Low-cost MR fluids with powdered iron

A magnetorheological fluid formulation comprising:

• a liquid vehicle mixture comprising at least two liquid components, each liquid component having a different surface functionality;
• magnetizable particles dispersed in the liquid vehicle mixture and comprising iron having a passivating oxide surface layer;
• at least one different organoclay for each liquid vehicle component, each organoclay having a surface chemistry which is preferentially compatible with the surface functionality of one of the liquid components relative to its compatibility to the remaining liquid components;
• and
• at least one additive selected from the group consisting of:
• an organomolybdenum complex, an organomolybdenum thiocarbamate, a zinc dithiophosphate, and an organothiocarbamate.

A magnetorheological fluid formulation comprising:

• a liquid vehicle mixture comprising a non-polar hydrocarbon liquid component and a polar diester liquid component;
• magnetizable particles dispersed in the liquid vehicle mixture, the magnetizable particles prepared by controlled water atomization and comprising iron having a passivating oxide surface layer of iron oxide and at least one alloying metal oxide, and having a mean particle diameter in the range of about 8-25 μm;
• a non-polar hydrocarbon-compatible organoclay and a polar ester-compatible organoclay;
• and
• at least one additive selected from the group consisting of:
• an organomolybdenum complex, an organomolybdenum thiocarbamate, a zinc dithiophosphate, and an organothiocarbamate.

A method of making an MR fluid comprising:

• blending a liquid vehicle mixture including at least two liquid components, each liquid component having a different surface functionality;
• adding at least one surface-treated organoclay for each liquid component in the liquid vehicle mixture, wherein the surface treatment of each added organoclay renders the organoclay preferentially compatible with the surface functionality of one of the liquid components relative to the compatibility of the organoclay to the remaining liquid components;
• and
• dispersing magnetizable particles in the liquid vehicle mixture, wherein the magnetizable particles are prepared by controlled water atomization and comprise iron having a passivating oxide surface layer, and a mean diameter in the range of about 8-25 μm.