Ms. Noy Fabri MSc candidate
David Wang Auditorium, 3rd floor Dalia Meidan Bldg.
It is well known that dopants and/or impurities can cause significant changes to the grain boundary mobility of materials. This can occur by equilibrium (Gibbsian) segregation of solutes to grain boundaries, generating solute-drag or solute-acceleration. Alternatively, dopants and/or impurities above the solubility limit can result in precipitation of secondary phases which can reduce grain boundary mobility by Zener drag. It has been proposed that precipitation of secondary phases in the liquid state accelerate grain growth kinetics while some studies reported a decrease in grain growth rate in the presence of a liquid phase. More recently, the influence of external electromagnetic fields has been demonstrated to increase sintering kinetics, and to change grain growth kinetics. Part of the ongoing debate on both subjects stems from the fact that densification and grain growth experiments were usually combined. To reduce the complexity and enable fundamental research on these phenomena, the present study focuses only on grain growth of dense polycrystalline alumina as a function of the parameters previously described.
In this study, the effective grain boundary mobility of dense alumina was measured as a function of key dopants (at concentrations above and below the solubility limit), atmosphere, and applied external fields. High purity alumina as well as industrial alumina was used. Over one order of magnitude increase in effective mobility was observed in all samples annealed in an electromagnetic field, regardless of dopant concentration. This includes samples doped with Mg, which is known to reduce grain boundary mobility by solute drag. Furthermore, the addition of a liquid phase at grain boundaries decreased the effective mobility of grain boundaries, which has practical implications for industrial processing of alumina. The possible means by which dopants and/or fields affect the mechanism(s) of grain boundary motion will be discussed.