On the influence of antioxidants and recycled MgO–C source material on the mechanical properties of carbon-bonded magnesia refractories

In the present study, the role of recycled source material and the addition of antioxidants to refractory MgO–C material commonly used in the steel industry were addressed from the perspective of fracture mechanics. Initially, the fracture behaviour of the fine grained MgO–C-matrix was assessed by sequential bending experiments (particle sizes <150 μm). Based on this, coarse grained parts with particle sizes up to 7 mm were prepared and characterised in regard to their high-temperature properties, i.e. the refractoriness under load, the thermal expansion behaviour and the Young's modulus as function of the temperature. Four differently designed batches were tested. One batch, consisting of all fresh source materials (MgO and C), served as reference. Furthermore, the additives Al, SiO₂ and TiO₂ were systematically added, and 50% of the source material was replaced by recycled MgO–C from the industry. During the batch production, environmentally friendly fructose, collagen and lignin served as temporary binding agents. It was found that while the addition of recycled MgO–C had a reducing effect on the mechanical properties, the opposite was observed for the addition of antioxidants.