- Materials
- Forms
- Reference Materials
-
Services
-
Services
-
-
Sectors
-
Supporting cutting edge research and development with advanced materials to your needs.
High performance materials for extreme conditions.
Innovative and lightweight materials with high mechanical properties and durability.
Materials used in chemical engineering from consumables to innovative solutions.
Advanced materials characterized by high electrical or insulation performance.
High quality materials for renewable energy.
Biocompatible and biodegradable materials to the highest standards.
High purity, biocompatible materials for high performance devices and applications.
High purity metals and alloys in various forms and crucibles suitable to your needs.
State of the art materials for the next generation of technologies.
High performance materials for extreme conditions.
Durable materials for corrosive environments.
Foils, disks or windows across a range of materials to facilitate your innovation.
Polymers, metal foils, and sustainable materials for your packaging needs.
Your requirements for unique products and attributes will be met across our 170,000+ product range and customization capabilities.
High-quality materials across branded products in various forms including rods, wires, and foils support space technology needs.
Highest quality materials to support your need for small-quantity specialist materials such as graphite and lithium compounds.
High purity materials to improve the reproducibility and reliability of your evaporation processes.
-
- Brands
-
Resources
-
Find out our latest news.
Read our latest insights, and opinions.
Discover our Innovation Discovered podcasts on innovation, products, interesting topics, and more.
Find out how we've worked with our partners
Our latest updates on what we are doing, find out more.
Find out more about us and the great roles we have available for talented individuals. Find out more.
Take a look at our global distributors.
Explore our FAQ resource to help answer your key questions.
Gain a clearer picture of the language used in scientific study
-
- About Us
Toggle Nav
Gold
Gold (Au, atomic number 79) is a Group 11 FCC noble metal with a melting point of 1,064 °C, density of 19.32 g/cm³, and the most chemically inert character of any metal — it does not react with oxygen, water, or most acids, dissolving only in aqua regia (HNO₃/HCl, 1:3) and in cyanide solutions in the presence of oxygen. Gold's chemical stability arises from relativistic contraction of the 6s orbital, which lowers its energy and increases the ionization potential — the same relativistic effect accounts for gold's characteristic yellow color (relativistic narrowing of the 5d→6s band gap allows absorption of blue light) and its anomalously high electron affinity for a metal. Gold is the most malleable and ductile of all metals: 1 gram can be beaten to a 1 m² leaf (~0.1 µm thick) or drawn to ~3 km of wire. It occurs as native metal in quartz veins and alluvial deposits, and is the only metal historically obtained without smelting.
Electronics is the largest technical application of gold (~300 tonnes/year), exploiting its unique combination of chemical inertness, electrical conductivity, and reliability: Au bond wires connect semiconductor die to package leads, Au electroplating protects connector contacts, and Au-based solders (Au-Sn, Au-Ge, Au-Si eutectic alloys) provide hermetic sealing in high-reliability packages for aerospace, defense, and medical devices. Gold's surface plasmon resonance (SPR) — collective oscillation of conduction electrons at ~520 nm in Au nanoparticles, tunable from 500–900 nm with particle size and shape — is the basis of a vast range of biosensing, diagnostic, and therapeutic applications. Colloidal Au nanoparticles (AuNPs, 5–100 nm) functionalized with antibodies, oligonucleotides, or peptides are the active element in lateral flow immunoassays (home pregnancy tests, COVID-19 rapid tests, ~1 billion produced/year) and in surface-enhanced Raman spectroscopy (SERS) substrates for single-molecule detection.
Nanoparticulate gold catalysis — discovered by Masatake Haruta in 1987 — revealed that Au, long considered catalytically inert, becomes highly active for CO oxidation at room temperature when deposited as ~2–5 nm particles on reducible oxide supports (TiO₂, Fe₂O₃, CeO₂), a finding that overturned a fundamental assumption of catalytic chemistry. Au/TiO₂ catalysts operate at temperatures as low as –70 °C for CO oxidation, relevant to CO sensors, air purification, and preferential oxidation of CO in H₂ streams for fuel cells. The combination of biocompatibility, ease of surface functionalization via Au-thiol self-assembled monolayers, and tunable SPR makes gold the pre-eminent substrate for scanning tunneling microscopy (STM), surface-enhanced spectroscopies, and biosensor development. ¹⁹⁸Au (t½ = 2.7 days, β⁻/γ) has been used clinically for radiation synovectomy and solid tumor treatment, and gold-198 nanoparticles are in clinical development for prostate cancer brachytherapy.
General Properties
| Property | Value | Notes |
|---|---|---|
| Atomic Number | 79 | Group 11, Period 6; 4f¹⁴5d¹⁰6s¹; oxidation states +1 (Au⁺, aurous, stable in AuCN and Au₂S) and +3 (Au³⁺, auric, stable in AuCl₄⁻ and HAuCl₄). Relativistic contraction of the 6s orbital is unusually large at Z=79, raising Au's ionization energy and electron affinity to near-halogen values and producing the characteristic yellow color. |
| Atomic Mass | 196.967 u | Gold is monoisotopic — ¹⁹⁷Au (100% natural abundance) is the only naturally occurring isotope, simplifying mass spectrometric analysis and making Au an ideal internal standard for ICP-MS. All other Au isotopes are radioactive. |
| Density (20 °C) | 19.32 g/cm³ | Among the densest elements — comparable to tungsten (19.25 g/cm³) and platinum (21.45 g/cm³). The high density is exploited historically in panning/gravity separation of placer gold and currently in density-based authentication of gold bullion against tungsten-filled counterfeits. |
| Melting Point | 1,064.18 °C (1,337.33 K) | A fixed point on the ITS-90 international temperature scale (1,064.18 °C), used to calibrate high-temperature thermocouples and radiation thermometers. The relatively low melting point for a dense metal enables gold wire bonding and soldering processes in electronics manufacturing. |
| Boiling Point | 2,856 °C | High enough to enable Au thermal evaporation for thin-film deposition (resistive boats or e-beam sources at ~1,400 °C in vacuum) and Au sputtering targets for PVD. Au evaporation is the standard method for preparing conductive coatings on biological SEM specimens. |
| Thermal Conductivity | 318 W/m·K | Third highest thermal conductivity of any pure metal after Ag (429 W/m·K) and Cu (401 W/m·K). Exploited in Au-coated thermal management components in spacecraft, high-power laser optics, and Au-bonded heat spreaders in high-reliability electronics where oxidation of Cu or Ag is unacceptable. |
| Electrical Resistivity | 22.14 nΩ·m (20 °C) | Fourth lowest resistivity of any pure metal after Ag (15.9), Cu (16.8), and Al (26.5 nΩ·m). Au's resistivity stability over time (no oxide film formation) makes it preferred over Cu/Ag for low-contact-resistance connectors and bond pads in high-reliability applications. |
| Crystal Structure | FCC, a = 4.078 Å (room temperature) | FCC structure gives Au 12 slip systems and is responsible for its exceptional ductility and malleability. The FCC (111) surface is the flattest and most thermodynamically stable Au surface — used as the standard substrate for thiol SAM formation and STM atomic-resolution imaging. |
Mechanical Properties
| Property | Value | Notes |
|---|---|---|
| Tensile Strength | 120–190 MPa | Low strength in pure form — Au is the softest precious metal. Au bond wire (typically 25 µm diameter, 99.99%) requires careful mechanical characterization (loop height control, wire pull strength) to ensure reliable interconnect integrity in semiconductor packages. |
| Yield Strength | 30–100 MPa | Very low yield strength — pure Au deforms easily under modest loads. Alloying (Au-Cu, Au-Ag, Au-Pt) dramatically increases strength for jewelry and industrial applications while maintaining corrosion resistance; karat gold alloys (18K = 75% Au) balance strength and color. |
| Young's Modulus | 78 GPa | Relatively low modulus for a dense FCC metal — lower than Cu (130 GPa) and Ag (83 GPa). The low modulus contributes to Au's extreme malleability and is relevant to the mechanical behavior of Au thin films and MEMS structures under thermal cycling. |
| Hardness | 25–35 HB | Among the softest pure metals; work hardens rapidly. Au electroplated contacts are often hardened by co-depositing with small amounts of Co, Ni, or Fe (hard gold, 130–200 HV) to improve wear resistance in connector applications. |
| Elongation at Break | 45–55% | Exceptional ductility — the highest of any metal, enabling Au to be beaten to ~0.1 µm thick leaf and drawn to wire of extraordinary fineness. Gold leaf (23–24 karat, ~0.1–0.3 µm) is used in architecture, conservation, and art gilding. |
| Poisson's Ratio | 0.44 | Among the highest Poisson's ratios of any FCC metal, approaching the theoretical incompressible limit of 0.5. Relevant to stress modeling of Au thin films on substrates with mismatched thermal expansion coefficients in microelectronics packaging. |
Chemical Properties
| Property | Value / Behavior | Notes |
|---|---|---|
| Oxidation States | +1 (aurous: AuCN, Au₂S, Au₂O); +3 (auric: AuCl₃, HAuCl₄, Au(OH)₃) | Au³⁺ in tetrachloroaurate (AuCl₄⁻, from aqua regia dissolution) is the primary precursor for AuNP synthesis (Turkevich citrate reduction, Brust-Schiffrin two-phase synthesis). Au⁺ in KAu(CN)₂ is the standard electroplating bath species for electronics gold plating. |
| Corrosion Resistance | Exceptional; inert to O₂, H₂O, most acids and alkalis; dissolves in aqua regia and in CN⁻/O₂ | Gold's thermodynamic nobility (standard reduction potential E° = +1.50 V for Au³⁺/Au, +1.83 V for Au⁺/Au) underpins its corrosion immunity. Cyanide leaching (Au + 2CN⁻ + ½O₂ + H₂O → Au(CN)₂⁻ + OH⁻) extracts ~75% of mined gold; aqua regia dissolution is used for gold assaying and recycling from electronic scrap. |
| Surface Oxide | Au₂O₃ forms above ~160 °C under oxidizing conditions; unstable — decomposes above ~300 °C | The instability of Au oxides is why Au surfaces remain clean and conductive indefinitely at ambient conditions — unlike Cu, Ag, or even Pt. This oxide-free surface is essential for reliable low-resistance electrical contacts, Au-thiol SAM formation, and Au-catalysis applications where a clean metal surface is required. |
| Identifier | Value |
|---|---|
| Symbol | Au |
| Atomic Number | 79 |
| CAS Number | 7440-57-5 |
| UN Number | N/A |
| EINECS Number | 231-165-9 |
| Isotope | Type | Notes |
|---|---|---|
| ¹⁹⁷Au | Stable | 100% natural abundance; I = 3/2, NMR-active. Gold is monoisotopic — ¹⁹⁷Au is the only naturally occurring isotope, giving Au uniquely simple mass spectra. ¹⁹⁷Au NMR (chemical shift range ~400 ppm) characterizes Au coordination compounds and Au cluster complexes in solution, though broad quadrupolar linewidths limit routine use. ¹⁹⁷Au(n,γ)¹⁹⁸Au (σ = 98.65 barn, one of the highest of any stable nuclide) makes Au an exceptionally sensitive neutron activation analysis (NAA) target and a key flux monitor in neutron irradiation experiments. |
| ¹⁹⁵Au | Radioactive | t½ = 186.1 days; EC decay to ¹⁹⁵Pt; emits X-rays and a 98.9 keV gamma. Produced by proton bombardment of Pt targets at cyclotrons. ¹⁹⁵Au's long half-life and low-energy gamma make it suitable for SPECT imaging of Au-based drug biodistribution and for Mössbauer spectroscopy studies of Au chemical bonding (¹⁹⁵Au Mössbauer is a sensitive probe of Au oxidation state and coordination geometry). |
| ¹⁹⁸Au | Radioactive | t½ = 2.694 days; β⁻ (Emax = 0.961 MeV) + γ (411.8 keV, 95.6%). Produced by ¹⁹⁷Au(n,γ)¹⁹⁸Au in reactors (σ = 98.65 barn). Used clinically for radiation synovectomy (injection into inflamed joints), hepatocellular carcinoma treatment, and in colloidal ¹⁹⁸AuNP form for prostate cancer brachytherapy (sub-mm particles implanted directly into tumor). The 411.8 keV gamma enables external dosimetry and SPECT imaging of ¹⁹⁸Au distribution during treatment. |
Scientific & Research Applications
| Use Case | Form Typically Used | Description |
|---|---|---|
| Gold Nanoparticle Synthesis & Biosensing | HAuCl₄ solution (from Au metal dissolution); Au seed nanoparticles (5–20 nm) | Citrate-capped AuNPs (Turkevich method) and thiol-stabilized AuNPs (Brust-Schiffrin) are functionalized with antibodies, DNA aptamers, or peptides for lateral flow immunoassays, SPR biosensors, and SERS substrates. Tunable SPR from 520 nm (spheres) to >900 nm (nanorods, nanostars) covers the biological tissue transparency window for in vivo imaging and photothermal therapy. |
| Surface Science & STM/AFM Substrates | Au(111) single crystal substrates; Au films on mica (template-stripped, atomically flat) | Au(111) is the standard substrate for STM atomic-resolution imaging, thiol SAM characterization by XPS/NEXAFS, and electrochemical studies of molecular adsorption. Template-stripped Au on mica provides atomically flat surfaces over cm² areas for nanoparticle assembly, single-molecule SERS, and plasmonics device fabrication. |
| Nanocatalysis Research | Au/TiO₂, Au/Fe₂O₃, Au/CeO₂ catalysts (2–5 nm Au particles, deposited by deposition-precipitation) | Supported AuNP catalysts are active for CO oxidation at –70 °C to room temperature, selective oxidation of alcohols/aldehydes, and preferential CO oxidation (PROX) in H₂ for fuel cell applications. Research focuses on the role of the Au-support interface, particle size dependence of activity, and sintering resistance under reaction conditions. |
| Thin-Film Deposition & Sputtering | Au sputtering targets (99.99–99.999%), Au evaporation pellets/wire | Au thin films (5–200 nm) deposited by thermal evaporation or DC magnetron sputtering are used for SEM specimen coating, electrical contacts on MEMS devices, Au bond pad definition in wafer-level packaging, and as seed layers for Au electroplating in microelectronics. Au's chemical inertness ensures film stability without oxidation protection. |
| Plasmonics & Optical Research | Au nanorods, nanotriangles, nanostars (colloidal); Au gratings and nanodisk arrays (e-beam lithography) | Au nanostructures support localized surface plasmon resonances (LSPRs) that concentrate electromagnetic fields in sub-nm "hot spots" — used for SERS detection of single molecules, tip-enhanced Raman spectroscopy (TERS), nonlinear optics, and optical tweezers. Au nanoantennas fabricated by e-beam lithography or focused ion beam milling are model plasmonic structures for near-field optical microscopy. |
Industrial & Commercial Applications
| Sector | Form / Grade Used | Description |
|---|---|---|
| Electronics & Microelectronics | Au bond wire (25 µm, 99.99%+); Au electroplate (KAu(CN)₂ bath, 99.99%); Au-Sn solder (80Au-20Sn eutectic) | Au bond wire connects die to package leads in ~80 billion semiconductor packages/year; Au electroplating protects connector contacts from oxidation and tarnish for decades of reliable service. Au-20Sn eutectic solder (mp 280 °C, flux-free, hermetic) seals lids onto ceramic packages in high-reliability RF, microwave, and aerospace applications where conventional Sn-Pb solders are prohibited. |
| Aerospace & Thermal Management | Au foil/film (99.99%), Au-coated polyimide film (Kapton) | Gold-coated multi-layer insulation (MLI) blankets are used on spacecraft to control radiative heat transfer — Au's low emissivity (~0.02) reflects infrared radiation and minimizes heat gain or loss in the vacuum of space. The James Webb Space Telescope's primary mirror segments are Au-coated beryllium, optimized for near-infrared reflectivity (>99% from 600 nm to 28 µm). |
| Medical Devices & Diagnostics | Au nanoparticles (colloidal, 20–40 nm); Au electrodes (99.99%); ¹⁹⁸Au for therapy | Au nanoparticles are the active colorimetric label in lateral flow immunoassays (pregnancy tests, COVID-19 rapid tests, influenza tests) — the familiar red line results from AuNP aggregation-induced color change. Au electrodes are used in implantable neural recording arrays, cochlear implants, and retinal prostheses due to biocompatibility and electrochemical stability. |
| Jewelry & Investment | Au alloys (18K = 75% Au, 14K = 58.3% Au); fine gold (99.99%, 99.999%) bullion | Jewelry accounts for ~50% of annual gold demand (~2,000 tonnes/year); alloying with Cu (rose gold), Ag (white gold precursor), Pd, and Ni controls color, hardness, and melting point while maintaining corrosion resistance. Investment gold (bars, coins) requires 99.5%+ purity (London Bullion Market Association "Good Delivery" standard: 99.5%). |
| Purity | Description |
|---|---|
| 99.9% (3N) | High-purity gold suitable for industrial-grade electronics, basic research, and standard coating applications where minor impurities are acceptable. |
| 99.95% (3N5) | Enhanced-purity gold ideal for demanding electronic and optical applications, offering improved consistency and performance in microfabrication processes. |
| 99.99% (4N) | Ultra-pure gold commonly used in precision electronics, high-end optical coatings, and sputtering targets where low impurity content is critical. |
| 99.999% (5N) | Research-grade gold used in advanced semiconductor processes, high-vacuum systems, and nanotechnology where maximum purity is essential for reproducibility and stability. |
| Synonym / Alternative Name | Context |
|---|---|
| Gold metal | Commercial designation for elemental Au in wire, foil, shot, powder, or target form; used in ASTM standards, London Bullion Market Association (LBMA) specifications, and trade documentation for electronics, jewelry, and investment gold supply chains. |
| Elemental Gold | Scientific designation distinguishing the pure element from HAuCl₄, KAu(CN)₂, and other Au compounds; used in nanomaterial synthesis literature to specify bulk Au as the precursor or substrate material. |
| Element 79 | Periodic table designation; used in XRF analytical software, ICP-MS databases, and nuclear data libraries (ENDF/B) where atomic number is the primary element identifier. |
| Aurum | Latin name for gold — the source of the chemical symbol Au; used in historical alchemical and early chemical literature; appears as the INN root in pharmaceutical gold compound nomenclature (auranofin, sodium aurothiomalate) and in the term "auric/aurous" for Au³⁺/Au⁺ oxidation state designation. |
| Or | French language name for gold; used in French scientific literature, EU regulatory and customs documentation, and heraldic notation where "or" (gold) and "argent" (silver) are the standard metallic tinctures. |
| Oro | Spanish and Italian language name for gold; used in scientific literature and industrial/trade documentation in Spanish- and Italian-speaking markets; Spain, Mexico, and Italy are significant gold jewelry manufacturing and trading centers. |