Technical Data for Gold

BASIC TECHNICAL DATA

Ever wondered what the difference was between gold plating and gold filling? Or how about 23 karats of gold and 10 karats? Ever wanted to know why this precious metal is so versatile? Read on.

Gold is a yellow, noble metal. Its chemical symbol is Au, from Aurora or dawn. The weight of gold or gold articles is usually expressed in troy ounces. (1 troy ounce = 1.097 ordinary ounces) The purity of gold articles is generally described in three ways: percent (parts of gold per 100), fineness (parts of gold per 1000) and karats (parts of gold per 24). Want to know more? Take a look below where we've provided you with just about all the technical information there is to know about gold.

Listed below is the technical data for gold. If you are to take a closer look at the numbers you will see how it is gold is such a versatile metal, and conversely, why gold is such an invaluable metal in today's society.

Basic Technical Gold Data
Atomic Number 79
Atomic Weight 196.9665 g/atom
Density (at 293 K) 19.32 g/cm3
Melting Point 1064.41 C (1337.59 K)
Boiling Point 2807.8 C (1337.59 K)
Modulus of Elasticity 79 G Pa
Brinell Hardness (annealed to 1031 K) 25 kgf/mm2
Reflectance at 0.40 um 38.7%
Reflectance at 0.55 um 81.6%
Reflectance at 0.70 um 96.7%
Relectance at 1.00 um 98.1%
Thermal Expansion (from 273 to 373 K) 1.416 x 10-7 K-1
Thermal Conductivity (at 273 K) 3.144 W/cm x K
Electrical resistivity (at 273 K) 2.05 x 10-6 ohm x cm
Heat of Fusion 1.268 x 104 J/g-atom
Heat of Evaporation (at 298 K) 3.653 x 105 J/g-atom
Heat Capacity at 298 K 0.1288 J/g x K
Magnetic Moment 0.1439 N x m
Standard Oxidation Potential (Au to Au+ + e) -1.68 V
Total Emissivity (from 493 to 893 K) 0.018 to 0.035
Sources: J. Gunther Cohn, "Selected Properties of Gold" Gold Bulletin Vol. 12 (1979). Encyclopedia of Chemical Technology, Gold and Gold Compounds, Vol. 11 (1979).


WEIGHTS & EQUIVALENTS

Gold Coated
Many gold-coated aricles are also used as substitutes for solid karat gold. The thickness of the coatings are often expressed in millionths of an inch, or microinches, and the table below provides a way to translate between these and other measurement units.

Thickness Equivalents
1 millionth inch (microinch)
=
.0254 micron
1 thousanth inch (mil)
=
25.4 microns
1 millionth meter (micron)
=
39.37 microinches
1 millimeter
=
39.37 mils

Following are the definitions of various gold-coated articles which are sometimes used in place of solid karat gold.

Gold Filled: also called gold overlay, a layer of at least 10-karat gold permanenetly bonded by heat and pressure to one of more surfaces of a supporting metal, then rolled or drawn to a prescribed thickness. The karat gold must be at least 1/20 by weight of the total meta content.

Rolled Gold Plate: Material consisting of a layer of plating of 10-karat gold or better which is mechanically bonded to a base metal. The karat gold content may be less than 1/20 but must be properly identified by weight in terms of total metal content.

Gold Electroplate: A coating of at least 10-karat gold or gold alloy plated on a base metal by electrolysis. The gold plating must be at least seven-millionths of an inch thick. Electroplating is widely used in the electronics and aerospace industries.

Gold Wash or Gold Flash: A film of gold less than seven-millionths of an inch thick, electroplated on a base metal.

Vermeil: Sterling silver coated or plated on all significant surfaces with gold or gold alloy of not less than 10-karat fineness.

Purity
The purity of gold articles may be described in three ways:

Percent, meaning parts of gold per 100
Fineness, meaning parts of gold per 1,000
Karat, meaning parts of gold per 24. Not to be confused with the carat, equaling a fifth of a gram, which is used to state the weight of a gem stone. The following table shows the examples of these value for some common grades of gold.


Percent Gold European System Karat System
100%
=
1000 fine
=
24 karat
91.7%
=
917 fine
=
22 karat
75.0%
=
750 fine
=
18 karat
58.3%
=
583 fine
=
14 karat
41.6%
=
416 fine
=
10 karat*
*The minimum amount of gold that a product can be composed of and carry the label "gold", according to the U.S. Federal Trade Commission "Guides to the Jewelry Industry."

Weight

The weight of gold or gold articles is usually expressed in troy ounces. the table below provides a convenient way to translate between troy ounces and other units of weight.

Weight Equivalents
1 troy ounce =
20 pennyweight
1 troy ounce =
1.097 ordinary ounces
1 troy ounce =
480 grains
1 troy ounce =
31.1 grams
1000 troy ounces =
31.1 kilograms
1 gram =
.03215 troy ounces
1 kilogram =
32.15 troy ounces
1 tonne =
32,151 troy ounces
1 avoirdupois (ordinary) ounce =
.911 troy ounces
1 avoirdupois (ordinary) pound =
14.58 troy ounces

 

COMMONLY USED JEWELRY ALLOYS

Composition in Percent Au
Gold
Ag
Silver
Cu
Copper
Zn
Zinc
Ni
Nickel
Ti
Titanium
Pd
Palladium
Fe
Iron
Si
Silicon
B
Boron
Co
Cobalt
Yellow Gold
23 karat 99.0* 0.8-1.0
18 karat 75.00 13.00 12.00
75.00 15.00 10.00
14 karat 58.33 4.00 31.24 6.43 0.10 0.05 0.01
58.33 24.78 26.75 0.14
10 karat 41.70 11.66 40.81 5.83 0.03 0.02
41.70 5.50 43.80 9.00
White Gold
18 karat 75.00 2.23 5.47 17.80
** 75.00 15.00 10.00
14 karat 58.33 28.32 4.80 8.55
** 58.33 32.17 9.50
10 karat 41.66 29.15 12.12 15.05 1.97
** 41.70 47.42 0.88 10.00
Rose Gold
18 karat 75.00 5.00 20.00
14 karat 58.33 2.08 39.59
10 karat 41.70 2.82 55.48
"* Represents minimum"
"** Experimental, nickel-free"
Source: W.S. Rapson, Gold Usage, (Academic Press), 1978.
Handy & Harman Refining Group, Inc.


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