| 摘要 |
<p>1498300 Low S-containing Cr 2 O 3 pigment BAYER AG 1 April 1975 [3 April 1974] 13188/75 Heading CIA Low S-containing Cr 2 O 3 pigment (e.g. less than 0À005% by wt.) is prepared by reducing a finely divided alkali metal chromate in a heated hydrogen-containing reaction zone at a temperature of from 900 to 1600‹ C., the reaction zone being followed by a dwell zone in which a temperature of 900-1600‹ C. is established by additional direct heating by introducing an oxygen-containing gas into the dwell zone; the Cr 2 O 3 is recovered in the form of an aqueous suspension. Reduction is preferably carried out in the presence of salt forming gas (e.g. Cl 2 , HCI, Br 2 , HBr, NO, NO 2 or CO 2 ) to bind the alkali metal ions. Ideally, the temperature difference between dwell and reaction zones is no more than 200‹ C. Advantageously, finely divided SiO 2 is added to the chromate before introduction into the reaction zone; the SiO 2 may be formed by vapour phase hydrolysis of SiCl 4 yielding 0À1 to 2% by wt. of SiO 2 .</p> |
