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Gold, Au

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

Component    Wt. % Au 100

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 Properties	Metric	English	Comments
Density	19.32 g/cc	0.698 lb/in³
Mechanical Properties
Hardness, Vickers	25	25
Tensile Strength, Ultimate	120 MPa	17400 psi	Annealed
Elongation at Break	30 %	30 %
Modulus of Elasticity	77.2 GPa	11200 ksi	60% Cold Worked
Poisson's Ratio	0.42	0.42
Shear Modulus	27.2 GPa	3950 ksi	60% Cold Worked; Calculated Value
Electrical Properties
Electrical Resistivity	2.2e-006 ohm-cm	2.2e-006 ohm-cm
Magnetic Susceptibility	-1.42e-007	-1.42e-007	cgs/g
Thermal Properties
Heat of Fusion	66.2 J/g	28.5 BTU/lb
CTE, linear 20°C	14.4 µm/m-°C	8 µin/in-°F	over the range 20-100ºC
CTE, linear 250°C	14.6 µm/m-°C	8.11 µin/in-°F
CTE, linear 500°C	15.2 µm/m-°C	8.44 µin/in-°F
CTE, linear 1000°C	16.7 µm/m-°C	9.28 µin/in-°F	at 950°C
Specific Heat Capacity	0.1323 J/g-°C	0.0316 BTU/lb-°F
Thermal Conductivity	301 W/m-K	2090 BTU-in/hr-ft²-°F
Melting Point	1064.43 °C	1950 °F
Optical Properties
Emissivity (0-1)	0.04	0.04	1000°C; total spectrum
Reflection Coefficient, Visible (0-1)	0.27	0.27	400 nm
Reflection Coefficient, Visible (0-1)	0.5	0.5	500 nm
Reflection Coefficient, Visible (0-1)	0.85	0.85	600 nm
Descriptive Properties
CAS Number	7440-57-5

References are available for this material.