NASA Technical Reports Server (NTRS) 19930007714: Microwave heating of lunar materials. Appendix A

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N93-16903
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Appendix A: Microwave Heating
'--/4,
of Lunar Materials
Thomas T. Meek
Introduction industrial use (0.915 GHz and
2.45 GHz). However, some work
Microwave heating of nonmetallic has recently been carried out at
inorganic material has been of 28 GHz* and 60 GHz (Meek et al.
interest for many years. Von 1986). At Los Alamos National
Hippel in the late 1940s and Laboratory, the work has centered
early 1950s investigated how about the fabrication of useful
microwave radiation up to 10 GHz engineering components.
couples to various insulator
materials. Perhaps the most work Table A-1 lists some materials that
has been done by Wayne Tinga have been thermally processed
at the University of Edmonton using microwave energy and
(Alberta, Canada). Most of the some products that have been
work to date has been done at the fabricated at both 2.45 GHz and
two frequency bands allowed in 60 GHz.
*Personal communication with H. D. Kimrey, Fusion Energy Division, Oak Ridge National
Laboratory.
TABLE A-1. Some Starting Materials Heated by Microwave Energy at Los Alamos
and Resultant Products
Material Product Processing Frequency,
temperature, GHz
oC
Owens-Illinois (OI)-
1756C glass Ceramic-glass seal 462 2.45
OI-0038 glass Ceramic-glass seal 735 2.45
1613 glass** Ceramic-glass seal 1450 2.45
Alkali basalt Sintered material 1200 2.45
AI203 Sintered material 1300-1900 2.45, 60
ZrO2 Sintered material 1300-1900 2.45, 60
Ilmenite Sintered material 1350 2.45
Apollo 11 regolith Sintered material 1100 60
SiC whisker-AI203 Composite material 1300-1900 2.45, 60
"1-1igh-temperature glass made at Los Alamos.
307
Usingmicrowaveenergytoprocess semiconductors. To heat traditional
lunar material offers a new, oxide materials, such as alpha
potentially very efficient way of alumina, we incorporate materials
heating these types of materials. that do couple to 2.45 GHz
Not only can lunar material be radiation, such as aluminum nitrate.
heated with less energy than that These materials cause the oxide
required by conventional methods, to heat to a few 100 degrees
but the heating is accomplished Celsius, after which the oxide will
more uniformly and in much less couple because its ability to absorb
time (Meek et al. 1985). electromagnetic energy (its loss
tangent) has increased sufficiently.
Discussion It is known that most lunar regolith,
down to a depth of 3 meters,
Many oxide materials are contains at least 106 imperfections
transparent to microwave energy at per cubic centimeter from cosmic
2.45 GHz and 0.915 GHz. Oxides rays, solar flares, and the solar
that possess impurities, such as wind (see fig. A-l). The defects
mobile ions or mobile defects, introduced into this soil over
that enhance their electrical millions of years' exposure to these
conductivity will, however, couple high-energy particles should
to electromagnetic radiation in this increase the loss tangent of this
frequency range. Heating will be material and allow it to be heated in
primarily electronic. a microwave field without the use
of coupling agents. Terrestrial
For example, beta alumina contains alkali basalt shows only weak
by weight 11 percent sodium, thus coupling initially; however, when
enabling it to couple efficiently to the intensity of the electric field is
2.45 GHz microwave radiation. increased, this material heats
Beta alumina, when placed in a rapidly. Recently we demonstrated
2.45 GHz microwave field of the ability to heat ilmenite to its
400 watts power can be heated melting temperature using
from room temperature to its 2.45 GHz microwave energy.
sintering temperature (1850°C)in Since ilmenite is present in
just a few seconds (Berteand and abundance on the lunar surface
Badot 1976). Materials such as in mare regions, it could act as a
cuprous oxide (Cu20), zinc oxide coupling agent to allow the initial
(ZnO), and zirconium dioxide heating of those lunar materials that
(ZrO2) will also couple efficiently may not couple at ambient
because they are defect-controlled temperature.
308
Figure A-1
Tracks ofCosmic Ray Particles and
Solar Flare Particles ina Plagioclase
Crystal
Theplagioclase crystal structure has been
severely damaged where these high-
energy particles havepenetrated into the
crystal. Etching of thecrystal withNaOH
has preferentially removed thedamaged
material, leaving elongated, rectangular
holes or tracks. Such track damage is
common inmanylunar regolith crystals.
Table A-2 shows observed heating where i- = heating rate in degrees
rates for some of the materials Celsius per minute
thermally processed using f = frequency in hertz
2.45 GHz and 60 GHz microwave E = electric field intensity in
energy. If the proper electric field volts/cm
intensity (E) or magnetic field k' = dielectric constant of
intensity (H) is used, rapid heating the material
of lunar materials will also occur, tan 8 = loss tangent of the
The following expression (PL_schner material
1966) shows the relationship p = density of the material
between the approximate heating Cp = heat capacity of the
rate and the applied electric field material
intensity for the heating of an
insulator material. Because heating on the Moon will
occur in a vacuum, where much
"i" -- 8 X 10-12 f E2 k' tan 8 greater electric field intensities can
be used, materials that would not
p Cp
couple on Earth may be heated
very easily and quickly.
309
TABLEA-2.
Heating Rates Observed for Different Insulator Materials
Heated at 2.45 GHz and 60 GHz
Material Observed heating rate, Frequency,
°C per hour GHz
1613 glass 33 000 2.45
OI-0038 glass 20 000 2.45
OI- !756C glass 12 000 2.45
Aluminum oxide 18000 60
Recommendations Meek, T. T., et al. 1986.
Microwave Processing of
Much work remains to fully Ceramics. J. Microwave Power
characterize some of the & Electromagnetic Energy 21:
phenomena observed to date 193-194.
with microwave-heated oxide
and composite materials. For Meek, Thomas T.; David T.
example, diffusion should be Vaniman; Franklin H. Cocks; and
modeled, reaction kinetics Robin A. Wright. 1985. Microwave
should be studied, and Processing of Lunar Materials:
sintering kinetics should be Potential Applications. In Lunar
better understood. Bases and Space Activities of the
21st Century, ed. W. W. Mendell,
479-486. Houston: Lunar &
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Power 11:315-320. Springer-Verlag.
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Microwave Power, pp. 19-29, Nov. New York: Academic Press.
Tinga, W. R., and E. M. Edwards. Von Hippel, Arthur R., ed. 1954.
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Von Hippel, Arthur Robert. 1954.
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311