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Chromium(III) oxide is amphoteric. Although insoluble in water, it reacts with acid to produce salts of hydrated chromium ions such as [Cr(H 2 O) 6] 3+. [11] It is also attacked by concentrated alkali to yield salts of [Cr(OH) 6] 3−. When heated with finely divided carbon or aluminium, it is reduced to chromium metal: Cr 2 O 3 + 2 Al → 2 Cr ...
As hexavalent chromium compounds are prohibited for use in the EU based on ROHS regulations and are toxic and carcinogenic, solutions based on molybdate are proposed as a replacement (e.g. molybdate 30-100g/ boric acid 10-18 g/manganese sulfate 0.5 - 5 g/1 liter of water, 0.1 - 20 A/dm2, 0.1–15 minutes). [32] [33]
Chromium compounds are compounds containing the element chromium (Cr). Chromium is a member of group 6 of the transition metals. The +3 and +6 states occur most commonly within chromium compounds, followed by +2; charges of +1, +4 and +5 for chromium are rare, but do nevertheless occasionally exist. [3] [4]
In the case of titanium, niobium, and stainless steel, the colour formed is dependent on the thickness of the oxide (which is determined by the anodizing voltage). Chemically coloring a metal is distinct from simply coating it using a method such as gilding or mercury silvering , because chemical coloring involves a chemical reaction, whereas ...
In physical chemistry and engineering, passivation is coating a material so that it becomes "passive", that is, less readily affected or corroded by the environment. . Passivation involves creation of an outer layer of shield material that is applied as a microcoating, created by chemical reaction with the base material, or allowed to build by spontaneous oxidation
The chromate coating acts as paint does, protecting the zinc from white corrosion, thus making the part considerably more durable, depending on the chromate layer's thickness. [ 8 ] [ 9 ] [ 10 ] The protective effect of chromate coatings on zinc is indicated by color, progressing from clear/blue to yellow, gold, olive drab and black.
The international pictogram for oxidizing chemicals. Dangerous goods label for oxidizing agents. An oxidizing agent (also known as an oxidant, oxidizer, electron recipient, or electron acceptor) is a substance in a redox chemical reaction that gains or "accepts"/"receives" an electron from a reducing agent (called the reductant, reducer, or electron donor).
According to Gettens, especially when mixed with organic colors, it can take on a green tone. This effect is attributed to reduction of some chromate to chromium(III) oxide. [6] Owing to its high lead content, the pigment is prone to discoloration over time, particularly in the presence of sulfur compounds.