Limitations on use of ZDDP as an antiwear additive in boundary lubrication

Wear tests on rubbing elements under various contact pressures, oil temperatures and surface roughness were performed to elucidate the limitation conditions on antiwear performance of a typical zinc dialkyl dithiophosphate (ZDDP) added to a paraffin base oil. The analysis results indicate that the antiwear performance of ZDDP depends on the rates of recovery and growth of effective surface films. If these rates exceed that of scraping the films off the rubbing surfaces, antiwear performance is evident. However, the rates of recovery and growth of surface films are influenced by some essential factors, including the oil temperature, contact pressure and the surface roughness and hardness of rubbing elements. Under some suitable conditions, ZDDPs show favorable antiwear performance, but under some severe conditions, such as high pressure (over 90 MPa), high temperature (over 200 °C) with an insufficient concentration of ZDDP and the rubbing of a rough and harder surface on a softer surface, the antiwear performance of ZDDPs is negligible.     

Tribological performance of raw and formulated RBD palm kernel with ZDDP additive

This study compares tribological performance of refined, bleached and deodorized (RBD) palm kernel (PK) as an alternative lubricant. An analysis was made for chemically modified RBD PK with zinc dialkyl dithiophosphate (ZDDP) additive to determine its tribological performance using modified pin-on-disc tribotester. Commercial mineral oil (SAE 40) was used as the benchmark in this study. The conditions for this experiment are sliding speed at 1.5 m/s, a normal load at 9.81 N, weight percentage of ZDDP for 0, 3 and 5%, lubricant quantity of 2.5 ml and test duration of 60 min. The findings revealed that RBD PK oil exhibits better anti-friction and anti-wear performance compared to commercial mineral oil (SAE 40). Besides, coefficient of friction is less dependent on ZDDP concentration, but anti-wear ability is dependent on the ZDDP additive concentration. ZDDP additive acts as a good anti-wear and antioxidant additive in RBD palm kernel.     

Effects of electric field on characteristics of nano-confined lubricant films with ZDDP additive

The consequence of bearings exposed to shaft voltage is a very important tribological problem, especially with the increasing use of variable-frequency drives (VFDs) to control alternate current (AC) motors. The emerging behavior of gas micro-bubbles and the film forming characteristics between base oil (liquid paraffin) films with and without ZDDP additive under an external electric field (EEF) in a nanogap have been compared. Experimental results indicated that the micro-bubble emerging intensity increases slightly when the additive is involved in the base oil. The magnitude of the electric current flowing through the lubricant film closely related to the intensity of the micro-bubble emerging. No obvious difference in the film thickness can be found between the liquid paraffin films with and without ZDDP additive. The influence of the EEF on the film thickness of the liquid paraffin with the additive is more significant.     

Comparing tribological behaviors of sulfur- and phosphorus-free organomolybdenum additive with ZDDP and MoDTC

A new kind of sulfur- and phosphorus-free organomolybdenum oil-based additive N, N-bis (2-hydroxyethyl)-dodecanamide molybdate (NNDM) was prepared. Its tribological performances as additive in base oil 150SN were examined on a four-ball tester, and compared with those of ZDDP and MoDTC under boundary lubrication condition. The tribofilm NNDM generated on the worn surface was analyzed by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). Results showed that NNDM blend oil exhibited excellent load-carrying capacity, significantly reduced friction coefficient and wear rate of worn surface, which could be attributed to high amount of long-chain alkylamide and MoO_x in NNDM tribofilm.     

Adsorption of ZDDP on iron surfaces and its relation with surface tension

This paper reports work on the relationship of surface tension of ZDDP solutions to adsorption isotherms. The surface tension of the solutions varies with their composition, and information about adsorption, decomposition or other chemical changes of ZDDP in solution can be obtained from the correlation of solution concentration and surface tension. From this work, the authors conclude that adsorption of ZDDP on iron can occur at even low concentrations, increasing with temperature, and that decomposition, association and interaction between components may occur in solution at high temperatures.     

Tribological behavior of aluminum alloys surface layer implanted with nitrogen ions by plasma immersion ion implantation

Some 2014 and 2024 aluminum alloys were implanted with nitrogen ions (N⁺) by Plasma Immersion Ion Implantation (PIII), and dose range was from 2×10¹⁷ to 1×10¹⁸ N⁺ cm⁻². The microstructure of surface layer was studied by Transmission Electron Microscopy (TEM). The depth profile of the implanted layer was investigated by Auger Electron Spectrometry (AES). The wear test was carried on a pin-on-disk wear tester. The micro-morphology of wear was observed by Scanning Electron Microscopy (SEM). The results reveal that: after implanted with nitrogen ions, the friction coefficient of surface layer decreased, and the relative wear resistance increased with the increase of the nitrogen dose. The tribological mechanism was mainly adhesive, and the adhesive wear tended to become weaker gradually with the increase of nitrogen dose. The upper two effects were mainly attributed to the formation of hard AlN precipitation and supersaturated solid solution of nitrogen in the surface layer.     

Tribological properties of Fe7Mo6-based-alloy lubricated with poly-alpha-olefin containing PN additive

Tribological properties of Fe–Mo type disk specimens were investigated against ASTM 52100 steel balls under the lubrication of poly-alpha-olefin (PAO) and PAO containing 1.5 mass% alkyl-phosphonic acid-triazole-methanamine (PN additive). Both the Fe₇Mo₆-based alloy and Mo disk specimens exhibited lower friction and lower wear rates than the Fe and gray cast iron disk specimens under the lubrication of PAO. The friction coefficients of the Fe₇Mo₆-based alloy disk specimens were reduced to 0.07 by adding 1.5 mass% PN additive to PAO. No wear volume loss was observed on the Fe₇Mo₆-based alloy disk specimens when they were lubricated with PAO containing 1.5 mass% PN additive.     

Fretting wear behavior of nitrogen ion implanted titanium alloys in bovine serum lubrication

Nitrogen ion implantation was performed on biomedical titanium alloys by using of the PBII technology to improve the surface mechanical properties for the application of artificial joints. The titanium nitride phase was characterized with X-ray photoelectron spectroscopy (XPS). The nanohardness of the titanium alloys and implanted samples were measured by using of in-situ nano-mechanical testing system (TriboIndenter). Then, the fretting wear of nitrogen ion implanted titanium alloys was done on the universal multifunctional tester (UMT) with ball-on-flat fretting style in bovine serum lubrication. The fretting wear mechanism was investigated with scanning electron microscopy (SEM) and 3D surface profiler. The XPS analysis results indicate that nitrogen diffuses into the titanium alloy and forms a hard TiN layer on the Ti6Al4V alloys. The nanohardness increases from 6.40 to 7.7 GPa at the normal load of 2 mN, which reveals that nitrogen ion implantation is an effective way to enhance the surface hardness of Ti6Al4V. The coefficients of friction for Ti6Al4V alloy in bovine serum are obviously lower than that in dry friction, but the coefficients of friction for nitrogen ion implanted Ti6Al4V alloy in bovine serum are higher than that in dry friction. Fatigue wear controls the fretting failure mechanism of nitrogen ion implanted Ti6Al4V alloy fretting in bovine serum. The testing results in this paper prove that nitrogen ion implantation can effectively increase the fretting wear resistance for Ti6Al4V alloy in dry friction, and has a considerable improvement for Ti6Al4V alloy in bovine serum lubrication.     

Structure analysis by diffraction of amorphous zones created by Ni ion implantation into pure Al

The implantation of Ni ions into pure Al leads to the formation of approximately 10 nm amorphous zones (AZ) which induce diffuse rings in the diffraction pattern in addition to the diffraction spots of the crystal. Measurements by energy dispersive spectrometry and electron energy loss spectrometry attributed to the amorphous zones an average Ni concentration of 25 at%. The exact structure of these AZ is still unknown. The structure is characterized here by both the total and partial radial distribution functions (RDF). Structure factor deduced from experiments is compared to calculated one. For this purpose, molecular dynamic (MD) simulations are used to model the AZ structure. The RDF are determined using this structure and analytical calculation of the diffraction pattern is achieved. Simulations of the diffraction pattern of the simulated MD sample using both a kinematic and a dynamic approach are achieved to refine the analytical procedure used on the experimental diffraction patterns. It appears that the amorphous structure is well reproduced by the MD simulations. Analytical calculation reveals the presence of a well-established chemical order in the amorphous material.     

Evaluation of lubricating-oil performance and emissions with lubricant formulations using ZDDP as the selected additive in GDI engines: a simultaneous study of VOCs and soot in oil

Journal of Mechanical Science and Technology - This study investigated the effect of different antiwear additives on volatile organic compounds (VOCs) and particulate matter (PM) characteristics...     

Non-newtonian thermal analysis of an EHD contact lubricated with MIL-L-23699 oil

A thermal and non-Newtonian fluid model under elastohydrodynamic lubrication conditions is proposed, integrating some particularities, such as the separation between hydrodynamic and dissipative phenomena inside the contact. The concept of apparent viscosity is used to introduce the non-Newtonian behaviour of the lubricant and the thermal behaviour of the contact into the Reynolds equation, acting as a link element between the hydrodynamic and dissipative components of the EHD film, independently of the rheological and thermal models considered. The apparent viscosity enables the application of the rheological model better adapted to each lubricant, without appealing to special formulations of the EHD problem.The Newton–Raphson technique is used to obtain the lubricant film geometry and the pressure distribution inside the EHD contact. The shear stresses developed in the fluid film are evaluated assuming the non-linear Maxwell rheological model. The surfaces and lubricant temperature distributions are determined using the simplified Houpert's method, applied to the inlet contact zone, and the thermal method proposed by Tevaarwerk is applied in the high pressure contact zone.The non-Newtonian thermal EHD model is applied to the analysis of a contact lubricated with MIL-L-23699 oil. Significant results are obtained for the centre and minimum film thickness, for the inlet shear heating and film thickness reduction factor (φ_T), for the temperature rise of the lubricant and of the surfaces and for the friction coefficient inside the contact, considering wide ranges of the operating conditions (maximum Hertzian pressure, inlet oil temperature, rolling speed and slide-to-roll ratio).Finally, the numerical traction curves determined are compared with the corresponding experimental results, showing very good correlation.     

Microstructure and wear resistance of thermal sprayed steel coatings ion beam implanted with nitrogen

In the present study, the high-current-density nitrogen ion implantation technique is applied to enhance mechanical properties of thermal sprayed steel coatings. XRD measurements and optical microscopy of ion implanted coatings show clearly the presence of nitrogen solid solutions and precipitates of new phases in the surface layers of coatings. Phases formed are controlled by the temperature of ion beam processing, initial chemical composition and microstructure of coatings. Wear tests demonstrate that properly selected parameters of ion implantation dramatically improve wear and score-resistance of coatings. The influence of the microstructure and phase composition of nitrogen ion implanted layers on tribological properties is discussed.     

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 comparative study on the tribological behaviors of nitrided and sulfur-nitrided 35CrMo steel lubricated in PAO base oil with MoDTC additive

A nitrided layer on 35CrMo steel was prepared by the ion nitriding process, and then a sulfur-nitrided layer was obtained by low temperature ion sulfuration. The results showed that both the nitrided and sulfur-nitrided surfaces improved the wear resistance efficiently under PAO lubrication, and exhibited the best wear resistance and friction-reducing property under PAO with 0.75% MoDTC lubrication. Compared with the plain and nitrided surfaces, the sulfur-nitrided surface exhibited the best synergistic effect with MoDTC displaying the lowest friction coefficient and wear volume. The mechanism of the best effect was due to MoS₂ and FeS formed on the sulfur-nitrided surface.     

A comparative study on the tribological behaviors of nitrided and sulfur-nitrided 35CrMo steel lubricated in PAO base oil with MoDTC additive

A nitrided layer on 35CrMo steel was prepared by the ion nitriding process, and then a sulfur-nitrided layer was obtained by low temperature ion sulfuration. The results showed that both the nitrided and sulfur-nitrided surfaces improved the wear resistance efficiently under PAO lubrication, and exhibited the best wear resistance and friction-reducing property under PAO with 0.75% MoDTC lubrication. Compared with the plain and nitrided surfaces, the sulfur-nitrided surface exhibited the best synergistic effect with MoDTC displaying the lowest friction coefficient and wear volume. The mechanism of the best effect was due to MoS₂ and FeS formed on the sulfur-nitrided surface.     

Characterisation of a new batch of ion implanted Bi in silicon specimens for use as primary reference surface standards

A set of 100 silicon specimens has been prepared with a nominal implanted dose of 5×10¹⁵ Bi atoms cm⁻². The samples have been analysed by Rutherford backscattering. The lateral uniformity of the bismuth implantation has been tested by the intercomparison of all samples. Absolute calibration for six of the samples has been achieved by comparison with carefully deposited thin films.     

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.     

A tribological study of an S,P-containing benzotriazole derivative as an additive in pentaerythritol ester

The load-carrying capacity, antiwear and friction reduction properties of an S,P-containing benzotriazole derivative (BMDDP) added to a synthetic lubricant (pentaerythritol ester) were evaluated using a four-ball test machine. The results when compared with those of tricresyl phosphate (TCP) and zinc dialkyldithiophosphate (ZDDP) show that, in pentaerythritol ester, the novel compound (BMDDP) is an excellent multifunctional additive, which possesses better load-carrying capacity, antiwear and friction reduction properties than either TCP or ZDDP. The rubbed surfaces were analysed using XPS and EPMA, and the antiwear mechanism is discussed.     

The surface chemistry of chloroform as an extreme-pressure lubricant additive at high concentrations

Carbon tetrachloride is an extremely good extreme-pressure (EP) lubricant additive at low concentrations (<3 wt% chlorine) since it can react to form a high-melting-point Fe₃C antiseizure layer. In contrast, small hydrogen-containing additive molecules (CH₂Cl₂, CHCl₃) decompose to form FeCl₂ which melts at ~940 K and limits the maximum seizure load to ~3500 N as measured hi a pin and v-block apparatus. However, both thermodynamic calculations and results of a Mössbauer analysis of an iron foil heated in CHCl₃ at 830 K indicate that iron carbide can be formed from chloroform. In addition, it is also found in that case that a plot of seizure load versus concentration, after initially forming a plateau, once again increases with higher additive concentrations (>4 wt% chlorine) in accord with the idea that a higher melting point carbide film can be formed. It has been shown previously that asymptotes in the plot of removal rate versus applied load correspond to melting of the interfacial anti-seizure film. When using 9.0 wt% chlorine from chloroform as the additive, a drastic increase in removal rate is found at an interfacial temperature of ~940 K corresponding to the melting of FeCl₂ and an additional asymptote is evident at ~1500 K due to the melting of Fe₃C in accord with the thermodynamic and Mössbauer results.     

The performance and antiwear mechanism of S-containing organic borate as an oil additive

A sulphur-containing organic borate (BS-2) was prepared. Its friction and wear properties when added to n-tetradecane, and the effect on wear of addition of dodecyl amine to the synthesised S-containing borate oil, were measured using a Timken test machine. The results were compared with those of tridodecyl borate, and a combination of tridodecyl borate and sulphurised cotton seed oil. X-ray Photoelectron Spectroscopy (XPS) was used to examine the rubbed surfaces of the test blocks, while Scanning Electron Microscopy (SEM), Energy Dispersion Analysis of X-ray (EDAX) and X-ray Diffraction (XRD) were used to study the wear debris. It is found that S-containing organic borate exhibits a poorer antiwear property than tridodecyl borate but, with the addition of dodecyl amine to the S-containing borate, its antiwear property can be improved. XPS analyses indicate that sulphur on the rubbed surfaces exists in the forms of organic sulphide and FeSO₄, and the addition of amine reduces the adsorption and reaction of sulphur to the rubbing surfaces. SEM analyses revealed that the wear debris was in powder form, and the EDAX and XRD analyses indicated that iron sulphide, iron oxide and elemental iron were contained in the wear debris. A corrosive wear mechanism of steel test blocks lubricated by S-containing organic borate is proposed.