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Silver is a metallic chemical element with the chemical symbol Ag atomic number
47. A soft, white, lustrous transition metal. The metal occurs naturally
in its pure, free form (native silver), as an alloy with gold and other
metals, and in minerals such as argentite and chlorargyrite. Most silver
is produced as a by-product of copper, gold, lead, and zinc refining.
Structure:
Crystal
Structure: Face-centered cubic at 25 oC,
a = 0.408621 nm
Mass
Characteristics:
Atomic
Weight: 107.868
Density: 10.49 g/cm3 at 20 oC
Volume
Change on Freezing: 5% contraction
Thermal
Properties:
Melting
Point: 961.9 oC
Boiling
Point: 2163 oC
Coefficient
of Linear Thermal Expansion:
20 oC, 19.0 μm/m * K
-190 to 0 oC, 17.0
μm/m * K 0 to 900 oC,
Lt = Lo (1 + 19.494 x 10-6 t +
1.0379 x 10-6
t2 + 2.375 x 10-12t3, where t
is inoC
0 to 100oC, 19.68
μm/m * K
0 to 500 oC, 20.61
μm/m * K
Specific Heat: Solid: 25 oC,
0.235 kJ/kg * K
127 oC, 0.239 kJ/kg * K
527 oC, 0.262 * K
961 oC, 0.297 kJ/kg * K
Liquid: 961 to 2227 oC, 0.310 kJ/kg * K
Latent Heat of Fusion: 104.2 kJ/kg
Latent Heat of Vaporization: 2.63 MJ/kg
Recrystallization Temperature: 20 to 200 oC, depending on purity and amount of
cold work
Thermal Conductivity:428 W/m * K at 20 oC
356 W/m * K at 450 oC
Electrical Properties:
Electrical Conductivity: 108.4% IACS for extremely pure silver
Electrical Resistivity: 14.7 nΩ * m at 0 oC
Temperature Coefficient: from 0 to 100 oC, 0.0041 per K
Cold working of silver considerably
increases resistivity: 5% for 90% reduction. Annealing commercially pure
silver successively in air and hydrogen disrupts grain boundaries and
increases resistance. Tension reduces resistivity slightly as does
hydrostatic pressure: 12,000 kg/cm2 causes 4% reduction.
Thermal Electromotive Force: vs platinum, +0.74 mV; cold junction at 0 oC,
hot junction at 100 oC
Magnetic Properties:
Magnetic Susceptibility: Volume: -2.27 x 10-6 mks
Optical Properties:
Color: As a result of the high and fairly uniform
reflectance in the visible range, silver is considered white, but if human
eyes were sensitive to a slightly shorter wavelength region, silver would
appear to have color.
Reflectance: For clean silver, high in the visible an
infrared but low in near-ultraviolet.
Emittance: Solid silver at 0.65
μm: extremely low and not
known accurately; values of 0.044
μm at 940 oC and 0.072
μm
at 980 oC have been observed for liquid silver. Other
experiments showed no discontinuity at the melting point of silver, the
emissivity being about 0.055 at about 700 oC.
Mechanical Properties:
Tensile Properties: Considerable spread in values for tensile
strength and hardness of high-purity silver. Average tensile strength, 125
MPa for 5 mm wire annealed at 600 oC.
Hardness: High-purity silver; hydrogen anneal 650 oC,
25 HV; air anneal at 650 oC, 27 HV; electro-deposited silver
(higher electrical resistivity than wrought silver), 100 HV
Elastic Modulus: Strained 5%, then heated 0.5 hour at 350 oC,
71.0 GPa
Poisson's Ratio: Annealed: 0.37; hard drawn, 0.39
Liquid Surface Tension: 0.923 N/m at 995 oC
Applications:
Silver has long been
valued as a precious metal, and it is used to make ornaments, jewellery,
high-value tableware, utensils (hence the term silverware), and currency
coins. Today, silver metal is also used in electrical contacts and conductors,
in mirrors and in catalysis of chemical reactions. Its compounds are used in
photographic film and dilute silver nitrate solutions and other silver compounds
are used as disinfectants and microbiocides.
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