New nanotechnology solid lubricants for superior dry lubrication

摘要

This paper presents a new commercial breakthrough for advanced anti-friction materials based on unique inorganic nanospheres that can be used as dry lubricants, coatings, and for impregnating parts. The new material reduces friction and wear significantly better than other layered solid lubricants and is especially useful in self-lubricating, maintenance-free, and oil-free applications of the types encountered in aerospace markets. The material, NanoLub TM , is the world’s first commercial lubricant based on spherical inorganic nanoparticles. NanoLub’s particles have a unique structure of hollow nested spheres (see photo) of about only 0.1 micron in diameter. ( the size in the picture – 4050 nm) This paper presents tribological evaluations of tungsten and molybdenum disulphide NanoLub TM . The material reduces friction and wear under conditions that are especially relevant for space such as ultra-high vacuum, UV radiation, and high loads. Suitable applications could include rotors, bearings, robots, planetary rovers, space vehicles and transport devices. Extensive testing by a number of independent groups clearly shows that these special nanoparticles improve considerably the tribological properties of different contact pairs in comparison to other solid lubricants. Introduction The recent interest in nanoscale science and technology has lead to largte efforts to develop new strategies for the synthesis of nanomaterials of a controlled size and shape at commercially competitive prices. Numerous possible applications have been postulated for these new nanomaterials, but simple analysis shows that their use is closely related to reduced manufacturing costs. Nanomaterials are likely to be applied in important niches in various technologies, like ultrastrong nanocomposites, and as additives to various materials like lubricants. Common solid lubricants are layered compounds like graphite, molybdenum disulfide (MoS2), and tungsten disulfide (WS2). Their layers slide past each other to reduce friction. Layered compounds are not without their drawbacks however. The edges of the layers are chemically reactive, causing them to slowly decompose, break apart, and bind to the metal surface. The relative large size of the layered platelets prevents them from entering the pores of metal parts and thus they tend to accumulate and stick on the surface. These factors ultimately diminish their lubricating ability causing the metal parts to grind against each other and wear down. Thus, there is a need for smaller, more stable solid lubricants. We have found that certain inorganic compounds like MoS2 and WS2 that normally occur as flat platelets can be synthesized into nanospheres. The new nano-sphere structures are several times smaller than the typical layered form of the compound. In addition, each particle consists of a number of progressively smaller concentric spheres (like an onion) nested one within the other. The diameter of the nanoparticles is on the order of 100 nm (about a thousand times smaller than the diameter of a human hair). These nanoparticles, due to their special size, shape, chemistry, and structure, have unique and beneficial properties that are not possible with conventional size materials, making them attractive for many commercial applications. Fig. 1 is a high-resolution electron microscope photo of a typical multi-walled nanosphere. The clearly visible concentric spheres are a result of the special synthesis conditions. Fig. 1: IF nanoparticle The structure of each shell resembles the geodesic dome design of Buckminster Fuller and are thus termed ‘fullerenes’. Up until this discovery it was thought that fullerenes could only be made with carbon atoms. Our group was the first to show that certain inorganic (i.e., non-carbon) compounds could also be synthesized into fullerene-like structures, hence the name inorganic fullerene, or IF, nanoparticles. Results Thin films of IF nanoparticles were deposited on metal substrate