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Ruthenium has four crystal modifications and does not tarnish at ambient conditions; it oxidizes upon heating to 800 °C (1,070 K). Ruthenium dissolves in fused alkalis to give ruthenates (RuO 2− 4). It is not attacked by acids (even aqua regia) but is attacked by sodium hypochlorite at room temperature, and halogens at high temperatures. [11]
Although both have industrial uses, they are better known for their uses in art, jewelry, and coinage. Other precious metals include the platinum group metals: ruthenium, rhodium, palladium, osmium, iridium, and platinum, of which platinum is the most widely traded. [1]
Electrochemical coloring of metals based processes are black, green and blue nickel plating, black chromium plating, black rhodium plating and black ruthenium plating. [3] [4] Anodic oxidation of aluminum, titanium, niobium, tantalum and stainless steel are also electrochemical colouring processes. Multi-colored and green electrolytic patinas ...
Black gold is a type of gold used in jewelry. [16] [17] Black-colored gold can be produced by various methods: Patination by applying sulfur- and oxygen-containing compounds. Plasma-assisted chemical vapor deposition process involving amorphous carbon; Controlled oxidation of gold containing chromium or cobalt (e.g. 75% gold, 25% cobalt [4]).
The black tarnish commonly seen on silver arises from its sensitivity to sulphur containing gases such as hydrogen sulfide: 2 Ag + H 2 S + 1 / 2 O 2 → Ag 2 S + H 2 O. Rayner-Canham [ 4 ] contends that, "silver is so much more chemically-reactive and has such a different chemistry, that it should not be considered as a 'noble metal'."
Laurite is an opaque black, metallic ruthenium sulfide mineral with formula: RuS 2. It crystallizes in the isometric system. It is in the pyrite structural group. Though it's been found in many localities worldwide, it is extremely rare. Laurite has a Mohs hardness of 7.5 and a specific gravity of 6.43.