MadSci Network: Earth Sciences

Re: Which metal, if any, oxidizes purple?

Date: Tue Mar 2 03:27:05 2004
Posted By: Werner Sieber, Research Scientist, Coating Effects,
Area of science: Earth Sciences
ID: 1077942319.Es

Hi Dave,
Metal oxides can take on quite a variety of colors, depending not only on 
the elements, but on the oxide's (microscopic) solid structure. The color 
of the oxide is seldom a sure way to identify a metal. Colors may be due 
to the electronic absorption spectrum of the compound (oxides are chemical 
compounds), or to interference between incoming and reflected light on 
thin oxide layers. I suppose your question relates to the colored layers 
formed on blank metal if you heat it e.g. in a flame. Purple reflections 
may be seen on iron under such conditions: this is due to interference. On 
the other hand, hematite, Fe2O3, as a fine powder, can serve as a purple 
pigment. Rust, and other corrosion products, are seldom pure oxides. 
Copper, on heating,  can also take on purple hues: at certain 
temperatures, copper(I) oxide Cu2O, is stable. 
Best Regards
Werner Sieber

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