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The production of cement clinker is one of the most important industrial processes at world scale. Many technological innovations have been developed in order to increase the production at a lower cost, having in mind that the materials are exposed to severe operational conditions. The fabrication process of modern Portland clinker basically involves the firing at around 1500°C of limestone-CaCO3 accompanied by silica-SiO2 sources such as clays, sand, iron ore, shale, fly ashes and slags. The final product is a synthetic mineral called clinker which is basically formed by four crystalline phases: alite (Ca3SiO5), belite (β-Ca2SiO4), tricalcium aluminate (Ca3Al2O6) and ferrite (Ca2(AlxFe2-x)2O5); and other minor common components. Therefore the process involves aggressive basic environments and atmospheres, with high alkali and sulphur contents, that can strongly modify the microstructure and phase composition of the refractories of the kilns work zone (Kingery et al., 1976). On the other hand, over the last decades the substitution of fossil fuels for alternative or industrial wastes; such as rubber, used tires, fly ashes, among others; has affected drastically the useful life and performance of the refractory bricks which coat the rotary kilns. Nowadays the burning zone of the kilns is exposed to alkali salts, chlorine, sulphur oxides, proceeding from industrial by products or hazardous products of animal origin, that enhance the corrosion process of the kilns refractory. This technological problem is the reason for focussing in the development of new suitable refractories. Improvements have been made by using higher purity raw materials; however there are economic limits and therefore other more sustainable alternatives are necessarily searched. According to the modern tendencies in refractories the improvements in the thermal, chemical and mechanical properties of refractories are related to the optimization of the matrix, through the careful design of the mixture of the phases and the microstructural characteristics. As it is well known the performance of these structural parts is a function of the grain material, the nature of the bonding phase, and the distribution and shape of grains and pores. The increase in the proportion of “direct” bonding between refractory aggregate grains is very important. Furthermore the microstructural bonding is the main attribute for an adequate refractory matrix because it contributes to the resistance by the combination of rigidity and sufficient structural flexibility in order to prevent the formation of cracks and disintegration of the hot phase.

Characterization of the Firing Steps and Phases Formed in Mg-Zr-Containing Refractory Dolomitic Materials