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Ceramics & Glasses:

Category Summary

The largest part of ceramics produced worldwide have a crystalline structure. Crystalline ceramics are generally more brittle than metals, but this type of ceramics 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 minute cracks (Griffith cracks), which magnify the applied stress. Since ceramics often have high wear-resistance and hardness, most ceramic parts are formed as near net shape as possible.

The options to process crystalline ceramics are very limited. Crystalline 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. The bonding can also be done with the help of chemical processes. A combination is alsopossible.

Category Details

Features

In general ceramics share the following properties:

  • Hard
  • High compressive strength
  • Able to withstand high temperatures
  • Very good resistance to acidic or caustic environment

But keep the following in mind:

  • Brittle
  • Weak tensional strength
  • Weak flexurial strength
  • Weak resistance against shear stress
  • Limited machinabilty
  • Limited forming capabilities
  • Limited bonding capabilities

Ceramic processing options are very limited. Most ceramics are created with the help of a sintering orchemical bonding process. Other ceramic forming processes include: Dry pressing, Isostatic Pressing, Roll Compaction, Continuous Tape Casting, Slip Casting, Extrusion, Injection Moulding, Pre-Sinter Machining, Hot-Pressing, Hot-Isostatic Pressing, Grinding, Lapping and Polishing.

Classification

The most important subcategories of crystalline ceramics are:

Refractories

Refractories can withstand very high temperatures and maintain their physical properties within a furnace environment. They are therefore widely used to build structures that can resist the thermal shock, physical wear and corrosive chemicals associated with iron and steel production, copper and aluminium smelting, glass and ceramics production and similar processes. Refractories can be used for kiln linings, fire radiants or crucibles.

Structural

Structural ceramics are used building and construction. In general they are cheap and they can withstand the elements and in some cases high compressive forces. Examples are brick, floor tiles, roof tiles and ceramic pipes.

Technical

Technical ceramics are divided in oxides and nonoxides. They are engineered to have both the traditional properties of crystalline ceramics and one or more unique properties. Examples of these engineerd properties are higher resistance to tensional forces, flexurial forces or impact. These properties make ceramics suitable for a wide range of, specialty, applications.

Traditional

Traditional ceramics are very common around the house. They are used for utilitarian wares and artistic objects. Bone China, earthenware, porcelain and stoneware are all examples of traditional ceramics.

Classification Sources

Idemat 2003

Wikipedia

Health

Known health effects for this category.

Toxicity

There is no relevant data available on this level.

Environment

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