Page 229 - Chemical and process design handbook

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CHROMIC OXIDE

Chromium oxide (chromic oxide, CrO ) is one of the oldest known green
3
pigments. It is manufactured by calcining either sodium or potassium
dichromate with sulfur in a reverberatory furnace:
Na Cr O + S → Cr O + Na SO
2 2 7 2 3 2 4
.
Hydrated chromic oxide [Cr O(OH) , Cr O 2H O] is known as Guignet’s
2 4 2 3 2
green (emerald green) and possesses a much more brilliant green color than
the oxide and has good permanency.
Chromic oxide is manufactured by roasting a mixture of sodium dichro-
mate and boric acid at a dull red heat for several hours.

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