Tribological study and mechanism of B–N and B–S–N triazine borate esters as lubricant additives in mineral oil

The tribological study of N-containing heterocyclic borate esters as lubricating additives had been the research hotspot. In this work, B–N and B–S–N triazine borate esters were synthesized and their antiwear/extreme pressure (AW/EP) properties were studied. Results showed the synthetical additives had good AW performance. However, B–S–N triazine borate ester showed excellent EP property while B–N triazine borate ester hardly owned EP property. The hydrolytic stability of borate ester additives was improved by the formation of coordination of nitrogen to boron. The XANES spectroscopy analysis showed that there was a layer of borate–oxygen–iron inorganics in the tribofilms. The existence of iron sulfate and iron sulfide guaranteed good AW/EP properties of B–S–N triazine borate ester additive in mineral oil.     

Chemistry of Antiwear Films from Ashless Thiophosphate Oil Additives

X-ray absorption near-edge structure (XANES) spectroscopy has been combined with atomic force microscopy (AFM) to investigate the interaction of ashless thiophosphate oil additives on steel. Both mono- and dithiophosphates were studied and compared with one another in terms of chemistry and tribological performance. XANES revealed that, thermally, all three thiophosphate additives behaved similarly with steel to form a thermal film at temperatures of 150 °C. The thermal films all consisted of a layered structure comprised of Fe(II) polyphosphate and FeSO₄ in the bulk and iron polyphosphate of various chain length towards the surface. Tribochemical films generated at 5min, 1 h, and 6 h of wear testing revealed that for all three additives, the phosphorus chemistry of an antiwear (AW) film remained chemically consistent throughout all rubbing times. This suggests that the phosphorus chemistry of the AW film is determined in the initial stages of tribofilm formation. The iron polyphosphate chain length remained uniform throughout the AW film with short chain iron polyphosphates found both at the surface and in the bulk of the films. Mild AW conditions produced several different forms of sulfur at the various stages during wear testing. S K-edge XANES spectra for the 5-min tribofilms (both total electron yield and fluorescence yield) showed oxidized and reduced forms of sulfur throughout the films for all three additives. Over extended periods of rubbing (6 h), the more thermodynamically stable product, FeSO₄, was produced and became the major constituent of the tribofilms formed. Iron sulfate was present throughout the films with only traces of reduced sulfur present.AFM imaging of the AW films revealed that the morphology of the films varied from additive to additive and changed over the duration of wear testing. Generally, the AW films were composed of elongated pads orientated in the sliding direction. As rubbing continued, the pads of each AW film became more homogeneous. The larger pads of AW film appeared to have supported most of the load throughout the course of wear testing, resulting in better AW protection to the metal over increased periods of rubbing     

XPS and XANES characteristics of tribofilms and thermal films generated by two P- and/or S-containing additives in water-based lubricant

Two phosphates were synthesized and their tribological properties as water-soluble lubricant additives were evaluated by using four-ball tester. The micro/nano-scale chemical characteristics of tribofilms and thermal films formed from these additives in different conditions were explored by X-ray photoelectron spectroscopy (XPS) and X-ray absorption near-edge structure (XANES) spectroscopy. The results show that the additives have better anti-wear and friction reducing properties than the oleate solution at higher load. Surface analysis results indicate that tribofilms are mainly composed of absorbed layer and chemical reactant layer, in which phosphorus exists in the form of adsorbed molecule, phosphate or polyphosphate, and sulfur in the form of alkyldisulfide, sulfide and sulfate. As to the thermal films, phosphate (or polyphosphate) and sulfate are detected as the main components. The anti-wear and friction-reducing performances can be ascribed to the formation of films on the metal surface, and the mechanism of the process of molecules adsorption, new compounds production through tribochemical reactions, film formation and destruction.     

Tribological Performance and Wear Mechanism of Compound Containing S,P, and B as EP/AW Additives in Copper Foil Oil

Research and development on the high biodegradability of additives is indispensable for environmentally friendly lubricants, which is one of the key factors to advance lubricant technology toward “greener” chemistry. The tribological performance of fatty alcohol polyoxyethylene phosphate acid ester (EK), boron-containing amide (BT), dialkyl dithiophosphate ester (DDE), and a mixture of these (compound) as extreme pressure (EP)/antiwear (AW) additives in hydrogenated base oil (GH) were investigated using a four-ball testing machine. The elemental composition and chemical characteristics of the AW films generated on the surfaces of the steel balls were studied using X-ray photoelectron spectroscopy (XPS), and their AW mechanisms are hereby proposed. Thermal degradation tests were conducted to identify their thermal stabilities using thermogravimetry and differential scanning calorimetry. The results show that these additives can greatly improve the EP/AW properties of GH. XPS analyses of the worn surfaces indicate that decomposed borate esters and organic sulfide or nitrides were adsorbed on the worn surface, and the P and S elements of the compound reacted with the metal and existed in the form of phosphates and sulfates, both of which contributed to the formation of a boundary lubricating film. Moreover, these additives provide the lubricants with excellent oxidation resistance and thermal stability.     

Study of interaction of EP and AW additives with dispersants using XANES

The chemical interaction of two kinds of dispersants (bis-succinimide dispersant and borated bis-succinimide dispersant) with four kinds of antiwear (AW) and extreme pressure (EP) additives (zinc dialkyldithiophosphate, dialkyldithiophosphate ester, diphenylphosphate ester and dialkyldithiocarbamate) has been investigated under different contact pressures. The chemical compositions of the tribofilms have been studied by B, N, P and S X-ray absorption near edge structure (XANES) spectroscopy. The N K-edge XANES analysis has been used to follow the reaction pathway of amine and imide functional groups in the dispersants and their interactions with EP and AW additives. It has been found that AW additives react with amine to form amine phosphate at low load. However, at high load, there is a good evidence for the formation of a nitrate phase in the tribofilms, the first direct observation of oxidative dispersant loss in the rubbing contact. On the other hand, EP additives behave differently and in general are less reactive. The B K-edge XANES has been employed to follow the interaction of borated dispersant with the EP and AW additive. In general, boron originally in the trigonal coordination, is converted to a tetrahedral coordination form in the process of tribofilm formation.     

Improving the AW/EP ability of chemically modified palm oil by adding CuO and MoS2 nanoparticles

Improvement in the anti-wear (AW) and extreme pressure (EP) ability of chemically modified palm oil (CMPO) by adding nanoparticles was experimentally evaluated. Nanolubricants were synthesized by adding 1 wt% copper(II) oxide (CuO) and 1 wt% molybdenum disulfide (MoS₂) nanoparticles to CMPO. The AW/EP properties of the formulations were evaluated by four-ball and sliding wear tests. Wear surfaces were analyzed by scanning electron microscopy, along with energy-dispersive X-ray and micro-Raman scattering spectroscopy. The MoS₂ nanoparticles exhibited better AW/EP properties than did the CuO nanoparticles. The addition of 1 wt% oleic acid as a surfactant facilitated the reduction of agglomerates.     

Combination of ashless antiwear additives with metallic detergents: interactions with neutral and overbased calcium sulfonates

The interactions of neutral and overbased calcium sulfonate detergents with ashless thiophosphate oil additives under boundary lubrication were studied. The ashless additives used were neutral and acidic dialkyldithiophosphate (DTPs) and neutral triaryl monothiophosphate (MTP). This study uses three surface analytical tools to provide elemental and chemical information at the surface and in the bulk of the derived tribochemical films. The elemental composition of the tribofilms was studied using X-ray photoelectron spectroscopy (XPS) and energy-dispersive X-ray analysis (EDX) (combined with scanning electron microscopy (SEM)). Corresponding P and S X-ray absorption near edge structure (XANES) spectroscopy was also used to provide further insight into the chemical composition of the films. SEM images of the derived tribofilms revealed that each film had distinct topographical features associated with it. XPS and EDX revealed that when oil is blended with calcium sulfonate, considerable amount of calcium is incorporated into all the tribochemical films. The phosphorus content of the tribofilm was reduced substantially when the overbased detergent was combined with MTP additive. XANES spectroscopy of the P L-edge provided direct evidence for the formation of calcium phosphate in tribofilms from the ashless additives in combination with the detergent.S K-edge revealed that sulfate is the main sulfur species formed in the bulk for all three tribofilms in the presence of the neutral detergent while a mixture of sulfite and sulfide species are formed when the overbased was used. S L-edge XANES showed that calcium sulfonate has undergone some oxidation at the surface. A more antagonistic effect was observed for MTP, with the formation of a very thin phosphate film.Tribological performance was also evaluated. Surprisingly, combination of the neutral detergent with any of the AW additives did not result in any significant change in wear to the substrate. For MTP plus neutral detergent, the thinner phosphate film produced, combined with very little change in wear protection confirms that, not only is the tribochemistry dominated by calcium sulfonate, but also confirms the anti-scuffing and AW properties that are associated with it as well. Even more surprising, was the significant decrease in wear when the overbased detergent is used. This illustrates not only that the tribochemistry was dominated by the detergent, but also the exceptional AW properties of calcium carbonate.     

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.     

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.     

Tribological behaviour of antiwear additives used in hydraulic applications: Synergistic or antagonistic with other surface-active additives?

This paper examines the friction and antiwear (AW) properties using SRV (Schwing–Reib–Verschleiss) tribometer and film-forming properties using atomic force microscope (AFM) of one simple model formulation containing solely AW additive and seven oils containing mixture of additives including three zinc-based packages (ZP), ZP with additional AW additives, ZP with extreme pressure (EP) additives, ZP with viscosity index improvers (VII) and one zinc-free ashless package in steel/steel contacts. VII-containing oil show lower boundary and mixed friction coefficients than the other oils. Although all AW additive-containing oils formed tribofilms, AW properties of ZPs appear to be affected antagonistically by EP additives while synergistically by VII. Zn-free additives investigated in this study show higher wear than ZPs.     

Lubrication of aluminium–silicon surfaces with ZDDP and detergents

Abstract

A review of the lubrication of aluminium–silicon (Al-Si) substrates by zinc dialkyldithiophosphate (ZDDP) and detergent engine oil additives is presented. Greater attention has been paid to understand the interactions of ZDDP, rather than detergents, with the aforementioned non-ferrous substrates. Zinc dialkyldithiophosphate generates tribofilms on both aluminium and silicon regions of aluminium–silicon alloys. However, film formation is believed to occur on silicon grains within the alloy, and those layers observed on aluminium regions are material transfer or the product of ZDDP thermal decomposition. There were many similarities in terms of film thickness, reduced elastic modulus, tribochemistry and topography of ZDDP derived tribofilms on both ferrous and Al–Si substrates. Calcium carbonate based films were observed on silicon grains when the aluminium alloys were lubricated with overbased calcium sulphonate, the tribochemistry and topography of which were similar to layers formed on ferrous substrates. When lubricated with either fully formulated oil or lubricants containing both detergent and ZDDP, the subsequently generated films were of varying chemistry, but often contained zinc or calcium phosphate compounds. The antiwear characteristics of ZDDP and calcium sulphonate tribofilms on ferrous and aluminium–silicon substrates are discussed, with the mechanical and film thickness data for such layers presented.     

Influence of hindered phenol on the tribochemistry of polysulfides in mineral oil and synthetic diester

The influence of hindered phenol on tribological properties and mechanism of polysulfides in mineral oil and synthetic diester were investigated in this paper. Four‐ball machine was employed to evaluate the anti‐wear and friction‐reducing performance of the lubrication system and X‐ray absorption near‐edge structure spectroscopy was applied to detect the thermal and tribofilms. The tribological results indicate that when the phenol was added in trisulfide/synthetic diester system, the friction coefficient decreased. The anti‐wear performance of sulfides only depended on the concentration of sulfur in mineral oil. The results of X‐ray absorption near‐edge structure analysis indicate that sulfite can be found in thermal films by adding hindered phenol into mineral oil with trisulfide, while in other conditions, the thermal films only consist of sulfate. The results of the tribofilms show that for the trisulfide in mineral oil, hindered phenol changes the ratio of reduced and oxidised form of sulfur. Copyright © 2016 John Wiley & Sons, Ltd.     

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.     

Antiwear Action of Mineral Lubricants Modified by Conventional and Uncoventional Additives

The authors of this paper investigated the influence of esters of rapeseed oil fatty acids on the lubricating properties of mineral lubricants containing chosen AW/EP additives. Methyl esters, ethylene glycol esters, and glycerol esters as well as some commercial AW/EP packages based on zinc dialkyldithiophosphate, S–P organic compounds, and sulphurized esters of fatty acids were tested. The tribological tests were carried out with the use of a four-ball machine. Antiwear (AW) properties of tested compositions were determined using their limiting load of wear (G_oz(40)). It appears that the AW action of esters of rapeseed oil fatty acids depends on their structure. The best AW action is shown by compositions of mineral oil lubricants containing AW/EP additives and methyl esters of rapeseed oil fatty acids. The SEM/EDS analysis of the scar surface layer indicated that the presence of these esters in lubricants causes a change in the interaction between AW/EP additives and the metal surface. These observations were confirmed by the XPS surface analysis.     

单胺基双巯基三嗪衍生物的合成及摩擦学性能研究

为改善锂基脂极压抗磨性能使其适应于更为苛刻的工矿条件,合成了一系列单胺基双巯基三嗪衍生物,使用四球机考察了添加剂在锂基脂中的极压、抗磨、减摩性能。结果表明,此类添加剂均能改善锂基脂的极压、抗磨、减摩性能,碳链最短的2-二正丁胺基-4,6-二巯基-1,3,5-均三嗪(DBAT)的极压性能表现最佳,能够使锂基脂的pB值提高约50%,在不同负荷或不同质量分数的条件下DBAT表现出了最好的抗磨效果。使用SEM与XPS分析钢球表面典型元素的分布情况与化学态,发现由无机硫酸盐、硫化亚铁及有机含氮化合物所组成的保护膜可能是摩擦学性能提高的主要原因。     

X-Ray Photoelectron Spectroscopy Analysis of Antiwear Tribofilms Produced on Boundary-Lubricated Steel Surfaces from Sulfur- and Phosphorus-Containing Additives and Metal Deactivator Additive

X-ray photoelectron spectroscopy (XPS) was performed on AISI 52100 steel surfaces subjected to sliding in the boundary lubrication regime at 32 and 100°C. The specimens were lubricated with base oil blended with individual additives containing sulfur (S), phosphorus (P), or metal deactivator, as well as base oil with all the previous additives in the same amounts as in the single blends. XPS spectra were analyzed to confirm the formation and determine the chemical composition of the antiwear tribofilms produced on the steel surfaces during sliding. The use of S- and P-containing additives on the tested disk surfaces revealed that tribochemical reactions resulted in the formation of antiwear tribofilms containing S- and P-rich components. Results for the multi-additive blend provided evidence for two components in the produced tribofilm, appearing to consist primarily of sulfide and phosphate. This investigation provides new insight into the competing roles of these compounds on the tribological properties of the antiwear tribofilms. The significance of the sulfide components is demonstrated by the more pronounced antiwear effect of the S-containing additive in the multi-additive formulation.     

硫化亚铁固体润滑涂层的制备方法与摩擦学性能研究

描述了硫化亚铁固体润滑涂层的制备方法及摩擦学性能。结果表明,不同方法得到的硫化亚铁涂层都能具有优良的减摩、耐磨、抗擦伤性能,但其摩擦学性能有差异,适用工况条件也不同。并指出了制备方法中存在的缺陷,对其今后的发展作了展望。     

Calcium sulphonate and its interactions with ZDDP on both aluminium-silicon and model silicon surfaces

The boundary lubrication of an aluminium-silicon cylinder liner operating under mild wear conditions has been investigated. The interface was lubricated with synthetic six centistokes poly alpha olefin base oil, which contained either calcium sulphonate or calcium sulphonate and zinc dialkyldithiophosphate. Effective replication of silicon grains within an aluminium-silicon alloy using a silicon crystal substrate affords valuable reproduction of tribofilms. The physical and chemical characteristics of films generated on either substrate were comparable. A marked difference in structure was exhibited between the tribofilms formed from either lubricant. Detailed tribological and tribochemical analysis has been conducted on either substrate.     

The Correlation of Microchemical Properties to Antiwear (AW) Performance in Ashless Thiophosphate Oil Additives

X-ray absorption near-edge structure (XANES) spectroscopy at macro-scale (mm2) and X-ray photoelectron emissions microscopy (X-PEEM) at micro-scale (m2) have been used to investigate the chemistry and spatial distributions of chemical species in tribochemical films generated from ashless thiophosphate oil additives on steel. Two different ashless thiophosphate additives were used: a triaryl monothiophosphate (MTP) and a dialkyldithiophosphate (DTP). Atomic force microscopy (AFM) and secondary electron microscopy (SEM) were also used to investigate the thickness and the topography of the tribofilms. Macro-scale XANES analysis showed that both ashless thiophosphates reacted with the steel surface to produce short to medium chain polyphosphates as the main constituent and sulfur species as minor component. From the PEEM experiment, it was found that the DTP tribofilm was microchemically heterogeneous, with areas of varying degrees of polyphosphate chain length. Conversely, MTP formed a tribofilm microchemically homogeneous, with areas comprised of only short chain polyphosphates. From, the different areas of polyphosphate chain length within the DTP tribofilm, colour-coded polyphosphate distribution map was generated. AFM, X-PEEM and SEM revealed that the DTP film was thicker and was composed of AW pads that were wider in area than MTP. This resulted in a smaller wear scar width (WSW) value for DTP. This is the first time that all these analytical techniques have been combined to better understand the nature of the tribofilms from ashless additives. We have concluded that an ideal AW film is comprised of a thick film with pad-like structures that are wider in area and microchemically heterogeneous, with areas of varying polyphosphate chain length.     

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.