Electrically conductive ferrofluid compositions and method of preparing and using same

The electrically conductive ferrofluid composition, which composition consists essentially of:

• (a) a nonvolatile liquid carrier;
• (b) finely divided single domain ferromgnetic particles having an average particle size of from about 20 to 300 .ANG.;
• (c) electrically conductive carbon particles in an amount of from about 1 to 25 percent by weight of the composition, the undivided carbon particles having a particle size of 20 to 300 .ANG. and an aggregate particle size of up to 1 millimeter;
• (d) a surface active dispersing agent to disperse and stabilize the magnetic and carbon particles, the ratio of the dispersing agent to the carbon particles ranges from about 0.01/1 to 20/1 by weight;
• and
• (e) the composition characterized by thixotropic behavior and having an electrical resistivity of about 10.sup.3 ohm-cm or less.

An electrically conductive ferrofluid composition having an electrical resistivity of about 10.sup.3 ohm-cm or less, which composition consists essentially of:

• (a) a nonvolatile liquid carrier;
• (b) single domain magnetite particles in an amount of from about 5 to 20 weight percent of the composition and having a particle size of about 20 to 300 .ANG.;
• (c) carbon black particles derived from a furnace process in an amount of from about 5 to 18 weight percent of the composition and having a particle size of about 20 to 300 .ANG.;
• and
• (d) a cationic or nonionic surface active dispersing agent in an amount to disperse and stabilize the magnetite and carbon particles.