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   Tc

TECHNETIUM

( Gr. technetos, artificial)

Tc  at. wt. ˜98
     at. no. 43 
     m.p.  2200±50°C 
     b.p. 5030°C
     sp. gr. 11.50 (calc.)
     valence  0, +2, +4, + 5, +6, and +7.

Technetium was predicted on the basis of the periodic table, and was erroneously reported as having been discovered in 1925, at which time it was named masurium. The element was actually discovered by Perrier and Segrè in Italy in 1937. It was found in a sample of molybdenum, which was bombarded by deuterons in the Berkeley cyclotron, and which E. Lawrence sent to these investigators. Technetium was the first element to be produced artificially. Since its discovery, searches for the element in terrestrial materials have been made without success. If it does exist, the concentration must be very small. Surprisingly, it has been found in the spectrum of S, M, and N type stars, and its presence in stellar matter is leading to new theories of the production of heavy elements in the stars. Sixteen isotopes of technetium, with atomic masses ranging from 92 to 107, are known. Tc97 has a half-life of 2.6x 106 yrs. Tc98 has a half-life of 1.5 x lO6yrs. The isomeric isotope Tc95~, with a half-life of 61 days, is useful for tracer work, as it produces energetic gamma rays. Technetium metal has been produced in kilo- gram quantifies. The metal was first prepared by passing hydrogen gas at 1 1000C over Tc2S7. It is now conveniently prepared by the reduction of ammonium pertechnetate with hydrogen. Technetium is a silvery-gray metal that tarnishes slowly in moist air. Until 1960, technetium was available only in small amounts and the price was as high as $2800 per gm. It is now offered commercially to holders 9f A.E.C. permits at a price of $90 to $100/gm. The chemistry of technetium is said to be similar to that of rhenium. Technetium dissolves in nitric acid, aqua regia, and conc. sulfuric acid, but is not soluble in hydrochloric acid of any strength. The element is a remarkable corrosion inhibitor for steel. It is reported that mild carbon steels may be effectively protected by as little as 5 ppm of KTcO4 in aerated distilled water at temperatures up to 250°C. This corrosion protection is limited to closed systems, since technetium is radioactive and must be confined. Tc99 has a specific activity of 6.2 x 108 disintegrations per sec./gm. Activity of this level must not be allowed to spread. Tc99 is a contamination hazard and should be handled in a glove box. The metal is an excellent superconductor at 11°K and below.

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