Engineering Materials (Essay Sample)

Engineering Materials Questions
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Question 1
A crystal structure is characterized by the lattice parameters of the unit cell. A unit cell is a subdivision of the crystal structure that still describes the lattice. By convention, the smallest possible subdivision is chosen. Other characteristics include the number of atoms per unit cell as well as the packing factor of the atoms in the unit cell. Therefore, a material is said to be anisotropic when its properties differ when measured along different directions or planes within the crystal. On the other hand, a bulk material is said to be an isotropy because the properties of the material tend to be similar in all directions. However, there are two levels at which properties could be caused to be in different directions. The first is at the crystalline level in crystalline materials. The second is at the micro-structural level.
Question 2
By definition, an ionic bond is a type of bonding that forms when there is a transfer of valence electrons from an atom of lower electronegativity to the valence shell of an atom with higher electronegativity. For example, in the formation of sodium chloride, sodium will lose its electrons to sodium because it has a lower electronegativity. On the other hand, a covalent bond forms when atoms share electrons whose elctronegativity is 1.9 or less. In this type of bonding, a pair of electrons is shared by two atoms and at the same time fills the valence shell of each atom. For example, in the formation of methane, there is sharing of electrons between carbon and hydrogen atoms. Also, because of the strong force of attraction between atoms, ionic bonds tend to have a higher melting point while covalent bonds have lower melting points because these forces are weak.
Question 3
There are two basic types of selective laser sintering, direct and indirect. In the indirect technique, metal powders are mixed with a small amount of polymer. Alternatively, metallic and ceramic powders are coated with polymer. Particle binding occurs essentially through bonds between polymers. For instance, during the selective laser sintering of a steel powder, the polymer melts and forms necks between adjacent particles. The resulting part is called the ‘green part’. Owing to the melting of polymer, the green part is quite porous. Hence, it cannot be used without some post-processing. For direct technique, there is use of high-energy beam to directly consolidate a metal powder to densities greater than 80 percent of theoretical density.
Question 4
Metal Injection Molding (MIM) is a t...