Effect Of Nanostructured Surface Research Articles

Effect of Nanostructured Surface on the Corrosion Behavior of RAFM Steels

This study investigated the effect of a preformed nanostructured surface on the corrosion behavior of 9Cr2WVTa reduced activation ferritic/martensitic (RAFM) steel and 9Cr+AlSi steel (9Cr2WVTa with the 0.12 wt.% Al and 0.68 wt.% Si addition) at 700 °C in air and at 550 °C in liquid lead–bismuth eutectic (LBE) alloys. The nanostructured surface layer was fabricated by surface mechanical rolling treatment (SMRT). The results showed that the SMRT 9Cr+AlSi sample has a lower oxidation rate than the SMRT 9Cr2WVTa steel at 700 °C in air, due to the faster diffusion rates of Al, Cr and Si in the nanostructure and a higher diffusion driving force increased by Cr. The SMRT 9Cr+AlSi sample at 550 °C in oxygen-saturated LBE alloy also had a higher oxidation rate, due to the formation of Al and Si oxides in the internal oxide layer.

A comparative study of flow boiling HFE-7100 in silicon nanowire and plainwall microchannels

Extensive experimental investigations along with high speed visualizations have been performed to assess the flow boiling characteristics in Silicon Nanowire (SiNW) microchannels. Experiments have been also performed in Plainwall microchannels to compare their performances with SiNW configurations. HFE-7100 has been used as the working fluid and experiments are conducted in a forced convection loop at mass flux range of 400–1600 kg/m2s. Arrays of microchannel consist 5 (five) parallel straight microchannels with Width, Depth and Length dimension of 220 μm, 250 μm and 10 mm respectively. Flow boiling performances including heat transfer coefficient (HTC), pressure drop, two-phase flow instabilities and critical heat flux (CHF) have been studied in both the Silicon plainwall (smooth inner surface) and Silicon Nanowire (silicon nanostructured inner surface) microchannels. High speed flow visualizations have been performed at up to 70,000 frames per s (fps) to understand the difference in boiling mechanisms between Plainwall and SiNW. SiNW performs significantly enhanced HTC (up to 400% improvement), reduces flow boiling instabilities and pressure drop (up to 70% reduction) compared to Plainwall microchannels. However, little/insignificant effect of nanostructured surface has been observed on CHF. In addition, a major difference in two-phase flow regime development has been observed between the SiNW and Plainwall microchannels during flow visualization. Specifically, SiNWs introduce explosive bubble nucleation, reduce intermittent flow regimes (slug/churn), improve rewetting, maintain thin liquid film and thus, improve system performances.

Nanostructure Introduces Artifacts in Quantitative Immunofluorescence by Influencing Fluorophore Intensity

Quantitative analysis of fluorescence signals from cells reacted with fluorescently labeled probes is a widely-used method for assessing cell biology. This method has become especially powerful for screening novel nanostructured materials for their influence on cell behavior. However, the effect of nanostructured surface on fluorescence intensity has largely been ignored, which likely leads to erroneous conclusions about cell behavior. This paper investigates this possibility by using fibroblasts cultured on nanoporous gold (np-Au) as a model nanostructured material system. We found that fibroblasts stained for f-actin using phalloidin conjugated with common fluorophores display different levels of fluorescence on np-Au, planar gold, and glass, suggesting different levels of f-actin composition. However, direct quantification via western blots indicates that the actin expression is the same across all conditions. We further investigated whether the fluorescence intensity depended on np-Au feature size, complementing the findings with reflection dark field measurements from different np-Au surfaces. Overall, our experimental measurements in agreement with our electrodynamic simulations suggest that nanostructured surfaces alter the fluorescence intensity of fluorophores by modulating both the excitation and light emission processes. We conclude that comparison of fluorescence on materials with different nanostructures should be done with a quantification method decoupled from the nanostructure's influence.

Hot corrosion behaviour of Ti–6Al–4V modified by ultrasonic shot peening

Nanostructure of 17 to 25nm was developed in surface region of the titanium alloy Ti–6Al–4V, up to the depth of ~30μm, by ultrasonic shot peening. The effect of nanostructured surface was studied on corrosion behaviour of this alloy, in three different salt mixtures: 100wt.% NaCl, 75wt.% Na2SO4+25wt.% NaCl, and 90wt.% Na2SO4+5wt.% NaCl +5wt.% V2O5; at 400, 500 and 600°C. Specimens were subjected to heating and cooling cycles with different hold periods in three blocks for total exposure of 100h. The main corrosion products formed in the different salt mixtures were characterized as TiO2, Al2O3, V2O3, Ti2O3 and V2O5 oxides. The corrosion rate was found to be lower in the ultrasonic shot peened specimens as compared to those in the non-shot peened ones.

Effect of nanostructured surface of radiation-oxidized aluminum on radiolytic processes in n-hexane

The effect of a nanostructured surface of radiation-oxidized aluminum on radiolytic processes in n-hexane was investigated. It was ascertained that the decreased thickness of oxide films on Al surface by approximately two orders of magnitude (from 600 to 8 nm) led to an increase in the rate of molecular hydrogen formation by a factor of ∼7 (from 1.1 to 7.6 × 1015 molecule g−1 s−1); meanwhile, the radiation chemical yield of H2 changed from 4.3 to 8.2 molecules/100 eV. The results obtained were interpreted in terms of the difference in the degree of imperfection of the surfaces of radiation-generated Al plates and enhancement of radiation-generated centers, which was evidenced by AFM images and RTL measurements.

Pool Boiling Experiments on a Nano-Structured Surface

The effect of nano-structured surfaces on pool boiling was investigated. Saturated and subcooled pool boiling experiments were performed on a horizontal heater surface coated with vertically aligned multiwalled carbon nanotubes (MWCNTs). MWCNTs were synthesized using the chemical vapor deposition (CVD) process. In this paper, MWCNT forests of two distinctly different heights (Type A: 9-mum height, and Type B: 25-mu m height) were synthesized separately on silicon wafers. PF-5060 was used as the test liquid. The results show that Type-B MWCNTs yield distinctly higher heat fluxes under subcooled and saturated conditions for both nucleate and film boiling. Type-A MWCNTs provide similar enhancement in nucleate boiling (as Type-B) for both saturated and subcooled conditions. Type-B MWCNTs enhanced critical heat flux (CHF) by 40%. Increasing the height of the MWCNTs is also found to extend the wall super heat required for CHF. In contrast, Type-A MWCNTs provide only marginal enhancement in film boiling compared to bare silicon wafer, for both saturated and subcooled film boiling. Type-B MWCNTs enhanced the heat flux in the film boiling regime for the Leidenfrost point by 175% (compared to bare silicon wafer).