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Product category: Materials and components
News Release from: Morgan Electro Ceramics | Subject: Ceramic materials in the aerospace industry
Edited by the Engineeringtalk Editorial Team on 24 October 2005

Ceramic materials in the aerospace
industry

Keith Parker looks at how technical ceramics and other specialist materials have enabled designers and manufacturers in the aerospace industry to combine cost efficiency with safety and performance.

Never before has the aerospace industry, particularly those companies producing commercial aircraft, been under such pressure Operating in a still uncertain market with the focus firmly on the bottom line, carriers need aircraft to be as reliable and robust as possible whilst also meeting stringent safety regulations

The defence and space exploration sectors are also under pressure to curb spending, with the focus being on developing ways to increase performance.

Technical ceramics, such as alumina, silicon nitride and aluminium nitride, play an important role in aircraft instrumentation and control systems, engine monitoring, missile guidance systems and satellite positioning equipment.

They are found in seals for gas turbine engines, fuel line assembly, ignition systems, fire detection and suppression, instrument displays and speed probes.

The reason these materials are used for critical components in aircraft is because of their specific physical benefits.

They can retain dimensional stability through a range of high temperatures and have very high mechanical strength.

They also demonstrate excellent chemical resistance and stiffness to weight ratio, providing manufacturers with greater reassurance that the aircraft is as resilient (and therefore also as safe) as possible.

Electroceramic materials (piezoelectric and dielectric) are used in aerospace transducers and sensors such as accelerometers (for measurement of vibration), gyroscopes (for measurement of the acceleration and pitch of aircraft, missiles and satellites) and level sensors (eg fuel tanks).

One of the most successful recent commercial aircrafts, the Boeing 777, uses piezoceramic material within the 52 ultrasonic fuel tank probes located on each aircraft.

The sensors are installed at a variety of locations in each of fuel tanks.

A pulsed electric field is applied to the piezoceramic material, which then responds by oscillating.

This then sends a sound wave into the liquid, which will reflect on the air-liquid interface.

The reflected acoustic signal is then in turn picked up by the piezoelectric ceramic thus enabling current fuel level to be calculated based on a "time of flight" measurement.

Similar ultrasonic fuel probes are also used in fighter aircraft and other level sensing application because of their ability to provide highly accurate readings.

Aerospace manufacturers can use a variety of braze alloys in the construction and repair of gas turbine engines.

One particular example is the use of presintered preforms for high temperature braze repair applications.

With turbine temperatures reaching up to 1300C and the presence of hot corrosive gases, components experience considerable erosion and wear.

The presintered preforms consist of a blend of superalloy and low melting point braze and are customised to fit the shape of the component and then tack-welded into place and brazed.

The ability to provide a range of near net thicknesses can eliminate the need for most post-braze machining and extend the life of engine components by up to 300%, making it a more reliable and cost effective method than traditional welding which requires post-braze machining or grinding.

Already an OEM and DER approved process, PSP repairs are being used increasingly in smaller regional aircraft engines which see a different wear pattern associated with the higher number of take off and landing of short haul flights.

The need to identify cost-effective travel is not limited to commercial flights or defence.

NASA and ESA are continually investigating new technologies to reduce the costs associated with space travel.

Morgan Technical Ceramics' division in Erlangen, Germany has been working with a European space development programme for a number of years to help support its research of ion propulsion systems.

A lightweight alternative to traditional chemical propulsion, ion engines have the potential to push spacecraft up to ten times faster (per kilogram of fuel) and enable longer distances.

Ion propulsion technology, which uses electricity to charge heavy gas atoms that accelerate from the spacecraft at high velocity and push it forwards, traditionally incorporated quartz discharge vessels.

Quartz has now been replaced by alumina because of the need for a material with the same dielectric properties but with higher structural stability.

Alumina is easier to fabricate and offers good thermal shock resistance ensuring that the chamber can withstand the extremes of temperature that occur during plasma ignition.

It is also lighter, which reduces the cost associated with each launch of the craft.

Use of ceramic, in its earthenware and pottery form, can be traced back more than 10,000 years and today this inorganic, nonmetallic material is providing the platform for a modern-day revolution in materials technology.

Today's advanced ceramics offer powerful physical, thermal and electrical properties that have opened up hundreds of development opportunities for manufacturers not only in the aerospace industry but also within automotive, medical and telecommunications applications.

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