BRUCITE-BASED MAGNESIUM PHOSPHATE BONDING AGENT, ITS ANALYSIS AND APPLICATION FOR PERICLASE SINTERING

Abstract

Some results on magnesium phosphate binder obtained from natural brucite (mainly Mg(OH)2) and H3PO4 were discussed. Hereafter, it was named brucite phosphate (BPB). This binder then was used to the sintering of MgO (periclase). MgO is one of the most high-refractory materials and chemically stable to various aggressive mediums, so the aim was presented as actual. To determine the phase composition data on sample weight loss in different temperature intervals were compared. All weight losses were related to the multistage water moving away. Up to 140 °С it was the removal of crystalline hydrate water. Then monosubstituted magnesium hydrophosphate transformed into MgH2P2O7 and Mg2P4O12, that in principle was in accordance with literature data. Dehydration was accompanied with appropriate endothermal effects. There was a slight exothermal effect which could relate to a structure rearrangement (cyclization) of primary magnesium metaphosphates and/or some crystallization of anhydrous cyclophosphates from primarily obtained amorphous phase non-connected with a weight loss in the interval of 450-575 °С. At 500–1000 °С the phase composition remained constant that was in a good accordance with data obtained by other methods. By means of IR-spectroscopy, it was confirmed the formation of structure cycles composed from oxygen-phosphor tetrahedrons. To determine kinetics parameters of periclase sintering with BPB it was used a model being proposed that took the role of a physical consolidation and a chemical binding in the presence of binder into account under heating. The obtained parameters analysis showed that the forming conglomerate strength was provided with the sintering properly as well as with binder action; an estimated chemical factor contribution was maximal at low temperatures (1100-1200 °C). The activation energy value was practically identical to the activation energy of oxygen diffusion in MgO.