Magnetorheological Characterization of PTFE-Based Grease With MoS_2 Additive at Different Temperatures

摘要

Thermorheological characterizations of magnetorheological (MR) grease thickened with polytetrafluoroethylene (PTFE) and molybdenum disulphide (MoS_2) used as an additive for two different greases prepared with 50 (MRG50) and 70 (MRG70) weight fractions of spherical carbonyl iron (CI) particles, respectively, are presented. The magnetic properties and glass transition temperature of prepared MR greases (MRGs) have been measured using vibrating sample magnetometer (VSM) and differential scanning calorimetry (DSC), respectively. The MR properties are investigated at different temperatures ranging from 25℃ to 65℃ at magnetic fields ranging from 0 to 0.75 T under rotational and oscillatory sweep tests using a magnetorheometer. It is observed that for MRG70, the shear stress and apparent viscosity increase with increasing temperature. This is explained based on the formation of monolayers of MoS_2 as it interacts with MRG and the effect of thermal conductivity on magnetorheology. Yield stress of PTFE-based MRG has been shown to increase with temperature and magnetic field. Formation of PTFE particle clusters decreasing the localized heat dissipation has been explained to be the reason for this. With increasing magnetic field strength, the flow properties show an increasing trend. ON-state storage and loss modulus are studied to understand the effect of temperature and magnetic field on the viscoelasticity of PTFE-based MRG.