The chemical diffusivity of oxygen in liquid iron oxide and a calcium ferrite
- PDF / 253,530 Bytes
- 10 Pages / 612 x 792 pts (letter) Page_size
- 7 Downloads / 185 Views
I. INTRODUCTION
AN understanding of the overall rate of reduction or oxidation of iron oxide from an iron oxide-containing slag requires a knowledge of the transport properties of iron oxide in the slag.[1,2] Recent studies by Xie and Belton[3] showed that the chemical diffusivity of iron oxide in 40CaO-40SiO220Al2O3 slags increases with increasing concentration of iron oxide. They also found evidence that the chemical diffusivity of iron oxide in calcium silicate and calcium aluminosilicate slags, containing relatively low concentrations of iron oxide, increases with the state of oxidation. As a limiting case, the diffusivity of oxygen in liquid iron oxide and its dependence on the state of oxidation is of obvious interest. Calcium ferrite is an important slag system in iron-making and nonferrous metallurgical processes. The addition of calcium oxide to liquid iron oxide was found to increase the reduction rate of iron oxide by an order of magnitude.[4,5] A comparison of the diffusivity of oxygen in calcium ferrite and that in pure liquid iron oxide may also shed some light on the mechanism of the diffusion. The limited reported values for the chemical diffusivity of oxygen in pure liquid iron oxide[6,7,8] differ by two orders of magnitude. Grieveson and Turkdogan[6] studied oxidation and reduction of liquid iron oxide by CO2-CO mixtures at 1823 K. It was assumed that the diffusion in the melt was the rate-limiting step. The value of the interdiffusivity of oxygen and iron, thus, obtained was 5(61) 3 1025 cm2/s. Further work by Mori and Suzuki[7] determined the diffusivity in liquid iron oxide over a wider composition range within a temperature range of 1703 to 1823 K using a similar Y. LI, formerly Research Fellow, Department of Chemical Engineering, University of Newcastle, is Research Associate, Department of Materials Science and Engineering, Carnegie Mellon University. J.A. LUCAS, Senior Lecturer, is with the Department of Chemical Engineering, University of Newcastle, Callaghan, NSW, Australia. R.J. FRUEHAN, Professor, is with the Department of Materials Science and Engineering, Carnegie Mellon University, Pittsburgh, PA 15213. G.R. BELTON, formerly Professor, Department of Chemical Engineering, University of Newcastle, is deceased. This article is based on a presentation made in the “Geoffrey Belton Memorial Symposium,” held in January 2000, in Sydney, Australia, under the joint sponsorship of ISS and TMS. METALLURGICAL AND MATERIALS TRANSACTIONS B
experimental technique. At 1823 K, the interdiffusivity was found to decrease from about 4 3 1024 to 5 3 1025 cm2/s as Fe31/(Fe increased from 0.12 to 0.42. The activation energies for diffusion were found to be about 46 and 71 kJ/ mol at Fe31/(Fe of 0.12 and 0.33, respectively. With more accumulated data[9,10] on the chemical reaction rate at the interface between a slag and CO2-CO gases, Belton[11] has analyzed Grieveson and Turkdogan’s[6] data and has shown that the rate measured by Grieveson and Turkdogan could well be under the control of the slow gas-slag
Data Loading...
