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发表于 22-6-2008 08:00:23
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Gold
Au
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General Description: This metal has been known since prehistoric times
Gold is a soft metal with a characteristic yellow color. It is the most malleable and ductile of any element. It is unaffected by air, water, alkalis and acids, with the exception of "aqua regia", HNO3/HCl. The fact that it is chemically unreactive means that it is often found in its natural state. It is a good thermal and electrical conductor and has excellent reflective properties to both light and infrared. It has an abundance in the earth's crust of 0.0011 ppm.
Most of the metal is retained for use as bullion reserves, but some is used within the electronics and jewellery industries, where it is frequently alloyed with other elements to improve the mechanical properties of the metal (e.g. copper and silver). Other uses for the metal are as a heat reflecting coating for glass as well as as a decorative medium.
Atomic Properties
Atomic number 79
Atomic radius - Goldschmidt ( nm ) 0.144
Atomic weight ( amu ) 196.9665
Crystal structure Face Centered Cubic
Electronic structure Xe 4f14 5d10 6s1
Ionization potential No. eV
1 9.22
2 20.5
Natural isotope distribution Mass No. %
197 100
Photo-electric work function ( eV ) 4.8
Thermal neutron absorption cross-section ( Barns ) 98.8
Valences shown 1,3
Electrical Properties
Temperature coefficient ( K-1 ) 0.0040 @ 0-100C
Electrical resistivity ( μOhmcm ) 2.20 @ 20C
Thermal emf against Pt (cold 0C - hot 100C) ( mV ) +0.74
Mechanical Properties
Material condition Soft Hard Polycrystalline
Bulk modulus ( GPa ) 171
Hardness - Vickers 20-30 60
Poisson's ratio 0.42
Tensile modulus ( GPa ) 78.5
Tensile strength ( MPa ) 130 220
Yield strength ( MPa ) 205
Physical Properties
Boiling point ( C ) 3080
Density ( g cm-3 ) 19.30 @ 20C
Melting point ( C ) 1064.4
Thermal Properties
Coefficient of thermal expansion ( x10-6 K-1 ) 14.1 @ 0-100C
Latent heat of evaporation ( J g-1 ) 1738
Latent heat of fusion ( J g-1 ) 64.9
Specific heat ( J K-1 kg-1 ) 129 @ 25C
Thermal conductivity ( W m-1 K-1 ) 318 @ 0-100C |
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