IT'S ELEMENTAL!
TITANIUM THOMAS M. CONNELLY JR., DUPONT
T
HE FASCINATING CHEMISTRY OF
titanium is closely linked to the development of several modern industries that have improved the quality of our lives. Pure titanium metal does not occur in nature. It is derived primarily from ilmenite ore, a black mineral composed of FeTi0 3 and named for the Ilmen Lake and mountains of Russia. Ilmenite can be altered to a mixture of white to yellow titanium oxides known collectively as leucoxene ore, which is another source of titanium. Reduction to elemental titanium was not commercialized until the 1950s. Titanium's combination of high strength-toweight and corrosion resistance, either alone or as an alloy, provides tremendous performance enhancements compared with more traditional metals used in structural applications. Titanium metal greatly improves performance in many high-tech applications, from medical to military It is also used to replace damaged human bones and as part of dental implants. Military and aerospace applications such as the SR-71 Blackbird, a high-speed reconnaissance aircraft that serves as an invaluable asset for scientific and intelligence efforts, make extensive use of titanium and titanium alloy structural components. Exploration vehicles used in the high-pressure environment of deep oceans also rely on the high strength
TITANIUM AT A GLANCE Name: Named after the Titans of Greek mythology. Atomic mass: 47.87 History: Discovered in 1791 by the British pastor Rev. William Gregor. Occurrence: Primarily found in the minerals rutile, ilmenite, and sphene. Appearance: Silvery metallic solid or dark gray powder. Behavior: Very strong, light metal that is extraordinarily resistant to corrosion. Uses: An important alloying agent with aluminum, molybdenum, manganese, iron, and other metals. Alloys (amalgams) of titanium are principally used for aircraft and missiles where lightweight strength and ability to withstand extreme temperatures are important.
70
C & E N / S E P T E M B E R 8, 2 0 0 3
and light weight of titanium structures. The discovery and elucidation ofthe role oftitanium in Ziegler-Natta catalysts stands as a milestone in the evolution of polymerization chemistry The pioneering work that developed these heterogeneous systems led to the large-scale production of stereoregular polypropylene and other important polymers. The success of this work spurred development of other catalysts based on transition metals beyond titanium. The optical properties of the common white titanium dioxide make it the most widely used opacifier in industry Addition- BELOW THE SURFACE This ally titanium dioxide, also known as titania, crystalline atomic lattice of a Ti02 is the most stable of all known white pig- pigment particle has an essentially ments. DuPont has provided pigments uniform amorphous nanolayer of based on the chemistry of titanium to the silica coating. The inset shows the marketplace since the 1930s. DuPont's work pigment morphology. began with the previously developed "sulfate" process, where titaniferous ores were exploited for attachment of a variety of lidigested in sulfuric acid and subsequent- gands, some ofwhich—in conjunction with ly converted to either the anatase or ru- the host oxide—can exhibit extremely high tile polymorph. As a result of a highly light absorbance and photoactivity In adfocused effort, DuPont developed the "chlo- dition, titania can be a highly efficient semiride" process in the 1940s and commer- conducting material—readily transportcialized it in the 1950s. This process—in- ing photogenerated electrons into circuitry volving high temperatures, corrosive for practical harnessing of the electric outmaterials, solid-gas separations, put. The combination of these and a variety of other related properties has been capitalized chemical and engineering chalon in emerging photovoltaic delenges—was one of the most vice development. important developments for As a result of this potential for DuPont in the 20th century and new applications, DuPont has a is still used today strong interest in controlling the particle shape and size to optiThe hiding power of T i 0 2 mize interactions with light, depigment depends on optical THIS ELEMENT pendent upon the performance BROUGHT/, properties generated at the parTO YOU BY requirements of the end-use systicle level. Nanoparticles of titaDUPONT tem. This goal is challenging benia are transparent to visible light cause titanium dioxide particles but opaque to ultraviolet light. The performance and use of nanotitani- have complex crystal shapes and because um dioxide is becoming a hot commodity light scattering is affected by interactions in many emerging and traditional markets, between particles. including wide use in the sunscreen and DuPont maintains its strong interest in cosmetics industries. Other evolving ap- titanium-based products. This ubiquitous plications for nanotitanium dioxide include oxide has created and continues to create thermal coatings, structural plastics, and new frontiers for scientists and new prodenvironmental catalysts for water treat- ucts for end-use consumers. ment or auto emissions. Future products could include self-cleaning and self-sani- Thomas M. Connelly Jr. is a senior viceprestizing countertops and paints. ident and chiefscience and technology officer at Other advanced application areas for ti- DuPont. A chemical engineer by training Contania have recently emerged. One of the nelly has been with DuPont since 1977 and has most promising directions is photochem- served as managerfor a variety of DuPont busiistry The surface reactivity of Ti0 2 can be nesses in the U.S., Europe, and Asia. HTTP://WWW.CEN-0NLINE.ORG
|$
