IT'S ELEMENTAL! metal replacements for lead in small-arms ammunition, in other words, during the investigation of "green bullets." A perusal of the periodic table reveals very few candidates for replacing lead. Bismuth, tin, and RICK LOWDEN, OAK RIDGE NATIONAL LABORATORY zinc are interesting, but each has deficiencies. Tungsten is heavy and commonly used es. But one has to ask, "Do they glow?" U N G S T E N IS AN I N C R E D I B L E in ordnance but unfortunately is much too My personal introduction to tungsten material. It is dense and hard, as a structural material was at Kennamet- hard for most small-arms applications. and it has the lowest vapor presOne approach to the problem seemed al, a producer of tungsten carbide metalsure and highest melting temquite straightforward: Build a composite cutting tools, where I took an internship perature ofall metals. This comthat combined the properties of different in my senior year while studying chemistry bination of properties makes tungsten elements to produce a leadlike maextremely valuable for a myriad of applicaterial. A light, ductile metal like tin tions, while at the same time creates great could be used as the binder with challenges in the processing of the metal. tungsten included for mass. But As a child, I was fascinated by howthings tungsten is not easy to process, and work and spent a lot of time taking things bullets had to be cheap. A review of apart. As with most budding engineers, I the tungsten binary-phase diagrams rarely reassembled them. Incandescent revealed fewer than 40 systems, with bulbs were one of my first quarries, carefewintermetallic compounds. Most fully disassembled to reveal a hidden treaof the soft metals with low melting sure: a tungsten filament. It was amazing points do not wet tungsten, and, in that this tiny wire could be heated to whiteaddition, significant differences in hot temperatures to produce light. density make casting impossible. Also at an early age, I was introduced to had to be a method to comThere vacuum tubes, and to this day they are magbine tungsten and a ductile metal ical in my eyes. When a tungsten filament binder. is heated in a vacuum, the electrons near After World War I, resourceful T A K I N G A I M Lowden prepares to test the the surface become energetic enough to be window and curtain manufacturers form and function of 9-mm ammunition emitted into the surrounding space. Addisprinkled tungsten particulates onto fabricated from a tungsten-containing tional tungsten conductors, in the form of the surface of tin sheets, which were composite replacement for lead. grids and plates, can be added to the bulb, subsequently fed through a rolling and the electrons can then be manipulated mill to produce high-density, pliable sheets to switch, rectify and amplify These elecat a small liberal arts college in Latrobe, that could be used to make weights. The soPa. The position involved sample prepatronic switches were crucial in the develration for X-ray fluorescence. During vis- lution to the lead-replacement problem opment of modern electronics. was actually very simple. Powits to the powder metallurgy labTransistors and integrated circuits have der blends without additives oratory, I noticed paint cans on almost entirely displaced tubes; however, were pressed at room temperathe storage shelves, many withsome researchers are going "retro," explorout handles. Curiosity led me to ture to produce dense compacts. ing ttmgsten-containing miniaturized vacremove a can from a shelf, only It wasn't rocket science, but it uum triodes or "nanotriodes" that may one to be surprised when gravity worked, and the tungsten-tin day be used as miniature electronic switchquickly dragged it to the ground, composite is a leading candidate barely missing my toes. Although for replacing lead in small-calTUNGSTENATAGLANCE the can was less than half full of iber bullets and for a variety of THIS ELEMENT BROUGHT powder, it weighed almost 35 lb. other applications. Name: From the Swedish tung sten, TO YOU BY The powder was tungsten for Although we may not realize meaning heavy stone. The symbol is WYETH fabricating heavy-metal alloys. from mineral wolframite, from which it, tungsten continues to be a Later, I went to Oak Ridse the element was originally isolatedpart of our lives because it is still Atomic mass: 183.84. used in Hghting and electrical contacts; in National Laboratory while I studied for a History: Isolated in 1783 by Spanish electronics, including cell phones and graduate degree in metallurgy I specialchemists Juan Jose and Fausto Elhuyar. pagers; in cutting tools and engine compoized in vapor-phase processing of highOccurrence: China has 75% of the nents; in radiation shielding; and now in temperature materials, primarily structural world's tungsten ores. coatings and composites. Once again, tung- sporting goods such as golf balls and shot. Appearance: Silvery white metal. sten entered my life when I became inBehavior: Tungsten has the highest volved in a project to develop a small fiber- Rick Lowden is a metallurgist and senior remelting point and highest boiling point search engineer at Oak Ridge NationalLaboratoreinforced ceramic can with a tungsten of all metals. ry. Although his primary area ofexpertise is valayer deposited on its outer diameter. The Uses: Tungsten is used in high-temcans were to be used as thermionic emit- por-phase processing of materials, he has been intimately involvedin the developmentojpowderperature applications such as heating ters in advanced space power systems. I became intimately involved with tung- metal replacements for lead in ammunition—and elements and lightbulb filaments. being an avid shooter, it's been a dream come true. sten during the development of powder-
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