Lubricants are widely used in modern technology in order to reduce friction in moving mechanisms of motors, bearings, gears, etc. and to reduce friction in the machining of structural and other materials in machine tools (turning, milling, grinding, etc.). In terms of production and use, mineral oil is the basic component in lubricants. Usually, oil provides not one but several functions simultaneously: for instance, motor oil not only lubricates, but also cools and cleans engine parts.
With account of a wide field of using the lubricants, there exists the problem to control their quality during manufacturing and usage. Furthermore, analysis of the used lubricating oil allows determining the wear level of the equipment in which it is applied. This problem can be solved using a high-precision rapid control, which can be realized by applying surface plasmon resonance (SPR). Devices based on the SPR enable to quickly determine the optical properties of motor oils and to monitor wear processes in a real time scale.
To solve the problem, the optical measurement equipment developed in Ukraine was used. The equipment allows measuring the change in the refractive index of the tested samples. These changes characterize the processes of deterioration, polymerization, oxidation, etc. Experimental investigations of applied aspects for designing biosensors based on SPR were performed in the Lashkaryov Institute of Semiconductor Physics, NAS of Ukraine. One of the designed models is the spectrometer “Plasmon-71” (Fig.1) suitable for operation in labs of biochemical and biophysical profiles. This device enables one to measure changes in the refractive index over a wide range from 5 RU (relative unities) to 180 000 RU with the accuracy 4×10-6 RIU (refractive index unity).
Analysis of lubricant motor oil was also performed using the optical method for measuring the refractive indexes of the unused fresh lubricant motor oil and the lubricating motor oil used in the motor vehicle and comparing them. Using the SPR device, there were determined refractive indexes for motor oil before usage – „clear? (1.45903±0.00001 RIU) and after driving 3000 kilometers – „dirty? (1.46205±0.00001 RIU). Depicted in Fig. 2 are the SPR curves for these two samples of motor oil. Fig. 3 shows the kinetics of changes in reflection for the sample of dirty oil in time. One can observe changes in the refractive index for dirty motor oil, which means that hard wear debris is deposited on the surface of spectrometer sensor cheap. The slope of the curve is related with the amount and sizes of wear products.
Thus, capability to control deterioration of lubricating oils and level of motor's wear has been demonstrated. It will enable to widen usage of surface plasmon resonance in industry for diagnostics and monitoring new lubricating oil compositions and in manufacturing processes for precision measuring devices and reducing gear systems.