HIGH-TEMPERATURE ELECTRICAL CONDUCTIVITY AND DEFECT STRUCTURE OF DONOR-DOPED ALPHA - ALUMINUM OXIDE
Abstract (summary)
Direct current electrical conductivity and the corresponding ionic and electronic transference numbers deduced from emf measure-ments of oxygen and/or hydrogen concentration cells with Al(,2)O(,3) as an electrolyte are used to study the defect structure of Al(,2)O(,3) doped with hydrogen and yttrium. Hydrogen is found to be a donor and is used to exactly compensate an acceptor dominated material in order to determine the parameters of native ionic and electronic disorder in Al(,2)O(,3). Hydrogen solubility in Al(,2)O(,3) increases with decreasing the temperature of anneal, T(,sat), increasing P(,H(,2)),(,sat )and increasing P(,O(,2)),(,sat).(,)
Yittrium, though isolectronic with aluminum, acts as a donor,
(DIAGRAM, TABLE OR GRAPHIC OMITTED...PLEASE SEE DAI)
The observed favorable effect of yttrium additives on the oxidation of iron-chromium-aluminum super-alloys is attributed to its donor action in Al(,2)O(,3): the presence of
(DIAGRAM, TABLE OR GRAPHIC OMITTED...PLEASE SEE DAI)
species decreases the concentration of
(DIAGRAM, TABLE OR GRAPHIC OMITTED...PLEASE SEE DAI)
species without markedly increasing the
(DIAGRAM, TABLE OR GRAPHIC OMITTED...PLEASE SEE DAI)
concentration and thus causes the oxidation process to take place at the oxide-alloy interface leading to adherent, nonconvoluted protective scales.