Nanodiamond Lubricant Additive
Nanodiamonds (NDs), with 5nm primary particles sizes, are among the most promising nanoparticle lubricant additives since they are superhard and capable of dramatically reducing wear and friction of sliding surfaces. NDs in lubricants can provide the following global benefits for a wide range of industrial and transportation systems:
(i) reduced fuel consumption, (ii) reduced oil consumption through increased lubricant longevity, and (iii) increased longevity of components experiencing friction. D-TriboTM produced by Adámas Nanotechnologies, Inc. is a nanodiamond-based, engineered oil additive and has demonstrated very impressive performance in tests involving gasoline engines, diesel engines, and in laboratory tests, which are summarized below.
Laboratory Tests
Several hundred tests have been run at the International Technology Center (ITC) (Raleigh, NC, USA) using a Bruker's UMT-3 high-load tribometer for optimization of the D-TriboTM composition. The coefficient of friction measured as a function of time (Fig. 1) using a block-on-ring module (Fig. 2) for pure Mobil Super 5W30 SN oil and Mobil containing D-TriboTM are shown. Hardness of blocks and rings were H30 and H60, respectively. The size of the wear scar of the block tested with the additive in oil was twice less than that for pure oil (Fig. 2). Characterization of the friction surfaces after the tribotests using electron microscopy and Zygo 3D optical profiler demonstrated significant polishing of the surfaces in the tests performed with oil containing D-TriboTM (Fig.3). The mechanism of action is shown in Fig.4.
Figure 2. (Top) Scar profiles measured in the block-on-ring 7 hour test for pure Mobil Super 5W30 SN oil and the oil containing D-Tribo™ . Rotation speed was 200rpm and the load 30kg. Hardness of blocks and rings were H30 and H60, correspondingly.
Followed by Block-on-ring test module setup
Figure 1. Coefficient of friction measured as a function of time in the block-on-ring test for pure Mobil Super 5W30 SN oil and the oil containing D-Tribo™. Rotation speed was 200rpm and the load was 30kg.
Figure 3. Scanning electron microscopy images of the surfaces within scars in blocks formed during the 7 hour test for pure Mobil Super 5W30 SN oil and the oil containing D-Tribo™. Rotation speed was 200rpm and the load was 30kg. Hardness of blocks and rings were H30 and H60, respectively.
Figure 4. Possible mechanism of action of combination of nanodiamonds (NDs) and a typical antiwear additive (AW). NDs contribute to the efficient polishing of the asperities during the initial stage of sliding of the friction surfaces against each other, while the AW agents form a protective film.
After some time (a “work-in” period), a well-polished surface protected by a tribo film is formed possibly reinforced with incorporated ND particles. Reinforcement with NDs can be extended, in principle, to the incorporation of NDs into the metallic substrate, depending on the hardness of the substrate. It is presumed that the onset of the drop in the friction coefficient (Fig. 1) coincides with the point at which the surface is well polished. When the average roughness of the surface is highly uniform after polishing, not only does this remove high stress concentrators which increase wear, but it may also allow for a more uniform protective anti-wear film to be established. The amount of the AW additive needed for the protection is a few times (up to 5 times) less then typically recommended, when used in combination with NDs.
