Quality control and non-destructive monitoring are of notable interest of food and pharmaceutical industries. It relies on the ability of non-invasive inspection which can be employed for manufacturing process control. We hereby apply terahertz (THz) time-domain spectroscopy as non-destructive technique to monitor pure and degraded oils as well as hydrocarbon chemicals. Significant differences in the spectra of refractive index (RI) and absorption coefficient arising from the presence of ester linkages in the edible and technical oils were obtained. Explicit increase from 1.38 to 1.5 of the RI in all THz spectrum range was observed in hydrocarbons and mono-functional esters with the increase of molar mass. This fact is in contrast of RI dependence on molar mass in multi-functional esters, such as Adipate or vegetable oils, where it is around 1.54. Degradation products, Oleic Acid (OA) and water in particular, lead only to some changes in absorption coefficient and RI spectra of vegetable oils. We demonstrate that complex colloidal and supramolecular processes, such as dynamics of inverse micelles and oil hydrolysis, take part during oil degradation and are responsible for non-uniform dependence of optical properties on extent of degradation.
Metal particles, suspended as wear debris or as additives, have a major influence on lubrication technology. They are known mostly for negative roles, but even iron nanoparticles, which are likely to pass through most filters, have not yet been quantitatively evaluated for their effects on friction and wear. In this study iron and copper nanoparticle suspensions were formulated in high sulphur paraffinic mineral oils and food grade rapeseed oil. The suspension stabilisation mechanism based on steric repulsion appeared more effective than ionic repulsion principle. Iron nanoparticle suspensions were investigated using four ball antiwear tribotester. Iron nanoparticles did not show statistically significant effects on wear or friction in mineral oil suspension. However, addition of surfactants improved the tribological performance. Wear, friction and sample temperature data along with microscopy evaluation suggested that formation of protective films in the friction zone was the most likely reason for reduction of wear, average friction and the duration of break-in regime.
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