Molybdenum

Molybdenum has high value in steel alloys, where it hardens and toughens them.   Almost all ultra-strength steel contains molybdenum, especially the strength of steel at high temperatures, since molybdenum has a very high melting point.   Molybdenum is used in alloys, such as Hastelloys, which are heat-resistant and corrosion-resistant to chemicals.   It is used in electrodes for electrically-heated glass furnaces, nuclear reactors, airplane parts, and electronic filaments.   Mobybdenum is an effective catalyst in petroleum refining.   Molybdenum sulfide is used as a lubricant at high temperatures where petroleum would ordinarily decompose. ^{Lide 4-18}

Molybdenum is essential to animal and plant life.   Three molybdenum enzymes have been described in mammals: (1) Sulfite oxidase catalyzes the terminal step in oxidative degradation of sulfur-containing amino acids, (2) aldehyde oxidase is involved in detoxification of very diverse metabolites, and (3) xanthine oxidase is essential for purine catabolism. ^{Mendel n.p.}   Sources: legumes, cereal grains, liver, kidney.   Deficiencies are rare in humans with no known effects.   Animals experience slower weight gain and shortened life. ^{Brody 188}   Plants require molybdenum for enzymes that fixate nitrogen.

In plants, molybdenum is part of the enzyme that reduces nitrates to ammonia.   Without it, the synthesis of proteins is blocked and plant growth ceases.   Nitrogen-fixing bacteria also require it since seeds may not form completely.   Deficiency signs are pale green leaves with rolled or cupped margins. ^{Morgan n.p.}

Molybdenum was isolated in 1778 by Carl Scheele, a Swedish chemist.   It was prepared in impure form in 1782 by Peter Hjelm, a Swedish mineralogist.   Molybdenum is obtained from molybdenite, MoS₂, wulfenite, PbMoO₄, and powellite, Ca(MoW)O₄ ores.   Molybdenum also is obtained as a byproduct of copper and tungsten mining.   It is prepared from the powder made by the hydrogen reduction of purified molybdic trioxide or ammonium molybdate. ^{Lide 4-18}