoxidation of cast iron and steel. It illustrates the thermodynamics of the iron-carbon system and the iron-silicon system. The article examines solubility and saturation degrees of carbon in multicomponent iron-carbon systems. One of the main applications of the thermodynamics of the iron-carbon system is the calculation of structure-composition correlations. The article concludes with information on the structural diagrams for cast iron: the Maurer diagram and the Laplanche diagram.

This article provides accessible information on the thermodynamic properties of liquid aluminum-base and copper-base alloys with the help of phase diagrams. It contains tables that compile the thermodynamic data in the form of activities, activity coefficients, partial molar thermal properties, and integral molar properties for selected aluminum-based and copper-based alloys.

This article presents the background to the CALculation of PHAse Diagrams (CALPHAD) method, explaining how it works, and how it can be applied in industrial practice. The extension of CALPHAD methods as a core basis for the modeling of generalized material properties is explored. It informs that one of the aims of CALPHAD methods has been to calculate phase equilibria in the complex, multicomponent alloys that are used regularly by industry. The article discusses the application of CALPHAD calculations to industrial alloys. Modeling of general material properties, such as thermophysical and physical properties, temperature- and strain-rate-dependent mechanical properties, properties for use in the modeling of quench distortion, and properties for use in solidification modeling, is also reviewed. The article also describes the linking of thermodynamic, kinetic, and material property models.