The tribotechnical characteristics of polymer composites based on PTFE and layer silicates (serpentinite) were studied, depending on the test duration time. It was indicated that adding a serpentinite and magnesium spinel increased the wear resistance of the composite by up to 480 times compared to the original PTFE. It was found that particles of fillers and PTFE promote formation of a secondary structure on the friction surface, helping reduce the material wear process. The method of infrared (IR) spectroscopy and EDS showed that tribochemical reactions take place on the friction surface of composites.

Industries, especially those related to transportation, have relied extensively on petroleum products for lubrication, raising serious questions about the security of the world energy supply in the future. Observed that the end-products might be released back into the environment, posing major environmental risks. As a result, bio-based products have attracted increasing interest as prospective replacement to mineral-based type due to their important role in resolving the issues of pollution. With renewability and biodegradability as their greatest points, bio-based lubricants have been discovered to offer superior lubricating qualities to those of traditional mineral lubricants but currently have some undesirable qualities that need to be improved based on the literatures. Therefore, this research objective is to showcase the potential of bio-lubricants, both in terms of their environmental benefits and for technical applications, based on studies that have been published over the years. Review of the natural oil's molecular structures, physio-chemical characteristics, and lubricating ability is crucial for the creation and choice of lubricants. Owing to their accessibility in a wide range of characteristics, which are necessary for specific applications, bio-based lubricant is a possible replacement for a variety of applications, according to the primary findings. The results showed that sunflower oil improved in reducing friction and wear by 93.7% and 70.1%; and 77.7% and 74.1%, under TiO₂ and SiO₂ studied, against base lubricant values of 0.0511 and 11.2414 (mm³), respectively. However, to get beyond some of the restrictions such as poor low temperature and oxidative stability, adequate chemical modification is necessary in solving agglomeration challenges.

The lubrication performances of three different fully synthetic motorcycle oils have been investigated in an on-road test. One aim of this study is to quantify the viscosity loss due to shear degradation and show that it is a key degradation process for motorcycle engines. A further aim is to compare the wear performance of these three lubricants. It is found that - while shear degradation may be strong for certain oils - an expected immediate and concurrent increase of wear rate is not observed, which might be attributed to well performing anti-wear additive packages. Central to this work is the intention to understand more what constitutes optimal lubrication for an engine.

In the past ten years, the scope of influence of tribology in various fields has been expanded, and the research activities related to superlubricity have also increased greatly. The latest development of superlubricity in recent three years is summarized and the future research direction is prospected. Different aspects of superlubricity have been overviewed. As a highly interdisciplinary field, superlubricity's studies are widely distributed among various disciplines, and there are many aspects of superlubricity that are not covered in this review. Despite the limitations, our group hoped that the overview will bring together recent outstanding researches and be of benefit to the growing number of tribology researchers.

An overshoot phenomenon of bearing temperature in hydrodynamic journal bearings may be observed during a sudden start-up experiment. This phenomenon implies that the maximum bearing temperature in acceleration operation may exceed the predicted one which can be predicted accurately by applying a state-of-the-art steady state thermohydrodynamic lubrication (THL) model. This paper presents the maximum bearing temperature including the one during acceleration operation by using a simplified THL model that is newly proposed for a transient THL analysis. It is found that the overshooted temperature can be qualitatively predicted by using the transient THL model that incorporates properly the interaction between the motion of journal center and the viscous dissipation, even if it is a simple model. Next, the transient temperature during slow acceleration operation and also those toward higher dimensional steady state journal rotational speed are calculated and they are found to be in qualitative agreement with the measurements. The oil film characteristics such as oil film pressure, temperature and thickness after reaching the steady state equilibrium do not depend on the value of initial journal eccentricity ratio in the transient analysis. However, when the values are different, the characteristics immediately after starting rotation change largely. In the case of the value 1.00, it is found to give a prediction that agrees qualitatively with the characteristics measured in the experiment.

Eco-friendly lubricants have drawn a lot of interest in the lubrication industry as a way of promoting global sustainability in response to the growing environmental pollution danger posed by the use of petroleum-based lubricants. As a result of these, developing lubricants with organic additives stands as a promising technique in solving the environmental challenges caused by non-degradable materials. This research investigates the effect of bio-based water hyacinth (Eichhornia crassipes) (EC) carboxylmethyl cellulose (CMC) polymer in different base lubricants as well as under different volumetric blend to determine their compatibility effect on lowering friction and wear using base rapeseed oil (BRO) and mineral oil (MO) as a base lubricant sample. High frequency reciprocating rig tribo-tester machine was used in the experiment, followed by substrate surface analysis via energy dispersive x-ray spectroscopy. The additives were evaluated for their potential to improve tribology in terms of friction, surface roughness and wear reduction, load-carrying capacity, and mechanism of repair. Testing the additive concentrations, produced recommendable result at 0.8 mass% EC-CMC. The best performance was obtained when BRO70/MO30 was blended with 0.8 mass% EC-CMC. When compared to base BRO and MO lubricants under 80 N, 0.8 mass% BRO70/MO30 reduced the coefficient of friction and wear scar diameter by 44%, 32%, and 33%, 21% respectively. However, it was shown that nanoparticles had greater tribological performance at higher working capacities owing to the rapid and active tribo-film formation.

The adhesion of droplets to solid surfaces causes problems in many industrial fields. Solid surfaces can be classified as hydrophilic or hydrophobic on the basis of the equilibrium contact angle of a liquid droplet on the solid surface. Much attention has been paid to hydrophobic surfaces because liquids hardly stick to such surfaces, but only a few studies of the dynamic characteristics of liquids on these surfaces have been conducted. In this study, the extension–contraction method was used to investigate dynamic wetting and dewetting behaviors on a hydrophobic surface. The changes in the contact line displacements, contact line velocities, and dynamic contact angles when the water droplet volume was increased/decreased at a constant rate were measured using a high-speed camera. The results were analyzed based on the molecular kinetic theory, and the coefficients of contact line friction, average distances of molecular displacement, and frequencies of adsorption−desorption of molecules around the contact line during wetting and dewetting were calculated and compared. These parameters were compared with those obtained on hydrophilic surfaces, and the dynamic behavior of droplets on a hydrophobic surface was discussed.

The Japanese Society of Tribologists is pleased to announce that the 2022 Best Paper Award of the Society was awarded to the following papers from Tribology Online. The Award was presented to the authors by Mr. Takero Makino, the President of the Japanese Society of Tribologists, at the award ceremony in the JAST Annual Meeting in Tokyo on 30th May, 2023.

The titles and the authors of the awarded papers:

◊"ZDDP Tribofilm Formation on Non-Ferrous Surfaces," by Mao Ueda, Amir Kadiric, Hugh Spikes, Tribology Online, Vol. 15, No. 5 (2020) 318-331.

◊"Non-Linear Wear Propagation Property and Prediction Method Having Influencing Pitting Failure of Helical Gears," by Koji Kumagai, Hanlin Liu, Syuhei Kurokawa, Tribology Online, Vol.17, No.1 (2022) 44-53.

Congratulations!

The Best Paper Award is given annually to the author(s), either the JAST members or non-members, of the paper(s) judged as the best paper(s) published in Journal of Japanese Society of Tribologists (Toraiborojisuto) and Tribology Online (TROL) for the previous three years. All papers that appeared in Toraiborojisuto and TROL for the three years are reviewed by the JAST Awards Committee.