Molibdènum: Béda antara owahan

{{Elementbox_boilingpoint | k=4912 | c=4639 | f=8382 }}

'''Molybdenum''' ({{pronEng|məˈlɪbdənəm}}, saka [[Basa Yunani]] kang tegesé kaya timbel, kuwiiku klebu [[unsur kimia]] grup 6 kanthi simbul '''Mo''' lan [[nomer atom]] 42.

| accessdate = 2007-06-10 }}</ref> It does not react with oxygen or water at room temperature. At elevated temperatures, molybdenum trioxide is formed in the reaction 2Mo + 3O₂ → 2MoO₃.<ref>{{cite web| last = Winter| first = Mark| title = Chemistry| work = Molybdenum| publisher = The University of Sheffield| url = http://www.webelements.com/webelements/elements/text/Mo/chem.html| accessdate = 2007-06-10 }}</ref>

In its pure metal form, molybdenum is silvery white and very hard, though it is somewhat more [[ductile]] than tungsten. It has a [[melting point]] of 2623°C, and only [[tantalum]], [[osmium]], [[rhenium]], and [[tungsten]] have higher melting points.<ref name="CRCdescription" /> Molybdenum burns only at temperatures above 600°C.<ref name="Nostrand">{{Citation |contribution = Molybdenum |year = 2005| title = Van Nostrand's Encyclopedia of Chemistry| editor-last = Considine| editor-first = Glenn D.| pages = 1038-1040| place= New York| publisher = Wylie-Interscience| id = 0-471-61525-0 }}</ref> It also has the lowest heating expansion of any commercially used metal.<ref name="nbb" />

There are 35 known [[isotopes]] of molybdenum ranging in [[atomic mass]] from 83 to 117, as well as four metastable [[nuclear isomer]]s. Seven isotopes occur naturally, with atomic masses of 92, 94, 95, 96, 97, 98, and 100. Of these naturally occurring isotopes, five are stable, with atomic masses from 94 to 98. All unstable isotopes of molybdenum decay into isotopes of [[niobium]], [[technetium]], and [[ruthenium]].<ref name="CRCisotopes">{{Citation |year = 2006 |title = CRC Handbook of Chemistry and Physics |editor-last = Lide |editor-first = David R. |volume = 11 |pages = 87-88 |publisher = CRC |id = 0-8493-0487-3 }}</ref>

Though molybdenum forms compounds with various [[organic molecule]]s, including [[carbohydrate]]s and [[amino acid]]s, it is transported throughout the human body as MoO₄^2-.<ref name="IMOAoverview">{{cite web| last = Mitchell| first = Phillip C. H.| title = Overview of Environment Database| publisher = International Molybdenum Association| date= 2003| url = http://www.hse.imoa.info/Default.asp?page=110| accessdate = 2007-05-05 }}</ref> Molybdenum is present in approximately 20 enzymes in animals, including [[aldehyde oxidase]], [[sulfite oxidase]], [[xanthine oxidase]].<ref name="nbb" /> In some animals, the oxidation of [[xanthine]] to [[uric acid]], a process of [[purine]] [[catabolism]], is catalyzed by [[xanthine oxidase]], a molybdenum-containing enzyme. The activity of xanthine oxidase is directly proportional to the amount of molybdenum in the body. However, an extremely high concentration of molybdenum reverses the trend, and can act as an inhibitor in both purine catabolism and other processes. Molybdenum concentrations also affect [[protein synthesis]], [[metabolism]], and growth.<ref name="IMOAoverview" /> These enzymes in plants and animals catalyse the reaction of [[oxygen]] in small molecules, as part of the regulation of [[Nitrogen_cycle|nitrogen-]], [[Sulfur_cycle|sulfur-]] and [[Carbon_cycle|carbon cycle]]s.

Because of its lower density and more stable price, molybdenum is implemented in the place of tungsten.<ref name="Nostrand" /> Molybdenum can be implemented both as an alloying agent and as a flame-resistant coating for other metals. Although its melting point is 2623 °C, molybdenum rapidly oxidizes at temperatures above 760 °C, making it better-suited for use in vacuum environments.<ref name="azom">{{cite web| title = Molybdenum| publisher = AZoM.com Pty. Limited| date= 2007| url = http://www.azom.com/details.asp?ArticleID=616| accessdate = 2007-05-06 }}</ref>

Molybdenite (from the Greek Μόλυβδος ''molybdos'', meaning ''lead''),<ref name="CRCdescription">{{Citation| contribution = Molybdenum| year = 1994| title = CRC Handbook of Chemistry and Physics| editor-last = Lide| editor-first = David R.| volume = 4| pages = 18| publisher = Chemical Rubber Publishing Company| id = 0-8493-0474-1 }}</ref> the principal ore from which molybdenum is now extracted, was previously known as molybdena. Molybdena was confused with and often implemented as though it were [[graphite]]. Even when the two ores were distinguishable, molybdena was thought to be a [[lead]] ore.<ref name="nbb" /> In 1754, [[Bengt Qvist]] examined the mineral and determined that it did not contain lead.<ref name="vanderkroft">{{cite web| last = Van der Krogt| first = Peter| title = Molybdenum| work = Elementymology & Elements Multidict| date= 2006-01-10| url = http://www.vanderkroft.net/elements/elem/mo.html| accessdate = 2007-05-20 }}</ref>

Although current molybdenum production meets demand, refiners, or roasters, are expected to run into a shortfall between 2009 and 2015, depending on demand.

A roaster processes the moly into a fine powder, pellets, or other forms. Total world moly roaster capacity is currently 320 million pounds per year, barely enough to meet demand. There is not much excess roasting capacity, and no one is actively permitting for the production of any new roasters in the United States. Global roaster capacity also looks limited, and a future roaster shortage is predicted. The data above are based on the assumption that mines will be able to increase output.