Platinum alloys with lead, zinc and other metals at low temperatures; it is usually recovered from these alloys by cupellation.
Platinum alloys with steel in all proportions. With 10 per cent. platinum, rusting is prevented. A very elastic metal is produced by alloying platinum with from 5 to 10 per cent. gold.
The melting-point of silver is raised by alloying it with platinum, but its thermal conductivity is lowered.
| The following table gives the composition of the principal platinum and palladium alloys[[4]] p. 561: | ||||||||
|---|---|---|---|---|---|---|---|---|
| Pt. | Cu. | Ag. | Au. | Ni. | Pd. | Other Constituents. | ||
| Parts. | Parts. | Parts. | Parts. | Parts. | Parts. | Parts. | ||
| Jewellery alloys: | ||||||||
| Platinum alloy | 1 | 0–1 | 2–5 | |||||
| Platinor | 2 | 5 | 1 | 1 | Brass 2. | |||
| Palladium alloy | 9 | Rhodium 1. | ||||||
| Mock gold | 7 | 16 | Zinc 1. | |||||
| Mock gold | 1 | 1 | 6 | Brass 1. | ||||
| Mock gold | 1 | 4 | ||||||
| Coopers’ pen metal: | 4 | 1 | 3 | |||||
| Watch alloy | 13 | 11 | 18 | 6 | ||||
| Watch alloy | 25 | 4 | 1 | 70 | ||||
| Watch alloy | 63 | 18 | 17 | Cadmium 1. | ||||
| Platinum bronze | 1 | 90 | Tin 9. | |||||
| Dentists’ alloy | 5 | 3 | 4 | |||||
| Dentists’ alloy | 7 | 3 | 2 | |||||
| Dentists’ alloy | 6 | 1 | 2 | |||||
| Dentists’ alloy | 4 | 1 | ||||||
| Palladium alloy | 2 | 3 | ||||||
Alloy Substitutes for Platinum
On account of the scarcity and high price of the platinum metals, much attention has lately been directed towards the discovery of suitable substitutes.
In the electrical industry an alloy of 3 parts of palladium and 2 parts of silver is in use, also an alloy of nickel and chromium. Platinite, an iron-nickel alloy, containing 46 per cent. nickel and 0·15 per cent. carbon, has the same coefficient of expansion as glass, and, when coated with copper, is used to replace the platinum connection wires of incandescent lamps. Tungsten is sometimes used for certain ignition devices. For cathodes an alloy of 90 per cent. gold and 10 per cent. copper can be used to replace platinum; the same alloy, if electrically coated with platinum, and then carefully polished and burnished, is suitable for platinum anodes.
For platinum chemical laboratory ware, there are several substitutes, such as fused quartz; various iron, chromium, and nickel-chromium alloys; palau, a gold-iridium alloy marketed in California; rhotanum, a general name for gold-palladium alloys containing from 60 to 90 per cent. of gold, which are suitable for most chemical purposes, except for use with hot concentrated nitric acid, and for electrolytic anodes; amaloy, which is a complex alloy containing nickel, chromium, tungsten, etc., highly resistant to corrosion and to cold nitric and sulphuric acids[[9]] p. 600.
In the jewellery trade platinum has been replaced by an alloy of 90 per cent. palladium and 10 per cent. rhodium. For certain surgical work various stellite alloys, containing cobalt and chromium, and hardened by the addition of tungsten and molybdenum, are valuable substitutes for platinum, and are not affected by antiseptic solutions. In dental work pins are now made of tungsten coated with palladium[[10]] p. 549. For most technical purposes an alloy of tungsten and nickel with gold or silver is used in Germany; it may be cast, rolled or forged, is acid-resisting, and capable of taking a high polish[[11]]. White gold, another substitute for platinum, contains fine gold, from 75 to 85 per cent.; pure nickel, from 10 to 18 per cent.; and zinc, from 2 to 9 per cent. Illium, a chromium-nickel-copper alloy reported recently as the discovery of S. W. Parr, of Illinois, is a substitute for gold or platinum, costing only 25 cents per ounce. It is stated to have been a “50 per cent. standard of success.” The alloy withstands hot or cold, strong or diluted acid, can be both cast and machined, and is already used largely in the manufacture of calorimeter bombs[[12]].
The results of researches made to discover substitutes for platinum, and undertaken by the National Dental Association of America, are described at length by F. A. Fahrenwald, in a paper read in January 1916 before the American Institute of Mining Engineers.