The effect of lutetium dopant on oxygen permeability of alumina polycrystals under oxygen potential gradients at ultra-high temperatures

Control of Polymorphism and Mass-Transfer in Al2O3 Scale Formed by Oxidation of Alumina-Forming Alloys

“…Retardation of such mass transfer can be explained by a 'siteblocking' mechanism (Amissah et al, 2007, Cheng et al, 2008, Priester, 1989, Korinek et al, 1994 and/or grain boundary strengthening (Yoshida et al, 2002, Buban et al, 2006. Under the oxygen potential gradients used in this study, it was found that oxygen diffusitivity was unaffected by 0.05 mol% lutetia-doping (Matsudaira et al, 2010), and even for 0.2 mol% doping, the retardation was small compared to the effect in uniform environments. This may be related to the generation of a large number of oxygen vacancies in the vicinity of the grain boundaries under an oxygen potential gradient, despite the fact that Lu 3+ is isovalent with Al 3+ .…”

“…This phenomenon will be useful for elucidating how much the migration of oxygen and aluminum is affected by REs segregated at the grain boundaries. In this chapter, the effect of lutetium doping on oxygen permeability in polycrystalline alumina wafers exposed to steep oxygen potential gradients was evaluated at high temperatures to investigate the mass-transfer phenomena through the scale (Matsudaira et al, 2010). It is well known that lutetium doping can significantly improve high-temperature creep resistance in polycrystalline alumina (Matsunaga et al, 2003, Ikuhara et al, 2001, Yoshida et al, 2002; therefore, it is also expected to retard mass-transfer in alumina under oxygen potential gradients.…”

“…Equation (4) is applicable to the case of ideal oxygen permeation when there is no interaction between electrons and holes, or when either electrons or holes exclusively participate (Kitaoka et al, 2009, Matsudaira et al, 2010.…”

Grain Boundary Engineering of Alumina Ceramics

“…Polycrystalline alumina wafer specimens with or without REs such as Ln (Lu, Y) and Hf, which were cut from the sintered bodies and polished to a mirror-like finish, served as a model scale for the measurement of oxygen permeability constants using a technique described in detail elsewhere [16][17][18][19][20][21][22][23][24]. Ln doping was expected to effectively retard mass-transfer in alumina under application of a dµ O because Ln can significantly improve high-temperature GB creep resistance in polycrystalline alumina [25][26][27].…”

“…Therefore, it is extremely difficult to quantitatively determine the degree of influence for individual factors that influence the movement of each diffusion species. The oxygen permeability technique with polycrystalline α-alumina wafer, which served as a model scale, is thus expected to be very useful to accurately evaluate mass-transfer through the wafers because the dµ O applied to the wafers and the diffusion length are constant [16][17][18][19][20][21][22][23][24].…”