The role of zircon particle size distribution, surface area and contamination on the properties of silica–zircon ceramic materials

Zircon is used as an additive to silica ceramics for use in investment casting to improve their high temperature properties. However, little is known about the mechanisms by which this occurs. To investigate the effect of zircon addition to a silica ceramic a number of silica–zircon formulations were created utilising three different batches of zircon with different particle size distributions (PSDs), surface areas and contaminant inclusions. The contaminant inclusion of the zircon, present in the zircon from the ball-milling stage of manufacture, appeared to have a large effect on the room temperature flexural strength, high temperature flexural strength and high temperature creep properties. It is also suggested that any increase in post-fired cristobalite content and any change to crystal growth morphology was due to the inherent contaminant inclusions and not because of the zircon itself. Hence, use of silica–zircon materials in ceramics for investment casting should account for variation in the contaminant inclusion of the zircon in order to maintain the specific material properties required.