A multifunctional magnetic biochar composites for advanced magnetorheological fluid applications

Magnetorheological fluid (MRF), a smart suspension that respond to external magnetic fields, exhibits potential in engineering fields but is limited by its low mechanical properties and insufficient wear resistance. In this study, a magnetic biochar composite material (NiFe2O4/biochar) was proposed to ameliorate the magnetoinduced yield stress and tribologcial characteristic of MRF. The cooperativity between magnetism of nanoscale particle and lubrication of biochar helps to enhance the suspension stability, dynamic yield stress, and friction characteristics of MRF. A series of tests for MRF were used to verify the effectiveness of magnetic composite materials. Experimental results showed that the addition of 3 % NiFe2O4/biochar to the MRF significantly improved the dynamic yield stress by 26.13 % under a magnetic flux density of 400 mT. Furthermore, the composite material improved the anti-settling stability of the MRF, reducing the height of the supernatant by 31.64 % after 12 h. Tribological tests revealed that the composite material also enhanced wear resistance, as evidenced by a reduction in both the friction coefficient (from 0.251 to 0.241) and the wear scar diameter at a 3 % mass fraction. These findings suggest that NiFe2O4/biochar composite materials are an effective strategy for improving the performance of MRF, making it more suitable for diverse engineering applications, particularly in environments requiring enhanced stability and wear resistance.