Skip to main content
main-content

Über dieses Buch

Guiding readers from the significance, history, and sources of materials to advanced materials and processes, this textbook looks at the production and primary processing of inorganic materials, such as ceramics, metals, silicon, and some composite materials. The text encourages instructors to teach the production of all types of inorganic materials as one. While recognizing the differences between producing various types of materials, the authors focus on the commonality of thermodynamics, kinetics, transport phenomena, phase equilibria and transformation, process engineering, and surface chemistry to all inorganic materials. The text focuses on fundamentals and how fundamentals can be applied to understand how the major inorganic materials are produced and the initial stages of their processing. Understanding of these fundamentals will equip students for engineering future processes for producing materials or for studying the processing of the many less common materials not examined in this text. The text is intended for use in an undergraduate course at the junior or senior level, but will also serve as a useful introductory and reference work for graduate students and practicing scientists and engineers.

Inhaltsverzeichnis

Frontmatter

Chapter 1. Significance, History, and Sources of Materials

Abstract
To most engineers and scientists a material is a solid with useful structural, electrical (including electronic or magnetic), optical or corrosion-resistance properties. If we accept this definition then it is clear that the products of most of the major manufacturing industries are either materials or are fabricated from materials. The exceptions are the food, beverage, chemical and fuels industries; even within these industries materials play a key role. Examples are the steel, aluminum and glass used for packaging food and drink, corrosion-resistant materials used to build chemical reactors, and the bits used to drill oil wells. Materials, then, have a great importance in the economies of industrialized nations. In this text we shall be concerned with materials of mineral origin, so that steel, glass, silicon, and ceramic materials are included, but materials of animal or vegetable origin (wood, rubber, leather, etc.) are excluded. As extracted from the earth, the minerals (“raw materials” in Fig. 1.1) from which these materials are produced have a value of 0.4 percent of the U.S. gross domestic product. However, processing of these minerals (coupled with recycling of old materials) to produce metals, ceramics, etc. brings their value to over 4 percent of the GDP.1
James W. Evans, Lutgard C. De Jonghe

Chapter 2. Chemical Thermodynamics

Abstract
It is anticipated that the readers of this book will have had at least a beginning course in thermodynamics. This chapter will therefore serve as a brief review of those aspects of thermodynamics that are particularly relevant to the production of materials. In addition, this chapter will treat some topics (e.g., Ellingham diagrams) that are frequently given limited coverage in undergraduate courses but that are of great value to the practicing engineer or scientist (e.g., in rapidly determining whether a chemical reaction, proposed as a way of producing a material, will actually take place).
James W. Evans, Lutgard C. De Jonghe

Chapter 3. Reaction Kinetics

Abstract
In Chapter 2 we reviewed the principles of chemical thermodynamics that enable us to predict whether or not a particular reaction will take place, under specified conditions, and the quantities of reactants and products present when chemical equilibrium is reached and reaction stops. Thermodynamics therefore provides us with a first test of any scheme of reactions for producing a material: are the reactions feasible at practical temperatures and do they produce the desired material in sufficient yield? An equally important consideration, from the viewpoint of economics, is how rapidly the reaction takes place. A reaction may be thermodynamically feasible but take place so slowly that the productivity of a process involving the reaction is too low. “Too low” here means that the revenue derived from the material produced is too low to justify the investment of capital to build the plant or perhaps even too low to meet the operating costs (labor, energy, raw materials, etc.) of the process. This chapter is concerned with the rate at which reactions take place.
James W. Evans, Lutgard C. De Jonghe

Chapter 4. Powders and Particles

Abstract
Nearly all practical ceramics and some metal products are fabricated from powders. Typically, these powders are mixed with a few percent of various organic and inorganic additives, compacted to form a porous “green” body1, and heated (or “fired”) to a high temperature. During the heating the porosity in the sample is reduced or eliminated. This phenomenon is called sintering. Care must be taken to distinguish this sintering phenomenon from the sintering process described in Chapter 1. The properties of the sintered ceramic body depend to a large extent on the chemical and microstructural imperfections that were not eliminated or that were produced as a result of the sintering. Many imperfections can be traced back to the structure of the green compact or to the nature of the starting powder; therefore, in this chapter we examine powders. Powders can have a complex structure. Sometimes in describing powders confusion may arise through the inconsistent use of terminology. The terminology proposed by Onoda and Hench (1978) has been adopted here.
James W. Evans, Lutgard C. De Jonghe

Chapter 5. Surfaces and Colloids

Abstract
Ceramic fabrication processes would often benefit from using powders with very small particles. However, such powders are notoriously difficult to handle when dry. They get airborne very easily, making everything look messy very quickly, and often pose significant health hazards. They readily form fluffy aggregates that make it difficult to pour the powder into dies and molds. They stick strongly to die walls and trap large amounts of air when pressed in dies. These processing problems led to the belief that there was an optimum particle size of about 1 µm. The optimum was supposedly determined by a trade-off between the benefit of improving sintering rates and the detriment of increasing particle handling problems with decreasing particle size. However, handling of fine particles as suspensions in liquids (or colloids) rather than as dry powders can facilitate the ceramic forming processes and thus extend downward the range of practically useful particle sizes significantly. Actually, particle suspensions have traditionally been used in tape casting and slip casting, as described in Chapter 12. More recently, success in producing submicrometer, nearly monodispersed powders (consisting of particles of all the same size and shape) has made possible vast improvements in the perfection of the ceramic bodies obtained by colloidal consolidation methods. One could think of colloidal consolidation methods as a glorified name for what are really just variants of the old mudpie baking. The practical aspects of these methods are described in Chapter 12.
James W. Evans, Lutgard C. De Jonghe

Chapter 6. Fundamentals of Heat Treatment and Sintering

Abstract
So far in this book we have had little interest at the microscopic level in the structure of the solids that we have encountered. Exceptions have been in Chapter 3, where we recognized that a reacting solid might be porous (and the pores affect the rate of reaction), and in Chapter 4, which was concerned with the shape and size of the small particles that we frequently encounter in ceramic or powder metallurgical processing.
James W. Evans, Lutgard C. De Jonghe

Chapter 7. Process Engineering

Abstract
In this chapter we provide a brief introduction to the principles of process engineering. Process engineering is a large topic (much of it covered within chemical engineering) and a full introduction would require a book in itself. Our experience has been that, except for chemical engineering students, most students have had little or no exposure to process engineering, and therefore any text on how materials are produced must provide an introduction to the more important concepts. We begin with some definitions.
James W. Evans, Lutgard C. De Jonghe

Chapter 8. High-Temperature Processes for the Production of Metals and Glass

Abstract
The production of metals has long been associated with high temperatures. Man moved beyond the use of naturally occurring materials, such as wood and stone, in approximately 6000 B.C. It is probable that the discovery that subjecting certain rocks to high temperatures resulted in metals was made accidentally in a cooking fire or, more likely, a potter’s kiln. Since that time the major part of our metal production has been carried out in processes that employ temperatures in the range of 300 to 1600°C. This technology, known as pyrometallurgy, is treated first in this chapter. Alternative or complementary technologies — hydrometallurgy (employing aqueous solutions and comparatively low temperatures, say, less than 200°C) and electrometallurgy (exploiting direct current to bring about electrochemical reactions) — are treated in Chapter 9. At the end of the present chapter we include a brief treatment of the production of glass. Glass production bears a resemblance to pyrometallurgical operations in that high-temperature liquids are handled and ultimately cast into solid form.
James W. Evans, Lutgard C. De Jonghe

Chapter 9. Hydrometallurgy and Electrometallurgy

Abstract
In Chapter 8 we examined some traditional techniques for the production of “tonnage” metals such as steel, aluminum, and copper. These techniques involved high temperature, molten metals, and slags and difficulties posed by the emission into the environment of particles, sulfur dioxide, and so on. In the present chapter we examine some alternative techniques that make use of aqueous chemistry to extract metals from ores and concentrates. This “hydrometallurgical” technology employs much lower temperatures than those encountered in Chapter 8. Nevertheless, hydrometallurgical techniques still entail the consumption of considerable quantities of energy, particularly when the energy costs associated with producing reagents are considered. However, hydrometallurgical processes typically pose no air pollution difficulties, but steps must usually be taken to avoid water pollution.
James W. Evans, Lutgard C. De Jonghe

Chapter 10. Refining, Solidification, and Finishing of Metals

Abstract
Consider a metal produced by one of the pyrometallurgical operations described in Chapter 8. The metal would be molten and in a few instances it may be of sufficient purity to cast (solidify) immediately. Usually, however, the metal will contain sufficient impurities that a further refining step must be carried out to remove these impurities. This point (prior to the first solidification) may also be a good one at which to add other metals to produce an alloy. Finally, this might be an appropriate point to add recycled metal, because any impurities (e.g., paint or corrosion products) may be removed along with those present in the virgin metal.
James W. Evans, Lutgard C. De Jonghe

Chapter 11. Production of Powders

Abstract
In Chapter 4 we described the physical aspects of powders and, from the examples that were shown, it was clear that a wide variety of shapes and agglomeration states was possible. Much of the powder’s physical characteristics are determined by the way it is prepared. The preparation method will then have profound consequences for the fabricability of the ceramic or metal part from powder compacts. Often the variations in powder properties from batch to batch, prepared by the same method in the same factory, are sufficient to cause unacceptable variations in product properties. This susceptibility of fine powders to seemingly minor, and often unrecorded or undetected processing variations, is a major difficulty in the production of reliable and reproducible ceramic products.
James W. Evans, Lutgard C. De Jonghe

Chapter 12. Powder Compaction

Abstract
In Chapter 5 we mentioned the importance of the arrangements of the particles in a powder compact with respect to the perfection of the microstructure that results after sintering. Colloidal methods proved to be very fruitful in manipulating the structure of the starting powder compact, the green compact, especially for submicrometer powders. In many industrial applications, where mass production is desired, colloidal compaction methods have not yet been incorporated or can be adopted only with sacrifice of higher fabrication costs. To date, many articles prepared from powders are still made by various mechanical consolidation methods, such as die pressing, isostatic compaction, and extrusion. We describe these methods in a little more detail in this chapter. As before, the structure of the consolidated green powder compact will have a very strong effect on the properties of the final sintered product, and the factors that affect the homogeneity of the green compact need to be examined.
James W. Evans, Lutgard C. De Jonghe

Chapter 13. Sintering of Powder Compacts

Abstract
When we have compacted a powder to some shape, turning it into a useful part is, in principle, quite simple. All that should be necessary is to put the compact in a furnace for awhile, between 0.5 and 0.8 of its melting temperature, and hold it there for a few hours. Since elimination of internal surfaces means lowering the free energy of the system, diffusion should redistribute the atoms inside the powder compact, slowly trying to fill up the voids (pores). You could expect a final product that has some pores in it and in which the grain size has increased, in some cases significantly, compared to the initial particle size. Typically, if we start with a powder particle size of 1 µm or less, we might have a final grain size of 10 to sometimes 100 µm. Since there was no massive melting in the powder mix (we allow for some powder mixtures to have some liquid present during sintering) the compact retains its form, and the final shape is a shrunken version of the initial compact shape. For large parts we will need to guard against sagging during sintering and judicious support may have to be used.
James W. Evans, Lutgard C. De Jonghe

Chapter 14. Microstructure Development During Sintering

Abstract
The engineering properties of materials are strongly affected by their microstructure. The microstructural features of importance are many: grain size and grain shape, pore size and location, distribution of second phases (such as precipitates), and others. For polycrystalline ceramics, for example, it is frequently found that the fracture strength is proportional to the inverse square root of the grain size. Metals show a similar relationship for the stress at which they yield. As another example, metal alloys can be strengthened by the presence of dispersed second-phase particles. A well-known case is that of aluminum, a very soft material in its pure form, which can be hardened by the incorporation of a few percent of copper. The added copper, after appropriate heat treatment, forms very small Al-Cu precipitates that make plastic deformation of the alloy more dif-ficult than that of the pure aluminum. In another example, the high-temperature creep resistance of sintered silicon nitride depends strongly on the nature and amount of a thin glassy layer, perhaps only 2 nm wide, that is often present at the grain boundaries.
James W. Evans, Lutgard C. De Jonghe

Chapter 15. Densification Technology

Abstract
During sintering of ceramic or metal powder compacts, the useful properties of the materials are developed and the part takes on its final shape. After sintering, only finishing processes, such as surface grinding or a follow-up heat treatment to remove residual stresses, may remain. Perhaps the most significant factor determining the rate of progress in densification technology has been the attainment of increasingly higher furnace temperatures, and the improved control of the furnace environment. Some structural ceramics, such as silicon carbide, require temperatures over 2000°C to get sufficient densification; other ceramics, such as zinc oxide varistors, require exceptionally close control of the sintering temperature to achieve optimum properties; in yet others, such as the lead zirconate titanate family of electrooptical and ferroelectric ceramics, the furnace atmosphere must be controlled to avoid evaporation of volatile constituents.
James W. Evans, Lutgard C. De Jonghe

Chapter 16. Advanced Materials and Processes

Abstract
In the first seven chapters of this book, we attempted a succinct statement of the fundamentals of science and engineering thought necessary for an understanding of processes for producing materials. The remaining chapters up to the present one, have had as their focus the application of these fundamentals to the technology of what are frequently called “traditional” structural materials, such as steel, copper, alumina, and silicon carbide. These traditional materials are, in terms of economic measures such as tons produced or sales per year, the most important ones and likely to remain so well into the next century.
James W. Evans, Lutgard C. De Jonghe

Backmatter

Weitere Informationen

Premium Partner

    Marktübersichten

    Die im Laufe eines Jahres in der „adhäsion“ veröffentlichten Marktübersichten helfen Anwendern verschiedenster Branchen, sich einen gezielten Überblick über Lieferantenangebote zu verschaffen. 

    Bildnachweise