The effect of rare-earth dopants on the texturing of alumina under high-strength magnetic field

The use of magnetic fields in ceramic processing has been of interest recently for tailoring the microstructural grain alignment of ceramics in order to improve mechanical, optical, and other properties. However, a number of challenges exist, including the low magnetic response of most ceramic materials (e.g. alumina), and the lack of low viscosity bulk casting systems available for forming ceramics in a magnetic field. In this work, the low magnetic response of alumina was addressed by adding small amounts (~0.04 atom%) of various rare-earth dopants to phase-pure α-alumina to enhance the response of the bulk material, as supported by previous predictive modeling. After identifying the dopant with the highest magnetic response according to a novel, average facial angle alignment metric, a low-viscosity colloidal casting system, based on a single organic additive was selected to allow for the sintering of formed green bodies. This novel process was used to cast bulk ceramic parts under a magnetic field. The effect of magnetic alignment both in the green state and after sintering was investigated. It was found that both erbium and ytterbium improved the magnetic response of alumina, and that the alignment achieved in the green state was maintained through the sintering process, despite removal from the magnetic field.