Focused Ion Beam Transmission Electron Microscopy Research Articles

Maximization of the blue-white contrast of ancient porcelain decorations from Jingdezhen imperial kiln by Co-spinel formation

By analyzing the chromaticity values of the ancient blue-and-white porcelain combined with the imitated experiment, the color information is quantified and ‘color dispersion’ mechanism is clarified. Energy Dispersive X-Ray Fluorescence (EDXRF), field emission scanning electron microscopy (FE-SEM), the advanced focused ion beam transmission electron microscopy (FIB-TEM) technique, etc, were used to study the characteristics and the ‘color dispersion’ mechanism of the blue-and-white porcelain in Jingdezhen imperial kiln. The ‘color dispersion’ of the blue-and-white porcelain is mainly caused by Co-element structure stability, which is verified by the archaeological experiment results. Blue-and-white decoration lines diffusion length (named as ‘color dispersion’) are long (i.e. fuzzy) which has few or no spinel crystals in the body-glaze interaction layer of the blue-and-white porcelain. However, the blue and white porcelain with the clear lines has a large number of spinel crystals. The experimental results enrich the literature on the history of ceramic manufacturing techniques in Jingdezhen.

Spontaneous Reconstruction of Copper Active Sites during the Alkaline CORR: Degradation and Recovery of the Performance.

Understanding the reconstruction of electrocatalysts under operational conditions is essential for studying their catalytic mechanisms and industrial applications. Herein, using spatiotemporally resolved Raman spectroscopy with CO as a probe molecule, we resolved the spontaneous reconstruction of Cu active sites during cathodic CO reduction reactions (CORRs). Quasi-in situ focused ion beam transmission electron microscopy (FIB-TEM) revealed that under prolonged electrolysis, the Cu surface can reconstruct to form nanometer-sized Cu particles with (111)/(100) facets and abundant grain boundaries, which strongly favor the formation of an inactive *CObridge binding site and deteriorate the CORR performance. A short period of anodic oxidation can efficiently remove these reconstructed nanoparticles by quick dissolution of Cu, thus providing an effective strategy to regenerate the Cu catalysts and recover their CORR performance. This study provides real-time in situ observations of Cu reconstruction and changes in the binding of key reaction intermediates, highlighting the decisive role of the local active site, rather than the macroscopic morphology, on adsorption of key reaction intermediates and thus CORR performance.

Dissimilar diffusion bonding of bulk metallic glass: Amorphous/crystalline atomic-scale interaction

Dissimilar diffusion welding of a copper-based bulk metallic glass (BMG) with a stoichiometry of Cu 50 Zr 43 Al 7 and commercial pure aluminum was performed at evaluated different temperatures (below and higher than the glass transition temperature ~ 440 °C) and holding times (up to one hour). The main goal was to successfully bond these dissimilar materials without crystallizing the BMG part to avoid deteriorating properties. Optimum joining conditions were attained at a temperature of 430 °C (<T g ) and dwell time of 60 min. The diffusion-assisted atomic-scale interactions between the amorphous and crystalline structures were studied using electron microscopy. To this end, the interaction zone at the BMG/Al dissimilar interface was extracted and analyzed by focused ion beam/transmission electron microscopy (FIB/TEM) followed by elemental analysis and high resolution-transmission electron microscopy (HR-TEM) to reveal the nature of the diffused layer and orientation relationships within the structure. Based on microscopy observations, the formation of an interaction layer with a thickness in the range of 1–2 μm was observed, confirmed by diffusion of oxygen to this region. High-resolution atomic-scale observations supposed a gradient transition from crystallinity toward the amorphous state undergoing the formation of some semi-crystalline nano-scale layers. The activation energy for the thermally-assisted diffusion bonding process was estimated at ~486.7 kJ/mol, related to the substitutional diffusion of oxygen through the copper matrix after decomposition of the stable alumina oxide layer on the surface. Accordingly, an increased indentation hardness across the dissimilar interface was observed and attributed to the distribution of elements into the reaction layer and the formation of new phases. • Atomic-scale diffusion bonding of Cu-based BMG to Al was studied by FIB-TEM analysis. • Elemental inter-diffusion in amorphous-crystalline materials interaction characterized. • Decomposition of oxide surface layer and formation of a semi-crystalline phase at the interface associated bonding. • A gradual atomic structure transition from amorphous to crystallinity was revealed across the interface. • The activation energy of the bonding process was estimated at ~486.7 kJ/mol, nearby to substitutional diffusion of oxygen.

Nanostructural domains in martian apatites that record primary subsolidus exsolution of halogens: Insights into nakhlite petrogenesis

Abstract The microstructures of selected F-, Cl-, and OH-bearing martian apatite grains, two in Northwest Africa (NWA) 998 (cumulus apatites, embedded in pyroxene) and a set of four in Nakhla (intercumulus apatites), were studied by focused ion beam–transmission electron microscopy (FIB-TEM) techniques. Our results show that the nanostructure of martian apatite is characterized by a domain structure at the 5–10 nm scale defined by undulous lattice fringes and slight differences in contrast, indicative of localized elastic strain within the lattices and misorientations in the crystal. The domain structure records a primary post-magmatic signature formed during initial subsolidus cooling (T &amp;lt;800 °C), in which halogens clustered by phase separation (exsolution), but overall preserved continuity in the crystalline structure. Northwest Africa 998 apatites, with average Cl/F ratios of 1.26 and 2.11, show higher undulosity of the lattice fringes and more differences in contrast than Nakhla apatites (average Cl/F = 4.23), suggesting that when Cl/F is close to 1, there is more strain in the structure. Vacancies likely played a key role stabilizing these ternary apatites that otherwise would be immiscible. Apatites in Nakhla show larger variations in halogen and rare-earth element (REE) contents within and between grains that are only a few micrometers apart, consistent with growth under disequilibrium conditions and crystallization in open systems. Nakhla apatite preserves chemical zonation, where F, REEs, Si, and Fe are higher in the core and Cl increases toward the outer layers of the crystal. There is no evidence of subsolidus ionic diffusion or post-magmatic fluid interactions that affected bulk apatite compositions in NWA 998 or Nakhla. The observed zonation is consistent with crystallization from a late-stage melt that became Cl-enriched, and assimilation of volatile-rich crustal sediments is the most plausible mechanism for the observed zonation. This work has broader implications for interpreting the chemistry of apatite in other planetary systems.

Lubrication mechanism of a strong tribofilm by imidazolium ionic liquid

Friction modifiers (FMs) are surface-active additives added to base fluids to reduce friction between rubbing surfaces. Their effectiveness depends on their interactions with rubbing surfaces and may be mitigated by the choice of the base fluid. In this work, the performance of an imidazolium ionic liquid (ImIL) additive in polyethylene-glycol (PEG) and 1,4-butanediol for lubricating steel/steel and diamond-like-carbon/diamond-like carbon (DLC—DLC) contacts were investigated. ImIL-containing PEG reduces friction more effectively in steel—steel than DLC—DLC contacts. In contrast, adding ImIL in 1,4-butanediol results in an increase in friction in steel—steel contacts. Results from the Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and focused ion beam-transmission electron microscopy (FIB-TEM) reveal that a surface film is formed on steel during rubbing in ImIL-containing PEG. This film consists of two layers. The top layer is composed of amorphous carbon and are easily removed during rubbing. The bottom layer, which contains iron oxide and nitride compound, adheres strongly on the steel surface. This film maintains its effectiveness in a steel—steel contact even after ImIL additives are depleted. Such film is not observed in 1,4-butanediol where the adsorption of ImIL is hindered, as suggested by the quartz crystal microbalance (QCM) measurements. No benefit is observed when the base fluid on its own is sufficiently lubricious, as in the case of DLC surfaces.This work provides fundamental insights on how compatibilities among base fluid, FM, and rubbing surface affect the performance of IL as surface active additives. It reveals the structure of an ionic liquid (IL) surface film, which is effective and durable. The knowledge is useful for guiding future IL additive development.

In Situ FIB-TEM-TOF-SIMS Combination Technique: Application in the Analysis of Ultra-Light and Trace Elements in Phyllosilicates

At present, a single technical method has difficulty in obtaining microscopic data of ultra-light elements, trace elements, and crystal structures in samples simultaneously. This work combined an in situ focused ion beam—transmission electron microscopy—time of flight secondary ion mass spectrometry (FTT) technique and analyzed the composition and crystal structure of four phyllosilicate samples. These materials were comprised of antigorite, clinochlore, and cookeite phases. An FIB sample preparation technique was found to provide a sample thickness suitable for TEM observations and a degree of surface roughness appropriate for TOF-SIMS analysis. In addition, the relative amounts and distributions of various elements could be obtained, as well as crystal structure data, such that the composition and crystal structure of each specimen were determined. The in situ FTT method demonstrated herein successfully combines the advantages of all three analytical techniques and offers unique advantages with regard to analyzing ultra-light and trace elements as well as the structural data of phyllosilicates.

Understanding the pitting mechanism of super ferritic stainless steel in bromide solutions: The role of Ti/Nb–Mo precipitates with a core–shell structure

The core–shell structure of Ti/Nb precipitates in UNS S44660 was revealed by focused ion beam–transmission electron microscopy (FIB–TEM). In the bromide solution, the Nb in the shell is preferentially and selectively eluted, leaving a micro-crevice. The combined effect of the strong anodic adsorption of Br− and the large strain field in the shell promotes the free dissolution of residual Mo. Micro-crevices surround the Ti-rich nucleus and expand into pits. Consequently, pitting preferentially initiates at the Ti/Nb precipitates, which was verified by scratching electrode tests and immersion tests in bromide solutions.

Polychromatic polarization: Boosting the capabilities of the good old petrographic microscope

Abstract Polychromatic polarizing microscopy (PPM) is a new optical technique that allows for the inspection of materials with low birefringence, which produces retardance between 1 nm and 300 nm. In this region, where minerals display interference colors in the near-black to gray scale and where observations by conventional microscopy are limited or hampered, PPM produces a full spectrum color palette in which the hue depends on orientation of the slow axis. We applied PPM to ordinary 30 µm rock thin sections, with particular interest in the subtle birefringence of garnet due both to non-isotropic growth or to strain induced by external stresses or inclusions. The PPM produces striking, colorful images that highlight various types of microstructures that are virtually undetectable by conventional polarizing microscopy. PPM opens new avenues for microstructural analysis of geological materials. The direct detection and imaging of microstructures will provide a fast, non-destructive, and inexpensive alternative (or complement) to time-consuming and more costly scanning electron microscope–based analyses such as electron backscatter diffraction. This powerful imaging method provides a quick and better texturally constrained basis for locating targets for cutting-edge applications such as focused ion beam-transmission electron microscopy or atom probe tomography.

Tailoring polyimide composites with low friction and wear at high temperatures

AbstractIn this article, thermosetting polyimide (TPI) composites based on two ideal ingredients (graphite/graphene‐like carbon nitride, g‐C3N4) were designed with different fibers and their tribological performance was comprehensively investigated at different high temperatures. It was found that the synergistic effect between solid lubricants graphite blended with g‐C3N4 and reinforced fibers on friction and wear performance. Extremely lower friction and wear behavior of TPI composite is attained with aramid pulps (APs) at high temperatures. More importantly, an obvious transition of wear rate and friction took place with aramid pulps under 200°C. When the cross‐sections of the transfer films were analyzed using focused ion beam transmission electron microscopy (FIB‐TEM) and X‐ray photoelectron spectroscopy (XPS), it was found that graphite and g‐C3N4 combined with APs led to simultaneous improvement in load‐carrying capability of TPI matrix and durability of tribofilms subjected to complex physical and chemical reaction. Our work discloses a route for developing the TPI composite exposed to high temperatures with extremely lower friction and wear rate.

Surface restructuring of hematite photoanodes through ultrathin NiFeOx Catalyst: Amplified charge collection for solar water splitting and pollutant degradation

In this study, problems associated with hematite-based photoanodes are strategically solved using a ternary NiFeOx (NFO) top-layer for the first time, which is deposited using an atomic layer deposition (ALD) technique. Prior to the photoanode development, the ALD growth optimization of NiFeOx is carried out by the super-cycle combination approach and confirmed through structural analysis and high-resolution focused-ion beam transmission electron microscopy imaging. An ultrathin layer of NiFeOx (3 nm) with 25 at.% of Ni over hematite photoanodes (Sn-Fe2O3/NFO25) exhibits the highest photocurrent density at 1.23 VRHE. The roles of the surface states of hematite are elucidated through electrochemical and compositional investigations. The NiFeOx nanolayer effectively annihilates the surface states on the hematite nanorod, subsequently unraveling the inherent photovoltage. The new charge transport path is observed via interfacial analysis, where the valance band maximum VBM shuttles holes to the electrolyte at an accelerated rate. The synergistic effect of the passivation layer significantly enhances the rate of charge separation, which is also observed in photoelectrocatalytic degradation of tetracycline hydrochloride with Sn-Fe2O3/NFO25, compared with the pristine Sn-Fe2O3 photoanodes. The work puts forward a new strategy by incorporating ternary ALD systems to develop photoanodes that are effective in both water splitting and wastewater treatment technologies.

Evaluation of Anticorrosion Properties of Epoxy-Silane Hybrid Nanocomposite Coating on AA6082 Aluminum Alloy

The protection properties of (3-aminopropyl)trimethoxysilane (APTMS) incorporated epoxy coating on aluminum alloy were studied by electrochemical techniques such as electrochemical impedance spectroscopy (EIS) and scanning electrochemical microscopy (SECM) analysis in seawater. The epoxy-APTMS coated Al alloy displayed higher charge transfer resistance (Rct) as well as film resistance (Rf) at 1 day immersion. However, both Rct anf Rf values decreased slowly compared to pure epoxy coated alloy which showed significant decrease in Rct and Rf values with increase in immersion time in chloride media. The released Al3+ ions were detected using SECM by applying the tip potential of –0.85 V. It was evident from the SECM measurement that the dissolution of Al3+ ions was impeded at the scratch of epoxy-APTMS coated Al alloy due to the presence of electron donating amino group in APTMS which inhibited Al alloy degradation. The enrichment of Mg, Mn, Si and Al at the scratch of epoxy-APTMS coated Al alloy was confirmed by Field emission-scanning electron microscopy/energy dispersive X-Ray spectroscopy (FE-SEM/EDX) analysis. Focused ion beam-transmission electron microscopy (FIB-TEM) analysis proved the presence of thin films of nano level oxide layers containing Mg, Mn, Si and Al in the coatings, which decreased the corrosion rate of Al alloy. The enhanced adherence of epoxy-APTMS coating to Al alloy was due to the strong chemical bonding between epoxy-APTMS and Al alloy. Therefore, the pronounced protection performance against corrosion and good adhesion strength was due to the incorporation of APTMS with epoxy coatings.

Tribological performance and lubrication mechanism of new gemini quaternary phosphonium ionic liquid lubricants

This paper presents the synthesis and characterization of two types of halogen-free ionic liquids (ILs) that incorporate long-chain phosphate, diisooctyl phosphate (EDHPA), and dibutyl phosphate (DBHPA) as the anions, and the gemini quaternary phosphonium as the cation. Their tribological properties are subjected to evaluation by utilizing these ILs as neat lubricants for a friction pair, constituting of a steel disc and a steel ball, for two conditions, i.e., at room temperature (RT) and high temperature of 100 °C (HT). These as-prepared ILs are found to exhibit phenomenal traits such as high thermal stability and non-corrosive properties, along with being able to impart enhanced anti-wear (AW) and friction reduction (FR) performance to the friction pair in contrast to the commercially available lubricants, i.e., synthetic poly-α-olefin (PAO 10) and traditional IL 1-butyl-3-methylimidazolium hexafluorophosphate (L-P104). Various investigations are performed employing scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), and focused ion beam-transmission electron microscopy (FIB-TEM) analyses of the worn surface of the steel discs. These results yield the postulation that a chemical reaction, i.e., tribochemical reaction, is triggered during the relative motion of the two interacting surfaces. This reaction induces a protective phosphorous-containing boundary film on the surface of the worn steel, thereby evading any direct contact between the rubbing steel-steel interfaces.

Electrochemical, mechanical and adhesive properties of surface modified NiO-epoxy nanocomposite coatings on mild steel

The effect of surface modification of NiO (nickel oxide) nanoparticle by (3-Mercaptopropyl) triethoxysilane (MPTES) in the epoxy-NiO nanocomposite coatings on mild steel was analyzed by electrochemical impedance spectroscopy (EIS) and scanning electrochemical microscopy (SECM) techniques in seawater. MPTES was treated with the nanoparticle for the proper dispersion and chemical interaction of nanoparticle with the epoxy resin. The introduction of NiO nanoparticle in the epoxy coating enhances the charge transfer resistance (Rct) as well as the film resistance (Rf). The observation of iron dissolution and oxygen consumption was carried out using an appropriate potential at the SECM tip in the NiO modified nanocomposite coated steel. The pure epoxy and epoxy-NiO nanocomposite coated samples were used to study the mechanical, adhesion, and anticorrosion properties. The analysis by field emission-scanning electron microscopy/energy dispersive X-ray analysis (FE-SEM/EDX) displayed the enriched Ni was detected in the nanocomposite coating of steel. The presence of the nano level corrosion product containing Ni was confirmed by focused ion beam-transmission electron microscopy (FIB-TEM) analysis. The high corrosion protection properties of epoxy nanocomposite coatings were due to the formation of complex nanoscale layer and chemical interactions of epoxy resin with surface modified nanoparticle in nanocomposites.

DNA Origami for Silicon Patterning.

Desoxyribonucleic acid (DNA) origami architectures are a promising tool for ultimate lithography because of their ability to generate nanostructures with a minimum feature size down to 2 nm. In this paper, we developed a method for silicon (Si) nanopatterning to face up current limitations for high-resolution patterning with standard microelectronic processes. For the first time, a 2 nm-thick 2D DNA origami mask, with specific design composed of three different square holes (with a size of 10 and 20 nm), is used for positive pattern transfer into a Si substrate using a 15 nm-thick silicon dioxide (SiO2) layer as an intermediate hard mask. First, the origami mask is transferred onto the SiO2 underlayer, by an HF vapor-etching process. Then, the Si underlayer is etched using an HBr/O2 plasma. Each hole is transferred in the SiO2 layer and the 20 nm-sized holes are transferred into the final stack (Si). The resulting patterns exhibited a lateral resolution in the range of 20 nm and a depth of 40 nm. Patterns are fully characterized by atomic force microscopy, scanning electron microscopy, focused ion beam-transmission electron microscopy, and ellipsometry measurements.

Stability of Proton-Conducting Solid Oxide Electrolyzers for Hydrogen Production and Energy Storage

Proton-conducting solid oxide electrolyzers (H-SOEs) provide promising opportunity to produce pure and dry hydrogen in steam electrolysis at relatively low operating temperatures (550-700˚C) utilizing electricity and heat generated from renewable energy sources. Compared to traditional high temperature (750-1000˚C) oxygen-conducting solid oxide electrolyzers (O-SOEs), lower operating temperature of H-SOE offers ease of thermal management, active stack and BOP materials cost reduction and reduction in chromium evaporation from metallic components. Like O-SOEs, preserving the long-term stability of H-SOEs is one of the technical challenges for large-scale hydrogen production. In this technical contribution, results of experimental evaluation of H-SOEs under real-world operating conditions are presented. As fabricated and posttest cells have been characterized using operando electrochemical impedance spectroscopy, X-ray diffraction, focused ion beam-transmission electron microscopy and other bulk and surface characterization techniques to examine bulk, surface and interface stability of electrochemically active components. Phase and morphological changes, compositional uniformity and interfacial reaction products formation have been examined. Electrolyte/electrode materials stability, cell and gas seal fabrication processes, and gaseous impurities affecting long-term electrochemical performance will be discussed. H-SOE electrochemical performance model based on cell materials and operating conditions has been proposed and validated based on single cell testing data.

The formation of ZnO structures using thermal oxidation: How a previous chemical etching favors either needle-like or cross-linked structures

Thermal oxidation of Zn polycrystalline elemental foils –previously etched at different chemical conditions– was used to study the formation of ZnO structures. Two distinct etching solutions were used: 0.5 M HNO3 and 11 M HNO3. Based on field emission scanning electron microscopy results, by modifying the etching conditions, the ZnO structures were different regarding morphology: needle-like ZnO microstructure arrays were formed when Zn foil was chemically etched using the 0.5 M HNO3 solution, whilst a cross-linked morphology was obtained when the etching solution changed to 11 M HNO3 concentration. However, the elemental mapping showed identical chemical composition of both kinds of ZnO microstructures. The focused ion beam-transmission electron microscopy specimens revealed the occurrence of ZnO nanostructures, in both kinds of as-oxidized samples, obtained after 2 h of thermal oxidation at 400 °C. Finally, both needle- and cross-linked microstructures were evaluated in terms of their optical properties. According to the experimental findings, it was found that these structures can be applied in optoelectronic devices working around the green range of the visible electromagnetic spectrum, exhibiting the cross-linked sample the highest radiation intensity.

On the biogenicity of Fe-oxyhydroxide filaments in silicified low-temperature hydrothermal deposits: Implications for the identification of Fe-oxidizing bacteria in the rock record.

Microaerophilic Fe(II)-oxidizing bacteria produce biomineralized twisted and branched stalks, which are promising biosignatures of microbial Fe oxidation in ancient jaspers and iron formations. Extracellular Fe stalks retain their morphological characteristics under experimentally elevated temperatures, but the extent to which natural post-depositional processes affect fossil integrity remains to be resolved. We examined siliceous Fe deposits from laminated mounds and chimney structures from an extinct part of the Jan Mayen Vent Fields on the Arctic Mid-Ocean Ridge. Our aims were to determine how early seafloor diagenesis affects morphological and chemical signatures of Fe-oxyhydroxide biomineralization and how extracellular stalks differ from abiogenic features. Optical and scanning electron microscopy in combination with focused ion beam-transmission electron microscopy (FIB-TEM) was used to study the filamentous textures and cross sections of individual stalks. Our results revealed directional, dendritic, and radial arrangements of biogenic twisted stalks and randomly organized networks of hollow tubes. Stalks were encrusted by concentric Fe-oxyhydroxide laminae and silica casings. Element maps produced by energy dispersive X-ray spectroscopy (EDS) in TEM showed variations in the content of Si, P, and S within filaments, demonstrating that successive hydrothermal fluid pulses mediate early diagenetic alteration and modify the chemical composition and surface features of stalks through Fe-oxyhydroxide mineralization. The carbon content of the stalks was generally indistinguishable from background levels, suggesting that organic compounds were either scarce initially or lost due to percolating hydrothermal fluids. Dendrites and thicker abiotic filaments from a nearby chimney were composed of nanometer-sized microcrystalline iron particles and silica and showed Fe growth bands indicative of inorganic precipitation. Our study suggests that the identification of fossil stalks and sheaths of Fe-oxidizing bacteria in hydrothermal paleoenvironments may not rely on the detection of organic carbon and demonstrates that abiogenic filaments differ from stalks and sheaths of Fe-oxidizing bacteria with respect to width distribution, ultrastructure, and textural context.

Effect of engine oil additives reduction on the tribofilm structure of a cylinder liner model surface

PurposeThe purpose of this paper is to provide a general picture for describing the formed tribofilm, including chemical and physical aspects in the micro-scale and the nano-scale. In a previous study, the durability of zinc dialkyl dithiophosphate (ZDDP) tribofilms on cylinder liner samples has been investigated in a tribometer model system by using fresh and aged fully formulated oils and replacing them with PAO8 without additives. Analyses of the derived tribofilms by means of X-ray photoelectron spectroscopy and scanning electron microscopy could give some hints about the underlying mechanisms of the tribofilm build-up and wear performance, but a final model has not been achieved.Design/methodology/approachThus, characterisation of these tribofilms by means of focused ion beam-transmission electron microscopy (FIB-TEM) and energy dispersive X-ray spectroscopy is presented and a concluding model of the underlying mechanisms of tribofilm build-up is discussed in this paper.FindingsFor tribotests running first with fresh fully formulated engine oil, a rather homogeneous ZDDP-like tribofilm is found underneath a carbon rich tribofilm after changing to non-additivated PAO8. However, when the tests run first with aged fully formulated engine oil, no ZDDP-like tribofilm has been found after changing to non-additivated PAO8, but a wear protective carbon rich tribofilm.Originality/valueThe obtained results provide insights into the structure and durability of tribofilms. Carbon-based tribofilms are built up on the basis of non-additivated PAO8 because of the previously present ZDDP tribofilms, which suggests an alternative way to reducing the consumption of antiwear additives.

EFFECT OF ALLOYING ELEMENTS ON CORROSION POTENTIAL AND CORROSION PROPAGATION PROCESS OF MULTILAYER ALUMINUM-BRAZED SHEET

The cross-sectional depth microstructure profiles for a multilayer AA4045/AA3003*/AA4045 brazed sheet were observed and determined by focused ion beam-transmission electron microscopy (FIB-TEM) and energy dispersive spectrometer (EDS). The corrosion propagation of the multilayer brazed sheet in the sea water acidified accelerated test (SWAAT) was investigated by electrochemical impedance spectroscopy (EIS). The measured corrosion potentials of different layers of the multilayer aluminum sheet have been carried out according to ASTM G69-97 standard test method. To reveal the effect of the alloying elements on corrosion behavior, the theoretical corrosion potential of the band of dense precipitates (BDP) zone and core materials was also calculated according to the theoretical corrosion potential model. The electrochemical results showed that there were potential differences between the precipitates free zone (PFZ) and BDP zone as well as BDP zone and the core materials. The EIS test and equivalent circuits (EC) suggested that the capacitive time constant at low frequencies correspond to the corrosion of the BDP zone in the form of exfoliation corrosion. The corrosion propagation process could be identified into four stages: the dissolution of the eutectic [Formula: see text]-Al in the re-solidified cladding in the form of pitting corrosion; the corrosion of the primary [Formula: see text]-Al grain boundaries in the form of inter-granular corrosion (IGC); the corrosion of the BDP zone in the form of exfoliation corrosion; and the corrosion of the core material in the form of IGC.

Understanding the electrochemical behavior of bulk-synthesized MgZn2 intermetallic compound in aqueous NaCl solutions as a function of pH

The electrochemical behavior of a bulk-synthesized MgZn2 intermetallic compound in aerated 0.1 M NaCl solutions has been studied as a function of pH and applied potential using polarization techniques, electrochemical impedance spectroscopy (EIS), X-ray photoelectron spectroscopy (XPS), and focused ion beam-transmission electron microscopy (FIB-TEM). The anodic activity of MgZn2 is seen to decrease with an increase in pH value. Polarization tests reveal two limiting current densities in pH 4 solution at relatively high and low potentials. At pH 12, passivity is observed with a lower limiting current density compared to those observed at pH 4. The corrosion film formed after potentiostatic polarization in the pH 4 solution is composed of a bilayer at a less negative potential and a single layer at a more negative potential. In the case of pH 12 solution, a protective compact bilayer film is formed irrespective of the potential within the passive zone. Overall, the corrosion mechanism of MgZn2 is by early dissolution of Mg leading to a Zn-enriched surface whose subsequent dissolution depends on the value of the applied potential.