Time-dependent viscosity of structured clay suspensions under a fixed shear was revealed in the prepared slurry samples of clay lenses from the Athabasca oil sands deposit, differing from thixotropic or rheopectic suspensions. At a lower salt (Na or Ca) concentration, the viscosity oscillated with time, which was slowly damped with increasing salt concentrations. The viscosity increased without reaching a maximum plateau, even after a run of a few hours. At 1000 ppm Na concentration, a maximum viscosity was reached, followed by viscosity fluctuation within a narrow range to approach an equilibrium value with time. Both sample ageing and shear history affected the slurry viscosity. It was speculated that the Brownian motion of colloidal clay particles and the applied shear induced rearrangement and continued formation of clay microstructures with time, due to the rotation of anisotropic colloidal clay particles under simple shear flow. Its implications to oil sands research and operation were briefly discussed. 相似文献
Herein, we describe metal-free fluorocyclization of 2-alkynylbenzoates by N-fluoropyridinium salts. The present method allows the selective synthesis of 4-fluoroisocoumarins and 3,4,4-trifluoroisochromanones by minor modification of the reaction conditions. 相似文献
The growing demand of advanced electrochemical energy storage devices for various applications, including portable electronic products, electric vehicles, and large-scale energy storage grids, has triggered extensive research interests and efforts on various rechargeable batteries such as lithium/sodium-ion batteries (LIBs/NIBs), aluminium-ion batteries (AIBs), liquid metal batteries (LMBs), and molten-air batteries (MABs) in the past decades. A key issue to push forward the development of these batteries is the exploration of high-performance electrodes and electrolytes, which calls for efficient and versatile synthetic methods. Molten salts (MSs), liquid-phase ionic compounds or mixtures, provide an effective platform to widen the reaction temperatures and enrich the chemical environments for the synthesis of novel electrode materials and electrolytes. In this review, the general principles of molten salts and recent research progresses on molten salt-based battery materials are surveyed. Molten-salt synthesis of electrode materials, including sintering and electrolysis, are emerging as competitive substitutes for conventional synthesis techniques. These methods have shown their effectiveness and uniqueness in adjusting the crystal structure, morphology, and performance of electrode materials for LIBs/NIBs, as suggested by recent progresses and applications of diverse cathodes (layered oxides, spinel oxides, polyanions, etc.) and anodes (metal oxides, alloys, carbons, etc.). Furthermore, the applications of molten salts as effective electrolytes are demonstrated in representative new-type secondary batteries including AIBs, LMBs and MABs. Finally, the emerging opportunities, challenges, and interesting research trends are envisioned to promote the further development of molten-salt methodology for rechargeable batteries. 相似文献
A novel approach to preparing electrospun polyvinylidene fluoride (PVDF) nanofibers is proposed, with high piezoelectric performance. PVDF nanofibers are doped with inorganic salts without the use of any postpolarization treatment. Twenty‐six salts are doped into the nanofibers and their piezoelectric properties are studied. The salts are classified into three groups based on their differing piezoelectric enhancement effects. A piezoelectric nanogenerator fabricated with an optimized electrospun PVDF nanofiber mat shows a piezovoltage seven times greater than that of a device based on undoped nanofibers. The simple and low‐cost approach to fabricate these piezoelectric nanofiber mats may broaden the range of industrial applications of these materials in energy‐harvesting devices and portable sensors. 相似文献
Both hypervalent organoiodine(III) compounds and boronic acids/esters are non‐toxic and considered as environment‐friendly compounds and have had a remarkable impact on the field of synthetic organic chemistry. Numerous transformations have been carried out using hypervalent organoiodine(III) or boronic acids/esters – taken separately – with other reactants, but transformations with these two reagents taken together are comparatively less well reported. In this mini‐review, diverse reactions carried out with these two substrates in the presence of each other, have been discussed. Various functionalizations of boronic compounds, promoted by hypervalent organoiodine(III) reagents, both in the presence and absence of transition metals, have been reviewed. Different metal‐free iodine(III)–boron exchange reactions providing iodonium salts, various ipso transformations of boronic acids/esters and metal‐catalyzed cross‐coupling reactions of boronic compounds with hypervalent organoiodine(III) reagents are the prime focal areas of this article. Mechanistic aspects for certain reactions have also been delineated.
The first report on a phosphonium salt as an asymmetric catalyst was published in 1997, and thereafter this area of research remained fairly dormant for almost a decade. However, the second decade (2007–2017) has recorded a significant growth in the published literature and it has now emerged as a hot topic of research. The use of phosphonium salts as a phase‐transfer catalyst has gained momentum in recent years due to their ease of availability and simple preparation technique. Most of these asymmetric phosphonium salts are derived from readily available starting materials like chiral amino acids and binaphthyl rings. With a simple modification in the basic core of these moieties, they can be used to execute a number of enantioselective organic transformations. This review presents a comprehensive overview of the historical development of catalyst design, with its necessary modification and applications in selective organic transformations.
In the past thirty years, azido polymers have attracted wide attention in the field of energetic materials. Currently, the synthesized azido polymers have linear structure. In the present research, hyperbranched poly‐3‐azidomethyl‐3‐ hydroxymethyl oxetane (HBPAMHMO) was synthesized using an AB2 monomer, and its physical and chemical properties were studied. The results showed that the molecular weight of HBPAMHMO increased along with the increasing ratio of r ([monomer]0/[initiator]0), together with very narrow PDI (from 1.12 to 1.34), and moreover, the degree of branching increased along with the increase in polymerization temperature. As compared to linear azido polymer with similar structure, it has lower glass transition temperature, sensitivity, higher combustion heat and mechanical properties, suggesting a great prospect for numerous applications. 相似文献
The novel, thermally stable explosive 4,4′‐((2,4,6‐trinitro‐1,3‐phenylene)bis(oxy))bis(1,3‐dinitrobenzene) (Be referred to as ZXC‐ 5 in our laboratory) has been reported. ZXC‐5 can be synthesized by a simple synthetic method (The total synthesis of ZXC‐ 5 requires only two steps and the total yield of ZXC‐ 5 is more than 89 %) and shows the superior detonation performances (detonation pressure, detonation velocity, sensitivity toward mechanical stimuli, and temperature of decomposition). The structure of ZXC‐5 was characterized by multinuclear (1H, 13C) NMR and mass spectrometry. The structure in the crystalline state was confirmed by low‐temperature single‐crystal X‐ray diffraction. From the calculated standard molar enthalpy of formation and the measured densities, the detonation properties were predicted by using the EXPLO5 V6.01 thermochemical computer code. The sensitivity of ZXC‐ 5 towards impact, electrostatic discharge, and friction were also measured. 相似文献
Glycidyl azide‐butadiene block copolymers are potential binders for solid propellants. The azidic part contributes to the overall energy outputs, while the butadiene block improves the mechanical properties. Synthetic strategies proposed in literature are not appropriate for production of large‐scale quantities. The mesylation of one homopolymer, followed by reaction with the OH terminal groups of the second is proposed here. The reaction is simple and does not show the drawbacks of the previously suggested alternatives. The block copolymers can be used as “partially” energetic binders. Moreover, they work well as compatibilizer in mechanical blends of the two homopolymers, that otherwise rapidly segregate in two distinct phases. 相似文献
