Analysis of motor oils using an «Ékspress» spectrometer and microwave plasma source

It is known that the working properties of motor oil are determined by the presence of some elements of the periodic table. The properties of oil can vary significantly over time due to exposure to both high and extremely low pressures and temperatures. To ensure uninterrupted long-term operation of equipment, it is necessary to monitor various indicators of oil, including the determination of wear metals on a regular basis. Two methods of determining wear metals are most widely used: an electric arc with a rotating graphite disk and inductively coupled plasma. The goal of the work was to determine wear metals in oil using a microwave nitrogen plasma source and an «Ékspress» spectrometer according to ASTM D5185-09 method. Microwave plasma was produced using an industrial magnetron with a frequency of 2.5 GHz and a microwave resonator which provided toroidal plasma shape. Nitrogen (purity of 99.6%) was used as a plasma-forming gas. In accordance with the mentioned procedure, a series of wear metal samples was prepared by adding metal oxides to the base oil for comparison with the control experiment. After that, the solutions were diluted 1:10 by weight with kerosene to eliminate the difference in viscosity of the samples and ensure their spraying using a pneumatic spray. The spectrometer allows simultaneous recording of spectra in the region of 190 – 360 and 390 – 540 nm with an integration time of 70 msec. The intensity of C₂ and CN molecular bands was reduced by introducing air into the intermediate flame of the burner. The constructed calibration graphs for determination of Al, Pb, Fe, Cu, Cr, Cn were used in analysis of the control sample. It is shown that wear metals in oil can be determined using microwave plasma as a source of spectrum excitation.

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