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Advantages And Disadvantages Of Malo Refractory Bricks

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1. Introduction:
MgO-CaO or Mag-Dol refractory bricks have been considered as one type of chrome-free refractory bricks that are suitable for substituting the MgO-Cr2O3 refractories [1]. Typically, MgO-CaO refractory bricks composed of 50-80 wt. % of magnesia(MgO) [2]. There are two ways for produce MgO-CaO refractory bricks. The first way is using fused and sintered Co-clinker of magnesite(MgCO3) and dolomite(Mg.Ca(CO3)2) as a starting material for produce the MgO-CaO refractory bricks which would lead to more homogenous products with more desirable properties. Another way is mixing magnesite and dolomite together and calcination them at high temperature that let to produce an in–situ MgO-CaO refractory bricks …show more content…

The addition of nanoparticles must be more effective in decreasing the dihedral angle and encouraging direct bonding in comparison to micro-particles. In the present research, this phenomenon can be explained as follows: during the sintering process the nanoparticles (Al2O3 and Fe2O3) react with the CaO in matrix leading to the formation some low melting point phase’s in a faster way. Consequently, the capillary force from the wetting liquid eliminate porosity and reduce interfacial area. Since, diffusion rates in liquid are relatively high, this phenomenon results in faster bonding and densification with its corresponding improvement in physical and mechanical properties [14]. Also, For sample contains 3 wt.% Cr2O3 nanoparticles a homogeneous microstructure composed mainly of a well-distributed phases is observed. Using energy dispersive X-ray spectroscopy analysis (EDX), as a second phase, there are two phases surrounded by the magnesia and calcia ground mass. The first one corresponds to light gray particles composed by Ca and Cr elements, as it was identified by EDS. This phase is a spinel compound found in the XRD analysis and identified as CaCr2O4. The last phase corresponds to bright grey particles composed by Mg and Cr elements (identified by the EDS technique, (Table). From the EDS and XRD analysis, this phase was confirmed …show more content…

Hydration resistance Fig. shows the effect Fe2O3, Al2O3 and Cr2O3 nanoparticles addition on the hydration resistance of MgO-CaO specimens. Materials based on MgO and CaO can undergo hydration in humid atmosphere. In this case the powder grains break, the material is pulverized, and articles crack [3-9]. Several methods such as using pitch, tar, flake, and vein graphite minerals, treating MgO-CaO materials in a CO2atmosphere or addition of different oxide additives, such as V2O5 [11], CuO [12], FeTiO3 [13], La2O3 [14], TiO2[], Ce2O [15], ZrO2 [16], and Fe2O3, have been tested to control the hydration resitance of MgO-CaO refractories. all methods lead the accession of CaO and MgO to the moisture to decrease From Fig. it is observed that the mass gain of MgO-CaO specimens decreased with addition of Fe2O3, Al2O3 and Cr2O3 nanoparticles. For sample without addition, the mass gain after 96 hours was %, which was decreased with increasing the amount of nanoparticle additives. Increasing the amount of additives reduces the weight gain due to more grain growth and lower grain boundary and porosity for the samples contain nano Fe2O3 and Al2O3, and covered free CaO and MgO phases. The degree of hydration is related to the absorption of water on the crystal defect and grain boundary surface. It is known that the hydration resistance of CaO

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