Nineteen isotopes of technetium, with atomic masses ranging from 90 to 108, are known. The isomeric isotope 95mTc, with a half-life of 61 days, is useful for tracer work, as it produces energetic gamma rays. Technetium metal has been produced in kilogram quantities. The metal was first prepared by passing hydrogen gas at 1100C 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.
The chemistry of technetium is said to be similar to that of rhenium. Technetium dissolves in nitric acid, aqua regia, and conc. The element is a remarkable corrosion inhibitor for steel. This corrosion protection is limited to closed systems, since technetium is radioactive and must be confined. Activity of this level must not be allowed to spread.