Chromium(III) oxide is an inorganic compound. It is one of principal oxides of chromium and is used as a pigment. Cr2O3 adopts the corundum structure, consisting of a hexagonal close packed array of oxide anions with 2/3 of the octahedral holes occupied by chromium. In nature, it occurs as the rare mineral eskolaite. Similar to corundum, Cr2O3 is a hard, brittle material (Mohs hardness 8-8.5).
The International Agency for Research on Cancer (IARC) has concluded that there is inadequate evidence in humans or experimental animals for the carcinogenicity of Chromium (III) compounds. The overall evaluation concluded that Chromium (III) compounds are not classifiable as to their carcinogenicity to humans.
\It is not readily attacked by acids or bases, although molten alkali gives chromites (salts with the Cr2O24 anion, not to be confused with the related mineral chromite). Recommendations may be superseded by new developments in these fields; readers are therefore advised to regard these recommendations as general guidelines and to determine whether new information is available. It turns brown when heated, but reverts to its dark green color when cooled. The general guidelines contained in this document apply to all of the chromium (III) compounds. Examples of such compounds include chromium (III) oxide, chromium (III) acetate, and chromium (III) nitrate. For illustrative purposes, the physical and chemical properties of several chromium (III) compounds are presented below. It is also hygroscopic.
More information: The Functions of Chromium(III) oxide
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