Chemical Fact Sheet
Hafnium
| Chemical Abstract Number (CAS #) | 7440-58-6 |
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| Synonyms | CELTIUM; HAFNIUM-METAL,-DRY- (DOT); HAFNIUM-METAL,-WET- (DOT) |
| Analytical Methods | 200.8 - 6020 |
| Molecular Formula | Hf |
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Synopsis
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Hafnium - (Hsfnia, Latin name for Copenhagen), Hf; at.wt. 178.49(2); at.no. 72; m.p. 2233+/-20 deg C; b.p. 4603 deg C; sp.gr. 13.31 (20 deg C); valence 4. Hafnium was thought to be present in various minerals and concentrations many years prior to its discovery, in 1923, credited to D. Coster and G. von Hevesey. On the basis of the Bohr theory, the new element was expected to be associated with zirconium. It was finally identified in zircon from Norway, by means of X-ray spectroscopic analysis. It was named in honor of the city in which the discovery was made. Most zirconium minerals contain 1 to 5% hafnium. It was originally separated from zirconium by repeated recrystallization of the double ammonium or potassium fluorides bv von Hevesey and Jantzen. Metallic hafnium was first prepared by van Arkel and deBoer by passing the vapor of the tetraiodide over a heated tunasten filament. Almost all hafnium metal now produced is made by reducing the tetrachloride with magnesium or with sodium (Kroll Process). Hafnium is a ductile metal with a brilliant silver luster. Its properties are considerably influenced by the impurities of zirconium present. Of all the elements, zirconium and hafnium are two of the most difficult to separate. Their chemistry is almost identical, however, the density of zirconium is about half that of hafnium. Very pure hafnium has been produced, with zirconium being the major impurity. Natural hafnium contains six isotopes. one of which is slightly radioactive. Hafnium has a total of 40 recognized isotopes and isomers. Because hafnium has a good absorption cross section for thermal neutrons (almost 600 times that of zirconium). has excellent mechanical properties, and is extremely corrosion resistant, it is used for reactor control rods. Such rods are used in nuclear submarines. Hafnium has been successfully alloyed with iron, titanium, niobium, tantalum, and other metals. Hafnium carbide is the most refractory binary composition known, and the nitride is the most refractory of all known metal nitrides (m.p. 3310 deg C). Hafnium is used in gas-filled and incandescent lamps, and is an efficient "getter" for scavenging oxygen and nitrogen. Finely divided hafnium is pyrophoric and can ionite spontaneously in air. Care should be taken when machining the metal or when handling hot sponge hafnium. At 700 deg C hafnium rapidly absorbs hydrogen to form the composition HfH1.86. Hafnium is resistant to concentrated alkalis, but at elevated temperature reacts with oxygen, nitrogen, carbon, boron, sulfur, and silicon. Halogens react directly to form tetrahalides. The price of the metal is in the broad range of $1/g to $3/g, depending on purity and quantity. The yearly demand for hafnium in the U.S. is now in excess of 50,000 kg. |
| Use | USED FOR REACTOR CONTROL RODS, IN GAS-FILLED & INCANDESCENT LAMPS; SCAVENGER FOR OXYGEN & NITROGEN IN RADIO & TELEVISION TUBES; CATHODE IN X-RAY TUBES AS COATING ON TANTALUM FOR ROCKET ENGINE PARTS |
| Apparent Color | GRAY CRYSTALS; HIGHLY LUSTROUS METAL OF HEXAGONAL CRYSTAL STRUCTURE |
| Boiling Point | 4602 DEG C |
| Melting Point | 2227 +/- 20 DEG C |
| Molecular Weight | 178.49 |
| Density | 13.31 @ 20 DEG C |
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Chemical and Physical Properties |
ATOMIC NUMBER: 72; DUCTILE; HAS BEEN SUCCESSFULLY ALLOYED WITH IRON, TITANIUM, NIOBIUM, TANTALUM, & OTHER METALS; RAPIDLY ABSORBS HYDROGEN TO FORM HFH (1.86) @ 700 DEG C; HALOGENS REACT DIRECTLY TO FORM TETRAHALIDES; PROPERTIES ARE CONSIDERABLY INFLUENCED BY IMPURITIES OF ZIRCONIUM PRESENT HIGH THERMAL NEUTRON CROSS-SECTION (115 BARNS); HIGH STRENGTH REACTS READILY @ HIGH TEMPERATURES WITH WATER VAPOR; IONIC CRYSTAL RADII (FOR COORDINATION NUMBER 6): 0.81 (+4) A; ATOMIC RADIUS: 1.44 A; ELECTRONEGATIVTY: 1.3 (PAULING SCALE) ZIRCONIUM & HAFNIUM ARE MORE CLOSELY IDENTICAL IN CHEM PROPERTIES THAN ARE ANY OTHER PAIR IN THE PERIODIC TABLE VALENCE NUMBERS: 4,3,2; SIX NATURALLY OCCURRING ISOTOPES: 180 (35.22%); 178 (27.1%); 177 (18.56%); 179 (13.75%); 176 (5.21%); 174 (0.163%) |
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Environmental Impact |
HAFNIUM IS CONSIDERED TO BE LIMITED INDUSTRIAL HAZARD. |
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Environmental Fate |
ABUNDANCE IN EARTH'S CRUST: 5 PPM. MOST ZIRCONIUM MINERALS CONTAIN 1-5% HAFNIUM. |
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Disposal |
MAY BE DISPOSED OF IN SEALED CONTAINER IN A SECURED SANITARY LANDFILL. USED PAPERS & CLOTHS WHICH HAVE BECOME CONTAMINATED WITH POWDERS SHOULD BE KEPT WET IN COVERED CONTAINERS UNTIL THEY ARE REMOVED TO BE BURNED, WHICH SHOULD BE DONE @ LEAST DAILY. |
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