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Gold, Au


Subcategory: Gold Alloy; Metal; Nonferrous Metal; Precious Metal; Pure Element

Component   Wt. %
Au100 

Material Notes:
Gold is a noble metal and does not react with oxygen. This is why gold does not tarnish. Although it does not form oxides, it will form compounds with other metals and is rarely found in its pure form. It is usually associated with silver and often with mercury. When the silver content is a high, the metal is called electrum, a naturally occurring gold-silver alloy. Gold is also found in tellurides and ore containing quartz where it is either openly visible or enclosed in particles of sulfide minerals such as chalcopyrite, pyrrhotite, pyrite, and arsenopyrite.

Gold in its pure form is a very soft metal, so it is often alloyed with other metals for increased strength and hardness. When gold is alloyed, its ductility is diminished, but its malleability remains constant, except when large amounts of copper are added. Red or pink gold (also called rose gold) is gold that contains large percentages of copper and a small amount of silver. Green gold is usually gold alloyed with additional silver or with silver that has a small percentage of copper. White gold is usually 75% gold and 25% nickel (or nickel, zinc, and sometimes copper). Formally white gold was made with silver and/or palladium, but white gold made with nickel and zinc is harder, cheaper, and has better melting characteristics.

Physical PropertiesMetricEnglishComments
Density19.32 g/cc0.698 lb/in³ 

Mechanical Properties
Hardness, Vickers2525 
Tensile Strength, Ultimate120 MPa17400 psi Annealed
Elongation at Break30 %30 % 
Modulus of Elasticity77.2 GPa11200 ksi 60% Cold Worked
Poisson's Ratio0.420.42 
Shear Modulus27.2 GPa3950 ksi 60% Cold Worked; Calculated Value

Electrical Properties
Electrical Resistivity2.2e-006 ohm-cm2.2e-006 ohm-cm 
Magnetic Susceptibility-1.42e-007-1.42e-007 cgs/g

Thermal Properties
Heat of Fusion66.2 J/g28.5 BTU/lb 
CTE, linear 20°C14.4 µm/m-°C8 µin/in-°F over the range 20-100ºC
CTE, linear 250°C14.6 µm/m-°C8.11 µin/in-°F 
CTE, linear 500°C15.2 µm/m-°C8.44 µin/in-°F 
CTE, linear 1000°C16.7 µm/m-°C9.28 µin/in-°F at 950°C
Specific Heat Capacity0.1323 J/g-°C0.0316 BTU/lb-°F 
Thermal Conductivity301 W/m-K2090 BTU-in/hr-ft²-°F 
Melting Point1064.43 °C1950 °F 

Optical Properties
Emissivity (0-1)0.040.04 1000°C; total spectrum
Reflection Coefficient, Visible (0-1)0.270.27 400 nm
Reflection Coefficient, Visible (0-1)0.50.5 500 nm
Reflection Coefficient, Visible (0-1)0.850.85 600 nm

Descriptive Properties
CAS Number7440-57-5 

References are available for this material.

 


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