Tomorrow's Materials: Lighter, Tougher, Faster
We are familiar with composites in recreational applications such as tennis rackets, golf clubs and sailboat masts. These materials also bring comfort to thousands of people as prosthetic arms and legs that are much lighter than wood or metal versions. At higher performance levels, the success of our satellites and stealth aircraft depends on composites.
In aircraft, weight affects every performance factor, and composites offer high load bearing at minimal weight without deterioration at high or low temperatures. NSF-supported researchers and engineers are developing tough new materials like the resin and fiber composite used in the tail section of the Boeing 777. That composite is lighter than aluminum but far more durable and fatigue resistant at high altitudes. Use of such advanced composites reduces the weight of an 8,000-pound tail section by 15 percent which means designers can increase the aircraft's payload and fuel capacity.
Meanwhile, down on the ground, advanced composites are being evaluated for use in building the U.S. infrastructure for the 21st century. In one test, researchers at the Center for High-Performance Adhesives and Composites at Virginia Polytechnic Institute and State University have partnered with the Virginia Transportation Research Council, the state Transportation Department, the town of Blacksburg, and manufacturer Strongwell to test the long-term effectiveness of composites as an alternative to steel in bridges. (The center at Virginia Tech, one of the first Science and Technology Centers (STC) established by NSF, is transitioning to self-sufficiency after 11 years of Foundation support.) Deteriorating steel beams on the Tom's River bridge, located on a rural road near Virginia Tech, were replaced with structural beams made out of a strong composite. The new bridge was completed in 1997 and since then, Virginia Tech researchers have been closely monitoring it to determine how well the composite beams withstand the tests of time, traffic and weather. Depending on the results of this field test and others that are planned or underway, bridges constructed of composites could become as familiar in the future as tennis rackets and aircraft made of composites are today.
Standing Up Under Stress
Designing composites is one method of fabricating novel materials with special properties. Surface engineering is another. Thermal spray processinga group of techniques that can propel a range of materials including metals, ceramics, polymers, and composites onto substrates to form a new outer layerhas proven to be a cost-effective method for engineering surfaces that are resistant to corrosion, wear, high or low temperatures, or other stresses. Current applications include the aerospace, marine and automobile industries, power generation, paper processing and printing, and infrastructure building.
Despite this widespread use of thermal spray processing, the underlying science was little understood until recently. That's beginning to change, due in part to the work of researchers and students at the Center for Thermal Spray Research, the NSF-supported Materials Research Science and Engineering Center (MRSEC) based at the State University of New York (SUNY) at Stony Brook, who are studying the characteristics of various spray processes, feedstock materials, and resulting spray deposits. Their goals include the development of methodology for selecting source materials and achieving a fundamental understanding of flame-particle interactions and the physical properties of spray deposits. Earlier research by Herbert Herman, the Center's director and professor of materials science at SUNY-Stony Brook, and his students advanced the use of plasma guns to apply coatings that protect against very high temperatures and corrosive environments. Plasma-sprayed coatings are commonly used on components for aircraft engines and gas turbines and in other areas where materials are required to function under extreme conditions.
Superconductivity We Can Live With
A superconducting material transmits electricity with virtually no energy loss. In a world where every electrical cord steals some of the current passing through it, a room-temperature superconductor could save billions of dollars. Superconducting computers could run 100 times faster than today's fastest supercomputers.
To compare the normal electrical system with a superconductive one, imagine a ballroom filled with many dancers. In normal material, all of the dancers are moving in different directions at different times, and much of their energy is spent bumping into each other. In a superconductive material, the dancers are synchronized, moving in unison, and therefore can spend all of their energy on the dance and none on each other. The dancers represent the electrons of each material, chaotic in the normal setting and well-ordered when the material is superconductive. While the entire theory is more complicated, the overall effect is that the electrons in superconductive material move electrically more easily through the system without wasting energy bumping into each other.
Superconductivity, which occurs in many metals and alloys, isn't yet in widespread use, however. For most of the 20th century, the phenomenon required very cold temperatures. Superconductivity was first observed by Dutch physicist Heike Karmerlingh Onnes in 1911 when he cooled mercury down to -425° F, a few degrees above absolute zero. Until the mid-1980s, commercial superconductors usually used alloys of the metal niobium and required expensive liquid helium to maintain the temperature of the material near absolute zero. The need for expensive refrigerants and thermal insulation rendered these superconductors impractical for all but a limited number of applications. That began to change in 1986 when Alex Müller and Georg Bednorz, researchers at an IBM Research Laboratory in Switzerland, discovered a new class of ceramic materials that are superconductive at higher temperatures. So far, materials have been known to reach the superconductive state at temperatures as high as -209° F, making it possible to use liquid nitrogen coolant, a less costly alternative to liquid helium. Since the mid-1980s, much of the current research has focused on so-called high temperature superconductors. The new superconducting ceramics are hard and brittle, making them more difficult than metal alloys to form into wires. An interdisciplinary team at the NSF-supported MRSEC on Nanostructured Materials and Interfaces, based at the University of Wisconsin-Madison, is focusing on understanding the properties of the grain boundaries of high temperature superconductors. The center's research could lead to better materials processing and the development of a new generation of superconductors for high current and high magnetic field technology.
Even as research continues, superconductors are being used in a number of fields. One of the more visible is medicine. Superconductors have strong magnetic characteristics that have been harnessed in the creation of magnets for MRI (Magnetic Resonance Imaging) systems. An MRI takes images of a patient by recording the density of water molecules or sodium ions within the patient and analyzing the sources. When used for brain scans, this technique allows clinicians to identify the origin of focal epilepsy and to pinpoint the location of a tumor before starting surgery. Similar magnet resonance systems are used in manufacturing to test components for cracks and other defects. Other promising applications for superconductive materials include computers, electronics, communications, transportation, and advanced power systems.
One of the preeminent facilities for researchers and engineers to test superconductivity and conduct other materials research is the National High Magnetic Field Laboratory (NHMFL), a unique laboratory funded by NSF's Division of Materials Research and the state of Florida and operated as a partnership between Florida State University, the University of Florida, and the Los Alamos National Laboratory in New Mexico. Since it was established in 1990, the NHMFL has made its state-of-the-art magnets available to national users for research in a variety of disciplines including condensed matter physics, chemistry, engineering, geology, and biology, as well as materials science. The NHMFL features several of the world's most powerful magnets, including a hybrid magnet, developed jointly with the Massachusetts Institute of Technology, that delivers continuous magnetic fields of 45 tesla, which is about one million times the Earth's magnetic field. The 45 tesla hybrid consists of two very large magnets. A large resistive magnet (electromagnet) sits at the center of a huge superconducting magnet, which forms the outer layer and is the largest such magnet ever built and operated to such high field. The hybrid's record-setting constant magnetic field strength gives researchers a new scale of magnetic energy to create novel states of matter and probe deeper into electronic and magnetic materials than ever before.
The NHMFL's 45 tesla magnet is cooled to within a few degrees of absolute zero using a superfluid helium cryogenic system. The discovery of superfluid helium was made in 1971 by NSF-funded researchers at Cornell University who found that, at extremely low temperatures, the rare isotope hellium-3 has three superfluid states, where the motion of atoms becomes less chaotic. This discovery by David Lee, Douglas Osheroff, and Robert Richardson led to greatly increased activity in low temperature physics and furthered studies of superfluidity. Lee, Osheroff and Richardson received the 1996 Nobel Prize in Physics for their contributions to the field.