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Converters & Calculators
Chromium: Element Properties And Uses
Description
Chromium is a chemical element exhibiting specific properties that are required in numerous industrial processes. It is used in the production of stainless steel and applied as a protective coating.
Introduction to the Element
Chromium (Cr) is a transition metal belonging to Group 6 of the periodic table. It has an atomic number of 24 and is noted for its metallic lustre and hardness. In nature, chromium occurs predominantly in minerals such as chromite. It was first identified in 1797 by the French chemist Louis-Nicolas Vauquelin. Its most significant property is its resistance to tarnish and corrosion, thereby underscoring its value in industrial and commercial applications.
Chemical Properties Description
Chromium exhibits a broad spectrum of chemical properties that contribute to its utility in various applications.
- Oxidation States: Chromium can occur in several oxidation states ranging from -2 to +6. The most stable and commonly encountered states are +2, +3 and +6.
- Reactivity: Chromium reacts with atmospheric oxygen to produce a protective oxide layer that prevents further corrosion. It also reacts with non-metals, such as sulphur and halogens, thereby forming various compounds.
- Behaviour with Acids and Bases: Chromium(III) oxide (Cr₂O₃) is amphoteric, meaning it can react with both acids and bases.
- Toxicity: Whereas chromium in its +3 oxidation state is essential for human health, the +6 oxidation state is toxic and carcinogenic, particularly in industrial settings.
Physical Properties - Data Table
Chromium is a hard, steel-grey metal with high melting and boiling points. The following table summarises some of its key physical properties:
|
Property |
Value |
|
Atomic Number |
24 |
|
Atomic Mass |
52.00 g/mol |
|
Density |
7.19 g/cm³ |
|
Melting Point |
1 907°C |
|
Boiling Point |
2 671°C |
|
Electrical Resistivity |
2.3 x10⁻⁶ Ω·m |
|
Thermal Conductivity |
93 W/m·K |
|
Colour |
Silvery metallic |
Further details are available at Stanford Advanced Materials (SAM).
Common Uses
Due to its durability, hardness and corrosion resistance, chromium is used in a range of industrial and commercial applications.
- Stainless Steel: The most frequent use of chromium is in the manufacture of stainless steel. Chromium is alloyed with iron to produce steel that resists corrosion and staining.
- Chromium Plating: Chromium is employed to coat other metals, thereby providing a bright and long-lasting surface. This method is applied to automotive components, household appliances and decorative items.
- Pigments: Chromium compounds, such as chromium oxide (Cr₂O₃), are utilised as pigments in paints, dyes and inks. Chromium yellow (PbCrO₄) is a recognised pigment.
- Alloys: Chromium is a key constituent in many alloys used in aerospace, military and industrial applications.
- Wood Preservation: Chromium compounds, such as chromated copper arsenate (CCA), are applied to wood to prevent decay and insect infestation.
Processing Methods
Chromium is primarily extracted from chromite ore (FeCr₂O₄) by means of an aluminothermic reduction process. In this method, the ore is combined with aluminium powder and heated, resulting in the reduction of chromium oxide to produce metallic chromium. Additionally, chromium can be obtained by electrolysing chromium chloride in the presence of a molten salt.
Related Industrial Products
Chromium is incorporated in several industrial products:
- Stainless Steel: Contains chromium as a primary component, often in combination with nickel, molybdenum and other elements.
- Chromium Alloys: These alloys are used in applications that require high strength, heat resistance and toughness, for example in turbine blades and heavy machinery.
- Chromium-Containing Chemicals: These are employed in the production of various chemicals, including chromium salts, chromium dioxide (used for magnetic recording media) and other specialised compounds.
Frequently Asked Questions
What is chromium used for in everyday applications?
Chromium is primarily used in the manufacture of stainless steel, which is applied in kitchen appliances, cutlery and industrial machinery. It is also employed in the production of coatings and pigments.
How is chromium extracted?
Chromium is obtained from chromite ore through an aluminothermic process, in which aluminium powder is used to reduce chromium oxide.
Why is chromium hazardous?
Chromium, particularly in its hexavalent form (Cr⁶⁺), is toxic and carcinogenic. It poses a risk if inhaled or ingested, especially in industrial settings.
Is chromium important for human health?
Yes, chromium in its trivalent form (Cr³⁺) is an essential trace element that plays a role in glucose metabolism, although its exact function remains under investigation.
What is the primary source of chromium?
Chromium is primarily obtained from chromium ore, which is abundantly found in countries such as South Africa, India and Kazakhstan.
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