Yidong Zhao

Tribological study of hydrolytically stable S-containing alkyl phenylboric esters as lubricant additives

Three novel S-containing alkyl phenylboric esters, i.e., DSPB, TSPB and TBPB, were prepared and characterized. Compared with common boric esters, these three additives exhibit significant hydrolytic stability, which can be attributed to their specific molecular structures, in which a phenyl group conjugates with an electron-deficient boron that helps improve the hydrolytic stability of boric esters. The tribological properties were evaluated using a four ball tester, which suggests that all the synthesized compounds act as anti-wear additives and have relatively high load-carrying capacities. In particular, it should be noted that, among the synthesized compounds, DSPB exhibits both anti-wear and friction-reducing properties. Furthermore, the worn surface was investigated by X-ray absorption near edge structure spectroscopy (XANES). The results demonstrate that the resulting tribofilm consists of trigonal and tetragonal coordination boron, iron sulfide and disulfide, and iron sulfate. Moreover, atomic force microscopy (AFM) was used to characterize the morphology of the tribofilm and the large pads elongated and orientated in the sliding direction were observed, which contribute to the anti-wear (AW) and extreme pressure (EP) performances.

Tribological Behavior of Some Long-Chain Dimercaptothiadiazole Derivatives as Multifunctional Lubricant Additives in Vegetable Oil and Investigation of their Tribochemistry Using XANES

A series of novel long-chain dimercaptothiadiazole derivatives are prepared and used as antiwear (AW) and extreme pressure (EP) additives in vegetable oil, and their tribological performance is tested by using a four-ball tester. In order to understand the friction process further, X-ray absorption near edge structure spectroscopy is adopted to analyze the chemistry of tribofilms under AW/EP regime, and meanwhile thermal films are also considered for comparison. These derivatives are capable in improving the tribological characteristic of the base stock, and disubstituted derivatives are more effective than other derivatives. Though disubstituted derivatives and disubstituted polysulfur derivatives all fail in improving tribological performance at 0.1xa0wt%, they are still helpful at other additive concentrations. All these long-chain thiadiazole derivatives, in particular the disubstituted polysulfur ones, are good at improving the EP characteristic of the base colza oil. Thermal films generated from these derivatives are composed of ferrous sulfate and a small amount of adsorbed organic sulfide. During the heating process, these long-chain derivatives easily undergo thermal oxidation to generate high-valent sulfate on the metal surface. Ferrous sulfide is the main component of tribofilms generated by these derivatives, while ferrous sulfate in these films almost vanishes at 1.0xa0wt%. These long-chain derivatives tend to react with metal surface to generate low-valent sulfide under rubbing conditions. On the other hand, ferrous sulfide is also the main component of EP films generated by monosubstituted derivatives and disubstituted polysulfur derivatives at 1.0xa0wt%. But the EP films formed by disubstituted derivatives are composed of ferrous sulfide and ferrous sulfate.

The Tribological Chemistry of a Novel Borate Ester Additive and Its Interaction with ZDDP Using XANES and XPS

A novel borate ester containing heterocyclic group, 2,5-bis((2-((6-octadecyl-1,3,6,-dioxazaborocan-2-yl)oxy)propyl)thio)-1,3,4-thiadiazole (BDOT), was prepared and characterized. Its tribological properties and synergistic effect with zinc dialkyl dithiophosphate were evaluated using a four-ball tribometer. The results show that the novel borate additive possesses excellent anti-wear and friction-reducing properties compared with the performance of ZDDP. BDOT combined with ZDDP has a synergistic effect on the tribological properties, especially for the friction-reducing performance. The chemical state of nitrogen, boron and sulfur in thermal films and tribofilms was analyzed by XPS and XANES. XPS analysis suggests that the additive forms a protective film on the rubbing surfaces which is composed of B2O3, BN, FeSO4, FeS2 and Fe2O3. However, the B K-edge XANES shows that no BN was detected in the film. The synergistic effect between BDOT and ZDDP may be due to the formation of right concentration of FeS and FeSO4 in the tribofilm.

Tribological behaviours of surface-modified serpentine powder as lubricant additive

Purpose – The aim of this paper is to study the tribological performance and self-repairing performance of surface-modified nanoscale serpentine powders as lubricant additives in the mineral base oil (5-CST). Design/methodology/approach – Fourier transform infrared spectroscopy spectra and thermo-gravimetric analysis of both modified and unmodified serpentine were performed to analyse their grafting ratio and suspension after modified using a long-chain naphthene aliphatic acid. The tribological properties of surface-modified serpentine as lubricant additives in 5-CST were evaluated and the worn surfaces were investigated by X-ray photoelectron spectroscopy (XPS) and X-ray absorption near edge structure (XANES). Findings – The results show that the serpentine particles have high grafting ratio, improving the dispersity in 5-CST. When the serpentine concentration of 1.00 weight per cent is used as additives in 5-CST, friction coefficient reduces by 14.80 per cent under 294 N and wear scar diameter (WSD) de...

The tribological study of novel phosphorous–nitrogen type phosphoramidate additives in rapeseed oil

Two novel phosphorous–nitrogen type phosphoramidate derivatives, dibutyl octadecylphosphoramidate and dimethyl 4-dodecylphenylphosphoramidate, were synthesized and applied as lubricant additives in rapeseed oil. Using a four-ball machine and standard method, the tribological behaviors of these additives in rapeseed oil were compared with commercial lubricant additives dodecan-1-aminium butyl 7-methyloctyl phosphate (coded T308B) and dibutyl phosphonate (coded T304). The results show that the phosphoramidate derivatives possess excellent antiwear, friction-reducing properties and good extreme pressure capacities. The tribological mechanism was investigated by X-ray absorption near edge structure spectroscopy. It is proposed that the prepared compounds as additives in rapeseed oil form a protective film on the rubbed surface, and the film contains phosphate and/or polyphosphate which can affect the tribological behavior.

Tribological studies of highly hydrolytically stable N-containing long chain alkyl phenylborate esters in mineral oil

The tribological properties and hydrolytic stabilities of two novel N-containing long chain alkyl phenylborate esters, 2-(4-dodecylphenyl)-6-octadecyl-1,3,6,2-dioxazaborate (DBDB), and bis(2-(2-((E)-heptadec-8-enyl)-4,5-dihydro-1H-imidazol-1-yl) ethyl)-4-dodecylphenylborate (OMDB), as lubricating additives in mineral oil (HVI WH150) were evaluated. The results confirm that the two additives possess good anti-wear property and excellent hydrolytic stability, which demonstrates that the new approach by introducing long chain alkyl phenyl group is an effective way to improve the hydrolytic stability of borate esters. X-ray absorption near edge structure (XANES) spectroscopy was adopted to analyze the thermo-oxidative films and tribofilms generated from the synthesized additives in base oil to further understand their tribological behaviors on the metal surfaces. The XANES spectra reveal that the thermal films are mainly composed of trigonal coordination boron, while the tribofilms consist of trigonal and tetrahedral coordination borons in comparison with the model compounds, which suggests that the additive can generate the tetrahedral boron species or the trigonal boron species partially undergoing transformation to produce tetrahedral boron species during the vigorous condition of rubbing process.

The tribological performance of a long chain alkyl phenylboric ammonium derivative and its interaction with ZDDP

A long chain alkyl phenylboric ammonium derivative (DBBM) was synthesized as a lubricating additive. The tribological performances of DBBM and combinations of DBBM and ZDDP as additives were evaluated, which suggests that DBBM has better tribological properties than ZDDP. X-ray absorption near edge structure spectroscopy was used for the analysis of thermal films and tribofilms. The results indicate that the boron in additive mainly forms trigonal and tetrahedral coordination boron both in thermal films and tribofilms, while sulfur mainly generates iron sulfate in thermal films and iron sulfide, iron disulfide, and iron sulfate in tribofilms. It also can be found that it is more likely to form low valence sulfur when the concentration of ZDDP increases in the combinations.

Tribological behaviors of some novel dimercaptothiadiazole derivatives containing hydroxyl as multifunctional lubricant additives in biodegradable lithium grease

Purpose - In order to meet the requests of exploring environmental-friendly and multifunctional lubricant additives, some novel dimercaptothiadiazole derivatives containing hydroxyl are prepared and used as antiwear (AW) and extreme-pressure (EP) additives in biodegradable lithium grease. The paper aims to discuss these issues. Design/methodology/approach - The tribological performances of the grease samples containing these derivatives are evaluated by using a four-ball tester. X-ray absorption near edge structure (XANES) spectroscopy is used to analyze the chemistry of tribofilms under AW/EP regime, and thermal films are also considered for comparison. Findings - The tribological tests show that these derivatives are all effective in reducing wear, especially at lower additive concentrations, but they are basically failed in reducing friction. They are also helpful in improving the EP characteristic of the base grease. The thermal films generated by these derivatives are composed of adsorbed organic sulfide and ferrous sulfate, though for short-chain derivatives, organic sulfide is the only component at 5.0 wt.%. Ferrous sulfide is the main component of the tribofilms formed by these derivatives at various additive concentrations. But for short-chain derivatives, these tribofilms consist of ferrous sulfide and ferrous disulfide at 5.0 wt.%, and the appearance of disulfide suggests that the interfacial temperature between the upper ball and three lower balls under these conditions is considerably low. The EP films generated by short-chain derivatives are all composed of organic sulfide and ferrous sulfide, while for long-chain derivatives, ferrous sulfide is the main component. Originality/value - These low-toxic and oil-soluble dimercaptothiadiazole derivatives are effective in improving the tribological characteristic of the biodegradable lithium grease, and these heterocyclic derivatives may be good substitutes for some harmful traditional additives.