Technetium (original) (raw)

Technetium is a chemical element in the periodic table that has the symbol Tc and atomic number 43. A silvery gray, radioactive, crystalline transition metal that is not found in nature, technetium occurs as one of the fission products of uranium and is used in bone imaging and corrosion protection. Chemical properties of this element are intermediate between rhenium and manganese.

Notable Characteristics

Technetium is a silvery-gray metal that slowly tarnishes in moist air. Under oxidizing conditions technetium (VII) will exist as the pertechnetate ion, TcO4-. The chemistry of technetium is intermediate between rhenium and manganese. Technetium dissolves in aqua regia, nitric acid, and concentrated sulfuric acid, but it is not soluble in hydrochloric acid. This element is a very good corrosion inhibitor for steel and the metal is an excellent superconductor at temperatures below 11 K.

This element is unusual because it has no stable isotopes and is therefore extremely rare on earth. Common oxidation states of technetium include +2, +4, +5, +6 and +7.

Applications

Technetium is one of the most powerful known preventatives of rust, and is also a valuable source of beta rays. Ammonium pertechnate (NH4TcO4), is a specialized corrosion preventer for steel. Five parts per million of KTcOTcO4 in aerated distilled water protects mild carbon steel at temperatures up to 250 �C. This protection is limited to closed systems due to the radioactive nature of technetium. Other uses;

• Tcm-95 ("m" stands for meta state) with a half-life of 61 days is used in radioactive tracer studies.
• Tcm-99 (half-life 6.01 hours) is used in many radioactive isotope medical tests due to its short half-life, the gamma ray energy it emits, and its ability to chemically bind to many active biomolecules.
• Organic technetium compounds are used in bone imaging.
• Technetium is an excellent superconductor at tempuratures of 11 kelvins and below.
• Technetium is commercially available to holders of O.R.N.L. permits at a price of $60/g.

History

Technetium (

Greek technetos meaning "artificial") was discovered by Carlo Perrier and Emilio Segr� in Italy in 1937. The researchers found it in a sample of molybdenum sent to them by Ernest Lawrence. The sample was bombarded by deuterium nuclei in the University of California, Berkeley cyclotron which gave them the isotope Tc-97. Technetium was the first element to be artificially produced.

For a number of years there was a gap in the periodic table at element 43. Dmitri Mendeleev predicted that this missing element would be chemically similar to manganese and gave it the name ekamanganese. In 1925 element 43 was erroneously reported as discovered and was given the name masurium. The development of nuclear energy in the mid 20th century generated the first known samples of element 43 by nuclear reactions.

Occurrence

Once it was available in macroscopic quantities i.e. enough to determine its chemical and physical properties, it was discovered to exist naturally elsewhere in the universe. Some red giant stars (S-, M-, and N-types) contain an emission line in their spectrum corresponding to the presence of technetium. Its presence in red giants has led to the establishment of new theories about the production of heavy elements in stars.

Since its discovery, there have been many searches in terrestrial materials for natural sources. In 1962, technetium-99 was isolated and identified in pitchblende from Africa in very small quantities as a spontaneous fission product of uranium-238. This discovery was made by B.T. Kenna and P.K. Kuroda.

Tc-99 is produced as a byproduct from the fission of uranium in nuclear reactors and it is prepared by chemically separating it from reactor waste.

Isotopes

Technetium is one of two elements in the first 83 that have no stable isotopes (the other element is promethium). The most stable radioisotopes are Tc-98 with a half-life of 4.2 million years, Tc-97 (half-life: 2.6 million years) and Tc-99 (half-life: 211,100 years).

Twenty-two other radioisotopes have been characterized with atomic weights ranging from 87.933 amu (Tc-88) to 112.931 amu (Tc-113). Most of these have half-lives that are less than an hour except Tc-93 (2.75 hours), Tc-94 (293 minutes), Tc-95 (20 hours), and Tc-96 (4.28 days). There are also numerous meta states with Tcm-97 being the most stable with a half-life of 90.1 days (0.097 MeV). This is followed by Tcm-95 (half life: 61 days, 0.038 MeV), and Tcm-99 (half-life: 6.01 hours, 0.143 MeV).

The primary decay mode before the most stable isotope, Tc-98, is electron capture and the primary mode after is beta emission with one instance of election capture during the first mode of the two mode decay of Tc-100. The primary decay product before Tc-98 is molybdenum and the primary product after is ruthenium (the product of the first decay mode of Tc-100 is Mo, however).

Precautions

Compounds containing this element are encountered extremely rarely by most people and is for practical purposes not found in nature. Tc-99 is a contamination hazard and should be handled in a glove box. All isotopes of technetium are highly radioactive and are thus very toxic. Technetium has no natural biological role.

External Links

• WebElements.com - Technetium
• EnvironmentalChemistry.com - Technetium