Study of Friction and Wear Performance of Zinc Dialkyldithiophosphate in the Presence of Trace Ketone

This study reports the influence of methyl isopropyl ketone on the tribological performance of zinc dialkyldithiophosphate. The lubricity and friction and wear tests of 500 SN neutral base stock oil containing zinc dialkyldithiophosphate with methyl isopropyl ketone were carried out by MQ-800 four-ball and MM-200 block-on-ring tribometers respectively. The experimental results show that methyl isopropyl ketone decreases the wear resistance and the load-carrying capacity of zinc dialkyldithiophosphate. The friction reduction of zinc dialkyldithiophosphate was lowered as well because of the addition of ketone. The friction and wear mechanism of zinc dialkyldithiophosphate with trace ketone was studied by optical microscopy IR, SEM, XPS and ferrography. The variations of the tribological performance of zinc dialkyldithiophosphate with ketone could be partly attributed to the decreases of active species, such as phosphorus and zinc, which are responsible for the formation of anti-wear films, on the rubbing surface due to the existence of ketone.     

内燃机油添加剂之间相互作用的研究

探讨了内燃机油添加剂之间的相互作用，磺酸盐与水杨酸盐的相容性差，混合后有沉淀物生产；水杨酸盐与丁二酰亚胺，ＺＤＤＰ有较弱的相互作用，添加量小时无沉淀物生成，添加量大时才有沉淀物生成；磺酸盐与丁二酰亚胺，ＺＤＤＰ的相容性好，混合后沉淀物生成。该结论为内燃机油的调配，贮存和全用提供了科学依据。     

The use of X‐ray absorption spectroscopy for monitoring the thickness of antiwear films from ZDDP

X‐ray absorption near edge structure (XANES) spectroscopy at the P K‐edge was used to monitor ZDDP antiwear film thickness with rubbing time. Thermal immersion films of varying thickness were generated from the ZDDP and analysed using XANES spectroscopy and the particle induced X‐ray emission (PIXE) technique. P K‐edge XANES edge jumps and (1s → np) peak heights of the spectra were plotted against PIXE mass thickness values in order to establish calibration curves. Antiwear films were analysed using XANES spectroscopy, and average mass thicknesses were extrapolated from the calibration curves. A set of antiwear films formed in the presence of ZDDP and then further rubbed in base oil (no ZDDP) showed no significant decrease in film thickness. A set of antiwear films rubbed in the presence of ZDDP for various lengths of time showed an increase in film thickness, followed by thinning of the film. The decrease in film thickness is believed to be due to wear caused by the ZDDP solution decomposition products acting as an abrasive in the contact region. This revised version was published online in July 2006 with corrections to the Cover Date.     

TEM studies of anti-wear films/wear particles generated under boundary conditions lubrication

Friction and wear performance of engine oil were studied in presence of Zinc-dialkyldithiophosphate (ZDDP) and ZDDP–iron fluoride (FeF₃) combination using a ball-on-ring wear testing device under boundary conditions. Friction and wear performance of engine oil improves in presence of ZDDP–FeF₃ combination. In order to understand the wear mechanisms the microstructure and the chemical composition of wear debris generated during wear process were investigated using TEM together with EDX analyzes. Novel observations on the wear debris generated at different testing loads are presented. Independent of normal loads, amorphous debris containing P, O, Fe and Zn elements and crystalline debris of Fe₂O₃ are formed. No trace of S is present in amorphous debris under low load (2.32 GPa) conditions while S is a dominating element under high loaded (3.68 GPa) conditions. On the other hand, at lower loads a few iron oxide is formed while at higher loads larger sizes of iron oxides are formed resulting in larger friction and wear.     

Tribological,electrochemical, and spectral analysis of zinc dialkyldithiophosphates (ZDDP) of different thermal stabilities

The antiwear properties of five zinc dialkyldithiophosphates, which differed in thermal stability, were evaluated in a 4-ball machine by a preliminary wear track formation method. After testing the additives, the wear resistance of the films formed was measured by the increase in preliminary wear scar diameter over that of the additive-free oil. IR spectroscopy was then used to study the transformation products of additives after thermostatic testing at between 100 and 240°C on steel surfaces, where the interaction products were evaluated by electrode potential method. The interaction of the decomposition products of dithi-ophosphates with metal surfaces was found to be followed by a change in electrode potential. For the tested additives, a relationship is shown between antiwear effectiveness of the film on a friction track during tribological tests and the electrode potential value of the steel sample. Different parts of the relationship between the electrode potential and temperature relate to different stages of dithiophosphate decomposition measured by IR spectroscopy. It can be said that chemical modification of the steel surface which produces an improvement of antiwear properties, starts at the decomposition temperature of the dithiophosphate neutral salt.     

The influence of base oil properties on the efficiency of action of ZDDP-type additives

This paper deals with the analysis of the influence of base oil viscosity on the ability of ZDDP-containing lubricants to form protective layers (especially antiwear layers). The chemical structure of additives used was characterised according to their thermal stability, determined by differential scanning calorimetry (DSC). The additives were added to base oils of various viscosities. The prepared lubricants were tested using a four-ball machine, and analysed by DSC. The relationships between base oil viscosity and seizure load (P_t), weld load (P_w) and DSC test results are presented and discussed. The mechanism of interaction between ZDDP and the base oils was analysed by the use of a mathematical model.     

Tribochemistry and the development of AW and EP oil additives — a review

The antiwear (AW) and extreme pressure (EP) properties of chlorine, sulphur, phosphorus-containing organic compounds and zinc dialkyldithiophosphate (ZDDP) oil additives are affected greatly by their reactive ability to the metal surface, as well as by the chemical composition, chemical state, physical and mechanical properties of the protective films formed. Over four decades, research has taken place on boundary lubrication, and a much better understanding of the AW and EP action mechanism of one additive by itself in base oil has been obtained, and much more knowledge on the relationship between wear and decomposition of additives, adsorption and reaction of the additive or its decomposed products with metal, has been gained. A series of analytical methods and a great number of modern surface analytical tools have been set up and used for research in this area. The problems and some suggestions for the future study on boundary lubrication of oil additive are proposed.     

A new approach to the Noack volatility test

This paper reports on the method and preliminary results of a significant modification of the Noack volatility test. This modification permits collection and examination of the volatile products as well as of the residue. The analysis of such volatiles by chromatography and spectroscopy revealed surprising information that is especially relevant in the face of increasingly difficult automotive and heavy duty engine emission limitations. The data also showed very close agreement with the Unified Test Method for the Noack Volatility Test now covered by CEC L-40-T-87. Important to operators, the authors' modified Noack apparatus avoids the use of the toxic Wood's Metal of the earlier Noack apparatus.     

Evaluating thermal and thermooxidation stability for lubricating oils via microscale methods

Differential thermal analysis (DTA) and thermogravimetry (TG) methods have been developed to evaluate the thermal and thermooxidation stability of different lubricating oils. Measurements are carried out either by heating the oil sample at a constant rate (direct programme) or by keeping it at a fixed high temperature (isothermal programme). Oxygen at a constant flow rate is used for thermooxidation measurements. Tested samples included different viscosity grades: neutral base oils, unadditivated lubricating oil blends, and industrial oils. The mechanism of thermal decomposition for ZDDP and the estimation of its optimum concentration was also considered.     

Tribochemistry of ZDDP in molecular orbital calculations

The molecular orbital parameters of zinc dialkyldithiophosphate (ZDDP) and several metal-atom-cluster models were calculated. The nature and the strength of the interactions between the ZDDP molecules and different metal surfaces are analysed and discussed with the use of frontier orbital theory. By comparing the highest occupied molecular orbital energy (E_HOMO) and the lowest unoccupied molecular orbital energy (E_LUMO) of the ZDDP and the atoms cluster models of Al₆, Cu₆, and Fe₅, it is concluded that ZDDP behaves as an excellent boundary lubricant additive at the interface with iron. The derived molecular orbital parameters illustrate the advantages for tribochemistry studies.