Thesis defense of Kevin Lehninger

High-performance greases are indispensable functional materials in numerous industrial applications; as they must provide reliable lubrication under high mechanical loads and elevated temperatures. In particular; lithium soap-based greases occupy a dominant position due to their high thermal and mechanical stability. At the same time; the demand for lithium-free alternatives is increasing; as lithium is increasingly utilized as a strategically important raw material for battery technologies. The aim of this work is the systematic structural investigation of lithium-containing and lithium-free high-performance greases under varying pressure and temperature conditions. To this end; nine greases with different thickener systems were analyzed by means of small-angle and wide-angle X-ray scattering. \ithin the scope of this work; two novel high-pressure cells were designed and realized. üne cell is designed for SAXS experiments at pressures of up to 5 kbar; while a second cell enables SAXS measurements at pressures of up to 10kbar. The results demonstrate that lithium-containing greases exhibit pronounced crystalline structures. In contrast; lithium-free alternatives predominantly show amorphous or only weakly ordered microstructures; sharp reftections can be unambiguously attributed to crystalline additives. Temperature-induced structural reorganizations are observed in particular for polyurea- and calcium-complex greases; whereas pressure-induced phase transitions do not occur in any of the investigated systems. The present work thus provides a structure-based comparison of lithium-containing and lithium-free high-performance greases under extreme conditions and; at the same time; introduces powerful high-pressure tools for future investigations.