Structure characterization of aged automobile exhaust catalysts using electron probe microanalysis.

BACKGROUND: Driven by emission regulations, the technology of emission control catalysts has been under increasing need for development. Understanding the deactivation mechanism of aged or spent automobile exhaust catalysts is the key to extending their service lifetime. However, the lack of comprehensive microstructural characterization results in an incomplete understanding of their physicochemical properties. Deactivation mechanism of automobile exhaust catalysts is a considerably complex phenomenon, it can be classified into three groups based on its origin: thermal sintering, chemical poisoning and mechanical deactivation. RESULTS: In this study, an aged high-mileage automobile exhaust catalyst with Pd and Rh active phases supported on a cerium zirconium oxide doped alumina coating on cordierite was analysed; six consecutive monolithic blocks along the inlet to the outlet of the aged catalyst were extracted, and the corresponding metallographic samples were fabricated using the vacuum impregnation resin method. The purpose of this study was to accurately characterize the different regions of the monolith via electron probe microanalysis and to infer potential causes of catalyst deactivation. Two major causes of deactivation were found: (1) aggregation and alloying of precious-metal particles caused by thermal sintering and (2) chemical poisoning caused by sulphur and phosphorus. Other mechanisms, such as mechanical degradation, which mainly manifests as the loss or wear of the washed coating, were also found to be involved in deactivation. Additionally, the catalytic activity tests showed a considerable decrease in the aged catalyst. The poison concentration trends in the washcoat indicated that P is detrimental to CO oxidation, while S accumulation affects propane oxidation. SIGNIFICANCE: This analysis method can be of substantial practical significance in developing advanced washcoat materials. Meanwhile, it has great potential in the washcoat analysis of honeycomb-shaped monolithic catalyst, such as natural gas catalyst, diesel vehicle oxidation catalyst and other honeycomb catalysts applied in chemical industry.

Element Depletion Due to Missing Boundary Fluorescence in Electron Probe Microanalysis: The Case of Ni in Olivine.

Secondary fluorescence (SF) is known to be a potential source of error in electron probe microanalysis (EPMA) when analyzing for a trace or minor element near a phase boundary. This often overlooked effect leads to a concentration enhancement whenever the neighboring phase contains a high concentration of the analyzed element. Here we show that SF may also lead to a concentration decrease, which can be mistakenly interpreted as a depletion. To examine this issue, we compare Ni profiles measured on well-characterized, homogeneous olivine [(Mg,Fe)2SiO4] grains embedded in basaltic glass, with semi-analytical calculations and numerical simulations of SF across phase boundaries. We find that the Ni content consistently decreases with decreasing distance to the interface or grain radius, deviating from the expected concentration by ∼2-5% at 10 µm from the interface. This decrease is explained by the lower bremsstrahlung fluorescence emitted from the sample as compared to that emitted from the standard. The analytical error due to boundary fluorescence affecting other elements of petrologic importance in olivine is discussed.

Assessing the Accuracy of Mass Attenuation Coefficients for Soft X-ray EPMA.

The use of soft X-rays in electron probe microanalysis (EPMA) has gained renewed interest over the past decades due to the advent of new detector technologies. Because X-ray absorption is the dominant correction for soft X-rays, a reliable set of mass attenuation coefficients (MACs) is needed for accurate composition determination. Although several MAC tabulations cover the soft X-ray range, the accuracy of such tabulations below 1 keV is not firmly established. In this study, we assess the accuracy of MAC tabulations in the soft X-ray region by comparing tabulated values for Be, B, C, N, O, and F Kα X-rays with experimental data available in the literature. We find that the 1993 semi-empirical MAC compilation of Henke et al. [(1993). Low-energy X-ray interaction coefficients: Photoabsorption, scattering, transmission and reflection at E=50-30000 eV, Z=1-92. Atom Data Nucl Data Tables54, 181-342] and the more recent theoretical MAC calculations of Sabbatucci and Salvat [(2016). Theory and calculation of the atomic photoeffect. Rad Phys Chem121, 122-140] perform slightly better than the rest of the considered tabulations. The Sabbatucci-Salvat dataset also provides the best agreement with the few existing experimental measurements for Al L2,3M X-rays.

The accuracy of quantifying the degree of hard tissue calcification using an electron probe micro analyzer, micro-focus X-ray computed tomography, and tissue sectioning methods.

OBJECTIVES: Micro-focus X-ray computed tomography (µCT) helps evaluate specimens without destroying it. However, its accuracy of quantifying bone mineral density remains to be fully elucidated. We aimed to verify the accuracy of calcification assessed by µCT, by comparing the images of identical specimens obtained via different methods such as µCT and electron probe micro analyzer (EPMA) analyses. METHODS: The maxillae, mandibles, and tibiae of five-week-old male mice were analyzed. Calcification density was analyzed using µCT. The right sides of the specimens were decalcified and processed for Azan staining. The left side of the specimens underwent elemental mapping for Ca, Mg, and P using EPMA. RESULTS: µCT revealed a significant increase in calcification levels in the following order: enamel, dentin, cortical bone, and trabecular bone. These results reflected the Ca and P levels observed in the EPMA analyses. µCT demonstrated significant differences in the degree of calcification among the enamel tissues or dentin tissues, except for dentin in the maxillary incisors and molars. However, EPMA analysis did not demonstrate significant differences in the Ca and P levels among the same tissue samples. CONCLUSIONS: EPMA elemental analysis can be used to measure Ca and P levels for evaluating the calcification rate of hard tissues. Additionally, the study results validate the evaluation of calcification density via µCT. Furthermore, µCT can evaluate even minute differences in calcification rates compared with EPMA analysis.

Measurement and Calculation of X-Ray Production Efficiencies for Copper, Zirconium, and Tungsten.

Electron probe microanalysis (EPMA) is based on physical relations between measured X-ray intensities of characteristic lines and their X-ray production efficiency, which depends on the specimen composition. The quality of the analysis results relies on how realistically the physical relations describe the generation and emission of X-rays. Special experiments are necessary to measure X-ray production efficiencies. A challenge in these experiments is the determination of the detection efficiency of the spectrometer as a function of the photon energy. An energy-dispersive spectrometer was used in this work, for which the efficiency was determined at metrological synchrotron beamlines with an accuracy of ±2%. X-ray production efficiencies for the L series and the Kα series of copper and zirconium and for the M and L series of tungsten were determined at energies up to 30 keV in a scanning electron microscope. These experimental values were compared with calculated X-ray production efficiencies using physical relations and material constants applied in EPMA. The objective of the comparison is the further improvement of EPMA algorithms as well as extending the available database for X-ray production efficiencies. Experimental data for the X-ray production efficiency are also useful for the assessment of spectrum simulation software.

Trace Element Distribution in Zoned Kyanite of Thassos Island (Greece) Using Combined Spectroscopic Analyses.

Comprehensive mineralogical and petrographic studies require analytical methods capable to report the distribution of major to trace elements within crystals in order to unravel their formation conditions and subsequent evolution. Additionally, the investigation of transition elements (e.g., Ti, V, Cr, Mn, Fe, and Zn) is essential for the comprehension of substitution processes within colored minerals. This study is conducted on a zoned kyanite crystal from a deformed quartz vein found within garnet-kyanite-biotite-hematite-plagioclase±staurolite±sillimanite paragneiss of Thassos Island, Greece. Herein, we show the efficiency of combining conventional, for example, cathodoluminescence, electron probe microanalysis (EPMA), laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), and new methods, for example, micro-laser-induced breakdown spectroscopy (µLIBS), micro-X-ray fluorescence (µXRF), and Raman spectroscopy, to determine the chemical and crystallographic features of minerals. The simple chemistry of this crystal offers an ideal case to compare and valuate the potential of combined spectroscopy techniques to analyze minerals. We demonstrate that µLIBS and µXRF are perfectly adapted to perform multi-element imaging of major to trace elements down to the ppm level within a pluricentimetric crystal (2.3 x 0.5 cm) prior to quantitative analyses. We also highlight the benefit of cathodoluminescence and Raman mapping in the investigation of crystallographic features within minerals. The multispectroscopic approach enabled us to correlate growth stages of kyanite with the polymetamorphic history of the sample. Our results also highlight the spatial dependence of Ti for the generation of blue zonation by Fe2+-Ti4+ substitutions with Al3+.

Differential Quercus spp. pollen-particulate matter interaction is dependent on geographical areas.

Particulate matter (PM) and pollen interaction, either airborne or at the respiratory mucosa needs further clarification, as allergic reaction intensification can be related to the PM physical characteristics and toxicity. This study aimed to investigate the physical-chemical properties of PM that can adhere to the pollen wall during its transport or inhalation, using Quercus spp. as a model, in three Portuguese cities with different geographical locations, meteorological influence and urbanization levels. Possible sources were evaluated through air masses trajectory analysis using the HYSPLIT model and correlation with meteorological factors. The sampling was performed using a 7-days Hirst-type volumetric sampler, and the pollen grains were observed using a Field Emission Electron Probe Microanalyser for PM analysis. A secondary electron image of each pollen grain was taken, to determine the adhered particles characteristics and energy dispersive x-ray spectroscopy (EDS) spectra were obtained for individual particles. A total of 484 pollen grains was observed, with 7683 particles counted and 1914 EDS spectra analyzed. The particle's equivalent diameter ranged from 0.3-16 µm, with most having a diameter < 3 µm. For the three cities, there were significant differences in the number of particles per pollen and the % area occupied by the particles. Particles adhered were mainly Si-rich, but variations in other dominant groups were observed. For Évora and Guarda, Ca-rich, SO-rich were second and third more representative, while Porto were Organic and Cl-rich. Metals&Oxides were found in all cities with the highest number in Porto. P-rich particles were only found in Évora. Sea salt particles were observed in Évora, coincide with air mass trajectories possible carrying them from the Mediterranean Sea. In conclusion, the PM physical characteristics are similar between the studied cities, however, the dominant chemical composition is different, certainly impacting the exposome influence and pollen-allergy intensification towards the same pollen type and concentration.

The good, the bad and the ugly polishing: Effect of abrasive size on standardless EDS analysis of Portland cement clinker's calcium silicates.

Standardless Energy dispersive spectroscopy (EDS) on polished samples of Portland cement clinker is routinely performed both for unhydrated phases as well as in cement pastes. Typically, the calcium to silica ratio is investigated. EDS analyses are highly dependent on the polishing quality of the sample. It is thus worth studying the Ca/Si ratios of cement phases in a clinker since they can be used as a reference. Indeed, alite (Ca3SiO5 or C3S in cement chemistry notation) and belite (Ca2SiO4 or C2S) should have an atomic Ca/Si ratio of 3 and 2, respectively. EDS carried out under the scanning electron microscope (SEM) is routinely used on polished samples to assess the composition of such phases. In the present study, Ca/Si ratios are investigated on a commercial clinker polished at various steps (6, 3, 1 and 0.25 µm diamond pastes, 0.05 µm alumina). All along the polishing process, ratios are coherent with theoretical ones and with the reference ones obtained by electron probe microanalysis (EMPA) in the present study.

Organ-specific accumulation of selenium and mercury in Indo-Pacific bottlenose dolphins (Tursiops aduncus).

Delphinids are top ocean predators and accumulate high concentrations of mercury (Hg) through the food chain, particularly in organs such as liver and kidney, although the proportion of methylmercury (MeHg) is relatively low due to the demethylation process. Total mercury (T-Hg) levels in marine mammals have been shown to correlate with selenium (Se) concentrations, and ingested MeHg that is demethylated may be present in tissues as mercury selenide (HgSe). In this study, we determined T-Hg, MeHg and Se concentrations of three Indo-Pacific bottlenose dolphins (Tursiops aduncus), and we used the individual with the highest Hg concentration for electron probe microanalysis to assess the co-localization of Hg and Se in the tissues. By electron probe microanalysis, we found that Hg and Se were co-localized in large granules in hepatic Kupffer cells and in small granules in hepatocytes. The analysis suggested that MeHg was demethylated in hepatocytes and then phagocytosed by Kupffer cells. In the kidney, Hg and Se were co-localized in the glomerular capillary wall and in interstitial blood vessel walls. Hg and Se were also co-localized in the cytoplasm of large neurons and in glial cells in the cerebrum. Divalent Hg and HgSe cannot cross the blood-brain barrier, suggesting that MeHg is demethylated in the dolphin brain and that binding to Se suppresses Hg toxicity.

Electron Probe Microanalysis of Transition Metals using L lines: The Effect of Self-absorption.

Electron microprobe-based quantitative compositional measurement of first-row transition metals using their L$\alpha$ X-ray lines is hampered by, among other effects, self-absorption. This effect, which occurs when a broad X-ray line is located close to a broad absorption edge, is not accounted for by matrix corrections. To assess the error due to neglecting self-absorption, we calculate the L$\alpha$ X-ray intensity emitted from metallic Fe, Ni, Cu, and Zn targets, assuming a Lorentzian profile for the X-ray line and taking into account the energy dependence of the mass absorption coefficient near the absorption edge. We find that calculated X-ray intensities depart increasingly, for increasing electron beam energy, from those obtained assuming a narrow X-ray line and a single fixed absorption coefficient (conventional approach), with a maximum deviation of $\sim$15% for Ni and of $\sim$10% for Fe. In contrast, X-ray intensities calculated for metallic Zn and Cu do not differ significantly from those obtained using the conventional approach. The implications of these results for the analysis of transition-metal compounds by electron probe microanalysis as well as strategies to account for self-absorption effects are discussed.

Microstructural, microchemical, and mechanical changes associated with the clinical reuse of two nickel-titanium endodontic instruments.

BACKGROUND: Nickel-titanium (NiTi) instruments have represented a great technological development that enabled endodontists conforming irregular-shaped root canals. Notwithstanding, the repeated use of these instruments may lead to the fracture without any prior visible warning signs. This study aimed to evaluate how multiple clinical instrumentation/sterilization cycles of two NiTi mechanized instruments can affect their microstructural, microchemical, and mechanical characteristics. MATERIALS AND METHODS: In this observational descriptive study, a total of 140 NiTi instruments, 70 ProTaper Gold® (PTG) and 70 WaveOne Gold® (WOG) were analyzed. For each brand system, instruments were evaluated in the as-received condition (n = 10) and after one (n = 20), two (n = 20), and three (n = 20) instrumentation/sterilization cycles. Intraoperative instrumentation parameters were recorded for all used instruments. Afterward, the files were examined using scanning electron microscopy and energy-dispersive X-ray microanalysis. All of the instruments were tensile-fatigue tested until rupture in order to calculate the mechanical tensile strength and the maximum elongation percentage for the samples. Statistical analysis was completed using Chi-square, Kruskal-Wallis H-, or Mann-Whitney U-tests with a statistical significance set at P < 0.05. RESULTS: Significant increasing changes in surface topography (P < 0.05, Chi-square test) and chemical composition (P < 0.05, Kruskal-Wallis H-test) in both brand systems through instrumentation/sterilization cycles were detected. In addition, values of mechanical tensile strength and maximum elongation percentage increased significantly through instrumentation/sterilization cycles in the PTG group, whereas only the median values of mechanical tensile strength increased significantly in the WOG group (all P < 0.01, Kruskal-Wallis H-test). CONCLUSION: Although multiple instrumentation/sterilization cycles may render NiTi instruments more flexible and fatigue resistant, the significant changes detected in their surface topography and chemical composition should preclude their repeated clinical use in the routine endodontic practice as prevention for breakage.

Quantification of Trace-Level Silicon Doping in Al x Ga1-xN Films Using Wavelength-Dispersive X-Ray Microanalysis.

Wavelength-dispersive X-ray (WDX) spectroscopy was used to measure silicon atom concentrations in the range 35-100 ppm [corresponding to (3-9) × 1018 cm-3] in doped AlxGa1-xN films using an electron probe microanalyser also equipped with a cathodoluminescence (CL) spectrometer. Doping with Si is the usual way to produce the n-type conducting layers that are critical in GaN- and AlxGa1-xN-based devices such as LEDs and laser diodes. Previously, we have shown excellent agreement for Mg dopant concentrations in p-GaN measured by WDX with values from the more widely used technique of secondary ion mass spectrometry (SIMS). However, a discrepancy between these methods has been reported when quantifying the n-type dopant, silicon. We identify the cause of discrepancy as inherent sample contamination and propose a way to correct this using a calibration relation. This new approach, using a method combining data derived from SIMS measurements on both GaN and AlxGa1-xN samples, provides the means to measure the Si content in these samples with account taken of variations in the ZAF corrections. This method presents a cost-effective and time-saving way to measure the Si doping and can also benefit from simultaneously measuring other signals, such as CL and electron channeling contrast imaging.

A Simple Approach for Thickness Measurements Using Electron Probe Microanalysis.

A simple and fast method for thickness measurements using electron probe microanalysis (EPMA) is described. The method is applicable on samples with a thickness smaller than the electron depth range and does not require any knowledge of instrumental parameters. The thickness is determined by means of the distance that electrons travel inside the sample before crossing through it. Samples are first deposited on a substrate that, when reached by the transmitted electrons, produces an X-ray signal. The measured characteristic X-ray line intensity of the substrate is later used to determine the energy of transmitted electrons, which is proportional to the distance that electrons travel inside the sample. The study was performed on spherical K411 glass particles and cylindrical particles of U­Ce oxide with a size ranging from 0.2 to 4 µm. The measured thicknesses of all the studied particles showed good agreements with the real values. Although the method is only validated on particles with usual shapes, it can be applied to determine a local thickness of thin samples with irregular morphologies. This can help solving multiple issues in analysis with EPMA of non-bulk samples exhibiting complex geometries. Three dimensional microscopic imaging could also find a good utility in the described method.

An Improved Electron Microprobe Method for the Analysis of Halogens in Natural Silicate Glasses.

We present a new analytical method, which allows the simultaneous analysis of fluorine (F), chlorine (Cl), bromine (Br), and iodine (I) in geological samples. To account for interferences of Fe on the spectral lines of F, of Al on Br-lines, and of Ca on I-lines, we prepared four new halogen-free calibration glasses. The new method is used to analyze various glass reference materials and crystal-hosted melt inclusions from the Azores. Our results show that our new method allows reliable and reproducible analyses of all four halogens in silicate glasses.

Determination of Mass Attenuation Coefficients of Th, U, Np, and Pu for Oxygen Kα X-Rays Using an Electron Microprobe.

Mass attenuation coefficients (MACs) of Th, U, Np, and Pu for oxygen X-rays have been experimentally determined using an electron microprobe. The MACs were obtained by measuring relative X-ray intensities emitted from ThO2, UO2, NpO2, and PuO2 targets, for incident electron energies from 5 to 30 keV, and processing them with the help of the computer program XMAC. The accuracy of the measured MACs is estimated to be better than 5%. Results are compared with MAC tabulations commonly used in electron probe microanalysis as well as with theoretical photoionization calculations. It is concluded that the MACs implemented in the Monte Carlo simulation program PENELOPE which are based on the photoionization cross-section calculations of Sabbatucci & Salvat [(2016). Theory and calculation of the atomic photoeffect. Rad Phys Chem121, 122-140], provide the best agreement with our measurements. The use of different MAC schemes for the analysis of mixed actinide oxide materials is discussed.

Embracing Uncertainty: Modeling the Standard Uncertainty in Electron Probe Microanalysis-Part I.

This is the first in a series of articles which present a new framework for computing the standard uncertainty in electron excited X-ray microanalysis measurements. This article will discuss the framework and apply it to a handful of simple, but useful, subcomponents of the larger problem. Subsequent articles will handle more complex aspects of the measurement model. The result will be a framework in which sophisticated and practical models of the uncertainty for real-world measurements. It will include many long overlooked contributions like surface roughness and coating thickness. The result provides more than just error bars for our measurements. It also provides a framework for measurement optimization and, ultimately, the development of an expert system to guide both the novice and expert to design more effective measurement protocols.

Mercury and Selenium Localization in the Cerebrum, Cerebellum, Liver, and Kidney of a Minamata Disease Case.

Minamata disease is a methylmercury poisoning caused by consumption of marine food contaminated by man-made methylmercury environmental pollution, and its most prominent feature is marked pathological changes in the central nervous system. Morphological alterations are less pronounced in the liver and the kidney, although their mercury levels are higher than those of the brain. In marine mammals, methylmercury is known to be easily converted to inorganic mercury and it combines with selenium forming mercury selenide, which may counteract the toxicity of mercury. However, little is known about the formation of mercury and selenium complex in human organs. In the present study, we examined the cerebrum, cerebellum, liver, and kidney of a Minamata disease case to study the mercury and selenium localization using electron probe microanalysis. Our results indicated the mercury and selenium localization in the specified tissue of the brain, liver, and kidney such as glial cells, Kupffer cells, and renal tubules.

Improvement of Electron Probe Microanalysis of Boron Concentration in Silicate Glasses.

The determination of low boron concentrations in silicate glasses by electron probe microanalysis (EPMA) remains a significant challenge. The internal interferences from the diffraction crystal, i.e. the Mo-B4C large d-spacing layered synthetic microstructure crystal, can be thoroughly diminished by using an optimized differential mode of pulse height analysis (PHA). Although potential high-order spectral interferences from Ca, Fe, and Mn on the BKα peak can be significantly reduced by using an optimized differential mode of PHA, a quantitative calibration of the interferences is required to obtain accurate boron concentrations in silicate glasses that contain these elements. Furthermore, the first-order spectral interference from ClL-lines is so strong that they hinder reliable EPMA of boron concentrations in Cl-bearing silicate glasses. Our tests also indicate that, due to the strongly curved background shape on the high-energy side of BKα, an exponential regression is better than linear regression for estimating the on-peak background intensity based on measured off-peak background intensities. We propose that an optimal analytical setting for low boron concentrations in silicate glasses (≥0.2 wt% B2O3) would best involve a proper boron-rich glass standard, a low accelerating voltage, a high beam current, a large beam size, and a differential mode of PHA.

Scanning electron microscopy in analysis of urinary stones.

Urolithiasis is a frequent and in many cases serious disease. Proper analysis of kidney stone composition is crucial for appropriate treatment and prevention of disease recurrence. In this work, scanning electron microscopy (SEM) coupled with energy-dispersive spectroscopy was applied for a study of 30 samples covering the most common types of human kidney stones. The results are analyzed and evaluated in terms of applicability of the method for both routine kidney stone analysis as well as collecting of specific data. The method provides complex information about studied samples including morphology of the stones and of the present crystals or their aggregates. It also brings information on elemental composition of the phases. After application of standardization, quantitative microanalysis with detection limits of 400 ppm (Mg, P, S, Cl, K, Ca), 500 ppm (Na) and 1200 ppm (F) was obtained. Compositional mapping with EDS shows the elemental distribution within a sample. This study demonstrated that information on morphology and chemistry acquired by these methods was highly reliable for identification of phases, even when present in small amounts. It provided information on kidney stone structure, relationships between phases, major and minor element content, and variations in chemical composition related to the growth of the stones. SEM represents a powerful tool in urinary stone analysis, since a single facility can produce a wide spectrum of information. It can be suggested as a basic method used for routine urinary stone identification, whilst bringing additional detailed information that cannot be obtained by other methods.

Quantitative Determination of Low Contents of Manganese in Steels by EPMA.

The fluorescence effect induced by Kß photons is usually so small that it can be neglected. However, in the Fe-Mn system, omitting Kß fluorescence correction will lead to the overestimation of the Mn content especially when Mn is the minor alloy element. In this study, the error in the Mn concentration induced by Kß fluorescence was investigated by both Monte Carlo simulation, using the pyPENELOPE program, and systematic electron probe measurements on the Fe-0.53% Mn alloy standard by the aid of CalcZAF software. It is shown that the error caused by Kß fluorescence exceeds 4% for the Fe-0.53% Mn alloy. The problem can be overcome by utilizing CalcZAF in which ß-line fluorescence has been included, or by employing a similar standard Fe-0.85% Mn for Mn in the absence of ß-line fluorescence correction. In addition, a modified calibration curve method, using k-values instead of X-ray intensity as a variable, is presented and used to measure the Mn concentration. The accuracy of this method is as good as or better than that of the conventional matrix correction method. Compared with conventional calibration curve methods, it is time-saving because the k-value is not sensitive to instrument fluctuations and the established curve remains valid for a long period.