Chapter 15 Introduction to Nonferrous Metals 323 regular arrays of unit cells. Each atom lines up to its nearest neighbors in a pattern repeating for millions of atoms in every direction, as suggested by Figure 15-3. One million copper atoms along the edge of this row of unit cells is 0.316 mm (0.0124″) long. As you learned in Chapter 4, several different types of unit cells occur in metals, Figure 15-4. Pure iron may be body-centered cubic (bcc) or face- centered cubic (fcc) in unit cell structure, depending on temperature. Most nonferrous metals have unit cells of body-centered cubic (bcc), face-centered cubic (fcc), hexagonal close-packed (hcp), or body-centered tetragonal (bct) structure. The bcc, fcc, and hcp cells were first described in Chapter 4. A body-centered tetragonal (bct) unit cell resembles a bcc unit cell, with one atom at each corner and one atom at the exact center of the unit cell, but the a b c Goodheart-Willcox Publisher Figure 15-3. On the nanometer (nm) scale, the atoms in a metal follow a distinct order, so the distances between atoms and the angles formed between them are exactly the same in each unit cell. The unit cells repeat uniformly across the entire crystal. bcc fcc hcp bct Goodheart-Willcox Publisher Figure 15-4. Metals with body-centered cubic (bcc) structure at room temperature include iron (Fe), molybdenum (Mo), niobium (Nb), potassium (K), tungsten (W), and vanadium (V). Aluminum (Al), copper (Cu), gold (Au), silver (Ag), lead (Pb), nickel (Ni), and platinum (Pt) all have a face-centered cubic (fcc) structure at room temperature (as does iron at high temperature). Beryllium (Be), cobalt (Co), magnesium (Mg), titanium (Ti), zirconium (Zr), and zinc (Zn) form hexagonal close-packed (hcp) unit cells at room temperature. For the hcp structure, two additional unit cells are also shown to make the hexagonal structure clearer. Tin (Sn) has a body-centered tetragonal (bct) unit cell at room temperature. Copyright Goodheart-Willcox Co., Inc.