Group 9 element Group 9 element Group 9, numbered by IUPAC nomenclature, is a group of chemical element in the periodic table. Members are cobalt (Co), rhodium (Rh), iridium (Ir) and perhaps also the chemically uncharacterized meitnerium (Mt). These are all transition metals in the d-block. All known isotopes of meitnerium are radioactive with short half-lives, and it is not known to occur in nature; only minute quantities have been synthesized in laboratories. Like other groups, the members of this family show patterns in electron configuration, especially in the outermost shells, resulting in trends in chemical behavior; however, rhodium deviates from the pattern.
Cobalt the 20th century with the stellite alloys, containing chromium with varying quantities of tungsten and carbon. Alloys with chromium and tungsten carbides are very hard and wear-resistant. Special cobalt-chromium-molybdenum alloys like Vitallium are used for prosthetic parts (hip and knee replacements). Cobalt alloys are also used for dental prosthetics as a useful substitute for nickel, which may be allergenic. Some high-speed steels also contain cobalt for increased heat and wear resistance. The special alloys of aluminium, nickel, cobalt and iron, known as Alnico, and of samarium and cobalt (samarium-cobalt magnet) are used in permanent magnets. It is also alloyed with