Influência dos sais MgCl2 e CaCl2 no comportamento de hidratação do MgO

Abstract

Magnesium oxide (MgO) is a material of great technological interest for the steel making industry due to its competitive cost and high corrosion resistance when in contact with molten basic slags. However, the hydration of this oxide, resulting in Mg(OH)2, is followed by a significant volumetric expansion, preventing its use in refractory castables. This reaction can be affected by various parameters, such as: magnesia source, its purity level and reactivity, pH medium, CaO/SiO2 ratio of the mixture and the hydration time. In this work, suspensions containing different MgO sources (caustic or dead-burnt) and salts (MgCl2.6H2O and CaCl2.2H2O) were prepared in order to evaluate the hydration reaction and the deleterious effects associated with this transformation. Thermogravimetry, apparent volumetric expansion, scanning electron microscopy and X-ray diffraction techniques were used to follow the Mg(OH)2 formation. According to the results, the dead-burnt MgO (calcined at high temperatures)-based samples presented lower degree of hydration after curing at 50 °C for 7 days in humid environment (relative humidity =80%) and the expansive effects were minimized with the addition of 0.7 wt% of CaCl2.2H2O to this material.