Chasing the Holy Grail of Additives
One company is bringing an additive to market that promises extreme pressure, antiwear and friction reduction in either water or oil – a hitherto impossible achievement. Trevor Gauntlettasks whether it has discovered a substance that combines these disparate lubricant demands.
Aholy grail is an elusive object, sought as much for the challenge of finding it as for its great powers. One such grail in the lubricants industry is an additive that is effective in both water and oil. Another is a chemical or blend that provides friction reduction, antiwear and extreme pressure performance – functions that may sound similar but are actually different tasks for a lubricant.
In almost 80 years since the discovery of zinc dialkyldithiophosphates antiwear properties, any additives that could satisfy either of those criteria are likely to be radically different from each other. Is the nano scale where the grail could be found?
New Jersey-based Nanotech Industrial Solutions is trying to commercialize its near-spherical tungsten disulfide particles, based on intellectual property first developed at an Israeli research institute.
Fullerene Building Blocks
To understand the source of NIS additive technology, first it is important to take a look at its foundational chemistry – carbon fullerenes.
A fullerene is the carbon allotrope C60, named after the architect R. Buckminster Fuller, who popularized a structure formed from hexagons or pentagons called a geodesic dome. Similarly shaped, a fullerene is made up of 12 pentagons and 20 hexagons creating a sphere of 60 equivalent carbon atoms. Its discovery in 1984 won a Nobel Prize for Chemistry.
Within weeks of C60 being characterized, its discoverers had also characterized C70, an oblate or squashed spheroid comprising 25 hexagons and 12 pentagons. The pattern of hexagons and pentagons of C60 was identical to the pattern of panels common on soccer balls at the time, hence the nickname Buckyballs for C60, C70 and their larger analogues.
As they picked their way through the soot they created in the laboratory, the scientists discovered tubes of hexagons, otherwise known as carbon nanotubes, and multi-walled, onion-like structures of spheroids within spheroids, or tubes within tubes.
Now that people knew what to look for, it was quickly established that other materials with a tendency to form layered structures in the bulk (i.e., conventionally produced and not on a nano scale) could be coaxed into forming some of the spheroid, tube or onion-like structures that carbon could form on the nano scale.
One of those who was earliest to realize this was Reshef Tenne at Israels Weizmann Institute of Science. Tenne predicted that tungsten disulfide, which is layered when in bulk, would form caged structures rather than layers if it could be synthesized as nanoparticles. Tenne named these materials inorganic fullerene-like nanoparticles and nanotubes.
Detailed study of the growth mechanism of fullerene-like WS2 nanoparticles and nanotubes was undertaken. This development led to the scaling-up of their production and…commercialization…as superior solid lubricants with numerous potential applications, Tenne says on the institutes website.
Two companies were created to exploit the properties of inorganic fullerene-like WS2 nanoparticles, or IF-WS2, and these companies later merged to form NIS. The materials NIS manufactures are based on multi-walled onion-like particles.
Cushions, Rollers and Peeling Layers
As the IF-WS2 particles are near spheres less than a micron in diameter, they can fill surface cracks and hollows, preventing oil from entering. The spheres are compressible, so they prevent exposure to
the hydraulic pressures that can cause cracks to propagate. They can also roll within the contact, holding the two surfaces apart as they pass. NIS claims that this mechanism is predominant on very smooth surfaces.
When the hollow particles are held and compressed between two surfaces they flex and then display possibly their most striking property – exfoliation under high load. Conceptually, this has been described as a layer peeling off, as appears to be the case in the transmission electron micrograph in Figure 1. On close examination of many surfaces from different types of contact, multiple layers of WS2 can be found by the micrograph. These are aligned parallel to the surface of the underlying part.
Other micrograph imagery shows a different exfoliation mechanism. After the sphere flexes under load, the core of the particle is ejected from the outer layer in the same way as a seed is squeezed out of a ripe fruit. The outer layer can be seen to remain intact and in contact with one of the surfaces.
Extending Tool Life
IF-WS2 particles have found applications in metalworking processes such as stamping, extrusion and rolling, where they reduce friction and impact forces that can reduce the life of the tools. NIS has demonstrated the effectiveness of IF-WS2 in water as a top-treat to a semi-synthetic threading lubricant and IF-WS2 as a top-treat to an oil-based lubricant for stamping. Each showed a 40 percent plus increase in tool life.
A water-based dispersion consisting only of water, a stabilizing surfactant and IF-WS2 extended the life of milling tools in field trials relative to a conventional phosphorus-based emulsion. At 1.35 percent in water, IF-WS2 produces an impressive four ball weld load test result of 1,000 kilogram force – a level of protection rarely reached by legacy EP additives, even at higher treat rates in base oil or greases. By contrast, the weld load for water alone is 60 kgf. Increases in weld load for intermediate concentrations are directly proportional to the concentration of additive.
Similar reductions in wear scar diameter with increasing concentration of IF-WS2 are also reported. These progressive results are also associated with reductions in the coefficient of friction
A study employing the pin on disc test (ASTM G99) shows that the coefficient of friction decreases as the load increases. This unusual behavior is described by George Diloyan, CEO and chief technology officer of NIS.
Our ASTM G99 experiments show the changes in the wear protective mechanism of IF-WS2. At lower Hertzian pressures – loads up to 500 newtons – particles most likely either slide or rotate, thus friction is higher compared with higher loads. At higher Hertzian pressures, the exfoliation mechanism kicks in, significantly reducing friction, Diloyan told LubesnGreases.
The surface finish of many parts is significantly improved. In field trials in milling and grinding applications, IF-WS2 at around 0.4 percent in water, as part of NISs IW4110 package, gave much better finishes than the customers regular metalworking fluid.
Other benefits include less harmful mists and fewer dermal issues for operators, as IF-WS2 has been shown to be non-toxic. As IF-WS2 can be formulated in water only, there is less bio-activity in the fluids since an absence of base oil means a lower concentration of hydrocarbons.
Last year, Diloyan presented test data on a matrix of 13 lithium complex greases, featuring varying concentrations of IF-WS2, molybdenum disulfide and sulfur-based additives. NIS has run similar comparative tests with polytetrafluoroethylene added to a lithium complex base grease. In common with the water-based fluid tests, greases based on IF-WS2 performed better than the other greases in the matrix in a variety of weld load, wear and friction tests. Test data in calcium sulfonate greases is directionally similar, although fewer tests have been performed.
NIS is convinced that grease manufacturers can save money when formulating with its products.
If we compare the costs of making a grease with long-established grease packages based on sulfurized olefins with high concentrations of active sulfur plus molybdenum sulfide, the much lower treat rates of IF-WS2 mean that the cost of a grease is lower to achieve the same EP performance, says Diloyan.
The IF-WS2 can replace most EP or antiwear additives, so there is less requirement for additives to counteract those additives. For example, less corrosion preventives are needed because the highly reactive sulfur EP additives are no longer present.
NIS also claims its oil-based packages can prevent micro-pitting and surface fatigue in gear oil formulations, something that should be of interest to formulators of gear oils for wind turbines.
The shock absorbing properties of the IF-WS2 spheres should enhance the performance of lubricants for heavy duty axle oils and many applications in mining. In an FZG load stage test at 1,450 revolutions per minute and 90 degrees Celsius, an SAE 75W-80 axle oil that showed scuffing at load stage nine, reached load stage 12 with no scuffing when NISs IC3100 package was added to the axle oil.
NIS formulates packages and finished lubricants, as well as providing dispersions of IF-WS2 in water or oil (with some surfactant to maintain the dispersion).
There are several synergistic additives that work very well with IF-WS2, such as phosphate esters and organophosphates, Diloyan said.
With more than 10 years of commercialization and sales of IF-WS2-based lubricants claimed to be measured in thousands of tons per year, NIS is bullish about its future. It is confident that it has a strong intellectual property position, either holding or licensing patents for manufacture and application.
At the moment NISs position seems strong, as it believes it has tied up the whole area with its intellectual property. But a few competitors may yet come to market in the future, born out initiatives such as specialty chemicals company Nouryons startup collaboration innovation program Imagine Chemistry, which seeks to promote performance-boosting nano particles and label-free chemistries, both of which NISs products satisfy.
The scale-up of production of IF-WS2 particles of various morphologies; development of dispersion techniques for novel materials in various carriers and building performance additives for various applications are a solid basis for our future. We are very excited to see more research groups that are developing innovative products for lubricant market and continue collaborations with several research groups for technology success, Alexander Margolin, chief operating officer of Israeli company NanoMaterials Ltd., a subsidiary of NIS, told LubesnGreases.
After a long and arduous quest, maybe the lubricants industry has at last found its holy grail.
Trevor Gauntlett has more than 25 years experience in blue chip chemicals and oil companies, including 18 years as the technical expert on Shells Lubricants Additives procurement team. He can be contacted at firstname.lastname@example.org