George C. Phillips

A Concise Introduction to Ceramics

I-Overview of Ceramics.- 1. Ceramic Materials.- 1.1 Introduction.- 1.2 Ceramic Materials.- 1.3 Terminology.- 1.4 Formula Notation.- 2. Ceramic Raw Materials.- 2.1 Naturally Occurring Minerals.- 2.2 Manufactured Raw Materials.- 3. Nature of Clay.- 3.1 Physics of Clay.- 3.2 Clay-Water Systems.- 4. Forming from Powders.- 4.1 Powder Preparation.- 4.2 Dry Pressing.- 4.3 Plastic Forming.- 4.4 Casting.- 4.5 Thermal Treatments.- 5. Forming from Melts.- 5.1 Cooling Curves.- 5.2 Glass Forming Methods.- 5.3 Thermal Conditioning Glass.- 6. Miscellaneous Forming Techniques.- 6.1 Coatings.- 6.2 Single Crystals.- 6.3 Miscellaneous Formings.- 7. Traditional Ceramic Industries.- 7.1 Abrasives.- 7.2 Refractories.- 7.3 Whitewares.- 7.4 Structural Clay Products.- 7.5 Glasses.- 7.6 Porcelain Enamels.- 7.7 Cements.- II-The Nature of Ceramic Materials (Bonding/Crystal Concepts).- 8. Atomic Structure.- 8.1 Background.- 8.2 Electronic Configurations.- 8.3 Ionization.- 9. Bonding and Crystal Chemistry Concepts.- 9.1 Types of Bonding.- 9.2 Material Classes.- 9.3 Paulings Rules.- 9.4 Coordination Numbers.- 9.5 Bond Strength.- 10. Silicate Stuctures.- 10.1 Basis.- 10.2 Types of Silicates.- 10.3 Layer Minerals.- 11. Structure of Glass.- 11.1 Crystalline versus Glassy.- 11.2 Glass Formers.- 11.3 Glass Modifiers.- 11.4 Structure and Composition versus Properties.- 12. Oxide Crystal Structures.- 12.1 Basis.- 12.2 AmXn Compounds.- 12.3 ABmXn Compounds.- III-Characterization of Ceramic Materials.- 13. Analytical Techniques.- 13.1 Introduction.- 13.2 Microscopy.- 13.3 X-Ray Methods.- 13.4 Surface Measurements.- 14. Properties and Requirements of Ceramic Materials.- 14.1 Introduction.- 14.2 Properties.- 14.3 Requirements.- 15. Ceramic Surface Characteristics.- 15.1 Introduction.- 15.2 Dry-Pressed Alumina Surfaces.- 15.3 Surface Variations versus Processing Techniques.- 15.4 Quantitative Surface Techniques.- 16. Ceramic Strength Considerations.- 16.1 Introduction.- 16.2 Strength Measurements.- 16.3 Fracture Mechanics.- IV-Hi-Tech Applications of Ceramics.- 17. Structural and Electronic Applications.- 17.1 Introduction.- 17.2 Structural Applications.- 17.3 Magnetic Ceramics.- 17.4 Electronic Applications.- 18. Integrated Circuit Technology.- 18.1 Introduction.- 18.2 Semiconductors.- 18.3 Integrated Circuit Processing.- 18.4 Transistor Structures.- 18.5 Application and Development of Semiconductors.- 19. Ceramic Packaging of IC Devices.- 19.1 Introduction.- 19.2 Package Designs.- 19.3 Processing of Planar Substrates.- 19.4 Future Trends in Planar Ceramic Packaging.- 19.5 Multilayer Ceramics (MLC).- 20. The Future of Ceramics.

Nature of Clay

The classical definition of ceramics uses the word “clay” to describe ceramics. Prior to the 1940s most ceramic products used clay as part of their composition. Clay was a necessary ingredient because it served as the forming agent that allowed ceramic powders to be shaped from a dry to a slurry condition. It was not until the clay structure was better understood that substitutions could be made to perform the same role as clay in the ceramic composition [3].

Ceramic Surface Characteristics

This chapter illustrates the effects of material variations and processing techniques on polycrystalline ceramic surfaces. Dry-pressed high alumina ceramics are used as the basis for discussion [10]. The changes in surfaces are observed in thin-film circuit patterns that have been developed on these alumina surfaces.

Properties and Requirements of Ceramic Materials

The properties of a material are important because they dictate its ultimate usage. Because glasses, for example, are transparent, they are used primarily for windows and bottles where it is essential to see through the material. Ceramics, which are well known for their hardness and rigidity, often are used as abrasives. Other applications take advantage of a ceramic material’s electrical and thermal insulation characteristics [9].

Ceramic Raw Materials

The most commonly occurring elements in the earth’s crust are oxygen, which accounts for approximately 50 percent of the total; silicon, which is about 25 percent; aluminum, at around 8 percent; and iron, which makes up 6 percent. Thus, almost 90 percent of the available materials at the earth’s surface are made up of those four elements. The majority of such raw materials are oxides, specifically silicon oxides or silicates, which are ceramic materials. Plastics or polymers and most metals (with the exception of the noble metals) do not exist as raw materials or minerals in their natural states.

Bonding and Crystal Chemistry Concepts

The initial attraction of ions determines the type of bonding. There are three primary types and one secondary type of bonds: 1. Metallic, where one electron is shared by many positive ions, as shown in Figure 9-1. This arrangement is sometimes referred to as a “free electron gas.” 2. Covalent, where there is a sharing of electrons to attain the noble gas configuration, as shown in Figure 9-2. 3. Ionic, where an electrostatic attraction exists between oppositely charged ions, as shown in Figure 9-3. 4. Van der Waals, where secondary bonding originates from electrical dipoles, as represented in Figure 9-4.

Forming From Melts

The cooling curve representing a crystalline material that cools from a melt is shown in Figure 5-1. As the material starts to cool, it achieves a point of constant temperature for a period of time. During this “isotherm,” both a liquid and a solid phase are present. At equilibrium, the material cannot be cooled below this constant temperature until all of the liquid has solidified. Conversely, it cannot be heated above this temperature until all of the solid has melted. A good analogy to this curve is ice and water. When in equilibrium, ice water is always at a constant temperature (0°C). The mixture will not get warmer until the ice is gone or cooler until the liquid has solidified.

Forming From Powders

The considerations for powders are the particle size, which affects the resulting properties, and the particle size distribution, which affects the packing density. Smaller-particle-size compositions have higher strengths because they have more surface area, and therefore more bonds, than those with larger particles. Increased packing densities can be achieved by mixed sizing with coarse and fine grains. The porosity can be minimized, with the finer grains filling the interstitial vacancies between the larger grains. The ideal mixture is approximately 70 percent coarse grain and 30 percent fine grain.

Structure of Glass

Polymorphs are materials that have many (“poly”) structures (“morphs”), but the same chemistry. An example of polymorphs of silica is shown in Figure 11-1. Both structures are repetitive, and both are made from silicon tetrahedrons. They differ, however in their pattern or crystal structure.

Integrated Circuit Technology

Ceramic materials have played an integral and important part in the evolution of computers. Perhaps the best example of the importance of ceramic materials involves the ceramic processing used, in part, to make integrated electronic circuits on silicon semiconductor wafers. Such integrated circuits, which perform the basic operations of a computer, often are packaged on ceramic substrate materials (described in detail in Chapter 19).