The most important application of CaO in metallurgy is based on fact that it can react with silicates forming the mixture of oxides - the slag. From this point of view the iron and steel industry is very important user of lime because of for each tonne of produced iron approximately 80 kg of lime is used. Besides the using of lime as flux there is the possibility to use it as an active lining in order to improve the steel quality. Succesful implementation of such high refractory material with melting point of approx 2600 deg C could have some economical profit due to lack of high quality raw materials. Production of refractory materials includes the pre-treatment of raw materials, followed by shaping and high-temperature firing process in order to gain of semi-product or end product. There are not so many papers available dealing with pretreatment of raw material, i.e. limestone by milling. However, there exist some information about structural changes in milled magnesite, dolomite and calcite but still no sufficient knowledge to explain the behaviour of such materials. The energy-consuming milling process is often avoidable operation when various raw materials are treated and milling time optimization should save the energy. On the other hand, the real structure of materials could be fairly affected by milling. For this purpose the X-ray diffraction analysis could be used. The effect of milling time on structure of limestone and consequently on properties of CaO after burning at 1550 deg C by using of X-ray diffraction method were studied in this work.
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