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Ceramics in telecommunications

Outcomes

This section addresses aspects of the following syllabus outcomes:

Extract from Engineering Studies Stage 6 Syllabus © Board of Studies NSW 1999.

As you look around your world do you see any ceramic materials?

When people mention ceramics, the images that come to mind are of ceramic roof and bathroom tiles, pots and crockery. In fact, a lot of what you see is ceramic based. It may not be obvious but ceramics play an important role almost everywhere you look. The windows of houses and vehicles are ceramic, as well as bricks, telephone and power insulators, tiles, crockery and toilet bowls. All of these require ceramic engineers to design and manufacture the material to perform their required function. Also, don't forget bio-ceramics (as in hip replacements, etc) or space shuttle tiles, ceramics protecting soldiers during combat, ceramic engines that will be more fuel efficient, ceramic integrated circuits in computers, optical fibres used in telecommunication or even refractories (without these we wouldn't have any metals).  There are more, including high strength magnets and uranium oxide control rods in nuclear reactors.

Fig. 1 Typical ceramic insulator supporting a power line

What is a ceramic?

The definition found in a popular online dictionary defines it as a clay material that is fired at a high temperature to form such products as earthenware, porcelain or brick. The word can be traced back to the Greek term keramos, meaning potter’s clay or pottery.

Firing clay at an appropriate temperature causes a glassy matrix to form, which fuses (binds) the other materials together making a ceramic. By altering the composition, the firing temperature and length of the heating process, the engineer is able to vary the strength, porosity, toughness and other properties of the ceramic. The quality will also be hugely affected by the nature of the original clay selected.

Ceramics are typically oxides of metals, but may be other inorganic elements in combination with well-defined crystal lattice structures. They are generally hard, brittle and have very high melting points.

Naturally occurring ceramics

Igneous and metamorphic rocks are formed when heat and pressure derived from the earth’s core melts existing rock causing a glassy matrix to form and bind the rock together. Usually the temperatures are high enough to melt the entire rock so a dense, glassy, hard and brittle rock is formed. These rocks possess structures and properties similar to many manufactured ceramic materials. Examples would include basalt, granite, and diorite.

The early beginnings of manufactured ceramics

Early humans often found remnants of rocks that had been used to form the fireplace at the base of the campfire being melted by the heat of the fire to produce the glassy matrix typical of ceramic materials. The harder surfaces produced in this process were observed to improve the properties of the early tools they required for cutting and chopping so the process was then conducted deliberately to produce those materials. As early as 24000 BC, kilns partially dug into the ground were used to fire animal and human figurines made from clay.

Glass was discovered in Egypt around 8000 BC when overheating of kilns produced a coloured glaze on the pottery. It is estimated by experts that it was not until 1500 BC that glass was produced separately from the ceramic and fashioned into useful items.

A major development occurred in the second half of the 19th century, when ceramic materials for electrical insulation were developed. As other inventions came on the scene, including automobiles, radios, televisions and computers, ceramic and glass materials were needed to help them become a reality.

What is ceramic engineering?

Ceramic engineering is concerned with the development, production and use of ceramic materials. Recently, an exciting new generation of high-tech ceramics has emerged from the application of modern science and technology. These materials include new electronic and magnetic ceramics, ceramic engine parts, space shuttle tiles, ceramic high temperature superconductors, biomedical ceramics and many other new products. These feed off established, yet demanding, traditional areas of ceramics such as bricks, tableware, crockery, pottery, glass, refractories and cement.

Some forming processes involve the simple manipulation of ‘plastic’ clay into the required shape. In Art classes at high school you have probably made a dish or a sculpture by kneading clay in you hands and then pushing and pulling it to shape with your hands. As the material dries out it can then be tooled by cutting, filing, drilling or scraping as required. After further drying the object can be coated with a glaze which, when fired, will produce a non-porous, coloured surface coating.

Mechanised forms of this process include compression moulding, injection moulding, extrusion and rolling. These processes are similar to the way they apply to metals and plastics and the end product is an object ready for glazing and firing.

One significantly different process, for which there is no parallel with other materials, is slip casting. When sufficient water is added to clay, a smooth creamy consistency ‘slip’ is produced that can easily be poured into a mould. Typically, powdered ceramic is added to this mix to ensure high density of the finished product. Dry Plaster-of-Paris moulds receive the slip, which is allowed to stand in the mould for a brief period. Moisture from the slip, in contact with the mould, is absorbed into the plaster of the mould. The slip next to the mould becomes plastic as the moisture moves into the mould. After a while, the mould is inverted and the remaining slip poured out. Slip that has adhered to the plaster mould will now dry and shrink away from the mould retaining its high quality surface finish. When dry the moulded object is removed from the mould, trimmed, glazed and fired as required. Typical products made in this way include common tableware (jugs, etc) to large items such as bathroom toilets and sinks.

Activity 1

Using the web sites listed below, investigate the concept of ceramic filters used for the filtration of fluids such as water, molten metals or diesel.

1. http://www.madehow.com/Volume-5/Ceramic-Filter.html
2. http://www.tami-industries.com/frame.asp
3. http://www.aquatechnology.net/ceramicfiltration.html

Answer

Ceramics in telecommunications engineering

Without ceramics, the lucrative global electronics industry worth more than two trillion dollars would not exist. The wide range of electrical properties possessed by ceramics, including insulating, semi-conducting, superconducting, piezoelectric and magnetic characteristics are critical to products such as cell phones, computers, television, and other consumer electronic products. The global market for electronic ceramics alone is estimated at around $9 billion.

Fig. 2 Ceramic insulator used to support a railway electricity line

Designers are increasingly using ceramic solutions in electrical systems, and the material often provides an affordable solution to many of the issues that need to be overcome. Ceramic has, and will continue to play an important role in the development of mobile technology and the telecommunications market. As the industry continues to expand there appears to be more demand to use higher frequencies with improved controls on the specific frequency bands used. Ceramic provides an excellent materials choice for this application. New compositions are being continuously developed to give specific dielectric properties, with low electrical loss characteristics and temperature stability that are providing new solutions to some of the issues faced by design engineers.

Three specific properties are considered when choosing the right ceramic components. These are dielectric constant, low electrical loss and good temperature stability. Each of these properties can significantly affect the overall performance of the system.

One developer has been applying its materials and metallising expertise to the development of the next generation of mobile antenna components. This particular antenna uses a small ceramic cylinder on which copper tracks are deposited and then individually and automatically trimmed for optimum frequency response.

Other current applications for ceramics are the design of a ceramic capacitor suitable for the demands of modern high power radiobroadcast systems and the use of zirconia for ferrules and sleeves when connecting fibre optic cables.

The telecommunications market is not the only industry benefiting from the use of ceramics. Dielectric ceramic components are continuing to play an ever-increasing part in the medical and automotive markets. Opportunities for electrical sensing technology continue to seek the solutions that ceramic compositions can offer.

Cermets

Cermets are bonded materials containing mixtures of ceramics and metal/s. They often behave much like metals but have the great heat resistance of ceramics. There are now an extremely large and increasing number of applications, including disk drives, semiconductor manufacturing equipment, x-ray tables and cassettes. Advanced materials, some with ultra-high thermal conductivities are being used in industrial motors, heat sinks, servers, notebook computers, power modules, plasma displays, printed circuit board heat sinks, and radiators.

Advanced ceramics

Today’s advanced ceramics bear little resemblance to their origins. They offer unique and amazingly powerful physical, thermal and electrical properties that have opened up a whole new world of development opportunities for manufacturers in a wide range of industries.

A cost-effective, high performance alternative to traditional materials such as metals and plastics is provided by advanced ceramics. In general terms, advanced ceramics exhibit exceptional properties that make them highly resistant to melting, bending, stretching, corrosion or wear. Their suitability for use in mass production makes them one of the most versatile groups of materials in the world. They are hard, physically stable, have extreme heat resistance, chemical inertness, bio-compatibility, and have superior electrical properties.

Today, there are a wide range of advanced ceramics including partially stabilised zirconia, partially stabilised alumina, silicon carbide, steatite, silicon nitride, cordierite and many, many more, each with their own particular performance characteristics and benefits. New materials are being developed all the time in response to the challenges posed by new and changing applications.

Porous calcium phosphates have important bio-medical applications such as bone defect fillers, tissue engineering scaffolds, and drug delivery systems.

Copper-plated ceramic circuit boards

Since the 1930s many methods have been used to make electrical connections on insulating boards. Varying degrees of success have been achieved due to the often conflicting requirements of cost, insulation, temperature, track definition, track adhesion, signal speed, current-carrying capability, resistance to adverse working environments, physical strength and performance. However, during the last few years the process of copper-plating ceramic has been greatly improved.

Copper-plated ceramic addresses the interconnection requirements of many of the latest electronics systems. The insulator used is alumina ceramic. The insulation resistance of alumina is very high and does not change significantly with either temperature or humidity. The thermal conductivity is reasonable, being a little under one tenth that of copper but around one hundred times that of most organic materials. The conductor is pure electroplated copper. For all practical purposes only silver has higher electrical conductivity, but copper is cheaper, much more metallurgically stable and can be easily soldered.

Overall, the take-up of this technology has been impressive, more than fifteen million copper-plated ceramic circuits are now in service. Moreover, every twelve seconds, somewhere in the world a system is assembled which takes advantage of this technology.

Activity 2

View the Youtube video: Advanced ceramics, that is part of the Tech Talk series on ceramics. The video takes the viewer through a history of ceramics, discusses the definition and nature of ceramics and then examines the role of advanced ceramics in our world today. Among other things it discusses the use and advantages of silicon nitride, alumina nitride and silica nitride. Although the video is some 35 minutes in length, you will find it interesting and informative.

Hot isostatic pressing (HIP) technology

The demand for higher performance materials is growing. Such materials are denser, more reliable and longer lasting. The innovative nuclear Hot isostatic pressing (HIP) process uses very high heat and pressure to improve bonding, improve the microstructure and mechanical properties, and guarantee the designed lifespan of engineering materials. It also allows for new combinations of materials to produce new-generation alloys that cannot be readily made via melting.

Important applications of the HIP process include:

• Creating improved medical implants such as artificial bone, knee, hip, spinal and knuckle joints which are guaranteed to survive their designed lifespan.
• Producing dense glass for high-strength windows for spacecraft or military applications.
• Making complex castings, with comparable properties to forged component at far less expense.
• Making specialist parts for luxury sports vehicles, racing cars and motorbikes, luxury sport and leisure goods such as titanium golf club heads.
• Creating future-ceramics, including ceramic armour and transparent bullet-proof windows for defense vehicles, specialised tools for the machining industries, boron nitride for foundries.
• Making diamond and tungsten carbide cutting tools for exploration, mining, tunneling and petroleum industries.
• HIP gallium arsenide for the electronics industry as semiconductors, light emitting diodes, lasers, solar cells and other optoelectronic devices.
• Making sputtering target materials for the electronics industry suitable for vapour coatings.

What of the future?

There was a time in history when the field of ceramics was not that important relative to other available materials. In our current world, very few of the materials that we use are manufactured without the influence of ceramics and the importance of ceramics is growing all the time.

The following is a list of modern ceramics produced by a single major supplier to industry:

• Lightweight ceramic armour for soldiers and other military applications capable of protecting against threats as great as 12.7 millimetre armour piercing bullets.
• Evaporation boats for metallisation of materials for food packaging and other products. These facilitate the production of the aluminium coating inside chip packets, nut packets and drink containers.
• Reduced friction, ceramic diesel engine components.
• Functional and frictional coatings primarily for automotive applications.
• Ceramic-impregnated dispenser cathodes for microwave tubes, lasers and cathode ray tubes.
• Neutron absorbing materials that serve as part of a barrier system for spent fuel storage in the nuclear industry and in the transport of nuclear fresh fuel rods.
• Boron doping chemicals for semiconductor silicon manufacturing and for ion implanting of silicon wafers.
• Translucent ceramic orthodontic brackets that reveal the natural colour of the patient's teeth while performing the structural functions of traditional stainless steel brackets.
• Very fine, white, silky, smooth powder used as a base for a range of cosmetics including lipstick, eye shadow, facial creams and rouge.

Ceramic has, and will continue to play an important role in the development of mobile technology and the telecommunications market. As the industry continues to expand there appears to be more demand to use higher frequencies with better controls being required on the specific frequency bands being used. Ceramic provides an excellent choice, new compositions are being continuously developed to give specific dielectric properties, higher dielectric materials with low electrical loss characteristics and temperature stability are providing new solutions to some of the issues faced by designers.

Many engineering tasks can only be solved by the use of ceramic materials and these inorganic, non-metallic materials are providing the platform for a modern-day revolution in materials technology, which is helping to drive industrial development around the world.

New processes and advances in forming and manufacturing techniques introduced in recent years have led to the development of advanced ceramics with the properties and application potential to solve what were once regarded as seemingly impossible technical and engineering challenges.

Web links to useful resources

http://eprints.qut.edu.au/archive/00006794/
http://www.azom.com/details.asp?ArticleID=3629
http://www.azom.com/details.asp?ArticleID=3782
http://www.ceramics.org/aboutus/about_ceramics/index.aspx
http://www.newi.ac.uk/buckleyc/ceramics.htm
http://www.azom.com/details.asp?ArticleID=1739
http://www.esk.com/en/industries-applications/industries.html