Mfr. of yellow or yellow-brown iron oxide pigments - using iron turnings, ferrous chloride soln., nitrobenzene and sulphites

摘要

Yellow to yellow-brown iron oxide-hydrate pigments are mfd. by the oxidn. of iron and the simultaneous redn. of aromatic nitro-cpds. in the presence of iron salt solns. The oxidn. of the iron is carried out in the presence of the oxyacids of sulphur or their alkali(ne earth) metal salts where the average oxidn. stage of the sulphur is =5. The oxidn. of the iron is pref. carried out in the presence of the Na, K, NH4, Mg and/or the Ca salts of sulphurous acid, thiosulphurous acid, thio-sulphuric acid, dithionous acid, dithionic acid and/or pyrosulphurous acid, using 2-20% S w.r.t. the wt. of nitrobenzene. The iron oxide pigments obtd. may be used for the prodn. of yellow and red pigments. No foreign hydrolysable metal ions are used in the process which might form oxide or oxide-hydrate impurities in the iron oxide pigments so the iron oxide content in the latter is increased by 2-7%. By subsequent heating of the pigments, various shades of red can be obtd. The colour brightness and purity is superior to that of conventional pigments and the colouring power is increased by =45%; only a very small amt. of the sulphur cpds. are occluded in the pigments.