12.35 Define the term alloy Distinguish among solid solution alloys, heterogeneous alloys, and intermetallic compounds.
12.29 Consider the unit cells shown here for three different structures that are commonly observed for metallic elements. (a) Which structure(s) corresponds to the densest packing of atoms? (b) Which structure(s) corresponds to the least dense packing of atoms?
12.36 Distinguish between substitutional and interstitial alloys. What conditions favor formation of substitutional alloys?
12.39 Classify each of the following statements as true or false: (a) Substitutional alloys tend to be more ductile than interstitial alloys. (b) Interstitial alloys tend to form between elements with similar ionic radii. (c) Nonmetallic elements are never found in alloys.
12.33 Aluminum metal crystallizes in a cubic close-packed structure [face-centered cubic cell, Figure 12.14(a)]. (a) How many aluminum atoms are in a unit cell? (b) What is the coordination number of each aluminum atom? (c) Estimate the length of the unit cell edge, a, from the atomic radius of aluminum (1.43 Å). (d) Calculate the density of aluminum metal.
12.28 Which of the following substances would you expect to possess metallic properties: (a) TiCl4, (b) NiCo alloy, (c) W, (d) Ge, (e) ScN?
12.32 Calcium crystallizes with a body-centered cubic structure. (a) How many Ca atoms are contained in each unit cell? (b) How many nearest neighbors does each Ca atom possess? (c) Estimate the length of the unit cell edge, a, from the atomic radius of calcium (1.97 Å). (d) Estimate the density of Ca metal.
12.37 For each of the following alloy compositions indicate whether you would expect it to be a substitutional alloy, an interstitial alloy, or an intermetallic compound: (a) Fe0.97Si0.03, (b) Fe0.60Ni0.40, (c) SmCo5.
12.31 Iridium crystallizes in a face-centered cubic unit cell that has an edge length of 3.833 Å. (a) Calculate the atomic radius of an iridium atom. (b) Calculate the density of iridium metal.
12.34 An element crystallizes in a body-centered cubic lattice. The edge of the unit cell is 2.86 Å, and the density of the crystal is 7.92 g/cm3. Calculate the atomic weight of the element.3