Dispersive X-ray Spectroscopy Elemental Mapping Research Articles

Formation of Fully Stoichiometric, Oxidation-State Pure Neptunium and Plutonium Dioxides from Molecular Precursors.

Amidate-based ligands (N-(tert-butyl)isobutyramide, ITA) bind κ2 to form homoleptic, 8-coordinate complexes with tetravalent 237Np (Np(ITA)4, 1-Np) and 242Pu (Pu(ITA)4, 1-Pu). These compounds complete an isostructural series from Th, U-Pu and allow for the direct comparison between many of the early actinides with stable tetravalent oxidation states by nuclear magnetic resonance (NMR) spectroscopy and single crystal X-ray diffraction (SCXRD). The molecular precursors are subjected to controlled thermolysis under mild conditions with the exclusion of exogenous air and moisture, facilitating the removal of the volatile organic ligands and ligand byproducts. The preformed metal-oxygen bond in the precursor, as well as the metal oxidation state, are maintained through the decomposition, forming fully stoichiometric, oxidation-state pure NpO2 and PuO2. Powder X-ray diffraction (PXRD), scanning transmission electron microscopy (STEM), and energy dispersive X-ray spectroscopy (EDS) elemental mapping supported the evaluation of these high-purity materials. This chemistry is applicable to a wide range of metals, including actinides, with accessible tetravalent oxidation states, and provides a consistent route to analytical standards of importance to the field of nuclear nonproliferation, forensics, and fundamental studies.

Modeling and Analysis of Polarization Losses in Solid Oxide Fuel Cells with Siloxane Contamination

In this study, the degradation of the solid-oxide fuel cell (SOFC) nickel-yttria stabilized zirconia anode under decamethyltetrasiloxane (L4) contamination is examined with experiments and modeling. A model is developed for the polarization losses based on the charge transfer coefficient, α, and diffusion layer thickness, δ, and fitted to the experimental data to understand how the siloxane degrades the SOFC performance with time. The results of the model indicate that the total polarization losses increase approximately 44% over the course of the 180 min experiment at 350 mA cm−2. Activation losses dominate the polarization losses initially but decrease in their total contribution while concentration losses increase. Scanning electron microscopy (SEM) with wavelength dispersive X-ray spectroscopy (WDS) elemental mapping indicates that silicon deposition is highest at the outer edge of the anode and forms a barrier layer to fuel diffusion, increasing concentration losses. When the model is applied to other previous D4 and L4 siloxane experiments conducted over a period of 40 h, similar trends in polarization losses are observed. Polarization losses increase more rapidly with D4 compared to L4 siloxane contamination, with concentration losses increasing the fastest with both types of siloxane.

Cerium-modified Bi2FeMoO6: Microstructure, dielectric and optical properties

This paper presents an extensive investigation into the synthesis and characterization of Bi2FeMo1-xCexO6 (x = 0.0, 0.06, and 0.1) double perovskite type ceramic materials, fabricated using a high-temperature solid-state reaction method. The article delves into various aspects of these materials, including their structural, microstructural, dielectric, and optical properties. Structurally, the materials exhibit a rhombohedral crystal structure, having average crystallite sizes of 49.5 nm, 21.8 nm, and 26.4 nm for the respective compositions. Scanning electron microscopy reveals a uniform distribution of cylindrical and fractured spherical-shaped grains, complemented by well-defined grain boundaries. Energy dispersive X-ray spectroscopy analysis and elemental color mapping provide concrete evidence regarding the presence of key elements, such as Bi, Fe, Mo, Ce, and O, affirming the formation of highly dense and pure samples. Dielectric properties are comprehensively characterized across a wide temperature range of 25 °C to 500 °C and frequency range of 1 kHz to 1 MHz, highlighting the occurrence of the Maxwell-Wagner polarization effect at lower frequencies. The impedance study underscores the pivotal role of both grains and grain boundaries in determining the conductivity mechanism, with the x = 0.1 composition exhibiting superior semiconducting characteristics. Further examination of the modulus study and AC conductivity supports this finding. Additionally, the calculation of thermal activation energy suggests that the x = 0.1 composition boasts a more favorable thermally activated relaxation mechanism, rendering it a promising candidate for various device applications. Finally, an assessment of the UV–visible spectra reveals that the x = 0.1 composition possesses an ideal bandgap energy range, making it particularly suited for advanced optoelectronic devices.

Biomass-Derived Hard Carbon and Nitrogen-Sulfur Co-Doped Graphene for High-Performance Symmetric Sodium Ion Capacitor Devices

An inexpensive bio-mass-derived hard carbon from tamarind pods was used as an anode, and nitrogen and nitrogen (N)/sulfur (S) co-doped graphene were used as a cathode for novel hybrid Na-ion supercapacitors. The structural and surface morphological analyses are investigated using a range of techniques. The 3D network of the heteroatom-doped graphene skeleton edges for N and NS-doping conformations were assigned as N-RGOs (N1s-5.09 at.%) and NS-RGOs (N1s-7.66 at.% and S1s-2.22 at.%) based on energy dispersive X-ray spectroscopy elemental mapping. The negative electrode (T-HC) hard carbon was pre-treated by pre-sodiation with a half-cell process by galvanostatic charge–discharge in a sodium-ion battery at 0.01–2.5 V vs. Na/Na+. The T-HC//NS-RGO, T-HC//N-RGO, and T-HC//RGO were used to construct the Na-ion supercapacitor device. In the CV experiments, the electrochemical galvanostatic charge–discharge was studied at 1.0–4.2 V. The specific capacitance was 352.18 F/g for the T.HC/NS-RGO device and 180.93 F/g for the T.HC/N-RGO device; both were symmetric devices. T.HC/NS-RGO device performance revealed excellent cycling stability, with T-HC//NS-RGO showing 89.26% capacitance retention over 5000 cycles. A carbon–carbon symmetric device, such as a Na-ion hybrid capacitor, can exhibit the characteristics of both batteries and supercapacitors for future electric vehicles.

Suzuki hardening and segregation in Co0.95Cr0.8Fe0.25Ni1.8Mo0.475 high-entropy alloys

A Co0.95Cr0.8Fe0.25Ni1.8Mo0.475 high-entropy alloy was heavily cold-rolled and subsequently aged at 773 K. Aging-induced Suzuki hardening was observed. High-angle annular dark-field scanning transmission electron microscopy imaging and the corresponding energy dispersive X-ray spectroscopy elemental distribution mapping suggested the enrichment of Co atoms at stacking faults (SFs), which pinned down partial dislocations and enhanced the resistance of the alloy to plastic deformation. Furthermore, the enrichment of Co and Mo atoms at SFs was observed in a low dislocated, strain-aged specimen. The significant difference in the SF density of the specimens led to difference in segregation. The local stacking fault energy (SFE) with the segregation of Co and Mo atoms was calculated as −30.6 mJ/m2 at the aging temperature. The negative SFE did not restrict the SF expansion, indirectly resulting in the formation of wide SFs.

Dry Reforming of Ethane over FeNi/Al–Ce–O Catalysts: Composition-Induced Strong Metal–Support Interactions

Dry reforming of ethane (DRE) has received significant attention because of its potential to produce chemical raw materials and reduce carbon emissions. Herein, a composition-induced strong metal-support interaction (SMSI) effect over FeNi/Al–Ce–O catalysts is revealed via X-ray photoelectron spectroscopy (XPS), H 2 -temperature programmed reduction (TPR), and energy dispersive X-ray spectroscopy (EDS) elemental mapping. The introduction of Al into Al–Ce–O supports significantly influences the dispersion of surface active components and improves the catalytic performance for DRE over supported FeNi catalysts due to enhancement of the SMSI effect. The catalytic properties, for example, C 2 H 6 and CO 2 conversion, CO selectivity and yield, and turnover frequencies (TOFs), of supported FeNi catalysts first increase and then decrease with increasing Al content, following the same trend as the theoretical effective surface area (TESA) of the corresponding catalysts. The FeNi/Ce–Al 0.5 catalyst, with 50% Al content, exhibits the best DRE performance under steady-state conditions at 873 K. As observed by with in situ Fourier transform infrared spectroscopy (FTIR) analysis, the introduction of Al not only increases the content of surface Ce 3+ and oxygen vacancies but also promotes the dispersion of surface active components, which further alters the catalytic properties for DRE over supported FeNi catalysts.

Experimental observation of enhanced reverse saturable absorption in Bi 2 Se 3 nanoplates doped PMMA thin film

By employing the ultrafast Z-scan technique, we characterize the nonlinear absorption property of PMMA/Bismuth Selenide (Bi 2 Se 3) composite with varying concentrations. We report the fabrication of bismuth selenide (Bi 2 Se 3) nanoplate (topological insulator (TI)) doped poly methyl methacrylate (PMMA) thin film with varying doping concentrations. The effect of Bi 2 Se 3 on structural and linear properties of PMMA thin film has been investigated through UV-Vis spectroscopy, scanning electron microscope (SEM), and Energy dispersive x-ray spectroscopy (EDS) elemental mapping techniques. Furthermore, the nonlinear optical absorption property of PMMA and PMMA/Bi 2 Se 3 composites have been performed employing a single beam open aperture z-scan technique under femtosecond laser excitation at 750 nm. The z-scan results exhibit an enhancement of reverse saturable absorption (RSA) property with an increased nonlinear absorption coefficient (β) of the PMMA/Bi 2 Se 3 composites compared to pure PMMA measured with intensity at 320 GW cm−2. The RSA response gets enhanced with the increase in doping concentration also. Our experimental observations reveal that PMMA/Bi 2 Se 3 composite can provide a promising platform to realize photonic devices such as optical limiters, optical switches, and efficient protectors from high power sources.

Metallurgical aspects and electrical resistivity of hardfaced pure copper layers over AISI 347 with cold metal transfer process

Pure Copper having excellent electrical conductivity was deposited over AISI 347 substrate using Cold Metal Transfer (CMT) process to obtain quality weld overlays without defects. To improve the electrical conductivity post heat-treatment was performed. The microstructural examination revealed the presence of Cu-FCC and Fe-FCC along with retained delta ferrite at the bi-metallic interface. Also, the existence of bi-phasic spherulites rich in Fe and Cr were noticed in the weld overlay side while Cu spherulites were observed in the AISI 347 substrate adjacent to the bi-metallic interface. Energy Dispersive X-Ray Spectroscopy (EDS) elemental mapping and line scan data confirmed the presence of spherulites due to solid-state diffusion near the interface. The spherulite size was reduced in the heat-treated weld overlays and a small fraction of Cu spherulites were observed in the interface. The microhardness of the as-deposited and heat-treated weld overlays revealed the transition of elements at the bi-metallic interface. Post heat-treatment of Cu weld overlays improved the electrical conductivity significantly in comparison to the as-deposited ones. These electrical measurements suggest that pure Cu weld overlays with sufficient conductivity shall be attained with the CMT process for electrical and power generation applications.

Conversion of alkaline characteristics of bauxite residue by mechanical activated pretreatment: Implications for its dealkalization

Following the strict environmental policies of various countries, the strong alkalinity of bauxite residue (BR) has become a worldwide problem limiting the sustainable development of the global alumina industry. Continuous conversion of solid-phase alkalinity to free alkali is a major challenge for BR dealkalization to reduce its environmental impact. This work aimed to investigate the effect of mechanical grinding pretreatment on the transformation mechanisms of alkaline solids to free alkali at the BR interface under acids leaching, by monitoring the morphology, phase, and speciation transformations of Al and Si using primarily cross-section scanning electron microscopy−energy dispersive X-ray spectroscopy (SEM-EDS) elemental mapping, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS). The results indicated that particle grinding wrapped some of the alkaline minerals inside the particles to inhibit its release process. The leaching kinetics revealed the order of the buffering effect of minerals against acids leaching is firstly dissolved by minerals containing Na and Ca via the ion-exchange process, followed by Si and Al through the hydrolysis of the desilicated products. The mineral dissemination characteristics and surface compositions further confirmed the undissolved minerals block the interface reaction between embedded alkaline solids and acids to result in the difficult reaction dissolution of alkaline minerals, which is induced by ball milling. This novel approach provides new insight into the efficient dealkalization of BR on a large scale in the industry.

Regulating the nanoscale intimacy of metal and acidic sites in Ru/γ-Al2O3 for the selective conversions of lignin-derived phenols to jet fuels

Catalytic hydrodeoxygenation (HDO) of biomass-derived oxy-compounds to advanced hydrocarbon fuels usually requires bifunctional catalysts containing metals and acidic sites. The appropriate tuning of metal and/or acidic active sites at interfaces of bifunctional catalysts can significantly improve catalyst activity and product selectivity. Here, 4-trifuoromethyl salicylic acid (TFMSA), as a hydrothermal stable organic acid, was employed to tailor the bifunctional interface of Ru/γ-Al2O3 to enhance the catalytic performance on converting lignin-derived phenols to jet fuel range cycloalkanes. More than 80% phenol was converted into cyclohexane at 230 °C for 1 h over Ru/γ-Al2O3 modified by TFMSA, which was about three times higher than that over unmodified Ru/γ-Al2O3. X-ray diffraction (XRD), Transmission electron microscope (TEM), H2 chemisorption, and energy dispersive X-ray spectroscopy (EDS) elemental mapping results indicated that Ru nanoparticles and TFMSA were well distributed on γ-Al2O3, and a nanoscale intimacy between Ru and TFMSA was reached. Meanwhile, Fourier transform infrared spectroscopy after pyridine adsorption (Py-FT-IR) analysis proved that Brønsted acidic sites on the catalytic interfaces of TFMSA modified Ru/γ-Al2O3 had been improved. Moreover, the kinetic and density functional theory (DFT) results suggested that the synergistic effects of adjacent Ru nanoparticles and acidic sites were crutial for promoting the rate-limiting conversion step of phenol HDO to cyclohexane.

A novel biomass thermoresponsive konjac glucomannan composite gel developed to control the coal spontaneous combustion: Fire prevention and extinguishing properties

Spontaneous combustion in coal mines continues to pose a significant risk. A novel biomass composite thermoresponsive gel produced by mixing konjac glucomannan (KGM) with fly ash (FA) was prepared to prevent coal spontaneous combustion. The composite gel had a controllable gelation time, a good seepage capacity, a high water retention capacity, a good combustion inhibition effect and an excellent fire extinguishing effect. Scanning electron microscopy indicated that the FA strongly interfacially adhered to the three-dimensional KGM framework and the gel wrapped around the coal surfaces well. Energy dispersive X-ray spectroscopy element mapping indicated that the FA was mixed uniformly with the KGM gel. The KGM@FA gel oxidation characteristics were analyzed by thermogravimetry infrared analysis and low-temperature coal oxidation system. The KGM@FA gel was found to effectively inhibit coal temperature increases, heat accumulation and CO generation during the process of oxidation and combustion, which would decrease the likelihood of coal spontaneous combustion. Fire-extinguishing experiments indicated that the gel covered the surfaces of burning coal well and markedly decreased the fire temperature and CO emissions and therefore stably extinguished the fire without combustion restarting. The KGM@FA gel is therefore an effective fire prevention and extinction material.

Surface conversion of single-crystal Bi2Se3 to β-In2Se3

In this work, we demonstrate that the surface layers of single-crystal layered-2D Bi2Se3 can be converted to layered-2D rhombohedral β-In2Se3 by annealing under a trimethylindium (TMIn) flux. Samples were prepared in a metalorganic chemical vapor deposition (MOCVD) chamber, then transferred under vacuum to a surface analysis chamber for analysis with low-energy electron diffraction (LEED) and Auger electron spectroscopy. Additional ex situ characterization included x-ray diffraction, transmission-electron microscopy (TEM), energy dispersive x-ray spectroscopy (EDS) elemental mapping, and Raman spectroscopy. The resulting single-crystal β-In2Se3 adopts the rhombohedral crystal structure (space group R-3m) and orientation of the underlying Bi2Se3, and the excess Bi atoms generated by this process create an underlying region of Bi-rich BixSey. Due to the difference in bandgap between Bi2Se3 and In2Se3, this conversion reaction presents a pathway to lateral heterojunctions if only selected regions are converted by masking the surface to spatially define the TMIn exposure. The conversion may also have implications for heteroepitaxy, because the in-plane lattice constants of Bi2Se3 and In2Se3 (0001) surfaces match those of InP and GaAs (111), respectively, and the natural cleavage planes of a layered-2D crystal facilitate substrate removal and reuse.

Modeling, Optimization and Performance Evaluation of TiC/Graphite Reinforced Al 7075 Hybrid Composites Using Response Surface Methodology.

The tenacious thirst for fuel-saving and desirable physical and mechanical properties of the materials have compelled researchers to focus on a new generation of aluminum hybrid composites for automotive and aircraft applications. This work investigates the microhardness behavior and microstructural characterization of aluminum alloy (Al 7075)-titanium carbide (TiC)-graphite (Gr) hybrid composites. The hybrid composites were prepared via the powder metallurgy technique with the amounts of TiC (0, 3, 5, and 7 wt.%), reinforced to Al 7075 + 1 wt.% Gr. The microstructural characteristics were investigated by optical microscopy, scanning electron microscopy (SEM), X-ray diffraction (XRD) and energy dispersive X-ray spectroscopy (EDS) elemental mapping. A Box Behnken design (BBD) response surface methodology (RSM) approach was utilized for modeling and optimization of density and microhardness independent parameters and to develop an empirical model of density and microhardness in terms of process variables. Effects of independent parameters on the responses have been evaluated by analysis of variance (ANOVA). The density and microhardness of the Al 7075-TiC-Gr hybrid composites are found to be increased by increasing the weight percentage of TiC particles. The optimal conditions for obtaining the highest density and microhardness are estimated to be 6.79 wt.% TiC at temperature 626.13 °C and compaction pressure of 300 Mpa.

Gravity-driven ceramic membrane (GDCM) filtration treating manganese-contaminated surface water: Effects of ozone(O3)-aided pre-coating and membrane pore size

Achieving adequate manganese removal during water treatment is a challenging process. This study aimed to assess the effectiveness of gravity driven ceramic membrane (GDCM) filtration in the elimination of manganese from surface water. The impact of membrane pre-modification with birnessite and molecular weight cut-off on long-term water treatment efficiency was investigated by assessing filtration units with 300 kDa virgin membrane (300 kDa-blank), 300 kDa membrane pre-coated with manganese oxides (300 kDa-MnOx), and 15 kDa virgin membrane (15 kDa-blank). The results of 300 kDa-blank and 300 kDa-MnOx indicated that depositing manganese oxides (produced via ozone (O3) oxidation) prior to water treatment was conducive to ripening of cake layer which played a major role in Mn removal. Reducing membrane molecular cut-off from 300 to 15 kDa also significantly reduced permeate Mn concentration, achieving a removal efficiency of 75% at the end of the trial (highest of all the units). Relative to 300 kDa-blank, the greater manganese removals in the other two systems can be attributed to 1) the long hydraulic retention times resulting from the higher membrane resistance, and 2) the higher abundance of biologically produced Birnessite materials in the cake layers for manganese oxidation. Raman analysis and X-ray diffraction analysis showed that 15 kDa-blank achieved the highest level of Birnessite production and most cake materials featured a flower-like structure and relatively small size (as shown under a scanning electron microscope and Energy Dispersive X-Ray Spectroscopy element mapping analysis), suggesting a higher surface area for Mn oxidation.

Green fabrication of reduced graphene oxide decorated with Ag nanoparticles (rGO/Ag NPs) nanocomposite: A reusable catalyst for the degradation of environmental pollutants in aqueous medium

In this current work, a bio-inspired green approach has been followed to synthesize Ag nanoparticles (NPs), which were immobilized over reduced graphene oxide (rGO) as a suitable support. In the stepwise preparation of the bionanocomposite (rGO/Ag NPs) by using Menthapulegium flower extract, initially graphene oxide (GO) was reduced to rGO followed by in situ reduction of Ag+ ions to Ag NPs. In these reductions, different biomolecules such as, polyphenols, flavonoids, alkaloids, terpenoids and mild acids were employed as the natural reductant. The oxygenated functions in the aforementioned biomolecules, efficiently, assisted the capping and stabilizing the AgNPs. The as-synthesized nanocomposite was fully characterized using different techniques such as, UV–Vis spectroscopy, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), wavelength dispersive X-ray spectroscopy (WDX) elemental mapping, transmission electron microscopy (TEM), X-ray diffraction (XRD) and inductively coupled plasma (ICP). Diameter of the biosynthesized Ag NPs were found to be in the range of 20–25 nm. The constituent elements were found to be homogeneously dispersed as found from elemental mapping study. This novel prepared nano-composite showed excellent water dispersibility due to the hydrophilicity of biomolecules attached to them, which is essential criterion in heterogeneous catalysis. This composite was used as an effective catalyst in the reductive degradation of water contaminated by organic dyes such as methyl Orange (MO) and rhodamin B (RhB) using NaBH4 as reductive agent at room temperature. The progress of reduction was monitored by UV–Vis spectroscopy. Both the reactions followed pseudo-unimolecular kinetics and the corresponding rate constants were found being 0.098 s−1 and 0.096 s−1 respectively. The material was significantly robust as justified by the leaching as well as hot-filtration tests and its reusability for several times without any appreciable loss in its activity.

Temperature-dependent interfacial behaviour of Au@SiO2 core shell nanoparticles on Si3N4 support film

Structural, chemical, and thermodynamic behaviours of metallic nanostructures surrounded by a variety of ceramic/refractory materials play a crucial role in their high-temperature applications. In this work, we report the effect of high-temperature annealing on a system of Au@SiO2 core-shell nanoparticles dispersed on Si3N4 grids. The thermal degradation of the Au–SiO2–Si3N4 system has been explained using minute compositional changes at different interfaces involving Au–SiO2, SiO2–Si3N4 and Au–Si3N4. High Angle Annular Dark Field Imaging coupled with Energy Dispersive X-ray Spectroscopy elemental mapping technique has been used for the same. Possible reactions among SiO2 and Si3N4 substrate with the aid of Au at high temperature leading to thermal decomposition of the system have been explained using High-Resolution Transmission Electron Microscopy and Selected Area Electron Diffraction analysis.

Effect of nano Al2O3 coated Ag reinforced Cu matrix nanocomposites on mechanical and tribological behavior synthesis by P/M technique

In this study, copper powder was reinforced with different weight percentages of Al2O3 particles (0, 5, 10, and 15 wt.% Al2O3 coated Ag) to produce Cu-Al2O3 composites by mechanical alloying and uniaxial cold pressing/sintering route. Electro-less deposition was used to coat Al2O3 particles with Ag. The microstructure of the consolidated samples was investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX) elemental mapping. The porosity, microhardness, and wear behavior of the consolidated samples were also investigated as a function of Al2O3 content. The EDX mapping images reveal that the Al2O3 reinforcement particles were homogeneously distributed into the Cu matrix. Microstructural analysis shows that the addition of Al2O3 coated Ag particles improves density of the composites coating. SEM micrographs result shows that slight porosities exist in the composites produced. Furthermore, the average hardness of the composite coatings varies from 72.3 to 187.6 HV as Al2O3 content increases from 0 to 15 wt.%. The wear test results showed that the composite with higher Al2O3 content 15 wt.% showed the best wear resistance.

High-entropy sesquioxide X2O3 upconversion transparent ceramics

In this study, a high-entropy approach was used to design a highly transparent (81.3% in-line transmittance) sesquioxide X2O3 ceramics, in which a single-phase solid solution, with the general formula (Lu0.2Y0.395Gd0.2Yb0.2Tm0.005)2O3, was obtained after sintering under vacuum with La2O3 and ZrO2 as the sintering additives. Upconversion emission from Tm3+ ion at 485 nm was demonstrated upon the 980 nm laser emission excitation as a result of cooperative energy transfer from the Yb3+ ions. High-resolution scanning electron microscope (SEM) and Energy Dispersive X-Ray Spectroscopy (EDS) elemental mapping showed that the obtained transparent ceramics were pore-free and without segregation of different elements.

Improved Catalytic Performance of Ethane Dehydrogenation in the Presence of CO2 over Zr-Promoted Cr/SiO2.

The Zr-, Ce-, Sr-, and Sn-promoted Cr/SiO2 catalysts were prepared by the incipient wetness impregnation method, then characterized by N2 adsorption/desorption, X-ray diffraction, X-ray photoelectron spectroscopy, H2-TPR, CO2-TPD, UV–vis, high-angle annular dark-field imaging–scanning transmission electron microscopy—energy dispersive X-ray spectroscopy elemental mapping, Raman, and thermogravimetric techniques to study the structural evolution under the preparation/reaction conditions, and applied to catalyze ethane oxidative dehydrogenation with CO2. The results suggested that the Cr6+ species were indispensable for activating the dehydrogenation reaction thanks to the oxidation–reduction cycle between Cr6+ and Cr3+. The type of the promotor also affected significantly the ability of replenishing the lattice oxygen through the disassociation of CO2, leading to the different catalytic performances. The Zr-promoted sample had the best performance in converting the reactants as well as the catalytic stability.

Tribochemistry of TaN, TiAlN and TaAlN coatings under ambient atmosphere and high-vacuum sliding conditions

Tribochemical analysis of monolithic TaN, TiAlN, and TaAlN coatings deposited by reactive magnetron sputtering onto 316LN stainless steel (SS) substrates are described. Tribology experiments were carried out in ambient atmospheric and high-vacuum sliding conditions to investigate the tribo-atmospheric dependent friction and wear characteristics of these coatings. The lower friction coefficient and improved wear-resistant properties were observed for TaN and TiAlN coatings in the humid atmosphere than in high-vacuum testing condition. Interestingly, lower friction and wear resistance properties of TaAlN coated SS are significantly enhanced in atmospheric as well as high-vacuum sliding conditions because of their highly dense and fine-grained microstructure with stable cubic B1 TaAlN phase. Energy dispersive X-ray spectroscopy elemental mapping and micro-focused X-ray photoelectron spectroscopy were carried out on the wear tracks to explore the comprehensive tribo-environment dependent tribochemistry. Formations of alumina (Al2O3) rich tribolayer reduced the friction and enhanced the wear resistance of TaAlN/SS sample tested in atmospheric condition; whereas this coating is highly stable in the high-vacuum condition with higher wear resistance.