
Ternary gold alloys and alloys made of more than three elements
This group contains gold solders and alloys of white and green gold (gold with silver or cadmium).
Gold solder (fusible gold alloy)
According to the technical requirements of the authorised Assay Office the solder should have the same assay as the products which are being soldered. They should also be of the same color. Taking technological requirements into consideration, the solder should possess much lower temperature than the products that are being joined. Gold solders used for soldering have their special certification number BN-62/08998-01 (for Poland), one must remember that the technological requirements are the most important.
If it is unable to satisfy the requirements of an authorised Assay Office, a solder with lower assay can be used, nevertheless, the joined products should have better CCM (Common Control Mark), as a consequence the assay of those two elements joined together would not cause lowering the quality of the product and changing its hallmark.
Several low-melting point fusible metals are added to the alloys, e.g zinc (Zn) or cadmium (Cd) or both of them jointly (Zn+Cd). By gold alloys are meant Au-Ag-Cu-Zn and Au-Ag-Cu-Cd and other five-element alloys e.g. Au-Ag-Cu-Zn-Cd. Zinc added to an alloy improves its malleability, what is very useful for soldering. That is why zinc alloys (Au-Ag-Cu-Zn) are also very popular in casting, thin-walled constructions casting in particular.
Cadmium, on the other hand, functions as solder’s temperature reducer because its melting point is as low as 594.22 K (much lower than for zinc 692.68 K). In addition, cadmium possesses lower boiling point than zinc (cadmium – 1040 K, zinc – 1180), nevertheless, cadmium fumes are a serious health hazard for a human organism. Therefore, it should be added to an already melted Au-Ag-Cu alloy at the end of the process, possible losses should also be taken into consideration. Four-element alloys (e.g. Au-Ag-Cu-Cd) are often used for creation of green gold alloys.
White gold alloys
White gold alloys are not given the aforementioned hallmark. Nickel and palladium are used for making white gold mixes. In order to differentiate the metals that have been added to the alloy gold can have two different names: nickel white gold or palladium white gold.
Palladium white gold has a good white color and is often called a noble white gold. Some countries (e.g. Germany) consider palladium as valuable as gold that is why this alloy deserves the name. Even if a product contains 0.135 of palladium and only 0.450 of gold it is still hallmarked as a gold alloy with CNN Au 0.585.
White gold alloys are corrosion-proof, with platinum-like colour. They are widely used for framing brilliants since they do not change the colour of the gemstone, which would have a negative effect on its value. Moreover, alloys of white gold are treated as a decorative element if they are placed in gold alloys of various colours.
Nickel gold alloys
Gold with nickel form a solid solution, the metals can dissolve freely. Nickel white gold alloys made of three or four elements Au-Cu-Ni and Au-Cu-Ag-Ni or Au-Cu-Ni-Zn are often applied to jewelry production. This is done because nickel increases melting temperatures of alloys and improves their metal qualities. NIckel is usually added to gold in a ligature Cu-Ni, whereas in case of alloys which contain zinc nickel can be added in form of alloys of the Cu-Ni-Zn type, copper with nickel also known as a ‘nickel silver’. Adding zinc to white gold is done for the purpose of lowering its melting temperature and for ability of zinc to affect the colour of the mixture (which enables to limit the amount of nickel added to the alloy). Thank to the better access to nickel and its low price that kind of white gold is more common than other white gold alloys.
Palladium white gold
Gold with palladium alloys form solid solution, which means that they dissolve freely. This alloy is ductile and malleable. Surprisingly, addition of only over 16% of palladium to gold changes its colour completely.
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