Duplex Film Research Articles

Stable Ultra-thin Silver Films Grown by Soft Ion Beam-Enhanced Sputtering with an Aluminum Cap Layer.

Ultra-thin silver films are susceptible to ambient environments and form grayish layers in the silver mirroring process. The poor wettability together with the high diffusivity of surface atoms in the presence of oxygen accounts for the thermal instability of ultra-thin silver films in the air and at elevated temperatures. This work demonstrates an atomic-scale aluminum cap layer on the silver to enhance the thermal and environmental stabilities of ultra-thin silver films deposited by sputtering with the assistance of a soft ion beam reported in our previous work. The resulted film consists of an ion-beam-treated seed silver layer of ∼1 nm nominal thickness, a subsequent silver layer of ∼6 nm thickness produced by sputtering alone, and an aluminum cap layer of ∼0.2 nm nominal thickness. Although the aluminum cap is only one to two atomic layers and likely non-continuous, it significantly improved the thermal and ambient environmental stability of the ultra-thin silver films (∼7 nm thick) without affecting the film's optical and electrical properties. The improved environmental stability is attributed to the cathodic protection mechanism and reduced diffusivity of surface atoms. The improved thermal stability is attributed to the reduced mobility of surface atoms in the presence of aluminum atoms. Thermal treatment of the duplex film also improves the film's electrical conductivity and optical transmittance by enhancing its crystallinity. The annealed aluminum/silver duplex structure has exhibited the lowest electric resistivity among the reported ultra-thin silver films and high optical transmittance similar to the simulated theoretical results.

Langmuir Trough Study of the Interactions of Tear Mimetic Eyedrop Formulation with Human Meibum Films

Meibomian gland disease is associated with quantitative or qualitative deficiencies of meibum (MGS) that result in tear film instability. Thus, there is great demand for ophthalmic nanoemulsions that can replenish MGS and recover its performance at the air/tear surface. Rohto Dry Aid (RDA) utilizes TEARSHIELD TECHNOLOGYTM implementing a complex oil phase of non-polar and polar lipid-like molecules. Therefore, the interactions of RDA with MGS surface films deserve further study as they may provide valuable insights (i) into the mechanisms behind the nanoemulsion therapeutic action and (ii) for the design of novel ophthalmic formulations. Pseudobinary meibum/RDA films were formed at the air–water surface of the Langmuir trough. Surface pressure-area isocycles and stress relaxations were employed to probe the layer (i) reorganization upon cycling and (ii) dilatational elasticity, respectively. Film morphology was accessed by Brewster angle microscopy and the spreading properties of RDA-supplemented meibum were also probed. The diverse ingredients of the nanoemulsion oil phase complemented the non-polar and polar lipid constituents of the meibomian layers, which resulted in enhanced continuity of the MGS duplex film structure and facilitated the MGS spread and viscoelasticity. Nanoemulsions deserve further study as a potent tool for MGS-oriented therapy for dry eyes.

Improving bond of fiber-reinforced polymer bars with concrete through incorporating nanomaterials

The bond between FRP bars and concrete, the foremost performance for implementation of such reinforcements to corrosion-free concrete structures, is still unsatisfied due to the weak nature of duplex film in the interface. The existing approaches show low efficiency in improving the microstructures and bond between FRP bars and concrete. To address these issues, this paper provided a new approach for improving the bond between FRP bars and concrete by incorporating nanomaterials, as well as explored the modifying mechanisms and established the bond-slip models. For these purposes, the pull-out test, scanning electron microscope observation, as well as energy dispersive spectrometry analysis were performed. The experimental results demonstrated that the presence of nanomaterials increased the ultimate bond strengths between glass/carbon FRP bars and concrete by up to 16.2% and 37.8%, while the corresponding slips decreased by 28.7% and 35.4%, respectively. Such modification effects can be attributed to the optimized intrinsic composition and the reduced pore content of hydration products in the interface, especially in the duplex film, through the nanomaterial enrichment and nano-core effects. The bond-slip relationship between FRP bars and concrete with nanomaterials can be accurately predicted by the mBPE model.

Electrosynthesis of a Duplex Coating Consisting of a Cerium-Based Layer and a Polypyrrole Film for the Corrosion Protection of AISI 304 Stainless Steel

Duplex coating consisting of an inner cerium-based layer and polypyrrole (PPy) film topcoat was electrodeposited onto AISI 304 stainless steel. The cerium-based coating was electrodeposited in solutions containing cerium nitrate at 50 ºC. The polymeric outer layer was electropolymerized in the presence of sodium bis(2-ethylhexyl) sulfosuccinate (AOT). The electrosynthesis was done under potentiostat conditions. The coatings were characterized by scanning electron microscopy (SEM) and energy dispersive x-ray spectrometry (EDX). The morphology of the double-layered cerium polypyrrole film shows a granular structure with the presence of agglomerates of small grains. 
 The anticorrosive performance of the coatings was evaluated in sodium chloride solution by linear polarization, open circuit measurements, and electrochemical impedance spectroscopy (EIS). Single films, cerium layer and PPy coating, and the duplex film all reduce the corrosion rate of AISI 304 stainless steel in NaCl solution. The duplex coating presents an improved corrosion resistance concerning the single films. The combination of the characteristics of the single layers is responsible for the superior corrosion protection efficiency of the double-layered cerium polypyrrole coating.

Microstructure and oxidation behaviors at 800°C and 1250°C of MoSi2/ReSi2/NbSi2 compound coating prepared by electrodeposition and then pack cementation

Abstract Mo Re duplex film has been electrodeposited from aqueous solution innovatively and then applied to fabricate protective silicide coating for the Nb Ti Si based alloy successively. The XRD, SEM and EDS results indicated the formation of MoSi2/ReSi2/NbSi2 compound coating after halide reactivated pack cementation (HAPC) treatment. Pesting oxidation of MoSi2 layer was suppressed and the Nb Ti Si based alloy was effectively protected at 800 °C with a mass gain of 0.48 mg cm−2 after oxidation for 100 h. At 1250 °C, continuous mass gain was observed with a mass gain of 2.6 mg cm−2 after exposure of 10 h. The synergistic combination of MoSi2 and NbSi2 layer enabled admirable protection of the substrate, in which MoSi2 layer worked as the major anti-oxidation coating and the NbSi2 layer could be a reservoir for Si. The contrast experiments indicate that ReSi2 layer could improve the integrity and adherence of MoSi2 layer, reduce the outward diffusion of alloying elements and oxidation of NbSi2 layer, and then improve oxidation resistance of the compound coating ultimately.

Improvement in the corrosion protection and bactericidal properties of AZ91D magnesium alloy coated with a microstructured polypyrrole film

Abstract In this work hollow rectangular microtubes of polypyrrole (PPy) films were potentiostatically electrodeposited on magnesium alloy AZ91D in salicylate solution. The substrate was previously anodized under potentiostatic conditions in a molybdate solution in order to improve the adherence of polymer. Finally the duplex film was modified by the incorporation of silver species. The obtained coatings were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopies (XPS) and the antimicrobial activity against the bacteria Escherichia coli was evaluated. The corrosion protection properties of the coatings were examined in Ringer solution by monitoring the open circuit potential, polarization techniques and electrochemical spectroscopy (EIS). The duplex coating presents an improved anticorrosive performance with respect to the PPy film. The best results concerning corrosion protection and antibacterial activity were obtained for the silver-modified composite coating.

Effects of lead on oxidation behavior of Alloy 690TT within a high temperature aqueous environment

The chemical compositions, phases and structures of two oxide films on Alloy 690TT following exposure for 4400h in pure water with and without lead at 320°C were studied by surface analysis techniques. The analysis of a lead-doped oxide film prepared by a focused ion beam (FIB) demonstrated that both Cr-rich and Ni-rich oxides were alternatively distributed within the outer layer, whereas the inner layer was porous and poorly protected, causing severe corrosion of the alloy and a thicker film was formed. A duplex film model was proposed for the effects discussion of lead on the oxidation mechanism.

Electrochemical Behavior of Three 90Cu-10Ni Tubes from Different Manufacturers After Immersion in 3.5% NaCl Solution

Investigation on the electrochemical behavior and corrosion product films formed on three 90Cu-10Ni tubes designated as Tubes A, B and C from three different manufacturers with different service lives were carried out using electrochemical techniques, SEM, XRD and XPS after immersion in 3.5 wt.% NaCl solution. The results of polarization curve measurements showed noticeable decrease in the corrosion current densities (I corr) of the three tubes with immersion time, and the I corr of Tube C was comparatively lower than those of Tubes A and B at early immersion period. EIS measurements revealed duplex film layers on the surface of the samples with the inner film formation occurring at different times for different tubes as the film resistance R f2 revealed the formation of the inner compact layer in Tube C after 15-day immersion and in Tubes A and B after 30 days. Tube C showed better corrosion resistance which is due to early formation of the inner compact oxide film. The XPS analysis revealed Ni enrichment on the surface film of the three samples but Ni depletion as the immersion time is increased.

Electrochemical Stability of Cu–10Al–10Zn, Cu–10Al–10Ni, and Cu–10Ni–10Zn Ternary Alloys in Simulated Physiological Solutions

Copper-based alloys are widely used in the consumer electronics industry for components such as connector contacts, shielding gaskets, and terminals. Nickel silver is a general term for alloys that contain copper, nickel, and zinc. Nickel silver first became popular as a base metal for silver-plated cutlery and other silverware, notably electro-plated nickel silver, jewelery and coins. In this article, the electrochemical stability of Cu–10Ni–10Zn alloy was compared with that of pure copper and two of copper ternary alloys, namely Cu–10Al–10Zn and Cu–10Al–10Ni in synthetic sweat solution, Hank’s solution and in Ringer physiological solution. Corrosion behavior of the different electrodes was investigated using cyclic voltammetry, potentiodynamic polarization, and impedance spectroscopy techniques. The CVs showed peaks concerning the redox reactions for copper. These peaks were assigned to the formation and reduction of copper species. Furthermore, they showed that the copper oxidation was suppressed to a large extent by the presence of Ni and zinc in the alloy composition than the presence of Al and Zn or the presence of Al and Ni elements. Also, the results showed that the Cu–10Ni–10Zn alloy exhibited good corrosion resistance due to the formation of a protective passive film. The electrochemical impedance spectroscopy results indicated that either a duplex film with an inner barrier layer and an outer porous layer or a single passive layer was formed on the surface. The formation of such passive film was discussed, and the different alloy surfaces examined by scanning electron microscopy and subjected to EDAX analysis. The surface analysis has shown the participation of the different alloying elements in the passive film according to the alloy constituents. Addition of Ni decreases the rate of corrosion of the Cu, and the Cu–10Ni–10Zn was found to be the most corrosion-resistant alloy.

Effect of low levels of sulphate on the current density and film morphology during anodizing of aluminium in chromic acid

Previous work has shown that a low level of sulphate impurity in chromic acid can significantly change the growth rate and the morphology of porous anodic films formed on aluminium at a constant voltage. The changes were associated with incorporation of sulphate into the films. The present study employs electron microscopy to reveal the growth of larger pores and cells at longer times of anodizing than previously used, leading to a duplex film morphology, with finer pores in the outer region. The change in pore size correlates with a reduction in the concentration of sulphate in the film. However, the behaviour of a tungsten tracer indicates that the sulphate does not alter the mechanism of pore generation significantly. From the results of sequential anodizing in sulphate-containing and sulphate-depleted electrolytes, it is suggested that incorporated sulphate ions lead to the generation of a space charge layer, which has an important role in determining the current density.

Influences of alloyed Si on the corrosion resistance of Co–Cr–Mo alloy to molten Al by iso-thermal oxidation in air

The corrosion resistance of Co–Cr–Mo alloys with various Si concentrations after oxidation to molten Al was investigated. Si was helpful in forming a more homogeneous, compact Cr2O3 film after oxidation. Correspondingly, the Cr2O3-dominant film was more effective in enhancing the corrosion resistance than the duplex film of CoO and Cr2O3 of alloy with low Si concentration. In addition, local defects such as the cracks acted as initiation sites of failure in oxide film. Ascribed to its higher stability, Si-rich layer beneath the oxide film delayed the reaction between Al and matrix even after the failure of oxide film.

Structural and Rheological Properties of Meibomian Lipid

We explore the unique rheological and structural properties of human and bovine meibomian lipids to provide insight into the physical behavior of the human tear-film lipid layer (TFLL). Bulk rheological properties of pooled meibomian lipids were measured by a commercial stress-controlled rheometer; a home-built interfacial stress rheometer (ISR) probed the interfacial viscoelasticity of spread layers of meibomian lipids. Small- and wide-angle x-ray scattering detected the presence and melting of dispersed crystal structures. Microscope examination under cross polarizers provided confirmation of ordered crystals. A differential scanning calorimeter (DSC) analyzed phase transitions in bulk samples of bovine meibum. Bulk and interfacial rheology measurements show that meibum is extremely viscous and highly elastic. It is also a non-Newtonian, shear-thinning fluid. Small- and wide-angle x-ray diffraction (SAXS and WAXS), as well as differential scanning calorimetry (DSC) and polarizing microscopy, confirm the presence of suspended lamellar-crystal structures at physiologic temperature. We studied meibum architecture and its relation to bulk and interfacial rheology. Bovine and human meibomian lipids exhibit similar physical properties. From all structural probes utilized, we find a melt transition near eye temperature at which lamellar crystals liquefy. Our proposed structure for the tear-film lipid layer at physiologic temperature is a highly viscoelastic, shear-thinning liquid suspension consisting of lipid lamellar-crystallite particulates immersed in a continuous liquid phase with no long-range order. When spread over on-eye tear, the TFLL is a duplex film that exhibits bulk liquid properties and two separate interfaces, air/lipid and water/lipid, with aqueous protein and surfactantlike lipids adsorbed at the water/lipid surface.

Preparation of Duplex Film through Microarc Oxidation Coloring and Polymer Plating on Mg-Li Alloy and Its Corrosion Resistance

Preparation of Duplex Film through Microarc Oxidation Coloring and Polymer Plating on Mg-Li Alloy and Its Corrosion Resistance

Corrosion behavior of biomedical Ti–24Nb–4Zr–8Sn alloy in different simulated body solutions

Corrosion behavior of a multifunctional biomedical titanium alloy Ti–24Nb–4Zr–8Sn (wt.%) in 0.9% NaCl, Hank's solution and artificial saliva at 37°C was investigated using open circuit potential, impedance spectroscopy and potentiodynamic polarization techniques, and some results were compared with pure titanium and Ti–6Al–4V alloy. The results showed that the alloy exhibited good corrosion resistance due to the formation of a protective passive film consisting mainly of TiO2 and Nb2O5, and a little of ZrO2 and SnO2. Ca ions were detected in the passive film as the alloy immersed in Hank′s and artificial saliva solutions and they have negative effect on corrosion resistance. The EIS results indicated that either a duplex film with an inner barrier layer and an outer porous layer or a single passive layer was formed on the surface, and they all transformed into stable bilayer structure as the immersion time increased up to 24h. The polarization curves demonstrated that the alloy had a wider passive region than pure titanium and Ti–6Al–4V alloy and its corrosion current density (less than 0.1μA/cm2) is comparable to that of pure titanium.

Analysis of Comparison of Human Meibomian Lipid Films and Mixtures with Cholesteryl Esters In Vitro Films using High Resolution Color Microscopy

The lipid layer of the tears has been studied in vivo using high resolution color microscopy (HRCM). The purpose of these experiments was to gain further insight into the structure of the lipid layer by applying HRCM to in vitro meibomian lipid films. Films of human meibomian lipids, cholesteryl nervonate, cholesteryl palmitate, or their mixtures, were spread on a Langmuir trough. Changes to the films were monitored using HRCM as the films were compressed to different surface pressures. The penetration of albumin into a meibomian lipid film also was studied. Small amounts of meibomian lipids at low pressures formed very thin films estimated to be 5.2 nm thick. Compression caused spots to appear in the films. At higher concentrations, micro lenses were a feature of the film. Cholesteryl nervonate formed a multilayered oil slick that did not change with surface pressure. Cholesteryl palmitate formed a stiff film that collapsed at high compression. Mixtures of cholesteryl nervonate and meibomian lipids showed that they mixed to increase surface pressures above that of the individual components. HRCM also allowed albumin to be seen penetrating the meibomian lipid film. HRCM combined with in vitro surface pressure measurements using a Langmuir trough is useful for modeling meibomian lipid films. The films often resemble the appearance of the lipid layer of in vivo films. The data indicate that the lipid layer might be modeled best as a duplex film containing an array of liquid crystals.

Electrochemical corrosion behavior of Ti–24Nb–4Zr–8Sn alloy in a simulated physiological environment

Electrochemical corrosion behavior of a biomedical titanium alloy Ti–24Nb–4Zr–8Sn in weight percent was investigated in a phosphate buffered saline solution at 37°C utilizing open-circuit potential, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) techniques. Both commercially pure titanium and Ti–6Al–4V alloy were also investigated to make a comparison. The results show that all the samples were spontaneously passivated once immersion into the electrolyte. Ti–24Nb–4Zr–8Sn alloy exhibited a much wider passive region compared with pure titanium and Ti–6Al–4V and also relatively low corrosion current density which is comparable to that of pure titanium in the buffered saline solution, which was attributed to a stable passive film mainly consisted of titanium oxide and niobium oxide on its surface. The EIS results indicated the presence of a single passive layer with thickness ∼2nm for Ti–24Nb–4Zr–8Sn and pure titanium but a duplex film consisting an inner barrier layer and an outer porous layer on Ti–6Al–4V alloy with thickness of ∼3nm and ∼2.5nm, respectively.

Thermal properties of hydrated cement pastes studied by the photoacoustic technique

Photoacoustic (PA) technique has been applied to measure the effective thermal diffusivity (αeff) of hydrating cement pastes with a varying water to -cement ratio (w/c) and for variable duration (d) of hydration. Four samples with w/c = 0.3, 0.4, 0.5 and o.6 were prepared. The frequency variation of the PA signal for each sample was recorded at the begining (0 d), as well as one week and one month of hydration. The effective thermal effusivity (eeff) was obtained by measuring the variation of the signal with modulation frequency and the corresponding values of the effective thermal conductivity (keff) were calculated. The results for keff show a decrease at higher w/c (0.6), no change for other samples has been observed. The thickness of the duplex film of Ca(OH)2 and C-S-H formed on the surface of the samples of w/c = 0.5 were determined using the effective layer model in the 0 d and after one month of hydration; a remarkable increase was observed in the last case.

A Preliminary Quantitative XPS Study of the Surface Films Formed on Pure Magnesium and on Magnesium-Aluminium Intermetallics by Exposure to High-Purity Water

An XPS investigation was carried out on the surface film formed by exposure to high-purity water, on mechanically polished Mg and the two Mg-Al intermetallic compounds: Al3Mg2 and Mg17Al12. The result for mechanically polished pure Mg indicates that a film of MgO covered by a Mg(OH)2 layer, formed by the reaction of MgO with water vapour in the air. On immersion in distilled water, this film was hydrated to a duplex film with an inner MgO layer next to the Mg metal and an external porous layer of hydroxide. For both intermetallics, there was preferential dissolution of magnesium from the mechanically ground surface and also during aqueous immersion. After immersion, there was a 10 nm thick, stable film on the surface; the film composition on Al3Mg2 was whilst that on Mg17Al12 was .

A first quantitative XPS study of the surface films formed, by exposure to water, on Mg and on the Mg–Al intermetallics: Al 3Mg 2 and Mg 17Al 12

An XPS investigation was carried out of the surface films, formed by exposure to ultrapure water, on mechanically ground Mg and the two Mg–Al intermetallic compounds: Al 3Mg 2 and Mg 17Al 12. The mechanically ground Mg surface had a film of MgO at the Mg metal surface covered by a Mg(OH) 2 layer, formed by the reaction of the MgO with water vapour in the air. Upon immersion in ultrapure water, this film converted to a duplex film with an inner MgO layer next to the Mg metal and an external porous hydroxide layer. For both intermetallics, the XPS data is consistent with (i) preferential dissolution of Mg and (ii) a 10 nm thick film on the surface after immersion in ultrapure water; the film composition on Al 3Mg 2 was AlMg 1.4 O 0.2 (OH) 5.4 whilst on Mg 17Al 12 the composition was AlMg 2.5 (OH) 8 .

Structural investigation of re-deposited layers in JET

JET Mk-II Gas Box divertor tiles exposed in 1998–2001 have been analysed with various ion beam techniques, secondary ion mass spectrometry (SIMS) and Raman spectroscopy. Inner divertor wall tiles removed in 2001 were covered with a duplex film. The inner layer was very rich in metallic impurities, with Be/C ∼ 1 and H-isotopes only present at low concentrations. The outer layer contained higher concentrations of D than normal for plasma-facing surfaces in JET (D/C ∼ 0.4), and Be/C ∼ 0.14. Raman and SIMS analyses show that the deposited films on inner divertor tiles are hydrogenated amorphous carbon with low sp 3 fractions. The deposits have polymeric structure and low density. Both Raman scattering and SIMS indicate that films on inner divertor wall Tiles 1 and 3, and on floor Tile 4 have some differences in the chemical structure of the deposited films