Crystalline materials have both long range and short range o

Crystalline materials have both long range and short range order whereas glassy materials have only long range order. An FCC unit cell has twice as many atoms within is as a BCC unit cell but only two thirds the amount of the atoms in an HCp unit cell. {100} represents the family of planes that make up the sides of the cube of the BCC unit cell and for the FCC unit cell it is the {110} family of planes. If the length of the side of FCC unit cell is \"a\" nm then the linear density on the face diagonal[110] is ( )/a atoms/nm. A grain boundary is an example of an area defect. The Body centered cubic system ha the highest packing factor in the cubic system Covalent bonds are directional When two atoms (isolated )are at their equilibrium separation distance( ), the net energy between them is zero. In a pure, isotropic, polycrystalline metal, adjacent grains have the same composition and crystal structure but will have random orientation of that crystal structure. The planar density of (111) plane is smaller than that of (110) for the BCC crystal structure. The coordination number for the face-centered-cubic structure is 12. In metallic bonding, the valence electrons move freely within the electron sea which enables metals to have high ductility In order to have complete solid solubility between two metals, the atoms of the two elements must be of similar size, with no more than 15% difference in atomic radius, in order to minimize the lattice strain. When the metal is plastically deformed, it becomes stronger. Solids with higher binding energy between atoms will have lower Young\'s Moduli higher melting points than materials with lower binding energies. As the temperature of a metal increases, the vacancy concentration increases. Non steady diffusion such as diffusion of carbon into steel during carburizing, is dependent on temperature. Time of diffusion is much more important.

Solution

21. False ( amorphous materials exhibit short range order)

22. True

23. False ( Both are cubic structures)

24. True

25. False

26. True

27.

25.