## 4 Summary and Conclusions
Based on the results from FactSage of equiweight mixes castable with slag, the samples of 50 wt.% castable and 50 wt.% slag firing temperature of 1350 \({}^{\circ}\)C were selected for the X-ray diffraction (XRD) analysis. This allowed for a phase analysis because the synthesis processes took place, and the liquid phase content was so small that it did not affect the test results.XRD analysis allowed us to observe significant qualitative differences between the sample with a lower C/S mass ratio and the remaining samples. A graph was compiled with no-corroded castable C (7 wt.% Of MgO) with an equilibrium phase composition and three mixtures C_S1, C_S2, and C_S3. Note that only for sample C_S1, CAS2 was found during the analysis, which, together with gehlenite, reduces the melting point, and thus, causes the appearance of the liquid phase at lower temperatures. X-ray results carried out on the equiweight castable and slag mixes confirm the thermal analysis and the presence of the phases calculated by FactSage. HMTA showed that the CAS2 phase detected in the XRD analysis, observed only for the castable sample with the slag S1 (lowest C/S mass ratio), has a significant impact on the castable shrinkage caused by the formation of the liquid phase. The static corrosion test was conducted by means of the coating method on rectangular castable samples in contact with slag sat 1450 \({}^{\circ}\)C. The samples were tested in a perpendicular direction to the slag-refractory interface. The corrosion index \(I_{C}\) in the regions of castables affected by slags was calculated in the MATLAB program. Phases and phase distributions were evaluated by SEM-EDS on polished samples of castables (7 wt.% MgO) with slags S1, S2, and S3. On the basis of the analysis, SEM images were obtained, allowing for the determination of the distribution of individual phases in the sample, as well as for the determination of zones and subzones formed as a result of corrosion. A relationship was observed between the mass ratio of C/S in the slag and the tendency to form reaction zones. For the slag S1 with the lowest mass ratio C/S, only the slag zones below the slag-refractory interference contact line were observed, while for slags S2 and S3 with a higher mass ratio C/S, there are zones both above the slag-refractory interference and below the slag-refractory interference contact line. Based on the SEM-EDS analysis, it was found that the CA2 and CA6 phases form the deepest in the material. Some amounts of free oxides (MgO) could be observed for samples C_S2 and C_S3 above the contact line slag-refractory material. Moreover, the zone below the contact line slag-refractory material was slightly degraded. Thus, the reactions mainly ran between the slag components upstream of this line, and the CA2 phases of CA6 prevented further material degradation. The highest corrosion tendency, determined on the basis of \(I_{C}\), concerns the concretes with the lowest C/S ratio, which is confirmed in the HRTM analysis (sample with the highest shrinkage) and also in the SEM images, where the reaction zone was only below the slag-refractory material contact line. The most important conclusions from this work are included in several points:As the content of SiO\({}_{2}\)-rich phases in the slag increases, the tendency for accelerated liquid phase formation in a narrow temperature range also increases. * The macroscopic image is influenced by the composition and quantity of the liquid phase. * CAS\({}_{2}\), formed as a result of corrosion of the slag with a lower C/S content, reduces the temperature of the liquid phase formation and increases the degradation of the material
* The lower the C/S mass ratio in the slag, the greater the area of castable that will be degraded.