Abstract

Phosphate-bonded refractories may be applied as repairing materials due to their fast setting time and good thermo-mechanical properties in the 30-1000°C temperature range. Phosphoric acid and monoaluminum phosphate (MAP) solutions are commonly used as main binder additives in chemically-bonded compositions, but solid phosphate compounds can also be applied for this purpose. This work addresses the design of vibratable high-alumina castables containing MAP (liquid) or magnesium monophosphate (powder) as binding agents. Various experimental tests (flowability, setting time, cold and hot mechanical strength, thermal shock resistance, and others) were carried out and the developed compositions were compared with commercial products of different refractory producers. According to the attained results, both evaluated additives (MAP solutions or magnesium monophosphate) are very effective and they have the advantage of not inducing the castables’ temperature increase (such as the case of mixtures prepared with phosphoric acid) during the mixing and curing steps. Furthermore, the addition of a sintering additive (boron-based compound) to the evaluated formulations resulted in enhanced thermo-mechanical performance (mainly cold and hot mechanical strength, thermal shock and erosion resistance) in the 600-1000°C temperature range.