Silver

Silver — Material Page

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Silver (Ag, atomic number 47) is a Group 11 FCC transition metal with the highest electrical conductivity (15.87 nΩ·m resistivity), highest thermal conductivity (429 W/m·K), and highest optical reflectivity (>98% at 600 nm) of any element — three superlatives that together drive its dominant use in electronics, solar cells, and optical coatings. Ag has a melting point of 961.78 °C (an ITS-90 fixed point), density of 10.49 g/cm³, and is highly ductile and malleable. Its chemical symbol Ag derives from the Latin argentum, and it is one of the first metals exploited by human civilization (~5,000 BCE). Ag is produced primarily from argentite (Ag₂S), native silver, and as a byproduct of Cu, Pb-Zn, and Au mining; global annual production is ~25,000–27,000 tonnes, making it roughly 8× more abundant in production than Au. Ag's dominant oxidation state is +1 (Ag⁺, linear coordination); the Ag⁺/Ag standard reduction potential is +0.80 V, making Ag less noble than Au (+1.69 V) but more noble than Cu (+0.34 V).

Industrial electricity and electronics account for ~55% of Ag demand — photovoltaic (PV) solar cell front contacts are now the largest single Ag application (~150 µm Ag paste screen-printed on each cell), consuming ~140–160 Moz/year and growing rapidly with solar deployment; electrical contacts and connectors consume a further ~60–70 Moz/year. Ag-based electrical contacts (Ag-CdO, Ag-SnO₂, Ag-WC) are the universal choice for medium-voltage switching applications due to Ag's uniquely low contact resistance and resistance to arc welding under the short-duration arcs generated at make/break; the Ag-SnO₂ system has largely replaced the more toxic Ag-CdO in environmental-regulation-driven applications. Conductive Ag paste (isotropic and anisotropic) is the standard interconnect and die-attach material in surface-mount electronics packaging, LED modules, and RFID antennas, with Ag flake concentrations of 70–80 wt% providing near-bulk conductivity in cured films.

Silver nanoparticles (AgNPs, 1–100 nm) are the most widely studied antimicrobial nanomaterial — Ag⁺ ions released from AgNPs disrupt bacterial cell membrane integrity, inhibit respiratory enzymes, and damage DNA, providing broad-spectrum activity against both gram-positive and gram-negative bacteria including antibiotic-resistant strains (MRSA, VRE). AgNP-coated catheters, wound dressings (Acticoat, Mepilex Ag), and bone cements are approved medical devices exploiting this activity, though concerns over Ag ecotoxicity and potential contribution to antibiotic resistance gene spread continue to be studied. In optics, Ag thin films (~100 nm) are the standard back-reflector coating for solar cells (replacing Al in high-efficiency PERC/TOPCon designs), the reflective layer in low-emissivity (low-e) architectural glass (Ag sandwiched between ZnO or TiO₂ adhesion layers), and the plasmonic active material in SERS substrates where Ag nanospheres and nanotriangles provide the highest electromagnetic field enhancement of any metal at visible wavelengths.

General Properties

Property	Value	Notes
Atomic Number	47	Group 11, Period 5; 4d¹⁰5s¹; dominant oxidation state +1 (Ag⁺, linear coordination: AgCl, AgNO₃, ⁺). Ag⁺ is the basis of classical gravimetric and potentiometric analysis (AgCl precipitation, Ag/AgCl reference electrode, E° = +0.222 V vs. SHE). Ag(II) and Ag(III) occur in AgF₂ and certain fluoride complexes but are strongly oxidizing and rarely encountered in practical applications.
Atomic Mass	107.868 u	Two naturally occurring stable isotopes: ¹⁰⁷Ag (51.84%) and ¹⁰⁹Ag (48.16%), both I = 1/2 and NMR-active. The near-equal abundances make Ag isotope ratio measurement (¹⁰⁷Ag/¹⁰⁹Ag by MC-ICP-MS) straightforward; Ag isotope fractionation is used in geochemistry to trace ore deposit formation and early solar system processes (¹⁰⁷Pd → ¹⁰⁷Ag decay, t½ = 6.5 Myr, a short-lived radionuclide chronometer in meteorites).
Density (20 °C)	10.49 g/cm³	Moderate-high density; substantially lower than Au (19.32 g/cm³) and Pt (21.45 g/cm³). Ag's high conductivity at a density ~half that of Au makes it cost-effective for high-conductivity applications (wire, contacts, pastes) where volume rather than mass is the primary constraint.
Melting Point	961.78 °C (1,234.93 K)	An ITS-90 fixed point — the silver freezing point at 961.78 °C is one of the 17 defining fixed points of the International Temperature Scale of 1990. Used to calibrate high-accuracy thermocouples, radiation thermometers, and PRTs in national metrology laboratories and industrial calibration facilities.
Boiling Point	2,162 °C	High enough to allow Ag sputtering target use in PVD without significant target outgassing, and to support Ag wire as a resistive heating element for evaporative deposition of Ag thin films. The Ag boiling point is well above practical solar cell and glass coating deposition temperatures, preventing Ag evaporation losses during processing.
Thermal Conductivity	429 W/m·K	Highest thermal conductivity of any element — exceeds Cu (401 W/m·K) and Au (318 W/m·K). Ag's thermal conductivity is relevant to its use as a die-attach paste in power electronics (high thermal conductivity Ag sinter paste replaces solder for >200 W/cm² heat dissipation), as a thermal interface material in high-performance cooling systems, and as a back-contact paste in concentrator PV cells.
Electrical Resistivity	15.87 nΩ·m (20 °C)	Lowest electrical resistivity of any element — lower than Cu (16.78 nΩ·m) at 20 °C, though their values are very close and temperature-dependent crossover occurs near 0 °C. Ag's conductivity advantage over Cu (~6%) is insufficient to justify the cost premium for bulk wire, but Ag paste and plating are cost-effective where thin-film or contact resistance dominates (PV cells, RF connectors, PCB finishes).
Crystal Structure	FCC, a = 4.086 Å (room temperature)	FCC structure gives Ag the highest ductility and malleability among the Group 11 metals — Ag can be drawn into wire as fine as ~1 µm and rolled into foil thinner than 1 µm. The Ag(111) surface is the primary SERS substrate — periodic Ag nanostructure arrays on Ag(111) produce electromagnetic field enhancements of 10⁸–10¹⁰, enabling single-molecule Raman spectroscopy.

Mechanical Properties

Property	Value	Notes
Tensile Strength	140–170 MPa	Low strength in pure annealed form — comparable to Au; Ag is work-hardened for applications requiring higher strength (drawn wire, rolled foil). Sterling silver (Ag-7.5%Cu) and Ag-Pd alloys provide substantially higher strength while retaining adequate conductivity for electrical contact and tableware applications.
Yield Strength	50–55 MPa	Very low yield strength — Ag work-hardens significantly, with cold-drawn Ag wire reaching ~200 MPa YS. The low yield strength enables room-temperature sintering of Ag nanoparticle pastes (Ag sinter die-attach) at ~250 °C under modest pressure, forming nearly bulk-density Ag joints with high thermal and electrical conductivity.
Young's Modulus	83 GPa	Low modulus for a transition metal — similar to Au (78 GPa). The low modulus reduces thermal-stress-induced delamination in Ag thin-film coatings on flexible substrates and in Ag paste contacts on silicon solar cells under thermal cycling, where the large Ag/Si CTE mismatch (19 vs. 2.6 ppm/°C) is partially accommodated by Ag's compliance.
Hardness	24–26 HB (annealed)	Soft in pure annealed form — among the softest of the transition metals. Hardness increases significantly with cold work and with alloying: sterling silver (~65 HB), Ag-Pd alloys (~80–120 HB). The softness of pure Ag limits its use in unalloyed form for mechanical contact applications but is advantageous for deformation forming of fine wire and foil.
Elongation at Break	20–40%	High ductility in annealed form — enables fine wire drawing (to <25 µm for electronics bonding wire), thin foil rolling, and swaging for electrical contact blanks. Ag bonding wire is used in power device packaging where Au wire would be used in signal applications — Ag wire provides similar conductivity at lower cost.
Poisson's Ratio	0.37	High Poisson's ratio typical of FCC noble metals with weak d-electron character. Used in FEA modeling of Ag thin-film stress in low-e glass coatings under biaxial thermal loading and in Ag paste contact simulation for solar cell interconnect reliability analysis.

Chemical Properties

Property	Value / Behavior	Notes
Oxidation States	+1 (dominant: AgCl, AgNO₃, Ag₂O, ⁺); +2 (AgF₂, rare); +3 (AgF₃, rare)	Ag⁺ photoreduction (AgX + hν → Ag⁰ + X) is the basis of classical silver halide photography (AgBr/AgCl/AgI emulsions); Ag⁺ and AgNPs are the primary antibacterial Ag species in medical devices; ⁺ (Tollens' reagent) is the classical test for reducing sugars (Fehling/Tollens silver mirror reaction). Ag/AgCl (E° = +0.222 V) is the universal aqueous reference electrode in electrochemistry.
Corrosion & Tarnish	Tarnishes in air via Ag₂S formation (from atmospheric H₂S); resistant to O₂ and H₂O; attacked by HNO₃ and hot H₂SO₄	Ag tarnishing is primarily Ag₂S formation from trace H₂S (ppb levels in urban air), not surface oxidation — source description of "surface oxidation" is imprecise. Ag₂O does form electrochemically above ~0.4 V vs. RHE and in alkaline media, but is not the tarnish species in ambient air. Ag is resistant to most organic acids and alkalis, and to dilute H₂SO₄; it dissolves readily in HNO₃ (3Ag + 4HNO₃(dil) → 3AgNO₃ + NO + 2H₂O) and in hot concentrated H₂SO₄.
Surface Oxide / Tarnish	Ag₂S (black, tarnish in H₂S-containing air); Ag₂O (electrochemical, alkaline media)	Anti-tarnish coatings for Ag jewelry and silverware include Ag-Pd alloys, Ag-Au alloys, lacquer overcoats, and Ag₃N passivation. In PV solar cell contacts, Ag paste tarnishing (Ag₂S formation) in humid H₂S-containing environments can increase contact resistance over module lifetime — a reliability concern driving research into Ag-alloy and Ag-replacement pastes.

Identifier	Value
Symbol	Ag
Atomic Number	47
CAS Number	7440-22-4
UN Number	UN3077 (powder)
EINECS Number	231-131-3

Isotope	Type	Notes
¹⁰⁷Ag	Stable	51.84% natural abundance; I = 1/2, NMR-active. ¹⁰⁷Ag NMR (chemical shift range ~700 ppm; direct detection requires high-field NMR due to low sensitivity) characterizes Ag coordination in AgNP surface ligands, Ag⁺ electrolyte species, and Ag organometallic compounds. ¹⁰⁷Ag is the radiogenic daughter of ¹⁰⁷Pd (t½ = 6.5 Myr, extinct) — excess ¹⁰⁷Ag in iron meteorites (Gibeon, Santa Clara pallasite) was the first evidence for live ¹⁰⁷Pd in the early solar system, constraining the timescale of core formation in differentiated planetesimals to <5 Myr after CAI formation.
¹⁰⁹Ag	Stable	48.16% natural abundance; I = 1/2, NMR-active. ¹⁰⁹Ag NMR is preferred over ¹⁰⁷Ag for solution NMR due to its slightly higher receptivity. Used as the denominator isotope in ¹⁰⁷Ag/¹⁰⁹Ag ratio measurements by MC-ICP-MS for Ag isotope fractionation studies in hydrothermal ore deposits and for tracing Ag contamination from AgNP-containing consumer products in aquatic environments. ¹⁰⁹Ag(n,γ)¹¹⁰ᵐAg (σ = 91 barn) is the primary production route for ¹¹⁰ᵐAg.
¹¹⁰ᵐAg	Radioactive	t½ = 249.8 days; isomeric transition (IT) + β⁻ to ¹¹⁰Cd; emits multiple γ lines (657.8, 884.7, 937.5 keV — useful for detector calibration). Not listed in source; added here. Produced by ¹⁰⁹Ag(n,γ)¹¹⁰ᵐAg in reactor neutron fields and was released as a major non-fission radionuclide in the Chernobyl (1986) and Fukushima Daiichi (2011) accidents — used as an environmental tracer for these events in sediment and aquatic ecosystem monitoring programs. Also formed in Ag-bearing structural components of research reactors under neutron irradiation, relevant to decommissioning and waste management.

Scientific & Research Applications

Use Case	Form Typically Used	Description
Plasmonics & SERS	Ag nanoparticles (20–100 nm citrate-capped); Ag nanorods/nanotriangles; Ag thin films on substrates; Ag sputtering targets (99.99%+)	Ag nanostructures provide the highest electromagnetic field enhancement of any plasmonic metal at visible wavelengths — Ag nanotriangle arrays and Ag film-over-nanosphere (AgFON) substrates achieve enhancement factors of 10⁸–10¹⁰ for SERS, enabling single-molecule detection. Ag SPR sensors (localized, λ_max ~400 nm spheres, blue-shifted vs. Au ~520 nm) are used for refractive-index-based biomolecular binding assays.
Electrochemistry Reference Electrodes	Ag wire (99.99%+) with AgCl coating; Ag/AgCl pellet electrodes	Ag/AgCl (3 M KCl) is the universal aqueous reference electrode in analytical electrochemistry — stable, non-toxic, non-polarizable, and compatible with biological media. E° = +0.222 V vs. SHE; potential shifts by −0.059 V per decade increase in Cl⁻ concentration. Ag/Ag⁺ (in non-aqueous solvent) is the standard reference for non-aqueous electrochemistry (organic synthesis, ionic liquids, battery research).
Optical Mirror Coatings	Ag sputtering targets (99.99–99.999%); Ag evaporation sources (pellets, wire)	Ag thin films (~100 nm) have >98% reflectivity at 600–800 nm — higher than Au and Al in the visible/NIR range — making Ag the coating of choice for astronomical telescope mirrors (VLT, Gemini), high-power laser cavity mirrors, and solar concentrator reflectors. Protected Ag coatings (Ag/SiO₂/Al₂O₃ overcoat) resist tarnishing for decade-scale outdoor service.
Catalysis Research	Ag/α-Al₂O₃ extrudates; Ag foil (99.9%+); Ag powder	Ag/α-Al₂O₃ catalysts (8–15 wt% Ag) are the unique industrial catalyst for ethylene epoxidation (CH₂=CH₂ + ½O₂ → ethylene oxide at 200–280 °C), producing ~25 million tonnes/year of ethylene oxide globally — a selectivity of ~88–90% to EO vs. CO₂ is achieved with Cs/Re/S promoters. Ag is also used for selective oxidation of methanol to formaldehyde (BASF process) over Ag gauze or granules at ~600 °C.
Antimicrobial Research & Medical Devices	AgNPs (5–100 nm); Ag-coated surfaces; Ag wire (99.9%+); ionic Ag solutions	AgNPs release Ag⁺ ions that disrupt bacterial membrane integrity and inhibit respiratory enzymes — effective against MRSA, VRE, E. coli, and P. aeruginosa at MIC of 1–10 µg/mL. Approved applications include Acticoat Ag-nanocrystalline wound dressings, Ag-coated urinary catheters, and Ag-impregnated bone cements. Research ongoing on Ag ecotoxicity, AgNP fate in wastewater treatment, and potential contribution to antibiotic resistance gene transfer.

Industrial & Commercial Applications

Sector	Form / Grade Used	Description
Photovoltaic Solar Cell Contacts	Ag screen-printing paste (70–80 wt% Ag flake, 99.99%+ Ag); Ag sputtering targets	Screen-printed Ag paste front contacts (~150 µm wide lines) are the standard current collector for crystalline Si solar cells (PERC, TOPCon, HJT) — consuming ~140–160 Moz Ag/year globally (~20% of total Ag demand), the largest single industrial Ag use. Ag loading per cell has been reduced from ~400 mg to ~70–80 mg over two decades through finger line narrowing; HJT cells require low-temperature-cure Ag paste compatible with amorphous Si layers.
Electrical Contacts & Connectors	Ag-SnO₂ (85–88% Ag), Ag-CdO, Ag-WC contact composites; Ag-plated Cu bus bars and connectors	Ag-SnO₂ and Ag-CdO composites are the standard materials for medium-voltage contactors, circuit breakers, and relay contacts — Ag provides low contact resistance while the SnO₂/CdO dispersion suppresses arc welding and erosion under inductive switching. Ag-plated Cu bus bars, terminals, and spring contacts (5–25 µm Ag on Cu) dominate EV battery pack electrical interconnects due to superior contact resistance stability vs. bare Cu oxidation.
Electronics & Conductive Pastes	Ag flake paste (70–80 wt% Ag, 99.99%+); Ag ink (jetted, 30–60 wt% AgNPs); Ag sinter paste (micron + nano Ag)	Isotropic conductive Ag epoxy paste is the standard die-attach adhesive in LED packaging, sensor modules, and consumer electronics where solder reflow is impractical. Nano-Ag sinter paste (sintered at 200–250 °C under pressure) replaces Pb solder in SiC power module die-attach for >300 °C junction temperature capability. Jetted Ag nanoparticle ink (sintered at ~120–150 °C) enables printed electronics on PET and paper substrates for RFID antennas, wearable sensors, and flexible displays.
Low-Emissivity (Low-e) Glass Coatings	Ag thin film (10–15 nm, 99.99%+) by magnetron sputtering in online/offline coaters	Ag films (10–15 nm, between ZnO or TiO₂ adhesion/anti-reflection layers) in double- and triple-silver low-e glazing provide infrared reflectivity >85% while transmitting >70% of visible light — the dominant energy-efficient window technology in commercial and residential construction globally. A standard triple-silver low-e unit contains ~0.1 g Ag per m² of glazing; global production of ~8 billion m²/year of architectural glass consumes ~600–800 Moz Ag/year in this application.

Purity	Description
99.9% (3N)	Commercial-grade silver suitable for general research and industrial use.
99.95% (3N5)	Higher purity silver with reduced contaminants, suitable for advanced electronics and optics.
99.97% (3N7)	Enhanced purity silver with tighter impurity control for scientific and medical instrumentation.
99.99% (4N)	High-purity silver for precision electronics, superconducting applications, and sensitive coatings.
99.997% (4N7)	Ultra-clean silver used in vacuum electronics and photonic systems.
99.999% (5N)	Ultra-high purity silver used in plasma physics, cryogenics, and high-performance nanotechnology.

Synonym / Alternative Name	Context
Ag	Chemical symbol; from Latin argentum (shining, bright) — one of the oldest recorded element symbols, used since medieval alchemy. Primary identifier in ICP-MS databases, electrochemical literature (Ag/AgCl reference electrode), and precious metals commodity market reports (LBMA Good Delivery rules for silver bars).
Silver metal	Commercial designation for elemental Ag in wire, foil, powder, pellet, or sputtering target form; used in ASTM standards (B413 for silver), LBMA good-delivery specifications, and procurement documentation for PV paste, electrical contact, and optical coating manufacturers.
Silver precious metal	Trade designation classifying Ag alongside Au, Pt, and the PGMs in commodity markets; used in LBMA silver price fixing documentation, exchange-traded silver (XAG/USD), and insurance and logistics documentation for silver bullion transport — though Ag is the least expensive of the precious metals by weight.
Pure silver	Commercial and consumer designation for high-purity Ag (typically ≥99.9%) as distinct from sterling silver (92.5% Ag), coin silver (90% Ag), and silver-filled or silver-plated products; used in jewelry, bullion, and medical device procurement specifications.
Fine silver	Precious metals industry term for Ag of ≥99.9% purity — the standard for LBMA good-delivery silver bars (1,000 troy oz, ≥99.9% Ag) and for silver grain used in Ag paste manufacture, dental alloys, and brazing filler metal production. Distinguishes from sterling and coin silver alloys.
Elemental Silver	Scientific designation distinguishing pure Ag metal from AgCl, AgNO₃, AgNPs, and other Ag compounds; used in surface science, electrochemistry, and plasmonics literature specifying Ag metal substrates, single crystals (Ag(111)), or thin films distinct from silver oxide or silver salt species.
Element 47	Periodic table designation; used in XRF/ICP-MS analytical software, nuclear data libraries (ENDF/B-VIII) for ¹⁰⁷Ag/¹⁰⁹Ag cross-section data, and environmental monitoring databases tracking ¹¹⁰ᵐAg from Chernobyl and Fukushima fallout in sediment and biota samples.
Argentum	Latin name for silver; the etymological root of the chemical symbol Ag, of the word "argentiferous" (silver-bearing), and of Argentina (named for the silver the Spanish conquistadors expected to find there). Used in formal scientific nomenclature for Ag compounds (argentous/argentic) and in mineralogy (argentite = Ag₂S).
Argent	French language name for silver; used in French scientific literature, EU regulatory documentation (REACH, RoHS compliance for Ag in electronics), and heraldry (the color silver/white on coats of arms). Also used in English heraldry for the silver tincture.
Silber	German language name for silver; used in German scientific literature, DIN standards, and industrial documentation in German-speaking markets — Germany is a major consumer of Ag in electrical contacts (Ag-SnO₂ for circuit breakers) and in Ag paste for PV cells.
Plata	Spanish language name for silver; used in Spanish scientific literature and industrial documentation across Latin American and Spanish markets; etymological root of "platinum" (platina, little silver) — Spanish explorers named Pt for its resemblance to Ag found in Colombian gold sources.

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