The Future of Lubricants

In essence, a lubricant of any machinery lubrication is as important as the design of the components of the machinery. Equipment manufacturers perform extensive research and development in trying to optimise each and every component of the machine to deliver the best possible performance.

Similarly, the lubricant, as a component of that machine, is comprehensively researched and then evaluated to meet not only the various specifications and regulations to which it must comply, but also is fi eld-tested in most cases. The resulting information is fed back into the design of the lubricant.

Although conducted by oil companies, lubricant development typically is performed in close consultation with reliable equipment manufacturers. Many times, a particular equipment manufacturer desires to have some properties of the lubricant exceed specifications so that the equipment's performance is better than normal. Most equipment manufacturers as well as the users generally look for improved equipment protection, greater energy efficiency, long drain intervals and, of course, easy availability.

In the last 120 years of petroleum, from a basic single component lubricant of the early days, today’s lubricants are complex and may contain a very large number of components, which should not only be highly synergistic to each other by themselves, but also in conjunction with the operating environment of that equipment. The operating environment can have very large variations of temperature, loading, contaminants, etc. For example, in an internal combustion engine, the lubricant is expected to perform satisfactorily under any of these conditions.

This aspect of a modern lubricant is well researched and widely reported. The future of technology, of both the machine and the lubricant, needs additional perspectives of development. For instance, all environmental aspects are of prime concern, as is superior performance. The two sometimes do not go together, and consequently a judicious trade-off results. Today, some of the issues that are of significance include:

• Bio-based lubricants
• Well-to-wheel carbon footprint
• Sustainability
• Energy economy through friction reduction and
• Enhanced durability.

Two of the main new directions that are of interest today are briefly mentioned here. It is to be understood that one or more of such developments could work in conjunction. Also, the economics and energy efficiency of these is still not fully defined at the present time and research is in progress to fully establish these.

Aqueous Lubricants

Wouldn’t it be interesting if topping up an industrial fluid could be done by water alone? The idea of replacing conventional organic lubricants or solvents by water-based solutions is both appealing and exciting for many applications and in many different areas. Such solutions may not only have a high potential for improvements, but they also help address environmental concerns. Conventionally, these have been widely used in metal-working applications for a long time, where usually an aqueous solution of an organic, polar, surface-acting composition, which is a phosphate or phosphite of an alcohol-ether and soluble in water at room temperature, is used. Mineral or even synthetic oil-based lubricants suffer from the drawbacks of flammability, disposal problems and other hazards. Accordingly, for some time there has been increased interest in developing water-based lubricants.

For tribosystems involving thermoplastics, Lee and Spencer have investigated the adsorption and aqueous lubricating behavior of PLL-g-PEG for tribopairs involving thermoplastic materials,including polypropylene, pollyamide-6,6 and polyethylene. These materials are increasingly used today for many engineering applications. A major finding is that PLL-g-PEG adsorbs onto both hydrophobic, non-polar surfaces and hydrophilic, polar (negatively charged) surfaces from aqueous solutions, thus becoming a very unique and effective aqueous boundary lubricant additive for the sliding contact of thermoplastics against themselves as well as against many hydrophilic, polar materials, including metals (even stainless steel) and ceramics (such as zirconia).

A series of recent patents on aqueous lubricants include applications as metal-working lubricants, drawing lubricants, cold-forming lubricants, lubricants for conduits and raceways, lubricants for saw chains, non-flammable electric-discharge machining fluids, lubricants for plastic working, pre-lubricated cable fluids, smart cutting fluids, anti-traction compositions, and many others, signifying this fast-developing field. Such products use many compounds including PEG, polsymeric polyelectrolyte acrylates, polyalkine oxide compounds, polyacrylamide compounds and various others.

A recent patent by Stanton describes inclusion of neo-decanoic acid in aqueous lubricants, which reduces viscosity and improves lubricating effectiveness. Another patent by Schwartz describes a hydraulic fluid having improved anti-wear and corrosion inhibition properties. Hydraulic fluids and metal-working lubricants are thickened with a polyether-polyol modified with an alphaolefin-epoxide in another patent by Nassry. Unexpectedly, synergistic thickening results from the combination of polyether-polyol with the phosphate ester and water-soluble amine corrosion inhibitor components in the hydraulic fluids or metal-working lubricants. Lewis claims a new water-glycol energy-transmitting fluid, which is substantially free of ethylene glycol. Commercial water-based lubricants that do not contain VOCs or ozone-depleting substances are available today. Such formulations are applied in tube-bending, swaging, stretch forming, and skin forming of ferrous and non-ferrous metals, such as aluminium, titanium, and stainless steel. These lubricants prevent wear as well as reduce scratching, galling and metal-to-metal contact. They do not contain nitrites, sulfur, chlorine, phenols, DEA, glycol ethers or any other hazardous solvents.

A new class of aqueous lubricants using a suspension of uniform carbon microspheres has been studied by St. Dennis, et al. of Tulane University. The surfactant functionalized carbon microspheres employ a rolling mechanism similar to ball bearings to provide low-friction coefficients and minimize surface wear, even at high loads and high contact pressures.

Slick and Super-hard Solid Lubricant Coatings

High-tech self-lubricating coatings can be applied to almost any metal-using engines and in machinery. Compared to uncoated surfaces, in both laboratory and engine tests, such coatings can reduce friction by up to 80 percent and can greatly minimize wear and scuffing. Such coatings will be of considerable interest for use with newer lubricant alternatives, such as bio-lubricants, especially the ones that are biodegradable, non-toxic and sustainable. The sectors that may particularly benefit from these include shipping and railroad, yard equipment, construction equipment, conveyors, and many others. Such coatings today are looking at molybdenum, copper, silver, antimony and tin. High-tech vaporization, cold sprays, evaporation and vacuum technologies are used in their preparation. These coatings can also be nano-structured and/or nano-composite forms. These provide better performance under very severe sliding conditions. The coatings can be coupled with smart surface engineering strategies such as micro-texturing or patterning. For some applications, these coatings are now commercially available. The shortcomings of such coatings are to be clearly understood before deciding on a particular application.

Zabinski, et al. and others have investigated the multi-environmental lubrication performance and lubrication mechanism of MoS₂ / Sb₂O₃ / C composite films that exhibit adaptive behavior, where surface chemistry changes with the environment to maintain good friction and wear characteristics. This type of behavior is therefore nicknamed "chameleon". Even under dry nitrogen or vacuum conditions, these films showed super-low friction and long wear life. Such films have a tremendous future. In order to improve the fuel economy of modern engines, it is now common to include small quantities of oil-soluble molybdenum-based additives. Miklozic studied the MoS₂ formed in rubbed contacts through AFM and Raman spectroscopy and found that typically flake-like nano crystals with a diameter of 10 to 25 nanometers and 1 to 2 nanometers thick are formed on the high spots of the rubbed surfaces. Such surfaces with bonded flakes can dramatically influence friction behavior if these could be industrially prepared.

Industrial use of plasma-deposited coatings for components of automotive fuel-injection systems are reported by Treutler of Bosch. Diamond-like carbon (DLC) coatings show crucial advantages in a low wear, low friction design. He recommends such coatings with powerful system designs and cost-saving solutions, and as constructional elements of mechanical systems.

In summary, I think we are in for exciting times ahead and will see a lot of new developments on the ground.