The boiling point of gold is 2,856°C (5,173°F, 3,129 K). At this temperature and standard atmospheric pressure, liquid gold transitions to gold vapor — the metal atomizes into a gas of individual Au atoms and small clusters. This is the highest temperature at which gold exists as a condensed phase at one atmosphere.
Gold’s boiling point is remarkably high for a metal that melts at a relatively moderate 1,064°C. The 1,792°C gap between melting point and boiling point — gold’s liquid range — is one of the widest in the noble metal family. This wide liquid range reflects the strength of the Au-Au metallic bond in the liquid state, which persists across a large temperature range before the vapor pressure reaches one atmosphere.
Understanding gold’s boiling point and vapor pressure is directly relevant to physical vapor deposition (PVD) of gold films, induction melting practice, dental casting, jewelry refining, and high-vacuum applications where gold’s volatility at elevated temperatures must be controlled.
Gold Boiling Point: Complete Reference Values
All values from NIST Standard Reference Database (NIST-JANAF Thermochemical Tables):
| Property | Value |
|---|---|
| Boiling point (1 atm) | 2,856°C / 5,173°F / 3,129 K |
| Melting point | 1,064.18°C / 1,947.52°F / 1,337.33 K |
| Liquid range | 1,791.82°C (2,856 − 1,064) |
| Latent heat of fusion | 12.55 kJ/mol (63.7 kJ/kg) |
| Latent heat of vaporization | 324 kJ/mol (1,645 kJ/kg) |
| Ratio (vaporization/fusion) | 25.8× |
Source: NIST Standard Reference Database; CRC Handbook of Chemistry and Physics, 104th Edition.
Unit conversions:
- °C to °F: (2,856 × 9/5) + 32 = 5,173°F
- °C to K: 2,856 + 273.15 = 3,129.15 K (rounded to 3,129 K)
The latent heat ratio (25.8×) means that boiling gold requires approximately 26 times more energy than melting it. A kilogram of gold that has just been melted requires 1,645 kJ more energy to fully vaporize — a quantity that determines the energy cost of gold PVD processes and sets the scale for calculating evaporation rates in high-vacuum deposition chambers.
The Noble Metals: Boiling Points in Context
Gold is one of three classical noble metals, alongside silver and platinum. Their boiling points follow a pattern governed by electronic structure and relativistic effects:
| Metal | Atomic number | Melting point (°C) | Boiling point (°C) | Liquid range (°C) |
|---|---|---|---|---|
| Silver (Ag) | 47 | 962 | 2,162 | 1,200 |
| Gold (Au) | 79 | 1,064 | 2,856 | 1,792 |
| Platinum (Pt) | 78 | 1,768 | 3,825 | 2,057 |
| Copper (Cu) | 29 | 1,085 | 2,562 | 1,477 |
| Palladium (Pd) | 46 | 1,555 | 2,963 | 1,408 |
| Iridium (Ir) | 77 | 2,446 | 4,428 | 1,982 |
Gold’s boiling point (2,856°C) is notably higher than silver’s (2,162°C) and higher than copper’s (2,562°C) — the two metals it sits between in Group 11. Counterintuitively, gold also melts at a higher temperature than silver (1,064 vs. 962°C). Both anomalies — gold melting and boiling higher than the lighter Group 11 metal silver — trace to the same quantum mechanical phenomenon: relativistic contraction of gold’s 6s orbital.
Why Gold’s Boiling Point Is So High — Relativistic Orbital Effects
Gold’s exceptional properties — its characteristic yellow color, its anomalously high melting and boiling points relative to silver, its chemical nobility — all originate in the same quantum mechanical phenomenon: relativistic contraction of the 6s electron orbital.
The relativistic mechanism
Gold has an atomic number of 79. Its inner electrons, particularly the 1s electrons, travel at a significant fraction of the speed of light in their orbits around the nucleus. By special relativity, moving objects experience a relativistic mass increase — their effective mass increases as velocity approaches c. For electrons in the 1s orbital of gold, this effect is strong enough to cause the 1s orbital to contract toward the nucleus.
This contraction propagates outward through all s and p orbitals via quantum mechanical shielding effects. The 6s orbital in gold — the valence orbital whose electron participates in metallic bonding — contracts significantly relative to a non-relativistic calculation. The contraction lowers the energy of the 6s electron, pulling it closer to the nucleus and making it less available for bonding with neighboring gold atoms.
This sounds like it would weaken the Au-Au bond. In fact, it strengthens it: the contracted, lower-energy 6s orbital creates a directional, anisotropic interaction with neighboring gold atoms that is stronger than the non-relativistic case predicts. The net effect is a stronger Au-Au bond in both solid and liquid gold compared to what silver’s Ag-Ag bond achieves.
The quantitative consequence of the boiling point
The latent heat of vaporization — the energy needed to break all metallic bonds and convert liquid metal to vapor — scales with bond strength. For gold:
- Latent heat of vaporization: 324 kJ/mol
- For silver: 254 kJ/mol (21% lower)
- For copper: 305 kJ/mol (6% lower)
Gold’s vaporization enthalpy exceeds silver’s by 21% — directly reflecting the stronger Au-Au bond due to relativistic effects. At higher bonding energy, higher thermal energy (higher temperature) is required to overcome these bonds and generate sufficient vapor pressure to reach one atmosphere. Hence gold’s boiling point (2,856°C) is 694°C above silver’s (2,162°C).
Why this matters for the gold color connection
The same relativistic orbital contraction that raises gold’s boiling point above silver’s also explains gold’s distinctive yellow color. In silver, the energy gap between the 4d band and the 5s conduction band is large enough that photons in the visible spectrum cannot bridge it — silver reflects all visible wavelengths equally and appears white. In gold, the relativistic contraction raises the energy of the 5d band and lowers the 6s band, closing the gap to the point where blue and violet photons (approximately 2.5 eV, 400–500 nm) are absorbed by 5d→6s transitions. The remaining reflected light — predominantly yellow-red — gives gold its characteristic color. Boiling point, melting point, and color are all expressions of the same underlying physics.
Gold Vapor Pressure: The Practical Bridge Between Melting and Boiling
Gold does not wait until 2,856°C to begin evaporating. Above the melting point, liquid gold has a vapor pressure that increases exponentially with temperature. The vapor pressure at any given temperature is what determines gold loss during casting, the deposition rate in PVD, and the fume hazard in high-temperature gold processing.
| Temperature | Vapor pressure | Notes |
|---|---|---|
| 1,064°C (melting point) | ~10⁻⁸ atm (10 nPa) | Negligible evaporation |
| 1,200°C | ~10⁻⁷ atm | Still very low |
| 1,500°C | ~10⁻⁵ atm (1 Pa) | Detectable evaporation begins |
| 1,800°C | ~10⁻³ atm (100 Pa) | Significant evaporation |
| 2,200°C | ~0.05 atm (5 kPa) | Rapid evaporation |
| 2,500°C | ~0.3 atm (30 kPa) | Near-boiling behavior |
| 2,856°C | 1.0 atm (101 kPa) | Boiling point |
Source: NIST-JANAF Thermochemical Tables; CRC Handbook vapor pressure data.
The exponential relationship between temperature and vapor pressure (the Clausius-Clapeyron equation) means that gold evaporation is negligible at casting temperatures (1,100–1,200°C) but becomes important in vacuum deposition at 1,400–1,800°C. Gold is among the most common metals deposited by thermal evaporation in PVD precisely because its vapor pressure reaches useful deposition rates (approximately 1 Pa = 10⁻⁵ atm) at temperatures achievable with a tungsten or molybdenum evaporation boat.
Gold’s Boiling Point in Industrial Applications
Physical vapor deposition (PVD) of gold
PVD gold deposition is the dominant process for depositing gold films in electronics (connector contacts, bond pads, PCB surface finishes), optics (mirror coatings, beam splitters), and decorative applications (architectural glass, jewelry findings). In a thermal evaporation PVD system:
The gold source material (pellets, wire, or a molten pool) is heated in a tungsten or molybdenum boat under high vacuum (10⁻⁵ to 10⁻⁷ Torr, approximately 10⁻³ to 10⁻⁵ Pa). At this pressure, gold evaporates at approximately 1,000–1,200°C — far below its atmospheric boiling point of 2,856°C. The Clausius-Clapeyron relationship means that lowering the surrounding pressure to 10⁻⁵ atm reduces the evaporation temperature by approximately 800–1,000°C.
The deposition rate is controlled by the source temperature. Typical PVD gold deposition at 10⁻⁶ Torr background pressure uses source temperatures of approximately 1,400–1,600°C to achieve deposition rates of 1–10 nm/s. At 2,856°C, the atmospheric boiling point, deposition rates would be catastrophically fast and uncontrollable under vacuum conditions.
Gold casting: why the boiling point sets an upper limit
In dental and jewelry casting, gold alloys are melted in induction or resistance furnaces and centrifugally or vacuum-assist cast at approximately 50–100°C above the liquidus. For 18k yellow gold (liquidus ~920°C), pour temperatures of 970–1,020°C are typical — over 1,800°C below gold’s boiling point.
The boiling point is not directly limiting in casting, but gold’s vapor pressure at typical casting temperatures (0.1–1 Pa range at 1,000–1,100°C) means some gold vaporization occurs in the melt surface, particularly in open-flame torch melting where the flame temperature can locally exceed 2,000°C. Induction furnaces under controlled atmosphere are preferred for high-value gold casting precisely because they minimize localized overheating and gold vapor loss.
Gold in high-vacuum electronics
In ultra-high vacuum (UHV) systems used for semiconductor deposition, surface science, and electron microscopy, the gold components (substrates, apertures, sample holders) must not outgas at operating temperatures. At typical UHV operating temperatures below 300°C, gold’s vapor pressure is negligibly small. Gold’s stability and low vapor pressure in the 20–500°C range is one reason it is used as a coating on precision vacuum components, sample stages, and scanning tunneling microscope tips.
Boiling Points of Gold Alloys
Like the melting point, the boiling behavior of gold alloys is more complex than for pure gold. In alloys, the evaporation of individual components occurs at rates determined by each element’s partial pressure over the alloy melt. Lower-boiling-point constituents (silver, copper, zinc) evaporate preferentially at temperatures where gold vapor pressure is still negligible.
| Element | Boiling point (°C) | Relative to the gold boiling point |
|---|---|---|
| Zinc (Zn) | 907 | −-1,949 °C; boils below gold’s melting point |
| Silver (Ag) | 2,162 | −694°C |
| Copper (Cu) | 2,562 | −294°C |
| Gold (Au) | 2,856 | — Reference |
| Palladium (Pd) | 2,963 | +107°C |
| Platinum (Pt) | 3,825 | +969°C |
In 14k yellow gold (58.3% Au, balance Cu-Ag-Zn), zinc has a boiling point of only 907°C — below gold’s melting point. During torch melting of 14k gold at 900–950°C, zinc begins to volatilize actively. This is the source of the blue-white zinc oxide fume visible when melting high-zinc gold alloys, and the reason that zinc-containing gold alloys lose zinc progressively with each melt cycle if they are not refined or alloyed with fresh material.
White gold alloys using palladium (boiling point 2,963°C) or platinum (3,825°C) as the whitening element are far more stable under melting conditions than zinc-bearing white gold alloys — the palladium and platinum do not preferentially evaporate relative to gold at casting temperatures.
Frequently Asked Questions About the Boiling Point of Gold
Q: What is the boiling point of gold?
2,856°C (5,173°F, 3,129 K) at standard atmospheric pressure (1 atm, 101.325 kPa). This is the temperature at which gold’s vapor pressure reaches one atmosphere, causing liquid gold to transition to the vapor phase. Source: NIST Standard Reference Database (NIST-JANAF Thermochemical Tables).
Q: Why is gold’s boiling point so much higher than its melting point?
The 1,792°C gap between gold’s melting point (1,064°C) and boiling point (2,856°C) reflects the strength of the Au-Au metallic bond in the liquid state. Gold has anomalously strong metallic bonding for a Group 11 element because relativistic contraction of its 6s valence orbital strengthens the directionality and intensity of Au-Au bonding. The latent heat of vaporization (324 kJ/mol) is 25.8 times the latent heat of fusion (12.55 kJ/mol) — the bond energy per atom in liquid gold is much larger than the energy released on freezing.
Q: Is gold’s boiling point higher than silver’s?
Yes — gold (2,856°C) boils 694°C higher than silver (2,162°C), despite gold melting only 102°C higher. This means gold’s liquid range (1,792°C) is 592°C wider than silver’s (1,200°C). The explanation is relativistic: gold’s heavier nucleus produces stronger relativistic orbital contraction than silver’s, strengthening the Au-Au metallic bond in the liquid more than the Ag-Ag bond.
Q: Does gold evaporate before it reaches its boiling point?
Yes. At any temperature above absolute zero, gold has a nonzero vapor pressure. At the melting point (1,064°C), gold’s vapor pressure is approximately 10⁻⁸ atm — negligible in casting practice. At 1,500°C, approximately 10⁻⁵ atm — detectable in sensitive instruments. Gold PVD deposition typically operates at source temperatures of 1,400–1,600°C under vacuum (10⁻⁶ Torr), where the reduced surrounding pressure allows gold to evaporate rapidly at temperatures far below the atmospheric boiling point.
Q: Can gold vaporize in a jeweler’s torch?
A propane or oxyacetylene torch flame reaches approximately 2,000–3,100°C at its hottest zone. At these temperatures, particularly near the boiling point, gold vaporization can occur locally. Torch melting of gold is typically kept brief and at controlled temperatures to minimize vapor loss. In practice, gold vapor loss during standard jewelry casting is minimal because the bulk melt temperature is kept close to the liquidus (920–1,020°C, depending on karat) — far below the boiling point.
Q: How does the boiling point of gold affect PVD deposition?
The atmospheric boiling point (2,856°C) is not directly used in PVD processes. What matters is the vapor pressure-temperature relationship: at the 10⁻⁵ to 10⁻⁶ Torr vacuum pressure of a typical PVD chamber, gold achieves useful evaporation rates at approximately 1,200–1,600°C — roughly 1,200–1,700°C below the atmospheric boiling point. The high atmospheric boiling point of gold (indicating strong Au-Au bonding) means that the evaporation source must be heated considerably before useful deposition rates are achieved, requiring resistive or electron-beam heating of the gold source material.
References
- National Institute of Standards and Technology (NIST), NIST Standard Reference Database 69: NIST Chemistry WebBook, available at webbook.nist.gov; and Chase, M.W., et al., NIST-JANAF Thermochemical Tables, 4th Edition, AIP, 1998. (Gold boiling point 2,856°C / 3,129 K; latent heat of vaporization 324 kJ/mol; vapor pressure of liquid gold as a function of temperature; the primary thermodynamic reference for all gold phase transition data in this article.)
- Haynes, W.M., ed., CRC Handbook of Chemistry and Physics, 104th Edition. CRC Press, Boca Raton, FL, 2024. (Boiling points of gold, silver, copper, platinum, palladium, iridium, and zinc; vapor pressure tables for liquid metals; latent heats of fusion and vaporization for noble metals; relativistic effects in Group 11 element properties.)
- Kittel, C., Introduction to Solid State Physics, 8th Edition. Wiley, New York, 2005. (Relativistic orbital contraction in heavy elements; 6s orbital energy in gold vs. silver — the quantum mechanical basis for the anomalous boiling point, melting point, and color of gold; metallic bond strength and its relationship to vaporization enthalpy.)
- ASM Handbook, Volume 2: Properties and Selection — Nonferrous Alloys and Special-Purpose Materials, 10th Edition. ASM International, Materials Park, OH, 1990. (Gold and gold alloy thermal properties; casting temperature practice for karat gold alloys; volatilization of zinc from gold alloys; palladium and platinum stability in white gold alloys under melting conditions.)
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