Dense zircon (ZrSiO4) ceramics by high energy ball milling and spark plasma sintering

The addition of sintering additives has always been detrimental to the mechanical properties of sintered ceramics; therefore, methods to reduce or, as in this case, eliminate sintering additives are usually relevant. In this paper, dense zircon ceramics were obtained starting from mechanically activated powder compacted by spark plasma sintering without employing sintering additives. The high energy ball milling (HEBM) of starting powder was effective to enhance the sintering kinetics. The structural changes of the zircon powder introduced by the HEBM were evaluated. The phase composition and the microstructure of bulk zircon material were analyzed by SEM (EDAX) and XRD. The Vickers hardness and the fracture toughness were evaluated as well. Fully dense materials were obtained at 1400 °C with a heating rate of 100 °C/min, 10 min soaking time and 100 MPa uniaxial pressure. The zircon samples sintered at temperatures above 1400 °C were dissociated in monoclinic zirconia and amorphous silica. The dissociation was detrimental for the mechanical properties. Unlike conventional sintering methods (hot pressing, pressureless sintering) SPS permitted to overcome the dissociation of the zircon material and to obtain additive free, fully dense zircon ceramic with outstanding mechanical properties.