Magnesia Doloma Refractories Case Study

2.3 Magnesia-Doloma Refractories:
The MgO-CaO system is remarkable for the high liquidus and solidus temperatures over the complete range 100% MgO- 100% CaO, as the eutectic for the CaO–MgO binary system occurs at 2370 ºC [3, 52]. MgO–CaO bricks are high-value refractories composed of lime (CaO) and periclase (MgO). MgO –CaO refractories has some advantageous and disadvantageous compared to MgO and CaO refractories (Table 1).

Table 1

Typically, these refractories are composed by 50-80 wt. % of MgO . MgO-CaO refractories are considered as one type of chrome-free refractories that are suitable for substituting the MgO-Cr2O3. Different ways have been proposed to produce MgO-CaO refractories. A new approach is using sintered and fused
The results showed that the doping of NiO to natural dolomite changed the lattice constants of CaO and MgO and made the MgO lattice distortion happen, which consequentially reduced the activation energy of the grain growth and promoted the sintering of the dolomite. Without additive the bulk density and the apparent porosity of dolomite clinker after the sintering at 1600°C were 3.30 g/cm3 and 3.4%, the crystal size of MgO only was 3.26 μm. But when the addition of NiO accounted to 0.75%, the bulk density and the apparent porosity of dolomite clinker after the sintering at 1600°C were 3.33 g/cm3 and 2.7%, respectively. At same time, the crystal size of MgO reached to 3.54 μm[78]. Zhang Han et al. [74] studied the effect of CaF2 on the sintering properties of MgO-CaO materials. The results show that with increasing the addition of CaF2, the bulk density of the samples increased, while the apparent porosity decreased and the densification of MgO-CaO materials promoted. When the amount of CaF2exceeded 2wt. %, the densification degree of samples decreased. The nature of CaF2promoting densification of MgO-CaO materials could be concluded as follows: due to its thermal defects, F-entered into the octahedral voids that existed in CaF2crystal structures and produced F-vacancies with positive charge, then combined with O2-vacancies by electrostatic attraction during the migration process, which increased the diffusion speed of O2-and enhanced the diffusion of MgO, then promoted the growth of periclase grains. A. Ghosh et al. [73] the studied the densification and properties of lime with V2O5 additions. For this