Oil-Soluble Silver–Organic Molecule for in Situ Deposition of Lubricious Metallic Silver at High Temperatures

Abstract

A major challenge in lubrication technology is to enhance lubricant performance at extreme temperatures that exceed conventional engine oil thermal degradation limits. Soft noble metals such as silver have low reactivity and shear strength, which make them ideal solid lubricants for wear protection and friction reduction between contacting surfaces at high temperatures. However, achieving adequate dispersion in engine lubricants and metallic silver deposition over predetermined temperatures ranges presents a significant chemical challenge. Here we report the synthesis, characterization, and tribological implementation of the trimeric silver pyrazolate complex, [Ag(3,5-dimethyl-4-n-hexyl-pyrazolate)]3 (1). This complex is oil-soluble and undergoes clean thermolysis at ∼310 °C to deposit lubricious, protective metallic silver particles on metal/metal oxide surfaces. Temperature-controlled tribometer tests show that greater than 1 wt % loading of 1 reduces wear by 60% in PAO4, a poly-α-olefin lubricant base fluid, and by 70% in a commercial fully formulated 15W40 motor oil (FF oil). This silver-organic complex also imparts sufficient friction reduction so that the tribological transition from oil as the primary lubricant through its thermal degradation, to 1 as the primary lubricant, is experimentally undetectable.

Decisive Influence of the Metal in Multifunctional Gold, Silver, and Copper Metallacycles: High Quantum Yield Phosphorescence, Color Switching, and Liquid Crystalline Behavior

“…This silver complex was recently described as a novel precursor for the in situ deposition of metallic silver onto mechanical surfaces with applications as high performance lubricants. However, although a clean thermolysis at high temperatures was reported, the liquid crystalline properties of this complex were not studied …”

“…However, although a clean thermolysis at high temperatures was reported, the liquid crystalline properties of this complex were not studied. 43 A study by polarizing optical microscopy (POM) and DSC ( Figures 1 and S2) showed that the gold and silver complexes are columnar liquid crystals at high temperature. 44,45 When analyzing the samples, particular care was taken not to heat the material to the liquid phase in an effort to avoid decomposition and obtain reproducible results.…”

Robust Interfacial Tribofilms by Borate- and Polymer-Coated ZnO Nanoparticles Leading to Improved Wear Protection under a Boundary Lubrication Regime

“…Due to their small size and relatively large surface areas, nanomaterials can easily penetrate within microscale asperities of diverse geometrical contacts and fill the nanogrooves on the interface, thus providing increased contact surfaces to distribute high shear stresses and reduce friction and wear . Additionally, the application of nanomaterials as an engine oil additive provides superior wear protection, with less adverse impact on the exhaust emission catalysts, compared with the conventional engine oil additives like ZDDP. − Extensive research efforts have been devoted to evaluating the potential of both metal − and metal oxide − nanoparticles to improve the tribological protection of interfaces operating under a mixed or boundary lubrication. Among these additives, zinc oxide (ZnO) nanoparticles have received considerable interest reflecting their nontoxicity; high surface energy; and unique antioxidant, electrical, and thermal conductivity properties.…”

Nanolubricant additives: A review

“…Nanolubricant additives with low chemical activity such as copper, silver, and graphene always form a physical adsorption tribofilm. Desanker et al [149] confirmed the physical adsorption film which was formed by deposited silver nanoparticles via a scanning electron microscope (SEM) and energy dispersive spectrometer (EDS) analyses. Apart from physical adsorption film, nanoparticles containing [162] investigated the tribological properties of CeBO3 nanoparticles and studied the lubrication mechanism.…”