The CATOFIN© process produces propylene from propane using a CrOx /Al2O3 catalyst. Despite its use, there are still uncertainties surrounding the nature of Cr species formed during synthesis, regeneration, and aging. It has been observed that ppm levels of Cr2O3 can be oxidized to Cr(VI) in air; however, when Cr2O3 is in direct contact with Al2O3, Cr(VI) formation increased more than 100-fold. To confirm physical contact between Cr2O3 and Al2O3 results in increased Cr(VI) formation, Cr2O3 and Cr2O3/Al2O3 samples were synthesized, calcined, and characterized. Catalytic activity measurements confirm propylene selectivity inversely tracks with Cr(VI). Wet chemical titration and X-ray absorption spectroscopy (XAS) quantified and determined the structure of the Cr(VI) species. FEFF X-ray absorption near edge structure simulations determined the potential sensitivity of the XAS to the presence of Al3+/Cr3+ neighboring atoms. XAS correlated to FEFF simulations suggested that Al3+xCr3+2−xCr6+3O12 comprises a significant fraction of the Cr(VI) species formed.

The local structure, many-body effect, and charge redistribution of Pt and Ni in Pt–Ni alloys (Pt–Ni = 3:1, 1:1, and 1:3) have been studied by X-ray absorption spectroscopy and X-ray photoelectron spectroscopy (XPS). It is found that upon alloying, the skew many-body line shape of Pt 4f peaks in Pt metal becomes more symmetric in Pt alloys, while the associated Ni 2p peaks become more asymmetric and are accompanied by more intense shake-up satellites. This is because Pt gains while Ni loses valence d electrons, resulting in different phase shift of electrons scattered near the Fermi level. Meanwhile, the redistribution of the density of states (DOS) is confirmed by experiment and density functional theory calculations, suggesting that the centroid Ni d states tend to shift closer to the Fermi level, while Pt d states are down-shifted in alloys. This DOS redistribution causes the anomalous binding energy shift for both Pt and Ni core levels in XPS, which has not been well explained in the literature. These findings also suggest that the d-band centroid shift originates from two different mechanisms for Pt-based alloys and Pt-skinned core–shell catalysts.

Ancient dental calculus research currently relies on destructive techniques whereby archeological specimens are broken down to determine their contents. Two strategies that could partly remediate a permanent loss of the original sample and enhance future analysis and reproducibility include (1) structural surface characterization through spectroscopy along with crystallographic and spectroscopic analysis of its molecular structure, and (2) surface decontamination protocols in which the efficacy of cleaning dental calculus prior to extraction is demonstrated. Dental calculus provides ancient starch research a niche where granules may be adsorbed to minerals, coated, overgrown, entrapped, and/or protected from chemical degradation. While encapsulation offers protection from degradation, it does not shield the sample’s surface from contamination. The most common approach to retrieving microbotanical particles from archeological calculus has been the direct decalcification of the sample, after a cleaning stage variously consisting of immersion in water, acids, and mechanical dislodgment via gas, sonication, and/or toothbrushes. Little is known about the efficiency of these methods for a complete removal of sediment/soil and unrelated microbotanical matter. In this paper, controlled laboratory experimentation leads to chemical structural characterization and a decontamination protocol to eradicate starch granules. Several concentrations of acids, bases, and enzymes were tested at intervals to understand their potential to gelatinize and fully destroy starch granules; arriving at a procedure that effectively eradicates modern starch prior to dissolution without damaging the matrix or entrapped starch microremains. This is the first attempt at creating synthetic calculus to understand and systematically test effective decontamination protocols for ancient starch research.

This work investigates the wear characteristics of two different coating systems deposited on cemented carbide tools and used in the finish turning of an Inconel DA718 aerospace alloy. The two coatings were: (a) a new nanocomposite multilayer Ti25Al65Cr10N/Ti20Al52Cr22Si8N PVD coating, and (b) an AlTiN benchmark coating. Four different cutting speeds (60, 80, 100 and 120 m/min) were employed during this study. Wear behavior was characterized using three-dimensional volumetric wear progression, as well as flank wear progression, wear mechanism evaluation, and cutting force analysis. A tool life predictive model was created for this process based on both 3D and flank wear patterns. The tool with the nanocomposite coating outperformed the AlTiN benchmark coating under higher speed conditions, and both tools performed best under a surface speed of 80 m/min. The primary wear mechanisms responsible for the performance of these coatings differ in relation to the adaptive behavior of the nanocomposite coating. In addition, tool wear predictions modeled under different cutting conditions demonstrated an estimated accuracy of 93%.

Hard dry machining of AISI T1 and AISI D2 steels at comparable hardness (around 59 HRC) were performed at 50m/min, 80m/min and 100m/min cutting speeds separately with uncoated alumina ceramic tool inserts (Al2O3+TiC), in order to study the effect of cutting conditions on the generation of tribofilms. Comprehensive assessment of uncoated ceramic inserts in machining of T1 and D2 at different cutting speeds was made by optical microscope, scanning electron microscope and X-ray photoelectron spectroscopy. It was shown that higher cutting speeds increased the formation of thermal protective and/or lubricating tribofilms. In machining D2 steel, more intensive formation of Cr-O tribo-oxides brought a lower wear rate; while in cutting T1 steel, a higher amount of W-O tribofilms generation provided better lubrication. At higher cutting speeds, wear/friction behaviour changes were attributed to differences in two factors: first, from a traditional micro-scale standpoint, the distribution of carbide within steels and the accumulation of thermal and mechanical damages during different cutting conditions; second, from a new nano-scale viewpoint, the generation of protective/lubricating tribofilms due to change of machining conditions.

Experimental investigations of nano-scale spatio-temporal effects that occur on the friction surface under extreme tribological stimuli, in combination with thermodynamic modeling of the self-organization process, are presented in this paper. The study was performed on adaptive PVD (physical vapor deposited) coatings represented by the TiAlCrSiYN/TiAlCrN nano-multilayer PVD coating. A detailed analysis of the worn surface was conducted using scanning electron microscopy and energy dispersive spectroscopy (SEM/EDS), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and Auger electron spectroscopy (AES) methods. It was demonstrated that the coating studied exhibits a very fast adaptive response to the extreme external stimuli through the formation of an increased amount of protective surface tribo-films at the very beginning of the running-in stage of wear. Analysis performed on the friction surface indicates that all of the tribo-film formation processes occur in the nanoscopic scale. The tribo-films form as thermal barrier tribo-ceramics with a complex composition and very low thermal conductivity under high operating temperatures, thus demonstrating reduced friction which results in low cutting forces and wear values. This process presents an opportunity for the surface layer to attain a strong non-equilibrium state. This leads to the stabilization of the exchanging interactions between the tool and environment at a low wear level. This effect is the consequence of the synergistic behavior of complex matter represented by the dynamically formed nano-scale tribo-film layer.

In this work, machining of the superduplex stainless steel was investigated using cemented carbide turning inserts with chemical vapor deposited (CVD) TiCN + Al 2 O 3 as well as physical vapor deposited (PVD) TiCN and AlTiN coatings. These three coating system were tested during finish turning operation of superduplex stainless steel. It has been found that unfavorable friction and wear conditions were observed when TiCN- and TiCN + Al 2 O 3 -coated tools were used. On the other hand, the AlTiN-coated tool showed a self-adaptive behavior through the formation of tribo-film of aluminum oxide that improves frictional conditions and, consequently, wear resistance during machining of SDSS. This behavior shows that the tool life for inserts coated with PVD AlTiN was approximately two times higher than CVD TiCN + Al 2 O 3 . Another important result that can be observed in this work is related with the surface integrity that was improved when machined with cutting inserts coated with PVD AlTiN.

Tribological phenomena and tool wear mechanisms during machining of hard-to-cut TiAl6V4 aerospace alloy have been investigated in detail. Since cutting tool wear is directly affected by tribological phenomena occurring between the surfaces of the workpiece and the cutting tool, the performance of the cutting tool is strongly associated with the conditions of the machining process. The present work shows the effect of different machining conditions on the tribological and wear performance of TiB2-coated cutting tools compared to uncoated carbide tools. FEM modeling of the temperature profile on the friction surface was performed for wet machining conditions under varying cutting parameters. Comprehensive characterization of the TiB2 coated vs. uncoated cutting tool wear performance was made using optical 3D imaging, SEM/EDX and XPS methods respectively. The results obtained were linked to the FEM modeling. The studies carried out show that during machining of the TiAl6V4 alloy, the efficiency of the TiB2 coating application for carbide cutting tools strongly depends on cutting conditions. The TiB2 coating is very efficient under roughing at low speeds (with strong buildup edge formation). In contrast, it shows similar wear performance to the uncoated tool under finishing operations at higher cutting speeds when cratering wear predominates.

In this study, the wear mechanisms and tribological performance of uncoated and coated carbide tools were investigated during the turning of super duplex stainless steel (SDSS)—Grade UNS S32750, known commercially as SAF 2507. The tool wear was evaluated throughout the cutting tests and the wear mechanisms were investigated using an Alicona Infinite Focus microscope and a scanning electron microscope (SEM) equipped with energy dispersive spectroscopy (EDS). Tribo-film formation on the worn rake surface of the tool was analyzed using X-ray Photoelectron Spectroscopy (XPS). In addition, tribological performance was evaluated by studying chip characteristics such as thickness, compression ratio, shear angle, and undersurface morphology. Finally, surface integrity of the machined surface was investigated using the Alicona microscope to measure surface roughness and SEM to reveal the surface distortions created during the cutting process, combined with cutting force analyses. The results obtained showed that the predominant wear mechanisms are adhesion and chipping for all tools investigated and that the AlTiN coating system exhibited better performance in all aspects when compared with CVD TiCN + Al2O3 coated cutting insert and uncoated carbide insert; in particular, built-up edge formation was significantly reduced.

In addition to the bulk properties of a workpiece material, characteristics of the tribofilms formed as a result of workpiece material mass transfer to the friction surface play a significant role in friction control. This is especially true in cutting of hardened materials, where it is very difficult to use liquid based lubricants. To better understand wear performance and the formation of beneficial tribofilms, this study presents an assessment of uncoated mixed alumina ceramic tools (Al2O3+TiC) in the turning of two grades of steel, AISI T1 and AISI D2. Both workpiece materials were hardened to 59 HRC then machined under identical cutting conditions. Comprehensive characterization of the resulting wear patterns and the tribofilms formed at the tool/workpiece interface were made using X-ray Photoelectron Spectroscopy and Scanning Electron Microscopy. Metallographic studies on the workpiece material were performed before the machining process and the surface integrity of the machined part was investigated after machining. Tool life was 23% higher when turning D2 than T1. This improvement in cutting tool life and wear behaviour was attributed to a difference in: (1) tribofilm generation on the friction surface and (2) the amount and distribution of carbide phases in the workpiece materials. The results show that wear performance depends both on properties of the workpiece material and characteristics of the tribofilms formed on the friction surface.

An extensive study of surface/interface phenomena during wear of an adaptive TiAlCrSiYN/TiAlCrN nano‐multilayer coating deposited using physical vapor deposition was undertaken under increasingly severe tribological conditions associated with dry end milling of H13 hardened tool steel. The results of FEM modeling on the temperature/stress distribution at different cutting speeds outline actual cutting conditions on the both rake and flank frictional surfaces of the coated tool. Studies of the surface/interface phenomena were made by means of SEM/high‐resolution transmission electron microscopy/XPS analyses. Results demonstrate that intensifying tribological conditions facilitates improved wear performance of the adaptive coating layer. In extreme tribological conditions of ultra‐performance machining (cutting speed of 500 m/min), the self‐organization process establishes entirely through the formation of a nano‐scale layer of dynamically re‐generating tribo‐ceramic films. The formation of these surface nano‐films results in exceptionally efficient protection of the underlying coating layers. In response to the extreme external environment, the coating layer remained almost undamaged during a long run, demonstrating the capacity to efficiently replenish necessary tribo‐ceramic films. In this way, interconnection of various surface and undersurface processes is established in the hierarchically structured tribo‐films/coating layer. This integral performance is responsible for exceptional wear resistance under intensifying and extreme tribological conditions. Copyright © 2016 John Wiley & Sons, Ltd.

In this paper, we will develop a strategy for controlling the self-organized critical process using the example of extreme tribological conditions caused by intensive build-up edge (BUE) formation that take place during machining of hard-to-cut austentic superduplex stainless steel SDSS UNS32750. From a tribological viewpoint, machining of this material involves intensive seizure and build-up edge formation at the tool/chip interface, which can result in catastrophic tool failure. Built-up edge is considered to be a very damaging process in the system. The periodical breakage of the build-ups may eventually result in tool tip breakage and, thereby, lead to a catastrophe (complete loss of workability) in the system. The dynamic process of build-up edge formation is similar to an avalanche. It is governed by stick-slip phenomenon during friction and associated with the self-organized critical process. Investigation of wear patterns on the frictional surfaces of cutting tools using Scanning Electron Microscope (SEM), combined with chip undersurface characterization and frictional (cutting) force analyses, confirms this hypothesis. The control of self-organized criticality is accomplished through application of a nano-multilayer TiAl60CrSiYN/TiAlCrN thin film Physical Vapor Deposition (PVD) coating containing elevated aluminum content on a cemented carbide tool. The suggested coating enhanced the formation of protective nano-scale tribo-films on the friction surface under operation. Moreover, machining process optimization contributed to further enhancement of this beneficial process, as evidenced by X-ray Photoelectron Spectroscopy (XPS) studies of tribo-films. This resulted in a reduction of the scale of the build ups leading to overall wear performance improvement. A new thermodynamic analysis is proposed concerning entropy production during friction in machining with buildup edge formation. This model is able to predict various phenomena and shows a good agreement with experimental results. In the presented research we demonstrated a novel experimental approach for controlling self-organized criticality using an example of the machining with buildup edge formation, which is similar to avalanches. This was done through enhanced adaptive performance of the surface engineered tribo-system, in the aim of reducing the scale and frequency of the avalanches.

A nano- multilayer TiAlCrSiYN/TiAlCrN was deposited by Physical Vapor Deposition (PVD) on cemented carbide turning inserts. Assessment of the performance of the coated inserts in machining of DA718 Inconel was made at various cutting speeds during the initial, running-in stage of wear. Three types of machining conditions were used: i. Regular cutting speed (40m/min) used in industrial practice; ii. Higher cutting speed of 60m/min, and iii. Accelerated (higher speed followed by regular cutting speed). Comprehensive characterization of the tribofilms formed on the surface of the worn cutting tools was made using Auger Electron Spectroscopy and X-ray Photoelectron Spectroscopy analyses. SEM/EDS elemental mapping was used for evaluation of the wear patterns. It was shown that an initial short-term increase in the cutting speed during the running-in stage (condition iii) noticeably improves tool life. This is because during initial cutting at high speed, enhanced formation of protective/lubricious tribo-ceramic films on the friction surface takes place, with the subsequent slowdown in speed preventing total wearing out of the beneficial tribofilms. In this way, the tribofilm formation process can be enhanced at the start of the process and the benefits of these films can be realized over the life of the tool.

Rhodium complexes functionalized by N-heterocyclic carbene ligands react with dioxygen to form adducts. Depending on the specifics of the ancillary ligands, oxygen binds to Rh either as a peroxide to form a fully oxidized Rh(III) complex, or as singlet dioxygen in a Rh(I) square planar complex. We have shown through analysis of a series of compounds, some previously published and some novel, that the presence of additional ligands that would support the formation of an octahedral geometry, as typically found with Rh(III) complexes, is critical for formation of the peroxide. In addition, we have demonstrated through DFT studies, that the potential energy surface with regard to the O-O bond length is relatively shallow, which provides a rationale for the distribution of bond lengths observed for apparently similar complexes analyzed by crystallography.

Mononuclear cationic rhodium complexes of dioxygen have been synthesized and characterized. Crystallographic, spectroscopic, and computational results support the conclusion that these complexes are best described as Rh-III{O-2(2-)} (rhodium(III) peroxo) complexes, in contrast to recently reported neutral analogues that are best described as Rh-I(O-1(2)) adducts. The nature of the ligand trans to the O-2 ligand is crucial in defining the electronic nature of the RhO2 bonding. It is determined that pi-donor ligands such as the halides-in conjunction with sufficient steric bulk-can stabilize the formation of Rh-I{O-1(2)}. adducts, whereas stronger field ligands lead to the stabilization of asymmetric O-2 binding that ultimately favors formation of higher coordinate Rh-III peroxo species. The factors that control the relative stabilization of Rh-III{O-2(2-)} versus Rh-I{O-1(2)} species are related to the well established Dewar-Chatt-Duncanson model that has been successfully used to describe the bonding in isoelectronic transition metal alkene complexes. The specific factors that control the stabilization of one electromer (resonance structure) over another are explored and discussed in detail.

Metal complexation can have a major influence on the antiviral and coreceptor binding properties of cyclam and bicyclam macrocycles. We report the synthesis of the vanadyl cyclam complexes [V((IV))O(cyclam)SO(4)] (1) and [V((IV))O(cyclam)Cl]Cl (2) and the analogous xylylbicyclam sulfato (3) and chlorido (4) complexes. The X-ray crystal structures of 1.1.33CH(3)OH and 2.CH(3)OH.1.5H(2)O show short V=O bonds (1.6093(19) and 1.599(3) A, respectively) with monodentate sulfate H-bonded to ring NH groups for 1, but a long V-Cl bond (2.650(12) A) for 2. The solid-state structures of 3 and 4 were compared to those of 1 and 2 using vanadium K-edge extended X-ray absorption fine structure (EXAFS) data. These suggested that complex 4 was oligomeric and contained bridging chlorido ligands. Electron paramagnetic resonance (EPR) studies suggested that the SO(4)(2-) (from 1) and Cl(-) (from 2) ligands are readily substituted by water in solution, whereas these remain partially bound for the V(IV) xylylbicyclam complexes 3 and 4. The vanadyl xylylbicyclam complexes were highly active against HIV-1 (III(B)) and HIV-2 (ROD) strains with IC(50) values in the range 1-5 microM for 3 and 0.1-0.3 microM for 4; in contrast the vanadyl cyclam complexes 1 and 2 were inactive. The factors that contribute to the activity of these complexes are discussed. Studies of vanadyl cyclam docked into a model of the human CXCR4 coreceptor revealed that the coordination of vanadium to the carboxylate of Asp171 may be accompanied by H-bonding to the macrocycle and an attractive V=O...H interaction involving the backbone Trp195 alpha-carbon proton of CXCR4. In addition, hydrophobic interactions with Trp195 are present. Both ring configuration and the xylyl linker may play roles in determining the higher activity of the bicyclam complexes.

The nature of organic species associated with clay minerals plays a significant role in several processes, from hydrocarbon recovery in oil sands to contaminated soil remediation and water treatment. In this work, we address the use of scanning transmission X-ray microscopy (STXM) in conjunction with near edge X-ray absorption fine structure (NEXAFS) spectroscopy to study the microstructure and chemistry of organic–clay associations in situ. A model system based on methylene blue and illite is used to explore the sensitivity of NEXAFS microscopy to these interactions, and to identify and resolve experimental challenges in these measurements. We find that sample contamination from X-ray induced photodeposition is a significant problem in STXM microscopy, but also that this problem can be substantially reduced with a liquid nitrogen cooled anticontaminator. With appropriate sample preparation and experimental procedures, we find that STXM microscopy is sensitive to thin carbon adsorbates on clay surfaces.