Friction reduction and wear resistance of electro-co-deposited inorganic fullerene-like WS 2 coating for improved stainl
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Alex Gorodnev NanoMaterials Ltd., Nes Ziona 74140, Israel
Yishay Feldman, Ifat Kaplan-Ashiri, and Reshef Tennea) Department of Materials and Interfaces, Weizmann Institute of Science, Rehovot 76100, Israel
Niles Fleischer, Menachem Genut, and Noam Feuerstein NanoMaterials Ltd., Nes Ziona 74140, Israel (Received 13 April 2008; accepted 11 July 2008)
A new type of composite metal–nanoparticle coating that significantly reduces the friction force of various surfaces, particularly archwires in orthodontic applications, is demonstrated. The coating is based on electrodeposited Ni film impregnated with inorganic fullerene-like nanospheres of tungsten disulphide. The first encouraging tests have shown reduction of up to 60% of the friction force between coated rectangular archwires and self-ligating brackets in comparison with uncoated archwires. The coating not only significantly reduces friction of commercial archwires but also maintains this low value of friction for the duration of the tests in comparison to archwires coated with nickel film without the nanoparticles. The coated surfaces of the wires were examined by scanning electron microscopy equipped with energy dispersive analyzer and by x-ray powder diffraction methods before and after the friction tests. Using these analyses, it was possible to qualitatively estimate the state of the Ni+IF-WS2 coating before and after the friction test compared to Ni coated wires without IF-WS2. I. INTRODUCTION
Inorganic fullerene-like tungsten disulfide (IF-WS2) nanoparticles were described first in 1992,1 and their MoS22,3 and diselenide analogues4 were described in subsequent years. It was shown that under certain reducing and sulfidizing conditions, at elevated temperatures, tungsten oxide (WO3) nanoparticles could be transformed into nested WS2 fullerene-like (IF) nanostructures creating a structure resembling a multilayer nanosphere (onion-like) or a nanotube (INT). These nanoparticles are constructed of multiple layers, which can be represented as a sandwich of covalently bonded S-W-S moieties within the plane. The layers are weakly connected through van der Waals forces only. The size of these nanoparticles ranges from 20 to 200 nanometers, depending on the WO3 precursor size. Over the years, many works have been published showing the synthesis a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2008.0350 J. Mater. Res., Vol. 23, No. 11, Nov 2008
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of new IF and INT from different layered compounds. A number of review works summarize the progress in this field.5–8 It is known that WS2 and MoS2 particles with a layered structure, which crystallize in the form of platelets, provide good lubricity.9 They are found to provide good tribological behavior in vacuum, but they do not perform as well in ambient conditions.10 Under oxidative conditions, the metal sulfide is transformed during the tribological action into oxide, which is much more abrasive in nature.11 Fullere
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