What are ceramics?

27 Nov.,2024

 

What are ceramics?

A ceramic is an inorganic non-metallic solid made up of either metal or non-metal compounds that have been shaped and then hardened by heating to high temperatures. In general, they are hard, corrosion-resistant and brittle.

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'Ceramic' comes from the Greek word meaning &#;pottery&#;. The clay-based domestic wares, art objects and building products are familiar to us all, but pottery is just one part of the ceramic world.

Nowadays the term &#;ceramic&#; has a more expansive meaning and includes materials like glass, advanced ceramics and some cement systems as well.

Traditional ceramics &#; pottery

Pottery is one of the oldest human technologies. Fragments of clay pottery found recently in Hunan Province in China have been carbon dated to 17,500&#;18,300 years old.

The major types of pottery are described as earthenware, stoneware and porcelain.

Earthenware is used extensively for pottery tableware and decorative objects. It is one of the oldest materials used in pottery.

The clay is fired at relatively low temperatures (1,000&#;1,150°C), producing a slightly porous, coarse product. To overcome its porosity, the fired object is covered with finely ground glass powder suspended in water (glaze) and is then fired a second time. Faience, Delft and majolica are examples of earthenware.

Stoneware clay is fired at a high temperature (about 1,200°C) until made glass-like (vitrified). Because stoneware is non-porous, glaze is applied only for decoration. It is a sturdy, chip-resistant and durable material suitable for use in the kitchen for cooking, baking, storing liquids and as serving dishes.

Porcelain is a very hard, translucent white ceramic. The earliest forms of porcelain originated in China around BC, and by 600AD, Chinese porcelain was a prized commodity with Arabian traders. Because porcelain was associated with China and often used to make plates, cups, vases and other works of fine art, it often goes by the name of &#;fine china'.

To make porcelain, small amounts of glass, granite and feldspar minerals are ground up with fine white kaolin clay. Water is then added to the resulting fine white powder so that it can be kneaded and worked into shape. This is fired in a kiln to between 1,200&#;1,450°C. Decorative glazes are then applied followed by further firing.

Bone china &#; which is easier to make, harder to chip and stronger than porcelain &#; is made by adding ash from cattle bones to clay, feldspar minerals and fine silica sand.

Advanced ceramics &#; new materials

Advanced ceramics are not generally clay-based. Instead, they are either based on oxides or non-oxides or combinations of the two:

  • Typical oxides used are alumina (Al2O3) and zirconia (ZrO2).
  • Non-oxides are often carbides, borides, nitrides and silicides, for example, boron carbide (B4C),

    silicon

    carbide (SiC) and molybdenum disilicide (MoSi2).

Production processes firstly involve thoroughly blending the very fine constituent material powders. After shaping them into a green body, this is high-temperature fired (1,600&#;1,800°C). This step is often carried out in an oxygen-free atmosphere.

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The high temperature allows the tiny grains of the individual ceramic components to fuse together, forming a hard, tough, durable and corrosion-resistant product. This process is called sintering.

Applications of advanced ceramics

Advanced ceramic materials are now well established in many areas of everyday use, from fridge magnets to an increasing range or industries, including metals production and processing, aerospace, electronics, automotive and personnel protection.

In modern medicine, advanced ceramics &#; often referred to as bioceramics &#; play an increasingly important role. Bioceramics such as alumina and zirconia are hard, chemically inert materials that can be polished to a high finish. They are used as dental implants and as bone substitutes in orthopaedic operations such as hip and knee replacement. Find out more on the uses for advanced ceramics.

Nature of Science

Progress in the advanced ceramics field has come about as a consequence of creative and imaginative thinking by materials scientists. Thinking &#;outside of the square&#; can sometimes lead to the solving of an irksome problem.

Materials Science and Engineering: Ceramics - UMD MSE

 

Research in Ceramics by MSE @ UMD

 

Safer Batteries for EVs: Prof. Eric Wachsman's group develops solid state Li-ion batteries from layered ceramics in support of the growing market of electrical vehicles. By replacing the flammable liquid electrolyte, ceramic-based batteries improve safety (i.e. less likely to ignite following a car accident). More>>

 

From Digs to Dentistry: Mey Saied, an alumna of the MSE graduate program, used her expertise in ceramics to make better dental crowns while a student here at Maryland. She's also used MSE to study ancient pottery!

 

 

 

 

Watch a materials video demonstration about ceramics:

Superconductors and Levitation: A superconductor is a material that has no electrical resistance to current flow. A "high" temperature superconductor exhibits this property at liquid nitrogen temperatures (-321°F /-196°C). An important property of superconducting materials is the ability to repel magnetic fields. Placing a magnet above a superconductor will cause the magnet to levitate. Maglev trains make use of this phenomenon, as they are lifted and propelled forward by a magnetic field, free of friction. We can see this effect by placing a magnet atop a superconductor resting in liquid nitrogen. See a movie demonstrating levitation using a superconductor

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For more information online:

  • The American Ceramic Society
  • Weird, Weird Science: Zoom Into Concrete - John Sizemore offers movies on a variety of topics on his Dailymotion site. His "Zoom Into..." series of videos about materials includes Zoom Into Concrete.