If the chromic anhydride is pretreated, the performance of the produced pigment will be increased by 1200 ° C for 30 min, and the obtained chromium oxide has a specific surface area of 1.48 m 2 /g and the control product which is only thermally decomposed with chromic anhydride has a specific surface area of only 0.78 m 2 /g.
The chromic anhydride can also be treated with an aqueous ammonia solution such that the ratio NH3/CrO3 ≥ 0.1 and H2O > 3%. For example, 99.8% of chromic anhydride 100 parts are treated with 136 parts, 1O2 parts, 68 parts, 34 parts or 6.8 parts of ammonia solution, respectively, so that the ratio NH3/CrO3 is 2.0, 1.5, 1.0, 0.5 or 0.1, respectively. Heating at 1000 ° C for 30 min at 200 ° C, the specific surface area of chromium oxide is 2.76 m 2 / g, 2.64 m / g, 2.54 m / g, 1.98 m / g or 1.4 m / g, respectively, while untreated chromic anhydride The chromium oxide after thermal decomposition has a specific surface area of only 1.14 m/g.
The chromic anhydride aqueous solution is mixed with ethanol, treated at 98 ° C for 8 h, cooled, filtered and dried to obtain a black chrome oxide gel to a diameter of 1 um, and then calcined at 700 ° C for 3 h to obtain a granular chromium oxide with good dispersion performance and a specific surface area of 23.5. M2/g, density 5.21 g/cm3.
The chromic anhydride thermal decomposition method is also used to prepare chromium oxide having a valence of more than 4 and less than 6, such as Cr2O5 and Cr3O8. The difference from the Cr2O3 is that the heating rate is very slow, and the maximum temperature is only 254 ° C (made Cr2O8) or 370 ° C (made Cr2O5). These black powders are intermediates for the production of the magnetic recording material CrO2.
