15.11 Medical Ceramics

Ceramic on ceramic hip joint and x-ray of
replacement joint - source Orthoworks

Ceramics are used extensively for a broad range of internal medical applications, as they are non-poisonous and inert to body fluids, and promote tissue and bone growth. They can be used for bone and joint transplants, such as replacement hip and wrist joints, as the support for direct delivery of medicines internally and for implants such as pacemakers. Piezoelectric ceramics are being proposed that convert the energy of heartbeats to power the pacemaker, making batteries unnecessary. Ceramics are also used extensively in medical diagnostic equipment. Very recent research has shown that clusters of certain microscopic glass beads can detect a single sample of a virus.

The global market for medical ceramics was $10.4 Bn in 2011 and is expected to grow to 13.1 Bn by 2017.

15.12 Dentistry

In 1774 French chemist Duchateau had the idea of replacing the carved bone and ivory false teeth used at the time with porcelain ones. Another Frenchman, a dentist Dr de Chemant spent years perfecting the technique including colouring the teeth to match the originals. He was granted a British patent covering his porcelain teeth and metal spring fittings, and began selling his products in 1792. He obtained his porcelain from Wedgwood. In 1808 an Italian Dr Fonzi invented a porcelain tooth with a platinum hook to fasten it to a base. In 1820 Claudius Ash, a British goldsmith, produced an improved version with gold fittings.

Dental veneers - sources Wikipedia via
clausgast and mynewsmile

Porcelain teeth are made of two parts, a translucent self-glazing outer enamel and the body. The body, typically made from up to 90% potash feldspar, becomes a completely vitreous polycrystalline material having a slightly higher thermal expansion coefficient than the enamel to keep the latter in compression for strength. Some are made on a metal core with ceramic outer layers. Also cosmetic ceramic veneers some 0.5mm thick can be glued on to teeth that have had their natural enamel ground by an equivalent amount to retain the original size of the tooth. To strengthen the teeth, especially to resist cracking caused by grinding, glass ceramics and alumina have been used. Alumina together with 15% lanthanum glass was four times stronger than previous alternatives. In 1999, 35% zirconia was added to this composition, again considerably strengthening the tooth core. Today yttria doped or stabilised zirconia is used.

15.13 Filters

In 1854 Sir Henry Doulton used a porous ceramic filter to clean up water from the Thames, which at the time was spreading epidemics throughout London. The principle was that cholera and typhoid bacteria are greater in size than one micron, so a ceramic can be designed to allow water through but stop the bacteria. Today Doulton water filters incorporate activated carbon as well as silver impregnation or a colloidal coating to kill the trapped bacteria. The composition of the ceramic can be tailored to produce filters covering a wide range, including ones capable of extracting bacteria from the air. Ceramic filters and membranes have higher performance and durability than alternatives.

Doulton ceramic filter
containing activated
carbon

Ceramic gas filters and array
- source Glosfume

Automobile catalytic converter
- source weiku.com

Ceramic filters are also used to clean up the hot effluent gases from incinerators and fossil fuel power plant. They are typically made of alumino-silicate fibres and a silica binder. They are corrosion resistant and can also reduce dioxin production. Catalytic converters to remove harmful gasses in modern cars are made up of an alumina sponge-like filter structure with impregnated rare metal catalyst (platinum, rhodium or palladium). The latest converters will use a ceramic foam. There are even filters that can be used for molten metals.