Classification of Ceramics

CLASSIFICATION OF CERAMICS

A general classification of ceramics is difficult to make, because of the great versatility of these materials. However, ceramics may be classified as given below:

1. Natural and Manufactured ceramics

(a) Natural Ceramics

The most frequently used, naturally occuring Silica (SiO₂), Silicates and Clay minerals.

(b) Manufactured Ceramics

Such ceramics include: SiC, Al₂O₃, Silicon Nitride (Si₃,N₄) and many varieties of Oxides, Carbides, Nitrides, Borides and more complex ceramics.

Some of the naturally occuring ceramics are also, manufactured which results in their enhanced properties, as compared to natural ceramics.

For example, Magnesia (Magnesium Oxide, MgO) also occurs in nature, but for industrial use, it is made from the Carbonate of Hydroxide. However, all the ceramics not available naturally, are manufactured.

The natural ceramics are also called as "traditional ceramics", while manufactured ceramics are usually called as "High-tech ceramics" or "fine ceramics".

2. Functional Classification

This classification indicates particular industries and industrial applications of the ceramics, as given below:

(a) Abrasives: Alumina, Carborundum

(b) Pure Oxide Ceramics: MgO, Al₂O₃, SiO₂, Zirconia (ZrO₂) and Berylia (BeO) etc.

(c) Fired-clay products: Bricks, Tiles, Porcelain, etc.

(d) Inorganic glasses: Window glass, lead glass, etc.

 (e) Cementing materials: Portland cement, Lime, etc.

(f) Rocks: Granites, Sandstones, etc.

 (h) Refractories: Silica bricks, Magnesite, etc.

3. Structural Classification

This classification indicates the structural criteria as given

(i) Crystalline Ceramics : Single phase like MgO or multiphase from the MgO to Al₂O₃ binary system.

 (ii) Non-Crystalline Ceramics : Natural and synthetic glasses e.g., window glass.

(iii) Glass-bonded Ceramics: Fired clay products - Crystalline phases are held in glassy matrix.

(iv) Cement : Crystalline or in Crystalline iband non-Crystalline phases.

In general, ceramics are classified into two groups

1. Traditional ceramic materials

2. Engineering ceramic materials.

1. Traditional Ceramic Materials

Traditional ceramics are made from three basic  components: clay, silica, and feldspar. Example of traditional ceramics are glasses, tiles, bricks and porcelain.

Hydrated aluminium silicate (Al₂O₃ SiO₂ H₂O) is main constituent of clay along with small amounts of other oxides such as TiO₂, Fe₂O₃, MgO, CaO, K₂O and Na₂O. The clay provides workability of the material before firing hardens it and constitute the major body material.

The silica is used as refractory component in traditional ceramics. This is also called as flint or quartz having a high melting temperature. Potassium feldspar (K₂O Al₂O₃ 6SiO₂), has a low melting temperature and makes a glass when the ceramic mix is fired. It acts as a bonding material between refractory component.

Structural clay products such as building brick, sewer pipe, drain pipe, roof and floor tile etc. are made of natural clay, which contain all three basic components.

2. Engineering Ceramic Materials

Engineering ceramics are mainly pure compounds or oxides, carbides or nitrides of pure compounds. Some of the important engineering ceramics are alumina (Al₂O₃) silicon nitride (Si₃N₄), silicon carbide (SiC) and zirconia (ZrO₂).

Bonding in ceramics

Ceramics possess more ess more than one type of bond in a single material i.e. strong ionic bonds and covalent bonds. The presence of ionic bond makes ceramics hard.

However, the ionic bonds, cross-linking adjacent silicate chains, are weaker than covalent bonds linking the silicate groups. The ceramic materials, therefore, fracture along ionic bonds, parallel to the silicate chains.

In an ionically bonded ceramic crystal, each ion is surrounded by ions of of opposite charge. This holds the ions rigidly in place.

Ceramic materials, which consists of flakes or plates, (like in mica), possess sheet structure instead of chain structure. The adjacent sheet structures are attracted to each other by weak vander waals bonding or weaker ionic bonding or hydrogen bonding. уліти это?

Other Classification of ceramics

Ceramics can also be classified into three categories as

 (i) Crystalline ceramics

(ii) Non-crystalline (Amorphous) ceramics