Academic journal article The Technology Teacher

Understanding Materials

Academic journal article The Technology Teacher

Understanding Materials

Article excerpt

Almost everything people have ever done has involved materials (Jacobs & Kilduff, 1985). Historical evidence indicates that engineered materials have been available and utilized for the benefit of humankind since the Neolithic period, beginning about 10,000 BC (Thornton, 1985). Some of these materials have been in existence for thousands of years. Perhaps this is best expressed by the following passage from the first book of the Old Testament:

And they said one to another, Go to, let us make brick, and burn them thoroughly. And they had brick for stone, and slime had they for mortar (Genesis XI, 3).

At first, materials consisted of wood, stone, ceramic clays, and meteoric metals and ores, simply shaped into useful objects. Later, copper metallurgy was developed in Asia Minor, followed by the Iron Age promoted by the Romans for their military and civil needs (Thornton, 1985). From the Roman times to today, materials have undergone continuing evolution, with considerable improvement. Today's engineered materials are commonly divided into categories based on their physical and chemical characteristics. Included in those categories are: (a) metals, (b) ceramics, (c) polymers, and (d) composites.

Metals

Most of us are familiar with metals in a general way because of exposure to them through day-to-day use. Metals can usually be distinguished from other categories by some of their more obvious traits, such as reflectivity of light, thermal conductivity, electrical conductivity, hardness, toughness, and modulus of elasticity. Metals are large collections of millions of crystals composed of different types of atoms held together (Jacobs & Kilduff, 1985).

Ceramics

The term "ceramic" is derived from the Greek word "keramos," which literally means earth. Ceramics are defined as hard, brittle compounds of metallic and nonmetallic elements that have high melting temperatures and are chemically inert (Helsel & Liu, 2008). The advantages of ceramics over other materials are noticeable. These include high melting temperatures, high hardness, high modulus of elasticity, high compressive strength, and low electrical and thermal conductivity.

Polymers

"Poly" means many, and "mer" stands for monomer or unit (Helsel & Liu, 2008). The process of linking monomers together is known as polymerization, where polymers are being produced or plastics created that have properties different from the corresponding monomers. For industrial applications, there are two basic types of plastics; thermoplastics and thermosets. The main difference between the two types is that thermoplastics are polymers that soften when heated and regain their form when cooled, where thermosets can pass through only one heat cycle.

Composites

By definition, a composite is a material consisting of two or more integrated materials (Jacobs & Kilduff, 1985). One of the first composites was created several thousand years ago when our ancestors mixed clay and straw together to make bricks (Duvall and Hills, 2008). The main reason we create composites is to rectify weakness possessed by each constituent when it exists alone; composites are designed to serve special applications and meet certain criteria. Some of the most familiar composites include fiberglass and plywood.

Atomic Structure of Materials

An atom is the smallest particle of an element that possesses the physical and chemical properties of that element (Helsel & Liu, 2008). The average diameter of an atom is only about 10:0 of a meter (Jacobs & Kilduff, 1985) and it takes more than 106 atoms edge-to-edge to make the thickness of this page. Atoms consist of a nucleus and surrounding orbits that contain electrons. The nucleus is the densest part of the atom and consists of neutrons and protons. A proton is a particle of matter that carries a positive electrical charge equivalent to the negative charge of the electron. …

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