Novel Applications of Redox Reactions in Metal Ceramic Systems
Helen M. Chan
Fulbright Visiting Prof. (FELMI-TUG) and Dept. Materials Science & Engineering, Lehigh University, Bethlehem PA
17:15 - 18:15 Tuesday 17 January 2017 TUG P2 This talk will discuss two widely different applications of oxidation-reduction reactions. The first of these relate to the synthesis of novel ceramic-metal nanostructures1,2, the second to oxygen transport measurements in alumina doped with so-called reactive elements3,4.
1) Unique microstructures, comprising interpenetrating mixtures of metallic and ceramic phases can be achieved from the reduction of complex oxides of the type MIMIIOx+y. The less stable oxide is reduced, leaving the metal (MI), and the other oxide (MII Oy). Examples of ceramics which have been shown to be amenable to this approach include CuAlO2 (delafossite) and CoTiO3. CuAlO2 is of interest to the electronics community because it is a p-type transparent semiconductor. Processing of the bulk precursor oxides will be discussed, together with the influence of reduction conditions on the resulting ceramic metal structures.
2) During the oxidation of high temperature alloys, a slow-growing, protective alumina surface layer forms in-situ. The rate of growth of this layer is critical to the degree of oxidation resistance of such alloys, as well as to the lifetime of thermal barrier coatings. Certain additive elements (e.g. Y, Hf) can have a beneficial effect on the oxidation rate; this is the so-called reactive element (RE) effect. The rate of oxygen transport was probed by testing model alumina samples (both doped and undoped) containing a fine dispersion of Ni marker particles. A comparison of the oxidation rate constants and activation energies will be presented for undoped and RE -doped alumina, and discussed in terms of the grain boundary segregation behavior of these elements.
1. M. Kracum, A. Kundu, M.P. Harmer and H.M. Chan, “Novel Interpenetrating Cu-Al2O3 Structures by Controlled Reduction of Bulk CuAlO2” J. Mater. Sci., 50 (2015) 1818-24
2. Z. Yu, M. Kracum, A. Kundu, M.P. Harmer, H.M. Chan, “Microstructural Evolution of a Cu and θ-Al2O3 Composite Formed By Reduction of Delafossite CuAlO2: A HAADF-STEM Study,” Crystal Growth and Design, 16 (2016) 380–385
3. Q. Wu, H.M. Chan. J.M. Rickman, and M.P. Harmer, “Effect of Hf 4+ Concentration on Oxygen Grain-Boundary Diffusion in Alumina,” J. Am. Ceram. Soc., 98 (2015) 3346-51
4. Z. Yu, Q. Wu, J.M. Rickman, H.M. Chan and Martin P. Harmer, “Atomic - Resolution Observation of Hf-doped Alumina Grain Boundaries,” Scripta Mat. 68 (2013) 703-706
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