Revealed: all you need to know about Ceramics

While Ceramic products play huge role in improving the quality of life in the built environment, their  connection to  Clay is more often than not ,lost on many people .So  let  me  clear  the air and say  here and now that ceramics   are made from  Clay – a material that is not particularly prized for  building foundations on , but as it happens is the very  foundation of this hard ,durable and appealing material . Clay is type of fine grained heavy soil that is elastic when it’s wet (see image below).

Clay is formed from the wear and tear of igneous rocks like granite which have feldspar-an alumina silicate mineral. There are generally five types of clay   as follows:

  • Kaolin:-It’s also called china clay and is the purest  clay . It comes from the decomposition of the feldspar in granite rocks.
  • Illite:-it’s a micaceous clay. For your information, Mica is a transparent stone used to make electrical equipment.
  • Montmorillonite:-its aplastic clay of variable composition.
  • Ball clay:-It contains organic matter and often blended with other clay types like kaolin.
  • Terracotta clay:-This clay contains iron oxide that cause it to turn red when fired.

 

How ceramics are made

Ceramics are made from either wet or dry clay that is put through   baking process at very high temperatures. Wet clay which contains both chemical bonded and physical bonded water is first of all moulded into required items .The wet clay items   are then dried slowly   to allow them   to shrink without cracking. This   is followed by firing, during which time, all physically bonded water is lost at a temperature of about 100 degrees Celsius.

On the other side of the coin, dry clay powder is used when items to be made require higher accuracy for example floor tiles. The  dry  clay powder  is compressed  into  required  shape  and  baked  at  high temperature.

As  the  temperature   increases  beyond  500 degrees  Celsius , all  chemically bonded  water  is lost  as steam and vapours. At 800 degrees Celsius, Carbon in clay is burnt off as carbon dioxide   and the clay material begin to undergo a sintering process   that produces a porous material (has many small holes   that allow air to pass through).

As  the  temperature increases  toward  1200 degrees Celsius, the Alumina and  Silica  in clay  recrystallize  into material called  Mullite.With  additional increase in temperature   ceramic material   is formed  because  of  increased re crystallization. At temperature beyond 1300 degrees Celsius all remaining Silica is recrystallized. In short, a brand new Ceramic materials is formed because of the re crystallization of clay (alumina and silica) at very high temperatures.

At this very high temperature potassium or sodium may be added to the mix   which causes vitrification to occur producing an opaque ceramic product!

Ceramic products:

Ceramic products are widely used in building construction as floor, wall, roof ,sanitary materials  as well as many  other uses   as  expounded  below..

1.Fire-clay

The Clay used here is a blend of Silica Alumina and iron oxide (high silica content of 40-80%, and iron oxide 2-3 %).Fire-clay is used  to make refractory products which are  not affected  by  high temperature of   fires. In particular dense  products  are used  in  fire resistance applications  while on the other  hand   lower density  products are often used  for example  in flue  linings(metal tubes use to take smoke and heat from a fire  to the outside of  house).White glazed  fireplace is  also used   to make urinals  and laboratory  sinks.

2.Brick and roofing tiles

Whereas Bricks are made from   clay composed of 40-65% Silica, 1-25% Alumina and 3-9%   iron oxide, Roofing tiles manufacture   is more demanding  –it requires  same clay type   used in brick making but must be  of a  finer quality . Also certain floor tile can be manufactured with this clay but then it will require firing up to 1130 degrees Celsius to produce sufficient vitrification(Image below).

3.Terracotta

Terracotta is a brown red clay used to make building materials. The clay use must be of finer grade than that used in making roofing tiles. Terracotta clay is use in manufacture of Terracotta floor tiles and decorative   tiles.

4.Stoneware

Stoneware is made from secondary or impure clays. It’s   used to make vitrified clay pipes, wall cladding and floor tiles.

5.Earthenware

A mix of various clays is used to make earthenware. This is often used to make drainage products.

6.Wall tiles

Made from a mix of various clays   and magnesium silicate or limestone   that is turned into dry powder and pressed into tiles. The tiles are the glazed to improve their aesthetic appeal and    make them water proof.

7.Vitreous china

Vitreous china is made from blend of kaolin clay, ball clay, and quartz.  It’s used to manufacture water closets, wash basins, floor tiles    and swimming pools.

©Copyright 2017 eastafricaminihardware.com

Sources: Materials for Architects and Builders by Arthur Lyons, PhD.

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