Novel boron compounds in lubrication
Lubricants are used to control friction and reduce wear by preventing direct contact between surfaces in a relative motion. Most of the modern lubricants and lubricant additives have been designed and optimized for ferrous materials. A growing trend towards wider use of lightweight and wear resistant non-ferrous materials calls for new efficient and environmentally friendly Lubricants. Boron compounds are attractive alternatives for the commercially available lubricants and lubricant additives. Some boron compounds have already been proven as efficient friction modifiers, antioxidants, corrosion inhibitors and antiwear additives in lubricants.
In this work we focus on design, synthesis, physicochemical characterization and tribological studies of novel boron compounds. Boron based ionic liquids (ILs) and dithiocarbamates (B-DTCs) were designed, synthesized and tribologically characterized. The work was carried out in the following steps: (i) design and synthesis of novel boron compounds; (ii) physicochemical characterization of the synthesized compounds by FTIR, liquid-state (1H, 13C, and 11B) and solid-state (13C and 11B) nuclear magnetic resonance (NMR) spectroscopy, elemental analysis, thermal analysis (TG, DTA, DSC and QMS), powder XRD, density and viscosity measurements; (iii) tribological characterization using four-ball and pin-on-disc tribometers and (iv) surface analysis using Scanning Electron Microscopy coupled with X-ray Energy Dispersive Spectroscopy (SEM/EDS), optical interferometer and stylus profilometer. Some of these new boron-based compounds revealed significantly better antiwear and friction reducing performance on steel-steel contacts compared with fully formulated engine oils.
(i) Nine novel ILs of pryrrolidinium bis(salicylato)borate were synthesized and physicochemically characterized. They are solid at room temperature and some of them behave as plastic crystals. Some of these ILs were tested as lubricants at 100 ºC, i.e. above their melting points. These ILs have shown significantly better antiwear and friction reducing performance in lubrication of steel-steel contacts compared to fully formulated synthetic engine oil 5W40.
(ii) Nine novel room temperature ionic liquids (RTILs) of pyrrolidinium bis(mandelato)borate were synthesized and physicochemically characterized. These ILs were tribologically tested as 3 wt % additives in polyethylene glycol (PEG) and they have shown considerably better antiwear and friction reducing properties in boundary lubrication of steel-steel contacts at room temperature compared with neat PEG and engine oil 5W40.
(iii) Boron based compounds containing alkylborate and dithiocarbamate groups with alkyl substitutes in one molecule were synthesized and physicochemically characterized. The influence of alkyl chain length (butyl and/or octyl substitutes at DTC and borate groups) and heterocyclicity in boron based dithiocarbamate compounds (B-DTCs) on their tribophysical properties as additives in a mineral oil was studied for steel-steel lubricated contacts.