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Ceramics

Introduction

A ceramic is generally defined as any inorganic nonmetallic material. Examples of such materials can be anything from NaCl (table salt) to clay (a complex silicate).  By this definition, ceramic materials would also include glasses; however it is considered that the definition "ceramics" must also be crystalline.

The word ceramics comes from the Greek word keramos which means pottery. Engineering ceramics are formed in the wet plastic state, dried and then sintered at high temperatures.  Monolithic engineering ceramics are derived mainly from inorganic materials and often possess non-metallic properties.

Ceramics are closely associated with our everyday life. Functional ceramics are distinguished from conventional ceramics (chinaware) and called "fine ceramics" or "engineering ceramics."

Typical Ceramics

    Engineering Ceramics Include

  1. alumina
  2. silicon carbide
  3. zirconia
  4. silicon nitride
  5. Diamond
  6. Cubic boron nitride
  7. Magnesia
  8. Tungsten Carbide
Properties

Engineering ceramics are ideally suited for high performance applications where a combination of properties such as wear resistance, hardness, stiffness and corrosion resistance are important. In addition to these properties, engineering ceramics have relatively high mechanical strength at high temperatures.

Engineering ceramics are distinguished from metals and some alloys by their exceptional properties.  They are very hard materials and are highly wear-resistant. Indeed, when compared to their metal counterparts, engineering ceramic parts and components are more durable and have longer life-spans under given operational conditions.  Ceramic cutting tools, for instance, require less sharpening or replacement due to wear, and will last at least 60 to 100 times longer than steel blades.

Engineering ceramics are chemically resistant to most acids, alkalis and organic solvents and can withstand high temperatures.  Metals weaken rapidly at temperatures above 816oC while engineering ceramics retain a good degree of their mechanical properties at much higher temperatures.

As most metals are approaching the limits of their capability, engineering ceramics are emerging as the most desirable alternative for various high performance high value applications. Frequently viewed as a direct replacement material for top of the range metals such as tool steels, stellite and tungsten carbides, the Ceramic materials produced are generally able to provide even better service if they are engineered for the applications

Engineers have long considered engineering ceramics as hard and brittle materials that are prone to catastrophic failure under tensile loading conditions and are considered to be unreliable materials.   However, technological developments over the last two decades have shown that ceramic materials, are viable alternatives to metals and alloys in many applications.   As an example Zirconias have better wear-resistant properties than metals, are usually corrosion-resistant, can withstand higher operating temperatures, possess a thermal expansion coefficient close to many metals, and can be appropriately bonded to metals.

Applications

Typical mechanical components include wear plates and thermal barriers, bearings for high speed and high stiffness spindles, bushes, gears and many others.

Typical Process components include pump shafts, seats, bearing surfaces, gears and even complete pump bodies, valve guides and seats.

Ceramics are used for cutting tools including razor blades for film and tape cutting to 300mm diameter circular slitters for the paper industry.

Ceramic turbine blades are used in most turbochargers providing lighter units than the steel alternatives allowing improved performance at higher temperatures.



Links Providing information on Ceramics
  1. Advanced Ceramics- MachinDesign.. A very informative article.
  2. Carborundum Universal.. A Typical Supplier with products and properties
  3. Dynamic Ceramics Manufactures site includes lots of useful information
  4. Properties of Ceramics- Engineers Toolbox Table of properties - Very useful
  5. Properties of Ceramics- Ferro Ceramics Table of properties - More detailed than above

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12/03/2010