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Engineering Materials - Ceramics


Materials: Ceramics


Introduction to Ceramics

Ceramic Parts Ceramics are inorganic non-metallic materials. Metal oxides (Al2O3, FeO, etc.) are common examples of ceramics, but other compounds such as carbides and nitrides are also included. Porcelain, glass, bricks and refractory materials are some examples of traditional ceramics. In the last 30 years, advances in material science have transformed formerly brittle ceramics into materials tough enough to withstand engine environments. Ceramics are used in a variety of applications including window glass, implantable teeth, brick, ceramic bones, nuclear fuel, tennis racquets, solid-state electronic devices, engine components, cutting tools, valves, bearings, and chemical-processing equipment.

The properties for which ceramics are most often selected include:

  • High-temperature resistance (High melting temperatures.)
  • High electrical resistivity (Although some ceramics are superconductors.)
  • Broad range of thermal conductivity (Some ceramics are excellent insulators)
  • High hardness (Many ceramics are brittle.)
  • Good chemical and corrosion resistance.
  • Low cost of raw materials and fabrication for some ceramics.
  • Good appearance control through surface treatments, colorization, etc.

Ceramics are generally more brittle than metals and can have similar stiffness (modulus of elasticity) and similar strength, particularly in compression. But in a tensile test they are likely to fail at a much lower applied stress. This is because the surfaces of ceramics nearly always contain minute cracks ("Griffith cracks"), which magnify the applied stress.

Since ceramics often have very high wear-resistance and hardness, most ceramic parts are formed as near net shape as possible. Ceramics are most often produced by compacting powders into a body which is then sintered at high temperatures. During sintering the body shrinks, the grains bond together and a solid material is produced. Other ceramic forming processes include: Dry Pressing, Isostatic Pressing, Roll Compaction, Continuous Tape Casting, Slip Casting, Extrusion, Injection Molding, Pre-Sinter Machining, Hot-Pressing, Hot Isostatic Pressing, Grinding, Lapping and Polishing.



Ceramics are generally separated into the following categories.

  1. Metallic Oxides

  2. Glass Ceramics

  3. Nitrides and Carbides

  4. Glass

  5. Carbon and Graphite

  6. Porcelain

  7. Ceramic Fibers
Ceramic Type
Characteristics
Metallic Oxides
Alumina
  • Abundant and easily fabricated.
  • Good strength and hardness.
  • Wear and Temperature Resistant.
  • Good electrical insulators.
  • Low dielectric loss.
Beryllium Oxides
  • Exceptionally high thermal conductivities (for ceramics) at low to moderate temperatures.
Zirconia
  • Extreme inertness to most metals.
  • Good toughness and strength.
Glass Ceramics
Glass-Ceramics
  • Low, medium or high thermal expansion depending on composition type.
  • Good electrical insulators.
  • Transparent
  • One can be machined with steel tools.
Nitrides and Carbides
Silicon Nitrides
  • Resistant to high temperatures, to thermal stress and shock.
  • High strength and oxidation resistant.
  • Good electrical insulators.
Boron Carbide
  • High hardness and low density.
  • Best abrasion resistance of any ceramic.
  • Low strength at high temperatures.
Silicon Carbides
  • Low electrical resistivity.
  • High strength and resistance to chemical attack, high temperature and thermal stress.
Tungsten Carbides
  • Used for tool tips.
  • Excellent hardness and mechanical strength.
  • Good thermal conductivity.
  • Good wear and abrasion resistance.
Glass
Glasses

  • Oxide (silica)
  • Silicates
  • Phosphates
  • Borosilicates
  • Good resistance to thermal shock.
  • Large range of special optical characteristics.
  • Transperent.
  • Low thermal expansion and high dielectric strength.
  • Good chemical resistance.
Carbon and Graphite
Carbons and Graphites
  • Poor strength except when produced as fibre.
  • Good electrical and thermal conductivity
  • Creep resistant at high temperatures in non-oxidizing conditions.
  • Self-lubricating.
  • Good refractoriness and thermal shock resistance.
  • Low density and chemically inert.
Carbon/Carbon Composites
  • High strength and low coefficient of thermal expansion at temperatures above 2000C.
  • Excellent thermal shock resistance.
  • Superior toughness, excellent thermal and electrical conductivity
  • Resistance to corrosion and abrasion.
  • High cost.
Porcelain
Porcelain
  • Good chemical and thermal resistance.
  • High density, strength, resistivity and dielectric strength
  • Good thermal shock, wear and hot strength.
  • Chemically inert.
Ceramic Fibers
Ceramic Fibers
  • Oxides spun to fiber and bulked to felt.
  • Used for high temperature insulation including former applications of asbestos.

Ceramic Links
Resource Sites
Introduction to Ceramics

A good article on the background of the ceramics industry provided by The American Ceramics Society.


Advanced Ceramic Technology Center

The Advanced Ceramic Technology Center has the resources to help U.S. industry overcome the high cost of machining and certifying structural ceramics, especially for stringent applications such as heat engines.


Ceramics Industry Magazine - Reference Tables

This site has some great references including: Material Properties, Drying/Firing Tables, Forming/Finishing Info., Refractories and Testing Methods.


Dynamic-Ceramic - Design Guides

A series of guides are intended to act as an aid to engineers and designers wishing to produce cost effective designs for advanced ceramic manufacture. The design tips also refer primarily to components which have to be finish ground to tight tolerances.


Dynamic-Ceramic - Material Properties

This site was designed to aid in the selection of advanced ceramics with a selection of pages, which provide both comparative data on the available materials in addition to a more in-depth analysis of the individual materials and their mechanical and physical properties.


Dynamic-Ceramic - Manufacturing Processes

Ceramic forming processes may be classified as traditional - die pressing, cold isostatic pressing, slip casting and extrusion - or as new and emerging, such as injection moulding and tape casting.

Magazines, Periodicals, Newsletters
Ceramic Industry Magazine

Ceramic Industry magazine is the exclusive voice of ceramic manufacturing, serving the advanced ceramics, glass, whitewares, structural clay, refractories and decorating technology industries.


Ceramic Bulletin

Ceramic Bulletin provides authoritative coverage of established and emerging processing technology that will impact ceramic manufacturing around the world.
Societies and Organizations
The American Ceramic Society

ACerS, an international association that provides the latest technical, scientific and educational information to its Members and others in the ceramics and related materials field, structures its services, staff and capabilities to meet the needs of the ceramics community, related fields, and the general public.


Swedish Ceramic Institute

Informative site with a 2-minute introduction to ceramics, material data and other useful information.

Meta Sites
Metallurgical and Materials Engineering Global Links

Ceramics and Industrial Minerals

Metallurgical and Materials Engineering Global Links

The WWW Virtual Library: Technical Ceramics

 

 

 




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