OAK RIDGE NATIONAL LABORATORY--R&D UPDATES
This article also appears in the Oak Ridge National Laboratory
Review (Vol. 25, No. 2), a quarterly research and development
magazine. If you'd like more information about the research
discussed in the article or about the Review, or if you have any
helpful comments, drop us a line. Thanks for reading the Review.
LASER TECHNIQUE DETECTS POLLUTANTS IN FISH
Using a laser and a mass spectrometer, ORNL researchers can detect
trace pollutants in fish and determine when and where the fish were
most exposed to these pollutants. The technique permits scientists
to map sources of contamination inexpensively and determine the
contamination history of a fish without harming it.
ORNL researchers led by Ed Arakawa, leader of the Physics of Solids
and Macromolecules Group in the Health and Safety Research
Division, have demonstrated the technique using fish scales from
striped bass. They believe they have detected polychlorinated
biphenyls (PCBs) in the scales of fish three years old or younger.
"The scales of a fish have annual growth regions like tree rings,"
says Arakawa. "Thus, we can determine in which seasons and in which
years it was exposed to certain pollutants, such as pesticides,
mercury and other heavy metals, and PCBs.
"Because we know the local striped bass spend the summer in the
Clinch River and the winter in Watts Bar Reservoir and because we
can pinpoint when the fish were exposed to certain pollutants, we
should be able to determine where contaminants are most
concentrated. The fish scales we examined indicated that the fish
were exposed to less pollution in the Clinch River than in the
Watts Bar Reservoir."
The technique includes the use of laser ablation to vaporize
different regions of a fish scale, which is composed of calcium and
magnesium. An ultraviolet light from an excimer laser knocks off a
few atoms from the fish scale and removes electrons from these
atoms, making them positively charged ions. These ions form a beam
that is pulled by an electric field into a time-of-flight mass
spectrometer.
Because of the different masses of the ions, they slow down at
different rates and are detected at different times, permitting
identification of the different elements in the fish scale. One of
the "peaks" on the mass spectrometer readouts for recent ORNL
experiments indicated the strong presence of chlorine. The source
of the chlorine, Arakawa says, is probably PCBs.
Chuck Coutant, an expert on the effects of water temperature on
fish, proposed the idea of applying the technique to detecting
pollutants in the scales of local fish. Coutant and Marshall Adams,
both of the Environmental Sciences Division, remove a few scales
from striped bass, which are then returned alive to the river, and
supply them to Arakawa's group for study. The original analysis was
done by Ida Lee, a postdoctoral scientist; physicist Samuel
McKenzie; and Arakawa.
If additional funding can be obtained, McKenzie and his colleagues
will use two ultraviolet lasers to extend the technique to
detecting pesticides and heavy metals and measuring pollutant
concentrations in fish scales. To determine the accuracy of their
technique, they will compare their measurements of pollutants in
the outer edge of scales of dead fish from the Savannah River Site
with the results of analyses of the total content of each fish.
--Carolyn Krause
NEW BIOPROCESSING R&D CENTER AT ORNL
A Bioprocessing Research and Development Center has been
established at ORNL in recognition of the increasing importance of
biotechnology to the nation's long-term security and economic
prosperity. Bioprocessing uses living organisms to produce new
products. Results from ORNL's expanded bioprocessing research and
development effort will be transferred to the industrial sector to
help make the United States more competitive in the marketplace.
Under the new initiative, scientists from ORNL's Chemical
Technology Division, supported by the Biology and Environmental
Sciences divisions, will develop bioprocesses for energy-related
programs and environmental control and will produce a variety of
commodity and specialty chemicals.
"The hallmark of our efforts, supported by some 25 years of past
experience in bioprocessing research, will be to expand
interactions with academia, other national laboratories, and
industry," says Chuck Scott, senior corporate fellow and newly
appointed director of the center. "Transferring bioprocessing
technologies to industry will be the ultimate goal of most of our
research and development work."
ORNL scientists will concentrate on bioprocessing systems that can
economically produce fuels and chemicals from fossil materials and
renewable feedstocks, including recycled waste material such as
paper. Researchers also will develop bioprocessing systems to
remove and degrade pollutants.
Funding for the center comes from the Department of Energy. Other
government agencies benefiting from ORNL's contributions will
include the Department of Defense and the Environmental Protection
Agency, which need advanced techniques for environmental control
technology and waste recycling; the National Institutes of Health,
which can use advanced processing techniques to produce therapeutic
agents; and the Department of Agriculture, which seeks processes
for the small-scale conversion of surplus and waste agricultural
products.
ORNL has established an interlaboratory initiative for
bioprocessing research and development with Argonne National
Laboratory in Argonne, Illinois; the Idaho National Engineering
Laboratory in Idaho Falls, Idaho; and the National Renewable Energy
Laboratory in Golden, Colorado. Laboratory scientists will also
collaborate with several university laboratories, including the
Center for Environmental Biotechnology at the University of
Tennessee in Knoxville.
ORNL's achievements in biotechnology over the years include (1)
creating advanced techniques for producing liquid and gaseous
biofuels to provide alternatives for meeting future energy demands,
(2) developing bioreactor systems for producing ethanol and other
chemicals, (3) removing nitrates and phenols from industrial
wastewaters using microorganisms, and (4) using biological agents
to remove hazardous material from polluted soil and groundwater.
Funding for programs within the Bioprocessing Research and
Development Center is being provided by several DOE offices,
including the Office of Energy Research, the Office of Technical
Coordination, the Office of Fossil Energy, and the Office of
Industrial Technologies.
--Brian Daly
OFF-THE-WALL IDEA FOR STRUCTURAL EVALUATION
Nondestructive evaluation (NDE) of structures, such as walls,
bridges, and overpasses, is used to determine how much they
deteriorate as they age. Traditionally, techniques such as
ultrasonics or radiography have been employed for NDE; however, the
limitations of these techniques make them unsuitable for many
situations.
Ultrasonic systems can measure the depth or thickness of some
materials with high precision, but they require a smooth surface
through which to pass sound waves. Radiography using X rays or
isotope sources is slow, requires the structure to be unoccupied,
and requires access to both sides of the wall. Infrared
thermography and ground-penetrating radar have also been applied to
NDE, but their drawbacks are low resolution and high cost.
When a group at the Oak Ridge Y-12 Plant began looking for an NDE
technique to examine the condition of the hollow clay tile block
walls of some of Y-12's older buildings, Don Bible, Carl Sohns,
Richard Crutcher, and Randal Maddox, all of ORNL's Instrumentation
and Controls Division, came up with the idea of using a low-power
microwave probe to do the job.
"DOE officials were concerned about the potential effect of an
earthquake on these walls," Bible says. "They knew how the walls
were supposed to have been built, and they knew they weren't always
built that way. They needed a nondestructive way of getting an
internal picture of the walls to locate irregularities. As a
result, we began to develop a portable microwave diagnostic
probe.
"At first, we tested mockup walls with sophisticated lab equipment
and various microwave frequencies. Then we came up with the idea of
transmitting a simple reference signal into the wall at an angle
and comparing the wave characteristics of the signal going in with
those of the reflected signal coming out."
The microwave signal transmitted into the structure is partially
reflected by different layers of materials or irregularities,
giving a composite reflection that contains information about each
internal layer. This composite signal is considered the "signature"
of the structure under test. "Standard" signatures are obtained
from structures of known composition that are in good condition.
When the signature of the test structure matches the standard
signature, the structure is considered normal. A test signature
that differs significantly from the standard may indicate
irregularities in composition or it may be a sign of structural
deterioration. By varying system parameters, such as the frequency
of the microwaves or the separation between transmitting and
receiving horns, the system can be customized for a wide variety of
structures.
A more rigorous challenge for the microwave probe was a test wall
built at the K-25 Site. "The K-25 wall incorporated a lot of
irregularities," Bible says. "They filled some blocks with mortar
and stuffed paper or rubber gloves into others--anything they could
think of that workers might have done while building the walls at
Y-12. That's when we decided to use a computer to compare test
signatures with an entire set of standard signatures representing
a range of possible wall characteristics."
Once tuned for a particular structure, the simple readout
eliminates problems of interpretation and allows large areas of a
structure to be rapidly examined. Eventually, Bible hopes to
incorporate the entire system into a simple, hand-held unit that
can be used by individuals with a minimum of training and will
display the results of its analysis on a liquid crystal display
screen.
The probe can also be used for inspection of building foundations,
concrete walls, bridge pillars, and road surfaces and for the
location of hidden polyvinylchloride pipes that elude metal
detectors. Bible expects that this inexpensive, easy-to-use probe
would benefit agencies charged with inspecting and maintaining the
nation's infrastructure, allowing limited funds to be used on
structures most in need of repair.
--Jim Pearce
STUDYING SNAILS AND STREAM HEALTH
A type of snail that is abundant in most streams in east Tennessee
is noticeably absent in contaminated Oak Ridge streams, indicating
a significant level of pollution. Such a snail could serve as a
sensitive indicator of and contributor to improved water quality in
Oak Ridge streams as remediation programs take effect.
These are two conclusions of a recent study by Walter Hill, a
research associate in the University of Tennessee's Graduate
Program in Ecology, and Arthur Stewart of ORNL's Environmental
Sciences Division. These stream ecologists have focused on snails
of the family Pleuroceridae and of the genus Elimia, which are
present in large numbers in freshwater habitats. Such snails are
particularly useful as indicators of the presence of
contamination.
Elimia snail studies have been funded by Oak Ridge biological
monitoring and abatement programs set up to assess the impacts of
pollutants on stream life. These programs are required by the
National Pollution Discharge Elimination System permits issued to
Department of Energy facilities, including those on the Oak Ridge
Reservation.
In their paper "Grazers, Periphyton and Toxicant Movement in
Streams," Hill and Stewart report that Elimia have probably been
eliminated from Oak Ridge streams because of pollutants such as
polychlorinated biphenyls (PCBs), heavy metals (mercury, cadmium,
and chromium), chlorinated drinking water, and once-through cooling
water discharges. The absence of Elimia, the scientists add, not
only makes it difficult to study the indirect biological effects of
contamination but may also lead to an increased accumulation of
contaminants in fish and other animals higher in the food web.
The ecologists have used Elimia to study growth rates in three
streams near ORNL and plan to transfer individually tagged snails
to polluted ORNL streams to determine whether decontamination
efforts have been successful.
"Elimia is the dominant invertebrate in many uncontaminated streams
in eastern Tennessee," says Hill. "Several thousand snails can be
found per square meter. This snail owes its dominance partly to its
thick shell, which protects it from scouring floods and predators
such as crayfish and fish."
This type of snail, Stewart says, is well suited for studying the
biological effects of toxic materials in streams. It can live in a
stream as long as 10 years, permitting extended studies of aquatic
conditions. It is sensitive to various toxic substances, and its
response can be measured. For example, it responds to toxicants by
eating less (reduced feeding rate) and by dispersing in a certain
pattern.
"Elimia tend to move upstream when water quality is good," Stewart
says, "and downstream when water quality is degraded. Because of
the large size of the snail, we can determine its rate and
direction of movement remotely with a video time-lapse
recording."
In addition to helping scientists monitor stream health, the snail
also may help preserve it. Elimia feed mainly on masses of algae,
bacteria, and other organic material that form a slimy film called
periphyton. High populations of the snail graze periphyton down to
a thin layer, preventing nuisance blooms. Other invertebrate
species do not control algal biomass as well as this snail.
"By feeding on periphyton," Hill says, "the snails increase the
movement of toxic substances downstream. If periphyton is allowed
to flourish, the sticky film will take up many toxicants, slowing
their net movement downstream. As a result, biologically available
concentrations of toxicants in streams with low populations of
Elimia snails can remain high, and the toxicants enter the food web
more easily."
A recent study showed that the concentrations of mercury, cadmium,
and chromium in East Fork Poplar Creek are many times higher in the
creek's periphyton than in the water itself. The creek receives
discharges from the Y-12 Plant, a nuclear weapons production
facility in Oak Ridge.
"The absence of this snail in Oak Ridge streams," Hill says,
"probably increases the movement of toxicants into stream food
webs. This effect results from the expansion of the periphyton
biomass, which accumulates contaminants in greater quantities the
more it grows. Soft-bodied grazers that feed on periphyton become
more abundant and further concentrate the pollutants, which move
into the food web because these species make a good food for
fish."
Hill and Stewart see the Elimia snail as an example of a sensitive
key species whose removal will amplify pollution effects. "As
ecotoxicologists," Hill says, "our challenge is to understand and
predict the ecological consequences of both direct and indirect
effects of pollution."
--Carolyn Krause
ORNL CONTRIBUTES TO WETLAND MANAGEMENT
To help the nation monitor gains and losses in its wetlands, ORNL
is playing an important role in designing a program to measure
changes in coastal land cover--marshes, swamps, forests, farms, and
urban areas--and to provide reliable data on these changes. Two
researchers in the Computing and Telecommunications Division at
ORNL are working with the National Marine Fisheries Service to
develop the CoastWatch Change Analysis Program (C-CAP). Since the
early 1980s Jerome Dobson, a senior research staff member, and
Edward Bright, a geographic information analyst, have been
developing the program, which is supported by the National Oceanic
and Atmospheric Administration (NOAA).
A recent proposal to change federal policy to open once-protected
wetlands to development angered some environmentalists. The
controversy hinged on questions on the definition of wetlands, the
role they play in the environment, and the wetland area lost to
development or natural changes.
Wetlands are those areas of the landscape where land and water
meet. They help to control flooding, purify water, and provide an
important habitat for fish and wildlife.
"The pressure to protect wetlands has been growing in concert with
the environmental movement," Dobson said. "As a result, several
agencies are supporting a national effort to map land cover and
detect wetland gains and losses." Mapping will be done with the aid
of geographic information systems, satellite and aerial data, and
various ground-based data bases.
Dobson said the greatest challenge lies in the sheer size of the
effort. "Detecting changes in small areas can be accomplished by
making image-to-image comparisons, but detecting changes for areas
that cover hundreds or thousands of square kilometers is more
difficult," he said. To obtain accurate comparisons, C-CAP
researchers first had to develop a consistent method of
categorizing land cover (e.g., agree where marshes end and
grasslands begin). In September, NOAA, the U.S. Fish and Wildlife
Service, the U.S. Geological Survey, and the Environmental
Protection Agency agreed on a standardized classification scheme
for defining categories of land cover.
For each area being monitored, current and earlier satellite scenes
must be selected, and careful attention must be given to cloud
cover, tidal stage, and vegetative season. Training samples
containing areas of known land cover are selected with the help of
wetlands ecologists and regional specialists and are then matched
with patterns of light reflected from the known area, as identified
through remote sensing by satellites.
Satellite images consist of 30-m2 rectangles called pixels; data
for each pixel indicate the amounts and wavelengths of light
reflected from the surface. The type of land cover in each pixel
can be determined through statistical analysis comparing unknown
pixels with the training samples, Dobson said. "This way we can
detect, for example, whether we're looking at an urban area or an
agricultural area." He explained that multiple samples of each
area are selected to represent each land-cover classification. Then
the classified land cover is graphically overlaid on a map.
After initial classifications have been made, the researchers begin
tests for reasonableness and consistency. These are accomplished by
comparing selected areas with other wetlands data sources and by
investigating the appearance of unlikely pixels, such as urban
pixels showing up in areas where cities are not known to exist, he
explained. "Once we're satisfied with the results for each current
scene, we add adjacent scenes to create a single regional data
base," Dobson said. "Then we repeat the entire process for the
earlier time period based on the same ground control points." He
said the process of detecting changes between the two scenes
consists of a pixel-by-pixel comparison and the creation of a
matrix for recording the changes.
Dobson said no literature previously existed on how to assess error
levels for changes from one time period to another. "We brought in
the top error-estimation specialists, who came up with a new and
clever solution that involved focusing first on the area and then
on the classification," he said.
Although national in scope, C-CAP will be administered as a series
of regional efforts with help from state governments and
universities. Candidates include Chesapeake Bay, Galveston Bay,
Tampa Bay, coastal South Carolina, North Carolina, and Rhode
Island. "Selected regions will be monitored every five years,
except for areas that have experienced environmental disasters or
rapid population growth," he said. "Those will be monitored more
frequently."
Dobson believes the methods and technology developed for C-CAP are
the same as those needed for global environmental monitoring and
modeling. "The same protocols developed for C-CAPand the care taken
in its development are needed for monitoring such problems as
deforestation and desertification. The consistent land-cover
classifications are especially important to global monitoring,
where we encounter very subtle gradients from temperate to tropical
vegetative species," Dobson said. "Also, if sea levels begin to
rise, the most sensitive indication of these changes will be
differences in coastal vegetation."
Accuracy assessments for C-CAP will soon be completed, and Dobson
said initial results have been encouraging. "If the results are as
good as we expect them to be, C-CAP will provide more than just an
effective measurement of changes in coastal wetlands. It will also
be an effective tool for analyzing public policy and practices to
ensure valuable U.S. wetlands are protected, and it could provide
environmental analysts with the means to monitor changes in global
environmental conditions."
--Karen Bowdle
WIRELESS ROBOTS IN HOT CELLS
Robots can now move freely in a highly radioactive environment too
hazardous for humans, thanks to a new method of wireless
communication developed at ORNL. With this invention, engineers in
ORNL's Instrumentation and Controls Division have made it possible
for untethered robots to operate freely in hot cells used for
reprocessing nuclear fuel.
Until recently, wireless communication in large-volume hot cells
had been considered impossible because the metal walls of the cell
cause electromagnetic echoes, or reflections, that confuse robots.
The new method employs directional radio waves of very high
frequency to reduce the reflections to an acceptable level. It also
eliminates damaged and tangled robot wires.
ORNL engineers have tested the new concept by constructing a
Transportable Reflecting Environment Communication System (TRECS).
The radio computer system sends signals to the robot's computer,
enabling it to perform duties within a cell about the size of a
football field.
TRECS' electronics are designed to withstand temperatures up to
60øC (140øF) and doses of gamma radiation up to one million rads
(200 rads is considered lethal to humans). Although relatively
maintenance-free, the system is designed modularly to facilitate
any needed remote maintenance.
Use of this system will eliminate the large cable bundles that
would otherwise be required between the walls of the cells and the
operating robots. "TRECS has been fully developed and tested and is
ready for commercialization," says Steve Schrock of ORNL's Robotics
and Process Systems Division. "We expect the system could be
adopted for use in hot cells toward the end of this decade."
As part of a DOE cooperative agreement with the French Commissariat
a l'Energie Atomique (CEA), French researchers recently tested the
TRECS on robotic equipment installed in metal-lined facilities in
France. Shrock said the testing was "very successful."
--Brian Daly
ORNL PRODUCES A NEW BATCH OF RESEARCH ISOTOPES
A campaign to produce isotopes of transuranic elements for use in
research at DOE laboratories and at other scientific facilities has
been successfully completed at ORNL's Radiochemical Engineering
Development Center (REDC). This was the first group of such target
isotopes processed since operations resumed in early 1990 at the
Laboratory's High Flux Isotope Reactor (HFIR) following a
three-year shutdown for procedural reviews.
The REDC is the production, storage, and distribution center for
DOE's heavy-element research program. "It is the world's premier
facility for such work and the only outlet for many of the heavy
elements," said Bob Wham, REDC manager. "To continue advancing our
knowledge of heavy elements, there must be basic research. And this
center is the ground floor for that basic research."
Transuranic elements, which are called heavy elements because of
their high atomic weight, do not occur naturally on the earth. They
are artificially produced by bombarding the nuclei of elements such
as americium and curium with neutrons. At ORNL, such radioactive
isotopes are produced in the HFIR.
"We have an abundance of requests from the research community for
these ORNL-produced elements," Wham said, adding that the temporary
shutdown of the HFIR had created somewhat of a backlog.
"Laboratories and other facilities that depend on us to supply the
material for their research were anxious for us to be back in
business."
However, the interim period of the HFIR shutdown was not a time of
idleness for the REDC, according to Wham. "The HFIR shutdown
actually allowed us time to upgrade our system and to hone our
operation so that we can continue to accomplish the goals of our
campaigns safely and in compliance with regulations."
Uses for the heavy elements produced during the latest ORNL
campaign range from studies in nuclear physics to cancer research.
One transuranic element that has multiple applications is
californium. The Food and Drug Administration proposes using
californium-252 for determining the presence and concentration of
sodium in food. The isotope can be used for the simultaneous
detection in food of toxic heavy metals, such as arsenic or
mercury.
Californium is also part of a technique now being used at several
major airports in the United States and Europe to detect hidden
explosives in air passengers' luggage. Because it fissions
spontaneously and emits neutrons, californium is used by
universities as a "substitute reactor." Wham said that students
using the element learn how to develop reactor instrumentation and
to analyze the spectrum associated with fission without requiring
an actual nuclear reactor.
The REDC is operated for production 24 hours a day by members of
ORNL's Chemical Technology Division and support personnel from
other divisions.
--Wayne Scarbrough
GLOBAL CO2 EMISSIONS RISE AT A LOWER RATE
Global carbon dioxide (CO2) emissions from industrial sources
continue to rise but at a lower growth rate than in recent years.
According to a special issue of CDIAC Communications commemorating
the 10th anniversary of ORNL's Carbon Dioxide Information and
Analysis Center (CDIAC), the 1989 estimate for global emissions of
carbon represents a 1.2% growth over the 1988 value, "a notable
drop from growth rates of the past several years."
The 1989 value for global CO2 emissions from fossil-fuel
consumption, cement manufacturing, and gas flaring is 5.97 gigatons
(thousand million metric tons), compared with 5.90 gigatons for
1988. Emissions from the use of natural gas and other gas fuels and
from cement production contributed less than 4% to the total carbon
emissions for 1989, which was the sixth consecutive year that
global CO2 emissions have increased.
In commenting on CDIAC's 10th anniversary, Mike Farrell, former
director of the center, writes that, in 1982, he believed that
"climate change research was going to be highly theoretical and an
area that would never draw much attention from the public." Ten
years later, Farrell notes, "global change is the environmental
problem of the 1990s and beyond." In fact, Farrell, Paul Kanciruk,
and David Reichle, all of ORNL, presented papers at the world's
largest conference, the United Nations Conference on Environment
and Development (the so-called Earth Summit) in June 1992 in Rio de
Janeiro, Brazil.
CDIAC is a data management and distribution center. It develops,
collates, and provides extensive quality-assurance audits on data
bases that are critical to understanding global change. Future
initiatives include developing interactive data-analysis systems
using a network of computers dispersed throughout the world.
According to Farrell, recent statements by Allan Bromley, President
Bush's science advisor, and the establishment of the Interagency
Working Group on Data Management for Global Change under the
Committee on Earth and Environmental Sciences umbrella suggest that
issues in data management are now "recognized as equally important
in understanding global change as the research that produces the
data."
--Carolyn Krause
BROADBAND ABSORBER LEAVES OPTICAL SYSTEMS IN THE DARK
In precision optical systems, such as telescopes, camera lenses,
and test equipment, stray reflected light degrades optical
performance. Researchers minimize this light by using optically
black (nonreflective) surfaces, such as liners, baffles, and beam
stops. Unfortunately, the most common methods of creating optically
black surfaces--etching, coating, and anodization (an
electrochemical process that produces a layer of oxide on metal
surfaces)--all have shortcomings that restrict their usefulness.
Etching decreases reflectivity, but only if the wavelength of the
light is smaller than the etched surface features. Anodized and
coated materials are also effective optical absorbers, but their
light-absorbing surfaces are easily damaged. Anodized beryllium,
among the most widely used material for optical absorbers, is too
reflective to be used at certain wavelengths, and because beryllium
can be toxic, precautions increase processing costs.
To get around these shortcomings, Bob Lauf of ORNL's Metals and
Ceramics (M&C) Division and Roland Seals of the Oak Ridge Y-12
Plant's Development Division became interested in creating an
absorber that would perform over a broad band of wavelengths and be
durable enough to withstand normal handling.
They decided to study the feasibility of creating such a broadband
absorber using a composite material known as carbon-bonded carbon
fiber (CBCF). CBCF, used commercially as a high-temperature furnace
insulator, has also been manufactured by other M&C personnel for
use as thermal insulation for radioisotope thermoelectric
generators aboard the National Aeronautics and Space
Administration's space probe, Ulysses. The material is made by
mixing a water-based slurry of chopped carbon fibers and a resin
binder. The slurry is vacuum-molded, dried, and then heated slowly
to melt the resin and bind the fibers together. Finally, the resin
is converted to carbon at high temperatures, and the component is
machined to its final shape.
Lauf and Seals persuaded Clyde Hamby of the M&C Division to
formulate several batches of CBFC with less fiber and more binder,
hoping to create a material that was more rugged than standard
CBFC. After some tinkering with the recipe, Lauf and Seals found
what they were looking for.
The resulting material is uniquely well suited for use as an
optical absorber for a variety of reasons. First, because CBCF is
a bulk material rather than a surface enhancement or coating, it is
optically black throughout, making it immune to surface damage.
Another M&C co-worker, Al Akerman, demonstrated that CBFC can be
sanded and machined without losing its light-absorbing properties.
It is unaffected by small variations in processing, unlike anodized
or vapor-deposited coatings, which are highly sensitive to process
variables. In addition, it absorbs light over a much wider spectrum
than many standard optical absorbers--up to at least 50 microns,
compared with 10 microns for etched beryllium. Also, it is
lightweight, easily fabricated into almost any shape, and, because
of its low atomic weight, it is highly resistant to radiation and
thermal damage.
"This is an amazing material," says Lauf. "You can make a big
billet of CBCF, machine it to any shape you want, and it's
automatically optically black. It's much more robust than any of
the competing products. You can cut it, file it, or even machine
shapes into its surface. Also, because it's carbon, it's not toxic.
And it's pretty cheap as high-tech materials go."
CBCF can be used wherever low reflectivity is needed over a wide
range of optical wavelengths. Examples include liners and baffles
for telescopes and beam stops for laser equipment. In addition,
CBCF can be coated with metal and used as a diffuse-reflectivity
standard for calibration and testing of optical equipment. The
compound is ideally suited for use in standards and other
components that must be handled frequently because its optical
properties are not affected by surface contact.
For applications in which greater structural strength is needed,
CBCF can easily be bonded to a dense graphite backing. Or, if a
combination of reflection and absorption is needed, such as in
advanced annular baffle systems used to minimize unwanted light in
telescopes, it can be attached to sheets of reflective metal.
"We'd like to develop other spin-offs of this technology, " says
Lauf. "Using CBCF as an optical absorber is only the first."
--Jim Pearce
(keywords: pollutants, lasers, bioprocessing, microwave probe,
wetland management, robotics, isotopes, carbon dioxide, optical
absorbers)
------------------------------------------------------------------------
Please send us your comments.
Date Posted: 2/7/94 (ktb)