COMMON LATTICE TYPES

COMMON LATTICE TYPES DOE-HDBK-1017/1-93 Structure of Metals COMMON LATTICE TYPES All metals used in a reactor have crystalline structures. Crystalline microstructures are arranged in three-dimensional arrays called lattices. This chapter will discuss the three most common lattice structures and their characteristics. EO 1.2 DEFINE the following terms: a. Crystal structure b. Body-centered cubic structure c. Face-centered cubic structure d. Hexagonal close-packed structure EO 1.3 STATE the three lattice-type structures in metals. EO 1.4 Given a description or drawing, DISTINGUISH between the three most common types of crystalline structures. EO 1.5 IDENTIFY the crystalline structure possessed by a metal. In metals, and in many other solids, the atoms are arranged in regular arrays called crystals. A crystal structure consists of atoms arranged in a pattern that repeats periodically in a three-dimensional geometric lattice. The forces of chemical bonding causes this repetition. It is this repeated pattern which control properties like strength, ductility, density (described in Module 2, Properties of Metals), conductivity (property of conducting or transmitting heat, electricity, etc.), and shape. In general, the three most common basic crystal patterns associated with metals are: (a) the body-centered cubic, (b) the face-centered cubic, and (c) the hexagonal close-packed. Figure 2 shows these three patterns. In a body-centered cubic (BCC) arrangement of atoms, the unit cell consists of eight atoms at the corners of a cube and one atom at the body center of the cube. MS-01 Page 6 Rev. 0