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Performance of vacuum plasma spray and HVOF bond coatings at 900° and 1100 °C
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Bridging the Void: Halogen Bonding and Aromatic Interactions to Program Luminescence and Electronic Properties of π -Conjugated Materials in the Solid State
π-Conjugated materials are promising candidates for emerging organic optoelectronic devices empowered by molecular design. The unsolved challenges of predicting and controlling their packing as solids, central to their properties and performance, currently limits their practical application. As noncovalent interactions drive packing, control over such interactions are critical to bridging from chemical structure to functional properties. In molecular crystals, halogen bonding and interactions of aromatic rings have emerged as versatile tools for noncovalent control with tailored luminescence and electronic properties. Here, we describe how the interplay of these directional and tunable interactions can engineer properties, including stimuli-responsive behavior. Specifically, halogen bonding can provide robust designs for directing 2D molecular assembly, whereas the intentional interactions of aromatic rings can yield metastable, switchable packing modes, as well as programmed stacking between layers of chromophores. Examples, herein, demonstrate clear relationships between assembly by design and resulting solid-state properties, and strategies presented offer guidance for future designs of π-conjugated molecular materials using specific aromatic interactions and halogen bonding.
Hydrogen Bond Network Disruption by Hydration Layers in Water Solutions with Salt and Hydrogen-Bonding Polymers (PEO)
A mean field theory model describing the interaction of ion hydration layers with the network of hydrogen bonds of both water and the nonionic polymer poly(ethylene oxide) (PEO) is presented. The predictions of the model for types and statistics of hydrogen bonds, the number of water molecules bound to PEO, or their dependence on temperature are successfully verified from all-atom simulations at different NaCl and PEO concentrations. Furthermore, our simulations show that the binding of cations to PEO increases monotonically with salt concentration, in agreement with recent experimental results, through a mechanism in which the sum of the number of bound water and cations is independent of salt concentration. Here, the model introduced is general and can describe any salt or hydrogen-bond-forming polymer.
Catalytic 1,3-Proton Transfer in Alkenes Enabled by Fe=NR Bond Cooperativity: A Strategy for p K a -Dictated Regioselective Transposition of C=C Double Bonds
Transition metal catalyzed alkene double bond transposition usually involves metal hydride intermediates. Despite significant advances in the design of catalysts that dictate product selectivity, control over substrate selectivity is less advanced and transition metal catalysts that selectively transpose double bonds in substrates containing multiple 1-alkene functionalities are rare. Herein, we report that the three-coordinate high spin (S = 2) Fe(II) imido complex [Ph 2 B( t BuIm) 2 Fe=NDipp][K(18-C-6)THF 2 ] (1-K(18-C-6)) catalyzes 1,3-proton transfer from 1-alkene substrates to afford 2-alkene transposition products. Mechanistic investigations involving kinetics, competition, and isotope labeling studies, supported by experimentally calibrated DFT computations, strongly support an unusual nonhydridic mechanism for alkene transposition that is enabled by the cooperative action of the iron center and basic imido ligand. As dictated by the pK a of the allylic protons, this catalyst enables the regioselective transposition of C=C double bonds in substrates containing multiple 1-alkenes. The high spin (S = 2) state of the complex allows a wide scope of functional groups to be tolerated, including those that are typical catalyst poisons, such as amines, N-heterocycles, and phosphines. Furthermore, these results demonstrate a new strategy for metal-catalyzed alkene transposition with predictable substrate regioselectivity.
Resonant bonding leads to low lattice thermal conductivity
Understanding the lattice dynamics and low thermal conductivities of IV–VI, V 2 –VI 3 and V materials is critical to the development of better thermoelectric and phase-change materials. In this report we offer a link between chemical bonding and low thermal conductivity. Our first-principles calculations reveal that long-ranged interaction along the $\langle$100$\rangle$ direction of the rocksalt structure exist in lead chalcogenides, SnTe, Bi 2 Te 3 , Bi and Sb due to the resonant bonding that is common to all of them. This long-ranged interaction in lead chalcogenides and SnTe cause optical phonon softening, strong anharmonic scattering and large phase space for three-phonon scattering processes, which explain why rocksalt IV–VI compounds have much lower thermal conductivities than zincblende III–V compounds. The novel insights on the relationship between resonant bonding and low thermal conductivity will help in the development of better thermoelectric and phase change materials.
Sculpting carbon bonds for allotropic transformation through solid-state re-engineering of –sp2 carbon
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Formation of carbon–nitrogen bonds in carbon monoxide electrolysis
The electroreduction of CO 2 is a promising technology for carbon utilization. Although electrolysis of CO 2 or CO 2 -derived CO can generate important industrial multicarbon feedstocks such as ethylene, ethanol, n-propanol and acetate, most efforts have been devoted to promoting C–C bond formation. Here, we demonstrate that C–N bonds can be formed through co-electrolysis of CO and NH 3 with acetamide selectivity of nearly 40% at industrially relevant reaction rates. Full-solvent quantum mechanical calculations show that acetamide forms through nucleophilic addition of NH 3 to a surface-bound ketene intermediate, a step that is in competition with OH – addition, which leads to acetate. Here, the C–N formation mechanism was successfully extended to a series of amide products through amine nucleophilic attack on the ketene intermediate. This strategy enables us to form carbon–heteroatom bonds through the electroreduction of CO, expanding the scope of products available from CO 2 reduction.
Bond Valences and Anharmonicity in Vacancy-Ordered Double Perovskite Halides
We report that anharmonic lattice dynamics are intimately linked with optical and electronic properties in perovskite halides semiconductors. Vacancy-ordered double perovskites are a subset of the perovskite halide family containing isolated octahedral units. The absence of polyhedral connectivity engenders the vacancy-ordered double perovskites with additional degrees of dynamic freedom, which presents an ideal structural framework to study dynamic-property relationships in perovskite halide semiconductors. In the present study, we examine the structure and bonding origins of anharmonicity in the vacancy-ordered double perovskites Cs 2 Sn 1-x Te x I 6 . While X-ray diffraction indicates that all members adopt the cubic vacancy-ordered double perovskite structure, the local coordination environment probed by X-ray pair distribution function (XPDF) analysis reveals asymmetry of the Cs–I/I–I pair correlation that smoothly decreases with increasing tellurium content. Temperature-dependent neutron total scattering suggests that this asymmetry in the PDF occurs due to anharmonic lattice dynamics arising from octahedral tilting and Cs + displacements, as supported by Reverse Monte Carlo simulations of the Cs 2 SnI 6 and Cs 2 TeI 6 end members. We further correlate the trends in asymmetry and anharmonicity with the bond valence sum of the Cs + ion, and find that the anharmonicity vanishes when the bonding preferences of the Cs + are satisfied by the size of the cuboctahedral void. Lastly, this study presents a simple and effective approach for understanding the origin of anharmonicity in vacancy-ordered double perovskite materials.
Direct functionalization of C-H bonds by electrophilic anions
Bond formation between two of the most inert molecules, alkanes and [B12X12]2- (X = Cl, Br), is performed in a two step process. Fragmentation of [B12X12]2- in the gas phase generates highly reactive [B12X11]- ions which spontaneously react with alkanes. The reaction mechanism was investigated using tandem mass spectrometry and gas-phase vibrational spectroscopy combined with electronic structure calculations. This effort revealed the unprecedented and counterintuitive electrophilic substitution of a proton in an alkane by a negatively charged ion resulting in a B-C bond formation. The product is a dianionic [B12X11CnH2n+1]2- species, in which H+ is electrostatically bound to the dianion. High flux ion soft-landing was performed to co-deposit [B12X11]- and complex organic molecules (phthalates) in thin layers on surfaces. Molecular structure analysis of the product films revealed that C-H functionalization by [B12X11]- occured in the presence of other more reactive functional groups. This observation demonstrates the utility of highly reactive fragment ions for defined bond formation processes and may pave the way to the use of gas phase ion chemistry for chemical synthesis in the condensed phase.
Effect of bond thickness on fracture and fatigue strength of adhesively bonded composite joints
An experimental investigation of composite to composite bonded joints was undertaken to study the effect of bond thickness on debond growth rate under cyclic loading and critical strain energy release rate under static loading. Double cantilever beam specimens of graphite/epoxy adherends bonded with EC 3445 were tested under mode I loading. A different behavior of fracture and fatigue strength was observed with variation of bondline thickness.
A Dynamic Pathway for Stone-Wales Bond Rotation on Carbon Nanotubes through Diamond-Like Bonds
A new lower energy barrier with a two-step pathway of Stone-Wales (SW) ,ond rotation on carbon nanotubes (CNTs) is found through molecular dynamics (MD) simulations of CNTs under tension. The first step involves going over to a stable sp3-like metastable configuration with half rotated and partially tilted C-C bond. The second step involves going over to the fully rotated C-C bond with the formation of a SW defect in the nanotube. The energy barrier for this two-step dynamic pathway is significantly lower than the previously known static barrier for in-plane rotation of the C-C bond on a tensile strained (> 4%) CNT.
The Effects of Silicone Contamination on Bond Performance of Various Bond Systems
The sensitivity to silicone contamination of a wide variety of adhesive bond systems is discussed. Generalizations regarding factors that make some bond systems more sensitive to contamination than others are inferred and discussed. The effect of silane adhesion promoting primer on the contamination sensitivity of two epoxy/steel bond systems is also discussed.
Reduction-oxidation Enabled Glass-ceramics to Stainless Steel Bonding Part II interfacial bonding analysis
Among glass-ceramic compositions modified with a variety of oxidants (AgO, FeO, NiO, PbO, SnO, CuO, CoO, MoO 3 and WO 3 ) only CuO and CoO doped glass-ceramics showed existence of bonding oxides through reduction-oxidation (redox) at the GC-SS interface. The CuO-modified glass-ceramics demonstrate the formation of a continuous layer of strong bonding Cr 2 O 3 at the interface in low partial oxygen (PO 2 ) atmosphere. However, in a local reducing atmosphere, the CuO is preferentially reduced at the surface of glass-ceramic rather than the GC-SS interface for redox. The CoO-modified glass-ceramics demonstrate improved GC-SS bonding. But the low mobility of Co ++ ions in the GC limited the amount of CoO that can diffuse to and participate in redox at the interface.
Diffusion bonding of silicon carbide using iridium and hermetic silicon carbide-iridium bonds
An exemplary method of bonding of silicon carbide and objects having a hermetic silicon carbide-iridium-silicon carbide bond. The method includes the steps of inserting an iridium foil between two SiC layers; heating the iridium foil and SiC layers at a temperature of 1500 C in a vacuum of <10−5 ton; applying a pressure between 1 ksi and 7 ksi to the iridium foil and SiC layers; maintaining the temperature and pressure for 6-10 hours; and forming a hermetic seal having a leak rate <3×10−9 cm3/sec between the iridium foil and the two SiC layers. The SiC-iridium bonds lack cracks and are hermetic.
Diffusion bonded silicon carbide having iridium and hermetic silicon carbide-iridium bonds
Disclosed is a hermetic bond for a joint including a first layer of silicon carbide; a second layer of silicon carbide; and a bonding layer positioned between the first layer and the second layer, wherein the bonding layer includes an iridium layer, a first reaction zone positioned between the iridium foil layer and the first layer, and a second reaction zone positioned between the iridium foil layer and the second layer, wherein the first reaction zone and the second reaction zone include iridium silicides.
Sigma bond activation of deuterium mediated by atomic cerium cations: Experiment and theory
Reaction of ground-state Ce + (5d 2 4f 1 ) with deuterium in a reaction cell at a pressure of 1.5–4.0 Torr and temperatures ranging from approximately 265–515 K is studied. Rate constants for formation of CeD 2 + are acquired and vary from approximately 2.8 × 10 -14 to 2.1 ×10 -13 cm 3 /s. A negative temperature dependence is observed for the measured rate constants, indicating the reaction becomes less efficient as the temperature increases, consistent with an exothermic reaction. Electronic structure calculations were performed using density functional theory (DFT) at the PBE0 level to characterize all reactant and product species as well as to generate potential energy surfaces (PESs) for the insertion reaction. This combination of experimental and theoretical results suggest that Ce + inserts into the deuterium sigma bond in an overall exothermic and barrierless process.
Isotopic studies of trans- and cis-HOCO using rotational spectroscopy: Formation, chemical bonding, and molecular structures
HOCO is an important intermediate in combustion and atmospheric processes because the OH + CO → H + CO{sub 2} reaction represents the final step for the production of CO{sub 2} in hydrocarbon oxidation, and theoretical studies predict that this reaction proceeds via various intermediates, the most important being this radical. Isotopic investigations of trans- and cis-HOCO have been undertaken using Fourier transform microwave spectroscopy and millimeter-wave double resonance techniques in combination with a supersonic molecular beam discharge source to better understand the formation, chemical bonding, and molecular structures of this radical pair. We find that trans-HOCO can be produced almost equally well from either OH + CO or H + CO{sub 2} in our discharge source, but cis-HOCO appears to be roughly two times more abundant when starting from H + CO{sub 2}. Using isotopically labelled precursors, the OH + C{sup 18}O reaction predominately yields HOC{sup 18}O for both isomers, but H{sup 18}OCO is observed as well, typically at the level of 10%-20% that of HOC{sup 18}O; the opposite propensity is found for the {sup 18}OH + CO reaction. DO + C{sup 18}O yields similar ratios between DOC{sup 18}O and D{sup 18}OCO as those found for OH + C{sup 18}O, suggesting that some fraction of HOCO (or DOCO) may be formed from the back-reaction H + CO{sub 2}, which, at the high pressure of our gas expansion, can readily occur. The large {sup 13}C Fermi-contact term (a{sub F}) for trans- and cis-HO{sup 13}CO implicates significant unpaired electronic density in a σ-type orbital at the carbon atom, in good agreement with theoretical predictions. By correcting the experimental rotational constants for zero-point vibration motion calculated theoretically using second-order vibrational perturbation theory, precise geometrical structures have been derived for both isomers.