Carbon in the lining material is deposited from the products of combustion as a consequence of establishing the equilibrium of the Boudouard-Bell reaction and thus allowing the formation of low-meltable eutectic melts under reduction conditions. The difference in heat conductivity coefficients between grain and fire sand results in preferential deposition of carbon in the fire sand grain boundary (aggregate) – the binding phase produced by firing the initially hydraulic bond.

Treating aggregate to increase its resistance against carbon deposited on ceramics increases its lifespan and improves the corrosion resistance of refractory concrete monoliths.

Refractory material produced using an unequal content of aluminium oxide in the fire sand and binder is known to show worse refractory characteristics.

Fire sand is usually a phase with a higher content of aluminium oxide. A lower content of Al₂O₃ in the binder worsens the rheological behaviour of the material in heat and reduces its resistance against corrosion caused by melts and gases.

By reducing iron compounds with carbon monoxide or carbon deposited under the temperature equilibrium of the Boudouard reaction, eutectic melts of a low melting temperature are formed, which considerably decrease the heat and chemical resistance of the refractory lining and compromise its stability.

An increase in the resistance of refractory concretes used for lining the monolithic linings of heat units against the effect of carbon deposited on ceramics is achieved by modifying the aggregate (e.g. bauxite, fire clay, shale etc.) by surface treatment using whitewash. 

Whitewash for treating the aggregate surface is prepared using lime, dolomitic lime or semi-burnt lime (a mixture of MgO and CaCO₃).

By subsequent calcination at ≤1100 °C, a crust of hard-burnt lime forms on the aggregate grain surface under which an inter-layer is formed, the composition and thickness of which depends on the composition of the aggregate, the lime used for preparation of the whitewash, the temperature and time of calcination.

Aggregate grain treated in this way has increased resistance against the influence of eutectic iron melts under reduction conditions. At the same time, the wetting angle of the fire sand surface treated in this way by eutectic melts increases by ~20 % in the system SiO₂ – Al₂O₃ – Fe₂O₃, which also contributes to the overall increase in its resistance.

Carbon, which as a result of the Boudouard reaction does not deposit on the interface between the fire sand grain and the binding phase but in the layer of hard-burnt lime on the surface of the treated aggregate, further decreases its wetting by melts (e.g. melted slag); the corrosion resistance of the material is thus considerably increased. When using the material in applications where it might come into contact with melted slag, it is therefore appropriate to treat the fire sand surface with a thicker layer and use higher calcination temperatures.

The utility of this technology developed in the Faculty of Chemistry at Brno University of Technology consists in the greater resistance of refractory concretes used for the monolithic linings of heat units against the effects of carbon deposited on ceramics, and thus enables an increase in the resistance and an extension in the lifespan of the refractory linings of heat units heated using solid, liquid or gaseous fuels. The chance of material failure due to the negative effects of carbon deposited on ceramics is reduced, while the resistance of the refractory material against the influence of eutectic melts rich in iron oxides is increased. 

It is possible to foresee this licence having a wide application in industry, both in foundries and other branches of industry in which melts are processed using high-temperature processes. The increase in the corrosion resistance of linings is advantageous and attractive for the commercial sector.