Spherical magnetite particles

Claim 2

Powdery spherical magnetite particles having an apparent density of from 0.40 to 1.00 g/cm and containing from 0.1 to 5.0 atomic % of Si with respect to Fe.

Claim 3

A process for producing powdery spherical magnetite - particles containing Si, comprising providing an aqueous suspension of colloidal Fe(OH) 2 obtained by reacting an aqueous solution of a ferrous salt with from 0.80 to 0.99 equivalent of an alkali hydroxide based on the Fe 2+ content of the aqueous solution of the ferrous salt, a water-soluble silicate having been added to the alkali hydroxide or the aqueous suspension of colloidal Fe(OH) 2 in an amount of from 0.1 to 5.0 atomic % (calculated as Si) with respect to the Fe of the ferrous salt; oxidizing the Fe(OH) 2 in the aqueous suspension at a temperature from 70 to 100°C by blowing a molecular oxygen-containing gas into the suspension, thereby forming spherical magnetite particles after the oxidation reaction; adding an alkali hydroxide to the aqueous suspension in an amount of more than 1.00 equivalent with respect to residual Fe 2+ in the aqueous suspension; and subjecting the resultant aqueous suspension to an oxidation treatment by blowing a molecular oxygen-containing gas into the suspension at a temperature from 70 to 100°C.

Claim 4

A process for producing powdery spherical magnetite - particles containing Si, comprising providing an aqueous suspension of colloidal Fe(OH) 2 obtained by reacting an aqueous solution of a ferrous salt with from 0.80 to 0.99 equivalent of an alkali hydroxide based on the Fe 2+ content of the aqueous solution of the ferrous salt, a water-soluble silicate having been added to the alkali hydroxide or the aqueous suspension of colloidal Fe(OH) 2 in an amount of from 0.1 to 5.0 atomic % (calculated as Si) with respect to the Fe of the ferrous salt; oxidizing the Fe(OH) 2 in the aqueous suspension at a temperature from 70 to 100°C by blowing a molecular oxygen-containing gas into the suspension, thereby forming spherical magnetite particles after the oxidation reaction; adding an alkali hydroxide to the aqueous suspension in an amount of more than 1.00 equivalent with respect to residual Fe 2+ in the aqueous suspension; and subjecting the resultant aqueous suspension to an oxidation treatment by blowing a molecular oxygen-containing gas into the suspension at a temperature from 70 to 100°C.

Claim 5

A paint comprising magnetite particles as claimed in claim 1 or which have been produced by a process as claimed in claim 2 as a pigment dispersed in a vehicle therefor.

Claim 6

Magnetic toner particles suitable for use in electrophotography comprising magnetite particles as claimed in claim 1 or which have been produced by a process as claimed in claim 2 dispersed in a binder resin.