February 9, 2010

Characteristics of China Clay Required for Ceramic and Other Industries

China clay is used as an important raw material for a number of industries. The most important is the ceramic industry where it is used for the manufacture of earthware, fine china, tiles etc. and also in other industries such as paper, textile, rubber, pharmaceutical, leather, paint, plastics, petroleum, cosmetic etc. Use of China Clay as Raw Material in the Production of Refractory Insulation Bricks has been discussed in a separate post.

India has extensive deposits of all varieties of china clays most of which after mining and processing, get consumed by the various domestic industries while around 20% - 30% of its total annual production are exported to other countries. The chemical compositions, other properties, uses, and occurrences of Indian china clays have been discussed in detail in a separate article [Read]. 
As we know that the specific requirements of china clays for different industries are different. Here in this article we present the important characteristics [see the Table below] of china clay required for ceramic industry (IS: 2840 - 1993) -

Characteristics
Requirements
Type - I (unwashed)
Type - II (washed)
Grade 1
Grade 2
Grade 3
Grit content / Fineness               (+45 micron IS sieve, max%)
2
3
4
1
Particle size distribution (%)
(a) Coarser than 25 micron (max)
(b) Coarser than 10 micron (max)
(c) Finer than 2 micron (max)

3
10
70

6
12
65

9
15
45

1
5
75
Plasticity (by hand feel)
Very
Good
Fair
Very good
Water of plasticity (max %)
30
32
34
28
Attenberg Number (min)
18
15
12
20
Al2O3 % (min)
28
25
20
28
Fe2O3 % (max)
1.5
2.0
2.0
1.5
TiO2 % (max)
1.5
2.0
2.0
1.5
(Fe2O3 + TiO2) % (max)
2.75
3.5
3.75
2.5
LOI % (max) [dried at 110OC]
10.5
9.5
9.0
11.0
Shrinkage, linear % (max)          [dried at 110OC]
6
7
8
6
Water absorption % (max)        [after firing at 1350OC]
3
5
9
2
Colour after firing at 1350OC
Creamish white
Pale to dull cream
Light gray
White pale cream without specks
MOR (MPa) [at 110OC] (min)
3.5
3.0
2.5
4.0
        
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