|Coefficient of Thermal Expansion(×10-6 °C-1)||4.9|
- Stainless steel
- High speed steel
- Cleaning glassware via chromic acid
- Combined with Nickel for heating elements
- Elemental chromium does not occur naturally
- Iron chromium oxide (FeCr2O4) occurrs as the mineral Chromite
- Lead chromium oxide (PbCrO4) occurrs as the mineral Crocoite
Chromium is toxic and carcinogenic in its hexavalent state. Production of chromium metal often takes a path through (VI) to separate other materials, only to reduce it to (III) later. This makes chromium production via this path very dangerous.
Chromium can be produced in at least 9 different oxidation states. We will not attempt to show each one, but will note which is being discussed.
- Ferrochromium is produced from chromite via aluminothermic reduction
- 3 FeCr2O4 + 8 Al → 3 FeCr2 + 2 Al2O3
- Melt sodium carbonate and combine with minerals including (Fe,Al,O) + CrO3
- 4 FeCr2O4(s) + 8 Na2CO3(l) + 7 O2(g) → 2 Fe2O3(s) + 8 CO2(g) + 8 Na2CrO4(s) or
- 2 FeCr2O4 + 4 Na2CO3 + 3 O2 → 2 FeCO3 + 2 CO2 + 4 Na2CrO4 or
- 3 FeCr2O4 + 6 Na2CO3 + 5 O2 → Fe3O4 + 6 CO2 + 6 Na2CrO4
- N.B. In each case, The dichromate is soluble and the other materials are not.
- Add water in excess
- Residue is other rock forming materials (carbonates, oxides, silicon, calcium, iron, aluminum...) Discard or save and reuse
- Evaporate filtrate including sodium dichromate
- Carbothermically reduce the dichromate, giving III-oxide
- Na2Cr2O7 + 3 C → 2 Cr2O3 + 2 Na2CO3 + CO2
- Crocoite is treated with hydrochloric acid producing chromium trioxide.
- PbCrO4 + 2 HCl → PbCl2 + CrO3 + H2O
- Carbothermic reduction is possible, but impractical, requiring > 2050°C. Instead, either CrO3 or Cr2O3 can be reduced via |aluminothermic reduction:
- CrO3 + 2 Al → Cr + Al2O3