How is a composite material made?

How is a composite material made?

The need to produce new materials:

1. Ancient human beings used clay, wood, stone, glass or metal as building materials. These materials have limitations; they corrode or rot easily, are heavy, bulky or difficult to shape or carve.
2. Continuous research and development has been done in searching for new structural materials to fulfill our needs. These properties cannot be met by the conventional metals, alloys, ceramics and polymeric materials.
3. The new building materials must have varied and diversified properties such as low density, strong, stiff, abrasive, resistant to heat, impact and corrosion.
4. In designing new building materials, scientist and engineers combine various metals, ceramics and polymers to produce a new generation of extraordinary materials – composite materials.

What are composite materials?

1. A composite material is a structural material that is formed by combining two or more different substances like metals, alloys, glass, ceramics and polymers. Usually, the new composite materials formed have properties that are superior to those of the original components.
2. Composite materials combine the advantageous properties of more than one material and overcome the limitations of the component materials. Thus, they are more useful for particular purposes than the individual components.
3. During the production of a new composite material, normally a continuous serial of research and tests has to be done on its properties in different directions, its effects on human health and also on the environment.
4. Wood and bones are natural composite materials. Wood consists of strong and flexible cellulose fibre surrounded and held together by a stiffer material called lignin. Bone is a composite of the strong yet soft protein collagen and the hard, brittle mineral apatite.
5. Plywood is a conventional composite material. It is built in layers. Each layer is reinforced with long fibres laid in a single direction. It exhibits enhanced strength only along the direction of the fibres. Fibres woven into a three-dimensional structure can produce stronger plywood. These fibres are laid along three mutually perpendicular axes.

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What is an example of a composite material?

Some examples of common composite materials are reinforced concrete, specific super conductor, fibre optic, fibre glass and photochromic glass.

Reinforced concretes

• Concrete is a mixture of cement, sand, gravels and water and therefore is a composite material.
• When cement is mixed with water to form a paste, it is soft and can be moulded into different shapes. This paste hardens when dry into a hard but brittle solid called concrete.
• A concrete slab is weak in tensile strength and brittle. It will crack if a heavy load is placed on it but it is strong against compression, hard, fireproof, waterproof, easy to maintain and comparatively cheap.
• Steel is strong in tensile strength and corrode easily but expensive. Steel and concrete have about the same coefficient of expansion.
• To improve the tensile strength, steel is used to reinforce the concrete. When concrete is reinforced with steel wires, bars or netting, the resulting combination is a very tough material with more tensile strength and does not crack easily.
• Reinforced concrete is relatively cheap and can be moulded easily. Thus, it needs very low building cost and very little maintenance.
• Reinforced concrete is used to make multi-storey high-rise buildings, bridges, highways, airport runways and oil platforms.
• Concrete can also be reinforced with other materials such as glass fibre, silicon carbide, aluminium oxide particles and polymer fibres.
• The fibre reinforced concrete is of greater strength than ordinary concrete and has increased resistance to impact. It has been used in the construction of roads and aircraft runways and rocket launching pads.
• Concrete reinforced with polymer fibres is suitable to build buildings that are subjected to earthquakes.

Superconductors

• Superconductors are materials capable of conducting electricity without any electrical resistance when cooled to an extremely low temperature.
• Most of the known superconductors are alloys or compounds of metal or ceramic with metal oxides. Some superconductors are made from composite materials.
• A mixture of barium oxide, BaO, copper(II) oxide, CuO, and itrium oxide, Y₂O₃, can be made into ceramic superconductor called perovskite, YBa₂Cu₃O₃.
• These superconductors are widely used today. Superconductor can be made into a very powerful and light magnets.
• Superconductors are used in:
  (a) bullet trains in Japan
  (b) medical magnetic-imaging devices like magnetic resonance imaging (MRI) in hospitals
  (c) magnetic energy storage systems
  (d) magnetically levitated train
  (e) motors and generators
  (f) transformers
  (g) computer parts
  (h) very sensitive devices for measuring magnetic fields, voltage or current
• The main advantages of devices made from superconductors are low power dissipation, high-speed operation and high sensitivity.

Fibre optic

• Fibre optic is a composite material that is used to transmit electronic data, voice and images in digital form at great speed.
• A fibre optic cable consists of a bundle of glass threads with higher refractive index surrounded by a covering called clad which has a lower refractive index than glass. A light wave travels along the glass fibre by total internal reflection.
• Fibre optic is used in the field of telecommunication:
  (a) instrument to examine internal parts of the body (endoscopy)
  (b) inspecting the interiors of manufactured structural products
  (c) replacing copper wires in long distance telephone lines
  (d) linking computers within local area networks (LAN)
  (e) closed circuit television security system
  (f) as laser beam to perform surgery
  (g) cellular phones
  (h) video cameras
• Advantages of fibre optic over the traditional metal communications lines are:
  (a) Cheap in material cost
  (b) Thinner, easily bent and lighter
  (c) Less susceptible to interference
  (d) Greater bandwidth than metal cables, thus can carry more data
  (e) Chemically more stable
  (f) Data transmitted by fibre optic cables can be transmitted digitally rather than analogically.
  (g) High transmission capacity
• The main disadvantages of fibre optic cables are that the cables are much more expensive to install, more fragile and are difficult to split.

Fibreglass

• Fibreglass has been used to make many of our household products such as water storage tanks, badminton rackets, helmets, small boats, skis and motor vehicle bodies.

Photochromic glass

• A photochromic material is one that changes from transparent to coloured when it is exposed to ultraviolet light, and reverts to transparency when the light is dimmed or blocked.
• Photochromic glass can be produced by embedding photochromic substances like fine silver chloride or silver halide crystals in glass or transparent polymers as the matrix.
• When exposed to light, the silver ions, Ag+ are converted to silver and the glass darkens. The photochromic glass becomes transparent again when the silver atoms lose electrons to form silver ions when light is blocked. This is because the halogen formed during the decomposition of silver halide cannot escape from the glass, so it recombines with the silver atom in the dark and image fades.
• The chemical can also undergo a chemical process that causes it to change shape. The new structure absorbs a portion of the light causing the lenses to darken. The number of atoms that change shape varies with the intensity of the light.
• Photochromic glass is used to make:
  (a) optical lenses in glasses
  (b) car windshields
  (c) smart energy efficient windows in buildings
  (d) information display panels
  (e) photoelectrochromic panels for computers
  (f) camera lenses
  (g) optical switches
  (h) light detector devices
  (i) automatic light-control devices
  (j) light intensity meters for measuring the intensity of light
• When making lens and windshield, the photochromic glass helps
  (a) to protect our eyes from harmful ultraviolet rays and glare from the sun.
  (b) to control the amount of light that passes through automatically.
  (c) our eyes to cope when they are exposed to different light conditions.
  (d) to reduce refraction of light.

Table shows the comparison of the properties between composite materials with those of their original materials.