# US 4,376,656 A · Heat resistant yellow iron oxide pigment

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- Number: US 4,376,656 A
- Document ID: US4376656A
- Status: Granted
- Kind: A
- Application number: 06/311,847
- Filed: 1981-10-16
- Granted: 1983-03-15
- Earliest claimed: 1979-05-30
- Assignees: Titan Kogyo Kabushiki Kaisha
- Inventors: Jihei Senda; Yoshihiro Inoue; Toshiaki Uenishi; Hidefumi Harada; Kouji Nakata; Akio Akagi; Yakanori Yamasaki
- Web page: https://patentgrep.com/patent/US4376656A

## CPC

- C09C 3/063: {Coating}
- C09C 1/24: Oxides of iron
- C01P 2002/50: Solid solutions
- C01P 2002/70: defined by measured X-ray, neutron or electron diffraction data
- C01P 2004/80: Particles consisting of a mixture of two or more inorganic phases
- C01P 2006/37: Stability against thermal decomposition
- C01P 2006/60: Optical properties, e.g. expressed in CIELAB-values
- C01P 2006/80: Compositional purity
- C09C: TREATMENT OF INORGANIC MATERIALS, OTHER THAN FIBROUS FILLERS, TO ENHANCE THEIR PIGMENTING OR FILLING PROPERTIES (treatment of materials specially adapted to enhance their filling properties in mortars, concrete or artificial stone C04B14/00, C04B18/00, C04B20/00); PREPARATION OF CARBON BLACK {; PREPARATION OF INORGANIC MATERIALS WHICH ARE NO SINGLE CHEMICAL COMPOUNDS AND WHICH ARE MAINLY USED AS PIGMENTS OR FILLERS}
- C01P: INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS

## Abstract

Yellow iron oxide pigments having improved heat stability are prepared by subjecting an alkaline slurry of conventional yellow iron oxide, a soluble ferric salt, sodium aluminate, and a third metal component, exemplified by antimony ion or a zinc ion/titanium ion combination, to a hydrothermal (autoclave) treatment at about 100.degree.-240.degree. C. The separated solid product has a heat stability temperature (based on the color change from yellow to red when heated) appreciably higher than that of the starting iron oxide.

## Claims

### Claim 1

A method of preparing a yellow iron oxide pigment having improved heat stability, comprising
(a) forming an aqueous slurry of from about 30 to about 200 parts of yellow iron oxide (.alpha.-FeOOH), from about 1 to about 100 parts of a soluble ferric salt selected from the group consisting of ferric sulfate, ferric chloride, ferric nitrate, ferric oxalate and ferric thiocyanate, an amount of an alkali metal hydroxide to provide the slurry with a pH of greater than 10, and from about 20 to about 100 parts of a water-soluble or alkali-soluble aluminum salt selected from the group consisting of sodium aluminate, potassium aluminate, aluminum chloride, and aluminum nitrate,
(b) adding to the above slurry from about 20 to about 100 parts as a third metallic component, a metal ion or ions having the characteristics of
(1) being capable of forming a solid solution with yellow iron oxide and
(2) having a valence of +3, or wherein a combination of ions is used having an average valence of +3, and
wherein the expression
2.5<.SIGMA.X.sub.1 .multidot.V.sub.1 <3.5
is satisfied, in which X.sub.1 =mole fraction of each metal ion added as the third component and V.sub.1 =valence thereof, the parts (a) and (b) being based on 1000 parts of water,
(c) subjecting the resultant mixture to hydrothermal treatment carried out at a temperature of from about 100.degree. C. to about 240.degree. C., for a time greater than 30 minutes, to form, on the surface of the iron oxide particle, a layer comprising (Fe Al)OOH and at least one other metal compound, in the form of a solid solution,
(d) separating the treated mixture into a solid phase and a liquid phase, and
(e) recovering the solid phase.

### Claim 2 (depends on 1)

The method of claim 1, wherein
(a) The soluble ferric salt is ferric sulfate,
(b) the alkali metal hydroxide is sodium hydroxide,
(c) the soluble aluminum salt is an alkali metal aluminate,
(d) the third metallic component is selected from the group of ions consisting of antimony, bismuth, and a combination of ions having an average valence of +3, and
(e) from about 0.3-5.0 wt.%, based on the aluminum of the soluble aluminum salt of a soluble silicate of an alkali metal hydroxide is added to the mixture prior to the hydrothermal treatment.

### Claim 3 (depends on 2)

The method of claim 2, wherein
(a) the amount of soluble aluminate added is more than 20 wt.%, based on the soluble ferric salt,
(b) the third metallic component, added as a single compound, is a compound of antimony or bismuth,
(c) the third metallic component, added as a combination of ions having an average valence of +3, is selected from the pairs consisting of Zn.sup.+2 /Sn.sup.+4, Zn.sup.+2 /Ti.sup.+4, Na.sup.+ /Nb.sup.+5, Mg.sup.+2 /Zr.sup.+4, Li.sup.+ /Nb.sup.+ 5, and K.sup.+ /Ta.sup.+5,
(d) the time of the hydrothermal treatment varies from 1/2 to about 4 hours, and
(e) the solid phase from the hydrothermal treatment is water-washed until the electric conductance of the filtrate has a value of not more than 100 .mu. /cm.

### Claim 4

A method of preparing a yellow iron oxide pigment having improved heat stability, comprising
(a) forming a first aqueous slurry of from about 30 to about 200 grams of yellow iron oxide per liter of a dilute aqueous alkaline solution,
(b) subjecting the slurry to a first hydrothermal treatment carried out at a temperature of from about 100.degree. C. to about 240.degree. C., for a time greater than 30 minutes,
(c) separating the resultant solid phase from the liquid phase,
(d) forming a second aqueous slurry of from about 30 to about 200 parts of the treated yellow iron oxide of step (c), from about 1 to about 100 parts of a soluble ferric salt selected from the group consisting of ferric sulfate, ferric chloride, ferric nitrate, ferric oxalate and ferric thiocyanate, an amount of alkali metal hydroxide to provide the slurry with a pH of greater than 10, and from about 20 to about 100 parts of a water-soluble or alkali-soluble aluminum salt selected from the group consisting of sodium aluminate, potassium aluminate, aluminum chloride and aluminum nitrate,
(e) adding to the above slurry from about 20 to about 100 parts as a third metallic component, a metal ion or ions having the characteristics of
(1) being capable of forming a solid solution with yellow iron oxide and
(2) having a valence of +3, or wherein a combination of ions is used, having an average valence of +3, and
wherein the expression
2. 5<.SIGMA.X.sub.1 .multidot.V.sub.1 <3.5
is satisfied, in which X.sub.1 =mole fraction of each metal ion added as the third component and V.sub.1 =valence thereof, the parts of (d) and (e) being based on 1000 parts of water,
(f) subjecting the resultant mixture to a second hydrothermal treatment carried out at a temperature of from about 100.degree. C. to about 240.degree. C., for a time greater than 30 minutes, to form, on the surface of the iron oxide particle, a layer comprising (Fe Al)OOH and at least one other metal compound, in the form of a solid solution,
(g) separating the treated mixture into a solid phase and a liquid phase, and
(h) recovering the solid phase.

### Claim 5 (depends on 4)

The method of claim 4, wherein
(a) the slurry of step 4(a) wherein the dilute alkaline solution is a dilute alkali metal hydroxide solution, the normality of the hydroxide solution being between about 0.5 and 3 N,
(b) the soluble ferric salt is ferric sulfate,
(c) the alkali metal hydroxide is sodium hydroxide,
(d) the soluble aluminum salt is an alkali metal aluminate,
(e) the third metallic component is selected from the ion group consisting of antimony, gallium, indium, scandium, yttrium, and bismuth, and a combination of ions having an average valence of +3, and
(f) from about 0.3-5.0 wt.%, based on the aluminum of the soluble aluminum salt of a soluble silicate of an alkali metal hydroxide is added to the mixture prior to the second hydrothermal treatment.

### Claim 6 (depends on 5)

The method of claim 5, wherein
(a) the amount of soluble aluminate added is more than 20 wt.%, based on the soluble ferric salt,
(b) the third metallic component, added as a single compound, is a compound of antimony or bismuth,
(c) the third metallic component, added as a combination of ions having an average valance of +3, is selected from the pairs consisting of Zn.sup.+2 /Sn.sup.+4, Zn.sup.+2 /Ti.sup.+4, Na.sup.+ /Nb.sup.+5, Mg.sup.+2 /Zr.sup.+4, Li.sup.+ /Nb.sup.+5, and K.sup.+ /Ta.sup.+5,
(d) the time of the first hydrothermal treatment varies from 1/2 to about 4 hours,
(e) the time of the second treatment varies from about 1/2 to about 4 hours, and
(f) the alkaline solution of the first slurry is a sodium hydroxide solution of about 1 N concentration.

### Claim 7

A method of preparing a yellow iron oxide pigment having improved heat stability, comprising
(a) forming a aqueous slurry of from about 30 to about 200 parts of yellow iron oxide (.alpha.-FeOOH), from about 1 to about 100 parts of a soluble ferric salt selected from the group consisting of ferric sulfate, ferric chloride, ferric nitrate, ferric oxalate and ferric thiocyanate, an amount of an alkali metal hydroxide to provide the slurry with a pH of greater than 10, and from about 20 to about 100 parts of a water-soluble or alkali-soluble aluminum salt selected from the group consisting of sodium aluminate, potassium aluminate, aluminum chloride, and aluminum nitrate,
(b) adding to the above slurry from about 20 to about 100 parts as a third metallic component, a metal ion or ions having the characteristics of
(1) being capable of forming a solid solution with yellow iron oxide and
(2) having a valence of +3, or wherein a combination of ions is used, having an average valence of +3, and wherein the expression
2.5<.SIGMA.X.sub.1 .multidot.V.sub.1 <3.5
is satisfied, in which X.sub.1 =mole fraction of each metal ion added as the third component and V.sub.1 =valence thereof, the parts of (a) and (b) being based on 1000 parts of water,
(c) subjecting the resultant mixture to a first hydrothermal treatment carried out at a temperature of from about 100.degree. C. to about 240.degree. C., for a time greater than 30 minutes, to form, on the surface of the iron oxide particle, a layer comprising (Fe Al)OOH and at least one other metal compound, in the form of a solid solution,
(d) separating the treated mixture into a solid phase and a liquid phase,
(e) forming an aqueous slurry of the solid phase,
(f) subjecting the slurry to a second hydrothermal treatment carried out a temperature of from about 250.degree. C. to about 350.degree. C., for a time period greater than 30 minutes, at a temperature higher that that of the first treatment,
(g) separating the treated mixture into a second solid phase and a second liquid phase, and
(h) recovering the second solid phase.

### Claim 8 (depends on 7)

The method of claim 7, wherein
(a) The soluble ferric salt is ferric sulfate,
(b) the alkali metal hydroxide is sodium hydroxide,
(c) the soluble aluminum salt is an alkali metal aluminate,
(d) the third metallic component is selected from the group consisting of antimony, gallium, indium, scandium, yttrium, and bismuth, and a combination of ions having an average valence of +3, and
(e) from about 0.3-5.0 wt. %, based on the aluminum of the soluble aluminum salt of a soluble silicate of an alkali metal hydroxide is added to the mixture prior to the hydrothermal treatment.

### Claim 9 (depends on 8)

The method of claim 8, wherein
(a) the third metallic component, added as a single compound, is a compound of antimony or bismuth,
(b) the third metallic component, added as a combination of ions having an average valence of +3, is selected from the pairs consisting of Zn.sup.+2 /Sn.sup.+4, Zn.sup.+2 /Ti.sup.+4, Na.sup.+ /Nb.sup.+5, Mg.sup.+2 /Zr.sup.+4, Li.sup.+ /Nb.sup.+5, and K.sup.+ /Ta.sup.+5,
(c) the time of the first hydrothermal treatment varies from 1/2 to about 4 hours, and
(d) the time of the second treatment varies from about 1/2 to about 10 hours.