# Evaluation of Factors Affecting the MgO-C Refractory Lining Degradation in a Basic Oxygen Furnace
## 3 Results
### Refractory Lining Wear Mechanism in Basic Oxygen Furnace
#### 3.6.3 Protective Layer Formation Mechanism of Gunning Material on MgO-C Refractory Lining in BOFs  
Gunning repair materials are characterized by easy sinterability, connectivity, and self-compacting ability due to the formation of dicalcium ferrite (Ca\({}_{2}\)Fe\({}_{2}\)O\({}_{5}\)) (Equation (9)). The MgO-2 CaO.SiO\({}_{2}\) system melts at 1800 \({}^{\circ}\)C. The melting point is rapidly reduced to 1308 \({}^{\circ}\)C by the presence of 2 CaO.Fe\({}_{2}\)O\({}_{3}\). The cumulative value of Fe\({}_{2}\)O\({}_{3}\) causes an increase in melt quantity. If this state is not changed, the layer of gunning material is destroyed and washed away. A significant change is caused by the decomposition of dicalcium ferrite (Ca\({}_{2}\)Fe\({}_{2}\)O\({}_{5}\)), which is unstable at low O\({}_{2}\) partial pressure, or by a reduction in the gaseous environment of CO.  
\[4\ \mathrm{CaO}+4\ \mathrm{FeO}+\mathrm{O}_{\mathrm{(g)}}=2\ \mathrm{Ca}_{2}\mathrm{Fe}_{2} \mathrm{O}_{5} \tag{9}\]  
In the strong reduction environment, Ca\({}_{2}\)Fe\({}_{2}\)O\({}_{5}\) begins to reduce from 900 \({}^{\circ}\)C to form finely diffused CaO, FeO, and Fe. If there is sufficient MgO in the system and the temperature exceeds 1200 \({}^{\circ}\)C, FeO enters into solid solution in periclase, and CaO is excluded as a solid phase beyond solubility. The process occurs by Equation (10):  
\[2\ \mathrm{Ca}_{2}\mathrm{Fe}_{2}\mathrm{O}_{5}+\mathrm{x}\ \mathrm{MgO}=(\mathrm{x}+4)\ \mathrm{(Mg,\ Fe)O}+4\ \mathrm{CaO}+\mathrm{O}_{2};\ \mathrm{x}>9.3 \tag{10}\]  
The condition for the layer of gunning mixture to be formed and solidified is that it is covered with metal or the partial pressure of O\({}_{2}\) is sufficiently low, and CO is present in significant concentrations. An analysis of the mechanism by which the gunning repair mix detaches from the refractory lining indicates that the FeO content of the converter slag, as well as the FeO content of the gunning material itself, has the greatest effect on the process by which the gunning mixture detaches from the BOF refractory lining. Since the gunning repair mixes are only chemically bonded to the converter-shaped refractory lining, there is a synergy with BOF converter slag infiltration into the gunning material to detach the gunning mixture from the converter-working refractory lining. This leads to an increased consumption of gunning repair mixture, as documented in Figure 23.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Iron Oxide**} & \multirow{2}{*}{**Reaction**} & \multicolumn{2}{c}{**\(\Delta\)G kJ.mol\({}^{-1}\)**} \\ \cline{3-4}  & & **1300 \({}^{\circ}\)C** & **1700 \({}^{\circ}\)C** \\ \hline \multirow{2}{*}{Fe\({}_{2}\)O\({}_{3}\)} & Fe\({}_{2}\)O\({}_{5}\) + 3C = 2 Fe + 3 CO & \(-\)332.842 & \(-\)534.580 \\ \hline \multirow{2}{*}{FeO} & FeO + C = Fe + CO & \(-\)88.797 & \(-\)144.791 \\ \hline \hline \end{tabular}
\end{table}
Table 13: The most expected carbon reactions from refractory and iron oxides.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Name**} & **Chemical** & \multicolumn{2}{c}{\(\Delta\)G kJ.mol\({}^{-1}\)} & **Melting** \\  & **Formula** & **1300 \({}^{\circ}\)C** & **1700 \({}^{\circ}\)C** & **Point \({}^{\circ}\)C** \\ \hline \multirow{2}{*}{Larnite} & Ca\({}_{2}\)SiO\({}_{4}\)(L) & \(-\)141.138 & \(-\)148.840 & – \\ \hline \hline \end{tabular}
\end{table}
Table 12: Thermodynamic parameters of incipient dicalcium silicate.