Ceramics materials: Ceramic materials are non-metallic solids made of inorganic compounds such as oxides, nitrides, borides and carbides. Theses materials are fabricated by first shaping the powder with or without the application of pressure into a compact form and after that it is subjected to high temperature. Ceramics possesses electrical, magnetic, chemical and thermal properties which are exceptionally good.
Examples: MgO, CdS, SiC, Al2O3, glass, cement, garnets, ferrites, concrete etc.
Applications: Ceramic materials are utilized for making electronic control devices, computers, structures, components of nuclear engineering and aerospace field.
COMPOSITES: Composites are mixture of materials such as metal and alloys and ceramics, metals and organic polymers, ceramics and organic polymers.
Examples: Vinyl coated steels, steel reinforced concrete, fiber reinforced plastics, carbon reinforced rubber etc.
Applications: These materials are used for making sports items, structures, and electrical devices.
SEMICONDUCTORS: Semiconductors are solid materials, either non-metallic elements or compounds which allow electrons to pass through them. These materials occupy intermediate position between conductors and insulators. Semiconductors usually have high resistivity, negative temperature coefficient of resistance and are generally hard and brittle. Examples: Germanium (Ge), Arsenic (As), Silicon (Si), Boron (B), Sulphur (S), Selenium (Se).
Applications: Semiconductors are utilized in making devices used in areas of telecommunication and radio communication, electronics and power engineering, photocells, rectifiers etc.
ORGANIC POLYMERS: Polymers consist of carbon chemically combined with usually with hydrogen, oxygen or other non- metallic substances. They are formed by polymerization reaction in which simple molecules are chemically combined into long chain molecules. Examples: Nylon, Teflon, Polyethylene, PVC, Terylene, Cotton etc.
Applications: Polymers are used in making packings, pipes, covers and insulating materials etc.
PLASTICS: Plastics are commonly known as synthetic resins or polymers. In Greek terminology, the term polymer comprises ‘poly’ means ‘many’ and ‘mers’ means ‘parts’. Thus, the term, polymer represents a substance built up of several repeating units, each unit being known as a monomer. Thousands of such units or monomers join together in a polymerization reaction to form a ‘polymer’. Some natural polymers like starch, resins, shellac, cellulose, proteins, etc are vary common in today’s use. Synthetic polymers possess a number of large applications in engineering work. Therefore plastic materials are fairly hard and rigid and can be readily molded into different shapes by heating or pressure or both. Various useful articles can be produced from them rapidly, accurately and with very good surface quality. They can be easily produced in different colors or as transparent. They are recognized by their extreme lightness, good corrosion resistance and high dielectric strength. Plastics are synthetic resins characterized as a group by plastic deformation under stress. These materials generally are organic high
polymers (i.e. consisting of large chain like molecules containing carbon) which are formed in a plastic state either during or after their transition from a low molecular weight chemical to a high molecular weight solid material. These materials are very attractive organic engineering materials and find extensive applications in industrial and commercial work such as electrical appliances, automotive parts, communication products bodies (Telephone, Radio, TV), and those making household goods. They possess a combination of properties which make them preferable to other materials existing in universe.
Properties of plastics: The properties of plastics are given as under.
- Plastics are light in weight and at the same time they possess good toughness strength and rigidity.
- They are less brittle than glass, yet they can be made equally transparent and smooth.
- Their high dielectric strength makes them suitable for electric insulation.
- They resist corrosion and the action of chemicals.
- The ease with which they can be mass-produced contributes greatly to their popularity as wrappers and bags.
- They possess the property of low moisture absorption.
- They can be easily molded to desired shapes.
- They can easily be made colored.
- They are bad conductance of heat.
- They are hard, rigid and heat resistance.
- They possesses good deformability, good resiatance against weather conditions, good colorability, good damping characteristics and good resistance to peeling. Plastics are broadly classified into thermo plastics and thermo-setting plastics.
Thermo Plastics: Those plastics which can be easily softened again and again by heating are called thermoplastic. They can be reprocessed safely. They retain their plasticity at high temperature, i.e. they preserve an ability to be repeatedly formed by heat and pressure. Therefore, they can be heated and reshaped by pressing many times. On cooling they become hard. They are some times also called as cold-setting plastics. They can be very easily shaped into tubes, sheets, films, and many other shapes as per the need.
Types of Thermo Plastics:
- P.V.C (Polyvinyl chloride)
- Auorinated polymers,
- Polycarbonate etc.
The reason for the re-softening of thermoplastic resins with heat is that they are composed of linear or long chain molecules. Application of heat weakens the intermolecular bonds by increasing thermal agitation of the molecules, and the material softens and thus plastic can be easily molded and remolded without damage.