Noble metal


Noble metal

Noble metals are metals that are resistant to corrosion or oxidation, unlike most base metals. They tend to be precious metals, often due to rarity in the crust of the Earth. The noble metals are considered to be (in order of increasing atomic number)

*Copper
*Ruthenium
*Rhodium
*Palladium
*Silver
*Rhenium
*Osmium
*Iridium
*Platinum
*Gold
*Mercury

Some of the noble metals can be dissolved in aqua regia, a highly concentrated mixture of acids.

The term can also be used in a relative sense. A "Galvanic series" is a hierarchy of metals (or other electrically conductive materials, including composites and semimetals) that runs from "noble" to "active", and allows designers to see at a glance how materials will interact in the environment used to generate the series. In this sense of the word, graphite is more noble than silver (even though it is alchemically more base) and the relative nobility of many materials is highly dependent upon context, as for aluminium and stainless steel in conditions of varying pH.

In physics the definition of a noble metal is even more strict. It is required that the d-bands of the electronic structure are filled. Taking this into account, only copper, silver and gold are noble metals, as all d-like band are filled and don't cross the Fermi level. For platinum two d-bands cross the Fermi level, changing its chemical behaviour; it is used (in contrast to gold, for example) as a catalyst. The different reactivity can easily be seen while preparing clean metal surfaces in ultra high vacuum; surfaces of noble metals (e.g., gold) are easy to clean and stay clean for a long time, while those of platinum or palladium, for example, are covered by carbon monoxide very quickly.

ee also

*Base metal
*Precious metal
*Synthesis of noble metalsSilver and copper corrode and oxidize easily and readily, thus the copper sheets with a patina of oxidation used in architectural designs and the resultant market for a myriad of silver polishing compounds.

External links

* To see which bands cross the Fermi level, the Fermi surfaces of almost all the metals can be found at the [http://www.phys.ufl.edu/fermisurface/ Fermi Surface Database]
* The following article might also clarify the correlation between "band structure" and the term "noble metal": cite journal | doi = 10.1209/epl/i2005-10075-5 | title = Making a noble metal of Pd | year = 2005 | author = Hüger, E.; Osuch, K.
journal = EPL (Europhysics Letters) | volume = 71 | pages = 276


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Look at other dictionaries:

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  • noble metal — noun any metal that is resistant to corrosion or oxidation • Hypernyms: ↑metallic element, ↑metal • Hyponyms: ↑gold, ↑Au, ↑atomic number 79, ↑platinum, ↑Pt, ↑ …   Useful english dictionary

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  • noble metal — any of a number of metals, as gold, silver, mercury, or platinum, that resist oxidation when heated in air, and solution by inorganic acids. [1350 1400; ME: precious metal] * * * ▪ chemistry       any of several metallic chemical elements that… …   Universalium

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  • noble metal — noun Chemistry a metal (e.g. gold, silver, or platinum) that resists attack by acids and other reagents and does not corrode …   English new terms dictionary

  • noble metal — /ˈnoʊbəl mɛtl/ (say nohbuhl metl) noun a metal which is highly resistant to corrosion and oxidation …   Australian English dictionary

  • noble metal — A rare or precious metal (such as gold, silver, mercury, platinum) which conducts electricity very well, resists corrosion, and is inert; some are used as catalysts in catalytic converters …   Dictionary of automotive terms

  • noble metal — metals such as gold, silver and platinum which are resistant to corrosion by all but the most powerful acids …   Mechanics glossary


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