Hevesy, Georg von

Hevesy, Georg von (1885-1966), Hungarian chemist and Nobel laureate, born in Budapest, and educated in Berlin and Freiburg, Germany. In 1923, with Dutch physicist Dirk Coster, Hevesy discovered the chemical element hafnium. He was awarded the 1943 Nobel Prize in chemistry for developing the use of radioactive trace elements in chemical and biological research (See also Isotopic Tracer).

Hevesy, Georg Charles von

born Aug. 1, 1885, Budapest, Austria-Hungary [now in Hungary]

died July 5, 1966, Freiburg im Breisgau, W.Ger.

also called George Charles de Hevesy chemist and recipient of the 1943 Nobel Prize for Chemistry. His development of isotopic tracer techniques greatly advanced understanding of the chemical nature of life processes. In 1923 he also discovered, with the Dutch physicist DirkCoster, the element hafnium.

Educated at the Technische Hochschule in Berlin and the University of Freiburg, Hevesy in 1911 began work at the University of Manchester, England, under Ernest Rutherford on the chemical separation of radium. Though his attempts proved unproductive, they stimulated him to explore the use of radioactive isotopes as tracers. He joined Friedrich Paneth at Vienna (1912) and made significant progress in tracer studies. Invited to Copenhagen (1920), Hevesy and Coster, pursuing a suggestion of Niels Bohr, discovered hafnium among ores of zirconium.

Hevesy became a professor at Freiburg in 1926 and began to calculate the relative abundance of the chemical elements. In 1934, after preparing a radioactive isotope of phosphorus, he analyzed various physiological processes by tracing the course of “labeled” radioactive phosphorus through the body. These experiments revealed the dynamic state of the body constituents. After fleeing from the Nazis in 1943, Hevesy became a professor at the Institute of Organic Chemistry, Stockholm. His published works include the two-volume Adventures in Radioisotope Research (1962).

Hafnium

Hafnium, symbol Hf, metallic element that closely resembles zirconium. Hafnium is one of the transition elements of the periodic table (see Periodic Law); the atomic number of hafnium is 72.

Hafnium was discovered in Copenhagen in 1923 by the Hungarian chemist Georg von Hevesy and the Dutch physicist Dirk Coster. On the basis of a prediction by the Danish physicist Niels Bohr that element 72 would resemble zirconium in structure, they looked for the element in zirconium ores. Hafnium is found in nearly all ores of zirconium and is 45th in order of abundance of the elements in the crust of the earth. It resembles zirconium so closely in chemical properties and crystal structure that separation of the two elements is extremely difficult. Separation is accomplished most efficiently by means of the ion-exchange technique. Hafnium is used in the manufacture of tungsten filaments. Because of its resistance to high temperatures, it is used with zirconium as a structural material in nuclear power plants.

Hafnium melts at about 2227° C (about 4041° F), boils at about 4602° C (about 8316° F), and has a specific gravity of 13.3. The atomic weight of hafnium is 178.49.

hafnium

Hungarian-Swedish chemist George Charles de Hevesy discovered (1923) hafnium in Norwegian and Greenland zircons by analyzing their X-ray spectra. They named the new element for Copenhagen (in New Latin, Hafnia), the city in which it was discovered. Hafnium is dispersed in the Earth's crust to the extent of three parts per million and is invariably found in zirconium minerals up to a few percent compared with zirconium. Altered zircons, like some alvites and cyrtolites, products of residual crystallization, show greater percentages of hafnium (up to 17 percent hafnium oxide in cyrtolite from Rockport, Mass., U.S.). Commercial sources of hafnium-bearing zirconium minerals are found in beach sands and river gravel in the United States (principally Florida), Australia, Brazil, western Africa, and India. Hafnium vapour has been identified in the Sun's atmosphere.

Ion-exchange and solvent-extraction techniques have supplanted fractional crystallization and distillation as the preferred methods of separating hafnium from zirconium. The metal itself is prepared by magnesium reduction of hafnium tetrachloride (Kroll process) and by the thermal decomposition of tetraiodide (de Boer–van Arkel process).

Hafnium is used for fabricating nuclear-control rods because it easily absorbs thermal neutrons and has excellent mechanical properties. Hafnium produces a protective film of oxide or nitride upon contact with air and thus has high corrosion resistance. It formsalloys with iron, niobium, tantalum, titanium, and other transition metals. The alloy tantalum hafnium carbide (Ta4HfC5), with a melting point of 4,215° C (7,619° F), is one of the most refractory substances known.

Hafnium is chemically similar to zirconium. Both transition metals have similar electronic configurations, and their ionic radii and atomic radii are nearly identical because of the influence of the lanthanide contraction (q.v.). The most common oxidation state in hafnium is +4, although a few trivalent compounds are known. Natural hafnium is a mixture of six stable isotopes: hafnium-174 (0.2 percent), hafnium-176 (5.2 percent), hafnium-177 (18.6 percent), hafnium-178 (27.1 percent), hafnium-179 (13.7 percent), and hafnium-180 (35.2 percent).