Reduction of ilmenite in a nonequilibrium hydrogen plasma
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D.E. BULLARD, Senior Research Engineer, is with the U.S. Steel Research Center, Monroville, PA 15146. D.C. LYNCH, Professor and Associate Department Head, is with the Department of Materials Science and Engineering, University of Arizona, Tucson, AZ 85721. Manuscript submitted October 2, 1996. METALLURGICAL AND MATERIALS TRANSACTIONS B
Fig. 1—Experimental apparatus.
Fig. 2—Specimen holder shown in relation to mass spectrometer tapping tube.
by as much as 100 K. Rotation reduced temperature variation to below 1 K. The specimen temperature was monitored with a single color, optical pyrometer (Mikron (Wycoff, NJ) M90), as discussed in Reference 2. Upon completion of an experiment, the plasma was extinguished and the specimen was allowed to cool in the chamber under a continuous flow of hydrogen. The chamber was then flushed and backfilled with dry nitrogen. A Scintag (Santa Clara, CA) XDS 2000 X-ray diffractometer was used to verify that Fe and TiO2 were produced during reaction. The specimen in its holder was inserted directly into the diffractometer so that the surface material contacted by the plasma could be examined directly. The results of a typical experiment, as monitored by the mass spectrometer, are shown in Figure 3. The specimen was raised into the plasma 4 minutes after ignition of the plasma. The intensity of the water vapor signal rose rapidly, peaked, and then trailed off, slowly decreasing in 6 minutes by only 17 pct from the maximum. When the plasma was extinguished, the signal for the water vapor dropped off precipitously. VOLUME 28B, JUNE 1997—517
Fig. 3—Plot of water peak height (in arbitrary units) produced during reduction of ilmenite with hydrogen plasma; experimental conditions were 0.8 kW and 3500 Pa.
The shape of the water vapor signal as a function of time in Figure 3 suggests that the impact of the plasma extends beyond reduction of just the surface material. In reduction experiments of TiO2 with a hydrogen plasma, the water vapor signal rose rapidly and dropped almost as quickly as it rose.[2] That result was interpreted to indicate that once the surface material reacted, the impact of the plasma ceased as the plasma could not extend into the interstices of the bed. X-ray analysis indicated that the TiO2 particulate was reacted to a depth of approximately 5 mm. The fact that the maximum water vapor signal remains relatively constant for ilmenite reduction suggests that possibly more than surface material in the bed was involved. The specimen could be viewed through a window in the top cap of the reaction chamber. Visual observation during an experiment indicated that the ilmenite powder responded to the electromagnetic radiation and plasma by translational motion and vibration. This was particularly true of surface particles that were not constrained by the specimen holder or locked in the bed by material above it. The motion is believed to be associated with charging and then discharging of the metallic iron produced as a result of reduction. It is hypothesized that this motion of
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