Sintered silicophosphate glass ceramics from MBM ash and recycled soda–lime–silica glass

Abstract

Meat and bone meal ash, mixed with recycled soda–lime–silica glass and small amounts of additives, was successfully valorised in the processing of sintered glass ceramics, after melting and forming two calcium phosphate glasses. Sintering was applied to fine powders (<37 μm) at temperatures of 700–1070°C for 0·5–2 h, after very rapid heating (40°C min−1). Mixtures with small additions of CaO and CaF2 led to fluorapatite–wollastonite glass ceramics, which retained a significant porosity even at 1070°C, due to the delay in viscous flow caused by rapid crystallisation. This feature was exploited for strong open celled macrocellular glass ceramics, obtained by sintering glass powders mixed with polyethylene sacrificial templates. Mixtures with small additions of CaO and Na2O led to dense and strong combeite glass ceramics (bending strength, >100 MPa), sinterable at particularly low temperatures (800°C). Both porous and dense glass ceramics could be exploited as low cost and high strength materials, or even as biomaterials, due to the biocompatibility of the crystal phases.