Abstract: The subject invention provides a magnetorheological (MR) composition having improved resistance to oxidation and increased dispersability in a carrier fluid. The composition includes a plurality of metal particles and a surfactant including a hydrocarbon with at least one of a hydroxyl, a carbonyl, and an amine group bonded to the hydrocarbon for reacting with the metal particles. The surfactant is present in an amount such that from about 1% to about 20% of the amount of the surfactant is adsorbed to the metal particles. The surfactant is reacted with the metal particles such that about 75% to about 100% of a maximum amount of the surfactant adsorbs to the metal particles for improving the resistance of the metal particles to oxidation and for increasing the dispersability of the magnetorheological composition in the carrier fluid. The MR composition according to the subject invention is utilized in a magnetorheological (MR) fluid.

Abstract: The subject invention provides a magnetorheological (MR) composition having improved resistance to oxidation and increased dispersability in a carrier fluid. The composition includes a plurality of metal particles and a surfactant including a hydrocarbon with at least one of a hydroxyl, a carbonyl, and an amine group bonded to the hydrocarbon for reacting with the metal particles. The surfactant is present in an amount such that from about 1% to about 20% of the amount of the surfactant is adsorbed to the metal particles. The surfactant is reacted with the metal particles such that about 75% to about 100% of a maximum amount of the surfactant adsorbs to the metal particles for improving the resistance of the metal particles to oxidation and for increasing the dispersability of the magnetorheological composition in the carrier fluid. The MR composition according to the subject invention is utilized in a magnetorheological (MR) fluid.

Abstract: Hydrophobic metal particles that are useful as the magnetizable particles in magnetorheological fluids and magnetorheological elastomers are provided. Hydrophilic metal particles, such as carbonyl iron particles, are made hydrophobic by reacting a surface hydroxyl on the solid metal particle with a reactive surfactant. Particles are coated with the reactive surfactant to cover at least about 90% of the surface of the particles and then washed with a low viscosity synthetic hydrocarbon to remove any excess surfactant. The particles are stabilized against oxidation and irreversible coagulation during further processing, and formulation and use in magnetorheological fluids and elastomers.

Abstract: Magnetorheological fluids containing carbonyl iron particles with surface hydroxyl groups and high specific surface area in combination with nonpolar vehicles such as polyalphaolefins and glycol esters can be formulated to resist particle separation under high separation force applications. When the nonpolar vehicle having a suitably high molecular weight is used, the fluids may be used at working temperatures of the order of 200.degree. C.

Abstract: A significant increase in the yield stress of a magnetorheological fluid can be obtained at a given volume fraction of solid magnetic particles by employing as the particulate component a mixture of a first component of relatively large particles and a second component of relatively small particles such that the mean diameter of the large particles is at least 5 times the mean diameter of the small particles. The mixture of large and small particles provides a substantial increase in the yield stress without an increase in the viscosity of the mixture in the absence of a magnetic field.