Effect of borate addition on the sintered properties of pulverised fuel ash

The effect of borate addition on the properties of sintered pulverised fuel ash (PFA) has been investigated. PFA from a major coal-fired power station in the UK has been formed into monolithic ceramic samples using dry powder compaction and sintering. Borax pentahydrate (Na2B4O7·5H2O), anhydrous borax (Na2B4O7) and boric acid (H3BO3) were individually added to the PFA and the effects of firing between 1000 and 1200 °C have been investigated. Physical properties (density, water absorption and linear shrinkage), mechanical properties (bending strength and Vickers hardness), phase composition (X-ray diffraction) and sintered microstructure (scanning electron microscopy) are reported. Milling PFA containing 8% (by weight) of borax pentahydrate, to an average particle size of 7.25 μm and sintering at 1130 °C for 1 h, produces ceramics with properties comparable to those of commercial unglazed ceramic wall and floor tiles. The results indicate that PFA could be used to produce commercial ceramics using an economic manufacturing process, although current formulations display excessive shrinkage.