Surface Temperature During Friction Tests: the Influence of Green-Synthesized ZnO Particles as Oil Additive

The use of inorganic particles in lubricants has proven to be effective in reducing friction under lubrication conditions. In this study, two different morphologies of ZnO were synthesised by green synthesis, using Moscato grape waste as a coadjuvant. The use of two different precursors resulted in the formation of nano and microparticles, endowed with rounded and pyramidal shape respectively. Tribochemical reactions always occur in dynamic and complex contact situations where mechanical and thermal effects act simultaneously, both influencing the materials degradation. Based on this, the measurement of the temperature during tribological tests appears a crucial factor. This work analyses the applicability of thermographic measurements to monitor the interface temperature during sliding tests. A calibrated thermal imaging camera was integrated into the test setup to capture real-time surface temperature maps during sliding contact with the purpose to investigate the effectiveness of the thermal measurement on metals, also under lubricated conditions. In this way, the influence of ZnO addition to lubricants on both temperature and friction could be followed in situ. Thermal profiles obtained using an infrared thermal camera were analyzed, and the results were correlated with friction. Wear behavior was studied by scanning electron microscopy. The results reveal that ZnO induces a reduction in friction and wear, although no significant influence on fluid viscosity and heat dissipation was observed. Furthermore, full-field thermal imaging appears a powerful tool for monitoring local temperature variations.