Emergency responders and soldiers wearing respirators and protective suits often find that enduring the gear can be as tough as doing the work. In a short time, they can get too hot and feel faint as they carry out such arduous tasks as tactical training or cleaning walls contaminated with anthrax particles. Firefighters work up a sweat while fighting fires, and if their skin gets exposed, the sweat can turn to steam, leaving them with scalding burns. Eventually, these wearers of “moon” suits must change out oxygen sources so they can breathe. They must be sure they don’t suffocate from the buildup of their own toxic emissions of carbon dioxide (CO2), the problem faced by the astronauts participating in the failed Apollo 13 moon mission. All of these problems cause flagging productivity in wearers of protective suits.
ADVANCED PROTECTIVE SUIT
One goal of both the U.S. Army and the Office of Homeland Security is an “isolated working environment” for a warrior or first responder in the form of a technologically advanced suit. It would provide the wearercovered from head to toe with a helmet, respirator, protective suit, and special bootswith so-called microclimate conditioning. That means personal cooling to prevent excessive sweating, a constant source of oxygen to breathe, a means to remove the wearer’s own CO2 emissions to prevent suffocation, and advanced filtration to keep out hazardous particles that could be released into the atmosphere by terrorists or enemy warriors.
Several technologies developed by ORNL materials researchers could be integrated into a “technologically advanced suit” to provide microclimate conditioning so emergency responders and soldiers are more comfortable and productive for a longer time. Other ORNL materials technologies could be used to protect against and combat terrorism.
Personal cooling. J. Allen Crabtree, now with the Department of Energy’s Spallation Neutron Source Project at ORNL, and Moshe Siman-Tov (retired from ORNL) developed a personal cooling system in the mid-1990s to increase the comfort of police officers wearing bulletproof vests (but it could also be used by firefighters and soldiers). It consists of a uniformly porous plastic material that is thin and lightweight, along with a battery-powered fan in a belt pack. In the 1990s, these two researchers and Theresa Stovall, all then with ORNL’s former Engineering Technology Division, worked under a cooperative research and development agreement with Safariland of Ontario to devise a cooling system that weighs less than two pounds, is 0.6 cm (1/4 in.) thick, and keeps the bulletproof vest wearer reasonably comfortable for four hours.
The ORNL researchers designed a material consisting of polyethylene treated with a surfactant to make the plastic hydrophilic to wick sweat. The thin material consists mainly of parallel channels. A battery-powered fan blows ambient air through the channels across the chest and back, inducing evaporation. The air, which becomes saturated by evaporated sweat, is carried through the channels and discharged from the system. In this way, the body is kept cool and dry.
Prototypes of the personal cooling system were fabricated by Poretechnology, Inc., of Framingham, Massachusetts. The patented technology has been licensed to a new local company named Thermal X.
“We envision making cheap, disposable cooling vests that fit in big pockets in the front and back of a T-shirt,” Crabtree says. “We might also add a relative humidity sensor to the belt pack to automatically regulate the speed of the fan. That way the battery will last longer, extending the time that the body is kept comfortable.”
In April 2002, using funds from the U.S. Navy for a one-year research project, James Klett of ORNL’ s Metals and Ceramics (M&C) Division and his colleagues began devising a way to use ORNL’s new graphite foam (a product based on a discovery by Klett in 1996) to improve personal cooling systems for military helicopter air crews.
“These naval aviators could wear a suit that blows cold air over their bodies to evaporate their sweat,” he says. “The Navy wants us to figure out how to incorporate our graphite foam into the pilots’ cooling systems so they can stay comfortable twice as long, from two hours to four hours.”
Klett hopes to incorporate the graphite foam, which conducts heat unusually fast, into a “thermal battery.” Because of its high bulk-thermal conductivity and open porous structure, this lightweight foam could be impregnated with zeolite, which absorbs water like silica gel packets. In a thermal battery, the heat from the body causes water from one chamber to evaporate through a tube into a second chamber. The zeolite in that chamber would absorb the water, and the graphite foam would carry the heat outside the body. Air blown over this system would cool the body, keeping the worker’s efficiency from plummeting.
ORNL researchers will refine the thermal battery system to make it more efficient, lightweight, and compact. They will then incorporate the system into the flight suit and helmet.
“Our approach can enhance the cooling of individuals by providing them with cool air for both their lungs and their body surface,” Klett says. “Respiratory cooling can significantly augment evaporative cooling because the lungs have a high surface area, and blood flowing between them and the rest of the body is an effective heat-transfer medium. This principle has been demonstrated by our prototype respiratory cooling devices used by NASCAR racecar drivers, who must function at peak performance for several hours at high ambient temperatures in heavy, fire-resistant suits. Many drivers have said these cooling devices helped their performance.”
Portable oxygen generator. Tim Armstrong and other M&C Division members in the Fuel Cells and Functional Materials Program he leads are developing a portable oxygen generator. It would provide oxygen to the warrior or responder for a longer time than do today’s oxygen canisters, which must be changed out every two hours.
“The oxygen generator works on the principle of electrically driven oxygen diffusion through hot ceramic membranes to provide pure makeup oxygen for a sealed rebreather system,” Armstrong says. “Oxygen molecules in air break down into charged oxygen ions that diffuse through the membrane when an electric potential is placed across it. These ions recombine on the inner surface to replenish an individual’s pure oxygen supply. No toxic chemical or biological agents can diffuse through the membrane.
“Our new solid-state-oxygen-generator designs will deliver 10 times more oxygen per unit volume than any other existing generator. It can easily be scaled to a small size and weight for dismounted operations and can operate indefinitely without replacement components.”
CO2 scrubber. A team led by Tim Burchell of the M&C Division has developed an advanced filtration system for scrubbing out CO2 and other undesirable gases from air or a process gas being cleaned. The heart of the system is a set of electrically regenerable carbon fiber composite molecular sieves (CFCMS). Initially designed to capture CO2 emitted from coal-fired power plants and gas turbines, this very porous, lightweight filter could be used for microclimate conditioning. Because the CFCMS filter is electrically conductive, CO2 and other target impurities can be removed from the saturated sieve by running an electrical current through it at low voltage. Preliminary tests at Edgewood Chem-bio Center and Porton Down, England, have demonstrated that the CFMCS material effectively removes all simulants and agents for which it has been examined. They have evaluated adsorption of Hexane and DMMP (common nontoxic simulants used to judge filter performance) and CK (cyanogen chloride, a nerve agent). This filtration system not only adsorbs airborne impurities but also takes them up 5 to 10 times faster using 2 to 10 times less energy than competitive technologies.
Because of the threats of biological, chemical, or nuclear releases during modern warfare, the technologically advanced protective suit will likely be an improvement over the Army’s mission-oriented protected posture suits that offer different levels of protection. It will be an integral part of the gear carried by the soldier of the future. ORNL helped the Army define the equipment requirements for tomorrow’s soldier, the “objective force warrior.”
Objective force warrior. “Today’s soldier is not equipped much differently from the soldier of World War II or even the Roman legionnaire,” says Bob Leicht, senior program manager in ORNL’s National Security Directorate. “Today’s soldier may carry an M-16 variant rifle, bayonet, pistol, knife, and an antitank rocket, all of which are stand-alone, low-tech systems. The U.S. Army’s goal is to make a soldier a ‘system within a system,’ a sensor and weapons platform linked back to his or her platoon leader and squad leader who in turn are linked to senior commanders.”
Tomorrow’s objective force warrior will have a wearable computer, sensors, wireless receivers and transmitters, a device to stop the bleeding from wounds and apply medicine, and an “exoskeleton” made of a flexible material that becomes hard as steel when a bullet or knife strikes it. An exoskeleton could be similar to the powered armor being developed at ORNL under the direction of François Pin of the Engineering Science and Technology Division, to help soldiers run faster and farther and increase their ability to carry heavier loads.
Because the objective force warrior will have sophisticated suites of electronics for sensors, computers, communication, and weapons systems, compact electric-power systems are required. Power will also be needed for microclimate conditioning, protection from chemical and biological warfare agents, and remote medical assessment and treatment.
Fuel cells for soldiers. To meet those demands, ORNL researchers led by M&C’s Tim Armstrong have designed a new portable fuel-cell-based package consisting of a solid-oxide fuel cell (SOFC) with an internal reformer that can provide up to 100 watts (W) of electricity. This lightweight system would be smaller than a hockey puck, weigh slightly over 1 pound, and require only about 3 pounds of diesel fuel to supply about 20 W of power for a 10-day mission. Carrying a system this light would be greatly preferable to carrying the batteries now required for the same job, which weigh roughly 100 pounds. The basis for this concept is funded by DOE’s Office of Fossil Energy.
ORNL researchers led by Armstrong are proposing to work with the Army and NewGen Fuel Cells, LLC to design an SOFC with a power density of 2 kW/L for a cost as low as $155/kW. The fuel cell would have a molded design and no metallic interconnect components, making it easy to manufacture and stack. The SOFC would operate on synthetic diesel fuel, from which hydrogen would be removed by an internal reformer. The hydrogen from the fuel would then react with oxygen from the air to generate electricity and water.
BLAST-RESISTANT MATERIALS FOR AIRCRAFT BAGGAGE HOLDS
Because of the slim possibility that a suitcase containing an explosive might somehow end up on an airplane, the National Safe Skies Alliance (funded by the U.S. Transportation Security Administration) supports the development of better blast-resistant materials to protect aircraft passengers and flight crews. Such materials must be lightweight, fire resistant, and able to absorb the energy from an explosion without failing.
Two blast-resistant composite materials that meet these criteria have been developed by M&C’s Jim Hansen and Barbara Frame. “We believe these materials will decrease the vulnerability of an aircraft and its passengers to a terrorist’s bomb,” Hansen says. “Our composite material could be used for shielding or liners to mitigate blast effects.”
The materials were proven shock-hole and fire resistant through large-scale tests conducted by the National Safe Skies Alliance in February 2002 at Aberdeen Proving Ground in Maryland. (A shock hole is the hole that the shock from a blast punches into the test panel.) In one set of tests, explosives were added to lost luggage and detonated behind panels of ORNL’s blast-resistant materials. The ORNL materials survived both the blast from the explosive and the fire that resulted when clothing inside the luggage ignited.
One material consists of alternating layers of a phenolic resin film and a fabric woven from a PBO organic fiber. [PBO stands for the fiber composition poly(p-phenylene-2,6-benzobisoxazole).] The layers of the commercially made materials are stacked and consolidated under heat and pressure to form a 23-layer composite. A 1.5-m2 (16-ft2) panel of this material, which is 0.3 cm (1/8 in.) thick and weighs only 5 kg (12 lbs), has survived both shock-hole and ballistic tests. Its aerial density is 3.66 kg/m2 (0.75 lb/ft2).
A shotgun slug test has been developed by ORNL researchers to screen composite materials by evaluating their high-rate energy absorption capability. “We shot lead shotgun slugs at a panel of this material from as close as 20 feet (6 m) and the panel permanently deformed but did not break,” Hansen says. “We placed it in a Bunsen burner and it did not fail when exposed to fire.”
Frame, who developed and applied a process for producing this layered material to make the resin and fabric as strong and light as possible, says, “This material is blast-resistant because the fibers in the fabric of the material absorb energy by stretching. The resin in the material gives the fabric structure so the material can be used for hardening components.”
This ORNL material has higher specific strength and specific stiffness than do other composite materials used for ballistic and blast protection. The ORNL material might also be a good candidate for aircraft cockpit doors, armored vehicles for highly ranked government officials, and future cars (to make them more crashworthy, as well as lighter and more energy efficient).
Another material developed by these researchers is a composite sandwich in which polyethylene fibers, called Spectra, are incorporated with an aluminum honeycomb core. “The sandwich core absorbs energy but has a rigid structure,” Frame says. “This material would be rugged enough for a baggage hold, battered by suitcases thrown into it day after day.”
Researchers have been working on this project for four years, using the most recent advances in fiber and resin technologies for energy absorption. This work builds on insights for producing blast-resistant materials that came from work done previously at ORNL. In the mid-1990s with funding from the Federal Aviation Administration and other federal agencies, Al Akerman and Mike Kass (then of ORNL’s Engineering Technology Division) led projects to test layered-composite armor against threats ranging from explosives to bullets. In the late 1980s for the Strategic Defense Initiative (dubbed Star Wars research), ORNL researchers experimented with metal plates alternated with carbon felt as a possible material for armor for space vehicles.
IMPROVED WEAPONS AND AMMUNITION
U.S. military planners envision mechanized weapons systems and designer ammunition in the arsenal of tomorrow’s warriors. Additionally, these technologies could also be useful for police officers. ORNL researchers can provide help for both these areas.
Gun-barrel coatings. Future mechanized weapons systems will use advanced propellants to engage the enemy at greater distances and with increased effect. The problem is that advanced propellants will produce temperatures and pressures well beyond the capability of current protective gun- barrel coatings, causing them to erode and rendering a barrel unusable after a few rounds. Thus, affordable, non-eroding coating materials are needed to meet demands for increased performance.
A new process using the world’s most powerful plasma-arc lamp (located at ORNL) could apply durable, metallurgically bonded coatings that are impervious to the new propellants. This process, which would be carried out at DOE’s Infrared Processing Center at ORNL, would cause no damage to the steel of the gun tubes. In the ORNL process, high-intensity infrared energy is projected onto a precursor containing a refractory metal coating. The extremely high rate of heating causes the powder coating to fuse to the metal, while simultaneously limiting the depth of material heating, alteration of properties, and heat-induced damage in the metal being coated.
“This process can produce fully dense coatings consisting of materials having a high melting point and can metallurgically bond them to substrates having a lower melting point,” says M&C’s Craig Blue, of the Infrared Processing Center. “We are using our lamp to investigate the possible use of a class of molybdenum-rhenium alloys, which are leading candidate materials for coating gun barrels.”
Designer bullets. Advanced, or “designer,” bullets are also of interest to U.S. military planners and emergency responders. In the early 1990s M&C’s Rick Lowden found a way to press tungsten powder and tin together to make cold-welded slugs, or tungsten-tin bullets, to replace lead bullets used for target practice. Lead bullets were a problem for the U.S. Army and DOE because lead is a hazardous waste that can be washed by rain from target ranges into nearby waterways, threatening wildlife. Tungsten and tin are not hazardous wastes; they can be easily separated from soil and recycled.
ORNL’s bullets also proved to have another advantage. If an ORNL bullet richochets off a hard wall instead of striking a person directly, the bullet literally turns into dust, minimizing collateral damage. Lead bullets hitting walls have fragmented into large pieces and bounced back, injuring police officers standing nearby. ORNL-designed bullets are now being used on government target ranges and by police forces.
“Our bullets can be made of tin or plastic filled with tungsten powder,” Lowden says. “We can design these bullets to control their impact on or penetration of intended and unintended targets. Our bullets are also ballistically efficient because they are heavy. They can be shot further and straighter than lead bullets and they can be made to be nonlethal or to carry a detectable substance.”
According to Bill Corwin, manager of M&C’s Defense Materials Program, “These bullets would also be useful if a terrorist were inside a nuclear power plant. A police officer could shoot designer bullets at the terrorist and the stray bullets would turn to dust rather than bore holes in the plant’s pipes or other sensitive equipment. Designer bullets could be made to kill terrorists in an urban setting without injuring people standing nearby. The goals of these advanced bullets are increased safety for noncombatants and increased lethality for combatants.”
ORNL’s materials technologies could make it easier for emergency responders and soldiers to do their jobs, protect Americans against terrorist threats, and improve our nation’s ability to fight the war against terrorism.
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