echemi logo
Product
  • Product
  • Supplier
  • Inquiry
    Home > Chemicals Industry > Chemical Technology > The nature of elemental element of chromium subgroup

    The nature of elemental element of chromium subgroup

    • Last Update: 2021-06-30
    • Source: Internet
    • Author: User
    Search more information of high quality chemicals, good prices and reliable suppliers, visit www.echemi.com

    The chromium subgroup is an element of group VIB in the periodic table, including three elements: chromium (Cr), molybdenum (Mo), and tungsten (W)
    .


    The valence electron layer structure of the ground state atoms of chromium and molybdenum is (n-1)d 5n s l , while that of tungsten is 5d 5 6s 2 , and their s electrons and d electrons are involved in bonding, and the highest oxidation state is +6


    Chromium The most important chromite mineral is a FeCr 2 O .
    4
    (i.
    e.
    , · of FeO of Cr 2 O .
    3
    ), the other has a chromium ore crocoite PbCrO .
    4
    , chromium ore salary of Cr 2 O .
    3
    and the like
    .


    The mass fraction of chromium in the earth's crust is 1×10%, ranking 21st


    Simple substance of chromium subgroup elements

    1.
    The nature of the element

    The melting point (1907°C) and boiling point (2671°C) of chromium elemental substance are both high, and chromium is the most hard metal
    .


    This is consistent with chromium's many single electrons and strong metal bonds


    The passivation of chromium with dilute nitric acid , concentrated nitric acid or aqua regia is generally believed to be due to the formation of a dense oxide on the metal surface
    .


    If the purity of chromium is very high, it can resist the erosion of dilute sulfuric acid


    Chromium is an active metal and is easily soluble in hydrochloric acid to produce a blue CrCl 2 solution.
    Cr 2+ is unstable and quickly oxidized to Cr 3+
    .



    Molybdenum and tungsten are heavy metals with higher melting points and boiling points, among which tungsten is the metal with the highest melting point (which can be used as a filament)
    .


    Molybdenum and tungsten are eutecticized with KNO 2 , KCIO 3 or Na 2 O 2 and are oxidized to MoO 4 2- and wO 4 2-


    2.


    Refinement of simple substance

    The chromite and sodium carbonate are strongly thermally converted into water-soluble chromate (where iron is converted into insoluble Fe 2 O 3 ), and further leached with water and acidified to precipitate dichromate
    .


    The dichromate is heated and reduced to convert to Cr 2 O 3 , and Cr 2 O 3 is reduced with aluminum or the like to obtain metallic chromium


    The carbon used for chromite ore is reduced in an electric arc furnace to generate a carbon-containing ferrochrome alloy, which can be directly used to make alloy steel
    .

    FeCr 2 O 4 +4C=2Cr(s)+Fe+4CO

    Molybdenite ore is burned in the air to form MoO 3 , and MoO 3 is converted to (NH 4 ) 2 MoO 4 and then refined to obtain pure MoO 3 , which is reduced with H 2 , A1 or C at high temperature to produce metal Molybdenum
    .




    Metal tungsten is prepared by high temperature reduction of pure WO 3 with H 2
    .

    WO 3 +3H=W+3H 2 O

    The eutectic product of wolframite and sodium hydroxide obtains soluble N 2 WO 4 through water leaching
    .
    After acidification, tungstic acid H 2 WO 4 is precipitated
    .

    The action of scheelite and hydrochloric acid can also produce insoluble tungstic acid
    .
    Tungstic acid is sintered to obtain WO 3
    .

    Related Links: Compounds of Vanadium Subgroup Elements

     

     

    This article is an English version of an article which is originally in the Chinese language on echemi.com and is provided for information purposes only. This website makes no representation or warranty of any kind, either expressed or implied, as to the accuracy, completeness ownership or reliability of the article or any translations thereof. If you have any concerns or complaints relating to the article, please send an email, providing a detailed description of the concern or complaint, to service@echemi.com. A staff member will contact you within 5 working days. Once verified, infringing content will be removed immediately.

    Contact Us

    The source of this page with content of products and services is from Internet, which doesn't represent ECHEMI's opinion. If you have any queries, please write to service@echemi.com. It will be replied within 5 days.

    Moreover, if you find any instances of plagiarism from the page, please send email to service@echemi.com with relevant evidence.