Earthen material exists in many forms such as sand, clay, mud, stone, rocks, and so forth. These various forms of soil can be used as material for making different objects. Such objects are collectively referred to as ceramics. In large-scale manufacture of ceramics, other elements such as silica, alumina and feldspar are usually added to the earthen material so as to improve its quality.
Generally, ceramics can be differentiated from other materials by the following attributes.
- They are highly heat resistant: Because they withstand very high temperatures, ceramics, notably refractory bricks are used for constructing furnaces, incinerators and other objects, and machine parts where excessive heat production is an important consideration.
- They do not conduct electricity: A material, which does not allow electricity to pass through it, is called an insulator. Asbestos is used as an insulator in electrical equipment. Glass is used as an insulator for high-tension electricity transmission wires.
- They are resistant to corrosive chemicals such as alkalis, acids, salty water (brine) as well as corrosive air: Tiles are used for covering bathroom and toilet walls. Sinks, wash basins, water closets and baths are almost always made of ceramic since they come in contact with human effluents and disinfecting chemicals which are corrosive in nature. Glass is used for making containers used for storing chemicals. Other examples of their use in this regard exist.
- Ceramics can withstand high compressive loads: Ceramics resist compressive forces quite well and are widely used for constructing buildings. However both compressive and tensile (related to tension) forces are encountered in a building. Consequently, steel (which is very strong under tension but quite weak in compression) is used to reinforce (strengthen) concrete. Bricks are used for walls.
- Ceramics can easily be decorated: Ceramics are receptive of various colours and designs. Flower vases, ashtrays, sculptures and numerous beautifully designed decorations are made of ceramics. Also, because they can be glazed, ceramics are used in making ornamental wares.
- Ceramics are brittle: Because ceramics are brittle, they readily crack when dropped on hard surfaces.
- Several other properties: Their abundance and their simple processing procedure ensure wide availability and ready applicability. They do not decay and they require minimal maintenance. Because of this they are preferred for making things such as electric and telephone poles. Ceramics are porous in structure. This property is made use of in the design of mud or clay water pots, which are commonly used in traditional African homes.
Plastic and Rubber
In a general sense, the word plastic is used for any material which can be moulded and will retain the shape imposed upon it. However in a specific sense, plastics are synthetic (i.e. artificially made) materials capable of being formed into useable products by heating, moulding, grinding and such similar processes. Plastics come in forms such as those used for domestic, industrial and other purposes. Varieties of industrial plastics are structural foams, reinforced plastics, sheets and films, laminates, composite and others.
Classes of Plastics
Plastics may be classified into two depending on how they behave under the application of heat. These are thermosetting plastics and thermoplastics.
- Thermosetting Plastics: These are plastics, which after being formed cannot be softened by heating. Because of this, they are employed in high temperature applications such as handles of electric irons and kettles as well as cooking utensils. Thermosetting plastics (or simply thermosets) are also used for making parts which are likely to be exposed to high heat for example buttons of clothes as in the case of ironing. Thermosets are hard and more adapted to rugged use than the other class of plastics. Consequently, they, rather than the other type of plastics, are used for making bodies of electronic goods. Moreover, thermosets are resistant to chemical solvents.
- Thermoplastics: Thermoplastics are differentiated by the fact that they can be softened or in fact turned to liquid form by the addition of sufficient heat. Most plastic ware used in the home are thermoplastics. Examples are bowls, plates, cups, and buckets. Nylon is a thermoplastic. Thermoplastics are softer than thermosets.
Rubber is an organic substance, which can either be artificially made or obtained from natural sources. It is elastic and tough. Rubber is not very resistant to heat and thus easily melts and burns when exposed to high temperatures. Rubber is so named because of its ability to erase (i.e. rub off) pencil marks.
Classes of Rubber
Two classes of rubber exist. These are natural rubber and synthetic or artificial rubber.
- Natural rubber: This includes all types of rubber produced from latex. Latex is a milky fluid, which occurs under the bark of many tropical trees.
- Synthetic rubber: This group of rubbers is artificially produced by combining several materials, which are mostly organic compounds mainly from petroleum. Both rubber and plastic are non-metallic organic (i.e. carbon-containing) materials.