An alloy is a combination of metals or of metals and other elements.
Examples
- Crown gold
- A 22 karat (kt) (916 2⁄3 fine) gold alloy used for English & UK gold coins from 1526 (Henry VIII) to 1914 (as currency), and since then for trade and bullion coins. (22⁄24 gold, 2⁄24 copper)
- 𝜌 = 17.61 g/㎝³
- “Standard gold” (US)
- A 900 fine gold alloy used for US coins. (90% gold, ≤5% silver, 5-10% copper)
- 𝜌 = 17.43±.12 g/㎝³
- “Crown electrum” (d20)
- A 4 ℥ 17 3⁄4 ʤ gold, 6 ℥ 3½ ʤ silver, 18 3⁄4 ʤ copper alloy worth 1⁄2 of crown gold by weight (presuming that sterling silver is worth 1⁄10 of crown gold by weight). (i.e. the d20 gold-silver standard)
- Britannia silver
- An 11 ℥ 10 ʤ (958 fine) silver alloy required in England for “wrought plate” (non-monetary silversmithing) from 1697–1720 to inhibit coin clipping and melting. (23⁄24 silver, 1⁄24 copper)
- 𝜌 = 10.42 g/㎝³
- Sterling silver
- An 11 ℥ 2 1⁄4 ʤ (926 fine) fine silver alloy used for English & UK silver coins from before 1158 (Henry II) to 1919. (92.6% silver, 7.4% copper)
- 𝜌 = 10.37 g/㎝³
- “Standard silver” (US)
- A 900 fine silver alloy used for US coins from ____ to 1964. (90% silver, 10% copper)
- 𝜌 = 10.32 g/㎝³
| “Coin gold” (d20)
|
906 fine gold
|
29⁄32 gold, 3⁄32 copper
|
𝜌 = 17.42
|
| “Coin electrum” (d20)
|
906 fine electrum
|
25⁄64 Au, 33⁄64 Ag, 3⁄32 Cu
|
𝜌 = 12.53
|
| “Coin silver” (d20)
|
906 fine silver
|
29⁄32 silver, 3⁄32 copper
|
𝜌 = 10.33
|
| “Coin copper” (d20)
|
906 fine copper
|
29⁄32 copper, 3⁄32 tin/zinc
|
𝜌 = 8.76
|
Density
- ᴍ = material constituent
- 𝜌 = density (i.e. g/㎝³)
- 𝐴ᵣ = atomic weight
- 𝑤 = mass fraction (i.e. 9⁄10, .900 or 90%)
- 𝑎𝑡٪ = atomic percent
- Alloy (general)
- Au-Ag
- 𝜌Au-Ag = 𝜌Au 𝑤Au + 𝜌Ag 𝑤Ag − 4 exp(0.005 𝑤Au) 𝑤Au 𝑤Ag
- Au-Cu
- 𝜌Au-Cu = 𝜌Au 𝑤Au + 𝜌Cu 𝑤Cu − 5 exp(0.01 𝑤Au) 𝑤Au 𝑤Cu
- Ag-Cu
- 𝜌Ag-Cu = 𝜌Ag 𝑤Ag + 𝜌Cu 𝑤Cu − 0.12 exp(0.02 𝑤Cu) 𝑤Ag 𝑤Cu
- Au-Ag-Cu
- 𝜌Au-Ag-Cu = 1.004 𝑎𝑡٪Au 𝜌Au + 1.03 𝑎𝑡٪Ag 𝜌Ag + 0.096 𝑎𝑡٪Cu 𝜌Cu + x − y
- x = 0.35 ( cos(45+0.45 𝑎𝑡٪Au) + cos(45+0.45 𝑎𝑡٪Ag) + sin(𝑎𝑡٪Au) )
- y = 0.005 (𝑎𝑡٪Au+𝑎𝑡٪Ag) cos(0.9 𝑎𝑡٪Cu) + 0.2 cos(3.2 𝑎𝑡٪Cu)
-
References
- Kraut, J.C.; Stern, W.B. (June 2000) “The Density of Gold-Silver-Copper Alloys and its Calculation from the Chemical Composition”. Gold Bulletin, Vol. 33, Iss. 2, pp. 52–55. Springer-Verlag. doi:https://doi.org/10.1007/BF03216580.
- Good, David; Cabri, Louis J.; Ames (April 2017) “PGM Facies variations for Cu-PGE deposits in the Coldwell Alkaline Complex, Ontario, Canada”. Ore Geology Reviews, Iss. 90. doi:10.1016/j.oregeorev.2017.04.028.
- aurian silver (<50 at% Ag)
- electrum (50–80 at% Ag)
- gold (>80 at% Ag)