15.15 Gas generation

Electrochemical cells (similar to fuel cells described later) can be used to generate or absorb oxygen from the air. They are typically based on ceramics made from, for example, strontium iron cobalt oxide. The ceramic is formed as tubes with 300-micron-thick walls, 300mm long and operate at 750 ºC. Similarly hydrogen can be separated from various gasses using a cermet of barium cerium yttrium oxide that has great potential in the “hydrogen economy”, particularly as a fuel for fuel cells.

15.16 Nanotubes

Titanium dioxide nanotubes
- source Penn State University

Nanotechnology was the term coined by Taniguchi in 1974 to describe mechanical parts, finishes and tolerances in the nanometer (millionth of a millimetre) region. There is a great deal of development work being carried out on nanotechnology today that could have a huge effect on the future. For example tiny tubes have been made out of lanthanum strontium cobalt ferric oxide ceramic that can also filter oxygen out of the air. They could be used to provide pure oxygen to the combustion chamber of gas turbines in power stations. At present air containing 80% nitrogen is fed into these turbines, which causes oxides of nitrogen to be formed that contribute to climate change. If only oxygen is used, only water and carbon dioxide are produced. Development is underway to store huge quantities of carbon dioxide underground, so with this ceramic application, there is the potential to cut damaging emissions to practically zero.

Similarly, solar cells made of tightly packed titanium dioxide nanotubes, having a deposit of potassium on their surface together with carbon to help absorb the sunlight, can be used to separate hydrogen from water. Again this could be an important development as another source of hydrogen that could be used as a fuel in the “hydrogen economy”.

15.17 General Electrical Uses

Domestic ceramic electrical fittings,
two light fittings and junction box
- Image courtesy of the Potteries
Museum and Art Gallery,
Stoke-on-Trent

Electrical ceramics and glasses, being chemically inert and durable, find extensive use in household, laboratory and industrial electrical applications. Their main purpose is as insulators in electrical circuits to provide physical separation between conductors and prevent current flowing between them. An early use in the electrical industry some 100 years ago was as outdoor insulators, because of their high electrical resistivity and ability to withstand extremes of weather.

The first speciality electrical ceramic was porcelain, which was made by the whitewares industry using the traditional kaolin/feldspar/quartz porcelain body. It was used to make insulators and bushings (the connections to electrical equipment). Conventional porcelains have a relatively low mechanical strength, fair thermal shock resistance and poor high frequency characteristics, but are used commonly for frequencies below 10,000 Hz (10 kHz) because of their low cost. There are different grades of porcelain available that are tailored to the physical requirement and to achieve lowest cost. So porcelains with lower mullite levels, fired at 1260 to 1320 ºC, are often used, unglazed, for high-volume low-cost applications such as bases of light bulbs, light fittings, fuse blocks, bushings, hot plates and toaster insulation. For more demanding applications, harder porcelains having high mullite levels are made with fewer impurities in the raw materials that are fired at 1350 to 1450 ºC. Higher voltage ceramic components are vitrified with as little as 0.1% porosity/water absorption to ensure high resistance to electric breakdown.