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Chromium(Cr)

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harlow
6 diapositives · 464 Views · Aug 28, 2014

Chromium(Cr). Cha racteristics. Silvery Lustrous, hard, strong, malleable, ductile high melting point High corrosion resistance form intensely coloured compounds exhibits a wide range of possible oxidation states, +3 and +6 states are most commonly observed in chromium compounds.

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Chromium(Cr)
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  1. Chromium(Cr)

  2. Characteristics • Silvery • Lustrous, hard, strong, malleable, ductile • high melting point • High corrosion resistance • form intensely coloured compounds • exhibits a wide range of possible oxidation states, +3 and +6 states are most commonly observed in chromium compounds

  3. Applications Metallurgy • important alloying material • have strengthening effect of forming stable metal carbides and strong increase in corrosion resistance • e.g. Stainless steel - formed when chromium is added to iron in sufficient concentrations • Anodizing of aluminium – chromic acid (H2CrO4) is used and an oxide layer is formed on the aluminium

  4. Dye and pigment • Crocoite (lead chromate PbCrO4) → yellow pigment • Does not photo degrade and has a strong color, • Use of chrome yellow declined due to environmental and safety concerns replaced by organic pigments or other lead-free alternatives • Other pigments based on chromium are: • Chrome red, which is a basic lead chromate (PbCrO4·Pb(OH)2) • Chrome green, a mixture of Prussian blue and chrome yellow • Chrome oxide green is Chromium (III) oxide

  5. Wood preservative • Chromium(VI) salts are used • Chromated copper arsenate (CCA) is used in timber treatment to protect wood from decay fungi, wood attacking insects, including termites, and marine borers • Improve the weather-resistance • Assist paint adherence in the long term. Tanning • Chromium(III) salts, chrome alum/potassium sulfate, (KCr(SO4)2) and chromium(III) sulfate(Cr2(SO4)3 • 12(H2O) are used in the tanning of leather • Chromium(III) stabilizes the leather by cross linking the collagen fibers

  6. Refractory material • Chromite (an iron chromium oxide: FeCr2O4 and Cr(III) oxide (an iron chromium oxide: FeCr2O4 and Cr(III) oxide • High heat resistivity • High melting point • E.g. blast furnaces, cement kilns, molds for the firing of bricks and as foundry sands for the casting of metals. • For high temperature refractory applications Catalysts • Several chromium compounds are used for processing hydrocarbons • e.g. Phillips catalysts - for the production of polyethylene are mixtures of chromium and silicon dioxide or mixtures of chromium and titanium and aluminium oxide. • Fe-Cr mixed oxides - as high-temperature catalysts for the water gas shift reaction