Wetting, cladding and corrosion properties of alkaline slag on dense corundum refractories

The alkaline slag produced in the process of recovering heat and Na2CO3 in the black liquor heat treatment of papermaking leads to damage to refractory materials. In this paper, the wetting and erosion cladding properties of alkaline slag on the surface of dense corundum refractories were studied. The experiment was conducted in a high-temperature tubular furnace with different atmospheres (oxidizing atmosphere and reducing atmosphere), various heating rates (10 °C/min, 15 °C/min, 20 °C/min), and multiple angles between the refractory and horizontal planes (0°, 5°, 10°, 15°, 20°). The wetting process of the slag on the refractory surface was observed by a CCD camera. The apparent contact angle and slag column height were measured with ImageJ software. The microstructure, element change and compounds of the cladding layer and interface layer were analysed using SEM-EDS and XRD. The results show that the corrosion of refractories by the slag comes from the following procedure: alumina dissolved and migrated to the cladding layer, then the slag penetrated the dense corundum refractories through the grain boundaries and the channels formed by the dissolution of alumina. Thermodynamic calculation and analysis of experimental results show that the slag and refractories dissolved each other at high temperature and reacted with each other to form mullite, nepheline and feldspar.