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A thermogravimetric study of the oxidative growth of Al2O3/Al alloy composites

Vlach, KC and Salas, O and Ni, H and Jayaram, V and Levi, CG and Mehrabian, R (1991) A thermogravimetric study of the oxidative growth of Al2O3/Al alloy composites. In: Journal of Materials Research, 6 (9). pp. 1982-1995.

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Abstract

The oxidation of liquid Al–Mg–Si alloys at 900–1400 °C was studied by thermogravimetric analysis (TGA). The development of a semi-protective surface layer of MgO/MgAl2O4 allows the continuous formation of an Al2O3-matrix composite containing an interpenetrating network of metal microchannels at 1000–1350 °C. An initial incubation period precedes bulk oxidation, wherein Al2O3 grows from a near-surface alloy layer by reaction of oxygen supplied by the dissolution of the surface oxides and Al supplied from a bulk alloy reservoir through the microchannel network. The typical oxidation rate during bulk growth displays an initial acceleration followed by a parabolic deceleration in a regime apparently limited by Al transport to the near-surface layer. Both regimes may be influenced by the Si content in this layer, which rises due to preferential Al and Mg oxidation. The growth rates increase with temperature to a maximum at ~1300 °C, with a nominal activation energy of 270 kJ/mole for an Al-2.85 wt. % Mg-5.4 wt. % Si alloy in O2 at furnace temperatures of 1000–1300 °C. An oscillatory rate regime observed at 1000–1075 °C resulted in a banded structure of varying Al2O3-to-metal volume fraction.

Item Type: Journal Article
Additional Information: Copyright of this article belongs to The Materials Research Society.
Keywords: Aluminum;Oxides;Carbon;System.
Department/Centre: Division of Mechanical Sciences > Materials Engineering (formerly Metallurgy)
Date Deposited: 09 Nov 2010 08:33
Last Modified: 08 Jul 2011 07:45
URI: http://eprints.iisc.ernet.in/id/eprint/33636

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