Surface force microscope observations of corrosive tribological wear on single crystal NaNO3 exposed to moist air

Abstract

Simultaneous tribological loading and exposure to a chemically reactive environment can yield wear processes not produced by either stimulus alone. We report surface force microscopic (SFM) observations of cleaved, single crystal NaNO3 in air, where tribological loading was provided by the SFM tip itself and chemical exposure was due to controlled introduction of water vapor at relative humidities from 10 to 65%. Scanning in the contact mode with nN loads at 30-50% relative humidity produces readily visible surface modifications, including preferential removal of material along steps. Material transfer along the surface can yield parallel ridges and depressions tens of nanometer high. In contrast, scanning in the tapping mode under certain humidity conditions produces localized deposition, possibly reflecting the "dehydration" of solvated ions and subsequent incorporation into the solid phase. We discuss the influence of contact force, tip velocity, relative humidity, and possible mechanochemistry on the rates of wear and deposition.

Atomic layer wear of single-crystal calcite in aqueous solution using scanning force microscopy

“…The saturated solution was prepared from reagent grade CaCl 2 •2H 2 O and NaHCO 3 in deionized water to yield Ca 2ϩ and CO 3 2Ϫ concentrations of 60 M, and adjusting the pH to 9 with NaOH. At this high pH, the carbonate in solution appears principally as CO 3 2Ϫ , rather than HCO 3 Ϫ , simplifying the solution chemistry. This solution is somewhat undersaturated; nevertheless, the step velocities associated with dissolution were quite low ͑Ͻ1 Å/s͒ relative to the mechanically induced enhancements described below.…”

“…1,2 Scanning force microscopy ͑SFM͒ ͓or alternatively, atomic force microscopy ͑AFM͔͒ is a particularly valuable tool to examine this synergism due to the ability to localize the tribological stimuli and to image the resulting wear patterns with nm-scale resolution. 3 With an appropriate choice of substrate, corrosive fluid, and scanning conditions, the resulting wear processes can be observed with spatial resolutions on the order of tens of nm and time resolutions on the order of seconds. In this work, we investigate further the corrosive wear of single-crystal CaCO 3 ͑calcite͒ in an aqueous solution.…”

Influence of Humidity on Adhesion: An Atomic Force Microscope Study

“…Nakahara et al [38] who observed that wear of NaNO 3 crystals in friction force microscopy experiments increased with humidity. Third, on mica we observed significantly less wear than on silicon wafers (Fig.…”

Nanotribology: experimental facts and theoretical models

“…It is possible that such (linear) dependences are specific for tribochemical wear. In the case of a NaNO 3 wet surface in contact with a probe, the splitting of diatomic steps into monoatomic ones and a material transport from steps to above-spaced terraces were noted [89]. The influence of humidity on the force interaction of a probe with a surface was also studied [16,17].…”

“…Electron friction. The mechanism of electron friction due to the generation of electron ± hole pairs was first analyzed by Persson (see references in work [89]) in connection with the problem of damping the lateral oscillation of films adsorbed on a metallic substrate. An interrelation between the friction force resulting from the scattering of conduction electrons by oscillating adsorbate atoms and the change of resistance of a metal was used.…”