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Effect of Humidity on Friction and Wear—A Critical Review

by Zhe Chen 1, Xin He 1, Chen Xiao 2 and Seong H. Kim 1,2,*
Department of Chemical Engineering and Materials Research Institute, Pennsylvania State University, University Park, PA 16802, USA
Tribology Research Institute, State Key Laboratory of Traction Power, Southwest Jiaotong University, Chengdu 610031, China
Author to whom correspondence should be addressed.
Lubricants 2018, 6(3), 74;
Received: 22 July 2018 / Revised: 12 August 2018 / Accepted: 20 August 2018 / Published: 22 August 2018
(This article belongs to the Special Issue Advanced Lubrication for Energy Efficiency)
The friction and wear behavior of materials are not intrinsic properties, but extrinsic properties; in other words, they can drastically vary depending on test and environmental conditions. In ambient air, humidity is one such extrinsic parameter. This paper reviews the effects of humidity on macro- and nano-scale friction and wear of various types of materials. The materials included in this review are graphite and graphene, diamond-like carbon (DLC) films, ultrananocrystalline diamond (UNCD), transition metal dichalcogenides (TMDs), hexagonal boron nitride (h-BN), boric acid, silicon, silicon oxide, silicates, advanced ceramics, and metals. Details of underlying mechanisms governing friction and wear behaviors vary depending on materials and humidity; nonetheless, a comparison of various material cases revealed an overarching trend. Tribochemical reactions between the tribo-materials and the adsorbed water molecules play significant roles; such reactions can occur at defect sites in the case of two-dimensionally layered materials and carbon-based materials, or even on low energy surfaces in the case of metals and oxide materials. It is extremely important to consider the effects of adsorbed water layer thickness and structure for a full understanding of tribological properties of materials in ambient air. View Full-Text
Keywords: humidity; friction; wear humidity; friction; wear
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MDPI and ACS Style

Chen, Z.; He, X.; Xiao, C.; Kim, S.H. Effect of Humidity on Friction and Wear—A Critical Review. Lubricants 2018, 6, 74.

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