The Department of Materials Science and Engineering (MSE) is investigating the use of monatomic chlorine produced in a cold plasma to recover oxygen and metallurgically significant metals from lunar materials. Development of techniques for the production of the chlorine radical (and other energetic radicals for these processes) using local planetary resources is a key step for a successful approach. It was demonstrated terrestrially that the use of UV light to energize the photogeneration of OH radicals from ozone or hydrogen peroxide in aqueous solutions can lead to rapid reaction rates for the breakdown of toxic organic compounds in water. A key question is how to use the expanded solar resource at the lunar surface to generate process-useful radicals. This project is aimed at investigating that question

Fazzolari, R.

Lynch, D. C.

Osborn, D. E.

English

NASA Technical Reports Server

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Innovative Techniques for the Production of Energetic Radicals _,/!_'_
1 /for Lunar Materials Processing Including Photogeneration
Via Concentrated Solar Energy _%_'D. E. Osborn, D. C. Lynch, and R. Fazzolari
Department of Materials Science and Engineering
and
Solar and Energy Research Facility, Department of Nuclear and Energy Engineering
The University of Arizona
Introduction
The Department of Materials Science and Engineering (MSE), with funding from the
NASA Space Engineering Research Center (SERC) for Utilization of Local Planetary
Resources, is investigating use of monatomic chlorine produced in a "cold" plasma to
recover oxygen and metallurgically significant metals from lunar materials (Lynch 1989).
Development of techniques for the production of the chlorine radical (and other
energetic radicals for these processes) using local planetary resources is a key step for
a successful approach.
It has been demonstrated terrestrially that the use of UV light to energize the
photogeneration of OH* radicals from ozone or hydrogen peroxide in aqueous solutions
can lead to rapid reaction rates for the breakdown of toxic organic compounds in water
(Osborn et al. 1988). A key question is how to use the expanded solar resource at the
lunar surface to generate process-useful radicals. This project is aimed at investigating
that question as a joint effort of MSE and the Solar and Energy Research Facility (SERF)
of the Department of Nuclear and Energy Engineering (NEE). It is being conducted by
Donald E. Osborn under the supervision of Dr. David Lynch.
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Approach
Sunlight provides useful energy for processing in the forms of both thermal and
quantum energy. While the use of thermal energy is well accepted, the use of quantum
energy of the solar photons (photonic processes) for chemical reactions presents new
and exciting possibilities.
Photonic Processing. Sunlight is electromagnetic radiation that is normally divided
into three major bands: Ultraviolet (UV) ranges from about 180 nm to 380 nm, visible
ranges from 380 nm to 780 nm, and infrared (IR) ranges from 780 nm to about 10,000
nm. The energy of a photon varies inversely with wavelength as follows:
hc
E- T;hV.
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where E is energy, h is Planck's constant, ), is wavelength, and v is frequency.
considers a gram-mole (gmol) of photons, the energy associated with a
wavelength is
28591
E - _ kcal/gmol .
If one
given
The shorter wavelengths are the most energetic.
Light can affect material in two basic ways: thermally or through photonic
processes• The absorption of light can lead to an increase _n the vibrational, rotational,
and translational energy of the atoms of the material. Macroscopically, this shows up
as an increase in temperature and, once absorbed, the effectiveness of the energy is
not dependent on the wavelength of the light. Photonic processes are wavelength
dependent and are characterized by a threshold wavelength that is specific for each
process and material.
If light is absorbed by a molecule and if it has sufficient energy (i.e., short enough
wavelength), it can cause a transition of electrons from one orbital to another. If the
==
electron belongs to a chemical bond, the bond may be broken by this transition• UV
and near UV, as the most energetic wavelengths, can break a wide variety of bonds, as
seen in Table 1.5• While it may not be possible with the wavelengths available to
break the bonds of the material of interest directly, a photocatalytic process may be
used, or energetic free radicals that can break the bonds can be photogenerated.
Some of the photochemical reactions that can lead to such free radicals are shown in
Table 1.6.
It has been demonstrated that the combination of ozone and UV photons produces
rapid reactions in the form of photochemical oxidation of halogenated organic
compounds (Fletcher 1987). Ozone and hydrogen peroxide decomposition to free
radicals is accelerated by absorption of UV light. Free radicals, having a considerably
higher oxidation potential than molecular ozone, produce the favorable reaction rates•
Experiments by Osborn et al. (1988) demonstrate the increased reaction rate for the
decomposition of a red organic dye using UV from natural sunlight in combination with
H202 or TiO 2. The process produces free radicals that lead to bond breaking and
reduction of the color of the dye solution (Figure 1.19)• Further experiments at a
concentration of 6 suns show greatly enhanced reaction rates over the 1-sun case.
The concentrated solar irradiation could be used in materials processes by using
the UV and near-UV photons to form free radicals desired for "cold" plama processing
(Lynch 1989). These radicals could include monatomic CI, F, O, H, and OH* for
reduction and oxidation.
[-44
Table 1.5 Dissociation energies for chemical bonds (Legan 1982).
Bond D (Kcal/mol) Xp (nm)
CI-CI 58 490
C-CI 81 353
C-F 116 247
C-H 99 290
C-O 86 334
C--C 83 346
C=C 146 196
C=C 200 143
H-H 104 274
O-O 119 240
O-H 118 243
H-CI 103 279
F-F 37 780
Table 1.6 Photochemical reactions leading to free radicals.
Reaction Xp (nm) Resultant Radicals
H20 + hv= H*+ OH*
H202 + hv = 20H*
02 + hv = 03
Fe+2 + hv = Fe*3
0 3 + hv = 0 2 + O*
CI2 +hv=2CL*
185
254
254
254
310
49O
Atomic hydrogen and hydroxy
Hydroxy
Ozone
Ferrous ion to ferric ion
Atomic oxygen (Note: O* + H20 = 20H*)
Atomic chlorine
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SOLAR DECOMPOSITION- UA/SERF
RED ORGANIC DYE- WEAK
_er'f'_lrw_r-
Figure 1.19 Effect of solar light on red dye.
Extraterrestrial Radiation. While the UV content of the solar spectrum at the
Earth's surface is very limited in quantity and decreases rapidly with decreasing
wavelength, sunlight at the Moon's surface or in Earth orbit contains both greatly
increased levels of total UV and the shorter wavelengths. For Earth-based systems, we
have little UV below 320-340 nm. Extraterrestrial solar radiation, however, extends
below 240 nm, with significantly higher levels throughout the UV band (see Table 1.7).
The use of AI reflectors would permit the concentration of this energy, with good
reflectance throughout the solar UV band. Appropriate spectrally selective filters could
remove excess energy at unwanted wavelengths if excess thermal energy is a problem
(Osborn 1986).
Table 1.7 UV content in sunlight for AM0, AM1, and AM4 (W/m2).
AM0 AM1 AM4
< 400 nm 118.1 88.4 11.1
< 310 nm 22.5 0.5 0.0
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Chlorination Kinetics
Extensive studies of chlorination kinetics of several materials were undertaken by
the Bureau of Mines (Landsberg and Block 1965). The experiment being conducted
under this project extends the Bureau of Mines' Work and seeks to determine the effect
of concentrated solar energy on the chlorination kinetics of iron and molybdenum.
Those metals were chosen because the rate of chlorination of Mo is known to be
limited by the dissociation of CI2, while that for Fe is not. Furthermore, the rate
constants for reactions are well established. In addition, the reaction products are
volatile at reasonable temperatures (250-450°C). Simulated solar light should lead to
the dissociation of CI 2 and thereby enhance the rate of chlorination of Mo. The
increase should, initially, be linear with the intensity of the simulated solar energy. The
solar energy should have no effect on the chlorination rate of Fe, unless a new reaction
path is created with the presence of monatomic chlorine.
The objective of these experiments is to test the hypothesis that solar energy can
be used to produce reactive radicals. If the experiments are successful, an attempt will
be made to use solar energy in the chlorination of metal oxides and thereby the
liberation of 02 .
£xperirnental Setup. The experimental apparatus is shown in Figure 1.20. The
sample to be chlorinated will be suspended by a fiber resistant to the chlorine
environment. The fiber is attached to one arm of the Cahn R-100 electrobalance. A
tare weight is suspended from the other arm. The balance is enclosed by a bell jar
and base plate. The balance will be flushed with argon gas to protect it from the
corrosive environment. A 1-inch fused silica tube extends from the balance into a
resistance wound furnace. The tube is U-shaped so that an argon-chlorine gas mixture
is preheated in the electric furnace before it contacts the metallic specimen. The
specimen will be positioned just above the electric furnace, where the simulated solar
light can be absorbed by the specimen and gas mixture near the specimen. A solar
reflector will be used to concentrate the light around the specimen. During an
experiment, the region of the silica tube above the furnace will be insulated with
ceramic wool to minimize heat loss.
A thermocouple will be extended down the tube to a position near or in contact
with the specimen to record its temperature during an experiment. The thermocouple
will be placed in contact with the specimen when it is necessary to determine how
much addtional heating the simulated solar energy provides.
The chlorine-argon gas mixture is supplied from a pressure-regulated cylinder with
a needle valve. If deemed necessary, the gas mixture can be scrubbed in concentrated
sulfuric acid and passed over calcium chloride pellets before being metered by a
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ORIGINAL PAGE IS
OF POOR QtJALITY
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Figure 1.20 Experimental apparatus.
calibrated orifice-manometer. An accuracy of *-2% is desired for gas flow rates. A
total, gas flow rate of 500 cc/minute or greater will be used with chlorine
concentrations ranging from 0 to 12%.
The metal specimens will be both annealed and cold rolled. They will be rubbed
with abrasive powder and rinsed with acetone to remove scale and thereby provide a
uniform surface. The surface area should be about 4-5 cm 2.
Results to Date. The primary effort in the past 5 months has involved design and
construction of the experimental apparatus. A photograph of the nearly completed unit
is shown in Figure 1.20. The system includes a Cahn microbalance, resistance wound
furnace, solar simulator, gas delivery system, reaction chamber, furnace control unit,
and associated electronics. The apparatus is undergoing initial testing at this time.
Future Work
Three major experimental tests will be performed. The first seeks to confirm the
Bureau of Mines' results and to determine the chlorination rates without UV light. The
second set of experiments will determine the reaction rates under the same conditions,
but with UV light. The third stage of the experimental program will extend those tests
to lower reaction temperatures and varying concentrations of light. Chlorine levels will
vary from 0% to 12%, and the reaction temperature between 3000 and 450°C.
_ _, _ _.: _'_'___ _, _. "
These experiments will help to establish the experimental and theoretical basis for
the direct production of energetic radicals from solar energy and the use of those
radicals in the processing of lunar materials.
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References
Fletcher, D. B., 1987, "UV/Ozone Process Treats Toxics," Water World News, Vol. 3, No.
3, pp. 25-27.
Glaze, W. H., Kang, J. W., and Chapin, D. H., 1987, "The Chemistry of Water Treatment
Processes Involving Ozone, Hydrogen Peroxide and Ultra Violet Ratiation," Ozone
Science and Engineering, Vol. 9, pp. 335-352.
Landsberg, A. and Block, F., 1965, "A Study of the Chlorination Kinetics of Germanium,
Silicon, Iron, Tungsten, Molybdenum, Columbium, and Tantalum," Report 6649,
U.S. Bureau of Mines.
Legan, R. W., 1982, "Ultraviolet Light Takes on CPI Role," Chemical Engineering, Vol.
89, No. 2, pp. 95-100.
Lynch, D. C., 1989, "Chlorination Processing of Local Planetary Ores for Oxygen and
Metallurgically Important Metals," Annual Progress Report 1989-99, NASA Space
Engineering Research Center, University of Arizona, pp. 1-25-35.
Osborn, D. E., 1986, "Spectrally Selective Beam Splitters Designed to Decouple
Quantum and Thermal Solar Energy Conversion in Hybrid Concentrating Systems,"
Final Report, SERI Contract XK-4-04070-01 and Sandia Contract 04-5348,
University of Arizona.
Osborn, D. E., Sierka, R., and Karpiscak, M., 1988, "Solar Thermal Water Reclamation
and Toxic Waste Destruction," Final Report SERI Contract XX-7-07199-1,
University of Arizona.
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Innovative techniques for the production of energetic radicals for lunar materials processing including photogeneration via concentrated solar energy

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