Subsequent Scanning Electron Microscopy Research Articles

Effect of relative humidity on corrosion of Q235 carbon steel under thin electrolyte layer in simulated marine atmosphere

PurposeThe purpose of this paper is to obtain the environmental factor, which has the greatest effect on the corrosion rate of Q235 carbon steel under thin electrolyte layer, and to analyze the effect of this factor on the corrosion morphology, corrosion products and polarization process of Q235 carbon steel.Design/methodology/approachAn electrochemical device, which can be used under thin electrolyte layer is designed to measure the corrosion current in different environments. Response surface methodology (RSM) is introduced to analyze the effect of environmental factors on corrosion rate. Scanning electron microscope (SEM) and X-ray diffraction (XRD) technique are used to analyze the results. The Tafel slopes of anode and cathode in different humidity and solution are calculated by least square method.FindingsThe three environmental factors are ranked according to importance, namely, humidity, temperature and chloride ion deposition rate. In a high humidity environment, the relative content of α-FeOOH in the corrosion product is high and the relative content of β-FeOOH is low. The higher the humidity, the lower the degree of anodic blockage, whereas the degree of cathodic blockage is independent of humidity. The above experiments confirm the effectiveness and efficiency of the device, indicating it can be used for the screening of corrosive environmental factors.Originality/valueIn this paper, an electrochemical device under thin film is designed, which can simulate atmospheric corrosion well. Subsequent SEM and XRD confirmed the reliability of the data measured by this device. The introduction of a scientific RSM can overcome the limitations of orthogonal experiments and more specifically and intuitively analyze the effects of environmental factors on corrosion rates.

Insight into the microphysics of antigorite deformation from spherical nanoindentation.

The mechanical behaviour of antigorite strongly influences the strength and deformation of the subduction interface. Although there is microstructural evidence elucidating the nature of brittle deformation at low pressures, there is often conflicting evidence regarding the potential for plastic deformation in the ductile regime at higher pressures. Here, we present a series of spherical nanoindentation experiments on aggregates of natural antigorite. These experiments effectively investigate the single-crystal mechanical behaviour because the volume of deformed material is significantly smaller than the grain size. Individual indents reveal elastic loading followed by yield and strain hardening. The magnitude of the yield stress is a function of crystal orientation, with lower values associated with indents parallel to the basal plane. Unloading paths reveal more strain recovery than expected for purely elastic unloading. The magnitude of inelastic strain recovery is highest for indents parallel to the basal plane. We also imposed indents with cyclical loading paths, and observed strain energy dissipation during unloading-loading cycles conducted up to a fixed maximum indentation load and depth. The magnitude of this dissipated strain energy was highest for indents parallel to the basal plane. Subsequent scanning electron microscopy revealed surface impressions accommodated by shear cracks and a general lack of dislocation-induced lattice misorientation. Based on these observations, we suggest that antigorite deformation at high pressures is dominated by sliding on shear cracks. We develop a microphysical model that is able to quantitatively explain Young's modulus and dissipated strain energy data during cyclic loading experiments, based on either frictional or cohesive sliding of an array of cracks contained in the basal plane. This article is part of a discussion meeting issue 'Serpentinite in the earth system'.

Synthesis and application of a polymeric intumescent flame retardant for cotton fabric

A novel polymeric intumescent flame retardant containing phosphorus, nitrogen and sulphur (poly(ditrimethylolphosphono thiourea (PDTPT)) was synthesized, and its chemical structure was characterized by Fourier-transform infrared spectroscopy, $$^{{1}}$$ H and $$^{{31}}$$ P nuclear magnetic resonance spectroscopy and elemental analysis. The molecular weight and thermal properties of PDTPT were measured by using gel permeation chromatography and thermogravimetric analysis. PDTPT exhibited good thermal stability, char formation and swelling performance. The initial thermal decomposition temperature and quality residual rate at 600°C of PDTPT were 282°C and 48.8%, respectively. When the mass fraction of PDTPT was 25 wt%, the limiting oxygen index-value of the cotton fabric/PDTPT composite was 27, an increase from 18 for the pure cotton fabric. Subsequent thermal analysis and scanning electron microscopy showed that PDTPT addition reduced the initial degradation temperature and the weight loss rate of the cotton fabric by forming a thick and tight carbon layer on its surface.

Indirect morphological analysis of particles in polymer particle composites via non-destructive permittivity measurements

Polymers with special properties (e.g. electrical, optical or mechanical) are often obtained via the addition of fillers. The composites' final properties rely on the preservation of these fillers during blending, which is, in particular, challenging for high aspect ratio particles, like shear-sensitive flaky particles (ssFP). Thus, in cases of ssFP off- or in-line monitoring is indicated. This study addresses the lack of suitable non-destructive monitoring methods appropriate for ssFP possessing a thickness below 1μm and an area equivalent diameter of several 10μm. An elegant method was developed to validate the integrity of ssFP within composites, which is based on the measurement of the composites' permittivity and applying precise micro-structure property correlations to indirectly determine the fillers' morphological features. The main hypothesis tested was that a reduction of the particles aspect ratio by a factor of larger than 5 can be detected by the measurement of the composites' permittivity. In this study, polyethylene or epoxy resin were blended with the mica-based ssFP Iriodin 153 which features a mean area equivalent diameter of 42μm and an average thickness of about 1μm. The micro-structure property correlation presented by G. Ondracek [Z. f. Werkstofftechnik, 8:280-287, 1977] provided the necessary theoretical backbone to indirectly infer geometrical changes to the ssFP from permittivity measurements of the composite. An excellent match was obtained between the indirectly (permittivity measurements) and the directly (ashing of matrix and subsequent scanning electron microscopy) determined particles' aspect ratios which related directly to the particles' area equivalent diameter because the thickness of the particles was almost constant. This preliminary study established the presented technique as a promising non-destructive test method to monitor the integrity of ssFPs embedded in polymers. In principle this technique is adaptable for in-line process monitoring.

Plasmon-directed polymerization: Regulating polymer growth with light

Plasmon-induced polymerization can facilitate the site-selectivity and orientation of polymer growth, which enriches the toolbox of polymerization and nanofabrication. Here, we demonstrate plasmon-induced polymerization, accomplished by low-power laser excitation of gold nanoparticles (NPs). We selectively control the growth of polymers around single plasmonic NPs while monitoring the polymerization using dark field spectroscopy and subsequent scanning electron microscopy. This plasmon-induced polymerization, generated by hot electron initiation, not only precisely controls the thickness and composition of the polymer coatings but also regulates the location and orientation of the growth, which are strongly influenced by the laser polarization and near-field distribution around the plasmonic NPs. A saturation increase in the polymer thickness provides a strong support for our mechanism. This facile approach of nanoscale polymerization directed by light not only provides new opportunities in nanosynthesis and nanofabrication for functional devices, but also opens many routes for polymer physics and chemistry at the nanoscale level.

On anisotropy, strain rate and size effects in vat photopolymerization based specimens

The influence of build orientation, layer thickness, strain rate and size effect on the Young’s modulus, ultimate tensile strength and fracture strains in vat photopolymerization based additively manufactured specimens is investigated. Mechanical testing and subsequent scanning electron microscopy tests on additively manufactured specimens are conducted. Anisotropy in mechanical behavior is only observed in specimens fabricated in different planes. An increase in layer thickness and decrease in strain rate resulted in lower strength, stiffness and higher fracture strains. No significant size effect on strength and failure strains is observed. Cure kinetics is found to have significant influence on mechanical properties of additively manufactured specimens.

Isolation of Exosome-Like Nanoparticles and Analysis of MicroRNAs Derived from Coconut Water Based on Small RNA High-Throughput Sequencing.

In this study, the presence of microRNAs in coconut water was identified by real-time polymerase chain reaction (PCR) based on the results of high-throughput small RNA sequencing. In addition, the differences in microRNA content between immature and mature coconut water were compared. A total of 47 known microRNAs belonging to 25 families and 14 new microRNAs were identified in coconut endosperm. Through analysis using a target gene prediction software, potential microRNA target genes were identified in the human genome. Real-time PCR showed that the level of most microRNAs was higher in mature coconut water than in immature coconut water. Then, exosome-like nanoparticles were isolated from coconut water. After ultracentrifugation, some particle structures were seen in coconut water samples using 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate fluorescence staining. Subsequent scanning electron microscopy observation and dynamic light scattering analysis also revealed some exosome-like nanoparticles in coconut water, and the mean diameters of the particles detected by the two methods were 13.16 and 59.72 nm, respectively. In conclusion, there are extracellular microRNAs in coconut water, and their levels are higher in mature coconut water than in immature coconut water. Some exosome-like nanoparticles were isolated from coconut water, and the diameter of these particles was smaller than that of animal-derived exosomes.

Scale effect in mechanical characterization of WC-Co composites

The study of mechanical response of materials at small length scales has gained importance due to the recent advances in micro- and nano-fabrication as well as testing systems. However, most of the reported work has been dedicated to investigate single-crystals or boundary-containing metallic systems, while much less attention has been paid to composite materials, and in particular those combining soft and hard phases. In this work, a systematic procedure is followed for machining micropillars of diameters ranging from 1 to 4μm in a WC-Co composite with a WC mean grain size around 1μm, by means of focused ion beam milling. In-situ uniaxial compression of the micropillars and subsequent field emission scanning electron microscopy inspection were conducted. Clear size effects are evidenced. Smaller test specimens (probe size approaching the mean WC size) exhibit deformation/failure mechanisms observed for WC crystals; while for bigger sample sizes, the mechanical response involves several mechanisms directly linked with the microstructural characteristics of the bulk-like cemented carbide material. On the other hand, independent of micropillar size, carbide-carbide or carbide-binder interfaces are found to be preferential sites for nucleation of critical damage events.

Preparation of High-Quality Load-Preserved Fabric Clay Samples for Microstructural Characterizations: A Pragmatic Guide Featuring a 3-D–Printed Oedometer

Abstract High-quality samples are always critical in the meaningful microstructural characterizations of clay. A practical guide, together with a real sample tested as an example, is therefore proposed in this study, aiming to prepare high-quality load-preserved fabric clay samples subjected to 1-D consolidation for the pore size and fabric characterizations. In this guide, several issues often encountered in sample preparations that may induce measurement bias are tackled with feasible solutions proposed. A tailor-made oedometer is also invented and produced using a 3-D printing technique to achieve the goal. First, a homogenous and uniform kaolinite sample is prepared from a slurry state and then positioned in the 3-D–printed oedometer for 1-D consolidation tests. Then, together with the desired load, the whole 3-D–printed oedometer containing the consolidated kaolinite sample is submerged into liquid nitrogen to rapid freeze the sample to preserve the fabric associations not affected by the unloading effects. Afterward, to use the same sample for different tests to facilitate comparisons, the sample is cut in half while frozen. On one hand, this creates an observation plane along the center of the sample with the morphological information preserved for the subsequent scanning electron microscopy (SEM) analyses. On the other hand, each half of the sample individually undergoes the mercury intrusion porosimetry (MIP) and nitrogen adsorption (NA) analyses to obtain complementary information on the pore-size distribution. The samples must be dewatered by freeze drying before conducting these tests. During the freeze-drying process, the cut sample is protected by a 3-D–printed container, which has a reference mark to indicate the sample orientation. In each of the SEM images taken, the associated position and orientation are controlled, and the number of the images taken for analyses is maximized to enhance the statistical representation of the analyzed results.

In-plane and through-plane non-uniform carbon corrosion of polymer electrolyte fuel cell cathode catalyst layer during extended potential cycles

The impact of electrochemical carbon corrosion via potential cycling durability tests mimicking start-stop operation events on the microstructure of the cathode catalyst layer in polymer electrolyte fuel cells (PEFCs) is investigated using focused ion beam (FIB) fabrication without/with the pore-filling technique and subsequent scanning electron microscope (SEM) observations. FIB/SEM investigations without pore-filling reveals that the durability test induces non-uniform cathode shrinking across the in-plane direction; the thickness of the catalyst layer decreases more under the gas flow channel compared to the area under the rim of the flow field. Furthermore, FIB/SEM investigations with the pore-filling technique reveal that the durability test also induces non-uniform cathode shrinking in the through-plane direction; the pores in the area close to the membrane are more shrunken compared with those close to the microporous layer. In particular, a thin area (1–1.5 μm) close to the membrane is found to be severely damaged; it includes closed pores that hinder mass transport through the catalyst layer. It is suggested that uneven carbon corrosion and catalyst layer compaction are responsible for the performance loss during potential cycling operation of PEFCs.

Fabrication and structural properties of AlN submicron periodic lateral polar structures and waveguides for UV-C applications

Periodically poled AlN thin films with submicron domain widths were fabricated for nonlinear applications in the UV-VIS region. A procedure utilizing metalorganic chemical vapor deposition growth of AlN in combination with laser interference lithography was developed for making a nanoscale lateral polarity structure (LPS) with domain size down to 600 nm. The Al-polar and N-polar domains were identified by wet etching the periodic LPS in a potassium hydroxide solution and subsequent scanning electron microscopy (SEM) characterization. Fully coalesced and well-defined vertical interfaces between the adjacent domains were established by cross-sectional SEM. AlN LPSs were mechanically polished and surface roughness with a root mean square value of ∼10 nm over a 90 μm × 90 μm area was achieved. 3.8 μm wide and 650 nm thick AlN LPS waveguides were fabricated. The achieved domain sizes, surface roughness, and waveguides are suitable for second harmonic generation in the UVC spectrum.

Qualifying Electrically Conductive Cold Embedding-Media for Scanning Electron Microscopy

The choice of embedding-media for metallographic specimen preparation, where subsequent scanning electron microscopy will be performed, is highly important since the quality of the analytical results in the specimen’s near-surface region is limited by the properties of the embedding-material. Due to their high electrical conductivity and only slight tendency to form gaps between near the sample surface, warm curing embedding-media are usually best suited. Hot embedding-presses use relatively high pressures at elevated temperatures that can be detrimental for sensitive materials or coatings. Cold embedding with conventional embedding-media, which does not require high pressure mounting, requires compromising for a material with a lower electric conductivity, a higher amount of pores in the material, and inferior interfacial connectivity to the specimen. For this reason, the development of alternative electrically conductive and cold hardening embedding-media is of great interest for metallographic sample preparation of electron microscopy specimens. In the present study, various embedding-media were evaluated with respect to their suitability for scanning electron microscopy and a novel conductive mounting compound has been identified and qualified.

Scanning Electron Microscopy Observation of Interface Between Single Neurons and Conductive Surfaces.

Interfaces between single neurons and conductive substrates were investigated using focused ion beam (FIB) milling and subsequent scanning electron microscopy (SEM) observation. The interfaces play an important role in controlling neuronal growth when we fabricate neuron-nanostructure integrated devices. Cross sectional images of cultivated neurons obtained with an FIB/SEM dual system show the clear affinity of the neurons for the substrates. Very few neurons attached themselves to indium tin oxide (ITO) and this repulsion yielded a wide interspace at the neuron-ITO interface. A neuron-gold interface exhibited partial adhesion. On the other hand, a neuron-titanium interface showed good adhesion and small interspaces were observed. These results are consistent with an assessment made using fluorescence microscopy. We expect the much higher spatial resolution of SEM images to provide us with more detailed information. Our study shows that the interface between a single neuron and a substrate offers useful information as regards improving surface properties and establishing neuron-nanostructure integrated devices.

Experimental explanation of the formation mechanism of surface mound-structures by femtosecond laser on polycrystalline Ni60Nb40.

Femtosecond laser surface processing (FLSP) is an emerging technique for creating functionalized surfaces with specialized properties, such as broadband optical absorption or superhydrophobicity/superhydrophilicity. It has been demonstrated in the past that FLSP can be used to form two distinct classes of mound-like, self-organized micro/nanostructures on the surfaces of various metals. Here, the formation mechanisms of below surface growth (BSG) and above surface growth (ASG) mounds on polycrystalline Ni60Nb40 are studied. Cross-sectional imaging of these mounds by focused ion beam milling and subsequent scanning electron microscopy revealed evidence of the unique formation processes for each class of microstructure. BSG-mound formation during FLSP did not alter the microstructure of the base material, indicating preferential valley ablation as the primary formation mechanism. For ASG-mounds, the microstructure at the peaks of the mounds was clearly different from the base material. Transmission electron microscopy revealed that hydrodynamic melting of the surface occurred during FLSP under ASG-mound forming conditions. Thus, there is a clear difference in the formation mechanisms of ASG- and BSG-mounds during FLSP.

Far-field optical nanothermometry using individual sub-50 nm upconverting nanoparticles

We demonstrate far-field optical thermometry using individual NaYF4 nanoparticles doped with 2% Er(3+) and 20% Yb(3+). Isolated 20 × 20 × 40 nm(3) particles were identified using only far-field optical imaging, confirmed by subsequent scanning electron microscopy. The luminescence thermometry response for five such single particles was characterized for temperatures from 300 K to 400 K. A standard Arrhenius model widely used for larger particles can still be accurately applied to these sub-50 nm particles, with good particle-to-particle uniformity (response coefficients exhibited standard deviations below 5%). With its spatial resolution on the order of 50 nm when imaging a single particle, far below the diffraction limit, this technique has potential applications for both fundamental thermal measurements and nanoscale metrology in industrial applications.

Application of full-surface view in situ thermography measurements during ultrasonic fatigue of cast steel G42CrMo4

In the present investigation a full-surface view in situ thermography method is adapted to an ultrasonic fatigue testing system. Full-surface view in situ thermography measurements were successfully performed in the high cycle fatigue and in the very high cycle fatigue regime on cast steel G42CrMo4in the quenched and tempered state. The method enables the monitoring of the entire cylindrical specimen circumference during fatigue testing by infrared temperature field measurements with one thermocamera and two mirrors. Moreover, by correlating fractography and thermography the precise determination of the location of the crack initiation site and the time of final crack growth is possible. The technique is applied to study crack initiation at non-metallic inclusions in the investigated cast steel specimens. Moreover, the effect of a novel carbon-bonded metal melt filter coated with a functionalized spinel (MgAl2O4) coating is evaluated by ultrasonic fatigue testing in combination with the full-surface view in situ thermography technique and subsequent scanning electron microscopy.

Photoemission electron microscopy of localized surface plasmons in silver nanostructures at telecommunication wavelengths

We image the field enhancement at Ag nanostructures using femtosecond laser pulses with a center wavelength of 1.55 μm. Imaging is based on non-linear photoemission observed in a photoemission electron microscope (PEEM). The images are directly compared to ultra violet PEEM and scanning electron microscopy (SEM) imaging of the same structures. Further, we have carried out atomic scale scanning tunneling microscopy on the same type of Ag nanostructures and on the Au substrate. Measuring the photoelectron spectrum from individual Ag particles shows a larger contribution from higher order photoemission processes above the work function threshold than would be predicted by a fully perturbative model, consistent with recent results using shorter wavelengths. Investigating a wide selection of both Ag nanoparticles and nanowires, field enhancement is observed from 30% of the Ag nanoparticles and from none of the nanowires. No laser-induced damage is observed of the nanostructures neither during the PEEM experiments nor in subsequent SEM analysis. By direct comparison of SEM and PEEM images of the same nanostructures, we can conclude that the field enhancement is independent of the average nanostructure size and shape. Instead, we propose that the variations in observed field enhancement could originate from the wedge interface between the substrate and particles electrically connected to the substrate.

Synthesis and characterization of copper-infiltrated carbonized wood monoliths for supercapacitor electrodes

Copper nanoparticle-loaded carbonized wood electrodes were synthesized and characterized for the use as supercapacitor electrodes. The electrodes were fabricated by soaking beech wood samples in Cu(NO3)2 solution followed by carbonization at 800°C under a N2 atmosphere. The copper nanoparticle content in the electrodes was controlled by varying the concentration of the Cu(NO3)2 solution from 0.5 to 2M. Subsequent X-ray diffraction and scanning electron microscopy measurements confirm that cubic copper was formed and the copper nanoparticles were anchored uniformly both on the surface as well as deep within the pores of the wood electrode. Cyclic voltammetry measurements showed that all of the electrodes had a typical pseudo-capacitive behavior, as indicated by the presence of redox reaction peaks. Charge–discharge testing also confirmed the pseudo-capacitive nature of the electrodes. The reversible oxidation of Cu into Cu2O and CuO was verified by performing X-ray photoelectron spectroscopy at different stages of the charge–discharge cycle. The Cu-loaded wood electrodes exhibited excellent cyclability and retaining 95% of their specific capacitance even after 2000 cycles. A maximum specific capacitance of 888F/g was observed while discharging the 7wt% Cu electrode at 200mA/g in a 2M KOH electrolyte solution. These results demonstrated the potential of the copper nanoparticle-loaded wood electrodes as cheap and high performance supercapacitor electrodes.

Polyethylene/paraffin binary composites for phase change material energy storage in building: A morphology, thermal properties, and paraffin leakage study

Phase change materials (PCMs) are able to melt and solidify at a certain temperature with a high heat of fusion. These promising functional materials for acting as energy as latent heat storage units have one major problem, leakage of the PCMs when molten. Polymer/phase change material (PCM) blends were investigated as a possible solution of PCM leakage. In this research, paraffin was used as the PCM and three types polyethylene (PE) were used as the structural matrix. To investigate the morphology of PE/ paraffin blends and evaluate the influence on blend behavior, paraffin was blended with either high density polyethylene (HDPE), low density polyethylene (LDPE), or linear low density polyethylene (LLDPE) using a parallel co-rotating twin screw extruder. Chloroform extraction was utilized to estimate the maximum amount of paraffin able to be released by the PE network at equilibrium. Scanning electron microscope (SEM) images of chloroform-extracted samples were collected to investigate the blend structure. Thermal transition temperatures and crystallinity of components in the blends were characterized by differential scanning calorimetry (DSC) and polarized optical microscopy (POM) was used to investigate crystal perfection changes of the polyethylenes before and after blending with paraffin. Paraffin leakage of the blends was investigated by accelerated degradation test in an oven at 60°C. The leakage behavior was analyzed by Korsmeyer–Peppas equation to determine the underlying mechanisms. Chloroform extraction indicated that almost all the paraffin would leak out from the blends in the long run. A co-continuous structure of the blends was evident from the chloroform extraction and subsequent SEM images. While this co-continuous structure controlled leakage behavior, it had little influence on paraffin thermal transition temperatures and crystallinity based on DSC study. In contrast, PE crystal perfection decreased with paraffin level as evident in POM images. This structure resulted in leakage of paraffin in all formulations.

Electrochemical stability of Sm(0.5)Sr(0.5)CoO(3-δ)-infiltrated YSZ for solid oxide fuel cells/electrolysis cells.

Composite SSC (Sm(0.5)Sr(0.5)CoO(3-δ))-YSZ (yttria stabilized zirconia) oxygen electrodes were prepared by an infiltration process. X-ray diffraction (XRD) analysis and scanning electron microscopy (SEM) of the composite electrodes showed the formation of SSC perovskite and a well-connected network of SSC particles in the porous YSZ backbone, respectively. The electrochemical performance of the cell was investigated under both fuel cell and steam electrolysis modes using polarization curves and electrochemical impedance spectroscopy (EIS). The cell experienced a large degradation rate at 700 °C with a constant voltage of 0.7 V for over 100 h under power generation operation. The subsequent post-cell SEM micrograph revealed that agglomeration of the infiltrated SSC particles was possibly the cause for the performance deterioration. Furthermore, the long-term stability of the cell was examined at 700 °C with a constant voltage of 1.3 V under steam electrolysis mode. SEM associated with energy dispersive X-ray spectroscopy (EDS) was employed to characterize the post-test cell after the long-term electrolysis operation and it indicated that besides the agglomeration of SSC particles, the delamination of the SSC-YSZ oxygen electrode from the YSZ electrolyte, as well as segregation of cobalt-enriched particles (particularly cobalt oxides) at the interface, was probably responsible for the cell degradation under the steam electrolysis mode.