Rongguang Wang

Evaluation of the wettability of metal surfaces by micro-pure water by means of atomic force microscopy

Abstract The wetting characteristics of polished, air oxidized and pure water immersed pure chromium, nickel, iron and SUS304 steel surfaces were observed with a digital microscope and an atomic force microscope. The macro- and micro-wetting contact angles were measured and compared and the influence of the surface composition on wettabilities is discussed. The surfaces represent not only pure metals (chromium, nickel and iron) but also their oxides and hydroxides. The macro- and micro-wettabilities were different for pure chromium, nickel, iron and SUS304 steel. The micro-wettabilities were higher than the macro-wettabilities for all specimens and the scatter of values was large. The micro-water droplets were more stable than the macro-water. The wettabilities also changed with the change in surface composition resulting from different pretreatments such as wet polishing, air oxidation and pure water immersion.

Micropure water wettability evaluation of SUS304 steel with a tapping mode of atomic force microscope

Abstract Micro pure water wetting morphologies on SUS304 steel surface before and after immersion corrosion in 3.5 mass% sodium chloride aqueous solution were observed with a tapping mode of atomic force microscope. The micro pure water wettabilities of these were evaluated.

Micro pure water wettability evaluation with an AC no-contact mode of atomic force microscope

The macro and micro water droplets on natural mica and pure chromium surface were observed with an AC no-contact mode of atomic force microscope. The micro pure water wettabilities of mica and chromium were evaluated according to the observation results. The observation of micro water droplets on mica and pure chromium surfaces becomes possible with the AC no-contact mode of atomic force microscope even if the cantilever is not metal film-coated and not applied with any bias voltage. The micro water wettabilities on mica and pure chromium surfaces were evaluated by the equation θ=2tan−1(h/r), where θ is the contact angle between micro water droplet and substrate, h is the height of the water droplet and r is the radius of the water droplet. The wettabilities of mica and pure chromium are different from each other and the micro wettability is higher than the macro one even on the same material surface according to the measured data in this paper.

Condensation and evaporation behaviors of micro-water droplets on SUS304 steel observed using the ac noncontact mode of AFM

The condensation and evaporation behaviors of micro-water droplets on SUS304 steel were ex-situ and in-situ observed in ambient air with the ac noncontact mode of atomic force microscope. The change of water volumes and surface areas were introduced to characterize the condensation and evaporation processes.

Analysis of air adsorptive on solid surfaces by AFM and XPS

Abstract Solid surfaces of HOPG, pure copper, chromium, zinc, copper and SUS304 steel were observed in ambient air with an a.c. non-contact mode of atomic force microscope(AFM). A type of film-like-domains (adsorptive) was detected on the above surfaces. The thickness of the adsorptive was about 1.2–2.4 nm in this case. The film-like-adsorptive was confirmed to be a liquid layer by the static contact-mode scanning, the measurement of the elasticity and viscosity images, and the detection of the condensation/evaporation phenomena when the relative humidity changed. The liquid layer is considered to be condensed water covered with organic contaminant.

Nondestructive Measurement of Fatigue Damage of Thermally Sprayed Al2O3/NiCr Using ESPI Method Under High Temperature

High-temperature fatigue (R = 0) damage and deformation behaviors of SUS304 steel thermally sprayed with an Al2O3/NiCr coating were investigated using a servopulse fatigue-testing machine, SEM, and an electronic speckle pattern interferometry (ESPI) method. The relation between crack/delamination and strain variation is discussed. Surface cracks occurred at the outer Al2O3 coating but stopped at the inner NiCr coating after one fatigue cycle when the tensile stress was 202 MPa at 873 K. They propagated into the NiCr coating but stopped at the substrate, and local delamination occurred along the NiCr/substrate interface after 1 × 105 cycles test in condition (σmax = 202 MPa, T = 873 K). Cracks and delamination largely decreased when σmax = 115 MPa or T = 573 K. No influence of cycle frequencies (6.7 or 14 Hz) was detected. The strain value measured by ESPI method was confirmed to be almost the same as that obtained with strain gauges at 293 K. Strain values along cracks measured with the ESPI method were much larger than other areas as a result of crack opening under the tensile load, referred to as the strain concentration zone in this work. Positions of strain concentration zones on strain distribution figures by the ESPI method corresponded well to positions of cracks on sprayed coatings. Moreover, strain values largely decreased where local delamination occurred.

Influence of Heat Treatment on Corrosion and Wear Resistances of Mild Steel with Ni‐P‐Al2O3 Composite Film

Several heat treatment processes were applied on the mild steel of SS400, which were coated with Ni-P-Al2O3 composite film through an electroless plating process by blending A12O3 particles in mean diameter of 0.05µm at the amount of 1.0g/L. The corrosion resistance and the wear resistance were respectively investigated by polarization measurement and pin-on-disk method. It is observed from the specimen surface that damage and deformation occurred after heat treatment in the Ni-P nodules embedded with Al2O3 particles; therefore, both the corrosion resistance and the wear resistance were accordingly changed. Both the increase in the heating up time and the prolonging of the temperature holding time are confirmed to be helpful to enhance the corrosion and the wear resistances of the Ni-P-Al2O3 film coated steel.

Producing micro-droplet of dilute sulphuric acid on pure iron surface and observing its corrosion behaviour by atomic force microscopy

A simple method was presented to produce a micro-droplet of sulphuric acid on a pre-selected micro-zone on a pure iron surface with the tip of an AFM cantilever. The three-dimensional shape of the droplet was imaged with the AC non-contact mode of the AFM, and the liquid/solid interface was observed in situ during corrosion using the contact mode. The substrate surface beneath the droplet was lowered by approximately 19 nm after 3.6 ks of adhesion. This method has important implications for experimental studies of micro-zone corrosion or lubrication.