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Wilson P.J.,University of Birmingham | Wilson P.J.,Ross Ceramic Ltd. | Blackburn S.,University of Birmingham | Greenwood R.W.,University of Birmingham | And 2 more authors.
Journal of the European Ceramic Society | Year: 2011

The amount of alumina contamination present in ball-milled silica powders has been shown to increase with increased mill time for materials manufactured during the same time period. This alumina contamination level has also been observed to vary depending on the date, and possibly the state of repair, of the ball mill itself. The associated alumina level has been shown to significantly influence the high temperature properties (at 1475°C) of the materials, with high contamination levels not only resulting in increased flexural strength and creep resistance, but also increasing the thermal contraction of the materials when dilatometer measurements were performed to 1600°C. © 2011. Source


Wilson P.J.,University of Birmingham | Wilson P.J.,Ross Ceramic Ltd. | Blackburn S.,University of Birmingham | Greenwood R.W.,University of Birmingham | And 2 more authors.
Journal of the European Ceramic Society | Year: 2011

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. © 2011 Elsevier Ltd. Source

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