High-alumina phosphate-bonded refractory castables: Al(OH)3 sources and their effects

Abstract Monoaluminium phosphate [Al(H 2 PO 4 ) 3 or MAP] is pointed out as the most applied chemical binder in the refractory field due to its solubility in water, high bonding strength and reaction with basic and amphoteric raw materials at low temperatures. Nevertheless, different routes can induce the in situ generation of Al(H 2 PO 4 ) 3 in castable compositions. This work evaluates the effect of two Al(OH) 3 sources added to refractory formulations or H 3 PO 4 solutions (with distinct concentrations) in order to highlight their influence on the phase evolution and thermo-mechanical properties of the prepared samples. Various experimental tests (flowability, setting time, cold and hot mechanical strength, thermogravimetric measurements, X-ray diffraction and hot elastic modulus) were carried out. According to the attained results, the most promising binding system was obtained by the mixture of H 3 PO 4 solution with 48 wt% of concentration+Al(OH) 3 particles prior to preparing the castables. Furthermore, the work suggests that a systemic analysis of various parameters (acid concentration, liquid solution amount, type and amount of setting and sintering agents, etc. ) should be conducted in order to attain improved phosphate-bonded products.