Chapter 4 - Structures of materials

Abstract

This chapter provides an overview of the close-packed crystalline structures of metals and ionic solids, the concept of polymers, and the structure of solids with covalent bonds, that is, organic polymers and nonionic ceramics. Crystal has the stablest physical state on earth at low temperature. It is the common structure of metals and a large number of ceramics. Certain ceramics and practically all the organic materials commercially available at the date of writing are polymers. This chain structure, which considerably increases the melt viscosity, dramatically reduces the ability to crystallize and leads to amorphous or semi-crystalline materials. The metallic bond is strong and non-oriented. Metal atoms tend to adopt the most compact arrangement possible with, as a consequence, the formation of simple, high-density, close-packed crystal structures. In crystalline systems, the empty spaces between spherical atoms constitute interstitial sites. Polymers are made up of long chains of atoms joined to each other by covalent bonds. A polymer is a macromolecule obtained by the repetition of a building block. The chapter also explains the principal characteristics of solids with covalent bonds. Solids with isotropic bonds form compact crystal structures where the organization is determined primarily by the volume occupied by the atoms and their relative size.