Mineralizing alumina–magnesia cement-bonded castables containing magnesium borates

Add time:07/29/2019    Source:sciencedirect.com

In situ spinel (MgAl2O4) generation in Al2O3–MgO refractory compositions at high temperature is pointed out as one of the most important reactions to improve their thermo-mechanical performance in service. However, this transformation effectively takes place above 1200 °C. Magnesium borates are alternative compounds that can be used as mineralizer agents to speed up such a reaction. Aiming to develop improved spinel-containing castables and identify the impact of adding boron-based additives to the mixtures, this work evaluated the phase evolution of aqueous suspensions, matrix (fine components) and overall Al2O3–MgO refractory compositions containing 0% or 1%-p of a magnesium borate source. According to the XRD results of the castables׳ matrix, spinel formation took place at relative low temperatures (above 850 °C) due to reactions involving 1 wt% of the added magnesium borates and the available alumina sources (reactive alumina or Al2O3 containing in the cement). In general, these samples also presented lower elastic modulus values in the range of 30–1400 °C, which was mainly related to the presence of the liquid phase, volumetric expansion associated to spinel and CA6 formation. Faster MgAl2O4 and CA6 generation observed in the sinterability measurements indicated that the consequent drawback of the selected mineralizer addition was the greater volumetric expansion of the Al2O3–MgO refractory, leading to flaws nucleation and affecting its porosity level.

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