technetium tech·ne·ti·um (těk-nē'shē-əm, -shəm)
A radioactive metal, the first synthetically produced element, used as a tracer and to inhibit corrosion in steel. Atomic number 43; melting point 2,200°C; specific gravity 11.50; valence 0, 2, 4, 5, 6, 7.
A silvery-gray, radioactive metallic element. It was the first element to be artificially made, and it is produced naturally in extremely small amounts during the radioactive decay of uranium. Technetium is used to remove corrosion from steel. Its longest-lived isotope is Tc 98 with a half-life of 4,200,000 years. Atomic number 43; melting point 2,200°C; specific gravity 11.50; valence 0, 2, 4, 5, 6, 7. See Periodic Table.