Platinum (Pt) is a transition metal with an atomic number 78.
The atomic mass of platinum is 194.9647911(9) (the most abundant and stable 195Pt isotope).
A nucleus of 195Pt is composed of 78 protons and 117 neutrons.
Platinum is found in alluvial or secondary deposits mostly in chemically uncombined state (as a natural pure metal or platinum-iridium alloy).
Platinum occurs also in a combined form as PtS (platinum sulfide), PtAs2 (platinum arsenide), PtTe2 (platinum telluride), PtSb (platinum antimonide).
The most prominent properties of platinum:
Pure platinum is rarely used in jewelry because of its low hardness (about 40 Vickers in annealed state).
Alloying platinum with iridium (Ir) has a strong hardening effect even at relatively low iridium concentrations.
Alloying platinum with cobalt (Co) results in significant hardness increase due to the grain refining effect of cobalt.
Pt950/Co is the most popular Pt-Co alloy. It is the best platinum alloy for fabricating cast pieces due to its excellent Casting properties - fine and detailed products may be fabricated from the alloy. Pt950/Co has a high hardness (135 HV as annealed and up to 185 HV in cold worked state) and good scratch resistance. Unlike other platinum alloys Pt950/Co tarnishes when heated.
Platinum-palladium alloys are traditionally popular in Japan and Hong Kong.
The Pt-Pd alloys are relatively soft therefore the pieces made of them are cold worked (burnished) in order to increase the surface hardness by cold.
The alloys have grey color. Rhodium Electroplating is used to improve their appearance.
Pt950/Ru is very hard alloy with the hardness 130 HV in annealed state and up to 210 HV in cold worked state. The Casting properties of the alloy are moderate therefore fine pieces can not be cast. The alloy has good wear and scratch resistances.
Platinum-Gold alloys are heat treatable which means that they may be strengthened by precipitation hardening method: solution treatment at a temperature 1100-1800ºF (599-982ºC) followed by quenching and aging.
In hardened state Pt-Au alloys are brittle and not suitable for Forging.
From all alloying elements tungsten (W) exerts the greatest effect on the platinum alloy hardness.
Platinum-tungsten alloys are used for fabricating springs (e.g. a tongue of a bracelet lock).
The alloys are heat treatable and may be strengthed by precipitation hardening (solution treatment-quenching-aging).
Hardness 300 HV may be achieved by the heat treatment.
The alloys available on the market:
Pt960/Cu alloy is a popular general purpose alloy in Germany an some other European countries.
The alloy is rarely used for casting since it has moderate Casting properties and also oxidizes in molten state.
Pt960/Cu alloy has good ductility and malleability. It’s hardness is 120 HV in the annealed state.