Plate-like magnetite particles, plate-like maghemite particles and process for producing the same

Claim 2

Poreless and non-sintered plate-like magnetite particles having average plate surface diameters of from 0.03 to 0.50 µm and a specific surface area of from 7 to 30 m²/g.

Claim 3

Particles according to claim 1, wherein the particles have an aspect ratio of from 2 : 1 to 10 : 1.

Claim 4

Poreless and non-sintered plate-like maghemite particles having average plate surface diameters of from 0.03 to 0.50 µm and a specific surface area of from 7 to 30 m²/g.

Claim 5

Poreless and non-sintered plate-like maghemite particles having average plate surface diameters of from 0.03 to 0.50 µm and a specific surface area of from 7 to 30 m²/g.

Claim 6

Particles according to claim 3, wherein the particles have an aspect ratio of from 2 : 1 to 10 : 1.

Claim 7

A process for producing poreless and non-sintered plate-like magnetite particles, which process comprises reacting a ferrous salt in aqueous solution with an alkali carbonate in aqueous solution to form an aqueous solution of FeCO₃, and passing an O₂-containing gas through the FeCO₃-containing solution to oxidize the FeCO₃ to form the magnetite particles, wherein the ferrous salt and the alkali carbonate are reacted in a molar ratio defined by formula (I): and the oxidization is carried out be adding an aliphatic oxycarboxylic acid, or a salt thereof, in an amount of from 0.01 to 2.0 mol% based on the Fe to the aqueous solution of a ferrous salt, the aqueous solution of an alkali carbonate or the FeCO₃-containing aqueous solution before passing the O₂-containing gas through the FeCO₃-containing solution.

Claim 8

A process for producing poreless and non-sintered plate-like magnetite particles, which process comprises reacting a ferrous salt in aqueous solution with an alkali carbonate in aqueous solution to form an aqueous solution of FeCO₃, and passing an O₂-containing gas through the FeCO₃-containing solution to oxidize the FeCO₃ to form the magnetite particles, wherein the ferrous salt and the alkali carbonate are reacted in a molar ratio defined by formula (I): and the oxidization is carried out be adding an aliphatic oxycarboxylic acid, or a salt thereof, in an amount of from 0.01 to 2.0 mol% based on the Fe to the aqueous solution of a ferrous salt, the aqueous solution of an alkali carbonate or the FeCO₃-containing aqueous solution before passing the O₂-containing gas through the FeCO₃-containing solution.

Claim 9

A process for producing poreless and non-sintered plate-like maghemite particles, which comprises heating plate-like magnetite particles obtained from a process as defined in claim 5 in air at from 200 to 400 °C.

Claim 10

A process according to claim 5, wherein the final magnetite particles have average plate surface diameters of from 0.03 to 0.50 µm and a specific surface area of from 7 to 30 m²/g.

Claim 11

A process according to claim 6, wherein the final maghemite particles have average plate surface diameters of from 0.03 to 0.50 µm and a specific surface area of from 7 to 30 m²/g.

Claim 12

A magnetic recording medium, electromagnetic wave absorber, electromagnetic wave shield, paint or colourant comprising particles as defined in any one of claims 1 to 4.