Heating effects on physical and strength characteristics of fireclay from the Nigerian Coal Measures Formation

The phase and oxidation changes upon heating a fireclay are accompanied by changes in physical and mechanical properties of the clay. Tests were carried out on the fireclay to a maximum temperature of 1300°C. Upon heating, the colour changed slightly from dull grey to light grey. The bulk density continuously increased with increasing temperature. The specific gravity remained fairly constant up to the dehydration temperature of clay bodies, which is about 500°C. It subsequently dropped appreciably, bottomed out at about 550°C and then rose continuously at higher temperatures. At about 900°C it showed maximum rate of rise with temperature. The hot strength on heating remained constant up to around 700°C. Thereafter it increased sharply to a peak of about 10 × 103 kN/m2 at about 900°C. Clay cubes, continuously heated up to 1300°C and crushed as they were cooled to selected temperatures, showed a behaviour different from that on heating. On cooling from the peak temperature the strength significantly improved up to a temperature of about 800°C and then remained fairly constant to room temperature. The difference in strengths on heating and cooling can be attributed to a better and uninterrupted heating schedule in the latter. Test results indicate good quality fireclay. The presently underutilized clay has a lot of potential uses in a number of industries such as ceramic, rubber, paint and construction.