Advanced ceramics have an amazing range of properties and uses. They can be designed and engineered to solve just about any problem or challenge we face.
The discovery of electricity, early advances in chemistry, the invention of the automobile and the artificial production of certain types of gemstones all played a role in the development of advanced ceramics.
Advanced ceramics enhance our lives by their constant usefulness. They play a critical role in electronics, telecommunications, manufacturing, transportation, medicine, defence and space exploration.
Sialons and the New Zealand connection
Sialons – based on the elements silicon (Si), aluminium (Al), oxygen (O) and nitrogen (N) – are a new family of ceramic materials.
The presence of nitrogen in the chemical structure of the ceramic is what makes the difference in terms of the properties the sialons show. Some have high thermal resistance, some have extreme hardness and others have extreme toughness.
Researchers like Ian Brown working at Industrial Research Limited (IRL) in Wellington have developed oxygen-enriched sialons called O-Sialons. These are made by combining claysilica sand and silicon metal to create a plastic mix that can be shaped to order.
O-Sialons have excellent thermal shock resistance and can withstand rapid heating to high temperatures followed by rapid cooling over many cycles with little structural damage. These properties have led to its use in the construction of pipes, tubes and conduits to contain and channel non-ferrous molten metals like aluminium and its alloys.
Boron carbide and body armour
The high degree of hardness of some advanced ceramics is put to use in the design of body armour used by soldiers and police officers.
One type of body armour uses the extremely hard ceramic known as boron carbide (B4C).
The ceramic is bonded onto a plate of fibreglass. When a bullet strikes the ceramic plate, the bullet shatters into little pieces.
The ceramic also shatters near where the bullet hits but the fibreglass backing catches the fragments of bullet and ceramic.
The person wearing the armour may receive bruising, but at least the bullet did not penetrate and potentially kill the wearer.
Alumina and electronics
The largest market for advanced ceramics is in the electronics industry.
Ceramics can display a range of electrical properties from insulators to resistors to semiconductors.
The large ceramic insulators that hold the high-voltage electrical transmission wires are made of alumina (Al2O3
Ceramic insulators like alumina are also very good heat conductors.
Ceramic insulators like alumina are also very good heat conductors. They can be used as backing material or mounting brackets to which other electrical components are attached, for example, the electronic systems in a modern car are mounted on alumina.
When the electronics unit is working, it generates heat and the alumina backing conducts the heat away. This allows the electronic systems to function efficiently.
Ceramic high-temperature superconductors
Researchers based at Industrial Research Limited in Wellington have developed a superconducting ceramic known as BSCCO (pronounced ‘bisco’) based on the elements bismuth, strontium, calcium, copper and oxygen.
This ceramic is splatter-coated onto a nickel/tungsten alloy tape. On reducing the temperature of the ceramic to -170°C (liquid nitrogen boils at -196°C), the electrical resistance drops to close to 0. Not only does it increase the capacity of the ceramic to carry much higher electric currents but also it does so with very low energy losses.
The tape can then be used in the production of high-field electromagnets such as those used in hospital imaging devices like PET and MRI scanners. By moving from expensive liquid helium to cheaper liquid nitrogen as the coolant, considerable running cost savings can be made.
Ceramic materials can also be magnetic. Magnetic ceramics are widely used. Some types can be permanently magnetised, and these find use in motors for electric toothbrushes and knives, speakers, all of the motors that power the accessories in a car such as electric windows, windscreen wipers and household magnets. A common type of ceramic magnet is composed of strontium and iron oxides.
Other types can be magnetised and demagnetised readily, and these are used in television, radio, communication systems and electronic ignition systems.
Household magnet applications can be found in the:
- garden – lawn mower, trimmers
- workshop – electric drill, circular saw
- garage – door opener, freezer, car
- laundry – clothes dryer, washing machine
- kitchen – microwave, dishwasher, fridge
- office – computer, printer, telephone
- lounge – TV, DVD player, sound system
- bathroom – electric shaver, hair dryer.
Ceramics and the space shuttle
The friction of the atmosphere on the space shuttle during ascent into space and on re-entry generates very high temperatures on its outer surfaces. To protect the space shuttle, the outer surface is covered with more than 27,000 ceramic tiles that act as a thermal barrier.
The tiles are made of silica fibres that have been bonded together to form an open mesh structure. As a result, they are very lightweight and have excellent thermal insulation properties. The tiles vary in thickness, and each is given a code number so that, if one is lost on a mission, an exact replacement can be produced and fitted in the correct place.
Nature of science
The world we live in is understandable. As the breadth of our knowledge expands, so does the depth of our understanding. Advances in ceramics serve to illustrate this point.