Tribological studies on a novel borate ester containing benzothiazol-2-yl and disulfide groups as multifunctional additive

A novel borate ester derivative containing benzothiazol-2-yl and disulfide group (BTSB) was synthesized and characterized. Its tribological properties used as EP and multifunctional additive in rapeseed oil were evaluated using a four-ball tribometer, and its action mechanisms were investigated by the X-ray photoelectron spectroscopy. Results show that the BTSB possesses comprehensive tribological properties in load-carrying, friction-reducing, antiwear, corrosion-inhibiting, and anti-oxidation, which probably has a chance to replace ZDDP partially. Moreover, the decomposed borate esters, organic sulfide and nitrogen adsorbed on worn surface were detected, and S element in BTSB reacted with metal and generated FeSO₄, both of which contributed to the formation of boundary lubricating film.     

The tribological properties and action mechanism of non-active organic molybdate ester and its combination with ZDDP

A non-active molybdate ester (ME) was synthesized in a batch process. Its tribological performance and its synergistic effect with ZDDP in 5CST were evaluated using a four-ball machine, and the chemistry of tribofilms was analyzed with XANES. The results indicate that ME possesses excellent anti-wear and friction-reducing properties, not load-carrying capacity. Both ME and ZDDP show excellent synergistic tribological behavior in 5CST. According to the XANES results, the tribochemical films generated from ME alone are mainly composed of MoO₃, and the tribochemical films generated from the oil blends containing ME and ZDDP consist mainly of MoS₂, sulphate and polyphosphate.     

The Tribological Performance of S-[2-(Acetamido) Benzothiazol-1-yl] N,N-Dioctyl Dithiocarbamate as an Additive in Rapeseed Oil

A new derivative of benzothiazol, S-[2-(acetamido) benzothiazol-1-yl] N,N-dioctyl dithiocarbamate, was synthesized. The tribological behavior of the synthesized compound as an additive in rapeseed oil was evaluated using a four-ball friction and wear tester, and compared with that of zinc butyloctyl dithiophosphate (ZDDP) and zinc dibutyl dithiocarbamate (ZDTC). The morphologies and elemental chemical states on the worn surfaces of the lubricated GCr15 steel were investigated by means of X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). The biodegradability (fate) and microbial toxicity (effects) measurement of the additive were also performed. The results indicate that the compound possesses excellent load-carrying capacity, antiwear and friction-reducing properties as compared with rapeseed oil alone. The antiwear and friction reduction properties of the novel compound are similar to those of ZDDP and ZDTC; and its load-carrying capacity is similar to ZDTC, but is better than ZDDP. The excellent tribological behavior of the novel compound is attributed to chemical adsorption on and tribochemical reaction with the steel surface, with the generation of a surface protective film composed of FeS, FeSO₄, etc. Measurements of biodegradability and microbial toxicity show that the additive has high biodegradability, and microbial toxicity needed to be further lowered.     

Tribological studies on a new borated mannich base containing benzotriazole group as additive for environmentally adapted lubricant

A novel borated mannich base containing benzotriazole group additive (abbreviated as BTBM) is synthesised and characterised. Its tribological properties as an additive in rapeseed oil are evaluated and compared with zinc dialkyldithiophosphate (ZDDP). The results show that BTBM have high P_B value, but bad anti sintering ability. The anti-wear property of BTBM is not as good as ZDDP; however, it shows excellent property in friction-reducing and expects to be a comprehensive friction modifier. X-ray photoelectron spectroscopy results indicate that BTBM can form adsorption layer consisting of fracted organic borates or deposited B₂O₃ and organic nitrogen compounds settled layer in the process of friction. As corrosion inhibitor, BMBT can inhibit the corrosion of active S element to copper significantly.     

Preparation of borate ester and evaluation of its tribological properties as an additive in different base oils

N‐containing borate ester (MEBE) with five‐member ring structure as a lubricant additive was synthesised. The tribological properties in liquid paraffin (LP), poly‐alpha‐olefin (PAO) and dioctyl sebacate (DOS) were evaluated, and the action mechanisms in different base oils were also explored. It was found that as‐synthesised borate ester possesses excellent antiwear performance in LP and PAO. XPS analysis suggests that the additive forms a protective film on the rubbing surfaces which is composed of BN, Fe₂O₃, polyoxyethylene ether and N‐containing organic compounds. The inorganic and organic protective films in the metal surface effectively improve the antiwear ability of the base stock. However, when the additive MEBE was introducted into DOS base oil which is prone to adsorbing to the metal surface because of the high polarity of DOS, it influences the compactness of the film formed by the DOS, resulting in weak antiwear property. Copyright © 2016 John Wiley & Sons, Ltd.     

The Tribological Chemistry of Novel Triazine Derivatives as Additives in Synthetic Diester

Two novel triazine derivatives 2-tris(2-ethylhexyl)-3,3′,3″-(1,3,5-triazine-2,4,6-triyl)-tris(sulfanediyl)tripropanoate (TE TST) and 2-ethylhexyl-3-(4,6-dimercapto-1,3,5-triazin-2-ylthio) propanoate (EDTYP) were synthesized. Their tribological properties in synthetic diester were evaluated using a four-ball tribometer, and the thermal films and tribofilms were investigated using X-ray absorption near-edge structure (XANES) spectroscopy. The copper corrosion-inhibiting performance was explored as well. The additives can improve the extreme pressure performance of base stock. TETST displays good antiwear property and EDTYP possesses excellent friction-reducing ability. Surface analysis indicated that the thermal films are exclusively composed of FeSO₄, and the tribofilms are constituted by FeS, FeS₂, and FeSO₄. The mechanism obtained from the XANES analysis fit well with the results of tribological tests.     

含硫氮硼酸酯在菜子油中的摩擦学性能研究

合成了一种新型含硫氮硼酸酯润滑油添加剂,利用四球摩擦磨损试验机考察了其在菜子油中的摩擦学性能,并用x射线光电子能谱仪分析了磨斑表面的元素化学状态。结果表明：含硫氮硼酸酯可显著改善菜子油的减摩抗磨性能和承载能力;含上述添加剂的菜子油在摩擦过程中发生了摩擦化学反应,生成了含菜子油甘油酯、有机硫化物、硫酸亚铁、三氧化二硼等组成的边界润滑膜,从而改善了菜子油的摩擦学性能。     

Interaction of ZDDP with Borated Dispersant Using XANES and XPS

The thermochemical reaction and tribochemical reaction of zinc dialkyldithiophosphate (ZDDP), a borated dispersant, and the mixture of ZDDP and borated dispersant on steel surfaces were investigated. Both pin-on-disk and ball-on-disk were used to generate tribofilms. The chemical state of nitrogen, boron, phosphorus, and sulfur in heated oil solutions, thermal films, and tribofilms were analyzed by X-ray absorption near edge structure (XANES) spectroscopy to obtain the chemical nature of species on the surface and in the bulk of the films. High-resolution X-ray photoelectron spectroscopy (XPS) has also been used to analyze boron (B) in tribofilms.

The borated dispersant in base oil by itself yields good anti-wear behavior. This can be attributed to the presence of boron in the dispersant. The wear scar widths (WSW) for ZDDP alone, and in combination with the dispersant, yield similar results within the experimental error. It was found that the borated dispersant facilitates the decomposition of ZDDP and the formation of phosphate in tribofilms and thermal films. B K-edge XANES shows that boron has a trigonal coordination in the untreated additive, but the coordination changes partially to a tetrahedral coordination in the tribofilm upon rubbing. No BN was detected in the film analyzed by B K-edge or N K-edge. Boron 1s XPS also did not show the presence of BN in the film.     

A tribological study of (2‐sulphurone‐benzothiazole)‐3‐methyl‐dibutyl borate

An organic compound containing S, N, B, and O was synthesised by reacting 2‐mercaptobenzothiazole and formalin in ethanol solution, the resulting product then being reacted with butanol and boric acid in toluene solution. The tribological performance of the novel compound when added to liquid paraffin was evaluated using a four‐ball tester and a ring‐on‐block machine. The relationship between performance and concentration was analysed, and the results show that the compound possesses good antiwear and load‐carrying abilities. The mechanism of action of the additive was investigated using X‐ray photo‐electron spectroscopy (XPS). Surface analysis indicated the formation of a protective film containing FeSO₄, an organo‐sulphur compound, FeS₂, borate, and an organonitrogen compound. This protective film formed during sliding processes contributes to the increase in wear resistance.     

Tribological characteristics of ashless dithiocarbamate derivatives and their combinations with ZDDP as additives in mineral oil

Two ashless dithiocarbamate derivatives, octyl 2-(dibutylcarmothioylthio) acetate (DDCO) and S-dodecyl 2-(dibutylcarbamothioylthio) ethanthioate (DDCS), were prepared. Thermal stabilities tests were conducted with a thermo-gravimetric analyzer (TGA). The tribological properties of each compound and their combinations with ZDDP in a mineral oil (HVI WH150) were evaluated using a four-ball tester. X-ray absorption near-edge structure (XANES) spectroscopy was used to characterize the chemical properties of tribofilms generated from DDCO, DDCS and their combinations with ZDDP. According to the TGA results, the synthesized compounds possess good thermal stability (initial decomposition temperatures are above 270 °C). It can be found that all the prepared compounds have better friction-reducing capacity than ZDDP, with anti-wear performance and extreme pressure property worse than ZDDP. However, their combinations with ZDDP perform better than ZDDP in tribological properties. The results of the XANES analyses indicate that the composition of the tribofilms from DDCO or DDCS is organic sulphide on the outer surface and pyrite with a little sulphite in the inner layer, which also suggests the -SC(=S)-N- part in additives structure plays key role in tribol-chemical behaviour. The XANES spectra of the combinations exhibit interestingly that the addition of DDCO or DDCS can increase the length of polyphosphate chain in the tribofilms.     

A High-Performance Multifunctional Lubricant Additive for Water–Glycol Hydraulic Fluid

A water-soluble boron (B)-containing thiophosphite derivative (BTP) was synthesized, and its tribological, anticorrosion, and antirust properties as an additive for the base liquid of water–glycol hydraulic fluid were evaluated in detail. The results of tests demonstrated that BTP is indeed a high-performance and multifunctional water-soluble lubricant additive that was able to remarkably improve the extreme pressure, friction-reducing, antiwear, anticorrosion, and rust-inhibiting properties of the base liquid when added at a low adding concentration (<3 wt%). Based on a performance comparison of BTP and thiophosphite (TP), whose chemical structure is similar to that of BTP but without B, a number of primary conclusions were drawn. The B element existing as alkanolamine borate group could greatly improve the extreme pressure, antiwear, and antirust performance of BTP, especially the antirust performance, but had only a small effect on the friction-reducing and anticorrosion properties. Based on characterizations and analyses of the worn surfaces, we propose that the antiwear mechanism consists of the prepared compound BTP reacting with the steel surface during the friction process to generate a protective film mainly composed of phosphate, sulfide, sulfate, organic amine, and B₂O₃.     

Tribological behavior and tribofilm composition in lubricated systems containing surface-capped molybdenum sulfide nanoparticles

The tribological behavior of surface-capped MoS₃ nanoparticles (nano-MoS₃) in hydrocarbon oils was studied both alone and in combination with ZDDP. It was found that the nano-MoS₃ additive alone demonstrates pro-wear properties and decreases the friction coefficient only at high temperatures. The combination with ZDDP demonstrates synergism in antiwear and antifriction activity even at low ZDDP content. X-ray Absorption Near Edge Structure (XANES) spectroscopy at the sulfur, molybdenum and phosphorus edges was used to identify the chemical species in tribochemical films. It was established that the nano-MoS₃-formed tribofilms are composed of oxidized sulfur and molybdenum species while tribofilms formed by combination with ZDDP are composed of phosphate layers incorporating MoS₂-type fragments providing friction reduction.     

Study on the tribological properties of surfactant-modified MoS2 micrometer spheres as an additive in liquid paraffin

Tribological properties of MoS₂ micrometer spheres modified by self-prepared surfactant as an additive in liquid paraffin (LP) are studied and compared with those of the commercial colloidal MoS₂ on a four-ball tester and an Optimol SRV oscillating friction and wear tester. The worn surfaces are examined with SEM and XPS, respectively. Results show that MoS₂ micrometer sphere is a much better extreme-pressure additive and anti-wear and friction-reducing additive in LP than the commercial colloidal MoS₂. The boundary lubrication mechanism can be deduced as an effective chemical adsorption protective film formed by the long chain alkyl and active elements (S and N) in the prepared surfactant and tribochemical reaction film composed of the tribochemical reaction products of the additive. Moreover, sliding and rolling frictions exist simultaneously in the MoS₂ micrometer spheres /LP lubricating system, which also do more contributions to the good tribological properties.     

Preparation and tribological properties of the N‐containing heterocyclic borate esters and Cu microparticles as lubricant additives in base oil

In this paper, four kinds of N‐containing heterocyclic borate esters and polyvinyl pyrrolidone‐protected Cu microparticles were synthesised and characterised. Their tribological properties as lubricant additives in industrial white oil were evaluated using a four‐ball tribometer, and their lubrication mechanisms were investigated by X‐ray photoelectron spectroscopy. The results showed that the anti‐friction and anti‐wear performance of the base oil can be significantly improved by the addition of N‐containing borate esters and Cu microparticles, and they present synergistic tribological effect. Moreover, X‐ray photoelectron spectroscopy results showed a lubricating tribochemical reaction film containing B₂O₃, FeB, FeO, Fe₂O₃ and so on is formed on the worn surface. In addition, Cu microparticles as rolling bearings, which transform sliding friction to rolling sliding and the formation of the Cu microparticles deposited film, are probably responsible for the improvement of tribological performance. Copyright © 2017 John Wiley & Sons, Ltd.     

Tribological properties and tribochemical mechanism of lanthanum and boron compounds in oil

Lanthanum dialkyldithiophosphate (LaDDP) was synthesised. The tribological properties of a combination additive of LaDDP and an organo‐borate (OB) in oil were evaluated with a four‐ball test machine. The results show that the combination of LaDDP and OB gives better load‐carrying capacity and anti‐wear and friction‐reducing properties than the individual components. Rubbed surfaces after the friction tests were investigated using X‐ray photoelectron spectroscopy, Auger electron spectroscopy, and microhardness testing. The results indicate that a boundary film is composed of deposit films (including La₂O₃ and B₂O₃), chemical reaction films (including FeSO₄, FePO₄, and FeS), and a tribodiffusion layer (including La and B). Lanthanum can promote the decomposition of OB and the tribodiffusion of boron. From a mass spectroscopy analysis a tribochemical mechanism is suggested.     

Tribological behaviors and mechanism of sulfur- and phosphorus-free organic molybdate ester with zinc dialkyldithiophosphate

An oil-soluble sulfur- and phosphorus-free organic molybdate ester (ME) was synthesized. The antiwear and friction-reducing properties of ME with zinc dialkyldithiophosphate (ZDDP) in base oils were evaluated by four-ball tester. The results show that ME addition effectively reduced wear scar diameter (WSD) and friction coefficient (μ) as well as good antiwear synergism with ZDDP. The topography, composition and chemical states of typical elements on the worn scar were analyzed by scanning electron microscopy (SEM) with energy dispersive X-ray (EDX) and X-ray photoelectron spectrometer (XPS). Smooth and light topography of worn scar further confirms the good antiwear synergism of ME with ZDDP. EDX and XPS analyses indicate that tribo-chemically boundary films formed on the rubbing surface consist of metal oxides, sulfides and phosphates, leading to enhancement of the antiwear and friction-reducing properties of the lubricants, and that the considerable MoS₂ layer especially plays an important role in improving antiwear and friction-reducing properties of oils. The proposed antiwear mechanism involves a synergy between ME and ZDDP.     

新型S-N型三取代三嗪衍生物的合成及其与磷酸三甲酚酯在菜子油中的摩擦学研究

合成了一种新型无磷三正辛硫基取代三嗪衍生物（TOTY）,利用四球摩擦磨损试验机考察了单剂TOTT、磷酸三甲酚酯（TCP）以及含不同质量比的TOTY和TCP的复合添加剂在菜子油中的摩擦学研究;用x射线光电子能谱仪（XPS）和扫描电子显微镜（SEM）分析了磨损表面形貌和元素化学形态。结果表明：所考察的添加剂都能有效提高基础油的承载能力;在一定的条件下,单剂TOTY和TCP能够有效地提高基础油的减摩和抗磨性能;TOTY／TCP复合剂在基础油中表现出协同抗磨和减摩效应。在摩擦过程中,含上述添加剂的菜子油与摩擦副表面发生了复杂的摩擦化学反应,在摩擦副表面生成混合边界润滑膜,从而起到了减摩抗磨作用。     

Study of silane-based antiwear additives: Wear and chemistry

The chemistry and wear performance of a silane-containing additive in combination with conventional commercial engine oil additives such as zinc dialkyldithiophosphate (ZDDP), calcium-type detergent (Ca detergent), and B- and N-containing dispersant were investigated. The tribological behavior of the low-sulfur base stock 100 N blended with the above additives was investigated using a pin-on-disc Plint friction and wear tester at 100 °C. The wear scar width (WSW) of the upper steel pins was determined using an optical microscope. X-ray absorption near-edge structure (XANES) spectroscopy and X-ray photoelectron spectroscopy (XPS) were used to analyze the chemistry and thickness of the thin tribofilm formed on the disc. The morphologies of the wear scars on the lower steel discs were observed using an atomic force microscope (AFM). It was found when the silane additive is mixed with Ca detergent and B- and N-containing dispersant, the antiwear performance of the blend was greatly improved, while the friction coefficient remained almost unchanged. Indeed, the wear performance was comparable to or better than ZDDP on its own, and much better than a commercial oil blend. The silane additive is converted to hydrous SiO₂ by the water in the oil, and this SiO₂ then interacted chemically with the surface and Ca in the detergent under sliding to form a relatively thick tribofilm containing mainly a Ca silicate species. The incorporation of Si and B had little effect on the tribochemistry of ZDDP in the oil blends. When ZDDP and B- and N-containing dispersants were mixed with the silane additive, polyphosphate-type tribofilms, similar to that of ZDDP alone, were formed. However, addition of ZDDP had adverse effects on the wear performance of the silane-based blend.     

Action Mechanism of WS2 Nanoparticles with ZDDP Additive in Boundary Lubrication Regime

The effect in the tribological performance of WS₂ fullerene-like nanoparticles in PAO base oil when adding a ZDDP additive was studied at 100 °C in the boundary lubrication regime. The tribological properties of the dispersion surpass those obtained without one of the two additives. The friction modifier properties of the particles are improved in the presence of ZDDP, while the anti-wear properties of the ZDDP are increased when the particles are added to the dispersion. The composition of the formed tribofilm was investigated. Results show that a 50–60 nm tribofilm is formed on the steel surface composed by WS₂ mixed on the ZDDP chemical tribofilm. A WS₂-rich layer is observed at the top of the tribofilm. A correlation between the chemical composition of the tribofilm and the tribological properties of the “PAO + WS₂ + ZDDP” dispersion was made. Synergy between the two additives was proven.     

Influence of temperature and ZDDP concentration on tribochemistry of surface-capped molybdenum sulfide nanoparticles studied by XANES spectroscopy

The tribological behavior of surface-capped MoS₃ nanoparticles (nano-MoS₃) in hydrocarbon oils was studied in combination with ZDDP at test temperatures in the range of 100–160 °C and at ZDDP content of 0–1.0 wt% in oil. It was demonstrated that this combination of additives demonstrates high antiwear and antifriction efficiency, especially at high temperatures and low ZDDP content. X-ray Absorption Near Edge Structure (XANES) spectroscopy at the sulfur, molybdenum, and phosphorus edges was used to identify the chemical species in the tribochemical films. It was established that the tribofilms formed by combination of ZDDP and nano-MoS₃ contain phosphate-based layers incorporating MoS₂-type fragments. An increase in temperature and ZDDP content results in an increase in tribofilm thickness, while the relative Mo content in tribofilm decreases. Under the tested conditions, the best tribological properties are demonstrated by the composition comprising 500 ppm Mo and 0.1 wt% ZDDP in oil.