Belite clusters and crystal sizes  Belite crystals begin to form in a kiln feed at quite an early stage of burning at contact points between silica and lime particles.   Very fine, poorly formed crystals can be present at temperatures below 800 ᵒ C, before the feed has entered the rotary kiln in a preheater system. The mineral belite is normally present in the cement kiln as one or more of three polymorphs known with increasing formation temperature as β , α ’ (alpha prime) and α . There is also a lower temperature form γ which is very rare in clinker and also the α ’ is subdivided into low and high temperature forms.  In the cement kiln as the temperature rises above 1100 ᵒ C   belite is present as α ’ crystals. These are very fine, relatively pure crystals which grow only slowly until, at about 1400 ᵒ C, they undergo a transformation to larger crystals of α belite. The α form absorbs impurities as it rapidly grows. In the burning zone of the kiln most of the belite crystals

Clinker cooling The cooling of clinker covers the period from when it passes the hottest part of the burning zone until it reaches ambient temperature in storage. The microstructure of the clinker and the properties of the cement which is produced from it can be strongly affected by this stage of production depending on factors such as the distance from the burning zone from the kiln outlet, the range of temperatures through which the clinker minerals pass, the presence of rings or snowmen, whether coating is loose or the cooler  type and the rate of cooling after leaving the rotary kiln. Slow cooling is generally a negative influence on quality for reasons which can be observed by microscopic examination of clinker as discussed below. Matrix crystal size The liquid phase of cement clinker comprises the aluminate phase and the ferrite phase as well as a few others such as the alkali sulphates. When a liquid cools below its crystallisation temperature the size of the cryst

Arthur Harrisson - Clinker microscopy  Arthur Harrisson trained as a geologist and worked for the British Geological Survey for five years before joining the Research Department of Blue Circle Cement. There he developed an expertise in cement chemistry and cement clinker microscopy. He has since occupied the positions of plant chemist, quality and environmental officer and chief chemist For Rugby Cement (now CEMEX) and Buxton Lime and Cement (part of Tarmac). Since 2010 he has operated a microscope laboratory in North Wales where he has examined clinkers from all around the World. Arthur also uses his experience with cement raw materials to assess the quality of potential reserves and to assist in Due Diligence operations prior to major sales but this note refers to the examination of clinker by optical microscopy. This is a very brief summary of the possibilities for operational and quality improvements using regular microscopic examination. Further information can be f