Rheological properties of lithium-aluminum mixed-soap-based magnetorheological greases with clay minerals

Magnetorheological grease (MRG) uses a high-viscosity grease as the base carrier fluid to improve settling stability, which in turn increases the zero-field viscosity, further limiting the adjustable range. Meanwhile, the preparation and reaction of mixed-soap greases have received little attention from researchers. In this study, a new low-viscosity lithium-aluminum mixed-soap-based magnetorheological grease (LAMRG) is formulated and prepared. Additionally, four types of clay minerals (Sepiolite, Kaolin, Bentonite, and Attapulgite) are added to the LAMRG base solution to create different LAMRG mixtures to investigate and compare their impact on sedimentation stability. Results show that adding a small amount of clay minerals can enhance the settling stability of LAMRG, particularly Sepiolite, a non-metallic clay with a unique pore structure and high specific surface area. Rheological properties of the LAMRG base solution (ALC) and LAMRG mixture containing Sepiolite (ALCH), are tested using a rotational rheometer at different magnetic field strengths. Results demonstrate that LAMRG exhibits the same hysteresis characteristics as conventional MRGs, and the addition of Sepiolite significantly improves viscosity, shear stress, and viscosity tunable range of LAMRG to a certain extent. However, this addition also reduces the MR effect of LAMRG, decreasing the energy storage modulus and loss modulus at high magnetic field strength, but hardly affecting the transient response. In conclusion, combining Sepiolite with mixed-soap-based MRGs helps to apply magnetorheological materials to more demanding specialty equipment.