Corrosion mechanism of silica bricks containing high amorphous for hot stoves

Abstract

Increasing the temperature of hot stoves renders previously reliable silica bricks unstable. In this study, investigations on postmortem silica bricks used in hot stoves for more than 10 years were conducted, and the corrosion mechanism of the bricks during service was analysed. The results show that silica bricks prepared using CaO-FeOx mineralizers have excellent corrosion resistance to alkaline gases such as K2O(g) and Na2O(g) in hot stove gas, but are severely affected by Al2O3 microparticles or CO(g) owing to their high amorphous content. The high amorphous content is due to the use of CaO-FeOx mineralizers to eliminate quartz from silica bricks. Under the working conditions of the hot stove, the amorphous SiO2–CaO-FeOx in the brick transitions towards SiO2–CaO–Al2O3-FeOx liquids with a high Fe2+/Fe3+ ratio owing to the attachment of Al2O3 microparticles and the reduction of CO(g) on Fe3+. This transformation reduces the viscosity of the liquid and enhances its solvent effect on SiO2, thereby accelerating the dissolution-crystallisation of SiO2 in the liquid and the migration of the liquid in the brick, ultimately leads to the structural rearrangement of the brick. After more than 10 years of service, the postmortem brick displays perforations of varying sizes, reaching a maximum diameter of 5 mm. Its structure is characterised by two distinct sections with obvious interfaces: the upper part exhibits a high-porosity structure with a porosity greater than 20 %, while the bottom is dense with a porosity of less than 10 %. The delamination of the postmortem brick is caused by the long-term migration of liquids under the action of gravity, whereas the accumulation of the liquid also forms obvious transverse microcracks in the brick owing to its hysteresis response to temperature changes. A corrosion model was constructed to demonstrate the corrosion mechanism of silica bricks in a hot stove.