Chromium(Cr)

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

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 (H 2 CrO 4 ) is used and an oxide layer is formed on the aluminium

Dye and pigment  Crocoite (lead chromate PbCrO 4 ) → 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 (PbCrO 4 ·Pb(OH) 2 ) Chrome green, a mixture of Prussian blue and chrome yellow Chrome oxide green is Chromium (III) oxide

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(SO 4 ) 2 ) and chromium(III) sulfate(Cr 2 (SO 4 ) 3 12(H 2 O) are used in the tanning of leather  Chromium(III) stabilizes the leather by cross linking the collagen fibers

Refractory material  Chromite (an iron chromium oxide: FeCr 2 O 4 and Cr(III) oxide (an iron chromium oxide: FeCr 2 O 4 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