1. Introduction
Nickel is a critical metal widely used in industrial, aerospace, energy, and chemical applications due to its corrosion resistance, mechanical strength, and thermal stability.
Understanding its density is fundamental for engineers and material scientists because it influences weight calculations, component design, thermal behavior, and overall material performance.
The reference density of pure nickel at room temperature (20 °C) is approximately 8.908 g/cm³ (or 8,908 kg/m³).
This intrinsic property underpins nickel’s applications in high-performance alloys, structural components, and specialized coatings.
2. What is the Density of Nickel
Density is defined as mass per unit volume (ρ = m/V). For nickel, its density arises from the atomic mass (58.6934 u) and its face-centered cubic (FCC) crystal structure, which packs atoms efficiently.
At standard temperature and pressure, nickel exhibits a stable FCC lattice with a lattice constant of 0.352 nm, producing its characteristic density of 8.908 g/cm³.
3. Factors Affecting Nickel Density
Nickel’s density (~8.908 g/cm³ at 20 °C for ultra-high-purity metal) is not a fixed constant; it varies with purity, alloying, temperature, and pressure.
Purity: The Primary Driver of Density Variability
The reference density of 8.908 g/cm³ applies exclusively to ultra-high-purity nickel (≥99.99%), such as electrolytic nickel used in electronics and precision instruments.
In industrial practice, nickel rarely reaches this purity.
Impurities, whether intentional (alloying elements) or accidental (residual ores, processing contaminants), displace nickel atoms in the crystal lattice, altering density based on their atomic mass and concentration.
Common impurities and their effects (data from ASM Handbook, Volume 2):
| Impurity | Density (g/cm³) | Typical Concentration in Commercial Nickel | Resulting Nickel Density (g/cm³) | Density Change vs. Pure Nickel |
| Iron (Fe) | 7.874 | 0.5–1.0% | 8.85–8.90 | −0.01 to −0.06 |
| Copper (Cu) | 8.96 | 0.1–0.5% | 8.91–8.93 | +0.002 to +0.02 |
| Carbon (C, graphite) | 2.267 | 0.01–0.05% | 8.90–8.91 | −0.001 to −0.008 |
| Sulfur (S) | 2.07 | 0.005–0.01% | 8.905–8.907 | −0.001 to −0.003 |
| Oxygen (O, gas) | 1.429 | 0.001–0.005% | 8.907–8.908 | Negligible |
Alloying: Tailoring Density for Performance
Nickel forms alloys with elements such as copper (Cu), chromium (Cr), molybdenum (Mo), tungsten (W), and iron (Fe), producing materials with densities that differ substantially from pure nickel.
Selected alloys and densities:
| Alloy | Composition | Density (g/cm³) | Difference vs. Ni | Primary Application |
| Monel 400 | 65% Ni, 34% Cu, 1% Fe | 8.80 | −0.108 | Marine corrosion resistance |
| Inconel 625 | 59% Ni, 21.5% Cr, 9% Mo, 5% Fe | 8.44 | −0.468 | High-temperature creep resistance |
| Hastelloy X | 47% Ni, 22% Cr, 18.5% Fe, 9% Mo | 8.30 | −0.608 | Gas turbine combustion chambers |
| Nickel-Tungsten (30% W) | 70% Ni, 30% W | 10.0 | +1.092 | Radiation shielding, wear resistance |
| Invar 36 | 64% Fe, 36% Ni | 8.05 | −0.858 | Low thermal expansion tools |
Temperature: Thermal Expansion and Density Reduction
Nickel expands with heat, reducing its density.
The linear coefficient of thermal expansion (CTE) for nickel is ~13.4 × 10⁻⁶/°C; the approximate volumetric CTE is ~40.2 × 10⁻⁶/°C. Using these values, nickel’s density decreases with temperature:
- At 100°C: Density ≈ 8.908 g/cm³ × (1 – (40.2 × 10⁻⁶/°C × 80°C)) ≈ 8.88 g/cm³
- At 500°C: Density ≈ 8.908 g/cm³ × (1 – (40.2 × 10⁻⁶/°C × 480°C)) ≈ 8.73 g/cm³
- At 1455°C (melting point, liquid nickel): Density ≈ 8.70 g/cm³ (liquid metals are less dense than solids due to increased atomic disorder)
This temperature-dependent density is critical for:
- High-temperature casting: Molds must account for density changes during solidification to avoid shrinkage defects.
- Aerospace components: Nickel superalloys in jet engines (operating at 1000–1200°C) experience density reductions that affect thermal conductivity and structural stability.
Pressure: Compression and Density Increase
Nickel’s bulk modulus (~170 GPa) measures resistance to compression. High pressure slightly increases density:
- At 1 GPa (≈10,000 atm, typical of deep-sea environments): Density increases by ~0.5% (≈8.95 g/cm³).
- At 10 GPa (extreme pressure, e.g., planetary cores): Density rises to ~9.3 g/cm³.
Deep-sea equipment: Nickel-plated components in submersibles must withstand pressure-induced density changes without structural failure.
High-pressure metalworking: Processes like hot isostatic pressing (HIP) use pressure to densify nickel alloys, reducing porosity and increasing final density.
4. Density Measurement
Archimedes’ Principle and Hydrostatic Weighing
Nickel samples are submerged in a fluid, and density is calculated from buoyant forces. This method is simple and reliable for bulk components.
X-Ray Diffraction (XRD)
XRD calculates density from the lattice parameter of nickel’s crystal structure (measured via X-ray scattering). This method is:
- Non-destructive: Ideal for valuable or delicate samples (e.g., aerospace components).
- Highly precise: ±0.0001 g/cm³ for pure nickel, as it directly measures atomic packing rather than bulk properties.
- Limitations: Requires a well-crystallized sample (not suitable for powders or amorphous nickel).
Pycnometry (for Powders)
For nickel powders (used in additive manufacturing or coatings), gas pycnometry (ASTM D6226) measures true density by displacing a gas (e.g., helium) in a sealed chamber.
This avoids errors from voids in powder beds, yielding densities within ±0.002 g/cm³ of the theoretical value.
Measurement Variability
Reported densities can vary slightly due to impurities, porosity, measurement method, and temperature, typically within ±0.01–0.02 g/cm³ for high-quality nickel.
5. Industrial Relevance of Nickel Density
The density of nickel is not just a theoretical property—it directly impacts how the metal and its alloys are designed, processed, and applied across industries.
From aerospace turbines to chemical plants and additive manufacturing, density plays a pivotal role in material performance and engineering efficiency.
Aerospace and Aviation: Balancing Weight and Strength
Aircraft and spacecraft demand materials with high strength-to-weight ratios.
While pure nickel is relatively dense (8.908 g/cm³), nickel-based superalloys such as Inconel 625 (8.44 g/cm³) or Hastelloy X (8.30 g/cm³) provide a compromise:
- Lower density reduces total engine or structural weight, saving fuel and extending range.
- High-temperature stability ensures resistance to creep and fatigue at >1000 °C.
Example: A 1% reduction in turbine disk mass through alloy density optimization can save hundreds of kilograms of jet fuel annually per aircraft.
Automotive and Heavy Machinery: Durability and Efficiency
Nickel density is also relevant for ground transport:
- Electric vehicles (EVs): Nickel-rich cathode materials (e.g., NMC, NCA) affect battery energy density, where weight savings improve driving range.
- Heavy equipment: Nickel steels and nickel-copper alloys (densities ~7.8–8.8 g/cm³) provide toughness and wear resistance in construction machinery and mining equipment.
Chemical and Petrochemical Processing: Corrosion Resistance with Mass Efficiency
In chemical plants and refineries, nickel alloys must resist corrosive acids, alkalis, and high-pressure gases:
- Monel 400 (8.80 g/cm³): Chosen for marine pipelines and seawater handling due to excellent corrosion resistance.
- Hastelloy C-series (~8.9 g/cm³): Used in acid processing reactors, where density is balanced against corrosion resistance and mechanical integrity.
Density affects not only mechanical strength but also thermal conductivity and heat transfer efficiency, both critical in chemical reactors.
Casting, Forging, and Additive Manufacturing: Controlling Solidification
Nickel’s density behavior during thermal processing directly influences manufacturing outcomes:
- Casting: Density reduction upon melting (8.908 → ~8.70 g/cm³) must be accounted for to prevent shrinkage porosity in molds.
- Forging and HIP (Hot Isostatic Pressing): Applied pressure densifies nickel alloys, closing voids and increasing mechanical strength.
- Additive Manufacturing (AM): Powder-bed fusion and directed energy deposition rely on consistent powder density for predictable flowability, layer uniformity, and final part density.
Energy and Nuclear Applications: When High Density is a Benefit
In some industries, higher density is advantageous:
- Nickel-tungsten alloys (~10.0 g/cm³): Provide radiation shielding in nuclear reactors and medical imaging.
- Nickel-based anodes and cathodes: Density influences current efficiency and thermal stability in fuel cells and electrolyzers.
6. Quick Reference Table: Pure Nickel and Common Alloys
| Material / Alloy | Composition (Major Elements) | Density (g/cm³ @ 20 °C) | Melting Point (°C) | Key Applications |
| Pure Nickel (99.99%) | ≥99.99% Ni | 8.908 | 1455 | Electronics, thermocouples, electroplating |
| Commercial Nickel (Grade 200) | ≥99.0% Ni + Fe impurities | 8.85–8.90 | 1445–1455 | Chemical processing equipment, marine hardware |
| Monel 400 | ~65% Ni, 34% Cu, 1% Fe | 8.80 | 1350–1400 | Marine engineering, pumps, heat exchangers |
| Inconel 600 | ~72% Ni, 14–17% Cr, 6–10% Fe | 8.47 | 1354–1413 | Chemical processing, furnace components, nuclear reactors |
| Inconel 625 | ~59% Ni, 21.5% Cr, 9% Mo, 5% Fe | 8.44 | 1290–1350 | Aerospace turbines, nuclear reactors, chemical plants |
| Waspaloy | ~58% Ni, 19% Cr, 13% Co, 4% Mo, Ti, Al | 8.19 | 1320–1380 | Jet engine turbine disks, aerospace fasteners |
Nimonic 80A |
~76% Ni, 20% Cr, Ti, Al | 8.19 | 1320–1385 | Gas turbines, exhaust valves, high-temperature springs |
| Hastelloy X | ~47% Ni, 22% Cr, 18.5% Fe, 9% Mo | 8.30 | 1260–1355 | Gas turbine combustion chambers, high-temperature ducts |
| Hastelloy C-22 | ~56% Ni, 22% Cr, 13% Mo, 3% W, Fe | 8.69 | 1350–1400 | Chemical reactors, scrubbers, pollution control |
| Hastelloy C-276 | ~57% Ni, 16% Mo, 15% Cr, 5% Fe, W | 8.89 | 1325–1370 | Flue gas scrubbers, chemical processing, pollution control |
| Incoloy 825 | ~42% Ni, 21.5% Cr, 30–35% Fe, 3% Mo | 8.14 | 1385–1400 | Acid-resistant piping, marine exhaust systems |
| Nickel–Tungsten (30% W) | ~70% Ni, 30% W | 10.0 | ~1455–1500 | Radiation shielding, wear-resistant parts |
| Invar 36 | ~64% Fe, 36% Ni | 8.05 | 1430–1440 | Precision instruments, low thermal expansion applications |
7. Conclusion
Nickel’s density is a fundamental physical property influencing design, manufacturing, and performance in high-tech industries.
Factors such as purity, alloying, temperature, and pressure create minor variations, but understanding these nuances is critical for engineers and material scientists.
Nickel’s combination of high density, mechanical strength, and thermal resilience makes it indispensable across aerospace, chemical, energy, and electronics sectors.
FAQs
Does the form of nickel (solid vs. powder) affect its density?
Yes. “True density” (density of the nickel itself) is the same for solids and powders (~8.908 g/cm³ for pure nickel), but “bulk density” (mass/volume of the powder bed) is lower (4–5 g/cm³) due to voids between particles.
Gas pycnometry measures true density, while tap density measures bulk density.
How does cold working affect nickel’s density?
Cold working (e.g., rolling, forging) increases nickel’s density slightly (~0.1–0.2%) by reducing lattice defects (dislocations) and compressing voids.
For example, cold-rolled nickel has a density of ~8.92 g/cm³, vs. 8.908 g/cm³ for annealed nickel.
Is nickel’s density higher than other common metals?
Yes. Nickel is denser than aluminum (2.70 g/cm³), iron (7.87 g/cm³), and titanium (4.51 g/cm³) but less dense than copper (8.96 g/cm³), brass (8.4–8.7 g/cm³), and tungsten (19.3 g/cm³).
Can density be used to distinguish nickel from counterfeit metals?
Yes. For example, nickel-plated steel (density ~7.9 g/cm³) has a lower density than pure nickel (8.908 g/cm³), making Archimedes’ principle a simple way to detect counterfeits (e.g., fake nickel coins).
What is the density of nickel in space (vacuum, extreme temperature)?
In a vacuum, density is unaffected (only temperature and pressure matter). At cryogenic temperatures (-200°C), nickel’s density increases to ~8.95 g/cm³ (due to lattice contraction).
In microgravity, density measurement via Archimedes’ principle is impossible, so XRD is used instead.
