| 摘要 |
Carrier particles of substantially uniform particle size and substantially spherical shape comprising hard magnetic ferrite material having a single-phase hexagonal crystalline structure of the formula: MO(solid dot)(Fe2O3)x (A) where M is strontium or barium and x is 5 to 6 suitable for magnetic brush development of electrostatic charge patterns and having a reduced tendency towards early life dusting, are prepared by: (i) mixing an aqueous solution containing strontium ions and iron (III) ions or barium ions and iron (III) ions in amounts sufficient to provide the strontium ferrite or barium ferrite of formula (A); (ii) reacting the mixture formed in step (i) with an alkaline aqueous ammonium hydroxide solution having an alkalinity of at least 0.1N to form finely divided co-precipitated particles of strontium hydroxide and iron (III) hydroxide or barium hydroxide and iron (III) hydroxide; (iii) separating the co-precipitated particles from the aqueous mother liquor; (iv) washing the resultant co-precipitated particles; (v) mixing the washed co-precipitated particles obtained from step (iv) with an organic binder and water, as a solvent, to form a slurry; (vi) spray drying the slurry to obtain green beads of substantially uniform particle size and substantially spherical shape, and (vii) firing the beads at a temperature ranging from approximately 900 degrees C. to 1100 degrees C. for a period of time of from approximately 7 to 10 hours and obtaining magnetic carrier particles of substantially uniform particle size and substantially spherical shape comprising hard magnetic ferrite material having a single-phase, hexagonal crystalline structure of the formula (A).
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