We are facing a problem in bringing the whiteness of material that is close to cement composition in our RandD trials. We would like to know the effect of each oxide and cooling method on whiteness of the material.

The principal colouring oxides are those of the first row of the transition metals. In cement the most likely to cause problems are iron, manganese and chromium in that order. The cooling of the clinker is absolutely fundamental to achieving the desired whiteness. You must (i) burn the clinker as close to the nose ring as possible to eliminate the possibility of oxidation of FeO to Fe₂O₃ in the kiln, and (ii) immediately quench cool the clinker in water. Air-cooled blast furnace slag can be added to the inlet of the cement kiln in the patented Cemstar process developed by TXI cement in the USA. I know a number of US cement companies are doing this. This is in the manufacture of cement powder. Another use is as an aggregate in the manufacture of concrete.

I would be very interested to hear any pointers you might have about where how best to get started on using microscopy as a further tool for examining clinker ? Where training might be obtained ? Anyone you might recommend that I could contact and who could possibly come on site and provide this training ?

An article describing the work we have been doing in Slovakia will appear in the February 2003 issue of International Cement Review. In part this describes how microscopy is used in combination with pattern recognition in hour-to-hour control of the real mineralogy of clinker.