Material Science /Science exam question

There are three basic types of engineering materials. Give the names of these material types.?

Traditionally the three major classes of materials are metals, polymers, and ceramics. Examples of these are steel, cloth, and pottery.

Which elements represent the main components of polymers?

It turns out that most polymers, both natural and synthetic, have mainly carbonhydrogenoxygen, and nitrogen as their most common elements.

Give 5 characteristic physical properties of polymers and compare them with metals.

All metals are characterized by metallic properties, e.g. lustre, opacity, malleability, ductility and electrical conductivity.

The desired properties for engineering purposes are often found in alloys. Typical examples of metallic materials are iron, aluminium, copper, zinc, etc. and their alloys. Metals are extremely good conductors of electricity.

Metals are quite strong, yet deformable, which accounts for their extensive use in structural applications. Metallic materials are always crystalline in nature.

Polymers are organic substances and derivatives of carbon and hydrogen. Polymers include familiar plastic and rubber materials. Usually, polymers are classified into three categories: thermoplastic polymers, thermosetting polymers and elastomers, better-called rubbers. Polymers have very large molecular structures. Most plastic polymers are light in weight and are soft in comparison to metals. Polymer materials have typically low densities and may be extremely flexible and widely used as insulators, both thermal and electrical. Few examples of polymers are polyesters, phenolics, polyethene.

The atomic number of oxygen is 8. How many protons are included in the nucleus and how many electrons circulate around the nucleus?

8 protons and 8 electrons.

Explain the term „isotope“ in the context of materials science.

Isotopes are atoms of the same element that have different numbers of neutrons but the same number of protons and electrons. The difference in the number of neutrons between the various isotopes of an element means that the various isotopes have different masses.

Explain the term „ion“?

An atom or molecule with a net electric charge due to the loss or gain of one or more electrons.

Give the names of three primary bonding types and give an example for each type.

1:ionic bonding: It is done between metal and non-metal. The metal loses an electron and gives it to the nonmetal. For example Na+ and Cl- so they make NaCl

2:Covalent Bonding: It is done between 2 non-metals and they both share electrons, for example, H+ and OH- and they make H2O

3:Metallic Bonding: It is the strong attraction between closely packed positive metal ions and a ‘sea’ of delocalised electrons. An example is any metal like Zinc Iron etc.

How do primary and secondary bonds differ from each other with respect to bonding force?

Primary bonds are formed when the bonding process involves a transfer or sharing of electrons. Secondary bonds are formed from the subtle attraction forces between positive and negative charges.

a) What is the meaning of the term „allotropy/polymorphy” in the context of materials science?

Allotropy: Existence of an element into more than one physical forms E.g: Coal, lamp black, coke, Diamond, graphite.

  • Allotropy refers to an element, it should be reserved for the different crystalline phases of a given pure element.

Give the names of two allotropic materials.

– Iron: 𝛼-iron (Ferrite), 𝛾-iron (Austenite), 𝛿-iron (𝛿-Ferrite) – Tin: 𝛼-tin, 𝛽-tin, 𝛾-tin.

Give the names of the lattice structures and specify the corresponding parameters 𝑛 and 𝑃𝐷.

Image result for bcc structureAtoms per unit cell, 𝒏 2 density 0.68

Image result for fcc structureAtoms per unit cell 4 PD 0.74

Related image Atoms per unit cell 6 PD 0.74.

Interstitials defects are a variety of crystallographic defects where atoms assume a normally unoccupied site in the crystal structure. In interstitial defects three or more atoms may share one lattice site, thereby increasing its total energy.

Image result for edge dislocation

Related image

Edge Dislocations

One of the most common crystal structure defects is known as an edge dislocation. This occurs when there are extra atoms inserted into a plane in the crystal lattice. Edge dislocations make it easier for atoms to slip past one another, making it easier for the metal to deform.

At higher angles, the lattice cannot compensate and deformation rather than dislocation makes for a weaker join; a high angle grain boundary. It is then more common that the crystal cracks along this line or the boundary opens up because of higher built-in strain. SINGLE CRYSTALS & GRAIN STRUCTURE.

In thermal equilibrium, each phase (i.e. liquid, solid etc.) of physical matter comes to an end at a transitional point, or spatial interface, called a phase boundary.

What is the physical process, described analytically by Fick’s laws?

Fick’s law describes the distribution and mixing of particles in groundwater by dispersion.

What is the difference between Fick’s first law and Fick’s second law?

Fick’s first law applies to steady-state systems, where concentration keeps constant. • But in many cases of diffusion, the concentration, however, changes with time, how to describe the diffusion kinetics in these cases — demanding Fick’s Second Law.

Comments are closed.