Sohn International Symposium ADVANCED PROCESSING OF METALS AND MATERIALS
VOLUME 5 - NEW, IMPROVED AND EXISTING TECHNOLOGIES:
IRON AND STEEL and RECYCLING AND WASTE TREATMENT
Edited by F. Kongoli and R.G. Reddy TMS (The Minerals, Metals & Materials Society), 2006
EXPERIMENTAL ANALYSIS FOR THERMALLY NON-EQUILIBRIUM
STATE UNDER MICROWAVE IRRADIATIONS
A GREENER PROCESS FOR STEEL MAKING
1
Motoyasu Sato, 1Akihiro Matsubara, 1Sadatsugu Takayama, 1Shigeru Sudo 1Osamu Motojima,
2
Kazuhiro Nagata, 2Kotaro Ishizaki, 3Tetsuro Hayashi,
4
Dinesh Agrawal, 4 Rustum Roy
1
NIFS (National Institute for Fusion Science); 322-6 Oroshi,Toki,Gifu, 509-5292 Japan
2
Graduate School of Science and Engineering;Tokyo Institute Of Technology
3
Research Institute of Industrial Products Gifu Prefectural Government
1288 Ozeki, Seki-city, Gifu 501-3265 Japan
4
Materials Research Institute, Penn State University; University Park, PA 16802 USA
Keywords: Carbon dioxide emission, Microwave Energy, Pig Iron, Thermally non-equilibrium
Abstract
Highly pure pig irons were produced in a multimode microwave reactor from powdered iron ores
with carbon as a reducing agent in the nitrogen atmosphere. The grains in compacted powder
absorb microwave energy selectively. Microwave-matter interaction creates thermal nonequilibrium state microscopically and enhances chemical reactions and the phase mixing at the
grain boundaries very rapidly.
The visible light spectroscopic techniques was used to monitor the progress of the reactions. Up
to 650°C, the heated powders radiate the continuous spectrum of blackbody emission. The small
non-equilibrium hot spots rise, move and finally burst in to brighter light emitting from all over
the surface at 650°C. CN molecules and Fe (I ) atoms were identified in the recorded spectrum.
These bursts are similar to the “ignition propagation” normally observed in chemical reactions.
The line spectra originated from CO molecules have not been detected yet. The solid-solid
reaction could be expected between the iron oxides and carbon to produce CO2 directly. A loss in
the sample weight was accelerated during the excess-emission. These are the clear evidence that
microwaves cause thermally non-equilibrium state and accelerate reduction process.
The reduction of iron ore is completed at 1380°C and relatively very pure pig iron was produced.
It should be noted that the impurity level of Mg, S, Si, P and Ti is only 5-10% of what is found in
the pig irons produced by modern conventional blast furnaces in the steel industries. The
necessary amount of carbon needed was 1/2 compared to conventional blast furnace to produce
the unit weight of steel, if we applied renewable energy or nuclear power for the microwave
excitations.
Introduction
As the Kyoto protocol come into effect, aggressive preservation of resources and energy savings
are becoming progressively pressing needs for our country. However, the effectiveness of
improvement of conventional industrial process is reaching its limits, hence calling for a new
perspective to approach this problem. To put it on one extreme, the essence of civilization is to
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produce, heat, and process materials. Since the beginning of industrialization, the process of
heating has been based on the utilization of external heating sources via conduction,
transmission, and radiation. Should this process be given a drastic change, the most effective
energy saving can be achieved. Utilizing microwave energy for heating purposes has its
distinctive characteristics in that it does not use an external heating source. Researchers in
academia and industry have been working in the area of microwave processing of a variety of
materials for many years. But what is new and unique about the present work is that for the first
time the Penn State's experiments have shown that it can be applied as efficiently and effectively
(if not more) to powdered metals as to the ceramic systems(1). Going further, there are even
greater potential of the possibilities surrounding the exploitation of their radically different
effects of the E and H components of the microwave electromagnetic field(2).
Although many hypotheses have been presented through studies to investigate mechanism of
microwave heating worldwide, no conclusive results have been presented to date. Using a digital
microscope, we recorded a visual movie image in-situ observation of heating process of powder
consisting Fe3O4 and BaCO3 by microwave(3)(4)(5). Random generation, movement, and
disappearance of hot spots in the order of 100 micron were observed throughout duration of a
few seconds. The temperature, size, shape, and the duration of the hot spots maintained certain
regularity. This is the first case in the world of capturing formation of micron scale strong
thermally non-equilibrium or localized temperature gradients (a few hundred oC/100 micron, a
few thousand oC/mm) system during heating. In materials comprised of two compounds (even in
multi compound system), occurrence of selective heating due to different microwave absorption
rates of different phases, resulting in to a large temperature difference between the phases, is
expected. This opens up the possibility of “field engineering” of most sophisticated value added
electronic and optical materials. And also how localized an-isothermal situations in a microwave
field can cause drastic enhancements in the reaction and diffusion kinetics.
Nagata, et al of Tokyo Institute of Technology had been working on development of unique ultra
high purity iron refinement technology that is based on ancient Japanese iron refinement method
called "Tatara Process". The encounters with the report of microwave heating of powder metals
gave them an idea that rapid reduction of iron should be possible by application of microwaves
without relying on burning of carbon for de-oxidation.
Joint experiments with NIFS et al proved that high purity iron (2% carbon density) with less than
1/10th of impurities, such as manganese, sulfur, phosphor, silicon, titanium, etc., as compared to
irons from modern pile furnace can be produced in a short time, while reducing consumption of
carbon to 1/2 (5) . This result developed into a new research theme of Suppressed CO2 Emission,
Rapid Iron Refinement Method by Microwave Processing, which is aimed for reduction of
several millions of tons of CO2 emission (per single pile furnace).
The magnetite could be heated by the H-field of microwave and carbon by the E-field during the
process. The amount of energy would be supplied by microwave for removing oxygen from
magnetite. If the renewable energy, such as solar, hydro and nuclear power, is applied to
generate microwave, it can reduce the emission of CO2 at least 50% of what is necessary in the
conventional blast furnaces.
The field in which microwave heating is effective in energy saving is in the high temperature
region of 1000 oC to 2000 oC. Materials industries, such as metal refinery, steel production,
sintering, and nanotechnology are among them. Application of microwaves in the iron industry,
which is the backbone of these key industries, is the field where the greatest effect in reduction
of carbon dioxide emission is expected. Iron ore refinement by means of pile furnace has utilized
same basic structure based on the same principle for two hundred years. We have conducted a
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series of experiments to prove effectiveness of rapid and high purity refinement under low
temperature and high oxygen potential by means of microwave application, and achieved highly
positive results. This paper provides the results achieved so far of this ongoing project.
Experimental
The experiments of reduction of iron oxide have been successfully conducted in a microwave
batch furnace. The chamber of furnace is made of a stainless steel with hexagonal cross-section
of 1.1m wide and 1.2m long that reduces the microwave energy concentration to the center of the
cylinder. The metal rotators also scatter the standing mode in the chamber (Figure 1). The
uniform heating in expected in the region of operation inside the chamber. Five magnetrons
radiate 2.5~12.5 kW microwave at 2.45 GHz. The chamber was evacuated down to 0.1 Pa and
refilled by nitrogen gas. Nitrogen is kept flowing at 2~5 litter/minutes at a little higher than the
ambient pressure.
The diagnostic systems were prepared to investigate the process under the thermally nonequilibrium reactions. The visible light spectrometer will detect the line spectrum overlapping to
continuous spectra of the blackbody emissions. The combination of visible light spectrometer to
the infrared pyrometer was the basic diagnostic tool. The system monitored in-situ the average
temperatures and nonlinear excitations on the surface of the sample in the spot size of 10 mm.
The entire process was monitored by high resolution video camera.
Both the natural iron ore with coal and the purified reagent of Fe3O4 with graphite were prepared
for the experiments. The iron ores milled into powders under 100P. The coal was under 50P. The
grain sizes and the mixed weight ratios are listed in Table-1.
The mixed powders were filled in a crucible with the tap density around 30%. The crucible was
thermally insulated by the alumina-silica fiberboard. The insulation package containing the
crucible installed in the microwave furnace as illustrated in figure-2.
Fiber optics for
spectrometer
Infrared
pyrometer
Video camera
Spectrometer
Mode stair
Thermal
insulator
Fig. 1. Pictures and the illustration of diagnostic system by visible lights
159
Grain size (P
Pure Sample #1
Pure Sample #2
Pure Sample #3
Pure Sample #4
Fe3O4
50~100
Carbon
10
Fe3O4 : C Ratio
Theoretical Value
2:1
Weight
Mol
50 : 50
1 : 19.2
82 : 18
1 : 4.23
89 : 11
1:2
95 : 5
1:1
Remarks
Expected products
Fe3O4+2C = Fe + CO2
+2% FeC
Fe3O4+C = 2FeO+ Fe
Iron Ores #1
89 : 11
Table-1 Grain size and mixing ratio of magnetite and carbon of the samples
Thermal
Insulators
68 mm
SiC plate
for Hybrid
Heating
Figure-2 Heating unit filling up the sample in the crucible,
Note: SiC plate was used only in an experiment of hybrid heating.
Experiment (I) Microwave Processing of Fe304 Powder Mixed with
Graphite of Equivalent Mol Concentration for the Reduction
The first experiment was done using the sample with pure reagent of Fe3O4 and pure graphite
powders that listed as the Sample#3 in table-1. The weight ratio of magnetite and graphite was
89:11. The amount of carbon was equivalent to the mol concentration for de-oxidation of the
magnetite to pig iron that contained 2% carbon. Total weight of the sample and volume were
89.3g and 89 cc respectively. The applied power was 5kW.
The temporal evolutions of line mission spectra, typical video pictures, infrared temperature and
microwave output power were displayed respectively from top to the bottom in the figure-3. The
process showed three steps: 1. RT to <690 °C, 2. Temperature jump from 690°C to 980°C in a
few seconds and slower temperature rise to 1150°C. 3. Formation of the pig iron. The small
drops appeared and agglomerated to larger drops. The slag was being released mechanically in
the agglomeration.
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Step I (Room Temperature ~ 600 oC)
The microwave power was limited at 2.5 kW until the evaporation of combined water in the
crystal. The heating rate began to slow down, but the temperature kept rising from 400 to 600 oC
in 300 seconds. Small hot spots, less than 1 mm in diameter, blinked in the cracks on the surface
of the sample as shown in the left two video pictures in figure 3. They became stronger and more
frequent when the temperature closes to 690 oC.
4
T = 887OC, Mainly CN
4
T = 1262OC, Mainly Fe
4
3
3
3
2
2
2
1
1
1
T = 1438OC, Mainly Fe
0
0
0
370380390400410420430440 370380390400410420430440 370380390400410420430440
λ (nm)
λ (nm)
λ (nm)
Step II
Step I
Step III
Video Pictures
8000
800
Visible Light
80
8
Spectroscopy
T ( C)
O
Microwave Power
100
200
300
400
500
600
700
800
900
1000
1100
time (sec)
Figure –3 Line mission spectrums, typical video pictures, infrared temperature
and microwave output power V.S. time
161
MW power (kW)
IR Temperature
1600
1400
1200
1000
800
600
400
200
0
10
8
6
4
2
0
1200
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Figure 4. Ignition Propagation at 690 oC and temperature jump
Step II (Temperature jump from 690 oC to 950 oC and de-oxidation up to 1350 oC )
At about 690 oC, as illustrated in figure 4, very bright discharge flashed and it extended to all
over the sample surface in 0.1 seconds. Then in the next 2~3 seconds, the bright flame burst up
and sparks sprayed out through a hole drilled on top of the insulator. It is not clear how deep the
flash penetrates into the body of the sample. During the bursts, the temperature jumped to 950
o
C. After the burst, it kept on rising from 950 oC to 1150 oC. The flame continues until the
reaction is completed.
The emissions of line spectra that consisted of carbon-nitride (CN) and Iron atoms (Fe I) were
initiated at the burst. The CN decreased and disappeared in a few minutes. The emission by Fe(I)
continued, while the CN lines decreased and disappeared in a few minutes. No emission lines of
CO or CO2 were detected. The emission and flame disappeared when the microwave power was
turned off.
Step III Formation of Molten Metal
The video showed that the surface of the sample became brighter during the process and the
smaller. When the temperature reached to 1350 oC, molten metal appeared in the crucible as
shown in figure-7.
The visible light emissions idicated that the strongest peak was that of Fe(I). The excitation
levels for them were estimated to be of several electron volts. It was much higher than the bulk
kinetic energy of Fe atoms which is 1100 oC ( 0.1eV) by infrared pyrometer. It suggests that the
thermally non-equilibrium state was excited by the microwave at the atomic level.
162
Experiment (II) Investigations for Optimum Quantity of Carbon Content
All energy is supplied by the burning of carbons (cokes) in the conventional blast furnace. It is
the most interested question “How much energy can be replaced by microwave irradiation?”.
The samples with different weight ratios (mol concentrations) of magnetite and carbon were
examined under the identical conditions of experimental setup and same microwave power. The
samples were listed as the pure samples # 1 ~ #4 in the table-1. The atmosphere was nitrogen.
The processes were observed by visible light spectrometer and video monitors. The phase
composition of the products was investigated by XRD measurements.
Pure sample #1 (50:50)
It is very rich in carbon. The burst and temperature jump were not clear. CN line appeared at 700
o
C, but no emission was observed from steel components. The excess unreacted carbon
remained in the powder. Small drops, less than 1mm, were observed in the powders. The
amount of the Fe was too small to detect. The XRD patterns show only the peaks of graphite.
T = 990 0C (t = 472 sec)
3
CN
2.0x103
250
200
Profile of the spectra
1.5x103
150
1.0x103
CN
5.0x102
100
50
0.0
380 390 400 410 420 430 440 450
0
20
wavelength (nm)
Fe
2.5x103
Graphite
Intensity (a.u.)
3.0x10
30
40
50
60
1600
1400
ΔT
= 2.9 oC / sec
Δt
O
T ( C)
1200
1000
800
600
400
100
200
300
400
500
600
700
time (sec)
Residual graphite powder
with a bit of small iron balls
CN appears continuously.
Figure-5 Pure sample #1 (50:50) Experiment with very rich carbon
Pure sample #2(82:18)
The sample contained carbon almost twice for the reduction of magnetite in the sample. The
burst and temperature jump occurred at 700 oC. The metal was produced showing peaks of Fe by
XRD. But, the reduction was limited on the surface only in the crucible. The core of the sample
remained in powders form. The weight of the produced metal was less than 20% of theoretical
expectation.
163
T = 1030 0C (t = 804 sec)
Fe
400
Fe
6.0x102
Fe
Intensity (a.u.)
8.0x102
300
2
4.0x10
2.0x10
100
0.0
380 390 400 410 420 430 440 450
0
20
wavelength (nm)
D
2006/03/02 20 53 D
Graphite
200
2
30
40
50
60
k 20060222b
i
O
T ( C)
1600
1400
1200
ΔT
= 16 0C / sec
Δt
1000
800
600
400
500
600
time (sec)
700
800
900
1000
1100
T-jump is clear.
Fe and CN appear.
Figure-6 Pure sample #2(82:18)
The sample contained carbon twice for the reduction of magnetite
Pure sample#3(89:11)
This was the best. The products weight was 95% of the estimated weight. It is the stoichiometric
carbon amount needed for complete reduction of the magnetite in the sample. These experiments
were explained in the previous section.
Figure –7 The highest yield and best quality Pig Irons by the microwave
Pure samaple#4(95:5)
It is the low carbon experiment. The amount of carbon is just a half of what is needed to
complete reduction of the magnetite. Temperature jumps were observed. First jump was at 690
o
C with CN light emission. The temperature rose to 800 oC and it has the second jump to 1000
o
C. The emission of CN line did not show up. Only the Fe(I) lines were detected. The
temperature increased up to 1400 oC and finally a big molten metal drop remained at the bottom
of the crucible. The XRD shows that the major peaks were of FeO and Fe as a minor phase.
164
1.2x103
1.0x103
Fe
3000
Fe
2
8.0x10
FeO
T = 890 0C (t = 494 sec)
2500
6.0x102
2000
4.0x102
1500
1600
1400
O
T ( C)
1200
1000
390
400
410
420
430
440
450
FeO
0.0
380
500
0
20
ΔT
= 300 C / sec
Δt
30
40
Fe
2.0x102
50
60
1000
ΔT
= 14 0C / sec
Δt
800
600
400
200
300
400
500
600
700
800
time (sec)
Almost iron spectra.
The frame flashes, on the same time
temperature goes up and down.
Figure-7 Pure samaple#4 (95:5) Poor carbon experiment.
The amount of carbon is just a half to de-oxide the magnetite in the sample.
Experiment (III) Reduction of Natural Iron Ores in the Microwave Blast Furnace
The reductions of natural iron ores were examined in the microwave blast furnace. The natural
ore was the loadstone produced from Romeral Chili. It is the high quality ore containing
magnetite more than 90%. It was grinded to less than 100P. It was mixed with powdered natural
coal with the weight ratio of 81:11 in accordance with the experiments mentioned above. The
weight of the sample was 1kg. Microwave power was kept in the range 5~7.5 kW. The
atmosphere was nitrogen. The experiment showed almost identical steps of pure magnetite/
carbon compound with 89:11. The burst and temperature jump appeared at about 700 oC. The
yellow colored flame was seen more clearly than the pure regent, because natural powders
contained more Sodium.
The video camera visualized the metal formation process. About 1mm diameter metal drops
appeared in the powder, when the temperature exceeded 1150oC that was the melting
temperature of the pig iron containing 2% carbon. The drops became larger in the next 10
minutes as big as 5~8 mm diameter. They sunk into the powder by the gravity. New small drops
were born on the fresh powder and process repeated itself. The growth rate increased with the
temperature. Finally, almost all the powder was reduced to the metal at 1380oC.
The reduction process finished at 1380°C and the very pure pig iron was produced. The level of
the impurities such as Mg, S, Si, P and Ti, were only 10-20% of the levels normally observed in
the pig irons supplied by conventional blast furnaces, as shown in Figure–8.
The weight of pig iron was 530 grams. Assuming the ore contained 100% of magnetite, 638
gram of pig iron would be produced. The product weight was about 85 % of the ideal value.
165
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Impurity
Contents
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0.1
Åì
0.08
ånóÒ1
Inside 1
ånóÒ2
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ånóÒ3
Inside 3
ånóÒ4
surface
0.06
0.04
0.02
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Mn
S
Si
Ti
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Figure-8 Impurity in the Pig Iron By Microwave Reduction
Discussions
Optimized carbon content for microwave blast furnace
The series of our experiments show clearly in the microwave blast furnace that;
1) The amount of carbon must satisfy the chemical equation;
Fe3O4 + 2 C = 3 Fe + 2CO2 –75.66 kcal/mol.
2) The energy is supplied by microwave irradiation for heating powders and for making up the
difference of enthalpies between the iron oxide and carbon dioxide (–75.66 kcal/mol).
3) Carbon played only just as a reducing agent.
4) Pig iron was produce uniformly from the surface to the core of the sample mixed with carbon
at the optimized mol ratio.
The product remains at the stage of FeO in case of insufficient carbon.
5) The maximum temperature was 1380 oC to finish the reduction and to get liquid pig iron.
6) The impurity contents were 1/10 compared to the products by conventional blast furnace.
An innovation by microwave blast furnace is proposed here that the exhaust of CO2 can be
reduced almost one half in comparison of the existing blast furnaces, if the energy could be
supplied to microwave generators that is powered by the renewable energy or nuclear power
plants.
Our experiments make it clear that the penetration depth of the microwave is deep enough to
operate the microwave blast furnace in the industrial scale.
166
The innovation would be highly possible from the viewpoint of engineering. The next step must
be the demonstration of designing and building a larger scale microwave blast furnace appealing
to the steel industries.
Re-configuring the Science of Materials Synthesis/Reactions
Scientific interest in our results is more profound than mere heating mechanism of powders by
microwaves.
Classical chemistry considers the general reaction of say
A+B
C+D
Reactants
Products
by considering the free energy of the reactants and products, as these are varied by changing the
intensive variables – usually limited to temperature (T) and pressure (P). The equilibrium can be
shifted from one side to other; and the stable phases determined under specific selected
conditions, etc.
The classic thermodynamic approach, that is Electric field - Plasma (Electrons) – Material, is
tried to explain an energy transfer mechanism. As the emission spectra of Fe (I) were the result
of electron impact excitation, the flame should contain electrons and ions in the neutral gas
composed of CO am/or CO2. The microwave electric field coupled to the kinetic energy of the
electrons and dissipated into CO and /or CO2 molecules through the collision process. It also
excited and vaporized Fe atoms from the surface layer of each grain of iron oxide by collisions.
In the chemical reaction, the hot CO or CO2 gas transfers the heat to the reactant. Higher the
temperature of the gas is, larger the heat flux from gas to the reactants. Microwave assists to heat
up the gas more rapidly than by the burning of the carbon only. If the characteristic times of the
chemical reduction were longer than the period of thermalization, the chemical reaction could be
expected under the equilibrium state.
This approach is, of course, valid very generally if the temperature is caused exclusively by
phonon excitation alone (which to date has been the only condition considered in
thermodynamics). It is therefore self-evident that ALL equilibria in ALL chemical reactions will
be affected (to a greater or lesser extent) when the radiation can affect the electronic structure of
the phase, in any way other than through the kT thermal energy.
The next step in understanding then becomes the issue of how does the magnetic (or electric)
field couple to the crystalline phase and how does it create the excited state noted above.
According to a standard textbook on interaction of microwaves with matter the microwave
3
power absorbed per unit volume (P in W/m ) is expressed by the equation:
P = SfRH0H"( PP"+ where E and H are the electric and magnetic fields, f0 is the frequency, H" & P" dielectric and
magnetic loss factors respectively. However, in the vast literature on theories of microwavematter interaction, the magnetic field effects have been totally ignored. Our experimental results
already demand a major theoretical change. Magnetic fields do interact with matter and have
profound effects. Microwave energy coupling to the unpaired spins in the material is the key for
the chain reaction.
The following experiment suggests that the direct energy conversion from electromagnetic wave
to material. A paving plate made of SiC was inserted at the bottom of the crucible as shown in
167
figure-2. The part of the microwave energy was converted to thermal energy in the paving and
the sample was heated by conduction. The temperature rise of the surface by conduction was
identical to the pure microwave up to 700°C, however, neither temperature jump nor burst
appeared. The temperature saturated at 1000°C and the reduction of iron was very low.
The burst and jump were particular nonlinear phenomena depending on the microwave power.
The threshold was determined by the intensity of electromagnetic wave. In our experimental
conditions, the threshold powers were 2.5kW without the paving and more tan 12.5 kW with
paving. These experiments clearly show that the microwave electric and magnetic field supplied
the energy directly to the material to make chemical process, such as reduction and heating. The
burst itself and the high-temperature state after burst were sustained by the microwave power.
The equilibrium lines cross over at 690°C for carbon- carbon oxides and for Iron oxide on the
diagram of free energies V.S. temperatures (Ellinghum Diagram) as shown in figure-10. The
reaction can be separate at this point to the Step I and to Step II/III in figure-3. Below this
temperature, line emissions were not observed on the sample. The localized sparks were
triggered by the electric field of microwave. When the temperature reached to higher than the
cross point, a spark ignited the burst as shown in figure-4. The chemical reactions induced
locally both the reduction of iron oxide and the oxidation of the carbon (combustion) in the spot.
The non-equilibrium state was excited and the reductions were enhanced by microwave. The
oxidation of carbon gave the thermal energy to the near particles on a microscopic scale. When
the microwave + (microscopically) thermal energy transfer exceeds the enthalpy of the iron
oxide, it gives oxygen to the other carbon. The carbon then heats the next iron oxide. When the
input power of microwave is turned off, the emission-light disappeared in a moment and the
temperature rapidly decreased independently of the temperature. In case of conventional
furnace, that supplies the energy only by the burning of carbon, the process continued but very
gently. The role of the microwave is crucial for the present rapid phenomenon.
It has been now shown in the series of experiments (here and on a wide range of materials, Si,
TiO2, ferrites etc.) that microwave radiation simultaneously can cause a solid material to both
have its temperature raised, and to be transformed to an electronically (and hence
thermodynamically) excited state.
i.e.
Atº + hȣ (2.45GHz) = A*t1
Moreover, the figures and summaries of our data clearly demonstrate that:
A + hȣE (2.45GHz) = A*E
and
A + hȣH = A*H
and further that A*E  A*H
In a qualitative way we can be sure that the differences only in the field (E or H) must be
responsible for the data.
Reviewing our experimental results here, the excitation levels were estimated to be several
electron volts corresponding to the line emissions. On the other hand, the infrared pyrometer
168
indicated 950 oC that corresponded to 0.08eV. The existence of two different energy levels
suggest that the thermally non-equilibrium state was excited at the atomic level.
It is not able to distinguish the influence of the electric and magnetic field to the reactant in the
multimode cavity used in the steel making experiments. However, according to our previous
experiments using single mode cavity (2), carbon can be heated only in E-field and magnetite can
be heated more effectively in the magnetic field. As the carbon is electrically conductive
material, the current limit the penetration of microwave to the powders. If the carbon burned to
CO or CO2 gas, microwave can penetrate deeper in to the powders through the remaining spaces
between the grains of magnetite powders. The H-field heats up the magnetite more rapidly. It
wakes up the temperature jump and burst. The reaction speed increased. This is the other
considerable mechanism that does not depend on the thermodynamic equilibrium condition. In
the assumption, microwave directly couples to the irons. The energy transfer efficiency is
expected to be better than the pass through the kinetic energy of the electrons in the surface gas
or plasma.
Quantitative research must be done to clear the mechanism of microwave steel making.
Figure –10 Reaction Free Energy V.S. Temperature (Ellingham Diagram) of iron oxide
169
Acknowledgement
The research of visible light spectrum measurements has been supported by NIFS fund
No10204014KYAI001 and supported by Kansai Electric Power Co. Inc Japan. The research of
Prof Nagata has been supported by JSPS Category (s). The research of Profs. Roy and Agrawal
has been supported by the Office of Naval Research.
References
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(2) R.Roy, R.Peelamedu, L.Hutt, J.Cheng, D, Agrawal: “Definitive experimental evidence for
microwave effects: radically new effects of separated E and H fields”, Mat Res Innovation 6
(2002) p128-140
(3) M. Sato, R. Roy, P. Ramesh, D.Agrawall:”Microscopic Non-equilibrium Heating
- A Possible Mechanism of Microwave Effects” Proc. 4th International Symposium on
Microwave Science and Its Application to Related Fields, 2004
(4) M.Sato, A.Matsubara, K.Kawahata, O.Motojima, T.Hayashi, S. Takayama,
“Microscopically In-situ Investigation for Microwave” Processing of Metals by Visible Light
Spectroscopy, Proc. 11th International Conference on Microwave and High Frequency
Heating, O-24, Sep.11-15, 2005 Italy
(5) Kazuhiro NAGATA, Kotaro ISHIZAKI and Tetsuro HAYASHI, Low temperature
production of pig iron from carbon – composite pellets heated by microwave, 5th JapanBrazil Symposium on dust processing-energy-environment in metallurgical industries
proceedings, Volume 1, pp 617 - 625, September 2004
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