Process for producing magnetite particles

Abstract

This invention relates to a process for producing magnetite particles having a coercivity of 6.366 kA/m to 10.345 kA/m (=80 to 130 Oe) and an octahedral particle shape, comprising heating an alkaline component and an iron(II) component in the form of an aqueous solution to a temperature of 50° C. to 100° C., whereby the molar ratio of iron(II) component to one equivalent of alkaline component is 0.38 to 0.45, and treating the suspension with an oxidizing agent at a rate of oxidation of 20 to 50 mol. % Fe(II)/h until the iron compound has an Fe(III) content of more than 65 mol. %, and then again adding an Fe(II) component in the form of an aqueous solution at a molar ratio of Fe(II) to one equivalent of total alkaline component used is 0.47 to 0.49, and treating the suspension with an oxidizing agent, at a rate of oxidation is 20 to 50 mol. % Fe(II)/h until the iron compound has an Fe(III) content of more than 65 mol. %, and filtering the suspension, and washing, drying and grounding the residue.

1 - 5 . Cancelled  
     
     
         6 . A process for coloring matter comprising contacting the matter with an effective amount of a magnetite having a coercivity of 6.366 kA/m to 10.345 kA/m (=80 to 130 Oe) and an octahedral particle shape comprising 
 a) placing an alkaline component in the form of an aqueous solution under a protective gas.    b) heating the alkaline component to a temperature of 50° C. to 100° C.    c) adding an iron(II) component in the form of an aqueous solution whereby the molar ratio of iron(II) component to one equivalent of alkaline component is 0.38 to 0.45, while maintaining the temperature at 50° C. to 100° C.    d) treating the suspension obtained in c) with an oxidizing agent, whereby the rate of oxidation is 20 to 50 mol. % Fe(II)/h until the iron compound has an Fe(III) content of more than 65 mol. %.    e) after the oxidation in d), again adding an Fe(II) component in the form of an aqueous solution to the suspension obtained in d) whereby the molar ratio of Fe(II) in c) to one equivalent of total alkaline component used is 0.47 to 0.49.    f) treating the suspension obtained in e) with an oxidizing agent, whereby the rate of oxidation is 20 to 50 mol. % Fe(II)/h until the iron compound has an Fe(III) content of more than 65 mol. %.    g) filtering the suspension, and washing, drying and grounding the residue.    
     
     
         7 . The process of  claim 6 , wherein the matter comprises paper, plastic, paint, fiber, concrete, dye, concrete, or concrete moldings.  
     
     
         8 . The process of  claim 6 , wherein the matter is a device useful in electrophotography.  
     
     
         9 . The process of  claim 6 , wherein the matter is a device useful in magnetic toners.  
     
     
         10 . A magnetic toner comprising the magnetite obtained by the process of  claim 6.