# Evaluation of Factors Affecting the MgO-C Refractory Lining Degradation in a Basic Oxygen Furnace
## 1 Introduction
According to Equation (3), oxidation and sedimentation from the gas phase results in the formation of a dense, fine-grained periclase layer, which slows down the corrosion process of the MgO-C refractory by the barrier effect [13]. Despite the slowing down of corrosion by the dense layer, the reacted MgO (Equation (2)) is restored to the oxide form (Equation (3)), and the process still results in the loss of carbon [14]. Therefore, various forms of antioxidants have been used to mitigate such effects and enhance the oxidation resistance of MgO-C refractories [15; 16; 17]. \[2\mathrm{C}_{(s)}+\mathrm{O}_{2(g)}\to 2\mathrm{CO}_{(g)} \tag{1}\]  
\[\mathrm{C}_{(s)}+\mathrm{MgO}_{(s)}\to\mathrm{CO}_{(g)}+\mathrm{Mg}_{(g)} \tag{2}\]  
\[2\mathrm{Mg}_{(g)}+\mathrm{O}_{2(g)}\to 2\mathrm{MgO}_{(s)} \tag{3}\]  
Regarding kinetics, corrosion depends on the rate at which the slag drains MgO from the lining [18]. Therefore, saturating the slag with MgO is a simple way to reduce the dissolution potential of the major lining component, reduce its wear, and thus prolong the life of the structure [19]. The phase ratios in the system MgO-SiO\({}_{2}\)-R\({}_{2}\)O\({}_{3}\)--RO phase--(P\({}_{2}\)O\({}_{5}\)) are indicative of the amortization of the base lining from a chemical point of view. In slag with CaO/SiO\({}_{2}\) < 1, the periclase does not coexist and, therefore, dissolves. As the CaO/SiO\({}_{2}\) ratio (basicity) increases, the solubility of periclase decreases significantly, while at CaO/SiO\({}_{2}\) > 2, it changes insignificantly [20]. The corrosion rate of the MgO-C refractory lining is also affected by grain size, where small grains of MgO dissolve in the early silicate BOF slag to form Ca and Mg silicates. It is more difficult for the slag to penetrate the larger grains of MgO; therefore, the slag penetrates the lining along the grain boundaries [21]. Porosity also affects the corrosion rate of the MgO-C refractories. Low porosity reduces the surface area available for reaction with the melt [4]. It is advantageous if the pores are sufficiently filled with carbon compounds, which also increases density and reducesthe wettability of the MgO-C material [6]. The depth of BOF slag penetration depends on the refractory density, as it determines the size of the building material's contact area for reaction with the slag [5; 22]. The carbon in MgO-C refractories affects the corrosion process by reducing iron oxides, thus limiting their contact with the refractory lining. As the carbon in MgO-C increases, the wettability by BOF slag decreases; meanwhile, the pore surface area increases due to carbon depletion [23; 24; 25; 26]. The wettability is an important factor influencing the wear kinetics of the MgO-C refractory material. The wettability by molten BOF slag is critically dependent on the BOF slag's viscosity and surface tension, as well as the chemical reactions and adsorption at the interface MgO-C refractory--BOF slag. From a metallurgical point of view, the lowest possible wettability of the MgO-C material is desirable [4; 5; 21; 27]. The amount of MgO in the BOF slag also influences the corrosion kinetics of the MgO-C refractory. In practice, dolomitic lime, burnt dolomite, or caustically burnt magnesite is added to BOF slag because the low MgO slag has a high solubility capacity with the slag. The usual MgO additions range from 8% to 10% [19; 28; 29]. A major challenge for carbon-containing refractories is the oxidation of non-oxide constituents, particularly carbon. Various additives are incorporated as antioxidants to protect the castable from oxidation [30]. Metallic silicon and aluminum powder are the most extensively used antioxidants in MgO-C refractory compositions [5; 31; 32]. The slag that passes through the porous structure of the MgO-C refractory stops its penetration at a depth corresponding to the solid phase crystallization temperature. This phase comprises the slag and building material components [27].