25 октября, 2015 
Pokraskin Alkali dichromates are used as starting materials for the production of chromium(III) oxide pigments. They are available as bulk industrial products in the required purity. High impurity levels have an unfavorable effect on the hue.
Reduction of Alkali Dichromates
In industrial processes, solid alkali dichromates are reacted with reducing agents such as sulfur or carbon compounds. The reaction is strongly exothermic, and with sulfur proceeds as follows:
Na2Cr2O7 + S ^Cr2O3 + Na2SO4
Washing can then easily separate sodium sulfate because it is water-soluble. The use of sulfur was first described in 1820 [3.55]. Roth described the use of K2Cr2O7 in 1927 [3.56]. If charcoal is used in place of sulfur, Na2CO3 is formed as byproduct [3.57].
Finely divided sodium dichromate dihydrate is mixed homogeneously with sulfur. This mixture is then reacted in a furnace lined with refractory bricks at 750-900 °C. An excess of sulfur is used to ensure completion of the reaction. The reaction mass is leached with water to remove water-soluble components such as sodium sulfate and non-reacted chromate. The solid residue is then separated, dried, and ground.
If potassium dichromate is used instead of sodium dichromate, a green pigment with a more bluish hue is obtained.
If it is to be used as a pigment in paints and lacquers, chromium oxide green can be subjected to jet milling (micronization) to obtain the required properties (e. g., gloss).
Опубликовано в рубрике 