Ceramic Processing

Mohamed N. Rahaman

• Publisher: CRC Press
• Year: 2017
• ISBN:
  9781498716468
• Edition: 2
• Topic: Technologie et ingénierie
• Subtopic: Science des matériaux

Many of the properties critical to the engineering applications of ceramics are strongly dependent on their microstructure which, in turn, is dependent on the processing methods used to produce the ceramic material. Ceramic Processing, Second Edition provides a comprehensive treatment of the principles and practical methods used in producing ceramics with controlled microstructure.

Covering the main steps in the production of ceramics from powders, the book also provides succinct coverage of other methods for fabricating ceramics, such as sol?gel processing, reaction bonding, chemical vapor deposition and polymer pyrolysis.

While maintaining the objectives of the successful first edition, this new edition has been revised and updated to include recent developments and expanded to feature new chapters on additives used in ceramic processing; rheological properties of suspensions, slurries, and pastes; granulation, mixing, and packing of particles; and sintering theory and principles.

Intended as a textbook for undergraduate and graduate courses in ceramic processing, the book also provides an indispensable resource for research and development engineers in industry who are involved in the production of ceramics or who would like to develop a background in the processing of ceramics.

1	Ceramic Fabrication Processes An Introductory Overview

1.1 INTRODUCTION

The subject of ceramics covers a wide range of materials. Over the last few decades, attempts have been made to divide the subject into two parts: traditional ceramics and advanced ceramics. The use of the term advanced has, however, not received general acceptance and other forms such as technical, special, fine, and engineering will also be encountered. Traditional ceramics bear a close relationship to those materials that have been developed since the earliest civilizations. They are pottery, structural clay products, and clay-based refractories, with which we may also group cements, concretes, and glasses. While traditional ceramics still represent a major part of the ceramics industry, interest in recent years has focused on advanced ceramics; ceramics that, with minor exceptions, have been developed since approximately the 1950s. Advanced ceramics include ceramics for electrical, magnetic, electronic, and optical applications (sometimes referred to as functional ceramics ) and ceramics for structural applications at ambient as well as at elevated temperatures (structural ceramics). Although the distinction between traditional and advanced ceramics may be referred to in this book occasionally for convenience, we do not wish to overemphasize it. There is much to be gained through continued interaction between the traditional and the advanced sectors.

Chemically, with the exception of carbon, ceramics are non-metallic, inorganic compounds. Examples are the simple oxides such as alumina, Al² O³ , and zirconia, ZrO² ; silicates such as kaolinite, Al² Si² O⁵ (OH)⁴ , and mullite, Al⁶ Si² O¹³ ; complex oxides other than silicates such as barium titanate, BaTiO³ , and the superconducting material YBa² Cu³ O^6+δ (0 ≤ δ ≤ 1). In addition, there are nonoxides including carbides such as silicon carbide, SiC, and boron carbide, B⁴ C; nitrides such as silicon nitride, Si³ N⁴ , and boron nitride, BN; borides such as titanium diboride, TiB² ; silicides such as molybdenum disilicide, MoSi² ; and halides such as lithium fluoride, LiF. There are also compounds based on nitride-oxide or oxynitride systems such as sialons with the general formula Si^{6− z} Al^z N^{8− z} O^z where 0 < z < ~4.

Structurally, materials are either crystalline or amorphous (also referred to as glassy ), or are composed of a combination of crystalline and amorphous phases. The difficulty and expense of growing single crystals means that, normally, crystalline ceramics are actually polycrystalline; they are made up of a large number of small crystals (generally referred to as grains ) that are separated from one another by grain boundaries. In ceramics, we are concerned mainly with two types of structure, both of which have a profound effect on properties. The first type of structure is at the atomic scale: the type of bonding and the crystal structure (for a crystalline ceramic) or the amorphous structure (if it is glassy). The second type of structure is at a larger scale: the microstructure (often including the nanostructure), which refers to the nature, quantity, and distribution of the structural elements or phases in the ceramic (e.g., crystals, glass, and porosity).

It is sometimes useful to distinguish between the intrinsic properties of a material and the properties that depend on the microstructure. The intrinsic properties are determined by the structure at the atomic scale and are properties that are not susceptible to significant change by modification of the microstructure: properties such as the melting point, the coefficient of thermal expansion, and whether the material is brittle, magnetic, ferroelectric, or semiconducting. In comparison, many of the properties critical to engineering applications are strongly dependent on the microstructure (e.g., mechanical strength, dielectric constant, and electrical conductivity).

Intrinsically, ceramics usually have a high melting point and are often described as refractory. They are also usually hard, brittle, and chemically inert. This chemical inertness is usually taken for granted, for example, in ceramic and glass tableware and in the bricks, mortar, and glass of our houses. However, when used at high temperature, as in the chemical and metallurgical industries, this chemical inertness is severely tried. The electrical, magnetic, and dielectric behavior covers a wide range; for example, in the case of electrical behavior, from insulators to conductors. The applications of ceramics are many. Usually, for a given application, one property may be of particular importance but, in fact, all relevant properties need to be considered. We are, therefore, usually interested in combinations of properties. For traditional ceramics and glasses, familiar applications include structural building materials (e.g., bricks and roofing tile), refractories for furnace linings, tableware and sanitary ware, electrical insulation (e.g., electrical porcelain and steatite), glass containers, and glasses for buildings and transportation vehicles. The applications for which advanced ceramics have been developed or proposed are already very diverse, and this area is expected to continue to grow at a reasonable rate. Table 1.1 illustrates some of the applications for advanced ceramics [1].

TABLE 1.1

Applications of Advanced Ceramics Classified by Function

The important relationships between chemical composition, atomic structure, fabrication, microstructure, and properties of polycrystalline ceramics are illustrated in Figure 1.1. The intrinsic properties should be considered at the time of materials selection. For example, the phenomenon of ferroelectricity originates in the perovskite crystal structure, of which BaTiO³ is a good example. For the production of a ferroelectric material, we may therefore wish to select BaTiO³ . The role of the fabrication process, then, is to produce microstructures with the desired engineering properties. For example, the measured dielectric constant of the fabricated BaTiO³ (Figure 1.2) will depend significantly on the microstructure (grain size, porosity, and the presence of any secondary phases) [2].

FIGURE 1.1 The important relationships in ceramic fabrication.

FIGURE 1.2 Temperature dependence of dielectric constant for high-purity BaTiO³ ceramics with different average grain sizes. (From Kinoshita, K. and Yamaji, A., J. Appl. Phys ., 47, 371, 1976. With permission.)

1.2 CERAMIC FABRICATION PROCESSES

Ceramics can be fabricated by a variety of methods, some of which have their origins in early civilization. Our normal objective is the production, from suitable starting materials, of a solid product with the requisite shape such as a three-dimensional monolith, coating, or fiber, and with the requisite microstructure. As a first attempt, we divide the fabrication methods into three groups, depending on whether the starting materials involve a gaseous phase, a liquid phase, or a solid phase (Table 1.2). As the powder processing route is the most widely used and efficient method for large-scale production of three-dimensional monolithic ceramics, it will be considered in detail in this book. Then, other methods that can provide advantages in the production of ceramics with specific geometries, shapes, or microstructures will be described (Chapters 15 and 16). The focus will be on the processing of advanced ceramics, but some of the methods, in particular a few forming methods, have been developed in the traditional ceramics sector or can be applied to the production of traditional ceramics.

TABLE 1.2

Ceramic Fabrication Methods Classified by the Physical State of the Starting Material and the Common Shapes of the Product

The processing requirements for traditional and advanced ceramics are often different. Because traditional ceramics must meet less specific property requirements than advanced ceramics, they are often produced by low-cost methods. Traditional ceramics can be chemically inhomogeneous, often made from mixtures of starting materials, and have complex microstructures. In comparison, advanced ceramics must meet specific property requirements and, consequently, their composition and microstructure should be carefully controlled. Unless high porosity is a deliberate requirement, the target microstructure for advanced ceramics generally consists of three major components that will vary to some extent, depending on the required engineering properties and the economics of the fabrication pr...

Table of contents

• Cover-Page
• Half-Title Page
• Title Page
• Copyright Page
• Dedication
• Contents
• Preface
• Acknowledgements
• Author
• Chapter 1 Ceramic Fabrication Processes An Introductory Overview
• Chapter 2 Synthesis and Preparation of Powders: Mechanical Methods
• Chapter 3 Powder Synthesis by Chemical Methods
• Chapter 4 Synthesis of Ceramic Nanoparticles
• Chapter 5 Powder Characterization
• Chapter 6 Science of Colloidal Processing
• Chapter 7 Rheology of Colloidal Suspensions, Slurries, and Pastes
• Chapter 8 Processing Additives
• Chapter 9 Granulation, Mixing, and Packing of Particles
• Chapter 10 Forming of CeramicsConventional Methods
• Chapter 11 Additive Manufacturing of Ceramics
• Chapter 12 Drying, Debinding, and Microstructural Characterization of Green Articles
• Chapter 13 Principles of Sintering and Microstructural Development
• Chapter 14 Sintering Process Variables and Techniques
• Chapter 15 Sol−Gel Processing
• Chapter 16 Ceramic Fabrication Methods for Specific Shapes and Architectures
• Appendix I: Physical Constants
• Appendix II: SI Units – Names and Symbols
• Appendix III: Conversion of Units
• Appendix IV: Aperture Size of U.S. Standard Wire Mesh Sieves (ASTM E 11:87)
• Appendix V: Density and Melting Point of Some Elements, Ceramics, and Minerals
• Index