Research On Voltammetric Determination Of The Content Of Antioxidants In Lubricant And Its Applications

Lubricants are the "blood" of most mechanical equipments to maintain normal and safe operation, and its quality directly influence the energy consumption and reliability of mechanical equipments. As is known, lubricants undergo partly or completely degradation or even failure during their use. If the failed lubricants are not replaced timely, it will lead to the mechine accidents. While changing the lubricants too often, it would result in the waste of oil resources. Hence, predicting the remaining useful life of lubricants scientifically is significant for saving resources and safety production. However, the deterioration of lubricants performance is affected by many factors, most of which are uncertainties. What's more, there has so far not a good lubricant measuring scheme to evaluate the remaining useful life of lubricant. This paper was supported by National Program on Key Basic Research Project “Lubricanting additives' anti-friction and anti-oxidation performance and its effect law on synthetic lubricants” and National Natural Science Foundation Project “The research on the deterioration law of automobile lubricants and method of drain intervals of oils”. Based on developing the quick voltammetric determination of antioxidants in lubriants, combined with infrared spectroscopy and tribological performance testing, the prediction method of the remaining useful life of mineral oil and synthetic ester oil had explored. The main results of the study are as follows:(1) Based on PARSTAT 2273 electrochemical workstation, the developed electrolyte solution which are comprised by the sulfuric acid, ethanol and sodium dodecyl sulfate can be effectively used for detecting the lubricating antioxidants including phenol antioxidants(including polyphenol-type and phenol-ester type), amine antioxidants and ZDDP antioxidants, etc, which indicates that the electrolyte solution has great applicability for measuring antioxidants in lubricant.(2) Linear sweep voltammetry is just suitable for the determination of single antioxidant in lubricant, while differential pulse voltammetry can be used to determine single or multiple antioxidant content in lubricating oil, which indicats that compared with linear sweep voltammetry, differential pulse voltammetry has better sensitivity and resolution.(3) In 500 SN Mineral base oil, the T205 of ZDDP antioxidant is consumed linearly with aging time. The wear scar diameter of aging oil sample increases with the reduction of T205 antioxidant, which showing a good trend of increasing. The new antioxidant is added into the aging oil samples, the wear scar diameter of this sample become smaller. While compared with the new oil with the same content of antioxidant, the coefficient of friction and wear scar diameters of aged oil are bigger than new oil, indicating that the mineral base oil has occurred irreversible reaction during the oxidation process and the new antioxidants can significantly reduce the wear.(4) Differential pulse voltammetry with a glassy carbon electrode can be capable of analysis and identification of antioxidants in different brands of commercially available automobile lubricants. The results indicate that the different brands of commercially available lubricants have different types and relative content of antioxidants, so as to achieve different lubricating properties.(5) In laboratory aging simulation, the antioxidant content of synthetic and mineral oil is decreased with aging time, and the total acid number and viscosity of corresponding oil samples increase. For the quantitative determination of ZDDP additive in running automobile lubricants, the consumption amount of ZDDP additive in lubricating oil at the beginning of the lubricants' drain intervals is extremely large, and the later begining smaller, which is mainly the reason that the high concentration of ZDDP has chemical reactions with metal friction, leading to the decline of ZDDP additive. Besides, the running speed and running mileage have limited impact on the decreased amplitude of ZDDP in lubricating oil.