Comparative Studies between Chemical and Tribochemical Reactions of Some Metal Complexes Derived from N-(O-Hydoxyphenyl)-N'-phenylthiourea (L)

The reactions of N-(O-hydoxyphenyl)-N'-phenylthiourea (L) derived from with Cu+, Cu2+, Co2+ and Co3+ chloride and/or iodide afford new metal complexes. The isolated complexes were synthesized by two different techniques (chemical and tribochemical methods). Two complexes were synthesized by the direct chemical reactions of N-(O-hydoxyphenyl)-N'-phenylthiourea (L) with MCl2·XH2O (M = Co2+ and Cu2+;X = 6 in case of Co2+ and X = 2 in case of Cu2+) in absolute EtOH. The general formulae of the two complexes derived by the chemical method are [Cu(L)2(EtOH)2]Cl2 and [Co(L)2Cl2]Cl. These complexes were used to synthesize another two complexes using tribochemical reaction by grinding the previous chloride complexes with excess KI in agate mortar in the solid state. The isolated complexes have the general formulae, [Cu(L)I·H2O]·1/2H2O and [Co(L)I3(Et- OH)]·3EtOH. The results indicate the substitution of the chloride by iodide ions during grinding and extraction of the complexes by solvents. The IR spectra of the complexes suggest that L acts in a bidentate manner towards the metal ions. Moreover, the results of electronic spectra and magnetic measurements for the chloride complexes suggest distorted-octahedral structure for Cu2+ and low-spin octahedral structures around the CoII and Cu2+ ions, respectively. On the other hand the data suggest that the iodide complexes have square-planer and low-spin for the Cu+ and Co3+ ions, respectively. The results of mass spectra confirm the formulae proposed for the isolated complexes. The mechanisms of reduction of CuII and oxidation of CoII for the metal complexes were elucidated.

A review of current understanding in tribochemical reactions involving lubricant additives

Lubricants have played important roles in friction and wear reduction and increasing efficiency of mechanical systems.To optimize tribological performance,chemical reactions between a lubricant and a substrate must be designed strategically.Tribochemical reactions are chemical reactions enabled or accelerated by mechanical stimuli.Tribochemically activated lubricant additives play important roles in these reactions.In this review,current understanding in mechanisms of chemical reactions under shear has been discussed.Additives such as oil-soluble organics,ionic liquids(ILs),and nanoparticles(NPs)were analyzed in relation to the tribochemical reaction routes with elements in metallic substrates.The results indicated that phosphorus,sulfur,fluorine,and nitrogen are key elements for tribochemical reactions.The resulting tribofilms from zinc dithiophosphates(ZDDP)and molybdenum dithiocarbamate(MoDTC)have been widely reported,yet that from ILs and NPs need to investigate further.This review serves as a reference for researchers to design and optimize new lubricants.

Sensitivity and Compatibility Analysis of Sulfur and Phosphorus Type Additives in Rapeseed Oil

The effects of sulfur type additives T321 and phosphorous type additives P120 on the EP and AW abilities of rapeseed oil were investigated by a four-ball testing machine using the rapeseed oil as base oil.The effect of T321 mixed with P120 on the tribochemical performance of the rapeseed oil was studied.The result shows that the load carrying,extreme pressure and abrasion capacities of lubricant film can be improved by adding T321 and P120 as additives in rapeseed oil, respectively. The SEDX analysis on the surface of steel balls reveals that tribochemical reactions occur during the friction process, the barrier lubricating film is formed containing triglyceride and the additives can improve the anti-wear ability and load-carrying capacity.

Tribochemical synthesis of functionalized covalent organic frameworks for anti-wear and friction reduction

Tribochemistry can be defined as a field dealing with the chemical reactions occurring in the friction zone,capable of catalyzing mechanical and physico-chemical changes in the friction contact area,facilitating the formation of tribo-films,which is also an efficient approach to fabricate novel innovative materials.In this paper,we report the successful synthesis of the silicon oil(SO)-functionalized covalent organic frameworks(COFs)prepared via the tribochemical method when subjected to the reciprocating friction;during the friction process,the rich aldehyde-terminated COFs can bond with amino SO via the Schiff base reaction between aldehyde group and amino group to obtain the desired functionalized COFs(SO@COF-LZU1).The tribochemical reaction progress was tracked through in-situ monitoring of the friction coefficient and the operating conditions during the entire friction process.Noticeably,the friction coefficient continued to decrease until it finally stabilized as the reaction progressed,which revealed the formation of a protective tribo-film.Herein,an approximate tribochemical model was presented,wherein the reaction mechanism was investigated and analyzed by employing structural analysis techniques like magic angle spinning nuclear magnetic resonance(MAS NMR),transmission electron microscopy(TEM),and X-ray photoelectron spectroscopy(XPS).Furthermore,the tribochemical-induced SO@COF-LZU1 exhibited remarkable tribological performance with a low friction coefficient of 0.1 and 95.5%reduction in wear volume when used as additives of 500SN base oil.The prime focus of our research was on the preparation and functionalization of COF materials via tribochemical reactions,unraveling a new avenue for the rational design and preparation of functional materials.

A(CrFeNi)_(83)(AlTi)_(17) high-entropy alloy matrix solid-lubricating composite with exceptional tribological properties over a wide temperature range

High-entropy alloy matrix solid-lubricating composites(HSLCs)are promising anti-wear and friction-reduced materials to meet the demands of complicated engineering applications.Here we present a strat-egy to develop HSLCs by using the coupled high-entropy phases of(BCC+FCC+L2_(1))with near-equal volume fraction as the matrix material,instead of using the usual single phase-dominated high-entropy phases,which can preserve the intrinsic strength and deformability of the matrix while activating adap-tive wear protection during sliding.This enables a low coefficient of frictions of 0.23-0.31 and wear rates within the order of 10^(-6)-10^(-5) mm^(3) N m^(-1) for the(CrFeNi)_(83)(AlTi)_(17)-Ag-BaF_(2)/CaF_(2) HSLC between room-temperature and 800℃,considerably outperforming the reported HSLCs and conventional alloy matrix solid-lubricating composites.At low and moderate temperatures,the synergistic Ag-BaF_(2)/CaF_(2) lubricat-ing films eliminate the surface stress concentration upon wear,thus suppressing three-body abrasion and surface roughening during the groove multiplication process.At elevated temperatures,the high-entropy composite tribo-layers provide the friction interface with strong and deformable stress shielding,which avoids the oxidative and adhesive wear triggered by the delamination of the tribo-layer.Developing sim-ilar coupled high-entropy matrix phases may open an avenue for further optimization of the tribological properties of the HSLCs.

Characterization of the tribologically relevant cover layers formed on copper in oxygen and oxygen-free conditions

Engineering in vacuum or under a protective atmosphere permits the production of materials, wherever the absence of oxygen is an essential demand for a successful processing. However, very few studies have provided quantitative evidence of the effect of oxidized surfaces to tribological properties. In the current study on 99.99% pure copper, it is revealed that tribo-oxidation and the resulting increased abrasive wear can be suppressed by processing in an extreme high vacuum (XHV) adequate environment. The XHV adequate atmosphere was realized by using a silane-doped shielding gas (1.5 vol% SiH4 in argon). To analyse the influence of the ambient atmosphere on the tribological and mechanical properties, a ball–disk tribometer and a nanoindenter were used in air, argon, and silane-doped argon atmosphere for temperatures up to 800 ℃. Resistance measurements of the resulting coatings were carried out. To characterize the microstructures and the chemical compositions of the samples, the scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD) were used. The investigations have revealed a formation of η-Cu3Si in silane-doped atmosphere at 300 ℃, as well as various intermediate stages of copper silicides. At temperatures above 300 ℃, the formation of γ-Cu5Si were detected. The formation was linked to an increase in hardness from 1.95 to 5.44 GPa, while the Young’s modulus increased by 46% to 178 GPa, with the significant reduction of the wear volume by a factor of 4.5 and the suppression of further oxidation and susceptibility of chemical wear. In addition, the relevant diffusion processes were identified using molecular dynamics (MD) simulations.

Insight into macroscale superlubricity of polyol aqueous solution induced by protic ionic liquid

Currently,macroscale liquid superlubricity remains limited to low applied loads and typical ceramic friction pairs.In this study,a robust macroscale superlubricity with a coefficient of friction(COF)of approximately 0.006 is realized at the bearing steel interface induced by protic ionic liquids(ILs)in propylene glycol aqueous solution,and the lubrication system exhibits excellent anti-corrosion properties.Results show that superlubricity can be achieved by employing ILs with longer alkyl chains over a wide load(<350 N)and speed(>700 r/min)range.By systematically investigating factors affecting superlubricity,including the IL structure,ionization degree,test conditions,polyol,water-to-alcohol ratio,and lubrication state,the superlubricity mechanism is discussed.Notably,a thicker and denser stern layer can be formed using ILs with longer alkyl chains,which participates in the tribochemical reaction with the metal substrate to form a tribofilm during rubbing.The hydrogen bond network layer formed by the hydrogen ion and polycol aqueous solution can withstand high applied loads.Water can be used to reduce the shear stress of polyols,and enable superlubricity to be achieved under high-speed rotations.Moreover,an inevitable running-in period serves as a dispersing contact stress and dynamically forms a lubricating film,where the lubrication state locates mixed lubrication and then transforms into boundary lubrication as the roughness of the contact surface increases.This study is expected to significantly promote the development and application of superlubricity in the engineering field.