The Challenge

Recent tribological measurements have suggested that the compact surface layers may not be simple monolayers and in fact, extend further into the bulk. Experimental studies of in situ friction-reducing surface structures are very challenging as it requires a combination of a surface-specific technique coupled with the harsh conditions applied within an engine where the probe does perturb the buried surface structure. Synchrotron specular X-ray and neutron reflectivity are ideally suited to these demands but a dedicated sample environment was needed to replicate the conditions inside the operating engine.

The Solution

A team from Infineum and the Universities of Cambridge and Kent worked with Diamond and the Science and Technology Facilities Council (STFC) scientists to design and test a novel sample environment, a tribometer, designed to perform experiments replicating the conditions inside a working engine while simultaneously collecting surface specific structural information. The tribometer is compatible with I07 at Diamond along with neutron instruments at the ILL (France) and ISIS (UK) allowing the team to monitor different aspects of the surface chemistry. X-ray reflectivity (XRR) data was obtained from adsorption of glycerol monooleate (GMO) at the iron oxide – dodecane interface at different shear rates.

The Benefits

The combination of X-ray and neutron data provided a powerful probe of the buried surface structure of OFM layers at the iron oxide-dodecane under different tribological conditions, representing different friction conditions. This information is key to understanding structure at interfaces, necessary for developing design rules for the next generation of engine oil formulations. Due to the sensitivity of X-rays to a wide range of elements, it has also been suggested that the tribometer could be powerfully employed for studying surface-active compounds with greater electron densities under shear, such as inorganic friction modifiers.