Oxygen Transport in Melts Based on V 2 O 5
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INTRODUCTION
METALS may experience accelerated oxidation in contact with V2O5 at elevated temperatures in air. This phenomenon was called a catastrophic oxidation of metals (COM).[1–9] In catastrophic oxidation, metal is subject to degradation at much higher rates than in ordinary high-temperature oxidation. It is established that the COM is caused by the formation of oxygen ion-conducting liquid channels in the oxide scale.[7–9] A high oxygen ionic conductivity is also established in V2O5-containing molten slags.[10] As molten slags are widely used to metal production,[11,12] the study of transport properties of oxide melts is important. The transport property data are needed to (i) solve industrial problems with process control and improve product quality and (ii) develop mathematical models of the process. In this paper, a model of oxygen ion transport in melts based on V2O5 is developed. II.
EXPERIMENTAL DATA
is higher than the k00 value of non-deposited copper oxidation by two orders of magnitude (Table I). The threshold temperature 833 K (560 °C) for catastrophic oxidation of the V2O5-deposited copper coincides with the eutectic point of Cu2O and V2O5. The existence of continuous liquid channels across the oxide scale was confirmed by the microstructure data.[9] The dependence of oxygen flux through the partly molten V2O5-12-18 wt pct CuV2O6 composites (simulating an oxide scale formed on the copper surface during COM) on the volume fraction of liquid is presented in Figure 2. The oxygen flux increases with volume fraction of liquid. B. Transport Properties of Slags The oxygen fluxes through the partly molten BiVO4-5 to 12 wt pct V2O5 and ZrV2O7-25 to 40 mol pct V2O5 slags as well as their oxygen ion transport numbers and electrical conductivities were measured.[10] Some results of the measurements are presented in Figures 3 and 4.
A. Kinetics of COM The V2O5-deposited copper experiences catastrophic oxidation at 833 K (560 °C) in air.[7–9] The kinetics of copper oxidation (in parabolic coordinates for different amounts of V2O5 deposit) is presented in Figure 1. Catastrophic oxidation of the V2O5-deposited copper is seen to follow a parabolic rate law which indicates that the process is diffusion-controlled, i.e.,: m2 ¼ k00 t; ½1 S where m is the mass, S is the metal surface area, k00 is the parabolic rate constant (kg2 m4 s1) and t is the time. The k00 value of V2O5-deposited copper oxidation
ANTON KLIMASHIN, Senior Researcher, and VALERY BELOUSOV, Head of Department, are with the A.A. Baikov Institute of Metallurgy and Materials Science, Russian Academy of Sciences, Leninskii pr., 49, Moscow, Russia, 119991. Contact e-mail: vbelousov@ imet.ac.ru Manuscript submitted February 25, 2015. Article published online November 30, 2015. METALLURGICAL AND MATERIALS TRANSACTIONS B
C. Structure of Molten V2O5 The structure of molten V2O5 and some double oxide systems based on it was studied by NMR, X-ray, neutron, and electron diffraction, etc.[13–22] It was established that the intramolecular coordination of atom
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