Gold Au

spore: profile
id: gold
spore_version: 0.2
family: precious-metals
name: Gold
abbreviation: Au
role: conductor, contact plating and infrared mirror coating
category: metals
type: precious-metals
summary: >
  Gold is a soft, dense, very corrosion-resistant metal. A supplier datasheet gives a density of 19.3 g/cm3, a melting point of
  1064.18 degC and a thermal conductivity of 320 W/(m K). The Webb telescope mirrors carry a 100 nm gold layer measured at
  97.3% to 99.42% reflectance in the infrared, and gold appears in mobile-phone circuit boards at 142.6 to 702.3 g per tonne of board.
best_for: "Corrosion-free electrical contacts, bond wires and infrared mirror coatings (a protected gold coating on the Webb mirrors reflects 98.5% to 98.8% from 2.0 to 20.0 micrometres)"
weakest_at: "Softness and scratching when unprotected (NASA notes pure gold is very soft and covers it with silica), and embrittlement of solder joints at high gold content"
identity:
  formula: "Au"
  cas: "7440-57-5"
  crystal_system: cubic (face-centered)
  space_group: Fm-3m
  source: advent-datasheet
  where: "Technical data sheet, Overview block (CAS 7440-57-5) and Crystal Structure block (Face-centered Cubic, space group Fm_3m #225; written Fm-3m here)"
tags:
  environments: [deep-space]
  stresses: [extreme-cold, total-radiation-dose, thermal-cycling]
  applications: [optics-and-cameras, electronics-and-chips, thermal-control]
properties:
  - benchmark: density
    label: Density (solid, STP)
    value: 19.3
    unit: g/cm3
    scope: material
    conditions: {state: "solid", reference_state: "standard temperature and pressure (as labelled by the datasheet)", purity: "not stated (element data)"}
    method: Value listed in a supplier technical data sheet whose source line reads Wolfram Research / periodictable.com
    status: ground
    note: PubChem lists the same 19.3 for density, and 19.3 at 25 degC from the US Department of Energy PAC database, but does not print a unit for it. The datasheet also gives 17.31 g/cm3 for the liquid at the melting point.
    source: advent-datasheet
    where: Technical data sheet, Mechanical Properties block, row Density (solid, STP)
  - benchmark: melting_point
    label: Melting point
    value: 1064.76
    unit: degC
    scope: material
    conditions: {pressure: "not stated", purity: "not stated", entry: "Hazardous Substances Data Bank (HSDB) record GOLD, ELEMENTAL, shown on PubChem"}
    method: Reference value quoted in PubChem from HSDB
    status: ground
    note: The Advent datasheet gives 1064.18 degC (1337.33 K) for the same property, so the two sources differ by 0.58 degC.
    source: pubchem-gold
    where: PubChem compound record Gold (CID 23985), Experimental Properties > Melting Point
  - benchmark: boiling_point
    label: Boiling point
    value: 2856
    unit: degC
    scope: material
    conditions: {pressure: "760 mm Hg", entry: "PAC Chemical Database, U.S. Department of Energy, shown on PubChem"}
    method: Reference value quoted in PubChem
    status: ground
    note: An older HSDB line on the same PubChem page gives 2700 degC. The Advent datasheet gives 2856 degC.
    source: pubchem-gold
    where: PubChem compound record Gold (CID 23985), Experimental Properties > Boiling Point
  - benchmark: electrical_resistivity
    label: Electrical resistivity
    value: 2.2e-8
    unit: ohm m
    scope: material
    conditions: {temperature: "not stated", purity: "not stated (element data)"}
    method: Value listed in a supplier technical data sheet whose source line reads Wolfram Research / periodictable.com
    status: ground
    note: The datasheet prints the unit as ohm m. Its conductivity row is 4.5e7 S/m.
    source: advent-datasheet
    where: Technical data sheet, Electrical Properties block, row Resistivity
  - benchmark: electrical_resistivity_0c
    label: Electrical resistivity at 0 degC
    value: 2.06
    unit: microohm cm
    scope: material
    conditions: {temperature: "0 degC", entry: "Hazardous Substances Data Bank (HSDB) record GOLD, ELEMENTAL, shown on PubChem"}
    method: Reference value quoted in PubChem from HSDB
    status: ground
    note: Equal to 2.06e-8 ohm m. The PubChem line also calls gold an excellent reflector of infrared and heat.
    source: pubchem-gold
    where: PubChem compound record Gold (CID 23985), Experimental Properties > Other Experimental Properties
  - benchmark: electrical_conductivity
    label: Electrical conductivity
    value: 4.5e7
    unit: S/m
    scope: material
    conditions: {temperature: "not stated", purity: "not stated (element data)"}
    method: Value listed in a supplier technical data sheet whose source line reads Wolfram Research / periodictable.com
    status: ground
    source: advent-datasheet
    where: Technical data sheet, Electrical Properties block, row Conductivity
  - benchmark: thermal_conductivity
    label: Thermal conductivity
    value: 320
    unit: W/(m K)
    scope: material
    conditions: {temperature: "not stated", purity: "not stated (element data)"}
    method: Value listed in a supplier technical data sheet whose source line reads Wolfram Research / periodictable.com
    status: ground
    source: advent-datasheet
    where: Technical data sheet, Thermal Properties block, row Thermal Conductivity
  - benchmark: cte
    label: Thermal expansion coefficient
    value: 14.2
    unit: ppm/K
    scope: material
    conditions: {temperature: "not stated", purity: "not stated (element data)"}
    method: The datasheet prints 0.0000142 K-1; Space Mushroom converted it to ppm/K (multiplied by one million)
    status: ground
    note: The conversion is the only change made to the datasheet figure.
    source: advent-datasheet
    where: Technical data sheet, Thermal Properties block, row Thermal Expansion
  - benchmark: specific_heat
    label: Specific heat (solid)
    value: 129.1
    unit: J/(kg K)
    scope: material
    conditions: {state: "solid", temperature: "not stated"}
    method: Value listed in a supplier technical data sheet whose source line reads Wolfram Research / periodictable.com
    status: ground
    source: advent-datasheet
    where: Technical data sheet, Thermal Properties block, row Specific Heat (solid)
  - benchmark: youngs_modulus
    label: Young's modulus
    value: 78
    unit: GPa
    scope: material
    conditions: {form: "not stated (element data)", temperature: "not stated"}
    method: Value listed in a supplier technical data sheet whose source line reads Wolfram Research / periodictable.com
    status: ground
    source: advent-datasheet
    where: Technical data sheet, Mechanical Properties block, row Young's Modulus
  - benchmark: shear_modulus
    label: Shear modulus
    value: 27
    unit: GPa
    scope: material
    conditions: {form: "not stated (element data)", temperature: "not stated"}
    method: Value listed in a supplier technical data sheet whose source line reads Wolfram Research / periodictable.com
    status: ground
    source: advent-datasheet
    where: Technical data sheet, Mechanical Properties block, row Shear Modulus
  - benchmark: poissons_ratio
    label: Poisson's ratio
    value: 0.44
    unit: dimensionless
    scope: material
    conditions: {form: "not stated (element data)", temperature: "not stated"}
    method: Value listed in a supplier technical data sheet whose source line reads Wolfram Research / periodictable.com
    status: ground
    source: advent-datasheet
    where: Technical data sheet, Mechanical Properties block, row Poisson's Ratio
  - benchmark: mohs_hardness
    label: Hardness (Mohs scale)
    value: 2.5
    value_high: 3.0
    bound: range
    unit: Mohs
    scope: material
    conditions: {entry: "Hazardous Substances Data Bank (HSDB) record GOLD, ELEMENTAL, shown on PubChem", form: "not stated"}
    method: Reference value quoted in PubChem from HSDB
    status: ground
    note: HSDB prints the range as Mohs 2.5-3.0. The same line gives a Brinell hardness of 18.5 with no unit printed. The Advent datasheet gives Mohs 2.5. Both place gold among soft metals.
    source: pubchem-gold
    where: PubChem compound record Gold (CID 23985), Experimental Properties > Other Experimental Properties (Hardness)
  - benchmark: wire_tensile_hard_50um
    label: Tensile strength, 99.99% gold wire, 0.05 mm, hard temper
    value: 342.7
    unit: MPa
    scope: material
    conditions: {product: "Advent AU5172 gold wire", diameter: "0.05 mm", purity: "99.99%", temper: "hard", batch: "Gi4428"}
    method: Value listed with the product's technical data by the supplier (batch analysis)
    status: ground
    note: Break load on the same page is 68.63 g. Other Advent wires differ widely with diameter and temper, for example 320 MPa for 0.125 mm hard wire (AU5173, 99.99+%) and 318 N/mm2 for 0.2 mm hard wire (AU5190). Test standard and gauge length are not stated.
    source: advent-wires
    where: Product page AU5172 Gold Wire, Technical Data (Tensile Strength 342.7MPa)
  - benchmark: wire_elongation_hard_50um
    label: Elongation, 99.99% gold wire, 0.05 mm, hard temper
    value: 0.7
    unit: "%"
    scope: material
    conditions: {product: "Advent AU5172 gold wire", diameter: "0.05 mm", purity: "99.99%", temper: "hard", batch: "Gi4428"}
    method: Value listed with the product's technical data by the supplier (batch analysis)
    status: ground
    note: Elongation of the 0.125 mm hard wire (AU5173) is listed as 10%, so elongation depends strongly on the wire.
    source: advent-wires
    where: Product page AU5172 Gold Wire, Technical Data (Elongation 0.7%)
  - benchmark: wire_tensile_annealed_750um
    label: Tensile strength, 99.99% gold wire, 0.75 mm, annealed
    value: 135
    unit: MPa
    scope: material
    conditions: {product: "Advent AU5188 gold wire", diameter: "0.75 mm", purity: "99.99% (batch purity 99.9917%)", temper: "annealed", batch: "Gi4837"}
    method: Value listed with the product's technical data by the supplier (printed as 135 N/mm2; 1 N/mm2 equals 1 MPa)
    status: ground
    note: The soft, annealed wire is much weaker than the hard-drawn wires above.
    source: advent-wires
    where: Product page AU5188 Gold Wire, Technical Data (Tensile strength 135 N/mm2)
  - benchmark: wire_elongation_annealed_750um
    label: Elongation, 99.99% gold wire, 0.75 mm, annealed
    value: 24
    unit: "%"
    scope: material
    conditions: {product: "Advent AU5188 gold wire", diameter: "0.75 mm", purity: "99.99% (batch purity 99.9917%)", temper: "annealed", batch: "Gi4837"}
    method: Value listed with the product's technical data by the supplier
    status: ground
    source: advent-wires
    where: Product page AU5188 Gold Wire, Technical Data (Elongation 24%)
  - benchmark: pcb_gold_content
    label: Gold content of mobile-phone circuit boards
    value: 142.6
    value_high: 702.3
    bound: range
    unit: g/t of board
    scope: material
    conditions: {samples: "8 board types (A to H) from defective or obsolete mobile phones made 2001 to 2005", method: "aqua regia digestion (60 degC, 2 hours, solid/liquid 1/25) then atomic absorption spectroscopy", board_state: "whole unbroken boards, triplicate tests"}
    method: Laboratory characterisation of gold content, Table 3 of the paper
    status: ground
    uncertainty: "Table 3 gives type C as 142.6 +/- 14.1 and type D as 702.3 +/- 25.5 g/t"
    note: Other board types in Table 3 sit between these (A 508.7, B 641.4, E 412.4, F 421.0, G 560.9, H 523.5 g/t). The authors say literature values are 300 to 350 g/t and that ores average only 5 to 10 g/t. The amount of gold per board changed over the years, so these 2001 to 2005 boards do not describe current phones.
    source: kasper2018
    where: Table 3 (Results of the characterization of PCBs); Results and Discussion, Characterization of PCBs; Conclusions
  - benchmark: ir_reflectance_1um
    label: Measured reflectance of protected gold mirror at 1.0 micrometre
    value: 97.3
    unit: "%"
    scope: material
    conditions: {specimen: "Webb primary mirror segment A1, protected gold coating on beryllium, average of seven witness samples", wavelength: "1.0 micrometre", requirement: "at least 96.3%", measurement: "visible/near-infrared spectrometer at 6 degrees incidence (800 nm to 2500 nm)"}
    method: Reflectance measured by the coating maker on witness samples after cryo cycling and humidity exposure
    status: ground
    note: Requirement in Table 1 is at least 96.3%. The paper says results for the other segments, the secondary and the fine steering mirror were similar.
    source: keskikuha2012
    where: Table 3 (Measured reflectance for PMSA A1); Table 1 for requirements
  - benchmark: ir_reflectance_2_20um
    label: Measured reflectance of protected gold mirror from 2.0 to 20.0 micrometres
    value: 98.5
    value_high: 98.8
    bound: range
    unit: "%"
    scope: material
    conditions: {specimen: "Webb primary mirror segment A1, protected gold coating on beryllium, average of seven witness samples", wavelength: "2.0 to 20.0 micrometres", requirement: "at least 97.9%", measurement: "FTIR spectrometer at 10 degrees incidence (2500 nm to 20 micrometres)"}
    method: Reflectance measured by the coating maker on witness samples after cryo cycling and humidity exposure
    status: ground
    note: The coating is gold under a thin silica overcoat. Cryogenic measurements from 300 K to 35 K showed no change in reflectance, apart from a very slight rise of about 0.01 between 0.60 and 1.0 micrometres.
    source: keskikuha2012
    where: Table 3 (Measured reflectance for PMSA A1); Section 2.1, Reflectance
  - benchmark: ir_reflectance_20_27um
    label: Measured reflectance of protected gold mirror from 20.1 to 27.0 micrometres
    value: 99.08
    value_high: 99.42
    bound: range
    unit: "%"
    scope: material
    conditions: {specimen: "Webb primary mirror segment A1, protected gold coating on beryllium, average of seven witness samples", wavelength: "20.1 to 27.0 micrometres", requirement: "at least 97.9%"}
    method: Reflectance reported in the paper's Table 3; the paper states reflectance measurements were made to 20 micrometres and that qualification showed the requirement met to 29 micrometres
    status: ground
    note: The paper says measurements on the flight witness samples were made to 20 micrometres, so values above 20 micrometres rest on qualification measurements as the paper describes them. The 27.1 to 29.0 micrometre goal range lists 99.16 to 99.35%.
    source: keskikuha2012
    where: Table 3 (Measured reflectance for PMSA A1); Section 3, Flight mirrors
  - benchmark: gold_layer_thickness_webb
    label: Gold layer thickness on the Webb mirrors
    value: 100
    unit: nm
    scope: material
    conditions: {process: "vacuum vapor deposition on beryllium mirror segments", overcoat: "thin amorphous SiO2 layer on top", description: "typical thickness, stated by NASA as 1000 Angstroms"}
    method: Typical value stated on the NASA Webb mirrors page
    status: flight
    note: The 2012 coating paper does not give a thickness figure in the text read; it says only that the gold layer was thinner than nominal on the tertiary mirror after interrupted deposition.
    source: nasa-webb-mirrors
    where: Webb's Mirrors page, Gold Coating section (Typical thickness of the gold is 1000 Angstroms (100 nanometers))
  - benchmark: ir_reflectance_plated_gold
    label: Near-infrared reflectance of electroplated gold (supplier process)
    value: 99.4
    unit: "%"
    scope: material
    conditions: {process: "Laser Gold, proprietary electrochemically deposited gold from Epner Technology", wavelength: "near infrared (range not given)", substrate: "beryllium mirror for the Mars Orbiter Laser Altimeter"}
    method: Reflectance quoted in a 1997 NASA Spinoff article about the supplier's process
    status: ground
    note: A supplier claim relayed by NASA Spinoff, not a measurement table, so it is weaker evidence than the Webb witness-sample data.
    source: nasa-spinoff1997
    where: Gold Coating article (In the near infrared wavelengths, Laser Gold's reflectance is an astounding 99.4 percent)
  - benchmark: proton_fluence_no_change
    label: Proton fluence with no measurable reflectance change in protected gold
    value: 2.98e15
    unit: protons/cm2
    scope: material
    conditions: {particles: "3 keV protons, then combined 3 keV protons and 10 keV electrons (electron fluence 8.05e14 electrons/cm2 on sample G4)", specimen: "protected gold coating (Quantum Coating Inc.) on aluminium substrates", vacuum: "about 1e-7 Torr", facility: "Goddard Solar Wind Facility, approximate L2 electron and proton environment", precision: "reflectance within about +/- 0.003"}
    method: In-situ reflectance measured before, during and after the exposure
    status: ground
    note: A dose tested, not a tolerance limit (the Figure 3 caption gives 2.98E15 p+/cm2 at 3 keV). The text of the paper writes the electron figure as up to 8 x 10^15 electrons/cm2, while the Figure 3 caption and the exposure-rate table are consistent with 8.05e14; the caption value is used here.
    source: keskikuha2012
    where: Section 2.1, Radiation Exposure; Figure 3 caption (sample G4); Table 2
corrosion:
  - environment: Oxygen, air and most acids
    headline: "Gold is not attacked by oxygen or acids at room conditions, so it does not tarnish."
    effect: "The HSDB entry quoted by PubChem calls gold extremely inactive and says it is not attacked by acids or oxygen, and only superficially attacked by aqueous halogens at room temperature. NASA Spinoff describes gold components in satellite microelectronics as corrosion-resistant, and a supplier quoted there lists corrosion resistance as a reason for choosing electroplated gold."
    rating: none
    conditions: {temperature: "room temperature (as stated for halogens)", entry: "HSDB GOLD, ELEMENTAL via PubChem"}
    source: pubchem-gold
    where: PubChem compound record Gold (CID 23985), Experimental Properties > Other Experimental Properties; NASA Spinoff 1997 Gold Coating article for the satellite statement
  - environment: Aqua regia, cyanide solutions and halogen-generating mixtures
    headline: "Gold dissolves in a 3:1 hydrochloric-nitric acid mixture and in cyanide solutions in air."
    effect: "HSDB says gold dissolves readily in 3:1 hydrochloric-nitric acid (aqua regia) to form HAuCl4, and in cyanide solutions in the presence of air or hydrogen peroxide. It also reacts with mixtures that generate nascent halogens, and with solutions of thiocyanates. Kasper and Veit used aqua regia at 60 degC for 2 hours to dissolve all the gold from circuit boards for analysis."
    rating: severe
    conditions: {aqua_regia_digestion: "60 degC, 2 hours, solid/liquid 1/25 (Kasper and Veit)", entry: "HSDB GOLD, ELEMENTAL via PubChem"}
    source: pubchem-gold
    where: PubChem compound record Gold (CID 23985), Experimental Properties > Solubility and Other Experimental Properties; Kasper and Veit, Materials and Methods
  - environment: Tin-lead solder
    headline: "Gold dissolving into solder can make the joint brittle if the gold content is high."
    effect: "A 1972 JPL memorandum says embrittlement is a possibility in any solder joint with a gold content greater than approximately 5% (citing earlier work) and that the white needle-like crystals of AuSn4 are reported to cause it. In JPL flight connector solder joints it found AuSn4 present but a maximum average gold content of 2.8% and no cracks after thermal shock, vibration and mechanical shock."
    rating: moderate
    conditions: {joint: "connector solder cups, unwicked and untinned joints examined", thermal_shock: "-100 to +130 degC", vibration: "up to 100 g peak", shock: "200 g peak", note: "1972 flight-connector practice, not current parts"}
    source: jpl-tm33-533
    where: Section I Introduction; Section IV Conclusion
risks:
  hazards:
    - text: "PubChem aggregates 506 company reports to the ECHA C&L Inventory for elemental gold: 502 of them (99.2%) report that it does not meet GHS hazard criteria, and 4 reports give hazard statement codes. The metal is listed as Not Classified."
      ghs: []
      source: pubchem-gold
      where: PubChem compound record Gold (CID 23985), Safety and Hazards > GHS Classification
    - text: "Haz-Map (quoted on PubChem) reports allergic contact dermatitis in electroplaters, photographers, guilders, machinists, dental technicians and jewelers, and notes a danger of skin sensitization from soluble gold compounds only. It also records that high doses of gold were embryotoxic in rats and rabbits and that rats inhaling gold nanoparticles showed mild lung inflammation. These points concern gold compounds, therapy and nanoparticles, not solid gold parts."
      ghs: []
      source: pubchem-gold
      where: PubChem compound record Gold (CID 23985), Safety and Hazards > Hazards Summary (Haz-Map)
  failure_risks:
    - mode: Embrittled solder joints
      trigger: "Gold-plated connector contacts soldered without removing gold, giving a high gold fraction in the joint"
      consequence: "AuSn4 crystals can embrittle the joint above roughly 5% gold. JPL's 1972 flight-connector joints averaged at most 2.8% gold and did not crack under its tests, so the risk depends on the joint."
      severity: moderate
      source: jpl-tm33-533
      where: Section I; Section IV
    - mode: Scratching of the soft metal surface
      trigger: "Handling, or particles moving over an unprotected gold mirror surface"
      consequence: "NASA says the Webb gold is pure and very soft, so a thin amorphous silica layer is deposited over it to protect it from scratches."
      severity: low
      source: nasa-webb-mirrors
      where: Webb's Mirrors page, Gold Coating section
  side_effects:
    - text: "On the Webb tertiary mirror, interruptions in gold deposition (tripped chamber circuit breakers) left the gold thinner than nominal, reflectance under 1% below requirement below 2.5 micrometres, and coating stress slightly over the 10 ksi limit. The mirror was accepted after witness-sample tests, and later flight mirrors were coated without failure."
      affects: "Coating process control for large mirrors"
      source: keskikuha2012
      where: Section 3, Flight mirrors
    - text: "The Webb gold coating cannot be stripped off; a failed coating would have meant grinding it off and re-polishing the mirror."
      affects: "Cost of a coating failure"
      source: keskikuha2012
      where: Section 2 and Section 3
  handling:
    - text: "For parts to be soldered, the NASA and JPL literature in this record treats gold in the joint as a concern. JPL wicked solder out of connector solder cups from 1965 to reduce gold in the joint and, in this 1972 study, tested whether that was still needed."
      source: jpl-tm33-533
      where: Section I Introduction
    - text: "NASA-STD-8739.11 tutorial (2025): minimum contact gold plating thickness of 50 microinches for Assurance Level 1 and 2 applications, recommended for Level 3. The same list prohibits cadmium and zinc finishes (vacuum sublimation and whiskers), silver underplate or finish (corrosion in atomic oxygen in low Earth orbit) and pure tin finish (whiskers)."
      source: nasa-nepp-rosol2025
      where: Slide 'Key Considerations' (page 6 of the tutorial)
  mitigations:
    - text: "Kasper and Veit tested thiosulfate as a less toxic alternative to cyanide for leaching gold from circuit boards: cyanide extracted 88% of the gold, sodium thiosulfate 70% and ammonium thiosulfate 75%, and electrowinning recovered 94% of the gold from thiosulfate solutions."
      source: kasper2018
      where: Abstract
uses:
  - application: optics-and-cameras
    device: "James Webb Space Telescope primary, secondary, tertiary and fine steering mirrors (beryllium with protected gold coating)"
    example: "All 21 flight mirrors (18 primary segments plus the secondary, tertiary and fine steering mirrors) were coated with protected gold, chosen for high reflectivity from 600 nm through the infrared, over JWST's 800 nm to 29 micrometre range. The coating is about 100 nm of gold applied by vacuum vapor deposition, under a thin silica overcoat."
    source: keskikuha2012
    where: Abstract; Section 1; Section 3; NASA Webb's Mirrors page for the thickness and process
  - application: optics-and-cameras
    device: "Cassini Composite Infrared Spectrometer (CIRS) primary mirror"
    example: "The Webb coating paper cites space flight heritage of the protected gold coating FSG98, including the Cassini CIRS primary mirror coated in 1996; a coated witness coupon re-measured 12 years later showed no reflectance degradation."
    source: keskikuha2012
    where: Section 2.1, Other Requirements (paragraph on the 10 year lifetime)
  - application: optics-and-cameras
    device: "Mars Orbiter Laser Altimeter (MOLA) telescope mirror on Mars Global Surveyor"
    example: "A half-metre beryllium mirror coated with electroplated gold (the Laser Gold process) for a laser instrument launched in 1996 to chart the Martian surface."
    source: nasa-spinoff1997
    where: Gold Coating article
  - application: thermal-control
    device: "Gold-coated mylar sheets on satellites; gold layer on an astronaut helmet visor"
    example: "NASA Spinoff says many satellites carry gold-coated mylar sheets to protect them from solar heat, and a thin gold layer on a helmet visor fends off solar radiation. No mission or measured values are given."
    source: nasa-spinoff1997
    where: Gold Coating article, opening paragraph
  - application: electronics-and-chips
    device: "Connector contacts on NASA flight hardware"
    example: "NASA-STD-8739.11 sets a minimum contact gold plating thickness of 50 microinches for Assurance Level 1 and 2 applications. JPL's 1972 study examined solder joints on gold-plated flight connector contacts."
    source: nasa-nepp-rosol2025
    where: Slide 'Key Considerations'; JPL TM 33-533 Section I
  - application: electronics-and-chips
    device: "Bonding wire, contacts and interconnects in electronics, and circuit boards in mobile phones"
    example: "The World Gold Council says AI computing is accelerating the use of bonding wire and contact and interconnect materials; electronics used 270.4 tonnes of gold in 2025. Kasper and Veit measured gold in mobile-phone circuit boards. Advent sells 99.99% gold wire in hard and annealed tempers."
    source: wgc-gdt2025
    where: Technology page, text and table (Tonnes 2024, 2025); Kasper and Veit Table 3; Advent product pages
supply:
  - subject: Gold (mine production and reserves)
    abundance: "USGS gives world reserves of 66,000 tons and, for the United States, identified and undiscovered resources of 33,000 tons."
    producers:
      - {country: China, share_percent: 11.5, year: 2025}
      - {country: Russia, share_percent: 9.4, year: 2025}
      - {country: Australia, share_percent: 8.5, year: 2025}
      - {country: Canada, share_percent: 6.1, year: 2025}
      - {country: United States, share_percent: 4.8, year: 2025}
    critical_lists: []
    recycling: "USGS: in 2025 an estimated 90 tons of new and old scrap was recycled in the United States, equivalent to about 60% of reported consumption. World Gold Council: recycled supply was 1,404 tonnes in 2025, up 3%."
    substitutes: ["USGS: base metals clad with gold alloys are widely used to economize on gold in electrical and electronic products and jewelry; generally, palladium, platinum and silver may substitute for gold."]
    source: usgs-mcs2026-gold
    where: "World Mine Production and Reserves table (2025e world total 3,300 tons; shares calculated by Space Mushroom from each country's 2025e figure: China 380, Russia 310, Australia 280, Canada 200, United States 160); World Resources; Recycling; Substitutes. World Gold Council figure from its Gold Demand Trends full-year 2025 page (Supply table, Recycled Gold)."
  - subject: Gold (world use, electronics share)
    abundance: "USGS estimates 2025 world gold consumption at 7% electrical and electronics, against 40% jewelry and 24% physical bars."
    producers: []
    critical_lists: []
    recycling: "World Gold Council: electronics demand was 270.4 tonnes in 2025 against 270.8 in 2024, and technology demand 322.8 tonnes; the Council says high prices push manufacturers to reduce or eliminate gold, and that PCB makers have accelerated thrifting."
    substitutes: ["World Gold Council: miniaturisation and thinner bonding wires reduce gold use, though it expects high-end and safety-critical devices to keep needing gold."]
    source: wgc-gdt2025
    where: Technology page, table and text (Technology 326.2 and 322.8; Electronics 270.8 and 270.4 tonnes); USGS MCS 2026 Gold, Events, Trends, and Issues (consumption shares)
documents:
  - {title: "WebElements: Gold, the essentials", type: database, url: "https://winter.group.shef.ac.uk/webelements/gold/", year: 2026}
  - {title: "WebElements: Gold, crystal structure", type: database, url: "https://winter.group.shef.ac.uk/webelements/gold/crystal_structure.html", year: 2026}
  - {title: "Advent Research Materials: Gold (Au) technical data sheet", type: datasheet, url: "https://www.advent-rm.com/getContentAsset/29ec1da7-f457-4f5e-85ee-6ca0cb5183b1/dfc3d011-8f63-43f6-9ed8-4b444333a1d0/Au_Gold_Technical_Datasheet.pdf?language=en-GB", year: 2026}
  - {title: "Advent Research Materials: AU5172, AU5173, AU5188 gold wire product pages", type: datasheet, url: "https://www.advent-rm.com/en-gb/products/pure-metals/gold/form/wire/line/au5172", year: 2026}
  - {title: "PubChem compound record: Gold (CID 23985)", type: database, url: "https://pubchem.ncbi.nlm.nih.gov/compound/Gold", year: 2026}
  - {title: "USGS Mineral Commodity Summaries 2026: Gold", type: report, url: "https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-gold.pdf", year: 2026}
  - {title: "World Gold Council: Gold Demand Trends, Q4 and Full Year 2025, Technology", type: report, url: "https://www.gold.org/goldhub/research/gold-demand-trends/gold-demand-trends-full-year-2025/technology", year: 2026}
  - {title: "Gold recovery from printed circuit boards of mobile phones scraps using a leaching solution alternative to cyanide (open access)", type: paper, url: "https://www.scielo.br/j/bjce/a/4J3QYYYrBR3SCRQhhj5sSrD/?lang=en", year: 2018}
  - {title: "James Webb Space Telescope Optical Telescope Element Mirror Coatings (NTRS 20120013496)", type: report, url: "https://ntrs.nasa.gov/api/citations/20120013496/downloads/20120013496.pdf", year: 2012}
  - {title: "NASA Science: Webb's Mirrors", type: report, url: "https://science.nasa.gov/mission/webb/webbs-mirrors/", year: 2025}
  - {title: "NASA Spinoff 1997: Gold Coating", type: report, url: "https://spinoff.nasa.gov/spinoff1997/hm2.html", year: 1997}
  - {title: "NASA-STD-8739.11 Tutorial Section C2, Connectors and Contacts (NEPP ETW 2025)", type: standard, url: "https://nepp.nasa.gov/etw/talks/11-AUG-MON/1410-Rosol-Connectors-v2-20250008276.pdf", year: 2025}
  - {title: "JPL Technical Memorandum 33-533: Investigation of Gold Embrittlement in Connector Solder Joints (NTRS 19720017872)", type: report, url: "https://ntrs.nasa.gov/api/citations/19720017872/downloads/19720017872.pdf", year: 1972}
gaps:
  - "Electrical resistivity, thermal conductivity, density and the mechanical constants of bulk gold come from a supplier data sheet that compiles Wolfram Research / periodictable.com data, plus PubChem/HSDB quotes. No primary handbook (NIST, CRC) value was opened, and temperatures and purity are not stated for most of them."
  - "No yield strength, ultimate strength or elongation for bulk or annealed pure gold sheet or bar from a handbook was found. Only supplier wire values (which depend on diameter and temper) are entered, and the test method and gauge length are not stated."
  - "The Vickers and Brinell hardness rows of the Advent data sheet (216 MPa and 2450 MPa) were not entered because they look inconsistent with each other; the HSDB Brinell figure of 18.5 has no unit. Only the Mohs range is entered."
  - "No atomic-oxygen erosion, ultraviolet, outgassing (ASTM E595) or vacuum cold-welding data for gold was found, so the space-environment record is limited to the Webb radiation test and the heritage statements."
  - "No emittance or solar absorptance values for gold thermal blankets or gold-coated mylar were found; the NASA Spinoff article gives the use but no numbers."
  - "No thin-film resistivity, adhesion-layer (for example titanium or chromium) or grain-size data for sputtered or evaporated gold films was found. The Webb paper does not state the adhesion layers."
  - "No bond-wire datasheet from a bonding-wire maker (Tanaka, Heraeus, Kulicke and Soffa) could be read in a usable form; a Tanaka table found online was garbled. Gold-aluminium intermetallic failure in wire bonds was not sourced."
  - "No source was found for gold-plated connector hardness, plating thickness classes or underplate specifications beyond the NASA-STD-8739.11 tutorial's 50 microinch minimum; Knoop hardness values from vendor pages were not used."
  - "A study of 45 mobile phones made 1998 to 2021 (RWTH Aachen repository) was found, but the repository blocked automated access, so it was not read. No per-phone gold mass is entered; only the g/t of board values of Kasper and Veit for 2001 to 2005 boards."
  - "Whether gold is on the USGS or European critical mineral lists was not checked, so critical_lists is left empty."
  - "The World Gold Council page was read only where it is public (tables and summary text); its full report is behind registration. World Gold Council mine production for 2025 (3,672 tonnes in its text) differs from the USGS estimate (3,300 tons) and was not entered as supply data."
  - "Gold-plated electronics on specific missions (connectors, wire bonds) could not be named from a source; the only missions named are Webb, Cassini (CIRS) and Mars Global Surveyor (MOLA), all for mirrors. Prices are omitted on purpose."
sources:
  webelements-gold-main:
    title: "Gold - 79Au: the essentials (WebElements, relative atomic mass)"
    url: https://winter.group.shef.ac.uk/webelements/gold/
    year: 2026
    kind: database
    license: "WebElements, free online reference"
  webelements-gold-crystal:
    title: "Gold - 79Au: crystal structure (WebElements)"
    url: https://winter.group.shef.ac.uk/webelements/gold/crystal_structure.html
    year: 2026
    kind: database
    license: "WebElements, free online reference"
  advent-datasheet:
    title: "Gold (Au) Technical Data Sheet, Advent Research Materials"
    id: "Source line on sheet: Wolfram Research / periodictable.com"
    url: https://www.advent-rm.com/getContentAsset/29ec1da7-f457-4f5e-85ee-6ca0cb5183b1/dfc3d011-8f63-43f6-9ed8-4b444333a1d0/Au_Gold_Technical_Datasheet.pdf?language=en-GB
    year: 2026
    kind: datasheet
    license: supplier document, linked not reproduced
  advent-wires:
    title: "Gold wire product pages AU5172 (0.05 mm hard), AU5173 (0.125 mm hard), AU5188 (0.75 mm annealed), Advent Research Materials"
    id: "Batches Gi4428, Gi4360, Gi4837"
    url: https://www.advent-rm.com/en-gb/products/pure-metals/gold/form/wire/line/au5172
    year: 2026
    kind: datasheet
    license: supplier web pages, linked not reproduced
  pubchem-gold:
    title: "PubChem compound record: Gold (CID 23985)"
    id: "CID 23985; CAS 7440-57-5; quotes HSDB, PAC Chemical Database (US DOE), Haz-Map and ECHA C&L"
    url: https://pubchem.ncbi.nlm.nih.gov/compound/Gold
    year: 2026
    kind: database
    license: public domain (NCBI)
  usgs-mcs2026-gold:
    title: Mineral Commodity Summaries 2026, Gold
    id: "USGS MCS 2026, February 2026"
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-gold.pdf
    year: 2026
    kind: report
    license: public domain (USGS)
  wgc-gdt2025:
    title: "Gold Demand Trends: Q4 and Full Year 2025, Technology and Supply (World Gold Council)"
    id: "GDT FY 2025"
    url: https://www.gold.org/goldhub/research/gold-demand-trends/gold-demand-trends-full-year-2025/technology
    year: 2026
    kind: report
    license: World Gold Council web content, cited not reproduced
  kasper2018:
    title: Gold recovery from printed circuit boards of mobile phones scraps using a leaching solution alternative to cyanide
    id: "doi:10.1590/0104-6632.20180353s20170291 (Braz. J. Chem. Eng. 35(3), Jul-Sep 2018)"
    url: https://www.scielo.br/j/bjce/a/4J3QYYYrBR3SCRQhhj5sSrD/?lang=en
    year: 2018
    kind: paper
    license: open access article on SciELO (check journal licence before reuse)
  keskikuha2012:
    title: James Webb Space Telescope Optical Telescope Element Mirror Coatings
    id: "NTRS 20120013496; Keski-Kuha et al., NASA Goddard"
    url: https://ntrs.nasa.gov/api/citations/20120013496/downloads/20120013496.pdf
    year: 2012
    kind: report
    license: public domain (NASA)
  nasa-webb-mirrors:
    title: "Webb's Mirrors, NASA Science"
    id: "science.nasa.gov/mission/webb/webbs-mirrors"
    url: https://science.nasa.gov/mission/webb/webbs-mirrors/
    year: 2025
    kind: web
    license: NASA web content
  nasa-spinoff1997:
    title: "Gold Coating, NASA Spinoff 1997"
    id: "spinoff.nasa.gov/spinoff1997/hm2.html"
    url: https://spinoff.nasa.gov/spinoff1997/hm2.html
    year: 1997
    kind: web
    license: NASA web content
  nasa-nepp-rosol2025:
    title: "NASA-STD-8739.11 Tutorial Section C2, Connectors and Contacts (J. Rosol, 2025 NEPP Electronics Technology Workshop)"
    id: "NTRS 20250008276; NEPP ETW 11 Aug 2025"
    url: https://nepp.nasa.gov/etw/talks/11-AUG-MON/1410-Rosol-Connectors-v2-20250008276.pdf
    year: 2025
    kind: standard
    license: public domain (NASA)
  jpl-tm33-533:
    title: Investigation of Gold Embrittlement in Connector Solder Joints
    id: "JPL Technical Memorandum 33-533, NTRS 19720017872, F. L. Lane, 1 April 1972"
    url: https://ntrs.nasa.gov/api/citations/19720017872/downloads/19720017872.pdf
    year: 1972
    kind: report
    license: public domain (NASA)
license: CC-BY-4.0

updated: "2026-10-17"
review:
  status: draft
  method: assistant
  checked_values: 24
  unreachable: 0
  caveats: 12
  note: "Written by an AI assistant on 2026-10-17. USGS, NASA (Webb coating paper, JPL memorandum, NEPP tutorial, Spinoff, Webb page), Kasper and Veit Table 3, the Advent data sheet and wire pages, PubChem and World Gold Council values were read from the source text, PDF or page text. Caveats: conductivities and mechanical constants are a supplier compilation without stated temperature or purity; wire strengths depend on diameter and temper; the Webb reflectance above 20 micrometres rests on qualification measurements as the paper describes; the 99.4% electroplated reflectance is a supplier claim; the electron fluence in the Webb radiation test is inconsistent between text and figure caption; the RWTH 45-phone study could not be read."
story:
  risk_groups:
    - title: For people
      level: 1
      verdict: "Not classified as a hazardous metal"
      lead: "Solid gold is reported as not hazard-classified by almost all companies in the ECHA inventory; the health concerns on record involve gold compounds and nanoparticles."
      points:
        - label: The metal
          line: "PubChem reports that 502 of 506 company reports to the ECHA inventory say elemental gold does not meet GHS hazard criteria. Four reports give hazard statement codes."
        - label: Skin
          line: "Haz-Map reports allergic contact dermatitis in electroplaters, jewelers, dental technicians and others, and a danger of skin sensitization from soluble compounds only."
        - label: Not solid-gold evidence
          line: "Embryotoxic effects in rats and rabbits and mild lung inflammation in rats came from high doses or gold nanoparticles, not from solid gold parts."
    - title: If it fails
      lead: "These results come from a 1972 solder-joint study, NASA coating work and supplier data, not from spacecraft failures."
      points:
        - label: Soft surface
          line: "NASA says the pure gold on the Webb mirrors is very soft, so a thin silica layer covers it to protect against scratches. The coating cannot be stripped off, only ground away."
        - label: Solder joints
          line: "Embrittlement is possible above roughly 5% gold in a solder joint. JPL measured a maximum average of 2.8% in its flight connector joints and found no cracks after thermal, vibration and shock tests."
    - title: Handling and recycling
      points:
        - label: Connector finishes
          line: "NASA's connector tutorial asks for at least 50 microinches of contact gold for Assurance Level 1 and 2 hardware and prohibits silver finishes because of atomic oxygen, and cadmium, zinc and pure tin finishes."
        - label: Leaching gold
          line: "Gold dissolves in aqua regia and in cyanide solutions. A 2018 study found thiosulfate extracted 70% to 75% of circuit-board gold, against 88% for a cyanide stripper."
  why: >-
    Gold (Au) is a dense, soft, yellow metal with a face-centered cubic crystal structure. Its density is 19.3 g/cm3
    and it melts at 1064.18 degC. It conducts electricity (resistivity 2.2e-8 ohm m) and heat (320 W/(m K)), and, unlike most metals,
    it is not attacked by oxygen or by acids, so a gold surface stays clean and electrically reliable. Those traits explain its
    jobs: plating on connector contacts, wire for connecting chips, and thin mirror coatings that reflect infrared light. Its softness is the price:
    hard-drawn 99.99% wire measured 342.7 MPa and annealed wire 135 MPa, and pure gold mirrors need a protective overcoat.
  uses:
    - where: Webb telescope mirrors
      line: >-
        All 21 flight mirrors (18 primary segments plus the secondary, tertiary and fine steering mirrors) carry a protected gold coating over beryllium.
        NASA gives a typical gold thickness of 100 nm, deposited in vacuum under a thin silica layer.
    - where: Cassini and Mars Global Surveyor instruments
      line: >-
        The Webb coating paper cites the Cassini CIRS primary mirror, coated in 1996, as flight heritage for protected gold. NASA Spinoff
        describes a half-metre beryllium mirror with electroplated gold on the Mars Orbiter Laser Altimeter of Mars Global Surveyor.
    - where: Satellite thermal sheets
      line: >-
        NASA Spinoff says many satellites carry gold-coated mylar sheets to protect them from solar heat. The article gives no mission
        or measured values.
    - where: Connectors and wiring
      line: >-
        NASA's connector standard tutorial sets a minimum contact gold plating of 50 microinches for Assurance Level 1 and 2. The World Gold Council
        says AI computing is raising use of gold bonding wire and contacts; electronics took 270.4 tonnes of gold in 2025.
    - where: Mobile-phone circuit boards
      line: >-
        A Brazilian study measured gold in eight types of mobile-phone circuit board made 2001 to 2005 at 142.6 to 702.3 grams per tonne of board.
  can_do:
    - label: Weight and heat
      value: 19.3 g/cm3
      line: >-
        Density is 19.3 g/cm3, so gold is very heavy for its volume. The melting point is 1064.18 degC from the supplier data sheet
        (1064.76 degC in the PubChem quote) and the specific heat is 129.1 J/(kg K).
    - label: Electrical conduction
      value: 4.5e7 S/m
      line: >-
        The data sheet gives a conductivity of 4.5e7 S/m and a resistivity of 2.2e-8 ohm m. PubChem quotes 2.06 microohm cm at 0 degC.
    - label: Heat conduction and expansion
      value: 320 W/(m K)
      line: >-
        Thermal conductivity is 320 W/(m K) and thermal expansion is 14.2 ppm/K, meaning a length grows by 14.2 millionths for each kelvin of warming.
    - label: Stiffness and hardness
      value: 78 GPa
      line: >-
        Young's modulus is 78 GPa, shear modulus 27 GPa and Poisson's ratio 0.44. Mohs hardness is 2.5 to 3.0, which is soft.
    - label: Wire strength
      value: 135 to 342.7 MPa
      line: >-
        A 0.05 mm hard 99.99% wire had a tensile strength of 342.7 MPa and 0.7% elongation. A 0.75 mm annealed wire had 135 MPa and 24%
        elongation. Strength and stretch depend strongly on diameter and temper.
    - label: Infrared reflectance
      value: 98.5% to 98.8% at 2.0 to 20.0 micrometres
      line: >-
        Protected gold on the Webb primary segment A1 measured 97.3% at 1.0 micrometre, 98.5% to 98.8% from 2.0 to 20.0 micrometres and
        99.08% to 99.42% from 20.1 to 27.0 micrometres. Cooling from 300 K to 35 K caused no change in reflectance.
    - label: Radiation
      value: No change at 2.98e15 protons/cm2
      line: >-
        Protected gold samples showed no change in reflectance within about 0.003 after 3 keV protons (2.98e15 protons/cm2) plus 10 keV
        electrons in a simulated Webb orbit environment. This is a dose tested, not a tolerance limit.
  compare: >-
    This record holds no gold-versus-other-metal numbers, so it does not rank gold against copper or aluminium. The USGS says
    palladium, platinum and silver may generally substitute for gold, and that base metals clad with gold alloys are used to economize on it. Inside this record, annealed wire (135 MPa,
    24% elongation) is much softer than hard-drawn wire (342.7 MPa, 0.7%). Mobile-phone boards held 142.6 to 702.3 g/t of gold, against 5 to
    10 g/t in ores, according to the authors of the study.
  compare_rows:
    - {label: Density, benchmark: density}
    - {label: Thermal conductivity, benchmark: thermal_conductivity}
    - {label: Thermal expansion, benchmark: cte}
  handling:
    - Solid gold is not hazard-classified by 502 of 506 company reports to ECHA; the skin-allergy concern is for soluble gold compounds.
    - Limit gold in solder joints; embrittlement is possible above roughly 5% gold, though JPL's flight joints averaged at most 2.8%.
    - Protect soft gold mirror surfaces with a thin silica overcoat; the Webb coating cannot be stripped off.
    - Gold dissolves in aqua regia and cyanide solutions; thiosulfate is a less toxic leaching option but extracted less (70% to 75% against 88%).
  good_for:
    - "Staying clean. Gold is not attacked by oxygen or acids, and satellite microelectronics use it for corrosion-resistant contacts."
    - "Infrared mirrors. A 100 nm gold layer on Webb reflects 98.5% to 98.8% of light from 2.0 to 20.0 micrometres."
    - "Conducting electricity. The data sheet gives 4.5e7 S/m, and gold wire in hard and annealed tempers is sold at 99.99% purity."
    - "Recycling. The USGS says about 90 tons of scrap was recycled in the United States in 2025, about 60% of reported consumption."
  watch_out:
    - "Softness. Mohs hardness is 2.5 to 3.0, annealed wire is 135 MPa, and NASA covers the Webb gold with silica against scratches."
    - "Solder embrittlement. Joints with more than roughly 5% gold can become brittle."
    - "Missing space-environment data. No atomic-oxygen, outgassing or thermal-blanket numbers were found for gold in this record."
    - "Supplier data. Conductivity and mechanical constants come from a supplier compilation without stated purity or temperature."
  verdict: "Gold is a soft, dense, corrosion-free metal with a long record as an infrared mirror coating (Webb, Cassini CIRS, Mars Global Surveyor) and as contact plating on flight connectors. This record has strong data on infrared reflectance and Webb radiation exposure but only supplier-level numbers for its electrical, thermal and mechanical constants."
  recipe:
    line: >-
      Gold is the element Au, atomic number 79, a single-element metal. Its crystal structure is cubic close-packed (ccp, space group Fm-3m, WebElements). USGS says gold is mined from lode and placer ore, and that about 7% of US gold was recovered as a by-product of processing base-metal ores, chiefly copper ores. Commercial-grade gold was produced at about 16 US refineries in 2025, and US scrap recovery was 90 tons (USGS). Most of the metal in use is refined bullion, so the grade is set at the refinery.
    parts:
      - name: Gold
        symbol: Au
        atoms: 1
        atomic_weight: 196.96657
        role: "The whole material. WebElements prints the relative atomic mass on its main page."