engleski

Thermal behavior and stability of mineral and synthetic lubricating oils

Thermal behavior and stability, together with viscosity are the most important properties of base oils regarding application. At low temperatures, lubricating oils must display good flow ability, while must not have high volatility and must be chemically stable and resistant to degradation at high temperatures. Chemical composition plays a major role, whereas the targeted properties can be considerably improved with some additives. Therefore, it is necessary to know in detail thermal properties of base and lubricating oils in a wide range of the application temperature by lubricants formulating. In this paper, the thermal properties of various mineral SN base oil and synthetic PAO base oils, are studied by techniques of differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The enthalpy and crystallization and melting temperature ranges of each base oil at low temperatures, from room temperature to -90 oC were established with the assistance of the DSC technique. Kinetics and the degradation of base oils up to the complete decomposition, usually at temperatures below 350 oC, were explored by TGA techniques. Results of the kinetic analysis are described by activation energy and a constant of the decomposition rate calculated using the Flynn-Wall method. The impact of polyolefinic (OCP) and polymethacrylate (PAMA) polymer viscosity index improvers, i.e. of pour point depressants on the oil properties at low and high temperatures is established and described. Toplinsko ponašanje i stabilnost, uz viskoznost, najvažnija su primjenska svojstva baznih ulja. Pri niskim temperaturama maziva ulja moraju biti teciva, a pri visokima ne smiju imati veliku isparivost i moraju biti kemijski postojana i otporna na razgradnju pri visokim temperaturama. Kemijski sastav ovdje igra glavnu ulogu, a uz pojedine dodatke ciljana svojstva se mogu i znatno poboljšati. Zbog toga je u formuliranju maziva potrebno detaljno poznavati toplinska svojstva baznih i mazivih ulja u širokom području primjenskih temperatura. U ovom radu toplinska svojstva raznih mineralnih baznih ulja grupe I (solvent neutral) i sintetičkih baznih ulja tipa PAO istražena su tehnikama diferencijalne pretražne kalorimetrije (DSC) i termo-gravimetrijske analize (TGA). DSC tehnikom su ustanovljene entalpije i temperaturna područja kristalizacije i taljenja za pojedina bazna ulja u području niskih temperatura, od sobne do -90 oC. TGA tehnikom su istraženi kinetika i stupnjevi razgradnje baznih ulja, sve do potpune razgradnje, uobičajeno pri temperaturama manjim od 350 oC. Rezultati kinetičke analize opisani su energijom aktivacije i konstantom brzine raspada izračunatima primjenom Flynn-Wallove metode. Ustanovljen je i opisan utjecaj poliolefinskih (OCP) i polimetakrilatnih (PAMA) polimernih poboljšavača indeksa viskoznosti, odnosno snižavala točke tečenja na niskotemperaturna i visokotemperaturna toplinska svojstva ulja.

thermal behavior; lubricating oils; mineral; synthetic

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