The conditions for the formation of lath and porous magnetite on reduction of hematite in H 2 /H 2 O gas mixtures
- PDF / 174,593 Bytes
- 2 Pages / 603.28 x 783.28 pts Page_size
- 85 Downloads / 195 Views
The portion of this work performed at Massachusetts Institute of Technology was supported by a grant from the National Science Foundation (DMR 79-26324).
REFERENCES I. C. S. Chai and T. W. Eagar: Metall. Trans. B, 1981, vol. 12B, p. 539. 2. S. S. Tuliani, T. Boniszewski, and N. E Eaton: Weld. Met. Fab., 1969, vol. 37, p. 327. 3. B.I. Lazarev, etal.: Weld. Prod., 1971, vol. 18, no. 5, p. 21. 4. T.H. North, H.B. Bell, A. Nowicki, and I. Craig: Weld. J., 1978, vol. 57, p. 63-s. 5. Yu. M. Zhuravlev: Weld. Prod., 1974, vol. 21, no. 3, p. 6. 6. J. Tanaka, T. Kitada, Y. Naganawa, Y. Kunisada, and H. Nakagawa: Proc. Int. Conf. Weld Pool. Chem. Met., The Welding Institute, London, 1980, p. 279. 7. M. L. E. Davis and N. Bailey: Proc. Int. Conf. on Weld Pool. Chem. Met., The Welding Institute, London, 1980, p. 289.
The Conditions for the Formation of Lath and Porous Magnetite on Reduction of Hematite in H2/HaO Gas Mixtures P. BAGULEY, D.H. St. JOHN, and P.C. HAYES Recent experiments ] on the reduction of hematite in CO/CO2 mixtures indicated that the formation of two distinct morphological types of magnetite during reduction at temperatures between 400 and 1000 ~ was a function of the oxygen potential in the reducing gas. Previous workers 2'3'4 observed a transition in the product morphology on increasing the reduction temperature and argued that porous magnetite was the low temperature transformation product and that lath magnetite was favored at high temperatures. There is, however, some disagreement in the reported temperature range over which this transition takes place. An explanation for these anomalies was put forward by Hayes and Grieveson 1who pointed out the progressively increasing oxygen potentials of the reducing gas mixtures with increasing temperature. This changing potential was either deliberately selected2 or the high chemical reaction rates resulted in gas starvation at the gas/sample interface. 3'' Hayes and Grieveson 1 used only CO/CO2/N2 gas mixtures during reduction, and it was thought desirable to test these early findings in H2/H20 mixtures. The chemical reac-
tion rate constants for reduction in hydrogen are known ~ to be at least an order of magnitude faster than CO/CO2 mixtures even at 900 ~ and even greater differences occur at lower temperatures. The present experiments therefore are designed to test the initial hypothesis that it is the oxygen potential of the gas which is important in determining the initial product morphology in this system. By using hydrogen/steam mixtures at one atmosphere total pressure any significant effect of chemical reaction rate on the product morphology should also be apparent. The hydrogen-steam gas mixtures were prepared from high purity hydrogen and steam obtained at a constant flow rate from a modified steam generator. The gas mixtures were passed through a Pyrex U-tube arrangement described in previous experiments 6 such that the linear flowrate over the 1 mm 3 hematite samples was approximately 0.7 m s -t. Samples, preheated to 200 ~ above the reaction tempe
Data Loading...
