Search Results for enthalpy of melting

This chapter describes the basics of energy and entropy and “free energy.” Fundamentals of internal energy U , the enthalpy H , entropy S , free energies G , and F of a substance are presented. The chapter also presents the thermal vibration model to promote a better understanding of the U , S , and F of the crystal. It covers basic concepts of thermodynamics of magnetic transition and discusses the role and the meaning of magnetic transition in iron and steel. The chapter concludes with a general discussion on an amorphous phase from a thermodynamic viewpoint.

This chapter presents abbreviations and symbols used for soldering.

This chapter discusses some of the methods and measurements used to construct phase diagrams. It explains how cooling curves were widely used to determine phase boundaries, and how equilibrated alloys examined under controlled heating and cooling provide information for constructing isothermal and vertical sections as well as liquid projections. It also explains how diffusion couples provide a window into local equilibria and identifies typical phase diagram construction errors along with problems stemming from phase-boundary curvatures and congruent transformations.

This chapter explains how the principles of chemical thermodynamics are used in the construction and interpretation of phase diagrams. After a brief review of the laws of thermodynamics, it describes the concept of Gibbs free energy and its application to transformations that occur in single-component and binary solid solutions. It then examines the relationship between the free energy of a solution and the chemical potentials of the individual components. It also explains how to account for the heat of mixing using quasi-chemical models, discusses the effect of interatomic bond energies and chemical potentials, and shows how the equilibrium state of an alloy can be obtained from free-energy curves.

This chapter explains the idea of solution theory and the nature of mixed materials. The chapter considers approximation of free energy by the regular solution model and sublattice model. It discusses chemical potential and nonrandom distribution based on the interactions between solute atoms.

This chapter covers the analytical methods developed to characterize ordering phenomena in crystal structures. The chapter gives examples of ordering phenomena and discusses models for long-range ordering, such as the Bragg-Williams-Gorsky (B-W-G) model, and for short-range ordering. Examples of ordering and phase separation due to ordering by the B-W-G model are described. The chapter includes an appendix covering the effect of phase separation inversion type.

This chapter provides a short introduction to phase transformations, namely, the liquid-to-solid phase transformations that occur during solidification and the solid-to-solid transformations that are important in processing, such as heat treatment. It also introduces the concept of free energy that governs whether or not a phase transformation is possible, and then the kinetic considerations that determine the rate at which transformations take place. The chapter also describes important solid-state transformations such as spinodal decomposition and martensitic transformation.

This appendix defines abbreviations, acronyms, and symbols presented within this book.

This chapter introduces many of the key concepts on which metallurgy is based. It begins with an overview of the atomic nature of matter and the forces that link atoms together in crystal lattice structures. It discusses the types of imperfections (or defects) that occur in the crystal structure of metals and their role in mechanical deformation, annealing, precipitation, and diffusion. It describes the concept of solid solutions and the effect of temperature on solubility and phase transformations. The chapter also discusses the formation of solidification structures, the use of equilibrium phase diagrams, the role of enthalpy and Gibb’s free energy in chemical reactions, and a method for determining phase compositions along the solidus and liquidus lines.

In an attempt to explain the stresses encountered in the plastics industry, this article first defines the different types of internal stresses in amorphous polymers. Each type of thermal stress is then discussed in detail, with reference to the mechanism of generation and the effect on engineering properties. Methods of detecting and measuring internal stresses are also presented. The article then describes the combined effects of thermal stresses and orientation that result from processing conditions. Finally, it discusses numerous aspects of physical aging and the use of high-modulus graphite fibers in amorphous polymers.

This appendix lists the intermetallic phase designations of aluminum-silicon casting alloys and defines symbols and abbreviations associated with the variables, processes, and tools used in microstructural examination.

Generally, binders consist of at least three ingredients: a backbone to provide strength (compounds such as polyethylene, polypropylene, ethylene vinyl acetate, and polystyrene); a filler, such as polyacetal and paraffin wax, to occupy space between particles; and additives, such as stearates, stearic acid, or magnesium stearate, as well as phosphates and sulfonates, to adjust viscosity, lubricate tooling, disperse particles, or induce binder wetting of the powder. In the case of binders deposited via ink jet printing, the binder contains solvents to lower the viscosity for easier jetting. The chapter provides a detailed description of these constituents. The requirements of a binder as well as the factors determining the physical and thermal properties of polymers are discussed. Then, two factors associated with solvation of polymers, namely solubility parameter and wetting, are covered. The chapter ends with information on the specification of polymers used in binders.

This chapter discusses the growing role of powder metallurgy in the production of intermetallic, Heusler, and high-entropy alloys. It reviews the challenges of producing these materials by conventional methods and the advantages of sinter-based PM techniques. It explains why PM processes are better suited for complex materials than casting and compares the properties of intermetallic, Heusler, and high-entropy alloys prepared by casting and powder-metal techniques.

This chapter describes the physical characteristics, properties, and behaviors of solid solutions under equilibrium conditions. It begins with a review of a single-component pure metal system and its unary phase diagram. It then examines the solid solution formed by copper and nickel atoms. It discusses the difference between interstitial and substitutional solid solutions and the factors that determine the type of solution that two metals are likely to form. It also addresses the development of intermediate phases, the role of free energy, transformation kinetics, liquid-to-solid and solid-state phase transformations, and the allotropic nature of metals.

This chapter provides a thorough review of the crystal structure of beryllium and its elastic, thermal, and nuclear properties. It also includes information on electrical and optical properties and an extensive amount of data in the form of tables and plots.

The microstructure of carbon steel is largely determined by the transformation of austenite to ferrite, cementite, and pearlite. This chapter focuses on the microstructures produced by diffusion-controlled transformations that occur at relatively low cooling rates. It describes the conditions that promote such transformations and, in turn, how they affect the structure of various phases and the rate at which they form. The chapter also discusses the concepts of transformation kinetics, minimum free energy, and nucleation and growth, and provides information on alloying, interphase precipitation, and various types of transformations.