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GB2271769A - Pure-colored iron oxide direct red pigments and a process for their production - Google Patents

Pure-colored iron oxide direct red pigments and a process for their production Download PDF

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Publication number
GB2271769A
GB2271769A GB9321805A GB9321805A GB2271769A GB 2271769 A GB2271769 A GB 2271769A GB 9321805 A GB9321805 A GB 9321805A GB 9321805 A GB9321805 A GB 9321805A GB 2271769 A GB2271769 A GB 2271769A
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iron
suspension
seed
iron oxide
pigments
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GB2271769B (en
GB9321805D0 (en
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Klaus Lerch
Gunter Buxbaum
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Bayer AG
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Bayer AG
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    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
    • C01G49/00—Compounds of iron
    • C01G49/02—Oxides; Hydroxides
    • C01G49/06—Ferric oxide [Fe2O3]
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09C—TREATMENT OF INORGANIC MATERIALS, OTHER THAN FIBROUS FILLERS, TO ENHANCE THEIR PIGMENTING OR FILLING PROPERTIES ; PREPARATION OF CARBON BLACK  ; PREPARATION OF INORGANIC MATERIALS WHICH ARE NO SINGLE CHEMICAL COMPOUNDS AND WHICH ARE MAINLY USED AS PIGMENTS OR FILLERS
    • C09C1/00—Treatment of specific inorganic materials other than fibrous fillers; Preparation of carbon black
    • C09C1/22—Compounds of iron
    • C09C1/24—Oxides of iron
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/01—Particle morphology depicted by an image
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/01—Particle morphology depicted by an image
    • C01P2004/03—Particle morphology depicted by an image obtained by SEM
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/30—Particle morphology extending in three dimensions
    • C01P2004/45—Aggregated particles or particles with an intergrown morphology
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/60—Particles characterised by their size
    • C01P2004/62—Submicrometer sized, i.e. from 0.1-1 micrometer
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2006/00—Physical properties of inorganic compounds
    • C01P2006/12—Surface area
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2006/00—Physical properties of inorganic compounds
    • C01P2006/60—Optical properties, e.g. expressed in CIELAB-values
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2006/00—Physical properties of inorganic compounds
    • C01P2006/60—Optical properties, e.g. expressed in CIELAB-values
    • C01P2006/62—L* (lightness axis)
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2006/00—Physical properties of inorganic compounds
    • C01P2006/60—Optical properties, e.g. expressed in CIELAB-values
    • C01P2006/63—Optical properties, e.g. expressed in CIELAB-values a* (red-green axis)
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2006/00—Physical properties of inorganic compounds
    • C01P2006/60—Optical properties, e.g. expressed in CIELAB-values
    • C01P2006/64—Optical properties, e.g. expressed in CIELAB-values b* (yellow-blue axis)
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2006/00—Physical properties of inorganic compounds
    • C01P2006/60—Optical properties, e.g. expressed in CIELAB-values
    • C01P2006/65—Chroma (C*)

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  • Chemical & Material Sciences (AREA)
  • Organic Chemistry (AREA)
  • Inorganic Chemistry (AREA)
  • Compounds Of Iron (AREA)
  • Pigments, Carbon Blacks, Or Wood Stains (AREA)

Abstract

Iron oxide direct red pigments, having a colour saturation in the building materials test of more than 45 CIELAB units are prepared by adding either (a) an iron (II) salt solution and metallic iron or (b) an iron (II) salt solution and an alkali solution to a seed suspension and oxidizing with an O2-containing gas, wherein the seed suspension is a suspension of yellow FeOOH star-shaped particles having a specific surface of >100 m<2>g and an average particle size <0.2 mu m. <IMAGE>

Description

2271769 PURE-COLORED IRON OXIDE DIRECT RED PIGMENTS, A PROCESS FOR THEIR
PRODUCTION AND THEIR USE This invention relates to new pure-colored iron oxide direct red pigments, to a process for their production and to their use for pigmenting building materials and ceramics.
There are four known processes for the production of red iron oxide pigments (T.C. Patton, Pigment Handbook Vol. 1, New York 1988, page 288). One of these methods is the direct precipitation of red iron oxides which is described in US-A 2,716,595. In this method, an iron(H) salt solution and an alkali solution are mixed in substantially equivalent quantities and air is passed through the iron(II) hydroxide or carbonate suspension obtained. The iron(III) oxide hydroxide seed suspension thus formed is made up into the red pigment in the presence of iron(II) salt by addition of metallic iron, heating and oxidation with oxygen-containing gases.
It is known from DE-B 1 084 405 that red pigments can only be produced from red seed suspensions and yellow pigments from yellow seed suspensions. Accordingly, the color of the end product is clearly determined by the seeds used.
NExtures of yellow and red iron oxide pigments only give brown and unattractive color tones. US-A 3,946,103 discloses a process using seed modifiers which enables pure red seed suspensions consisting of fine delta-FeOOH particles to be produced.
However, the pigments produced from those seed suspensions show inadequate purity of color so that the pure-colored aesthetic brick red tones required by the market for building materials cannot be achieved.
Accordingly, the problem addressed by the present invention was to provide improved iron oxide direct red pigments which would lead to pure- colored aesthetic brick red tones in building materials.
It has now surprisingly been found that these requirements are satisfied by new iron oxide direct red pigments which are not produced in the usual way from red seed suspensions, but instead from yellow seed suspensions, and which have a color saturation of more than 45 CIELAB units in the building materials test.
Accordingly the present invention relates to iron oxide direct red pigments, characterized in that they have a color saturation in the building materials test of more than 45 and preferably more than 45.8 CIELAB units.
In one particularly preferred embodiment, the pigments according to the invention are characterized in that, in the building materials test, the red component (a) is more than 28 and the yellow component (b) more than 29 CEELAB units.
The iron oxide direct red pigments according to the invention are obtainable by preparation of a yellow goethite seed suspension (alphaFeOOH), addition of iron(II) salt solution and metallic iron or addition of iron(II) salt solution and alkali solution, heating and oxidation with oxygen-containing gases.
It must be regarded as surprising that pure-colored iron oxide red pigments can be obtained by this process because, according to the prior art, only yellow iron oxide pigments can be produced from yellow seed suspensions.
Accordingly, the present invention relates to a process for the production of pure-colored saturated iron oxide direct red pigments by precipitation of iron(H) salts with an alkali solution and oxidation with oxygencontaining gases, addition of iron(II) salt solution and metallic iron or iron(II) salt solution and an alkali solution to a seed suspension and oxidation with oxygen-containing gases until the required color tone is obtained, wherein a yellow goethite seed suspension consisting essentially of stellately branched particles having a specific surface of greater than 100 m2/g and an average particle size of less than 0.2 Rm. is used as the seed suspension for synthesis of the pigment.
The BET surface is determined by the nitrogen one-point method (DIN 66 13 1) while particle size is determined from electron micrographs.
It is possible in the process according to the invention either directly to prepare the seed suspension in the suspension by establishing suitable conditions or to use separately prepared seeds.
The particles of the seed suspensions used in the process according to the )0 invention differ totally in shape from the conventional seeds used for the production of iron oxide yellow pigments.
Figure I shows the typical stellate branches of the goethite seeds used in the process according to the invention. For comparison, Fig. 2 shows a conventional 1. 1 yellow seed which consists of unbranched acicular individual particles and, in the pigment synthesis process, leads to a yellow iron oxide pigment.
The yellow geothite seed suspension (alpha FeOOH) is prepared by precipitation of iron(II) salts with an alkali solution followed by oxidation with oxygen-containing gases.
Z= -13 In one preferred embodiment of the process according to the invention, the seed suspension is prepared by a) forming an aqueous iron(II) sulfate solution having a concentration of from about 10 to 80 g/1 and preferably 20 to 40 g/1, b) c) adding about 0.8 to 1.0 and preferably 0.85 to 0.95 equivalent of an alkaline precipitant to said aqueous iron (II) sulfate solution to precipitate a suspension of iron (II) hydroxide or iron(II) carbonate, and addi2ing the iron (H) hydroxide or iron (II) carbonate by intensively aerating said suspension with an oxygen-containing gas to form a suspension of iron (III) oxide hydroxide of the (x-FeOOH modification.
Iron(II) salts from steel pickling plants and/or from the production of titanium dioxide may be used with particular advantage for the preparation of the iron(II) sulfate solution.
The temperature prevailing during seed formation is preferably in the range from 15 to 40C and, more preferably, in the range from 20 to 3511C.
A suspension of iron(II) hydroxide or carbonate is precipitated by addition of 0.8 to 1.0 equivalent and preferably 0.85 to 0.95 equivalent, NaOH, Na2C03, NH3, MgO and/or MgC03 preferably being used.
Precipitation is followed by oxidation preferably using air as the oxidizing agent. To this end, 20 to 300 liters air per hour and per liter suspension are introduced.
The seed suspension may then be advantageously subjected to ripening for I to 4 hours at 70 to 100'C.
A yellow seed suspension is obtained which, according to x-ray phase analysis (Siemens D-500), consists solely of goethite (alpha-FeOOH) (ASTM No.
29.07133).;" 1;' A quantity of seeds of 4 to 30 g/l, calculated as Ee,103, is preferably used for pigment formation, a quantity of 7 to 20 g/l being particularly preferred.
Pigment formation may advantageously be carried out by two methods.
In the first method, metallic iron and iron (II) salt solution are added to the seed suspension which is then heated to 70 to 100'C and preferably to 75 to 90"C and oxidized by aerating the suspensions with from about 0.2 to 50 1 air per hour and per liter suspension until the required color tone is obtained. This is the case after seed multiplication by a factor of 3 to 15 and preferably 4 to 10.
In the second method, the seed suspension is heated to 70 to 1000C and preferably to 75 to 90"C, iron(II) salt solution and an alkali solution are then added and the suspension is oxidized by aerating the suspension with from about I to 400 1 air per hour and per liter suspension until the required color tone is obtained, the pH value being in the range from 4 to 5. The required color tone is again obtained after seed multiplication by a factor of 33 to 15 and preferably 4 to 10.
The salt liquor can be removed by filtration and washing or by sedimentation. The red paste may be processed to slurries or dried and ground to form a powder-form pigment.
Soft pure-colored iron oxide pigments are obtained. a-Fe203 is detected by x-ray phase analysis (ASTM No. 33.0664).
To test the pigments for applications in building materials (DIN 53 237), pressings were produced from heavy spar. To this end, 0.5 g pigment and 10 g heavy spar were introduced into an approx. 250 ml glass shaking flask. After addition of 200 steel balls 5 mm. in diameter, the contents of the flask were shaken for 3 minutes by means of an automatic table vibrator. The mixture was compressed to form a cylinder.
The CIELAB data (DIN 6174) were determined using a color measuring instrument with an Ulbricht ball (lighting conditions d/8', standard light type C/2"); the surface reflection was included.
j 1.
J.
Table I shows the colorimetric data of a few pigments according to the invention and, for comparison, the corresponding data of a few commercial products.
The color saturation (C) is a measure of the color purity of the r pigments.
In the building materials test, the pigments according to the invention have higher color saturations than the hitherto known direct red pigments (Bayferrox 100 produced in accordance with US-A 3,946,103 or Pfizer Croma Red RO 3 0970) and the red pigments obtained by calcination of black pigments (produced, for example, in accordance with DE-A 463 773) (Bayferrox 1100).
In building materials applications, the aesthetic brick red tones required are obtained throug the pronounced yellow tinge (b) coupled with the high red gh component (a).
The present invention also relates to the use of the iron oxide red pigments produced in accordance with the invention for pigmenting building materials and ceramics both as powder-form pigments and in the form of pastes and slurries.
Figure I shows an iron oxide seed (goethite) produced by the process according to the invention which, in the pigment synthesis process, leads to a pure colored red pigment. For comparison, Fig. 2 shows a conventional yellow iron oxide seed (goethite) which leads to a yellow pigment in the pigment synthesis process.
Figure 3 shows the CIELAB data of some iron oxide red pigments in the building materials test (plotted in the a-b plane).
The following Examples, which are intended to illustrate the invention without limiting it in any way, describe the formation of the yellow seed suspension and the synthesis of the red pigment.
Example 1
22.3 1 of an iron sulfate solution from the production of titanium dioxide (concentration 25 g/1 FeS04) are initially introduced. The temperature is 31"C.
1.325 1 of a 4.75 N NaOH solution are added and the suspension is subsequently oxidized for 28 minutes with 52 1 air per hour and per liter suspension. The yellow seed suspension obtained is heated to 80"C and stirred for 2 hours.
1 Example 2
44 in 3 of an iron sulfate solution from the production of titanium dioxide (concentration 24.6 g/l FeS04) are initially introduced. The temperature is 290C.
2.85 m3 of a 4.5 N NaOH solution are added and the suspensio6 is subsequently oxidized for 30 minutes with 215 1 air per hour and per liter suspension.. The yellow seed suspension obtained is heated to 80'C and stirred for 2 hours.
Example 3
126 ml iron(II) sulfate solution (200 g/l FCS04), 1603 ml water and 450 metallic iron are added to 3271 ml of the seed suspension produced in accordance with Example 1. After heating to 85C, the suspension is oxidized with 20 1 air per hour and per liter suspension. After 40 hours, the yellow seed suspension has been converted into a pure-colored red pigment. The multiplication factor is 9. 6. The suspension is filtered, washed free from salts, dried at 85"C and the pigment obtained Z is ground.
Example 4
336 ml iron(II) sulfate solution (200 g/I FeS04), 6664 ml water and 1600 g metallic iron are added to 14,000 ml of the seed suspension prepared in accordance with Example 2. After heating to 85"C, the suspension is oxidized with 0. 5 1 air per hour and per liter suspension. After 18 hours, the yellow seed suspension has been converted into a pure-colored red pigment. The multiplication factor is 3. 7. The suspension is filtered, washed free from salts, dried at 85"C and the pigment obtained is ground.
51 -Z Example 5
The procedure is as in Example 4. After 22 hours and seed multiplication by a factor of 4.6, the suspension is filtered, washed free from salts, dried at WC and the pigment obtained is ground.
n - IL Table 1 Colorimetric data of iron oxide red pigments Testing in heavy spar (building materials applications) Pigment L a b C Remarks Pfizer Croma Red RO 309701) 51.0 28.8 22.8 36.7 Direct red Bayferrox 51002) 52.9 33 1.2 32.2 44.8 Direct red acc. to US-A-3,946,103 is Bayferrox 11002) 52.5 30.6 26.9 40.7 Calcined black iron oxide Example 3 54.6 3 2. 1 34.8 47.3 3 Example 4 57.9 30.0 '35.9 46.8 Example 5 54.5 33.1 31.6 45.8 1) A product of Pfizer 2) A product of Bayer AG WHAT I101 CLD IS:
1. An iron oxide direct red pigment having a color saturation in the building materials test of more than 45 CEELAB units.
2. Iron oxide direct red pigments as claimed in claim wherein, in the building materials test, the red component (a) is more than 28 CIELAB units and the yellow component (b) is more than 29 CIELAB units.
3. A process for the production of the pure-colored iron oxide red pigments claimed in claim 1, comprising addition of iron oxide (H) salt solution and metallic iron or iron(II) salt solution and an alkali solution to a seed suspension and oxidation with oxygen-containing gases until the required color tone is obtained, wherein a yellow goethite seed suspension consisting essentially of stellately branched particles having a specific surface of greater than 100 m/g and an average pardcle size of less than 0.2 gm, is used as the seed suspension for synthesis of the pigment.
4. A process as claimed in claim 3, wherein the seed suspension is prepared by a) forming an aqueous iron(II) sulfate solution having a concentration of from about 10 to 80 g/l; b) adding about 0.8 to 1.0 equivalent of an alkaline precipitant to said aqueous iron(H) sulfate solution to precipitate a suspension of iron(H) hydroxide or iron(H) carbonate; and C) oxidizing said iron(H) hydroxide or iron(H) carbonate by intensively aerating said suspension with an oxygen-containing gas to form said seed suspension.
5. A process as claimed in claim 4, wherein the precipitation and oxidation steps are carried out at a temperature of from about 15 to 40T. 6. A process as claimed in claim 4, wherein the precipitant comprises at least one substance selected from the group consisting of NaOR Na2C03, N1H3, MeO and M9C03. 7. A process as claimed in claim 4, wherein the seed suspension is ripened for 1 to 4 hours at a temperature of from about 70 to I 001C.
4 8. A process as claimed in claim 3, wherein the concentration of seeds in the seed suspension is from about 4 to 30 g/1. 9. A process as claimed in claim 3, wherein metallic iron and iron(II) salt solution are added to the seed suspension, the suspension is then heated to a temperature of from about 70 to 100T and is then oxidized by aerating the 1 suspension with from about 0.2 to 50 1 air per hour and per liter suspension until the required color tone is obtained.
10. A process as claimed in claim 3, wherein the seed suspension is heated to a temperature of from about 70 to 100T, iron(H) salt solution and alkali solution are then added and the suspension is then oxidized by aerating the suspension with from about I to 400 1 air per hour and per liter suspension until the required color tone is obtained.
11. An iron oxide direct red pigment as claimed in claim 1, having a color saturation in the building materials test of more than 45.8 CEELAB units.
12. A process as claimed in claim 4, wherein the aqueous iron(H) sulfate solution has a concentration of from about 20 to 40 g/l.
13. A process as claimed in claim 4, wherein about 0.85 to 0.95 equivalent of the alkaline precipitant is added in step b).
14. A process as claimed in claim 5, wherein the precipitation and oxidation steps are carried out at a temperature of from about 20 to 35T.
15. A process as claimed in claim 8, wherein the suspension is from about 7 to 20 --/1.
16. A process as claimed in claim 9, wherein the suspension is heated to a temperature of from about 75 to 90T.
17. A process as claimed in claim 10, wherein the suspension a temperature of from about 75 to 90T.
18.
air.
19. A process as claimed in claim 18, wherein said air is introduced to said suspension of iron(II) hydroxide or iron(II) carbonate in a quantity of from about to _300 liters of air per hour and per liter of said suspension.
20. Building materials containing the iron oxide direct red pigment claimed in claim 1.
is heated to A process as claimed in claim 4, wherein the oxygen-containing gas is
GB9321805A 1992-10-23 1993-10-22 Pure-colored iron oxide direct red pigments, a process for their production and their use Expired - Fee Related GB2271769B (en)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
DE4235944A DE4235944A1 (en) 1992-10-23 1992-10-23 Color-pure iron oxide direct red pigments, process for their preparation and their use
CN94101313.8A CN1106038A (en) 1992-10-23 1994-01-26 Pure-colored iron oxide direct red pigments, a process for their procuction and their use
CN94101312.XA CN1106037A (en) 1992-10-23 1994-01-26 Pure-colored iron oxide direct red pigments, a process for their procuction and their use

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GB9321805D0 GB9321805D0 (en) 1993-12-15
GB2271769A true GB2271769A (en) 1994-04-27
GB2271769B GB2271769B (en) 1995-09-13

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CN (2) CN1106038A (en)
DE (1) DE4235944A1 (en)
GB (1) GB2271769B (en)
IT (1) IT1270901B (en)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0645437A1 (en) * 1993-09-23 1995-03-29 Bayer Ag Pure-colored iron oxide direct red pigments, process for their manufacture and their use
EP0770647A2 (en) * 1995-10-26 1997-05-02 Bayer Ag Yellowish red iron oxide pigments of pure colour, process for preparing them and their use

Families Citing this family (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE50115834D1 (en) * 2000-09-26 2011-05-12 Lanxess Deutschland Gmbh CONTACT AND ADSORBER GRANULES
KR100772704B1 (en) 2005-09-29 2007-11-02 주식회사 하이닉스반도체 Method for manufacturing a semiconductor device having a tapered trench
DK3191409T3 (en) * 2014-09-11 2019-05-06 Lanxess Deutschland Gmbh RED IRON OXID PIGMENTS WITH IMPROVED COLOR VALUES
EP3216764A1 (en) * 2016-03-09 2017-09-13 LANXESS Deutschland GmbH Production of iron oxide red pigments
EP3683190B1 (en) * 2019-01-17 2022-03-09 LANXESS Deutschland GmbH Method for manufacturing hematite pigments

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB1554456A (en) * 1975-12-15 1979-10-24 Bayer Ag Process for the continuous production of iron oxide hydroxide
US4676838A (en) * 1984-11-09 1987-06-30 Bayer Aktiengesellschaft Lamellar iron oxide pigments, a process for the production thereof and the use thereof
US4753680A (en) * 1985-01-09 1988-06-28 Bayer Aktiengesellschaft Process for the preparation of bright, color-pure iron oxide red pigments

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB1554456A (en) * 1975-12-15 1979-10-24 Bayer Ag Process for the continuous production of iron oxide hydroxide
US4676838A (en) * 1984-11-09 1987-06-30 Bayer Aktiengesellschaft Lamellar iron oxide pigments, a process for the production thereof and the use thereof
US4753680A (en) * 1985-01-09 1988-06-28 Bayer Aktiengesellschaft Process for the preparation of bright, color-pure iron oxide red pigments

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0645437A1 (en) * 1993-09-23 1995-03-29 Bayer Ag Pure-colored iron oxide direct red pigments, process for their manufacture and their use
AU675161B2 (en) * 1993-09-23 1997-01-23 Bayer Aktiengesellschaft Pure-coloured iron oxide direct red pigments and a process for their production as well as their use
EP0770647A2 (en) * 1995-10-26 1997-05-02 Bayer Ag Yellowish red iron oxide pigments of pure colour, process for preparing them and their use
EP0770647A3 (en) * 1995-10-26 1998-07-01 Bayer Ag Yellowish red iron oxide pigments of pure colour, process for preparing them and their use

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JPH06256022A (en) 1994-09-13
GB2271769B (en) 1995-09-13
ITMI932169A0 (en) 1993-10-13
JP3659983B2 (en) 2005-06-15
CN1106037A (en) 1995-08-02
CN1106038A (en) 1995-08-02
IT1270901B (en) 1997-05-13
GB9321805D0 (en) 1993-12-15
ITMI932169A1 (en) 1995-04-13
DE4235944A1 (en) 1994-04-28

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