EP nanoparticles-based lubricant package

Dr. Neil Canter, Contributing Editor | TLT Tech Beat April 2009

These multifunctional, eco-friendly lubricants use a patent-pending process that exhibits lubricity and EP characteristics.

KEY CONCEPTS
• A new organic-inorganic nanoparticle-based package provides superior antiwear, friction-reducing and extreme pressure properties.
• The organic-inorganic nanoparticle-based package exhibits a lower wear scar diameter, coefficient of friction and a higher weld point than a dispersion of molybdenum disulfide in paraffinic oil.
• The properties of the organic-inorganic nanoparticle-based package can be tailored to meet specific applications.

Lubricants are needed to minimize the amount of friction and wear generated in machinery. In carrying out this function, lubricants need to be situated on the surfaces of metals and other substrates.

With many of the interactions between lubricants and metal surfaces occurring at the molecular level, there is a greater need to better understand how such basic lubricant additives as antiwear and extreme pressure (EP) agents perform at the nanoscale.

In previous TLT articles, discussions have been held about the growing field of nanotribology (1). Commercial products containing nanoparticle-based additives are growing in use to meet a variety of applications. Development of nanoparticle-containing lubricants and lubricant additives has been slow with problems encountered in stabilizing these species in carriers such as mineral oil.

Dr. Ajay Malshe, chief technology officer for NanoMech™, LLC, in Fayetteville, Ark., says, “Current nanoparticles for use as antiwear and EP agents are based mainly on inorganic chemistries that are applied as solid coatings or used in mineral oil-based dispersions. Solid coatings will perform well for a time but tend to be worn away due to the presence of sharp asperities. Inorganic-based nanoparticle oil dispersions are not stable, and the lubricant additive readily precipitates out or agglomerates into larger particles that are ineffective.”

Organic-based additives have not been found to be an option because they do not provide adequate antiwear and/or EP performance. One other factor in working with current additives of these types is that they have been under regulatory scrutiny for at least 25 years.

STLE-member Dr. Arpana Verma, senior product engineer at NanoMech, LLC, says, “In addition to performance, the drive is toward multifunctional, environmentally friendly lubricants whose cost is comparable to current products.”

Development of nanoparticles that can exhibit antiwear and EP performance, be compatible with current lubricant basestocks and exhibit even more environmentally friendly characteristics would be welcomed in the marketplace. Such a technology has not been available until now.

ORGANIC-INORGANIC NANOPARTICLE-BASED PACKAGE
NanoMech has integrated layered inorganic solid lubricant nanoparticles of molybdenum disulfide with canola oil to form a solid lubricant package using a patent-pending process that exhibits lubricity and EP characteristics. The product has been commercialized and is known as NanoGlide.®

Verma says, “We used a chemo-mechanical process to integrate molybdenum disulfide with the canola oil. This is an example of the flexibility of this manufacturing process. The unique process has allowed multiple chemical combinations that can address varying application demands.” Figure 1 shows the proposed design of a package based on a molybdenum disulfide nanoparticle that contains canola oil and lecithin.


Figure 1. The proposed image of an organic-inorganic nanoparticle-based package shows a molybdenum disulfide nanoparticle surrounded by canola oil and lecithin (phospholipid) molecules. (Courtesy of NanoMech™ LLC)

The same synthesis technique has been applied to other application-specific components such as ZDDP, MoDTP, borates and others to design and develop improved compatible lubricants. This also was explored with other solid lubricants, including tungsten disulfide and graphite. As a result, the EP nanoparticles-based package can be easily inserted into current lubricant systems.

The organic-inorganic nanoparticle-based package also can be readily incorporated into most conventional basestocks used in the preparation of lubricants. These include base oils (Group I and Group II), synthetics (such as polyalphaolefins and esters) and biodegradable feedstocks. The nanoparticle-based package also can be formulated into greases.

Four-ball wear (ASTM D4172) and the four-ball extreme pressure (ASTM D2783) methods were conducted on the organic-inorganic nanoparticle-based package at a 1% dispersion in paraffinic oil. Wear testing was run at 75 C with the AISI 52100 steel balls being rotated at 1,200 rpm for 60 minutes at a load of 40 kg. The wear scar diameter and the coefficient of friction for the organic-inorganic nanoparticle-based package derived from molybdenum disulfide and canola oil are 0.46 millimeters and 0.07, respectively.

In contrast, paraffinic oil with a 1.0% dispersion of molybdenum disulfide nanoparticles prepared just by simple processing displays a much higher wear scar diameter of 0.95 millimeters and a higher coefficient of friction of 0.09.

In EP performance testing under standard conditions, 1.5% of the organic-inorganic nanoparticle-based package displayed a weld point of 315 kg. In contrast, 1.5% of molybdenum disulfide, which was produced by a simple process, showed a weld load of less than 150 kg.

Verma says, “The test results show that the organic-inorganic nanoparticle-based package exhibits better stability in lubricant oil basestock, which translates into superior antiwear, friction-reducing and extreme pressure properties.” The use of canola oil also means that the organic-inorganic nanoparticle-based additive is environmentally friendly and can provide good sustainability.

Other types of lubricant additives can be incorporated into the organic-inorganic nanoparticle framework, as well. Verma adds, “We have also included sulfur- and phosphorus-based technologies in the matrix to tailor the properties of the organic-inorganic nanoparticle-based package to meet specific applications. The flexibility of the organic-inorganic nanoparticle should be of value in meeting the increasing demands placed on lubricants to function under more severe conditions over longer operating intervals.”

Malshe and Verma believe that the organic-inorganic nanoparticle-based package can be utilized in automotive lubricants, biodegradable lubricants, gear oils for multiple industries (earth movers and heavy machinery for infrastructure development, naval ships, etc.), greases and metalworking fluids. In the latter application, the organic-inorganic nanoparticle-based package was found to increase the G-ratio and reduce friction in minimum quantity lubrication grinding of cast iron (2).

Additional information can be found in a recent article in STLE’s peer-reviewed journal, Tribology Transactions (3). Further details about the organic-inorganic nanoparticle-based additive can be obtained by contacting Verma at arpana.verma@nanomech.biz. 

REFERENCES
1. Van Rensselar, J. (2009), “Nanotribology: From Lab to Real World,” TLT, 65 (1), pp. 34–41.
2. Kalita, P., Malshe, A., Shen, B. and Shih, A. (2008), “Performance of Novel MoS2 Nanoparticles Based Grinding Fluids in Minimum Quantity Lubrication Grinding,” Transactions of NAMRI/SME, 36, pp. 357–364.
3. Verma, A., Jiang, W., Safe, H., Brown, W. and Malshe, A. (2008), “Tribological Behavior of Deagglomerated Active Inorganic Nanoparticles for Advanced Lubrication,” Tribology Transactions, 51 (5), pp. 673-678.


Neil Canter heads his own consulting company, Chemical Solutions, in Willow Grove, Pa. Ideas for Tech Beat items can be sent to him at neilcanter@comcast.net.