Method for producing finely divided haematite and for producing iron oxide red pigments
AssigneeLANXESS Deutschland GmbH
InventorsGuido Ketteler, Udo Holtmann, Juergen Kischkewitz
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Abstract
The present invention relates to an improved process for the production of finely divided haematite and of iron oxide red pigments made up of the finely divided haematite and the use of the finely divided haematites and iron oxide red pigments produced by this process.
Claims20
A process for the production of finely divided haematit having a particle size of less than or equal to 100 nm and a specific BET surface area of 40 m2/g to 150 m2/g, measured in accordance with DIN 66131, the process comprising:
- a) adding dilute nitric acid to a mixture of metallic iron and water at a temperature of 60 to 120° C. to produce a reaction mixture, wherein the dilute nitric acid is added at a rate sufficient to raise the temperature of the reaction mixture to a temperature of 105 to 160° C., producing an aqueous suspension of finely divided haematite, and
- b) separating the aqueous suspension of finely divided haematite from any unreacted, metallic iron.
A process for the production of finely divided haematite having a particle size of less than or equal to 100 nm and a specific BET surface area of 40 m2/g to 150 m2/g, measured in accordance with DIN 66131, the process comprising:
- a) heating a mixture of metallic iron and water to a temperature of 60 to 120° C. in a closed, pressure-tight vessel to produce a heated mixture,
- b) adding dilute nitric acid to the heated mixture of step a) to produce a reaction mixture, wherein the dilute nitric acid is added at a rate of addition sufficient to raise the temperature of the reaction mixture by at least 15° C. within less than 120 minutes after the addition of nitric acid is complete, and reacting the nitric acid and metallic iron with a corresponding pressure increase in the vessel to a pressure greater than atmospheric pressure, wherein the reaction mixture reaches a temperature of 105 to 160° C. without supply of external heat, and whereby an aqueous suspension of finely divided haematite is produced, and
- c) separating the aqueous suspension of finely divided haematite from the metallic iron.
Dependencies are inferred from the claim text.