High‐Temperature Conductivity and Creep of Polycrystalline AI₂O₃ Doped with Fe and/or Ti

Abstract

Partial ionic and electronic dc conductivities and compressional creep rate were measured for hot-pressed polycrystalline AlrOs made from Al-isopropoxide (A1203(II)). The undoped material was found to contain 1.5X 1OI8 cm-J fixed valency acceptors (Mg). Properties of undoped material and material doped with Fe or Ti were investigated as a function of grain size, dopant concentration, oxygen pressure, and temperature. No fast ionic conduction along grain boundaries is found in either acceptor-or donor-dominated material. Absolute values of self-diffusion coefficients calculated from conductivity and creep indicate that both effects are limited by migration of Al, involving VAl"' in donor-, Al, ' . ' in acceptor-dominated material.In creep, oxygen is transported along grain boundaries in a neutral form (Oix). The po2 dependence of u, and oh are as expected on the basis of a defect model. That of creep is weaker for reasons that are not entirely clear. An ionic conductivity with low activation energy, observed a t low temperature, is attributed to the presence of AI-silicate second phase.

Current Isolation in Spark Plasma Sintering of Conductive and Nonconductive Ceramics

“…To evaluate the potential current flowing through the Al 2 O 3 sample, calculations for bulk Al 2 O 3 can be used as a minimum requirement. Because of impurities and measurement techniques, reported resistivity values vary in the literature even for undoped Al 2 O 3 18–21 . Using the lowest reported room temperature resistivity (1 × 10 13 Ω·m), 18 the current passing through a 1‐mm‐thick compact with 6 V applied would be a negligible 6 × 10 −13 A.…”

Electric‐Field Effects on Sintering and Reaction to Form Aluminum Titanate from Binary Alumina–Titania Sol–Gel Powders

“…The presence of TiO 2 in the system and its dissolution in Al 2 O 3 leads to an additional increase of electrical ionic conductivity of the latter. 20 Therefore, the applied electric field may create locally high temperatures with increased apparent diffusivities at particle surfaces, thereby enhancing densification.…”

Plastic deformation kinetics of fine-grained alumina

“…It is proposed [10][11][12][13] [2] to 6 ϫ 10 Ϫ4 Heuer et al [3] 1.2 to 10 99ϩ pure, 2500 CSR-C 1100 to 1700 2 ϫ 10 Ϫ6 6 to 170 1.1 to 1.6 2.5 490 to 570 GBS at smaller MgO to 3 ϫ grain sizes 10 Ϫ4 Sugita and 3 99ϩ 2300 MgO CR-C air 1300 to 1470 3 ϫ 10 Ϫ7 6.7 to 10 1.1 to 1.3 -400 to 520 local plastic Pask [4] and 2200 to 1 ϫ deformation NiO 10 Ϫ5 [5] to 2 ϫ 10 Ϫ6 Hou et al [6] 3 to 100 98ϩ pure, 80 Ti, CR-C O2 1400 to 1500 2 ϫ 10 Ϫ7 [7] to 3 ϫ 10 Ϫ4 Heuer et al [8] 1 to 5 --bend CSR-1315 to 1450 -20 to 55 ----C El-Aiat et 1 to 40 99ϩ various Fe CR-C O2 1400 to 1600 -5 to 50 1.2 to 1.3 2, 3 -DC-Al 3ϩ Dl al. [9] and Ti Porter [ [13] to 1 ϫ diffusion 10 Ϫ4 Cannon et 1 to 3 99ϩ 2 mol pct CR-C bend air O2 1000 to 1200 3 ϫ 10 Ϫ8 4 to 7 1.6 --GBS al. [14] ( [15,16] to 1 ϫ 10 Ϫ4 Venkatchari 1.6 99.5 2500 MgO CR-C -1420 2 ϫ 10 Ϫ4 5 to 65 ---DC-Al 3ϩ Dl and Raj [17] Gruffel et 0.66 to 1.5 99.5ϩ 500 MgO and CR-T air 1250 to 1450 1 ϫ 10 Ϫ6 10 to 30 ---SPD al.…”

“…The value and tempersizes between 1.35 and 2.50 m obtained by sintering for ature dependence of the shear modulus, G, were taken from 1 hour at 1550 ЊC to 1600 ЊC. Important to mention is that Frost and Ashby, [9] where for initial grain sizes larger than 2.5 m, the specimens broke in a brittle fashion at the test temperatures with very…”