Clinker cooling takes place in two stages, the first cooling stage occurrs within the kiln and the second occurrs in the clinker cooler.

The rate of cooling within the kiln depends upon the flame length, the position in the kiln and the throughput and speed of the kiln charge. The temperature of clinker at the outlet of the kiln is around between 1350 ^oC and 1200 ^oC. If the flame is long, this part of the cooling process will be very slow and alite and belite can grow into an excessive crystal size. In some cases, (when the cooler efficiency is low) alite partially decomposes into belite and free lime (see fig. 1).

Fig.1: Alite decomposition into belite and free lime. 250 X

The texture of the solidified liquid phase is quite dependent on the cooling rate. During slow cooling, the crystals have time to grow. Ferrite and aluminate form a coarsely grained matrix (see fig. 2). Alternatively, if the cooling process proceeds quickly, the opposite is true - the crystals are fine grained (see fig. 3).

Fig.2:	Differentiated aluminate (grey) and ferrite (white) caused by slow cooling. 640 X	Fig.3:	Finely grained aluminate and ferrite due to rapid cooling. 250 X

Cooling can also proceed so quickly that the crystals can only form in the submicroscopic range. Distinction between aluminate and ferrite is no longer possible by microscopy but can be effected by X-ray methods.