Chromium(III) oxide
Chromium(III) oxide (Cr2O3) is an inorganic compound commonly known as chromia. It is a green, crystalline solid that is insoluble in water. It is amphoteric, meaning it can react with both acids and bases.
Properties:
- Appearance: Green crystalline solid.
- Molar mass: 151.99 g/mol
- Density: 5.22 g/cm3
- Melting point: 2435 °C (4415 °F; 2708 K)
- Boiling point: ~4000 °C (7232 °F; 4273 K) (decomposes)
- Solubility: Insoluble in water, ethanol, and acetone. Soluble in hot concentrated acids and alkalis.
- Magnetic susceptibility (χ): +1.48 × 10−4 cm3/mol
Production:
Chromium(III) oxide can be produced through several methods, including:
- Decomposition of chromium salts: Heating chromium(VI) oxide (CrO3) or ammonium dichromate ((NH4)2Cr2O7) causes them to decompose, yielding chromium(III) oxide and other byproducts.
- Reaction of chromium with oxygen: Direct reaction of chromium metal with oxygen at elevated temperatures.
- Reduction of chromium(VI) oxide: Reducing chromium(VI) oxide with sulfur or other reducing agents.
Uses:
Chromium(III) oxide has a wide range of applications:
- Pigment: It is used extensively as a pigment for paints, ceramics, and inks, providing a stable green color. It is known for its colorfastness and resistance to fading.
- Abrasive: Due to its hardness, it is used as an abrasive for polishing metals and other materials, particularly in the form of "green rouge".
- Catalyst: It is used as a catalyst in various chemical reactions.
- Metallurgy: Used in the production of metallic chromium via the aluminothermic process.
- Refractory material: Because of its high melting point, it is used in refractory materials.
- Electronics: Used in some electronic components.
Safety:
Chromium(III) oxide is generally considered to be of low toxicity. However, inhalation of dust should be avoided. Prolonged or repeated exposure can cause skin and respiratory irritation. It is important to handle the compound with appropriate safety precautions, including wearing protective equipment such as gloves and a respirator when necessary.