Ball Clay
Ball Clay is a highly plastic variety of clay of Kaolinite group like China clay and fire clay, but has less refractoriness. The chemical composition of ball clay is similar to that of China clay, except that the ball clay contains a large proportion of silica.

The main utility of ball clay lies in the plasticity, high bonding qualities and tensile strength. It is therefore, used in bled with non- plastic to semi plastics clays for obtaining requisite plasticity. It is added in various proportions for the preparation of body composition of various sanitary wares, bathtub tiles, porcelain, etc.

The BIS has prescribed the following specification (IS: 4589 1968) for ball clay for use in the ceramic industry: -

The material shall be in the form of lumps or power, free from any foreign matter and shall be highly plastic when wet. The lumps shall slake in water and from a smooth suspension when dispersed. The color of the material when fired at 1350o C shall be light gray or light cream and free from any specks or patches.

Chemical Analysis:                        

Fe2O3  

1.5% max.

TiO2     

1.5% max.

Fe2O3   + TiOby weight

2.75% max.

Al2O3   by weight

25% min.

L. O. I.

10.5% min.

Separate reserves estimates of ball clay are not available and this mineral is not included in the list of minerals for the preparation of mineral inventory.

The group recommends the following grade for ceramic industry for estimation of reserves of ball clay.

Chemical     

Physical

Fe2O3  

1.5% max.

Fired color:

TiO2     

1.5% max.

Light gray or light cream

Fe2O3   + TiOby weight

2.75% max.

Free from any foreign matter.

Al2O3  

25% min.

Plasticity lightly plastic

L. O. I.

10.5% min.

When wet.


China Clay  
China clay, also called kaolin, falls under kaolinite group of clay minerals. It results from the alterations of feldspars, granite, gneiss and pegmatite rocks by hydrothermal action of aqueous solution. China clay usually carries some impurities in a small quantity such as silica, iron, magnesium, titanium, calcium, potassium, sodium oxides, mica, tourmaline, etc., which may be inherent in the parent rocks. The quality of china clay depends much upon the impurities present. China clay in mainly used in ceramics, textiles, Paper, rubber, paints, cosmetics and pharmaceuticals industries. It is also used in insecticides, white cement manufacturing.

The uses and specifications of china clay in different industries are discussed below:

(A) Ceramics:
The BIS has not standardized any specification for use of china clay in ceramic industry. However, for the manufacture of ceramic products, good quality china clay is required which should have water elasticity of 32%, shrinkage after drying should not be more than 7%, and total shrinkage after firing at a temperature of 1300o C not more than 10-14%, Grit should be low. For the manufacture of ordinary crockery and ceramic wares, presence of grit up to 2% is tolerated. But for the manufacture of high-class crockery, grit below 1% is generally preferred. In the manufacture of high-class ceramic products, the presence of lime, magnesia, iron oxides, alkalies and other impurities up to 2% is not harmful. Excess of iron, however, may color the products. Also for the manufacture of electrical switches, the iron content should be as low as possible.


(B) Textile and Paper coasting: -
China clay is utilized in textile industry and as a sizing and packing material. For this purpose, the clay should be white in color without tinting. Grit is the most objectionable ingredient. Oxides of magnesium and iron should be as low as possible. Dull white clay is utilized in making colored and khaki cloth.

China lay is used for paper coating purpose in order to provide a smooth, even surface and to impart a glaze. Various grades of paper quality china clay of fine mash are used depending up on the quality of paper required to be manufacture. The whiteness, ink absorption, chemical inertness, uniformity of particle size and retentive properties determine the suitability of china clay for use in paper coating.

BIS (IS: 505 - 1978) has standardized specifications for china clay for use in textile and paper coating industry as follows : -

S. No.            

Characteristics      

Textile & Paper

1.

Residue on 53 micron IS Sieve

0.1% (max.)

2.

Particles larger than 10 micron in diameter.

5.0% (max.)

3.

Particles smaller than 2 micron in diameter.       

62.0% (max.)

4.

Relative density at 27o C

2.5 to 2.9

5.

Loss on drying.

6.00% (max.)

6.

Loss on ignition

14.00% (max.)

7.

Matter soluble in HCL 

2.5% (max.)

8.

Fe2O3

0.7% (max.)

9.

Color reflectance to blue light of water, length 3040Ao 

80        85 %



(C ) Rubber:
In rubber industry, china clay is used as filler and as a reinforcing and stiffening agent. For these purposes, lightweight clay having a specific gravity 2.5 is tolerated. It should be of fine mesh and should be of fine mesh and should be absolutely free from copper, which is undesirable in rubber goods. The BIS (IS: 505 1978) has standardized the specifications given below:

S. No.            

Characteristics      

Rubber

1.

Residue on 53 micron IS Sieve

0.1% (max.)

2.

Particles larger than 10 micron in diameter.

7.0%

3.

Particles smaller than 2 micron in diameter.       

50.3% (min.)

4.

Loss on drying.

2.0% (max.)

5.

Loss on ignition

14.00% (max.)

6.

Matter soluble in water            

0.5% (max.)

7.

Matter soluble in HCL 

2.5% (max.)

8.

CaO

0.007% (max.)

9.

Fe2O3

0.7% (max.)

10.

MnO   

0.013% (max.)

11.

Oil absorption

50ml per 100g (min.)

(D) Paints:
China clay is used as an extender of suspending agent in the manufacture of while paints. The BIS has not standardized any specification for this use. However, the properties like anti-setting and tinting effects, colloidal nature, softness, freedom from grit, white color and fine size are some of the qualities which make chain clay suitable for use in paint and distemper manufacture.

(E) Cosmetic and Pharmaceutical:
There is no BIS specification. Superfine china clay is utilized for the manufacture of products like power, adhesives, surgical plaster, lotion and ointment for external use, porcelain for dental preparation. Chinaclay for medicinal purpose must be free from lead, arsenic and other metals that the human body will not tolerate. It should have no frothing. Particle size, frothing and sedimentation volumes are the three important factors considered in the selection of china clay for pharmaceutical purpose.

(F) Filler in paper:
Inferior grade china clay may be used in the manufacture of brown paper, newsprint, hardboard paper and straw paperboard. The BIS (IS: 505 1978) have standardized the specification as given below:

S. No.            

Characteristics      

Filler Paper

1.

Residue on 53 micron IS Sieve

1.00% (max.)

2.

Particles larger than 10 micron in diameter.

20.0% (max.)

3.

Particles smaller than 2 micron in diameter.       

35.0% (max.)

4.

Loss on drying.

6.0% (max.)

5.

Loss on ignition

14.0% (max.)

6.

Matter soluble in water            

0.5% (max.)

7.

Matter soluble in HCL 

2.5% (max.)

8.

Fe2O3

0.7% (max.)

9.

pH value of aqueous extract

4.50 to 7.5%


G. Insecticides:
China clay is used in the manufacture of disinfectant like DDT. The BIS (IS: 505 1978) has standardized the specification for use of china clay in insecticide industry as given below:

S. No.            

Characteristics      

Insecticide

1.

Residue on 53 micron IS Sieve

2.0% (max.)

2.

Particles larger than 10 micron in diameter.

20.0% (max.)

3.

Particles smaller than 2 micron in diameter.       

35.0% (max.)

4.

Loss on drying.

6.0% (max.)

5.

Loss on ignition

14.0% (max.)

6.

Matter soluble in HCL 

2.5% (max.)

7.

As2O3

10 ppm (max.) 

8.

Fe2O3

0.70% (max.)  

For used of china clay in other industries like white cement and refractory bricks, there is no standard specification what so ever. In case of manufactures of refractory bricks, the coarse fraction of china clay from the sedimentation tank is used.

Due to lack of adequate data, no attempt could be made in the inventory as on 01.01.1985 to classify the reserves of china clay according to its end use grades.

After examining the specifications standardized by BIS and the trends in the user industries, the group recommends end use classification of reserves: -

(A) Ceramic:

1.

Water elasticity

32%

2.

Shrinkage after drying

7% (max.)

3.

Shrinkage after firing

14% (max.)

4.

Color after firing

Perfectly white

5.

Grit     

2% (max.)

6.

Fe2O3  

1% (max.)


(B) Textile & Paper Coating:

1.

Residue on 53 micron IS Sieve

0.1% (max.)

2.

Particles larger than 10 micron in diameter.

5.0% (max.)

3.

Particles smaller than 2 micron in diameter.       

62.0% (max.)

4.

Relative density at 27o C

2.5 to 2.9

5.

Loss on drying.

6.0% (max.)

6.

Loss on ignition

14.0% (max.)

7.

Matter soluble in HCL 

2.5% (max.)

8.

Fe2O3

0.7% (max.)

9.

Color reflectance to blue light of water, length 3040Ao 

80 - 85 %


(C) Rubber:

1.

Residue on 53 micron IS Sieve

0.1% (max.)

2.

Particles larger than 10 micron in diameter.

7.0%

3.

Particles smaller than 2 micron in diameter.       

50.3% (min.)

4.

Loss on drying.

2.0% (max.)

5.

Loss on ignition

14.00% (max.)

6.

Matter soluble in water            

0.5% (max.)

7.

Matter soluble in HCL 

2.5% (max.)

8.

CaO

0.007% (max.)

9.

Fe2O3

0.7% (max.)

10.

MnO   

0.013% (max.)

11.

Oil absorption

50ml per 100g (min.)


(D) Filler in Paper:

1.

Residue on 53 micron IS Sieve

1.00% (max.)

2.

Particles larger than 10 micron in diameter.

20.0% (max.)

3.

Particles smaller than 2 micron in diameter.       

35.0% (max.)

4.

Loss on drying.

6.0% (max.)

5.

Loss on ignition

14.0% (max.)

6.

Matter soluble in water            

0.5% (max.)

7.

Matter soluble in HCL 

2.5% (max.)

8.

Fe2O3

0.7% (max.)

9.

pH value of aqueous extract

4.50 to 7.5%


(E) Insecticide:

1.

Residue on 53 micron IS Sieve

2.0% (max.)

2.

Particles larger than 10 micron in diameter.

20.0% (max.)

3.

Particles smaller than 2 micron in diameter.       

35.0% (max.)

4.

Loss on drying.

6.0% (max.)

5.

Loss on ignition

14.0% (max.)

6.

Matter soluble in HCL 

2.5% (max.)

7.

As2O3

10 ppm (max.) 

8.

Fe2O3

0.70% (max.)  


Fire Clay
The name fire clay is given to a group of refractory clays, which can stand temperatures above PCE 19. Fire clay in generally sedimentary in origin and is mainly found in coal measures as bedded deposits. In nature fire clay is usually found to contain Al2O3, SiO2 oxides of calcium iron, titanium and magnesium and alkalies. Refractories and plasticity are the two main properties needed in fire clay for its suitability in the manufacture of refractory bricks. However, all fire clays are not necessarily plastic clays. Depending upon the refractoriness fire clay can be used for manufacture of low duty, high duty or super duty firebrick.

The only industry in which fireclay is used is refractory industry. The I.S.I has not standardized any specification. Recently, the sub-committee on Refractory raw materials appointed by the Directorate General of Technical Development (DGTD) has recommended the following seven specifications.

(a) Non-plastic / semi-plastic clay

Grade - I

Grade - II

Grade - III

Al2O3

35.4%

32 - 35%

30 - 32%

Fe2O3

1.0% max.

1.0 - 1.5%

1.5 - 2%

PCE

33 (min.) (Orton)

32 (min.)

30 (min.)

(b) Plastic clay

Grade-I

Grade-II

Grade-III

Grade-IV

Al2O3

30 - 32%

28 - 30%

22 - 28%

18 - 20%

Fe2O3

1 - 1.5%

2 - 3%

1 - 2%

1.5 - 2%

PCE

30 (min.) (Orton)

28 (min.)

26 (min.)

18 - 21

In the inventory as on 01.01.1985 (as also in earlier inventories), no attempt has been made to classify the reserves according to different grades.

After examining the specifications prescribed by the Sub-Committee on Refractory Raw Materials of the D. G. T. D., the group recommends the following end-use classification of reserves:

(a) Non-plastic / semi-plastic clay

Al2O3

30% (min.)

Fe2O3

2% (max.)

PCE

30 (min.) (Orton cone)

(b) Plastic clay

Al2O3

18% (min.)

Fe2O3

3% (max.)

PCE

18 (min.) (Orton cone)

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