4831621704

135

1.6

1.8 2.0 Apparent density (g/cm^J)

2.2

5    10

Loss on ignition (wt. %)

15

Figurę 5.7

Linear regression and correlation between different bricks properties fired at 1050°C.

5.3.2.2 Color change

The color of sintered bricks is one ofthe factors that affect the bricks cjuality. Multiplc colors are developed by brick industries (red, yellow, grey, etc.) to meet the growing market demand. The naturo of the desired color is affected and controlled by the Chemical elements in the raw materials. Therefore, it was important to assess the variation of the color in calamine wastes based bricks. The review documentation suggested that the finał color of bricks depends significantly on the mass ratio of FezO.i/AhO? in calcium-poor clay and FezCh/CaO in calcium-rich clay (Bormans, 2004). Also, it is known that during the sintering process, particularly in oxidation atmosphere, the transformation of Fe^:^ to Fe³ inereases and the reddish color is accordingly enhanced. Generally, hematite (FezO?) gi\es a red color and magnetite (Fe?Ot) is responsible ofthe grey color. Likewise, the yellow color is caused by high