The new approach to the kinetics of triboreactions, based on a mathematical model denoted as
α
i
model implies energy emitted by the surface as impulses in the range of 1–5 eV. This communication ...looks for a better understanding of the mechanism of triboreactions by explaining the
α
i
model, proposed previously in terms of the thermodynamics of irreversible processes. The reaction rate
J
c
found by non-equilibrium thermodynamics is also consistent with two superimposed pathways for tribochemical reactions. In the former, the reaction follows the thermal mechanism typical of no friction conditions, in the latter, direct transfer of energy from triboelectrons to molecules generate special excited or activated molecules A*, such as radicals or ions which react rapidly to form the products, enhancing the global reaction rate.
X-ray absorption near-edge structure spectroscopy (XANES) has been used to investigate the chemistry and thickness of thermal and antiwear (AW) films generated on steel from oil solutions containing ...phosphate ester additives. DPP, a diaryl phosphate, reacted with steel to form a thermal phosphate film at lower temperatures than TPP, a triaryl phosphate and Irgalube 349, an amine phosphate. This phosphate film formation at lower temperatures resulted in better wear protection to the metal in tribochemical experiments, as indicated by a smaller wear-scar measurement for oil solutions containing the DPP additive. For TPP, a brief period of wear to the metal was necessary to initiate the tribochemical reaction between the additive and substrate. Once the tribochemical reaction begins, TPP is able to generate a tribochemical film of relatively the same thickness and chemistry as DPP. Irgalube 349 generated the thickest thermal films at temperatures greater than 150 °C, significantly thicker than any of the films generated from DPP and TPP. The substantial difference in thickness is believed to be due to the availability of alkyl/ammonium cations which enables continued growth of the phosphate film.
Over the decades, the application of mechanical force to influence chemical reactions has been called by various names: mechanochemistry, tribochemistry, mechanical alloying, to name but a few. The ...evolution of these terms has largely mirrored the understanding of the field. But what is meant by these terms, why have they evolved, and does it really matter how a process is called? Which parameters should be defined to describe unambiguously the experimental conditions such that others can reproduce the results, or to allow a meaningful comparison between processes explored under different conditions? Can the information on the process be encoded in a clear, concise, and self-explanatory way? We address these questions in this Opinion contribution, which we hop
The antiwear properties of zinc dialkyldithiophosphate (ZDDP), dispersants, and mixtures of ZDDP and different dispersants have been evaluated using a pin-on-flat Plint wear machine. Tribochemical ...interactions between ZDDP and dispersants have been investigated under boundary lubrication conditions by means of X-ray absorption near edge structure (XANES) spectroscopy, probing the phosphorus, sulfur and nitrogen absorption edges. The results show that the dispersants do not give any wear protection by themselves in the base oil. The dispersants also do not affect the antiwear property of ZDDP under the given testing conditions. The N K-edge XANES analysis indicates that dispersants contribute to the chemical composition of the tribofilms and form mixed ammonium/zinc polyphosphates. Phosphorus in the tribofilms is present mainly in the form of medium-chain polyphosphate on the surface and short-chain polyphosphate in the bulk. Sulfur appears in the tribofilms mainly as sulfide S-II, possibly zinc sulfide. The presence of dispersants in oil blends does not disturb the polyphosphate (and sulfide) formation, but it does decrease the chain length of the polyphosphate in the tribofilms.
Triboelectrochemical techniques use an electrochemical set-up (mainly of the three-electrode type) for controlling the potential of the surface of a conducting material subjected to rubbing in a ...tribometer. In this way it is possible to carry out friction and wear tests in electrolytic solutions under well-defined chemical conditions determined by the applied electrode potential. In addition, triboelectrochemical techniques offer the possibility of following in-situ and in real time the kinetics of electrochemical oxidation reactions (corrosion) by the simple measure of an electrical current. In the present study triboelectrochemical experiments were carried out on sputter deposited TiN coatings sliding against alumina in a borate solution (pH 8.4). The surface of selected worn coatings was characterised by X-ray photoelectron spectroscopy (XPS) and the topography by scanning electron microscopy (SEM). Results show that the rate of wear critically depends on the prevailing (electro)chemical conditions which determine the chemical surface state of the TiN coating. The behaviour is attributed to the lubricating properties of surface oxide films having a thickness in the nanometre range.
In this study, hydrogen formation was investigated during lubrication tests, which were carried out with synthetic hydrocarbon oil under high-vacuum conditions using disks made of Fe, Cr, SUS304, ...SUS440C, and SUJ2. The evolved gases were detected using a quadrupole mass spectrometer. Hydrogen evolution was observed at the beginning of the sliding. Hydrogen and hydrocarbons were formed simultaneously after 1 km of sliding distance. The hydrocarbon oil was decomposed tribochemically by the same point. When SUS304 was used as the specimen, a higher rate of hydrogen evolution was observed at the beginning of the sliding action compared to the other metals. X-ray photoelectron spectroscopy of the disk surface revealed that there was a thicker oxide film and large amount of chemisorbed water on SUS304. These results suggest that the chemisorbed water on SUS304 could be a source of hydrogen. When the SUS304 specimen was pretreated with heavy water, hydrogen deuteride ion was detected during the lubrication test. It can be concluded that chemisorbed water on metal surfaces is a source of tribochemically-formed hydrogen during lubrication tests. The sharp decrease in hydrogen evolution at the beginning of sliding is related to the destruction and removal of the oxide film.
In-vitro testing procedures have been successfully developed to investigate the effects of tribological process induced transformation of protein-based lubricant on the friction change of articular ...cartilages. Serum and albumin solutions were the biological lubricants used in this study. The results indicated that the lubricating ability for cartilages deteriorates after the biological lubricants were articulated between polyethylene and stainless steel materials. In addition, the secondary structure change of the albumin molecule has been characterized after the molecules were articulated by the artificial joint materials. We have provided evidence that the conformational change of protein lubricants leads to the friction increase of articular cartilage.
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.
An N‐modified nano / micrometre borate (MNMB) as an oil additive was synthesised by an ultrasonic dispersion and emulsion reaction in the microemulsion phase. The particles of the MNMB additive were ...between 20 and 500 nm in diameter. The tribological properties of the MNMB as an oil additive were investigated using a four‐ball tester. The results reveal that the MNMB possesses good tribological properties. When the boron concentration is 0. 05 wt. %, the wear‐scar diameter is smallest and the seizure load is highest. The antiwear and extreme‐pressure properties of the MNMB were best at a viscosity of 65. 3 mms2. Small‐area X‐ray photoelectron spectroscopy (XPS) and electron probe microanalysis (EPMA) indicate that the MNMB additive can form a tribological mixed reaction film containing C, O, B, N, and Na on a rubbing surface. The elemental boron exists in four different chemical states, but is mainly present in the form of BN on the rubbing surface.
The temperature dependence of friction coefficient of lubricant oils containing MoDTC was evaluated using a ball on disk tribometer at constant temperatures of 25, 40, 60 and 80°C. In the ...experiments, the friction coefficient gradually decreased and tended to become lower at steady state. The decreasing slope of the friction coefficient was steeper and the lower friction coefficient at the steady state was obtained at a higher oil temperature. The friction coefficient was also controlled by the concentration of MoDTC in oil. Considering that the results of lubricating tests supported the successive processes involving production and wear of MoS2, the friction coefficient can be controlled by the coverage of MoS2 which is determined by a balance of formation and wear of MoS2. An analysis formula was established based on kinetic assessment of the process in order to obtain the Arrhenius plots of the test results. There were two regions which had different slopes in the plot. The activation energies were 70 and 4 kJ/mol for the low and the high temperature regions, respectively. This result suggested that MoS2 production from MoDTC was reaction rate-limiting at low temperature and transport ratelimiting at high temperature.
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