Читать книгу Materials for Biomedical Engineering - Mohamed N. Rahaman - Страница 109

1 3.1 Aluminum has an atomic radius of 0.1431 nm and an FCC structure. Determine (i) the number of atoms in a unit cell, (ii) the unit cell length, and (iii) the density of aluminum. (Atomic weight of aluminum = 26.97; Avogadro number = 6.023 × 1023.)

2 3.2 Determine the atomic packing fraction for the simple cubic, BCC and FCC structures composed of a single type of atom. Explain the steps in your calculation.

3 3.3 A metal has an atomic radius r and a CPH structure. Determine the unit cell lengths in terms of r and the atomic packing fraction. Explain the steps in your calculation.

4 3.4 Using the unit cell illustrated in Figure 3.10 and the unit cell lengths a = b = 0.9430 nm and c = 0.6891 nm, determine the density of hydroxyapatite.

5 3.5 The use of fluorinated water or toothpaste is known to improve the resistance of teeth to decay. Can this be accounted for in terms of the structure of hydroxyapatite. Explain.

6 3.6 Some drug delivery devices are composed of drug molecules incorporated within a degradable polymer. As the polymer degrades, these molecules are released at a controllable rate. In this application, amorphous polymers are often preferred over semicrystalline polymers. Explain why.

7 3.7 Explain why copper forms a substitutional solid solution with zinc whereas carbon forms an interstitial solid solution with iron.

8 3.8 Using a diagram, explain how dislocations reduce the amount of stress required to cause plastic deformation.

9 3.9 Explain the meaning and significance of microstructure.

10 3.10 What microstructural features would be desirable for (i) a hydroxyapatite implant for healing bone defects; (ii) a lithium disilicate glass‐ceramic for use as a crown in dental restoration; (iii) a degradable polymer such as PLA reinforced with hydroxyapatite particles for healing bone defects? Explain.

11 3.11 Using the axes in Figure 3.25, sketch (i) two planes with Miller indices (122); (ii) a plane with Miller indices (322).

12 3.12 Determine the lattice directions of the lines OI, DE, FG, and HI in Figure 3.26.

13 3.13 Aluminum atoms (radius = 0.1431 nm) pack to form a FCC structure. Determine the number of atoms per square meter in the (100) and (111) planes of aluminum.

14 3.14 Using a unit cell, show the ions in the {100} and {111} planes of sodium chloride.