DE1293366B - Process for the production of iron oxide brown pigments - Google Patents

Description

When exposed to aromatic nitro compounds, e.g. B. nitrobenzene, on metallic iron in the presence of aqueous, acidic solutions, especially iron (III) chloride solutions, Depending on the reaction conditions, the iron becomes iron oxides of various compositions oxidized. Without the use of special additives, one obtains an unsuitable pigment, weakly colored, brownish black iron (II / 1II) oxide, from which by glowing in the air a weakly colored, inconsistent, bluish-red iron (III) oxide is formed.

The course of iron oxidation can be influenced by specific additives It is influenced that the iron compounds produced are strongly colored pigments. So you get z. B. deep black, by annealing in air depending on the reaction conditions Iron oxide compounds changing into bright yellow% to blue-red, high-quality pigments, when in the presence of concentrated solutions hydrolytically easily cleavable salts works, while additions of salts of trivalent or tetravalent metals, e.g. B. des Aluminum, chromium, rare earths and thorium, in any concentration favor the formation of yellow to yellow-brown pigments, which when glowing on the Air change into a bright red, strongly colored iron (III) oxide with a hematite structure. The same pigments are obtained when using aqueous suspensions poorly soluble oxides, hydroxides or basic salts of such trivalent or tetravalent ones Metals instead of the salt solutions mentioned.

Other known methods give black, yellow, brown or red iron oxide pigments, which glow in the air in bright yellow to -blue-red iron (III) oxide pigments pass over when you reduce the aromatic Nitro compound with iron and aqueous salt solutions in the presence of phosphoric acid or lead compounds or from yellow, red-brown or red iron (1II) hydroxides or iron oxide or hydroxide nuclei directing oxides.

Eisenoxidbraunpigihente were previously either after one of the mentioned Process for the production of brown pigments or by mechanical mixing of Iron oxide yellow (goethite), iron oxide red (hematite) and iron oxide black (magnetite) manufactured. According to X-ray examinations, however, there are also those through direct reduction obtained iron oxide brown pigments physical mixtures of the three components a-Fe00H, ca-Fe203 and Fe304 and identical in phase to those obtained by simply mixing produced iron oxide brown pigments. They are not temperature resistant. Above 180 ° C, strong changes occur due to the elimination of water and / or oxidation Color and magnetic properties - and the pigments eventually go with increasing temperature more and more into pure, red iron (III) oxide.

It is also already known - German patent specification 881562 - iron oxide pigments by precipitating iron oxide hydrates from containing water-soluble manganese compounds Manufacture iron salt solutions with basic agents. However, one gets from this after dehydration pigments, which consist only of a mixture of iron oxide and manganese oxide. In addition, this process is technically cumbersome and expensive.

Finally, in German patent specification 143 517, a method for the production of iron pigments described, liei -dem the -oxidation of iron sulfate carried out with nitro compounds in the presence of cast steel, iron turning or filing chips and the product obtained is then heated and oxidized in an oven.

Even if iron turnings may be small amounts of manganese (up to about 0.911 / o), the reference in this patent specification left that pigments range from reddish brown to dark brown in color, depending on the amount of used Iron sulfate, does not lead to the conclusion that this known method Incandescent brown iron oxides can be produced. According to the procedure of German Patent 143 517 namely the pigments at temperatures of 180 to 250 ° C dried and oxidized. However, it is known that the red-brown to brown color of pigments obtained under mild conditions at higher Temperature stress changes to red tones.

There has now been a process for making iron oxide brown pigments by oxidizing metallic iron with aromatic nitro compounds in the presence aqueous iron (II) salt solutions at elevated temperature and heating the so obtained Pigments found under oxidizing conditions, which is characterized that one mixes of metallic iron and metallic manganese in a weight ratio Iron to manganese from 10: 1 to 50: 1 in the presence of aqueous iron (II) salt solutions or Mixtures of iron (II) and manganese (II) salt solutions at temperatures from 70 to 100 ° C reacts with aromatic nitro compounds and the product obtained after washing out and optionally drying at temperatures of 600 to 800 ° C the air glows.

In the process according to the invention, instead of the mixtures from metallic iron and metallic manganese also iron-manganese alloys or Mixtures of metallic iron and manganese alloys or mixtures of metallic Manganese and iron alloys are used.

During the oxidation, the color of the pigments can change in a known manner by adding concentrated solutions of salts of trivalent or tetravalent metals or of suspensions of poorly soluble oxides, hydroxides or basic salts of these Metals or in the presence of phosphoric acid or lead compounds or from to yellow, red-brown or red iron hydroxides or iron oxide-directing iron oxide or hydroxide nuclei can be varied.

The pigment sludge obtained after the reaction according to the invention is made up of the unreacted metals and / or alloys and the other accompanying substances separated by decanting, washing and filtering off in the usual way and then either after previous drying at about 100 ° C or immediately at temperatures of Annealed in air at 600 to 800 ° C. Depending on the annealing temperature and the Content of manganese and the other metallic components various, up to Temperature resistant up to 800 ° C, non-ferromagnetic, from a single phase existing, real brown iron oxide pigments from the crystal structure of the hematite.

By varying the particle size, the particle shape, the Particle size distribution and the manganese content can affect the color of these pigments can be changed within wide limits, so that one arrives at color nuances that after the previously customary processes are only partially or not at all obtained could. This and the surprisingly good temperature resistance of the invention The iron oxide brown pigments that can be produced are completely new areas of application for iron oxide brown opened up, especially those in which the pigments are exposed to high temperatures are exposed.

As aromatic nitro compounds, for. B. aromatic mono- or Polynitro compounds and their halogen, amino, alkyl, aryl and sulfo derivatives be used.

As hydrolytically cleavable salts z. B. the chlorides, sulfates and acetates of iron, aluminum, chromium, rare earths and des Thoriums are used. The hydrolytically cleavable salts can also be added aqueous mineral acids, such as. B. hydrochloric acid and sulfuric acid, im Reaction medium itself can be generated.

The suitable reaction temperatures are between 70 and 100 ° C, preferably at about 90 to 95 ° C. Example 1 86m1 aniline salt solution (, o: 1.087), 172m1 FeCh solution (36% FeC12), 3.93g MnCl .. - 4H20, 80g iron, 3.2 g manganese, 10 ml of H2S04 (78%) and 20 ml of nitrobenzene are heated to 95 ° C. for 1 / s hour while stirring. Then 680 g iron, 27.2 g manganese in 30 minutes and 475 g in 120 minutes ml of nitrobenzene were added in part. At a reaction temperature of 95 ° C is the reaction ended after 5 hours.

The aniline-containing reaction product is subjected to steam distillation subjected, decanted several times, vacuumed and dried.

Annealing at 600 to 800 ° C gives the dried product a dark, slightly bluish red-brown pigment.

Example 2 217 ml of AlC13 solution (7.00% Al), 231 ml of H., 0.75 ml of nitrobenzene, 75 g of iron and 6.0- manganese are heated to 90 ° C. for 1½ hour while stirring. Then 335 ml of nitrobenzene and 455 g of iron together with 36.4 g of manganese are added in parts over 4 hours and the reaction mixture is then stirred for a further 5 hours at 90 ° C. and then worked up as indicated in Example 1. Annealing at 600 to 800 ° C gives a somewhat reddish, medium brown pigment.

Example 3 217m1 AIC13 solution (7.00% Al), 231m1 H20, 75 ml nitrobenzene, 75 g of iron and 4.5 g of manganese are heated to 90 ° C. for 1 / z hour with stirring and then 300 ml of ammonia water (10 0/0 NH3) were added. Then be in 2 hours 335 ml of nitrobenzene and 455 g of iron together with 27.3 g of manganese in 4 hours in part admitted. The reaction mixture is stirred for a further 5 hours at 90 ° C and then, as indicated in Example 1, worked up. By annealing at 600 to 800 ° C a dark brown pigment is obtained. Example 4 400m1 FeS04 solution (2011 / o FeS04), 4 g ZnC12, 48.1 g wrought iron, 1.90 g manganese, 3.63 g MnS04 - H20, 222 ml NaOH (19%) and 200 ml of nitrobenzene are heated to 90 ° C. with stirring and then mixed with 14 ml of sulfuric acid (78%). Then 325 ml of nitrobenzene are added in 2 hours and 528.9 g of wrought iron and 21.2 g of manganese were added in 5 hours. The reduction time at 90 ° C is a total of 10 hours. The reaction product is, as in the example 1 indicated, worked up. Annealing at 600 ° C. gives a bluish dark brown color Pigment.

Claims (1)

Claim: Process for the production of iron oxide brown pigments by oxidizing metallic iron with aromatic nitro compounds in the presence of aqueous iron (II) salt solutions at elevated temperature and heating the pigments thus obtained under oxidizing conditions, characterized in that mixtures of metallic iron and metallic manganese are im Weight ratio of iron to manganese of 10: 1 to 50: 1 in the presence of aqueous iron (II) salt solutions or mixtures of iron (II) and manganese (II) salt solutions at temperatures of 70 to 100 ° C with aromatic nitro compounds and that The product obtained after washing out and optionally drying at temperatures of 600 to 800 ° C glows in the air.