Titanium (Ti), a transition metal with atomic number 22, is renowned for its unique combination of low density and high strength. This article explores the density of titanium, its influencing factors, and its industrial significance.
1. Basic Density Values
- Pure Titanium:
At 20°C (68°F), the density of pure titanium is 4.506 g/cm³ (or 4,506 kg/m³). This is approximately:- 60% of steel’s density (~7.8 g/cm³)
- 1.7× aluminum’s density (~2.7 g/cm³)
- Alloys:
Common titanium alloys, such as Ti-6Al-4V (Grade 5), have slightly higher densities (~4.43 g/cm³) due to added elements like aluminum (Al) and vanadium (V).
2. Factors Affecting Density
a. Temperature
Density decreases with rising temperature due to thermal expansion. The relationship is modeled as:
ρ(T)=ρ01+βΔT
Where:
- ρ0 = Initial density (4.506 g/cm³ at 20°C)
- β = Volumetric thermal expansion coefficient (~8.6×10⁻⁶ °C⁻¹ for Ti)
- ΔT = Temperature change
Example: At 100°C, titanium’s density ≈ 4.485 g/cm³.
b. Alloy Composition
Adding elements like Al (2.7 g/cm³) or V (6.11 g/cm³) alters density. For instance:
- Ti-6Al-4V: ~4.43 g/cm³
- Ti-3Al-2.5V: ~4.48 g/cm³
c. Crystalline Structure
- α-phase (HCP structure at room temperature): Stable below 882°C.
- β-phase (BCC structure above 882°C): Slightly lower density due to atomic rearrangement.
3. Measurement Methods
Density is determined experimentally via:
- Archimedes’ Principle: Submersion in fluid to measure displaced volume.
- X-ray Diffraction (XRD): Calculates lattice parameters to derive theoretical density.
- Pycnometry: Gas displacement for porosity-free samples.
4. Comparative Density Table
| Material | Density (g/cm³) | Relative to Ti |
|---|---|---|
| Titanium (pure) | 4.506 | 1.0× |
| Aluminum | 2.70 | 0.6× |
| Steel (304) | 7.90 | 1.75× |
| Magnesium | 1.74 | 0.39× |
| Tungsten | 19.25 | 4.27× |
5. Industrial Significance
Titanium’s low density enables critical applications:
- Aerospace: Structural components (e.g., landing gear, engine parts) reduce weight while maintaining strength.
- Medical: Orthopedic implants (e.g., hip replacements) minimize stress shielding.
- Automotive: High-performance valves and connecting rods improve fuel efficiency.
- Marine: Corrosion-resistant offshore rig components.
6. Advanced Considerations
- Specific Strength: Titanium’s tensile strength (~434 MPa) divided by density yields ~96 MPa·cm³/g, surpassing most steels and aluminum alloys.
- Phase Transitions: Alloying stabilizes α or β phases, tailoring density and mechanical properties for specific uses.
- Additive Manufacturing: 3D-printed titanium parts retain near-theoretical density (>99.9%) with minimal porosity.
7. Limitations
- Cost: High extraction/processing expenses limit use to high-value industries.
- Machining Challenges: Low thermal conductivity increases tool wear during shaping.
Conclusion
Titanium’s density of ~4.5 g/cm³ positions it as a material of choice for weight-sensitive, high-strength applications. Ongoing research in alloy design and manufacturing (e.g., powder metallurgy) continues to expand its utility in cutting-edge technologies.
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