Monoaluminum phosphate-bonded refractory castables for petrochemical application

Phosphate-bonded refractories may be applied as repairing materials due to their short setting time and good thermo-mechanical properties in the 30-1000 °C temperature range. This works addresses the development of vibratable high-alumina castables containing commercial monoaluminum phosphate (MAP) solutions (Fosbind 151 and Fosbind 50) and dead-burnt magnesia (d<212 µm, setting agent) as the binder systems. Flowability, setting time, X-ray diffraction, cold erosion, thermal shock resistance, cold and hot modulus of rupture, thermogravimetric measurements and hot elastic modulus tests were carried out in order to understand the phase evolution and thermo-mechanical behavior of the refractories. Furthermore, the effect of adding a boron source (sintering additive) to the phosphate-bonded compositions was also investigated. According to the attained results, the reaction of MAP with MgO and the reactive aluminas of the compositions resulted in setting times of the mixtures around 90-120 min at 30 °C, which was associated with the in situ generation of magnesium and aluminum phosphates [MgHPO4·3H2O, Mg(H2PO4)2(H2O)2 and AlPO4.2H2O]. The boron-containing castables presented Al18B4O33 around 650-800 °C and this phase favored the increase of the samples' stiffness, mechanical strength, erosion and thermal shock resistance. The refractoriness under load measurements indicated that the maximum working temperature for the evaluated refractories was in the range of 1400-1500 °C.