Refractories

Refractories

Refractories are materials that can withstand high temperatures without softening or deformation in shape. Refractories are mainly used for construction of lining in furnaces, kilns, converters, etc. The main function of a refractory is to withstand and maintain high temperatures and to resist the abrasive and corrosive action of molten metals, slags and gases.

Objective of a refractory
The main objective of a refractory is to resist heat losses and also to resist the abrasive and corrosive action of molten metals, slags and gases at higher temperatures, without softening or deformation in shape.

Uses of Refractories

1. Refractories are mostly used for the construction of the lining of the furnaces, tanks, converters, kilns, crucibles, ladles, etc.

2. They are employed for the manufacture of cement, glass, ceramics, paper, metals (both ferrous and non-ferrous ), etc.

Characteristics or requisites of a good refractory

(i) It should be infusible at the operating temperatures.
(ii) It nshould be chemically inert towards the corrosive gases, metallic slags and liquids.
(iii) It should resist the abrading action of flue gases, flames, etc.
(iv) It should not crack and suffer loss in size, at the operating temperatures.
(v) It should expand and contract uniformly, with temperature rise and fall respectively.
(vi) It should be able to withstand overlying load of structures, at operating temperatures.
(vii) It should have high refractoriness.

Classification of refractories

Refractories are classified in the following two ways
According to their chemical properties.
According to their refractoriness.

I. According to their chemical properties
According to the chemical properties, refractories are classified into three main types
Examples (i) Silicon (i) Magnesite (i) Graphite
(ii) Alumina (ii) Dolomite (ii) Carborundum

1. Acidic Refractories
Acidic refractories consists of acidic materials loke alumina(al203) and
Silica (SiO2). They are not attacked by acidic materials, but easily attacked by
basic materials.
Example:
Silica, alumina, fire clay refractories.

2. Basic Refractories
Basic Refractories consist of basic materials like Ca02, Mgo, etc. They are
not attacked by basic materials, but are easily attacked by acidic materials.
Example:
Magnesite, Dolamite refractories.

3. Neutral Refractories
Neutral refractories are made from weakly acidic and basic materials like Carbon, Chromite, Zirconia, etc. They are not attacked by both acidic and basic materials.
Example:
Graphite, Chromite, Zirconia, Carborundum refractories.

II. According to their refractoriness
According to the refractoriness, refractories are classified into four types.
Type of Refractories with PCE value
Example
1. Low heat duty refractories
2. Intermediate heat duty refractories
3. High heat duty refractories
4. Super heat duty refractories