Clay firing

Clays are classified into six groups by the U.S. Bureau of Mines (1) kaolin, ball clay, fire clay, bentonite, fuller s earth, and common clay and shale. About half the toimage of clays produced in the United States is in the last category. In terms of monetary value, however, ka olin accounts for about two-thirds of the doUar volume. 

Figure 7. Test bars of Egyptian clays fired in the thermal gradient...

MASS PROPORTION Fe203 / CaO IN CALCIUM CONTAINING CLAY FIRING COLOUR... 

Turner and Turner [36] found the attack on the clay fired at 1400°C to be less corrosive than on the same clay fired only at 1300°C. A rapid increase in the extent of corrosion occurs with an increase in test temperature. Between 800 and 900°C, the rate of attack increases severalfold. The resistance to corrosion was found to be dependent on the density of the clay body as well as on chemical composition. 

Brick clays tend to be high in alkalis and iron, but low in alumina [14], The clays usually have moderate to high plasticity, which facilitates forming [25], Often, brick clays are actually shales [14], These clays fire at moderate temperatures (cone 1-5) and the resulting fired bodies are dark red. Clays with similar properties but different colors upon firing can be used to produce other products such as sewer tile and roofing tile [6], Nearly any red burning clay can be classified as brick clay. 

CERAMIC ware made of slightly POROUS opaque clay fired at low temperature. 

It is important in the manufacture of pottery that the clays are white-firing —when fired they should be just off-white or pale cream, and most ball clays fulfil this requirement. The South Devon clays are reported to fire whitest ( off-white to creamy-white ) the North Devon clays fire pale ivory to ivory , and those of Dorset fire ivory , buff or red. 

The materials that fulfil all the conditions stated in this definition are kaolin, china clay, bentonite, bleaching earth, common clay, ball clay, fire clay, and refractory clay. The different aspects of the definition are explained below. 

Figure 4.6 Calcareous illitic clay fired under strongly reducing conditions (fo2 < 10 atm Ni/ NiO buffer) at 1035°C. (a) Anorthite crystallized from glassy phase (b) Orthorhombic pseudohexagonal crystals of iron cordierite (Heimann etal., 1980).

Figure 4.7 Experimentally determined phase stability in a calcareous illitic clay fired in (a) oxidizing and (b) reducing atmospheres. Under oxidizing conditions, illite is found to be stable to higher temperatures, while...

Class 0 - Any totally inorganic material such as concrete, clay, fired clay, metal, plaster and masonry... 

The DTA technique has been applied to examine the fire clay products for underfiring. An example has been provided by Honeybome. In Fig. 28, thermograms of a brick from a certain locality are given. (A) refers to the locality, (B), (C), and (D) show the thermograms of the same clay fired to 600, 800, and 1000°C. The increase in the firing temperature modifies the thermograms, and at 1000°C, only the peak due to the inversion of quartz (570°C) remains. Curve (E) refers to a sample of facing... 

Clay (fire, ball, bentonite) Hydrated alumino- Filler, flow/rheology control... 

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