Formation of Nickel, Cobalt, Copper, and Iron Aluminates fromα- andγ-Alumina-Supported Oxides: A Comparative Study
✍ Scribed by P.H. Bolt; F.H.P.M. Habraken; J.W. Geus
- Publisher
- Elsevier Science
- Year
- 1998
- Tongue
- English
- Weight
- 651 KB
- Volume
- 135
- Category
- Article
- ISSN
- 0022-4596
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✦ Synopsis
The rates of metal aluminate formation in MeO x /Al 2 O 3 systems (Me ؍ Ni, Co, Cu, Fe) at 500-1000°C in O 2 or N 2 atmospheres were compared, using both -Al 2 O 3 and -Al 2 O 3 substrates. Interfacial reaction to MeAl 2 O 4 was assessed using Rutherford backscattering spectrometry and X-ray diffraction. The lateral homogeneity of the samples was investigated using scanning electron microscopy. The spinel formation rate follows the sequence FeAl 2 O 4 ( (NiAl 2 O 4 ( (CoAl 2 O 4 ( (CuAl 2 O 4 . This is explained in terms of thermodynamic limitations (FeAl 2 O 4 ) and site-preference energies (CoAl 2 O 4 , NiAl 2 O 4 ). The fast reaction to copper aluminate was accompanied by a severe rupture of the top layer (:1 m) of the substrate. Penetration of transition metal ions into -Al 2 O 3 substrates is notable at considerably lower temperatures than with -Al 2 O 3 substrates, mainly due to grain boundary diffusion. Annealing conditions that favor the formation of transition metal cations of a low valency (Co 2؉ , Cu ؉ ) are beneficial for reactions to aluminates.