Proceedings of ITC/ISHW2007

Microwave Frequency Effect for Reduction of Magnetite
A S. Takayama, G. Linka, S. Sanob, A. Matsubara c, M. Sato, M. Thumma
National Institute for Fusion Science,322-6 Oroshi-cho, Toki 509-5292, Japan
Forschungszentrum Karlsruhe GmbH, IHM, P.O.Box 3640, Karlsruhe 76021, Germanyb
Advanced Industrial Science and Technology,2266-98,Anagahora,Shimoshidami, Moriyama-ku, Nagoya
463-8560, Japan
cChubu University 1200, Matsumoto-cho, Kasugai-shi, Aichi 487-8501, Japan
takayama.sadatsugu@nifs.ac.jpa(Received day month year / Accepted day month year should be centered 10-point type)This paper describes experimental investigations on pig iron production by use of microwave heating. In order
to explore possible effects of the microwave frequency identical mixtures of magnetite and carbon powder wereprocessed in different microwave systems, operating at 2.45 GHz and 30 GHz, respectively．High quality pig iron
was obtained in the 30 GHz mm-wave system in air. However, at 2.45 GHz FeO was produced mainly at similar
conditions. This result might suggest that the chemical reduction of magnetite is more efficient with higher
microwave frequencies.
Keywords: microwave processing, millimeter-wave processing, magnetite, pig iron,

1. Inroduction
Microwave technology is not only a substitute forconventional heating, but it resides in the new domain ofmaterials science, namely, microscopic and strong thermal
non-equilibrium systems [1]. The application of
microwaves in the iron industry may be characterized by ahigh potential for an essential reduction of carbon dioxideemission. Iron ore refinement by means of blast furnaces
was realized with the same basic furnace structure basedon the same principle for two centuries. We haveconducted a series of experiments to prove effectiveness of
rapid and high purity refinement under low temperatureand oxygen-containing environment by means of
microwave application, and achieved highly positiveresults.
Nagata and coworkers of the Tokyo Institute ofTechnology have been working on the development of
unique ultra high purity iron refinement technology basedon an ancient Japanese iron refinement method called"Tatara" [2]. Their findings during microwave sintering of
powder metals led to the idea that rapid refinement of ironshould be possible by application of 2.45 GHz microwaves
instead of relying on burning of carbon for heat production.
Joint experiments at the National Institute on Fusion
Science (NIFS) and Forschungszentrum Karlsruhe (FZK)
proved that high purity iron (1% carbon concentration)with less than 1/10 of impurities as compared to irons thatthe modern blast furnaces can produce. More over it
reduced the carbon consumption to 2/3.
In order to investigate the effect of microwave
frequency, samples of magnetite powder mixed withcarbon powder were processed in different microwave
author’s e-mail: journal@jspf.or.jpsystems. The following paper discusses recent
experimental results obtained by millimeter-wave(mm-wave) processing and processing in a 2.45 GHz
microwave system.

2. Experimental Setup of theMM-wave Process
For mm-wave experiments, the applicator of acompact 30 GHz gyrotron system was used as shown in
Figure 1(a) [3]. The mm-wave power generated by a socalled gyrotron oscillator can be controlled from 0 - 15 kW.
This power is launched via a quasi-optical transmission
line through a vacuum-sealed boron nitride window into
the hexagonal applicator which is characterized by a very
homogeneous field distribution. The samples used weremixed powder of magnetite and carbon. The weight ratioof magnetite and carbon in the power mixture was 89 to 11
weight%. According to the corresponding chemical
equation this should allow to produce pig iron including
2 weight% of carbon. Such type of powder samples werefilled into an alumina crucible surrounded by thermal
insulation (see Fig. 1(b)). The temperature was measured
by two S-type thermocouples, one sticking in the center ofthe powder sample, another near the crucible wall. The
heating process was controlled along a preset
temperature-time program with a heating rate of 70 °C/min
using the temperature signal of the thermocouple placednear the sample surface.

Proceedings of ITC/ISHW2007

Fig.3

Fig.1 (a) 30GHz gyrotron system (top),(b) Experimental setup of the mm-wave (bottom)

Pig iron from the 30GHz mm-waves process.

Figure 2 shows the process temperatures measured
during mm-wave heating of a powder sample of about 80 g
mixed magnetite and carbon. It can be seen that during theinitial step of heating that means during the first 15minutes, the temperature measured at the sample surface
was higher than the temperature measured within thesample volume. However thereafter, at a temperature ofabout 1100 °C the absorption behavior of the powder ischanging dramatically. According to the Iron-Carbon phase
diagram this temperature is close to the point whereliquefaction of iron with 2% carbon content starts. Thatmeans microwave power is consumed by the melting
process and heating of the material stagnates. Due to thismelting process a strong rearrangement of the processedmaterial happens, leading to changes in the thermocouple
positions as well. Finally, when the material is completed
molten, the thermal conductivity of the material increased.
Thus the measured temperatures converge to each other.
Figure 3 shows a picture of the obtained pure pig iron.
EDX analysis along the cross section revealed a carbon
content of 1 weight%. No oxygen could be detected.

3. Experimental Setup for CM-wave Process

Temperature (degreeC)

1600
1400
1200

sample surface

1000
800
600

sample center

400
20000510152025Time (Minute)3035Fig.2 The measured temperatures of a mm-wave process.

The multimode test furnace at the National institutefor Fusion Science shown in Figure 4 was employed forthe present study at 2.45 GHz. According to the concepts
developed in Germany in order to improve thehomogeneity of the electromagnetic field, the applicator
shape is hexagonal [4]. The furnace with 0.92 m3 involume is equipped with five magnetrons. The
microwave power of a single magnetron is 2.5 kW. Twomode stirrers scatter the standing wave. The samples used
had the same weight ratio of magnetite and carbon power
as for the mm-wave process. The powder samples werefilled into an alumina crucible surrounded by thermal
insulation (see Figure 4) similar to the setup used for themm-wave process. The temperature was measured by anIR pyrometer. The heating process was controlled along apreset temperature-time program with a heating rate of
70 °C/min using the temperature signal of the IR
pyrometer measured at the top of the sample surface. In
addition, the multi-point emission spectroscopic
diagnostic was conducted through the viewing port on thefurnace.

Proceedings of ITC/ISHW2007
20060926_2

1600

12001000

BTemperature (degreeC)

1400

8006004002000010203040DTime (Minute)

5060

Fig.5
The measured temperatures of a cm-wave
process.

IRFig.6 Sample after 2.45GHz processing.

Insulator
Fig.4. (a) 2.45GHz magnetron system (top), (b)Experimental setup of cm-wave process (middle), (c)Sketch of experimental setup (bottom).

Figure 5 shows the process temperatures measured
during cm-wave heating of a powder sample of mixed
magnetite and carbon. After 15 minutes from start, strong
radiation appeared due the ignition of a plasma at thesample surface [5]. The spectral intensity of thecontinuous spectrum is at least three orders of magnitudelarger than that of black body emission for thetemperature range of 860 °C – 1070 °C measured by themulti-point emission spectroscopic diagnostic conducted
through the viewing port on the furnace. The pattern ofthe continuous spectrum is partly similar to a continuumof the emission light radiated by the free-band electrontransition.
The origin for the continuous emission spectrum will
be discussed. One candidate is a solid state fluorescencecalled cathodoluminescence induced by impingement of aplasma electron onto the sample surface of magnetite;

Proceedings of ITC/ISHW2007
this results in the excitation of electrons from the valenceband into the conduction band, and deexcitation with thebroadband emission.
Figure 6, shows a picture of the material obtained bythis process. The mainpart of the material was FeO as
detected by XRD analysis.

4. CONCLUSIONSHigh quality pig iron could be made from powder
samples of mixed magnetite and carbon by 30 GHz
mm-waves heating in air. However, in case of heating by
2.45 GHz at similar conditions, mainly FeO was produced.
Therefore, we expect that there is frequency dependence inthe reduction reaction.

ACKNOWLEDGEMENTS
This work was supported in part by KAKENHI(Grant-in-Aid for Scientific Research on Priority Areas)(1807004) of MEXT (Ministry of Education, Culture,Sports, Science and Technology).

References
[1]

[2]

[3]

[4]

[5]

R. Roy, R. Peelamedu, L. Hutt, J. Cheng, D.Agrawal,“Definitive experimental evidence for microwave effects:
radical new effects of separated E and H fields”, Mat. Res.
Innovation 6: 128-140, 2002.
K. Nagata, R. Kojima, T. Murakami, M. Susa, H.
Fukuyama, “Mechanisms of Pig-iron Making from
Magnetic Ore Pellets Containing Coal at Low
Temperature”, ISIJ International 41: 1316-1323, 2001.
G. Link et al., “Sintering of advanced ceramics using a30-GHz, 10-kW, cw industrial gyrotron”; IEEE
Transactions on Plasma Science, 27 (2): 547-554, 1999.
Feher L., Link G., DE-PS 19633245C1 (27.11.1997);
Feher L.; Nuss V.; Seitz T.; Flach A. DE-PS 10329411(31.1.2005).
A. Matsubara, et al., submitted to Proc.11thInternational Conference on Microwave and HighFrequency Heating, (3-6 Sep 2007, Oradea, Romania).