 # Engineering Materials Week 2

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3.1 What is the difference between atomic structure and crystal structure?
Atomic structure relates to the number of protons and neutrons in the nucleus of an atom. Crystal structure pertains to the arrangement of atoms in the crystalline solid material.
3.9 Calculate the radius of a tantalum atom, given that Ta has an BCC crystal structure, a density of 16.6 g/cm^3, and an atomic weight of 180.9 g/mol.
For BCC n=2 atoms/unit cell

3.47 Below are shown three different crystallographic planes for a unit cell of some hypothetical metal. (See book)
a. To what crystal system does the unit cell belong? This unit cell belongs to the orthorhombic crystal system
b. What would this crystal structure be called? This crystal structure would be called face-centered orthorhombic.
c. If the density of this metal is 18.91 g/cm^3, determine its atomic weight? A =18.91 g/cm3 × 3.75x10−24 cm3 × 6.023x1023 = 42.7 g/mol
3.65 Figure 3.24 shows the first five peaks of the x-ray diffraction pattern for tungsten, which has a BCC crystal structure; monochromatic x-radiation having a wavelength of 0.1542 nm was used.
a. Index (i.e. give h, k and l indices) for each of these peaks. The five peaks result by diffraction from the following planes: 110,200,211,220 and 310. b. Determine the interplanar spacing for each of the peaks. c. For each peak, determine the atomic radius for W and compare these with the value presented in Table 3.1.

Peak Index

R (nm)
200
58.4
0.1580
0.1369
211
73.3
0.1292
0.1370
220
87.0
0.1120
0.1371
310
100.7
0.1001
0.1371

4.9 Calculate the composition, in weight percent, of an alloy that contains 105 kg of iron, 0.2 kg of carbon, and 1.0 kg of chromium.

4.22 Sometimes it is desirable to be able to determine the weight of one element C1 that will produce a specified concentration in terms of the number of atoms per cubic centimeter, N1, for alloy composed of two types of atoms.

4.26 Cite the relative Burgers

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