(This article also appears in the Oak Ridge National Laboratory
Review (Vol. 26, No. 1), a quarterly research and development
magazine. If you'd like more information about the research
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helpful comments, drop us a line. Thanks for reading the Review.
ORNL RESULTS HELP FIRM DECIDE TO MARKET SILICON NITRIDE
The Norton Company, a ceramic manufacturer in Worcester, Massachusetts,
had a problem. The company had developed a new silicon nitride material
that might be more suitable for use in high-temperature gas turbines
than its current product. Its ceramicists had systematically adjusted
the chemistry of its commercial silicon nitride product, NT154, and
produced a new ceramic, NT164. However, the Norton researchers were not
sure if they had developed a product that was good enough to be
marketed. So Norton turned to ORNL for help through the user program at
the High Temperature Materials Laboratory (HTML). Norton engineers in
collaboration with ORNL researchers proposed through a user project to
test the mechanical properties of NT164 at high temperatures and compare
them with the results they had obtained earlier on NT154. In addition
they wanted to analyze the two ceramic materials using the HTML's
powerful microscopes. The challenge was to find differences in the
microstructure of the two materials that might account for differences
in mechanical properties.
As a result of the ORNL findings, Norton decided to commercialize NT164,
and Michael Jenkins, Matt Ferber, and Ted Nolan, all of ORNL's Metals
and Ceramics Division, received a 1992 Martin Marietta Energy Systems
Technical Achievement Award. They were cited "for significant materials
characterization and analysis contributions to the development and
commercialization of a high-performance silicon nitride ceramic."
Silicon nitride is the preferred material for components of
high-temperature gas turbines because of its combination of important
properties. It is very strong, hard, and highly resistant to wear,
oxidation, and decomposition at high temperatures. It is incredibly
resistant to thermal shock--large changes in temperature, such as a drop
from 1200 to 20 degrees Celsius in a matter of seconds--that would cause
ceramics such as alumina and silicon carbide to shatter.
Because the ceramic gas turbine could operate at higher temperatures
than the nickel-based superalloy engine, it would use fuel more
efficiently and produce less pollution. However, such an engine has not
been produced commercially yet because of problems in fabricating dense,
precisely shaped components that are reliable at high temperatures. To
overcome this problem Norton is developing new silicon nitride materials
by adjusting the chemistry of the silicon nitride (Si3N4) powders and
sintering aids (e.g., oxides of yttrium and aluminum) used to form the
material and make it dense.
The ORNL researchers tested the Norton ceramics for high-temperature
creep deformation--a gradual change in length, or strain, in a material
as a result of prolonged exposure to stress and high temperatures. They
also evaluated each ceramic for static fatigue--the time it takes for a
material to fail under a constant stress--to determine its long-term
The ORNL researchers subjected both materials to tensile tests, applying
stresses of 100 to 200 megapascals (MPa) at temperatures of 1260 and
1370 degrees Celsius, the temperature that turbine components must
endure. Dumbbell-like tensile specimens of each material held through
SupergripTM couplers were pulled at each end and heated to high
temperatures at the center. ORNL results showed that, under the same
conditions of 100 MPa and 1370 degrees Celsius, Norton's commercial
ceramic deformed at a higher rate and failed after 1200 hours, whereas
the new material survived for 4800 hours.
"We found that NT164 lasted four times as long yet accumulated three
times as much strain as NT154," says Jenkins, now with the University
of Washington in Seattle. "The new ceramic clearly was more resistant to
creep degradation and static fatigue and more reliable in the long term
than the already commercialized material."
To determine the reason for the mechanical superiority of the new
material, the ORNL researchers characterized the microstructure of both
ceramics using transmission electron microscopy.
"What we found was that NT164 had very little intragranular cavitation,"
Jenkins says. "It had little of the Swiss-cheese-like appearance of the
Commercial silicon nitride ceramics can also be processed to be
self-reinforced rather than reinforced with silicon carbide whiskers
(which may pose a health hazard if they are inhaled and deposited in the
lungs). By using sintering aids such as oxides of rare earths (e.g.,
yttria, ytterbia, and scandia) and applying proper processing
temperatures and pressures, long columnal grains are grown among the
uniformly sized grains. The long grains act like whiskers, bridging
cracks and toughening the material. During this processing, amorphous,
or noncrystalline, material may form between the ceramic's crystalline
grains, areas called grain boundaries.
When silicon nitride is exposed to high enough temperatures, this glassy
material softens, allowing creep deformation by mechanical and
diffusional mechanisms. In mechanical deformation, the silicon nitride
grains slide relative to each other; creep cavities or holes may
develop, and the ceramic becomes deformed. In diffusional deformation,
elemental material (e.g., silicon and nitrogen) may dissolve into the
glassy material, forming holes or cavities in the silicon nitride
grains, and redeposit or unite with other grain-boundary elements.
This elemental transport took place at junctions between two grains but
not at three-grain junctions where enough glassy material was trapped
and crystallized. The dissociated elements cannot move through the
crystalline regions in these "triple points," which are formed during
"By controlling the chemistry of the starting material and sintering
process for NT164, Norton researchers almost eliminated the formation of
the glassy material at the two grain boundaries," Jenkins says. "We
found that the glassy regions in NT164 were only about one nanometer
thick compared with several nanometers in NT154. Norton researchers made
grain boundaries so thin that the bulk of the glassy material was forced
into triple points where it becomes crystalline."
This collaborative work between ORNL and Norton, says Jenkins, is a good
example of how the diverse and unique user facilities and personnel
available at the HTML can help industrial firms solve problems.
MICROWAVE-PROCESSED SILICON NITRIDE IS COST-EFFECTIVE
Using microwaves, three Oak Ridge researchers have developed a
cost-effective method of making ceramic parts for advanced engines for
transportation. The Oak Ridge technique produces silicon nitride parts
that cost less and are denser than parts made by conventional processes
under ordinary conditions. The denser the material, the stronger and
usually more fracture resistant it is.
According to Terry Tiegs of ORNL, one of the developers of the
technique, applications include components for engines operated at high
temperatures, such as turbocharger rotors, valves and valve parts, and
pump seals. Other uses could include tools to cut metals and dies for
forming aluminum beverage cans.
Silicon nitride is the ceramic material of choice for components of
high-temperature engines being developed to improve the fuel efficiency
of cars and trucks. It is highly resistant to wear, deformation,
oxidation, and decomposition at high temperatures, and it is also
incredibly resistant to thermal shock--large changes in temperature that
would shatter other ceramics. In fact, the latest silicon nitride
materials have been shown to have outstanding characteristics for rotors
and stators in gas turbines for cars and trucks and for valve trains in
diesel- and gasoline-powered engines.
Some silicon nitride parts that meet the requirements for use in engine
applications have been made, but because of the processes used, these
components are much more expensive than metal parts. The Oak Ridge
process using microwave heating could produce ceramic parts that are
economically competitive with metal components. The chief reasons are
that the process uses a combination of low-cost raw materials (about
one-fourth that of the materials used in other processes) and a
simplified processing route made possible by the microwave heating.
The process was developed by Tiegs and James Kiggans, both of ORNL's
Metals and Ceramics Division, and Cressie Holcombe, a researcher in the
Development Division of the Oak Ridge Y-12 Plant.
In the ORNL process, a silicon nitride ceramic is fabricated in a
microwave field. Silicon powder mixed with additives in a preformed
shape is reacted with a nitrogen-containing gas as the ceramic part is
heated to 1200 to 1400 degrees Celsius by microwave power. As a result,
nitridation of the silicon (Si) to silicon nitride (Si3N4) occurs.
Without removing the parts from the microwave furnace or cooling them
down, the parts are then heated to 1750 to 1825 degrees Celsius, making
them extremely dense.
With conventional heating, the nitridation and densification steps have
to be done in two different furnaces. By using microwave heating to
accomplish both tasks, the fabrication times and labor costs are
According to the developers, microwave heating offers several advantages
over conventional heating. Nitridation begins at a lower temperature and
occurs at a faster rate. Nitridation and sintering (heating) are
accomplished in one continuous process. Densification rates are
increased. Finally, thicker parts can be made because nitridation
proceeds from the inside out.
Microwave heating of silicon nitride parts has been done in furnaces in
Building 4508 at ORNL. The process has been successfully tested on
silicon nitride parts containing sintering aids in a cooperative
research and development agreement (CRADA) with the Norton Company, the
ceramic manufacturer in Worcester, Massachusetts.
INCHWORM EXPLORES AND CLEANS UP PIPES
It could be creeping through the pipes under the buildings at ORNL. It
may be found in waste lines, storage tanks, or even in a stream. This
miniature robot, just one foot long, is called Inchworm, but it doesn't
measure marigolds. However, it can measure concentrations of acids and
other pollutants in waste streams, according to its inventor, Don Box,
of ORNL's Chemical Technology Division.
Ordinary mechanical robots are limited in where they can go. They
typically require electrical power to operate, and they have trouble
maneuvering in confined spaces and around corners. Inchworm, however,
has none of these limitations. Instead of using electricity, it operates
on low-pressure air and vacuum. It can go forward, backward, and around
corners at 90 degrees, and it can even move vertically.
Inchworm can go through round or square pipes and even small pipe
discontinuities. Versions of the robot can be built to fit into either
small or large pipes. Inchworm can even move through flowing water or
sludge. It carries a video camera and its own light source, and it can
be fitted with instruments and tools to perform a variety of tasks.
"If we had a waste stream with many different streams discharging into
it and someone discharged excess acid into the stream, Inchworm could
help find the source," Box says. "We could put it in the waste stream
and measure the pH with a probe as the robot moved along. By observing
where the pH changed, we could tell exactly where the acid was coming
from. If we wanted to know more about the acid, we could put some tubing
on the robot and draw up a sample as it entered the stream."
Another possible use for Inchworm is at the K-25 Site, where miles of
ducting are contaminated with uranium-235 (U235). Dry-ice blasting, a
new method of cleaning surfaces similar to sand blasting but using solid
carbon dioxide (CO2) pellets instead of sand, could be used to
decontaminate the pipes, but no method currently exists for moving the
blasting head into the pipelines.
"We could put the blasting head on the robot and let it blast its way
down the pipeline as the robot moves along it and then pull the CO2 back
with a vacuum and collect the U-235 particles," Box says. "This way we
could clean out these pipes more safely than we could with an acid
cleaning system or by cutting the pipe up first and then cleaning it
The demonstration model of Inchworm is about 0.3 meter (1 foot) long at
rest and 10 centimeters (4 inches) in diameter. It has expandable head
and tail ends linked by three columns of flexible tubing. Two
inexpensive pumps supply the air pressure and vacuum to run the robot.
Vacuum and pressure applied to the tubing in various combinations make
Inchworm go forward, backward, and around corners.
Box controls the robot with a set of switches now, but he is
computerizing the control mechanism so that it will work with a
joystick. Images from Inchworm's on-board, high-definition color
television camera appear on a video monitor magnified up to ten times.
In use, the robot looks very much like its namesake. It gives the
impression of being a living thing as it crawls through clear plastic
tubing in the laboratory.
Several industrial firms are very interested in the Inchworm robot, and
Box expects to be involved in a number of cooperative research and
development agreements as soon as his patent application is approved.
Inchworm will save its users time and money as well as improve worker
safety by creeping into places humans can't or shouldn't go because of
physical, chemical, biological, or radiological hazards.
FROZEN FRUIT FLY EMBRYOS HATCHED
Researchers from ORNL and the University of Chicago have succeeded in
thawing and hatching deep-frozen fruit fly embryos, some 25% of which
develop into fertile adult flies. The finding may enable biologists to
store, rather than maintain in living cultures, some 15,000 different
genetic stocks of mutant Drosophila, saving considerable time and money.
It may also help entomologists understand the genetic basis of malaria
transmission by mosquitos.
For 80 years fruit flies have been useful sources of information on
heredity. Geneticists like them because they have a life span of only 10
days, are easy to culture in the laboratory, and carry a small number of
chromosomes, some of which are large and easily visible in the
microscope at the larval stage. The fly is particularly appealing
because it easily undergoes changes in its genes to produce detectable
mutations. Furthermore, many of the genetic principles are applicable to
human genetics and the human genome program.
Some 15,000 genetically characterized strains of fruit flies, each
having a unique set of mutations, now exist in the world. However, only
about 20% are in active use; the rest represent completed research or
are available for future studies. Geneticists don't like the cost and
time required to maintain these stocks in living cultures by frequent
transfer of adults for breeding. They also worry that the frequent
transfer can result in genetic drift and mistakes that can lead to stock
For almost 20 years scientists sought unsuccessfully to preserve embryos
of live fruit flies by freezing them in liquid nitrogen. Ironically,
during that time, cryobiologists succeeded in freezing cow embryos from
superior cattle, and the technique has been used to increase the
production of high-quality beef. Embryos of mouse stocks at ORNL and at
the Jackson Laboratory in Bar Harbor, Maine, are now being frozen using
a technique based on the one first demonstrated by Peter Mazur, Stanley
Leibo, and David Whittingham in 1972 at ORNL.
Putting fruit flies to sleep in frozen storage has been easy, but making
sure they will wake up during thawing has been trickier than catching
one between your fingers. However, the problem of preserving them for
future use was finally solved in 1992 by Mazur, Kenneth Cole, Jerry
Hall, and Paul Schreuders, all of ORNL's Biology Division, and Anthony
Mahowald of the University of Chicago. Schreuders is also with the
University of Tennessee--Oak Ridge Graduate School of Biomedical
Sciences. They reported on their success in the December 18, 1992, issue
of Science magazine.
Incredibly, the frozen fruit fly embryos are among the most complex
organisms preserved by cryobiologists. These embryos each contain 50,000
cells, whereas the mouse embryos are generally frozen at the 8-cell
To preserve living cells, little or no ice can be allowed to form in
each cell and a special chemical must be added to each cell to protect
it from freezing damage. Thus, cells must be permeable, like a window
screen, so that water can be forced out by dehydration and the
cryoprotectant can be forced in. In conventional freezing used
successfully with mammalian embryos, water is withdrawn by osmosis from
cells and it freezes outside them.
The problem with Drosophila is that it is impermeable to both water and
the cryoprotectant. So the first task of the cryobiologists was to make
fruit fly cells permeable by dissolving the waxes on the embryo
membranes. The Oak Ridge group solved this problem by treating the
embryos with precisely controlled amounts of a gasoline-like alkane and
Then Mazur and his associates discovered that Drosophila embryos are so
sensitive to cold that those in the early stages died even before ice
had formed in the cells. They decided that con-ventional freezing would
not work and that ice formation must be prevented.
To achieve this end, they chose the alternative strategy of
vitrification--the formation of glassy, or noncrystalline material,
rather than ice crystals. Based on an approach reported by Peter
Steponkus and colleagues at Cornell University in 1990, vitrification
was accomplished by chilling the embryos to 205 degrees Celsius very
rapidly (100,000 degrees per minute) to "outrace" the lethal
consequences and by using up to 8 times the normal amount of
cryoprotectant (ethylene glycol) to dehydrate the cells and vitrify the
water. However, Mazur's group found that this strategy worked well only
on embryos in a certain developmental stage--those that were frozen 14.5
hours after the eggs were laid. The Oak Ridge group found that 68% of
these embryos hatched to larvae and that 40% of the resulting larvae
developed into normal adult flies.
The ORNL strategy may be useful for preserving mosquitos, houseflies,
and other nonmammalian embryos. Cryopreservation of various lines of
mosquitos could make possible identification of the gene that makes some
mosquito types susceptible to carrying malaria and of the gene that
makes other mosquito lines resistant to it.
According to the Science article by Mazur et al., "The optimal
developmental stages being frozen are probably the most complex systems
that have been cryobiologically preserved. The embryos are highly
differentiated into tissues and organs including muscle and nerve, which
indicates that differentiated multicellularity is not a barrier to
cryopreservation. The findings also represent perhaps the first case in
which vitrification procedures are required to obtain survival."
PROCESS DESTROYS NITRATES, PRODUCES CERAMIC
Using the same type of reaction that helps burn holes in safes and
military tanks, ORNL researchers have developed a simple process to
remove nitrate from liquid radioactive waste, greatly reducing the
amount of waste that must be stored. Nitrate, a pollutant in streams and
rivers, can be toxic to infants if present at high concentrations in
The ORNL process turns the nitrate into ammonia gas while co-producing
a ceramic waste form. The ammonia is later burned to form harmless
nitrogen and water vapor. The liquid-to-solid conversion can be achieved
using recycled aluminum from, for example, beverage cans or radioactive
aluminum scrap at Department of Energy sites.
At ORNL radioactive wastes containing sodium nitrate are stored in large
tanks. These wastes are the result of large-scale use of nitric acid for
chemical processing, especially of nuclear fuel in reprocessing
experiments. Some of this nitrate from 50,000-gallon tanks in Melton
Valley on the Oak Ridge Reservation is immobilized in cement-based
grout. A much larger volume of such waste exists at DOE's Savannah River
Site in South Carolina.
Because nitrate, which is highly mobile in the environment, can cause
suffocation by reducing the amount of oxygen carried by red blood cells,
the Environmental Protection Agency permits only 44 parts per million of
nitrate in drinking water. Thus, DOE sites have been immobilizing
radioactive waste liquids containing nitrate in cement-based grout,
increasing the amount of waste in the form of grout that must be stored
by 40 to 50%. The ORNL process can reduce the original volume of waste
by 55%, with good prospects for a 75% volume reduction soon.
"By immobilizing 100 gallons of nitrate-bearing liquid waste, the volume
of waste to be stored as grout can increase to 150 gallons," says
developer Al Mattus of the Chemical Technology Division. "If we are
given 100 gallons of liquid waste to process using the new method, we
end up having to store only 45 gallons of nitrate-free ceramic to meet
In the new process, aluminum powder is mixed with sodium nitrate (NaNO3)
in an alkaline solution. By feeding the powder into a chemical reactor
at a specific rate and constant low temperature (50 degrees Celsius),
Mattus can achieve a reaction between the metal and the oxide of
nitrogen (nitrate) that is similar to the reaction exploited by
safecrackers. "When powdered aluminum is mixed with a metal oxide and
ignited," Mattus says, "the result is a release of stored energy as
electrons, with a rapid release of heat as the oxide becomes molten
metal." A safecracker would use this reaction along with an explosive.
The products of the reaction in the ORNL process are ammonia gas (NH3)
and aluminum oxide, or alumina (Al2O3). This solid material, also known
as gibbsite, is mixed with silica to form a ceramic. The alumina settles
out in the chemical reactor, and the ammonia is released and later
burned to form harmless nitrogen and water vapor.
Mattus notes that this reaction is the opposite of the process used by
aluminum companies to convert alumina from bauxite ore to aluminum. "We
use the metal to release the energy put into it electrolytically and
form alumina again," he says.
Mattus says that the process will be demonstrated in a pilot plant being
built at ORNL (Building 2528). DOE has expressed interest in using the
ORNL process to address the massive nitrate problems of Hanford
Engineering Development Laboratory and other DOE sites.
A patent on the process has been filed. Martin Marietta Energy Systems,
Inc., is seeking to license the technology for commercial use, and
several companies have expressed interest in further developing and
marketing the process.
ORNL SYSTEM WILL SAVE NASA TIME AND MONEY
ORNL is developing a system to automatically monitor and verify the
status of electronic components in systems used for U.S. space launches.
The development is expected to help the National Aeronautics and Space
Administration (NASA) reduce its costs and number of launch delays.
Once perfected and deployed, this Intelligent Configuration
Identification System (ICIS) will eliminate the need for costly and
time-consuming physical inspections of the thousands of sensors on the
space vehicle and on the launch pad and the miles of cables running from
the sensors to the launch control complex, often called the firing room.
The result should be reduced turnaround time between launches and fewer
delayed or aborted launches.
"The amount of time spent tracking down broken wires in cables or
mismated cable connectors is amazing," says project engineer Mike
Hileman. "A system like ICIS could save a lot of time and money." The
ICIS project, sponsored by NASA, is being carried out by engineers in
ORNL's Instrumentation and Controls (I&C) Division.
ICIS was originally conceived as the solution to problems the Laboratory
had with several large data acquisition and control systems. "It can be
a nightmare trying to determine which of thousands of sensors are tied
to which channels of the data acquisition and control system," says
Hileman. "We had a real need for something that could automatically
determine the configuration of a system."
NASA had the same problem. Ground support personnel were spending many
hours verifying the cabling and configuration of their systems. The
space agency contacted ORNL after the I&C Division received an IR-100
award in 1987 for work on configuration and control systems. In 1989,
DOE and NASA entered into an agreement to develop the technology for
NASA's new National Launch System (NLS).
In July 1990, I&C engineers put the system through an initial
proof-of-concept demonstration for NASA at the Kennedy Space Center at
Cape Canaveral, Florida, based on the architecture used for the ground
support equipment for space shuttle launches. In January 1992, Allen
Blalock, Mike Hileman, and Jim McEvers demonstrated the system again at
the Johnson Space Center in Houston, Texas.
ICIS is being developed in support of the next generation of space
exploration vehicles as part of NLS. ICIS technology could also be used
for military applications, including damage assessment and monitoring
the health of ship or vehicle systems; for communications and power
systems; or for any large instrumentation and control network that is
frequently reconfigured. ICIS can determine the configuration of a
system, check for open or short circuits, and keep track of information
such as component serial numbers and calibration dates.
NLS will be made up of miles of cables and wires and thousands of
sensors and actuators that monitor and mechanically control a system's
components. Though not fundamentally different in kind from the current
launch system, the NLS will be much more complex. In addition to the
manned space program, many more unmanned missions are planned. Faster
turnaround times between launches will be essential. The size and
complexity of the system will make necessary an automated, real-time
quality assurance and monitoring system.
Traditionally, monitoring and control of systems have relied on manual
wiring checks. These checks are slow, and they cannot verify that wiring
is correct, determine the order of components in a system, or provide
information about cables and intermediate termination points in the
system. ICIS was developed to remedy these shortcomings.
ICIS requires only three types of components: sensor identification
modules at each end point of the system, cable or junction box
identification modules at each connection point, and a master module
tied to a personal computer. The system uses these modules to poll and
monitor the entire electronic network by exchanging signals with
individual subassemblies to verify their locations and conditions. "This
polling can be done without interfering with the data acquisition system
itself," Hileman notes. The procedure also provides information about
the integrity of the signal lines; for example, it can locate any short
or open circuits.
"For instance," says Jim McEvers, I&C's instrument-development group
leader, "ICIS transmits a signal to a sensor, asking, `Are you out
there, and if so, where and who are you?' The sensor then responds with
the requested information." Currently, to obtain this type of
information, someone must physically verify the location and status of
the component in question. "And that is painstaking and costly work,"
In the next phase of ICIS development, ORNL I&C engineers plan to reduce
the size of the hardware so that the sensor identification and
integrator modules fit inside and become integral parts of the cables
they will monitor. Also planned are the addition of the capability to
identify every cable conductor in a signal path, programmability of
identification modules by technicians in the field, development of a
programmer's station, and the ability to customize reports and graphic
displays for various applications. Ultimately, ICIS technology will be
transferred to private industrial firms.
ICIS has applications in all phases of space exploration. It can be
useful in pre-launch quality assurance and post-launch assessment. "Even
though launch engineers try to protect the hardware, cables may still be
damaged in a launch," Hileman says. "After a launch, ICIS could identify
which cables need to be replaced. This capability would decrease the
time needed for repairs between launches."
ICIS will provide real-time fault detection and monitoring of the space
vehicle's power, communication, and data systems. It may also be used on
the proposed space station to experiment with different system
configurations and for verification of the integrity of the station
after a system failure.
TREES' RESPONSES TO RISING CO2 LEVELS
Trees do not necessarily grow bigger and faster in an atmosphere
enriched in carbon dioxide (CO2), according to a study by Rich Norby,
Stan Wullschleger, Carla Gunderson, Gerry O'Neill, and others in ORNL's
Environmental Sciences Division. The researchers concluded that at least
one tree species may be responding to elevated CO2 concentrations by
growing additional fine roots rather than leaves that take up carbon.
The ORNL scientists are studying the effects of increased atmospheric
CO2 concentrations on photosynthesis and leaf respiration in forest tree
species, as well as other responses that may determine how trees in
natural forests will grow in the future. Their work is described in
detail in an article in the May 28, 1992, issue of Nature.
Photosynthesis is the tree's use of energy from sunlight to convert
atmospheric CO2 into carbohydrates. In a reverse reaction process, leaf
respiration is the release of CO2 from tree leaves back to the
atmosphere as carbohydrates are broken down for use as fuel by the tree.
The two processes together determine the tree's net carbon uptake and
potential for subsequent growth.
The concentration of CO2 in the atmosphere is increasing, largely
because of the combustion of fossil fuels for energy and the
deforestation of the earth, especially the cutting and burning of
tropical forests. Many scientists expect increased levels of atmospheric
CO2 to trap more heat near the earth's surface rather than allow it to
radiate into space, resulting in a rise in the average surface
temperature of the earth, commonly known as the greenhouse effect.
To accurately predict the amount of global warming, scientists must be
able to project the atmospheric level of CO2 at a given time. For these
models, they must have information about the uptake, storage, and
release of CO2 by plants.
In the past, most studies have focused on the uptake side of the
equation--photosynthesis. Those studies that dealt with leaf respiration
have used crop plants such as rice or alfalfa. However, as Wullschleger
points out, "You can't use rice as a model for something as complex as
a forest ecosystem."
"The trouble is that trees are a whole lot harder to deal with," Norby
observes. "Three years is the longest any of these forest trees have
been exposed to elevated CO2, so our results on carbon uptake and
release are really very important. We don't know if we can extrapolate
the results of agricultural studies to forests. Our objective is to
provide the right kind of input for such models."
Net carbon uptake by trees is important not only for slowing the
increase in atmospheric CO2 but also for making plant growth possible.
"The balance between carbon gained through photosynthesis and carbon
lost through leaf respiration is the difference between whether plants
grow or not," says Wullschleger. The increased plant growth seen under
high concentrations of CO2 was once thought to be primarily the result
of increased photosynthesis. Now it is known that decreased leaf
respiration also plays a role, and the ORNL study is the first to
document it in forest species.
One surprising finding of the study is that, although the yellow poplars
(Liriodendron tulipifera L.) used in the experiment did respond
predictably over three years to increased CO2 in the atmosphere by
increasing photosynthesis and decreasing leaf respiration, the trees
showed no significant increase in carbon storage or total biomass. The
reasons for this are not yet fully known, but Norby suspects that the
yellow poplar trees may be making adjustments in how they use the
carbon, such as growing additional fine roots instead of leaves. These
changes may make the tree better suited to the new environment, but at
the expense of short-term increases in growth. However, the white oak
(Quercus alba L.) trees in the same study were significantly larger when
grown in high CO2.
The experiment began in May 1989 on yellow poplar and white oak
seedlings, common tree species in the deciduous forests of eastern North
America. Yellow poplars and white oaks are important in these ecosystems
because of their abundance in the temperate forests of this region. The
two species have different nutrient requirements and growth habits,
making them good candidates for the study.
Six open-top chambers were constructed, each 3 meters in diameter and
2.4 meters in height (later increased to 3.6 meters in height for the
third growing season). Ten dormant seedlings of each species were
planted in the ground in each chamber. Later, the saplings were thinned
to five of each species. During the growing seasons, April to November,
the plants were exposed continuously to regulated levels of CO2
enrichment. The yellow poplar saplings were harvested in August 1991,
and the white oak saplings were harvested late in 1992.
The atmosphere in each of the chambers was carefully controlled. Three
levels of enrichment were chosen: ambient, ambient plus 150 parts per
million (ppm) CO2, and ambient plus 300 ppm CO2. Trees planted today may
one day be exposed to these CO2 concentrations, which are considered
likely to occur within the next 100 years.
Several factors differentiate this experiment from previous ones. The
trees were planted directly in the ground, not in pots, so the roots do
not become pot-bound, and the uptake of minerals from the soil is not
restricted. Second, they are not artificially irrigated or fertilized.
Third, the CO2 is provided 24 hours a day during the growing season.
This approach makes the experimental conditions as similar as possible
to those for trees growing in the wild in a CO2-rich atmosphere. The
ORNL researchers found that the short-term responses to CO2 enrichment
were indeed sustained over several years under realistic field
Predicting forest ecosystem responses to an atmosphere whose composition
is changing will be more difficult than previously assumed. Some
research indicates that forests have the potential to take up and store
more CO2 as its concentration in the atmosphere rises, but for accurate
modeling of the greenhouse effect and the forests of the future, more
long-term studies such as the ORNL experiments will be needed.
RISING UV RADIATION DAMAGES FOREST TREE POLLEN
The depletion of the earth's protective ozone layer has consequences
that range far beyond sunburned beachcombers. As the ozone layer thins,
more ultraviolet radiation from the sun penetrates to the earth's
surface. This ultraviolet light, which can cause skin cancer and
cataracts in unprotected humans, can also be damaging to trees.
To help determine the nature of this damage, geneticist Gerald A.
Tuskan, physiologist Tim J. Tschaplinski, and ecophysiologist Nelson T.
Edwards, all of ORNL's Environmental Sciences Division, are studying the
effects of ultraviolet B (UV-B) radiation on the pollen of various
forest tree species. Pollen, the mass of male microspores, is essential
to reproduction and the development of seeds.
Biologically active UV-B radiation, whose wavelengths range between 280
and 320 nanometers, is projected to increase by 2% for every 1% decrease
in stratospheric ozone that results from reactions with
chloro-fluorocarbon (CFC) molecules generated by human activities.
UV-B interacts with the leaves of some plants, decreasing photosynthesis
or increasing respiration. Photosynthesis is the process of using
energy from light to convert carbon dioxide to carbohydrates, and
respiration is the uptake of oxygen and the release of carbon dioxide by
leaves as carbohydrates are converted into energy for the plant. Both
processes are important to the energy metabolism of the tree.
As a result of the interference of UV-B radiation with these processes,
the tree's ability to capture and use the energy of sunlight may be
reduced, leading to greater susceptibility to pest damage or other
environmental stress. However, a tree may be most susceptible to the
effects of UV-B radiation during its reproductive cycle--that is, when
it is producing pollen.
"Pollen is the vehicle that ultimately allows all plants to reproduce,
adapt to stress, and survive," Tuskan notes. "Unlike leaves, pollen does
not have the physiological machinery to adjust to elevated UV-B
When reproduction is inhibited, the trees' ability to adapt to changing
conditions is decreased. Furthermore, global warming may change climate
zones, encouraging many tree species to migrate. Without seeds, this
migration cannot occur.
Over time, different tree species have adopted different pollination
strategies. Loblolly pine and red spruce trees are wind pollinated, and
yellow poplar is insect pollinated. Tuskan hypothesized that
wind-pollinated species would tolerate UV-B radiation the best, perhaps
because this pollination strategy naturally requires pollen to be
exposed to the presence of UV-B light. The pollen of insect-pollinated
trees, however, may lack this protection.
In Tuskan's experiment, pollen was collected from loblolly pine, red
spruce, and yellow poplar and tested for sensitivity to elevated UV-B
levels. UV-B radiation was chosen for the study because it is known to
cause genetic mutations and because the thinning ozone layer permits
proportionately more UV-B to penetrate to the earth's surface than other
types of UV radiation.
For the experiment, various samples of tree pollen were exposed to UV-B
radiation either at a simulated ambient level or at 30% or 100% above
this level for either 4 or 8 hours. These radiation levels correspond to
current conditions, a 15% depletion of the ozone layer, and a 50%
depletion of the ozone layer, respectively. A 15% depletion is the level
projected as a result of current CFC levels in the atmosphere. The
ultraviolet light was provided by UV-B-313 fluorescent lights, and the
desired levels were obtained using mylar filters.
After the pollen was exposed to UV-B radiation, the ORNL researchers
determined the percent germination of the pollen, pollen tube length,
percent abnormal pollen tube formation, and the identities and
concentrations of secondary plant metabolites that reduce the effect of
UV-B radiation on the plant. Pollen germination involves the formation
and elongation of the pollen tube through which the pollen nuclei
migrate to the receptive egg, resulting in fertilization.
UV-B-attenuating secondary plant metabolites are compounds formed in a
plant that absorb ultraviolet radiation. These compounds may not be
needed for plant growth and function, but they are thought to protect
the plant from the damaging effects of ultraviolet radiation.
Under the 8-hour exposures, pollen germination was at or near 0% in all
tested species. Under the 4-hour exposures, the insect-pollinated
species, yellow poplar, was more sensitive to UV-B radiation than were
the wind-pollinated species, as Tuskan hypothesized. Evidence of this
sensitivity included decreased germination rates and reduced pollen tube
In all species, however, the researchers found significant increases in
the frequency of abnormal pollen tube formation in pollen exposed to any
level of elevated UV-B radiation. For example, a species that normally
produces single pollen-tubes produced multiple or branched tubes after
UV-B exposure. If the defect prevents the male nuclei of the pollen from
reaching the female nuclei (eggs), reproduction will not occur.
By using reversed-phase, high-pressure liquid chromatography, the ORNL
researchers found large differences among the species in the types and
concentrations of UV-B-absorbing compounds. They are currently
attempting to identify the specific UV-B-absorbing compounds and relate
these differences among species to their various abilities to tolerate
elevated UV-B radiation.
The exact mechanism by which UV-B radiation damages pollen is still
undetermined. Damage may be physiological or genetic, or it may result
from disruption of the structure of the pollen membrane.
Forests are made up of many species. Some may be susceptible to rising
levels of UV-B, and others may not. Tuskan hopes the ORNL work will
enable scientists to accurately model the forests of the next century.
"This knowledge," he says, "could help policymakers decide how best to
protect the stratospheric ozone layer and maintain biological
COMPUTER MODELS FOR SPACESHIP DESIGN
ORNL researchers are employing computer modeling to design an ion
thruster, a space propulsion system that may one day be used on missions
to Mars and the other planets. "The fundamental attraction of an ion
thruster," explains John Whealton of ORNL's Fusion Energy Division, "is
that accelerated ions are a more efficient fuel than chemical
propellants. The farther away your destination is, the more important is
The ion engine is a type of electric propulsion system based on a
concept two decades old. Approximately 30 electric thrusters of other
types have actually flown in space. The National Aeronautics and Space
Administration (NASA) is looking at ion engines for cargo missions to
Mars and beyond. These systems would be advantageous for interplanetary
missions because their low propellant requirements make them less
massive than their chemical rocket counterparts.
Ion engines use noble gases such as xenon or argon as propellants.
Electrons from 10-V filaments strip electrons from the gas molecules,
forming positively charged ions. The resulting mixture of ions and
electrons forms a plasma. The plasma is kept in a chamber lined with
cusp field magnets to keep the charged particles from migrating to the
chamber walls. At one end of the plasma chamber is a series of two
plates with holes in them.
After the ions leave the chamber through the first plate, they are
directed toward the second plate by an accelerator powered by a 1000-V
power supply. The ions then escape into space as exhaust plasma, driving
the spacecraft in the opposite direction based on Isaac Newton's First
Law of Motion: "For every action, there is an equal and opposite
Electric power for the filaments and power supply could come from either
a nuclear reactor or solar cells. Of course, the weight of the power
supply could reduce the weight savings from the fuel.
NASA is interested in designing very reliable ion thrusters that will
operate for a year or more. The ORNL research, which is sponsored by the
space agency, is aimed at working out the fine details of the design,
especially those related to plasma edge effects.
At the walls of the plasma containment vessel, an abrupt change in
electrical potential occurs. Because this change in potential results in
a strong electric field, ions in the plasma accelerate toward the walls
at high speed. A hole in the vessel allows ions to be extracted and
accelerated to high speed. The paths of the ions, which can be complex,
are determined by the shape of the plasma boundaries. If not controlled,
the swiftly moving ions can damage the accelerator itself.
"From our fusion research we're uniquely expert at solving plasma edge
problems in two and three dimensions," says Whealton. "Our computer
software, developed over the past 15 years, is unique in that respect."
Along with Whealton, Richard J. Raridon of the Computing and
Telecommunications Division; David A. Kirkman, an undergraduate student
at the University of California-Irvine; and Russell Campbell, a physics
teacher at Rockville Public High School, are studying the
characteristics of ion thruster plasmas in both two and three
dimensions. The researchers are attempting to determine the optimum
configuration and operating conditions for an engine of this type. Of
particular concern are the perveance (the density of the plasma), the
geometry of the accelerator, the thickness of the accelerator
electrodes, and the density and shape of the exhaust plasma. Working
with the ORNL researchers are several high school teachers from the
Teachers Research Associates Program and a student from the Science and
Engineering Research Semester education program, both funded by DOE at
Interplanetary travel is not the only potential application of the ORNL
research. Ion sheath dynamics have uses unrelated to space. "The ability
to control the shape and brightness of an ion beam has a lot of
applications," says Whealton. "The configuration of an ion source and
plasma is relevant to semiconductor manufacturing, where ion beams can
be used to etch circuits into chips, and to fusion energy experiments in
which ion and neutral beams can heat and help confine the plasma. Also,
devices like the proposed Superconducting Super Collider and
accelerators for high-energy physics, in which beams of ions must be
tightly controlled and directed, could make use of this technology."
COMPUTERIZED TRAINING FOR INDUSTRY
Today's automated manufacturing plants bear little resemblance to plants
of 10 or 20 years ago. The rapid technological advances that have taken
place in process control systems during the last decade have resulted in
highly sophisticated manufacturing equipment--equipment that challenges
operators, supervisors, and maintenance personnel when something goes
wrong or needs repairs.
However, a recent development by a team of researchers in ORNL's
Instrumentation and Controls Division is helping to solve maintenance
and repair problems. Called the Knowledge-Based Assistant for
Troubleshooting Industrial Equipment (KATIE), this new computerized
system helps employees identify problems and understand how to perform
the steps needed to correct them.
"The majority of today's manufacturing systems demand an overwhelming
amount of information and expertise by maintenance personnel," said
Abigail G. Roberts, a development engineer in ORNL's Instrumentation and
Controls Division. To perform maintenance and repair tasks, she said,
employees usually need more than written instructions in maintenance
"KATIE provides more thorough step-by-step instructions at different
levels of expertise and easy access to on-line maintenance manuals,"
Roberts said. "But KATIE's video images and audio instructions for each
step in the process and the `why' feature are what provide users with a
more complete understanding of complex systems and the steps needed to
maintain or repair them."
Roberts explained that effective troubleshooting requires a thorough
knowledge of the system being repaired. But, because design engineers
are usually the only ones with such complete knowledge, the people who
actually maintain the system are usually unable to determine all
possible causes of a particular problem.
Because it is believed that almost anyone can identify symptoms, she and
other team members developed a Symptom Selector feature for KATIE.
Roberts said the Symptom Selector contains several full-screen videos,
which together show the whole system. She said the computer operator can
then select subsystems that are not functioning.
"We developed the shell, and systems experts assisted us in determining
particulars about each system, such as the components that should be
selectable with the mouse," she said. A mouse is a hand-controlled
device that allows a computer user to easily select and manipulate
graphics or text shown on a computer's monitor screen.
Roberts believes video images are KATIE's most impressive aspect. "We
decided to use still-frame video images over computer-generated graphics
because they cost less and give a clearer image. And because each
instruction step contains a picture, fewer words are needed," Roberts
She explained that KATIE's "authoring" system, a feature that allows
personnel familiar with the complex equipment to add information to the
knowledge base, is essential to the system's video capabilities. Roberts
said that videos are taken of the equipment and of steps being
performed, such as screws actually being removed. Then, by selecting
video-control symbols on the computer screen with a mouse, the video
images are captured, copied, and saved. Clicking on the "capture" symbol
results in a full-screen image on the monitor, while a second click
captures, compresses, and scales the current image into the computer's
video window. Finally, when the desired image is captured, clicking on
"save" actually stores the image in a computer file.
At the bottom of each picture are written instructions for each
particular step. However, Roberts said the team that designed KATIE
realized some personnel may need more instructions than others. "That's
why we decided to include a `detail' feature, which displays more
in-depth information and instruction," she said. "Also, because users
are more likely to follow an instruction if they understand the reason
for it, a `why' symbol is available that explains why the step is
necessary," she said. "It also helps to further educate the user."
Roberts went on to explain how KATIE handles new components or updated
operating procedures. "Each part of KATIE's knowledge base is distinct--
the instructions, the video images, everything." Because of this modular
design, she said additional capabilities can be independently added to
each area through KATIE's authoring system.
Because KATIE is "really just a shell," Roberts said it could be
customized to fit almost any system and respond to almost any need--
maintenance, troubleshooting, training.
"If the information you need can be expressed in a procedure format, and
if those procedures can be made easier by pictures and sound, then KATIE
is a good choice."
(keywords: ceramics, robotics, frozen fly embryos, nitrates, control
systems, carbon dioxide, ultraviolet radiationspaceship design,
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Date Posted: 1/26/94 (ktb)