Effects of Temperature and Pressure on ZDDP

Abstract

A recent theoretical study proposed that the anti-wear property of zinc dialkyl dithio phosphate (ZDDP) is due to the formation of chemically connected networks as a result of pressure-induced cross-linkage of phosphate groups of thermally decomposed ZDDP. To investigate the initial decomposition processes and the possibility of linking of phosphate groups in the decomposed product, in-situ high-pressure and high-temperature infrared (IR) spectroscopy using synchrotron radiation were performed on the original ZDDP. At room temperature no substantial structural change was observed up to 21.2 GPa, a pressure far exceeding the predicted onset of a structural transformation for the model zinc phosphate at 7 GPa. The observed Pressure induced broadening of the IR peaks is most likely associated with structural disorder or amorphization of ZDDP which is completely reversible upon decompression. When ZDDP is heated under pressure, an irreversible transformation was observed around 225°C and 18.4 GPa. The experimental results show that ZDDP undergoes substantial decomposition at high pressures and high temperatures but no hint of cross-linkage of phosphate groups was found.

A Deterministic Stress-Activated Model for Tribo-Film Growth and Wear Simulation

“…It should be noted that Young's modulus was found to be largely independent of the temperature [33,34], i.e., within 25-200°C (at 220°C, the ZDDP tribo-film will start to degrade [35]), while the hardness does depend on temperature [33]. Bosman and Schipper [36] proposed a compensation factor for the hardness as a function of temperature.…”

On the Mechanism of ZDDP Antiwear Film Formation

“…However, the pressures required were far in excess of the yield pressures of most materials and thus unlikely to occur in rubbing contacts. High-pressure infrared studies have also shown no evidence of structural changes in ZDDP up to 21 GPa [22]. It is well known that when solid surfaces rub together, the resulting plastic deformation and fracture processes that occur at contacting asperities generate localised charged regions that result in the emission of energetic particles including photons, electrons, ions and even X-rays [23][24][25].…”

Technical Report: The Diversity of Infrared Programs at the NSLS

“…Recent work at Beamline U2A includes the first high-pressure study down to the THz region on the doming modes and dynamics of model heme compounds [10], anomalous transformations in Ice VIII [11] (Figure 2), effects of temperature and pressure on zinc dialkyl dithio phosphate (ZDDP) [12], and the identification of both solid and fluid nanoscale inclusions in microdiamonds [13].…”

“…Although it was understood that the brightness advantage of the synchrotron source extended into the mid-IR, the earliest demonstrations of its use for microspectroscopy did not occur until the early 1990s when, for example, a custom IR microscope was used (6)(7)(8)(9)(10)(11)(12) and cryogenic temperatures in a diamond anvil cell. Results show that the unique low-temperature isostructural transition in ice VIII is a first-order thermodynamic transformation that arises from subtle phonon instabilities associated with an isostructural movement of molecules in the ice VIII structure.…”