Method for producing oxide coated iron powder of controlled resistance for electrostatic copying systems

Abstract

Abstract Oxide coated iron powder required as a carrier in electrostatic copying systems has a uniform oxide film, and has a resistance which can be selectively controlled between 102 and 1010 ohms, when produced by a five step program of: Step 1 - fluidizing iron powder in air while heating to a temperature between 500* and 750*F, to initiate an exothermic reaction; and thereafter to a higher peak temperature between 750* and 1600*F, desirably to about 950*F, principally by the heat of exothermically oxidizing iron, which can be supplemented by external heating. Step 2 - introducing an inert gas such as N2 into the air and maintaining the temperature of the iron powder essentially constant at its peak temperature. Step 3 - discontinuing the flow of air but maintaining fluidization by introducing a stream of inert gas such as N2, Ar or He while reducing the temperature to between 125* and 700*F. Step 4 - introducing air into the inert gas and cooling the fluidized iron powder to a temperature between 25* and 50*F below that at the end of step 3. The temperature at the beginning of this step determines the resistance of the product, the lower the temperature the lower the resistance, and vice versa. Step 5 - discontinuing the inert gas but maintaining fluidization in air while cooling the iron powder to a lower temperature suitable for removal.

Inventors

• 👤 Cabe J Mc
• 👤 J Perlowski
• 👤 R Schur

Bibliographic Details