United States Patent (19) 11) 4,084,984 Hund et al. 45 Apr. 18, 1978

(54) TEMPERATURE-STABLE INORGANIC (56) References Cited YELLOW PGMENTS U.S. PATENT DOCUMENTS 75) Inventors: Franz Hund, Krefeld-Bockum; 3,214,283 10/1965 Chopoorian ...... 106/304 Wilhelm Holzmagel; Henning Erfurth, Primary Examiner-Winston A. Douglas both of Krefeld; Friedrich Assistant Examiner-J. V. Howard Kinderwater, Leverkusen; Willi Attorney, Agent, or Firm-Burgess, Dinklage & Sprung Hennings, Krefeld, all of Germany 57 ABSTRACT 73) Assignee: Bayer Aktiengesellschaft, A temperature-stable inorganic yellow pigment of the Leverkusen, Germany composition FeTiO. . x TiO2, where x is from 0 to about 15, with a particle diameter of less than about 1 micron is produced by forming an aqueous suspension (21) Appl. No.: 497,366 of at least one finely divided iron compound selected from the group consisting of iron oxide, iron oxide 22 Filed: Aug. 14, 1974 hydroxide, iron hydroxide and iron carbonate and at least one finely divided titanium compound selected 30 Foreign Application Priority Data from the group consisting of titanium dioxide and tita nium dioxide oxide hydrate, the iron and titanium com Aug. 30, 1973 Germany ...... 2343704 pounds being present in accordance with the stoichio metric composition FeTiOs. x TiO, where x is from 0 51) Int, Cl’...... C09C 1/36 to about 15, removing the aqueous phase from the 52 U.S. C...... 106/300; 106/304; mixed suspension, and calcining the residue at a temper 106/306 ature from about 600 C to 1100 C. 58) Field of Search ...... 106/304,300; 42.3/598, 423/594 6 Claims, No Drawings 1. 4,084,984 2 trivalent iron and tetravalent titanium to temperatures TEMPERATURE-STABLE NORGANIC YELLOW of 1400° C. The high production temperature, or rather PGMENTS the sintering which it promotes, gives rise to the forma tion of very coarse solid particles having a particle Chromates (VI) of calcium, strontium, barium, lead 5 diameter which exceeds the optimum particle diameter and zinc, litharge (PbO), Naples yellow (lead antimon for pigments (0.1 to 1 micron), and which therefore ate), cadmium yellow, iron oxide yellow and the rutile have a dark, dirty brown color coupled with low tinting mixed phases of TiO, with nickel-antimony or chromi strength. However, the temperature-stable inorganic um-antimony oxides are used as inorganic yellow pig yellow to yellowish-brown pigments according to the ments. Of these inorganic yellow pigments, the iron 10 present invention based on FeTiOs crystallizing in the oxide yellows (a-and-y-FeCOH) are only temperature pseudobrookite lattice are obtained by virtue of the fact stable up to about 220 C. The yellow pigments contain that, by using suitable reactive iron and titanium com ing chromate (VI) and Pb cannot always be used either. pounds in suitable relative quantitative ratios at such a The fine, temperature-resistant yellow cadmium sulfide low calcination temperature, optionally even by using a and rutile mixed phase pigments are generally too ex 15 weakly reducing calcination atmosphere such as SO, or pensive for mass colouring purposes, Organic yellow CO for the first quarter of the overall calcination time, pigments are thermally and optically too unstable for the components are completely reacted to form the the above-mentioned applications and are also expen compound FeTiOs or its solid solution with TiO, in sive. Accordingly, there is a considerable demand for which the particle diameter of the pigments remains heat- and light-stable, relatively inexpensive inorganic 20 below 1.0 micron. Suitable reactive iron compounds yellow pigments of high tinting strength which can be include iron (II) oxide, iron (II) hydroxide, iron (II) used, for example, for coloring yellow, yellowish carbonate, iron (III) oxide hydroxide and amorphous brown to yellowish-orange, organic plastics processed iron (III) hydroxide or FeO in finely divided form. under heat at temperatures above 200 C (polyvinyl Iron (II) hydroxide or carbonate, iron oxide hydroxide chloride, polyethylene, polystyrene and others), or in 25 or amorphous iron hydroxide can be obtained for exam organic glazes for enamel and ceramics, ceramic masses ple in known manner from iron (II) salt solutions, pref. or concrete roof-tile granulates heated to temperatures erably from iron sulfate solutions with alkali metal, above 500 C. ammonium or alkaline earth metal hydroxide or carbon It is accordingly an object of the present invention to ate. Fe3O4 can be used with advantage in the form in provide stable yellow pigments. 30 which it accumulates after nitrobenzene reduction with This and other objects and advantages are realized in iron in concentrated FeCl-solution, i.e. in the form of a accordance with the present invention pursuant to finely divided black sludge (German Pat, No. 463,773). which there is provided a temperature-stable inorganic One particularly suitable reactive, finely divided tita yellow pigment of the composition FeTiO5. x. TiO, nium dioxide is the uncalcined, washed titanium dioxide where x is from 0 to about 15, with a particle diameter 35 aquate sludge which accumulates during the hydrolysis of less than about 1 micron. The invention also provides of titanium (IV) salts on an industrial scale, preferably a process for producing such a pigment comprising during the hydrolysis of titanium sulfate, The low sul forming an aqueous suspension of at least one finely fate content of the washed white sludge is of particular divided iron compound selected from the group consist advantage for establishing the weakly reducing calcina ing of iron oxide, iron oxide hydroxide iron hydroxide 40 tion atmosphere in the first quarter of the overall calci and iron carbonate and at least one finely divided tita nation time. Chloride hydrolysis sludge, like an iron (II) nium compound selected from the group consisting of hydroxide or carbonate precipitated from iron (II) chlo titanium dioxide and titanium dioxide oxide hydrate, the ride solution, can be improved in regard to its suitability iron and titanium compounds being present in accor as a starting material by the absorption of sulfate ions or dance with the stoichiometric composition FeTiO5. x 45 by the addition of elemental sulfur or carbon. Reducing TiO, where x is from 0 to about 15, removing the aque agents, such as finely divided carbon or sulfur, can be ous phase from the mixed suspension, and calcining the used in quantities of about 0.1 to 10% by weight, prefer residue at a temperature from about 600 C to 1100° C. ably in quantities of about 0.2 to 5% by weight (based The pigments according to the invention are heatsta on the end pigment). Under the same calcination condi ble, relatively inexpensive, yellow, yellowish-brown to 50 tions, the particle diameters of the pigments obtained yellowish-orange colored, inorganic pigments of high are finer, the more finely divided the starting materials tinting strength which consist of FeTiOs crystallizing used. Preferably the particle sizes of the starting iron in the pseudobrookite lattice or of mixtures of FeTiOs and titanium compounds is less than about 0.50 micron crystallizing in the pseudobrookite lattice with TiO, of and especially less than about 0.30 micron, They can be rutile or anatase structure. The excess TiO, in relation to 55 present as fine sludges. Such fine sizes necessarily result pure FeTiOs is probably present either in chemical in a large surface area, e.g. more than about 2 m/g and solution in the FeTiOs crystallizing in the pseubobroo preferably more than about 3 m/g. The yellow, yellow. kite lattice, with heterotype mixed-phase formation, or ish-orange or yellowish-brown colour attributable to in the form of TiO, crystallizing in the anatase or rutile the particle size of the calcined pigment can be influ lattice. enced not only by the particle size of the starting materi FeTiOs, pseudobrookite, crystallizes orthorhombi als, but also by their relative quantitative ratios, i.e. by cally with a = 9.79; b = 9.93 and c = 3.72 A and four the value of x in the general formula FeTiO, x. TiO, molecules of the compound in the elemental cell and is the where x is from 0 to 15, preferably from 0.5 to 10 and, thermodynamically stable modification from room tem with particular preference, from 1 to 5, With a given perature up to about 1200° C (C.R.Ser. C. 263, 1223, 65 starting material and calcination conditions, the color 1966). It has an average refractive index of about 2.40. It and tinting strength of the pigment may be changed is known that FeTiOs crystallizing in the pseudobroo from yellowish-brown through yellowish-orange and kite lattice can be obtained by heating compounds of yellow to a pale yellow by increasing x, values of about 4,084,984 3 4. 1 to 5 for x are of particular interest for a number of with cg of washed TiO,-white sludge resulting from the applications. Wherex has a value about 2 to 3, heatsta hydrolysis of titanium sulfate on a industrial scale with ble inorganic yellow pigments are obtained which, al a TiO-content of d%. The mixture was either filtered though substantially equivalent in terms of tinting under suction, concentrated by evaporation or spray strength to the thermally unstable iron oxide hydroxide 5 dried, and the filter cake or the dry product was cal yellow pigments crystallizing in the goethite lattice, cined in parallel current for the time indicated at the have a distinctly purer color. w temperature indicated either in an open, covered cruci In a first embodiment of the process according to the ble, covered for the first quarter of the overall calcina invention, a finely divided Fe3O-black sludge and a tion time and then opened, or in a rotary tubular kiln. TiO, white sludge are mixed in accordance with the O The pigment obtained after grinding, with the composi general formula FeTiO. x. TiO, the resulting mixed tion FeTiO3.x. TiO, varies from 0 Six S. 10 accord suspension is washed and/or concentrated by evapora ing to the data of Table 1. A reducing agent, for exam tion or spray-dried or filtered and dried, or only filtered, ple sulfur or finely divided carbon (carbon black), can and the filter cake or dry material is calcined at temper be added to the mixture of sludges in quantities of from atures above 600' C, preferably at temperatures of from 15 0.2 to 5.0%, based on the end pigment, so that under 750 to 1000' C, to form pigments of suitable particle size otherwise the same conditions the color of the pigments and with the required composition. can be made more yellow through the reducing effect In a second embodiment, a TiO-suspension is mixed of the gas atmosphere during the first part of the calci. with iron (II) salt solution and the mixture is adjusted nation process. The color of the pigment changes from with alkali metal, ammonium or alkaline earth metal 20 yellowish-brown to brownish-yellow, orangy yellow, hydroxide or carbonate to pH-values in the range of yellow and pale yellow with increasing value of x. about 5 to 12, preferably about 7 to 10. The resulting mixed precipitates can then be further treated in the EXAMPLE 2. same way as already described with reference to the In accordance with Table 2, a ml of an iron (II) sul first embodiment. 25 fate solution containing big of FeSO per liter were The color of the pigments produced in accordance mixed while stirring with c g of washed TiO-sludge with the invention can be further influenced by the resulting from the hydrolysis of titanium sulfate on an selection of the calcination temperature and duration of industrial scale with a TiO, content of d2%. 2 to 4 molar calcination. With increasing calcination temperature of NaOH or NaCO-solution was then added to the sus time of calcination, but under otherwise the same condi 30 pension up to or slightly above neutral point, so that the tions, the color changes from a pale yellow through a iron (II) ion was precipitated in the form of iron (II) pure, orangy yellow to a brownish yellow correspond hydroxide or carbonate. The mixed suspension was ing to the resulting growth of the pigment particles. The washed, suction filtered or spray-dried. The filter cake calcination time is from about 0.1 to 10 hours, prefera or the dry product was then calcined in parallel current bly from 0.5 to 5 hours. 35 or counter current for the period indicated at the tem The process according to the invention is illustrated perature indicated either in an open, covered crucible, in the following Examples. covered for the first quarter of calcination, and then opened, or in a tubular rotary kiln. The pigment ob . . . . . EXAMPLE.1 tained after grinding, with the composition FeTiO. x: In accordance with the data in Table 1, a g of a TiO, varies from 0 SxS 4. The color of the pigments washed Fe3Oblack sludge, of the kind which accumu changed from yellowish brown through brownish yel lates during nitrobenzene reduction with iron in con low, orangy yellow to pure yellow with increasing centrated FeCl-solution on an industrial scale, with an content of x. TiO2 (unless otherwise indicated, percent Fe3O-content (calculated from total iron) correspond age contents are expressed in per cent by weight). - ing to b% of FeO were mixed with intensive stirring Table 1 Production conditions and color of pigments according to Example 1 k in 2 of FeO. Calcination x in a in g calculated c in g d in % time and Color Example FeTiO, of FeO from total of TiO, of temperature of the No. x. TiO, sludge iron sludge TiO, in C Pigment 1.1 0.0 94.22 33.90 81.95 19.50 2. h. at 900 yellow-brown 1.2 : 0.5 80.87 39.50 98.88 24.24 1 h. at 900' brownish-yellow 1.3 1.0 94.22 33.90 163.90 1950 2 hr., at 900 yellow-orange 1.4 2.0 94.22 33.90 245.85 1950 2 h. at 900 yellow tinged with orange 1.5 3.0 94.22 33.90 327.78 1950 2 h. at 1000 yellow 1.6 3.0 - 98.57 32.40 280.20 22.81 h, at 800' dirty yellow 2% S - - 1.7 3.0+ . 88.63 36.04 248.14 25.76 h. at 800 dirty yellow 1% carbon black 1.8 4.0 78.67 40.60 327.43 24.40 1 h. at 900' dirty yellow 1.9 10.0 80.87 39.50 684.80 2S67 15 Mins at 900 45 Mins at 700 pale, light yellow . . 4,084,984 5 6 Table 2 Production conditions and color of pigments according to Example 2 Calcination x in a in ml c ing Temperature Example FeTiO of FeSO bin g/1 of TiO, din% C No. ió, solution of FeSO4 sludge of TiO, (time 1 hr) Color of the pigment 2. 0.0 688.7 22.06 54.70 25.83 800 yellowish brown 2.2 10 545.2 22.30 249.00 25.67 900 yellow-brown 2.3 2.0 272.6 22.30 186.80 25.67 900 brown-yellow 2.4 3.0 255.3 23.80 263.67 24.24 880 yellow 2.5 3.0 545.2 22.30 496.30 25.76 800 yellow tinged with brown 2.6 4.0 272.6 22.30 31.30 25.67 900 . pale yellow The pigments so produced can be incorporated to the selected from the group consisting of iron oxide, iron extent of about 0.5 to 5% or more by weight into molten oxide hydroxide, iron hydroxide and iron carbonate, plastics such as cellulose acetate which is used for mak 15 forming a sludge of said finely divided iron compound, ing shaped objects. It can also be mixed in similar adding to said sludge a titanium dioxide white sludge amounts into other organic plastics, inorganic glazes for resulting from the hydrolysis of a titanium (IV) salt, enamels and ceramics, ceramic masses or concrete roof thereby to form an aqueous suspension, the iron com tile granulates. pound and titanium dioxide being present in accordance It will be appreciated that the instant specification 20 with the stoichiometric composition FeTiO. x. TiO, and examples are set forth by way of illustration and not where x is from about 0.5 to about 10, removing the limitation, and that various modifications and changes aqueous phase from the mixed suspension, and calcining may be made without departing from the spirit and the residue at a temperature from about 600 C to 1100' scope of the present invention. C, the first quarter calcination being carried out in a What is claimed is: 25 weakly reducing atmosphere whereby the pigment par 1. A temperature-stable inorganic yellow pigment of ticles are less than about 1 micron, the composition FeTiO3. x. TiO2, where x is from about 4. A process according to claim3, wherein a reducing 0.5 to about 10, with a particle diameter of less than agent is added to the mixed suspension in about 0.1 to about 1 micron. 10% by weight, based on the end pigment, 2. A temperature-stable inorganic yellow pigment 30 5. A temperature-stable yellow pigment according to according to claim 1, wherein x is from about 1.0 to 5. claim 1 present as the coloring agent in an organic plas 3. A process for the production of a temperature tic, inorganic glaze of an enamel or ceramic, ceramic stable inorganic yellow pigment, comprising adding to a mass or concrete roof-tile granulate. solution of an iron (II) salt at least one alkali metal, 6. A pigment according to claim 5 present as the ammonium or alkaline earth metal hydroxide or carbon 35 coloring agent in an inorganic glaze of an enamel or ate to precipitate at least one finely divided iron com ceramic, ceramic mass or concrete roof-tile granulate. pound having a specific surface greater than 3 m/g and :

45

50

55

60

65