What are refractory materials, Classifications And Types?

Refractories are inorganic non-metallic material which may withstand heat without undergoing chemical changes while remaining in touch with molten slag, metal and gases.

Refectory may be classified on the basis of

• Chemical composition

• The methods of manufacture

• Their physical forms

Classification Based on Chemical

Composition

(I) Acid Refractories: Acid refractories are those which are attacked by alkalis (basic slags). These

are utilized in areas where slag and atmosphere are acidic. Examples of acid refractories are:

Silica (SiO2), Zirconia (ZrO2).

(II) Basic Refractories:-

Basic refractories get reacted with acid slags but they don’t react to alkaline slags. Since they do not react with alkaline slags, these refractories are of oxidation can be controlled.

Classification Based on Physical Form

• Shaped Refractories: These refractories have fixed shaped when delivered to the user. These are what we call bricks. Brick shape can be divided into two: standard shapes and special shapes. Standards shapes have dimension that are conformed to by most refractory manufacturers and are generally applicable to kilns and furnaces of an equivalent type.

Special shapes are specifically made for particular kilns and furnaces. This may not be applicable to another furnaces or kiln of the same type.

Shaped refractories are nearly always machine pressed, thus, high uniformity in properties are expected. Special shapes are most frequently hand-molded and are expected to exhibit slight variations in properties.

• Unshaped Refractories:

These refractories don’t have a definite form or shapes. They are only given shape upon application. It forms joint less lining and are better referred to as monolithic refractories. These are categorized as Plastic refractories, ramming mixes, gunning mixes

Refractories are classified as dense or insulating types. The most high-temperature refractories, like firebricks, are high-density (>120 lb/ft3). They offer excellent resistance in challenging operating environments, like slags with different chemical compositions, fumes, dust, and gases.

• Insulating refractories have lower densities (4 to 70 lb/ft3) and supply insulating properties, while offering resistance to corrosion and chemical reactions with the operating environment.

Fire-clay brick Refractories

• Fire-clay brick comprise about 75% of the assembly of refractories on a volume basis and are essentially hydrated aluminum silicates with minor proportions of other minerals.

They are extremely versatile; least costly of all refractory bricks and are extensively used in the iron and steel industry, non ferrous metallurgy, glass industry, cement industry etc.

Characteristically, fire-clay brick begin to melt far below their fusion temperature and under load actual deformation takes place. The amount of deformation depends upon the load, and, once started, this deformation is a slow but continuous process unless either the load or the temperature is reduced.

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