Precious metals and alloys

precious-metals

17 materials across 2 types

About precious metals and alloys

Precious metals (gold, silver, platinum, palladium, rhodium, iridium, ruthenium, osmium) and their alloys: density, melting point, resistivity and corrosion data with sources.

Precious metals resist corrosion and oxidation and conduct well. They are used for contacts, thermocouples, catalysts, electrodes, brazing and jewellery.

Alloys such as platinum-rhodium, platinum-iridium, palladium-silver, gold-tin and sterling silver trade a little conductivity for strength or a useful melting range.

At a glance

Highest density: Osmium reaches 22.6 g/cm³. Lowest: Silver alloys (Ag alloys) starts at 10 g/cm³. (16 of 17 grades have a sourced value.)
Highest melting point: Osmium reaches 3,045 °C. Lowest: AuSn starts at 280 °C. (16 of 17 grades have a sourced value.)
Highest electrical resistivity: Platinum-tungsten and platinum-copper alloys reaches 6.8e-7 Ω·m. Lowest: Silver (Ag) starts at 1.6e-8 Ω·m. (11 of 17 grades have a sourced value.)

Ranges run across the conditions each source reports (temper, heat treatment, form), measured at room temperature where the source says so.

How they compare

The same measurements for every material in the collection. A range means the grade has values under several conditions; "at least" means the source gives a specified minimum. "no data" means no sourced value yet. For ranked tables, open a benchmark.

Precious metals and alloys: how the grades compare
Material	Density	Melting point	Electrical resistivity	Thermal conductivity	Young's modulus	Thermal expansion
Gold (Au)conductor, contact plating and infrared mirror coating	19.3 g/cm³	1,065 °C	2.2e-8 Ω·m	320 W/(m·K)	no data	14.2 ppm/K
Silver (Ag)conductor / reflector / thermal-control layer	10.5 g/cm³	962 °C	1.6e-8 Ω·m	429 W/(m·K)	no data	19.1 ppm/K
Platinum (Pt)contact, catalyst and high-temperature sensing metal	21.4 to 21.5 g/cm³	1,768 to 1,769 °C	1.1e-7 Ω·m	71.6 to 74 W/(m·K)	168 to 170 GPa	8.93 ppm/K
Palladium (Pd)catalyst, electrical-contact and hydrogen-handling metal	12 g/cm³	1,555 °C	1.1e-7 Ω·m	72 W/(m·K)	121 GPa	11.8 ppm/K
Rhodiumreflective and high-temperature precious metal	12.4 g/cm³	1,964 °C	4.5e-8 Ω·m	150 W/(m·K)	380 GPa	8.46 ppm/K
Iridiumhigh-temperature oxidation-resistant metal	22.6 g/cm³	2,446 °C	47.1 nΩ·m	59 to 147 W/(m·K)	528 GPa	6.47 ppm/K
Rutheniumhard platinum-group metal for chip interconnects and contacts	12.2 to 12.4 g/cm³	2,310 to 2,334 °C	7.7e-8 Ω·m	117 to 120 W/(m·K)	447 GPa	6.78 ppm/K
Osmiumdense platinum-group metal for hard alloys, wear-resistant contacts and a space-flown optical coating	22.5 to 22.6 g/cm³	3,033 to 3,045 °C	8.8e-8 Ω·m	87.6 to 88 W/(m·K)	559 GPa	4.57 to 5.1 ppm/K
Gold alloys (Au alloys)electrical contact and microconnector metal, brazing filler, and jewellery alloy	15.8 to 16 g/cm³	360 to 1,410 °C	1.5e-7 Ω·m	49 W/(m·K)	no data	14 ppm/K
AuSneutectic high-temperature solder for hermetic seals and die attach	14.7 -	280 to 320 °C	no data	57 W/(m·K)	68 to 88 GPa	16 ppm/K
Sterling silverconductor / jewellery and joining alloy	10.4 g/cm³	788 to 891 °C	1.8e-8 Ω·m	no data	no data	19 ppm/K
Silver alloys (Ag alloys)brazing filler / conductor / electrical contact	10 to 10.9 g/cm³	780 to 975 °C	20.4 x10-9 ohm m	371 W/(m·K)	80 to 85 GPa	19.6 ppm/K
Pd-Aghydrogen membrane, electrical contact and thick-film conductor alloy	10.9 g/cm³	no data	1.5e-7 Ω·m	61 W/(m·K)	114 GPa	no data
Palladium alloyshydrogen separation membrane (Pd-Cu), electroplated contact coating (Pd-Ni) and high-temperature strain gage alloy (Pd-Cr)	10.8 g/cm³	1,397 °C	no data	no data	no data	no data
Pt-Rhthermocouple elements and glass-fibre bushing alloy for high temperatures	17.6 to 20 g/cm³	1,840 to 1,925 °C	no data	no data	208 to 276 GPa	no data
Platinum-iridium alloy (Pt-Ir)standards, electrodes and thermocouple wire	21.5 to 21.7 g/cm³	1,790 to 1,855 °C	no data	no data	202 to 255 GPa	no data
Platinum-tungsten and platinum-copper alloysresistance wire, probes and spark-plug electrodes (Pt-W); catalysts (Pt-Cu)	21.3 g/cm³	1,865 to 1,910 °C	6.2e-7 to 6.8e-7 Ω·m	no data	230 GPa	no data

What these materials are made of

Composition by weight, as printed in the sources for each grade (the first constituents listed).

Composition of each grade
Material	Main constituents
Gold (Au)	Au 100.0%
Silver (Ag)	Ag 100.0%
Platinum (Pt)	Pt 100.0%
Palladium (Pd)	Pd 100.0%
Rhodium	Rh 100.0%
Iridium	Ir 100.0%
Ruthenium	Ru 100.0%
Osmium	Os 100.0%
AuSn	Au 80% · Sn 20%
Platinum-iridium alloy (Pt-Ir)	Pt 90% · Ir 10%
Platinum-tungsten and platinum-copper alloys	Pt 92% · W 8%

Where they are used

Uses
Use	Grades
James Webb Space Telescope primary, secondary, tertiary and fine steering mirrors (beryllium with protected gold coating)	Gold (Au)
Cassini Composite Infrared Spectrometer (CIRS) primary mirror	Gold (Au)
Mars Orbiter Laser Altimeter (MOLA) telescope mirror on Mars Global Surveyor	Gold (Au)
Silvered FEP Teflon (second-surface mirror) thermal blankets	Silver (Ag)
Final contact metal on GaAs solar cells and evaporated contacts on thin silicon cells, with silver-plated Invar interconnect tabs	Silver (Ag)
Screen-printed silver ink front contacts for photovoltaic cells (research)	Silver (Ag)
Platinum resistance thermometers (RTDs) on the Space Shuttle Orbiter	Platinum (Pt)
Platinum-rhodium thermocouples (Type R) on the Orbiter skin and heat tiles	Platinum (Pt)
Butt-welded platinum-platinum 10 % rhodium thermocouples in a liquid-rocket injector test	Platinum (Pt)
Multilayer ceramic capacitors and hybridised integrated circuits	Palladium (Pd)
Printed circuit boards of mobile phones	Palladium (Pd)
Electrical contact material (supplier data for palladium)	Palladium (Pd)
Platinum-rhodium thermocouples for high-temperature measurement	Rhodium
High-reflectivity mirrors for cinema projectors and searchlights	Rhodium
Magnetron-sputtered rhodium first mirrors for ITER optical diagnostics	Rhodium
Iridium-coated rhenium thrust chamber, 22 N stationkeeping engine class	Iridium

When each grade fits

Best use and weak spots of each grade
Material	Best for	Weakest at
Gold (Au)	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)	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
Silver (Ag)	Electrical and heat conduction and light reflection (resistivity 1.63 microohm cm, thermal conductivity 429 W/(m K) at 0 to 100 degC)	Unprotected exposure to atomic oxygen in low Earth orbit (black oxide that cracks and spalls) and to sulphur compounds in air (silver sulphide tarnish)
Platinum (Pt)	Stable high-temperature sensing and electrical contacts: a platinum resistance element is linear and stable over a wide temperature range (Columbia Accident Investigation Board)	Softness in the annealed state (70 MPa yield), flammability of fine powder (PubChem hazard H228), and cost against cheaper metals
Palladium (Pd)	Catalysis and selective hydrogen passage (a 75% palladium-25% silver alloy dropped dissolved hydrogen from 60 psia to under 0.5 psia in a NASA-sponsored separator)	Hydrogen embrittlement: pure palladium membranes warp and fracture when the alpha-to-beta hydride transition expands the lattice by more than 10%, and supply is concentrated in two countries
Rhodium	Corrosion-resistant reflective and high-temperature sensing surfaces: not attacked by most acids, and does not normally form an oxide even when heated (Wikipedia)	Cost and supply concentration: USGS price 5,800 dollars per troy ounce in 2025e, and principal production in South Africa at 75 % (Wikipedia)
Iridium	Surviving hot oxidising gas and corrosive liquids: oxidation resistance to 800 °C in the datasheet and attack by no acid, including aqua regia, in the Wikipedia summary	Cold forming and machining (not ductile, hardly formable, limited machinability), and cost (USGS 2025 estimated price 4,400 dollars per troy ounce)
Ruthenium	Hard, dense electrical contacts and thin conducting layers where a very high melting point and acid resistance matter (Wikipedia, USGS)	Oxidation at high temperature: the source shows volatile RuO4 escaping from a thin film annealed at 600 °C in dry oxygen, and the metal is attacked by hypochlorite and halogens (Wikipedia)
Osmium	Hard, dense alloys and wear-resistant electrical contacts where hardness and durability matter (Goodfellow, Tanaka)	Oxidation when heated in air or as a fine powder, which forms osmium tetroxide, a volatile and highly toxic compound (PubChem, Dartmouth); coatings were lost to atomic oxygen in orbit (NASA NTRS)
Gold alloys (Au alloys)	Contacts, microconnectors and brazes that must resist oxidation and sulphur attack in a small volume (supplier statements for Au-Ni and Au-Pd)	Strength and hardness are set by the alloy and temper, and most alloys here have only supplier figures; Au-Ag and Au-Sb have almost no property data in this file
AuSn	Hermetic lid seals and die attach where a sharp, high melting point and fluxless soldering matter more than ductility (the supplier calls the alloy resistant to corrosion and oxidation)	Brittleness: the alloy is very hard and brittle, thin forms and fine wire are hard to produce, and AuSn4 growth on gold or nickel finishes can embrittle joints
Sterling silver	Silver-rich alloy that is harder than fine silver and still conducts electricity (supplier resistivity 1.8 µOhmcm, as-rolled disk)	Tarnishing in sulphur-bearing air and corrosion; no sterling-specific atomic-oxygen or tarnish rate was found in a source we could open
Silver alloys (Ag alloys)	Silver brazing of copper, nickel and steel at about 780 degC (BAg-8 eutectic, 72 Ag and 28 Cu)	Tarnish in sulphur-bearing air and atomic-oxygen exposure in orbit; no sourced rate for any of these alloys was read in this run
Pd-Ag	Hydrogen passage through thin walls, where silver keeps the metal from cracking (23 at% silver is the best composition per Witjens et al. 2004)	Hydrogen cracking when silver is too low, and silver migration in humid, biased thick-film lines (the Heraeus datasheet says palladium reduces the risk)
Palladium alloys	Hydrogen passage in sulfur-bearing gas, where a Pd-Cu membrane resists H2S better than pure palladium (DOE slides, with the composition caveat in the story)	Pd-Cr fine wire above 600 degC in air, where unprotected gages oxidise and lose electrical performance (NASA)
Pt-Rh	High-temperature thermocouples in air or other oxidizing and neutral atmospheres: NIST gives a standard range of -50 to 1768 °C for Types R and S and 0 to 1820 °C for Type B	Reducing atmospheres and silicon contamination at high temperature (NBS Monograph 40), grain growth and drift above about 1200 °C (Edler et al. 2021), and cost: USGS gives rhodium at 5,800 dollars per troy ounce in 2025e
Platinum-iridium alloy (Pt-Ir)	Reference artefacts and electrodes that need a dense, hard, stable metal. The kilogram and metre prototypes were made of it, and the alloy is harder than pure platinum.	Heavy for its size (21.54 g/cm3 for PtIr10) and soft when annealed (105 HV for PtIr10)
Platinum-tungsten and platinum-copper alloys	Fine resistance wire, probes and electrodes that must resist oxidation in air at high temperature (Pt-W), and dealloyed PtCu catalysts in acid electrolyte (Pt-Cu, laboratory).	Density (21.26 g/cm3) and conductivity (2.58 to 2.77 % IACS, a poor conductor). The PtCu catalyst loses much of its copper in acid.