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 state

s, +3 and +6 states are most commonly observed in chromium compounds

Applications Metallurgy important alloying material have strengthening effect of forming stable meta

l 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

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 (PbCr

O4·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 trea

tment 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(H2

O) are used in the tanning of leather Chromium(III) stabilizes the leather by cross linking the c

ollagen fibers

Refractory material Chromite (an iron chromium oxide: FeCr2O4 and Cr(III) oxid

e (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 brick

s and as foundry sands for the casting of metals. For high temperature refractory applications

Catalysts Several chromium compounds are used for processing hydr

ocarbons e.g. Phillips catalysts - for the production of polyethylene ar

e 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