Detailed Characterization Of Samples Research Articles

Application of Artificial Intelligence to the Alert of Explosions in Colombian Underground Mines

The use of Artificial Intelligence (AI), particularly of Artificial Neural Networks (ANN), in alerting possible scenarios of methane explosions in Colombian underground mines is illustrated by the analysis of an explosion that killed twelve miners. A combination of geological analysis, a detailed characterization of samples of coal dust and scene evidence, and an analysis with physical modeling tools supported the hypothesis of the existence of an initial methane explosion ignited by an unprotected tool that was followed by a coal dust explosion. The fact that one victim had a portable methane detector at the moment of the methane explosion suggested that the ubiquitous use of these systems in Colombian mines could be used to alert regulatory agencies of a possible methane explosion. This fact was illustrated with the generation of a database of possible readouts of methane concentration based on the recreation of the mine atmosphere before the explosion with Computational Fluid Dynamics (CFD). This database was used to train and test an ANN that included an input layer with two nodes, two hidden layers, each with eight nodes, and an output layer with one node. The inner layers applied a rectified linear unit activation function and the output layer a Sigmoid function. The performance of the ANN algorithm was considered acceptable as it correctly predicted the need for an explosion alert in 971.9 per thousand cases and illustrated how AI can process data that is currently discarded but that can be of importance to alert about methane explosions.

On the impact of radiative transfer in fluorescence imaging of bacterial films and suspensions

Fluorescence imaging and spectroscopy are convenient, rapid, and simple methods to analyze chemical samples including biological materials such as bacterial biofilms and suspensions. In principle, these techniques could be used to diagnose or discriminate between infectious bacteria in infections of the skin or ocular surface (microbial keratitis, MK). However, the extension of these techniques to macroscopic turbid media that strongly absorb and scatter light is difficult. Radiative transfer effects obscure the relationship between microscopic scattering and absorption properties and macroscopically observable quantities such as fluorescence intensity, transmission, and reflection. A combination of experimental measurements of aqueous bacteria cell suspensions and Monte Carlo radiation transfer simulations are performed to better understand these effects. Several general observations, e.g., that fluorescence intensity is maximized in scattering-dominated media, are discussed in detail. It was found that wavelength-dependent radiative transfer effects are observable even at moderate optical densities (OD ∼ 1; well below the diffusion limit). Careful consideration of radiative transfer effects using physically rigorous models is needed to determine single-cell scattering and absorption properties and interpret quantitative fluorescence measurements accurately in most cases of interest. A detailed discussion of radiative transfer effects and analytical models is provided. In the context of surface infections and MK, it was found that radiative transfer effects may be negligible for the model bacteria E. coli in some cases. However, more accurate measurements of microbe optical properties are needed to confirm and extend this conclusion to other species. Overall this work demonstrates that quantitative fluorescence imaging and spectroscopy of bacterial films and suspensions is feasible, but requires detailed sample characterization and careful consideration of radiative transfer effects.

GaN/ZnO hybrid nanostructures for improved photocatalytic performance: One-step synthesis.

Nanostructured semiconductor materials are considered potential candidates for the degradation of textile wastewater via the photocatalytic process. This study aims to produce hexagonal gallium nitride (GaN) nanoplates and zinc oxide (ZnO) nanoparticles in a deionized water environment utilizing a one-step arc discharge process. Detailed characterization of samples has been completed via scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and UV visible spectroscopy methods. The hybrid nanostructure morphologies consist of nanoplates and nanorods of different sizes. The photoperformance of GaN/ZnO hybrid nanostructures was assessed via the malachite green (MG) dye degradation under UV exposure. Under UV exposure, the degradation yield reached 98% in 60 min. Compared to individual ZnO and GaN nanoparticles, the photocatalytic reaction rate of the GaN/ZnO photocatalyst is 2.2 and 3.6 times faster, respectively. Besides, the GaN/ZnO hybrid nanostructures show excellent photocatalytic stability. The energy consumption of the photocatalytic degradation in the presence of GaN/ZnO hybrid nanostructures was 1.688 kWhL-1. These results demonstrate that the GaN/ZnO hybrid nanostructures with improved photocatalytic activity are a reasonable option for the decomposition of textile wastewater under UV light exposure.

Strain-rate dependent workability and plastic flow instability of a (Nb+V) stabilized microalloyed steel

In the current work, the strain-rate dependent workability and flow instability has been investigated in a (Nb+V) stabilized microalloyed steel. Uniaxial compression tests were conducted in intercritical and single phase austenitic temperature domain (700–1100 °C) at several strain-rates (0.01–10 s−1), using a thermo-mechanical simulator (Gleeble®−3800). The results show that the flow stress increases at higher strain-rates. A good sample processing window arises at medium strain-rates (0.1–1 s−1); whereas, flow instability (serrations) at high (10 s−1) and low (0.01 s−1) strain-rate plastic deformations. After a detailed sample characterization, it appears that the reasons for flow instability during the hot and warm deformations are the formation of micro-cracks or void nucleation at low (0.01 s−1) strain-rate; whereas, flow localization and shear banding by adiabatic heating at a higher strain-rate (10 s−1). In both cases (0.01 and 10 s−1), the serration arises at periodic intervals with negative strain-rate sensitivity. At a higher strain-rate (10 s−1), the flow instability dominates till 1100 °C, because of relieving the deformation-induced stored energy mainly by dynamic recovery. At lower deformation temperatures (i.e., 700–800 °C), fine ferrite grains nucleate around shear bands by the diffusional transformation of austenite. The dynamic recrystallization is either absent or incomplete in agreement with the experimental determination of Tnr (non-recrystallization temperature) and texture analysis. The overall flow instability characteristics in terms of temperature, strain and strain-rate substantiate well with the dynamic materials model, by the superposition of flow instability and power dissipation efficiency, on revisiting the processing map.

Characterization of bark, needles and cones from silver fir (Abies alba mill.) towards valorization of biomass forestry residues

Valorization of renewable biomass forestry gains more and more interest due to the exhaustible nature of fossil based resources and their negative environment impact. Therefore, this study involves thoroughly characterization of bark, needles and cones from silver fir (Abies alba Mill.) of two different ages (40 and 100 years) to determine their potential use as source of valuable compounds. Proximate/ultimate and compositional analysis as well as thermal behavior showed that the studied materials are promising candidates for biomass valorization by torrefaction and pyrolysis. In addition, it was revealed that fir samples contain significant amounts of phenolic and flavonoid compounds. The extractive fractions were found to be rich in highly valuable compounds such as terpenes, paraffins, phenols, acids and derivatives of abietic acid. This induced good antioxidant activity of the extractive fractions, with fast scavenging of DPPH radicals. The PCA and hierarchical clustering used for exploratory data analysis offered the possibility to combine multiple information obtained from detailed characterization of samples into a global view of the system. This allowed us to observe and distinguish similarities and differences among samples according to source and age. Needles stand out from bark and cones due to the high content of terpenes in extractives. Paraffins were the main components in the extractives from cones. Saccharides were found, in small amounts, only in the extractives of bark. Differences by age were also observed. The resulted outcomes provide a promising starting point in selecting suitable sources and procedures for valorization of renewable biomass forestry into energy and value added materials.

A Microscale Analysis of Hydrothermal Epidote: Implications for the Use of Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry Mineral Chemistry in Complex Alteration Environments

Abstract High-resolution, quantitative imaging of epidote from the Ann Mason fault block, Yerington district, Nevada, using scanning electron microscopy (SEM), X-ray fluorescence (XRF), and laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) has revealed at least two types of epidote (type 1 and type 2), each with different major and trace element chemistry. Type 1 epidote is coarser grained, typically greater than 50 μm in diameter, and forms euhedral crystals that display twins and sector zones enriched in Fe, Sr, and Mn. Type 2 epidote is finer grained, typically less than 30 μm in diameter, irregularly zoned with respect to Fe and Al, and forms polycrystalline aggregates that include void space. Two sources of intragranular compositional variability are defined in this study—one related to different generations of epidote only visible on the microscale, and the other related to crystallographic features such as sector zones and twins. Intragranular compositional variations within Yerington epidotes highlight the potential importance of detailed sample characterization in complex alteration environments prior to undertaking mineral chemistry studies in the context of resource exploration. Based on statistical analysis of LA-ICP-MS spot data from one sample, the optimal number of spot analyses to adequately represent the range in element concentrations within zoned or twinned crystals is determined to be at least 40.

PtIr protective coating system for precision glass molding tools: Design, evaluation and mechanism of degradation

During Precision Glass Molding (PGM), the molding tools have to withstand severe thermo-chemical and thermo-mechanical loads cyclically. To protect their high-quality surface against degradation and increase their service lifetime, protective coatings are applied on the molding tools. In this work, we designed four different PtIr protective coating systems, where the thickness of the PtIr layer and the adhesion layer were varied. Their lifetimes were evaluated and compared using an in-house built testing bench. Among all the studied coating systems, the protective coating, which consists of a 600-nm-thick PtIr layer and a 20-nm-thick Cr adhesion layer, showed the best durability. To understand the degradation mechanism of the coating during actual engineering production, an industrial PGM machine was used and emulation PGM tests were conducted. Detailed sample characterization was performed using an array of complementary techniques including white light interferometry (WLI), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), scanning transmission electron microscopy (STEM) and atom probe tomography (APT). Phenomena such as interdiffusion, oxidation, coating spallation and glass sticking on the coating were observed and are discussed in the context of optimization of the coating's performance and durability.

Fundamental Studies on Poly(2-oxazoline) Side Chain Isomers Using Tandem Mass Spectrometry and Ion Mobility-Mass Spectrometry.

When polymer mixtures become increasingly complex, the conventional analysis techniques become insufficient for complete characterization. Mass spectrometric techniques can satisfy this increasing demand for detailed sample characterization. Even though isobaric polymers are indistinguishable using simple mass spectrometry (MS) analyses, more advanced techniques such as tandem MS (MS/MS) or ion mobility (IM) can be used. Here, we report proof of concept for characterizing isomeric polymers, namely poly(2-n-propyl-2-oxazoline) (Pn-PrOx) and poly(2-isopropyl-2-oxazoline) (Pi-PrOx), using MS/MS and IM-MS. Pi-PrOx ions lose in intensity at higher accelerating voltages than Pn-PrOx ions during collision-induced dissociation (CID) MS/MS experiments. A Pn/i-PrOx mixture could also be titrated using survival yield calculations of either precursor ions or cation ejection species. IM-MS yielded shape differences in the degree of polymerization (DP) regions showing the structural rearrangements. Combined MS techniques are thus able to identify and deconvolute the molar mass distributions of the two isomers in a mixture. Finally, the MS/MS and IM-MS behaviors are compared for interpretation. Graphical Abstract .

Mechanism of Zr Incorporation in the Course of Hydrothermal Synthesis of Zeolite BEA.

The mechanism of Zr-BEA hydrothermal synthesis in fluoride media has been investigated through the detailed characterization of samples obtained at different synthesis times by XRD, XRF, TGA, multinuclear solid-state NMR, FTIR, SEM, TEM with EDS, XAS, and nitrogen sorption. The synthetic procedure involved hydrothermal crystallization of the gel with the following composition: 1SiO2:0.54TEAOH:0.54HF:0.005ZrO2:5.6H2O. The formation of open and closed Lewis acid sites was monitored by FTIR spectroscopy of adsorbed CO, while coordination of Zr was studied by XAS. The results show that the formation of Zr-BEA proceeds by two steps. In the first step, pure silica BEA is crystallized via a solid-solid hydrogel rearrangement mechanism. Zirconium species are occluded in Si-BEA crystals in the form of Zr-rich silicate particles. These particles do not provide for any appreciable Lewis acidity. In the second step, Zr incorporation into T positions of the zeolite structure takes place, leading to the formation of closed Zr sites, which are partially converted into open sites at longer synthesis times. It is demonstrated that the content of open and closed sites can be tuned by variation of the synthesis time.

Crystal Growth and Characterization of HgBa2Ca2Cu3O8+δ Superconductors with the Highest Critical Temperature at Ambient Pressure.

We report an original procedure for the elaboration of very high-quality single crystals of superconducting HgBa2Ca2Cu3O8+δ mercury cuprates. These single crystals are unique, with very high-quality surface paving the way for spectroscopic, transport, and thermodynamic probes in order to understand the hole-doped cuprate phase diagram. Annealing allows one to optimize Tc up to Tcmax = 133 K. The superconductivity transition width of about 2 K indicates that they are homogeneous. We show for the first time that, with adequate heat treatment, Hg-1223 can be largely underdoped and its doping level controlled. Importantly, the crystal structure was studied in detail by single-crystal X-ray diffraction, and we have identified the signature of the underdoping by a detailed sample characterization and micro-Raman spectroscopy measurements.

Optical absorption spectroscopy study of the causes for color variations in natural Fe-bearing gahnite: Insights from iron valency and site distribution data

Four gahnite single crystals with variable colors from pale blue to green have been studied by a multi-analytical approach with the aim to evaluate existing assignments of optical absorption bands. Combined information from electron microprobe analyses, Mossbauer spectroscopy, IR-spectroscopy, single-crystal X-ray structure refinements, and optical absorption spectroscopy confirms the conclusions of earlier studies that the absorption bands recorded in the visible spectral region up to ~540 nm (above ~18 500 cm −1 ) are related to electronic d-d transitions in tetrahedrally coordinated Fe 2+ . It also demonstrates that a set of absorption bands between ~550–625 nm (~16 000–18 200 cm −1 ) are caused by spin-allowed and spin-forbidden d-d transitions in tetrahedrally coordinated Co 2+ . Two absorption bands at higher wavelengths (~680 and ~800 nm, i.e., ~14 700 and ~12 500 cm −1 ) are assigned to electronic transitions in exchange coupled VI Fe 3+ - IV Fe 2+ pairs and a band at ~950 nm (~10 500 cm −1 ) is assigned to a spin-allowed electronic transition in VI Fe 2+ . Low-Fe gahnite crystals owe their blue color to traces of cobalt at concentration levels in the order of 200 ppm and less, while the green color of gahnite crystals with higher Fe-contents is due to a combination of electronic ligand-metal transitions causing strong UV-absorption and electronic transitions in exchange coupled Fe 2+ -Fe 3+ cation pairs that absorb in the red region of the visible spectrum. A detailed characterization of samples that includes cation site occupancy and iron valency data is demonstrated to be crucial for interpreting optical absorption spectra. Also electronic transitions in trace element chromophores below the detection limit of electron microprobe may participate to light absorption. All this information contribute to the comprehension of the causes of crystal color of minerals, gemstones, and ceramic pigments.

Metal release from limestones at high partial-pressures of CO2

CO2 leakage from underground CO2 sequestration and storage poses potential risks to degradation of water quality in shallow aquifers. Increased CO2 concentrations can result in decreased pH and lead to subsequent metal release from mineral dissolution or desorption from mineral surfaces. Dissolution of carbonate minerals present in aquifer sediments or rocks will buffer pH and is generally thought to reduce the potential risk of metal release in the event of a CO2 leak. As a result, much of the research on geochemical impacts of CO2 leakage has focused on siliciclastic aquifers with little to no carbonate minerals present. However, carbonate minerals contain trace amounts of metals in their crystal structure that will be released into solution with dissolution and may pose a risk to drinking water quality. Here, we perform laboratory water–rock experiments to analyze the potential for metal release due to carbonate mineral dissolution in limestone aquifers. Rock samples from three limestone aquifers were dissolved in batch reactors with varying partial-pressures of CO2 (from 0.01 to 1bar) in the headspace. As CO2 dissolved into the fluid and decreased the pH, the carbonate minerals dissolved and released metals into solution. The concentrations of calcium, magnesium, strontium, barium, thallium, uranium, and cobalt increased but remained below any regulatory limits. The concentrations of arsenic and nickel increased and exceeded primary drinking water standards set by the USEPA and the State of California, respectively. Potential sources of metals in the rocks were determined through detailed sample characterization using sequential extractions, laser ablation inductively coupled mass spectrometry, and high resolution mineralogical mapping with QEMSCAN. We found that calcite dissolution released more metals to solution than pyrite dissolution or metal desorption from mineral surfaces in these experiments. Geochemical models based on the experimental data were used to evaluate the relative importance of calcite dissolution versus pyrite dissolution over a 30-year time frame. Under both oxic and sub-oxic conditions, calcite dissolution is the dominant source of metals to solution immediately after exposure to CO2. Pyrite dissolution becomes the dominant source at later times as the fluid reaches equilibrium with respect to calcite. For all model scenarios, the cumulative contribution of metals to solution was dominated by calcite dissolution. Results from this study suggest that the pH-buffering benefit of carbonate mineral dissolution in the event of a CO2 leak may be offset by the potentially negative effect of trace metal release from the crystal structure. This study highlights the need for detailed sample characterization at individual sites to identify sources of metals when assessing the potential risk of CO2 leakage into shallow aquifers.

Metal release from dolomites at high partial-pressures of CO2

The potential for metal release associated with CO2 leakage from underground storage formations into shallow aquifers is an important consideration in assessment of risk associated with CO2 sequestration. Metal release can be driven by acidification of groundwaters caused by dissolution of CO2 and subsequent dissociation of carbonic acid. Thus, acidity is considered one of the main drivers for water quality degradation when evaluating potential impacts of CO2 leakage. Dissolution of carbonate minerals buffers the increased acidity. Thus, it is generally thought that carbonate aquifers will be less impacted by CO2 leakage than non-carbonate aquifers due to their high buffering potential. However, dissolution of carbonate minerals can also release trace metals, often present as impurities in the carbonate crystal structure, into solution. The impact of the release of trace metals through this mechanism on water quality remains relatively unknown. In a previous study we demonstrated that calcite dissolution contributed more metal release into solution than sulfide dissolution or desorption when limestone samples were dissolved in elevated CO2 conditions. The study presented in this paper expanded our work to dolomite formations and details a thorough investigation on the role of mineral composition and mechanisms on trace element release in the presence of CO2. Detailed characterization of samples from dolomite formations demonstrated stronger associations of metal releases with dissolution of carbonate mineral phases relative to sulfide minerals or surface sorption sites. Aqueous concentrations of Sr2+, CO2+, Mn2+, Ni2+, Tl+, and Zn2+ increased when these dolomite rocks were exposed to elevated concentrations of CO2. The aqueous concentrations of these metals correlate to aqueous concentrations of Ca2+ throughout the experiments. All of the experimental evidence points to carbonate minerals as the dominant source of metals from these dolomite rocks to solution under experimental CO2 leakage conditions. Aqueous concentrations of Ca2+ and Mg2+ predicted from numerical simulation of kinetic dolomite dissolution match those observed in the experiments when the surface area is three to five orders of magnitude lower than the surface area of the samples measured by gas adsorption.

Tip‐Enhanced Near‐Field Optical Microscopy

Spectroscopic methods with high spatial resolution are essential for understanding the physical and chemical properties of nanoscale materials, including quantum structures and biological surfaces. An optical technique is reviewed that relies on the enhanced electric fields in the proximity of a sharp, laser-irradiated metal tip. These fields are utilized for spatially confined probing of various optical signals, thus allowing for a detailed sample characterization far below the diffraction limit. In addition, tip-enhanced fields also provide the sensitivity crucial for the detection of nanoscale volumes. After outlining the principles of near-field optics, the mechanisms contributing to local field enhancement and how it can be used to enhance optical signals are discussed. Different experimental methods are presented and several recent examples of Raman and fluorescence microscopy with 10 nm spatial resolution of single molecules are reviewed.

Nondestructive, High-Resolution Materials Characterization with the Confocal Raman-AFM

Abstract Materials research, biomedical research, and semiconductor manufacturing can all benefit from nondestructive, high-resolution methods of analysis. As most materials are heterogeneous, it is important to not only acquire high resolution topographic information, but also to identify the chemical composition of samples. A combination of high resolution microscopy with chemically sensitive spectroscopy combined in one instrument allows the detailed characterization of samples with different analytical techniques. When individual instruments are used, returning to a previously surveyed sample area can be very time consuming if not impossible without surface markers.

Phase transitions and undercooling in confined gallium

Abstract Phase transitions in submicrometre gallium droplets confined in epoxy resin are revealed by single-energy X-ray absorption spectroscopy using synchrotron radiation, a technique previously applied in high-temperature studies of solid and liquid metals. These unconventional measurements are accompanied by a detailed characterization of samples using scanning electron microscopy and adiabatic calorimetry measurements. Exceptional undercooling down to 150 K is confirmed by the present data. Specific heat measurements performed during the warming cycles confirmed the presence of three different solid phases for gallium, namely β-Ga, γ-Ga and δ-Ga and the absence of the α-Ga stable phase at ambient conditions.