Iron and Its Density: Everything You Need to Know

1.0 Iron (Fe): The Foundation of Structural Materials and a Vital Element for Life

Iron (chemical symbol Fe, derived from the Latin ferrum) is a transition metal in Group 8 of the periodic table, with an atomic number of 26, relative atomic mass of 55.845, a density of 7.86 g/cm³, and a melting point of 1539°C. It appears silvery-gray and is one of the most abundant metals in the Earth’s crust. In nature, it commonly exists in both the ferrous (Fe²⁺) and ferric (Fe³⁺) oxidation states.

1.1 Physical and Chemical Properties:

• Metallic luster, silvery-gray appearance, hard yet ductile;
• High melting point (1539°C), suitable for high-temperature processing;
• A reactive metal, readily reacts with oxygen, water, and acids;
• Common oxidation states are +2 and +3.

1.2 Main Applications:

Steelmaking:

Iron’s most important application is in the production of steel. Steel is an alloy of iron and carbon, often mixed with manganese, chromium, nickel, and other elements to improve strength, toughness, or corrosion resistance. Steel is widely used in:

• Structural construction (e.g., bridges, high-rise buildings)
• Machinery and equipment manufacturing
• Transportation (cars, ships, railways)
• Home appliances and everyday goods

Industrial Chemicals and Fertilizers:

Iron compounds are used to produce dyes, catalysts, water treatment agents, and iron-based fertilizers.

1.3 Biological Role:

Iron is an essential trace element for living organisms. Its primary functions include:

• Constituting hemoglobin and myoglobin, involved in oxygen transport;
• Participating in mitochondrial energy metabolism;
• Serving as a component of various enzymes and proteins.

1.4 Historical and Cultural Significance:

• Human use of iron dates back to the Iron Age (around 1200 BCE), when iron tools and weapons replaced bronze ones, significantly advancing agricultural production and military capability;
• The widespread adoption of iron smelting technology marked a key milestone in human civilization.
• To this day, iron remains the most widely used metallic material globally.

Densities of selected elements

2.0 Understanding Density: Definition, Calculation, and Iron as an Example

2.1 What Is Density?

Density is a measure of how much matter is contained in a unit volume. It reflects how closely packed the particles of a substance are. The more tightly packed the particles are, the more particles can fit into a given space. Since particles have mass, materials with higher density will weigh more for the same volume.

Common units of density include:

• SI unit: kilograms per cubic meter (kg/m³)
• Laboratory units: grams per cubic centimeter (g/cm³) or grams per milliliter (g/mL)
• Density is commonly represented by the Greek letter ρ (rho)

2.2 Density Calculation Formula

Density (ρ) = Mass (m) / Volume (V)

Where:

• Mass is usually measured in grams (g)
• Volume can be expressed in milliliters (mL)or cubic centimeters (cm³)
  (Note: 1 mL = 1 cm³)

2.3 Example: Density of an Iron Block

An iron block has a mass of 23.6 grams, with dimensions of 2.0 cm × 2.0 cm × 0.75 cm. Determine its density and whether it is likely to be made of iron.

Volume = 2.0 × 2.0 × 0.75 = 3.0 cm³
Density = 23.6 g ÷ 3.0 cm³ = 7.87 g/cm³

Conclusion:
The object has a density of approximately 7.87 g/cm³, which is very close to the standard density of pure iron. Therefore, it is most likely pure iron or an iron-based alloy.

2.4 Density of Iron and Iron Alloys

The density of pure iron is approximately 7.874 g/cm³
(or 491.5 lb/ft³, 0.284 lb/in³)

The table below lists the densities of common types of iron and iron alloys at room temperature. These values are useful for material selection and engineering calculations.

Note-1: 6.95 to 7.35 g/cm3 (0.251 to 0.265 lb/in.3).

Note-2: 7.20 to 7.34 g/cm3 (0.260 to 0.265 lb/in.3).

3.0 Factors Affecting the Density of Iron

3.1 Atomic Structure

The density of iron is influenced by its crystal structure:

• Body-Centered Cubic (BCC) Structure:Ferrite (α-iron, BCC) has a slightly lower density compared to austenite (γ-iron, FCC) due to its atomic packing efficiency.
• Face-Centered Cubic (FCC) Structure: Found in austenite (γ-iron), which has a higher density

3.2 Temperature and Phase Transitions

As temperature increases, iron undergoes phase transitions that affect its crystal structure and thus its density:

• α-iron (BCC)transitions to γ-iron (FCC) at approximately 912°C
• γ-iron (FCC)transforms into δ-iron (BCC) at around 1394°C
• The melting pointof iron is approximately 1538°

3.3 Addition of Alloying Elements

• Adding elements such as carbonalters the structure and density of iron
• For example, increasing carbon content in steel leads to the formation of pearlite, and lowers the phase transition temperatureto around 727°C.

4.0 Frequently Asked Questions about the Density of Iron

Other: Density of aluminum

References:

https://www.princeton.edu/~maelabs/mae324/glos324/iron.htm

https://web.fscj.edu/Milczanowski/psc/lect/Ch4/slide6.htm

https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/iron-fertilizers