Ceramics-Silikáty

The critical points of refractory materials are the fine fraction (matrix) and the binder system ensuring mechanical strength during operation and after exposure to operating temperatures. In the case of biomass combustion in energy aggregates, it is advisable to use high-alumina and/or MgO refractory castables with a binder system without SiO₂ and CaO. Commercial refractory castables introduce SiO₂ and/or CaO components into the refractory castable as components of the binder system. The developed MgO refractory castable with alumina sol-gel bonding is a two-component material (MgO-MgAl₂O₄). In this work, the resistance of refractory castables (commercial high-alumina/Al₂O₃-CAB, and MgO-based/ MgO-S/G-For, and developed MgO castable/ MgO-S/G-Sp) against wood-waste ash was compared. The measured flow temperature of the ash was approximately 200 °C lower than the corrosion test temperature (1450 °C). The results of the corrosion static crucible tests carried out with ash confirmed: i) the porosity and pore size had a significant impact on the mechanism of corrosion by the low-viscosity melt; ii) the fine-grained components periclase, spinel, in situ spinel, reactive alumina in the matrix of refractories resisted K₂O-CaO-SiO₂ ash melt; the K₂O components CaO and SiO₂ penetrated through the pores into the matrix and slowly dissolved the grains, iii) increasing the Al₂O₃ and MgO concentration in the corrosive melt increased its viscosity, which slowed down the penetration of the melt through the porous matrix; iv) the thermally stable corrosion products eliminated the porosity and the corrosion barrier, a layer that slowed down the corrosion process. In developed (MgO-MgAl₂O₄) refractory castables with an alumina sol-gel bond, it is necessary to reduce the open porosity below a 15 vol.% and eliminate the proportion of pores of size ˃ 20 μ m. The corrosion mechanism of a refractory material with higher open porosity varies significantly with the viscosity of a corrosive glass-melt, i.e., not only with the composition of the melt, but also with the temperature. The material will need to be tested in a dynamic corrosion mode, under conditions simulating the conditions of biofuel combustion in high-temperature aggregates, and under these conditions, the corrosion mechanism will have to be described.