Tribological evaluation and antioxidant capabilities as additives of some organic compounds of zinc

Several organic compounds of zinc synthesized, blended in oil, and evaluated in laboratory bench test for antiwear/extreme pressure friction are presented. The influence of the nature of the structure on the antiwear/extreme pressure properties at wt. 1.5% concentration in a paraffinic oil is studied. Copyright © 2006 John Wiley & Sons, Ltd.     

Role of alkyl moieties in the antiwear and antioxidant performance of alkyl phosphorodithioates

Phosphorodithioate derivatives having different alkyl substitu‐ents have been synthesised, while keeping the core phosphorus‐sulphur moiety intact. The change in antiwear, extreme‐pressure, and antioxidant properties with the variation in sub‐stituents at oxygen and at sulphur linkages in the phosphorodithioates has been studied. The role of the heteroatoms with regard to the alkyl substituents has been examined. The experimental data show that the chemical structure of an additive influences its physicochemical and tribological properties.     

Performance evaluation of some organic compounds of zinc as additives for lubricating oils

Several organic compounds of zinc were synthesised, blended in oil, and evaluated in laboratory bench tests for AW/EP, friction, and deposition properties. Two of these, a zinc dithiophosphocarbamate and a package based on zinc dialkyldithiophosphate plus a sulphurised compound, appear to give the best overall performance.     

Industrial gear oil — a study of the interaction of antiwear and extreme-pressure additives

The load-carrying capacity of a base oil containing antiwear and extreme-pressure additives, sulphurized olefin (SO), dibutyl phosphite (DBP) and a thiophosphate-amine complex (SPN) was evaluated using a Timken Tester. The roughness and chemical composition of the rubbing surfaces were measured at different sliding times. A static oil immersion test of oil and steel block was carried out and the bonding strength of the protective film formed in the oil immersion test was investigated using a scratch tester. Results indicate that even with a very small amount of DBP blending with SO, a much higher Timken OK load could be obtained. The rubbing surface roughness of SO combined with DBP was much smoother than that of the SO or DBP oil alone. The scratch test of the block after immersion in the lubricant in static showed that with the combination of SO with DBP, a high-strength protective film on the steel block could be produced.     

Tribological properties of P‐ and N‐containing organic compounds as potential extreme‐pressure and antiwear additives

An amine salt of an alkoxylphosphate (a P‐ and N‐containing organic compound, PN) was synthesised. Its extreme‐pressure, antiwear, and friction‐reducing properties were evaluated as an additive in liquid paraffin and a mineral oil. Tests were performed on a four‐ball friction and wear tester with an AISI 52100 steel ball self‐mated pair and the results were compared with those of sulphurised olefin (SO), zinc di‐n‐butyldithio‐phosphate (ZDDP), and dibutylphosphite (DBP). The morphologies of the worn steel surfaces were observed using a scanning electron microscope, while the binding energies of some typical elements on the worn surfaces were determined using X‐ray photoelectron spectroscopy. The additives were found to increase the load‐carrying capacity and to reduce wear and friction coefficient considerably. PN as an additive exhibits better load‐carrying, antiwear, and friction‐reducing properties than SO, ZDDP, and DBP under the same test conditions.     

The performance of some antiwear additives and interference with other additives

This paper reports work on the evolution of films formed by some antiwear additives. Between having an additive solution in a fresh lubricant and the actual deposition of protective films on the rubbing surfaces there is a gap during which the normal actions of a given additive may be affected by the presence of another additive. Film thickness is one of the most important parameters affecting wear. Interference between additives can change the chemical composition and the thickness of the films formed and, consequently, can modify the antiwear properties of the original additive.     

A review of ultrafine particles as antiwear additives and friction modifiers in lubricating oils

This paper gives an overview of developments in the use of ultrafine particles in lubricating oils to reduce wear and friction. Work on several types of particles, such as graphite, MoS₂, PTFE, BN, fullerene, and Cu, as well as more novel and unusual particles used as lubricant additives, is reviewed. The paper summarises the results of a number of workers in this field. The tribological mechanism by which ultrafine particles operate is considered, and some conclusions, including possible future directions for research, are drawn.     

Effect of the type and concentration of lubricating additives on the antiwear and extreme pressure properties and rolling fatigue life of a four‐ball tribosystem

Tests were performed on two different four‐ball testers. The first was used to determine antiwear (AW) and extreme pressure (EP) properties at sliding friction. The second was used to assess the surface fatigue (pitting) life at rolling movement. Lubricating oils of various chemical compositions were tested. A base mineral oil was blended with two different commercial packages of lubricating additives of AW and EP types. The AW additives contained ZDDP and were blended with the base oil at 0.2 and 3wt %. The EP additives were organic compounds of sulphur and phosphorus, blended with the base oil at 1 and 10wt %. It is shown that AW additives not only improve AW and EP properties but also — at 0.2% — are beneficial for the fatigue life. An increase in the concentration of AW additives leads to an improvement of AW and EP properties but — for one of the packages — reduces the fatigue life. EP additives — at 1% concentration — significantly improve EP properties, and to a lesser extent AW properties. Such a concentration of EP additives has no influence on the fatigue life. An increase in the concentration of EP additives leads to a further improvement of EP and AW properties. However, this is accompanied by a considerable decrease in the fatigue life. By using a scanning electron microscope and energy dispersive spectrometer for analysis of the worn surface, mechanisms of action of various lubricating additives under different friction conditions were identified. Copyright © 2006 John Wiley & Sons, Ltd.     

二硫代磷酸O,O-二烷基酯-钼化合物的合成及其减摩性能研究

本文合成了由异磪基、异丁基、正戊基、正已基、正辛基和正癸基取代的二硫代磷酸O、O-二烷基酯及其双二硫物作为二齿硫配体与钼源化合物反应合成了油溶性硫-钼化合物。以1%浓度添加到矿物基础油中对极压减摩性能有显著改善。二硫代磷酸O、O-二正辛基酯-钼化合物具有最佳改进效果。     

s极压抗磨添加剂对润滑脂胶体性能的影响

利用离心分油试验机和滚筒试验机分别考察了3种不同的极压抗磨添加剂（T321，TCP和T202）以及其不同添加量、不同的实验温度或时间对锂．钙基润滑脂胶体性能的影响。研究发现，T202对润滑脂的分油影响较大；T321对润滑脂滚筒工作后的滴点有不同程度的提高；TCP对润滑脂的滴点和分油率的影响较小。对上述现象的机制分析可知，3种添加剂分子中的负电性双键、支链及润滑脂皂纤维分子问氢键不同程度影响皂纤维凝胶结构。     

极压抗磨添加剂对润滑脂胶体性能的影响

利用离心分油试验机和滚筒试验机分别考察了3种不同的极压抗磨添加剂(T321,TCP和T202)以及其不同添加量、不同的实验温度或时间对锂-钙基润滑脂胶体性能的影响。研究发现,T202对润滑脂的分油影响较大;T321对润滑脂滚筒工作后的滴点有不同程度的提高;TCP对润滑脂的滴点和分油率的影响较小。对上述现象的机制分析可知,3种添加剂分子中的负电性双键、支链及润滑脂皂纤维分子间氢键不同程度影响皂纤维凝胶结构。     

Synthesis and tribology of aluminium hexoxylborate as an antiwear additive in lubricating oil

An oil-soluble compound containing aluminium and boron has been synthesized. The tribological properties of the compound in SN500 oil were evaluated on a four-ball and block-on-ring test apparatus. The results showed that the wear resistance and load-carrying capacity of the oil were improved, and the friction coefficient was decreased. Evidence of deposition was found in the wear scar by SEM. It is concluded that this deposition provided the oil with its good wear resistance properties.     

The antiwear and extreme pressure action mechanism of CeF3 in grease

Cerium (III) fluoride as an antiwear or extreme pressure additive has been used in grease and bonded solid film lubricant, but its action mechanism has not been clarified. In this paper, the tribological characteristics of lithium grease containing CeF₃, CaF₂, SbF₃, CeO₂ and graphite fluoride ((CF)_n) were evaluated with an SRV tester. The results show that pastes containing CaF₂ and (CF)_n give good antiwear and anti-friction performance, but do not possess extreme pressure properties. Adding CeO₂ to grease offers no benefit to the antiwear and anti-friction performance of the paste. Paste containing SbF₃ has poor lubricating properties. XPS analysis shows that the good antiwear and extreme pressure properties of paste containing CeF₃ can be attributable to the formation of a physically adherent film and a chemical reaction film on the rubbing surface. Thermogravimetry shows that CeF₃ acts as an agent for the slow release of the fluorine element.     

Synthesis and characterization of novel liquid ester‐phenolic antioxidant based on dipentaerythritol

A new ester‐phenolic antioxidant based on dipentaerythritol was synthesised via a series of esterification reactions. The first esterification of dipentaerythritol with 3‐(3,5‐di‐tert‐butyl‐4‐hydroxyphenyl)propionic acid was carried out, and then the second esterification affords the final ester‐phenolic antioxidant by the reaction of the first esterification intermediates with isostearic acid. This antioxidant is functional complex which can act as not only antioxidant but also synthetic ester lubricant. The ester‐phenolic antioxidant was characterised with Fourier transform infrared spectroscopy (FTIR), rotary bomb oxidation test (RBOT) and thermogravimetric (TG)/differential scanning calorimetry (DSC) analysis. The FTIR analytical results confirmed the chemical structure of the as‐synthesised antioxidant. RBOT demonstrated that this phenolic antioxidant has excellent antioxidant efficiency. The analytical results of TG/DSC showed that this antioxidant had low volatility and good thermal stability. Copyright © 2012 John Wiley & Sons, Ltd.     

Wear and friction behaviour of CaCO3 nanoparticles used as additives in lubricating oils

For some years, reports have been published on adding solid lubricant powder to oil to improve the tribological properties of the latter, but the results have not been satisfactory. In this paper, we describe the preparation of CaCO₃ nanoparticles in a microemulsion consisting of sodium dodecyl‐sulphate (SDS)/isopentanol/cyclohexane/water, and assessment of the tribological behaviour of CaCO₃ nanoparticles as additives for lubricating oils. The CaCO₃ nanoparticles were characterised by transmission electron microscopy (TEM), and their tribological performance was tested in a four‐ball machine; the rubbing surface was analysed with X‐ray photoelectron microscopy (XPS). The results indicate that the size of CaCO₃ nanoparticles increased with the concentration of aqueous reactant, and that CaCO₃ nanoparticles exhibited good load‐carrying capacity, antiwear and friction‐reducing properties. The tribological properties of lubricating oils could be improved significantly by dispersing CaCO₃ nanoparticles in 500SN base oil containing dispersants such as polyisobutene‐butanediimide (T154), calcium alkylsulphonate (T101) and methyl‐tricaprylamine chloride (aliquat 336). The improvements in friction and wear were concluded to be due to the formation of a film containing CaCO₃ and CaO in the rubbing region, and the presence of nanoparticles, which may act in the same way as ball bearings, to facilitate sliding.     

Development of ashless multifunctional additives from cashew nutshell liquid

Aminodi(alkylphenyl) phosphorodithioates have been synthes‐ised by the condensation of di (alkylphenyl) phosphorodithioic acid, which was derived from a renewable, biodegradable, low‐cost, naturally occurring vegetable product, cashew nutshell liquid, with various amines. These ashless aminodi (alkyl‐phenyl) phosphorodithioates have been evaluated as anti‐oxidant, antiwear, friction‐modifying, and extreme‐pressure additives in lubricant compositions.     

EP/AW performance evaluation of some zinc alkyl/dialkyl/alkylaryl‐dithiocarbamates in four‐ball tests

Tribochemistry, the chemistry of interacting surfaces under the influence of a lubricant, helps in the appropriate selection of suitable lubricant additives for specific uses. Modern lubricants are usually formulated from a range of petroleum base oils or synthetic fluids incorporating a variety of chemical additives for performance enhancement. Extreme‐pressure (EP) and anti‐wear (AW) additives are used extensively in lubricants for hypoid gears and metal cutting and forming operations to reduce wear, modify friction, and prevent scuffing of moving metallic parts. The present paper includes the synthesis and the evaluation of the tribological properties of 0.5% (w/v) solutions of some zinc bis‐(alkyl/dialkyl/alkylaryldithiocarbamates) in paraffin oil using 12.7 mm diameter steel bearing ball specimens in four‐ball tests. All the synthesised zinc dithiocarbamate additives in general, and zinc bis‐(morpholinodithio‐carbamate) (A₄) in particular, exhibited good AW, EP, and friction‐reducing properties. Additive A₄ especially gave low values of wear‐scar diameter and coefficient of friction at higher loads and higher values of load wear index and flash temperature parameter during EP tests (ASTM D 2783) and afforded lower values of wear‐scar diameter in a one‐hour wear test (ASTM D 2266–67). The surface topography of the wear‐scar matrix of the used ball specimens was investigated by scanning electron microscopy.     

The properties of various antiwear and extreme‐pressure additives in pentaerythritol ester

The tribological properties of three representative antiwear and extreme‐pressure additives, tricresylphosphate (TCP), triphenylthiophosphate (TPPT), and α‐mercaptobenzothiazole (MBT), in pentaerythritol ester at different concentrations were studied. It was found that TCP could react with Fe to form an organic phosphate film containing 4% P on the scar surface, while TPPT formed a blended organic phosphate and inorganic FeS film, containing 4% P and 6% S, respectively. MBT formed an inorganic FeS film containing 45% S. Ferrographic analyses of wear particles collected from oil samples after four‐ball tests showed that the higher the temperature the better the tribological performance of the additivated ester, due to its reaction with the metal surface.     

The influence of tribochemical reactions of antiwear additives on heterogeneous surface layers in boundary lubrication

The article discusses methods for the deposition of antiwear, composite coatings with a metallic matrix. The Ni–P–Al₂O₃ composite layers were superimposed on carbon steel elements using the electroless plating technique. A comparative analysis of adsorptive interactions was carried out for model systems with antiwear characteristics, i.e., for the Ni–P matrix, and the composite material containing micro-dispersive corundum, i.e., Ni–P–Al₂O₃. The paper presents the results of tribological tests and analyses the effects of tribochemical interactions in the macroscale (using in a pin-on-disc system device) and in the micro/nanoscale—performed with the use of Atomic Force Microscopy (AFM).