17 research outputs found

    Stability of Tricalcium Silicate and Other Primary Phases in Portland Cement Clinker

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    The decomposition of alite (C<sub>3</sub>S) in Portland cement clinker was investigated by isothermal annealing, aiming to provide more fundamentals for the cooling process of cement clinker so as to search for potential chance for modification of the ongoing cooling process. Clinker phases were analyzed with quantitative X-ray diffraction technique. Scanning electron microscope and microscopy were used to investigate the microstructure. The fastest decomposition rate appeared at 1125ā€“1150 Ā°C in a temperatureā€“timeā€“transformation diagram. The decomposition of alite primarily occurred at the cracks, edges, and defects of the clinker. The resultant f-CaO segregated, which mainly controlled the decomposition rate of alite. The three-dimensional diffusion model (Jander) was suitable for the decomposition kinetics of alite with a non-Arrhenius behavior for the activation energy which was a piecewise linear function with temperature. Interstitial phases recrystallized during the annealing process, accompanied by an increase of the C<sub>3</sub>A and C<sub>4</sub>AF contents. The recrystallization of C<sub>3</sub>A was temperature-dependent, especially above 1000 Ā°C

    Use of Ball Drop Casting and Surface Modification for the Development of Amine-Functionalized Silica Aerogel Globules for Dynamic and Efficient Direct Air Capture

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    Amine-functionalized silica aerogel globules (AFSAGs) were first synthesized via a simple ball drop casting method followed by amine grafting. The effect of grafting time on the structure and CO2 adsorption performance of the AFSAGs was investigated. The CO2 adsorption performance was comprehensively studied by breakthrough curves, adsorption capacity and rates, surface amine loading and density, amine efficiency, adsorption halftime, and cyclic stability. The results demonstrate that prolonging the grafting time does not lead to a significant increase in surface amine content owing to pore space blockage by superabundant amine groups. The CO2 adsorption performance shows obvious dependence on surface amine density, determined by both the surface amine content and specific surface area, and working temperature. AFSAGs with a grafting time of 24 h (AFSAG24) with a moderate surface amine density have optimal CO2 adsorption capacities, which are 1.78 and 2.14 mmol/g at 25 Ā°C with dry and humid 400 ppm CO2, respectively. The amine efficiency of AFSAG24 with low CO2 concentrations, 0.38ā€“0.63 with dry 400 ppmāˆ’1% CO2, is the highest among the reported amine-functionalized adsorbents. After estimation with different diffusion models, the CO2 adsorption process of AFSAG24 is governed by film diffusion and intraparticle diffusion. In the range of 1ā€“4 mm, the ball size does not affect the CO2 adsorption capacity of AFSAG24 obviously. AFSAG24 offers significant advantages for practical direct air capture compared with its state-of-the-art counterparts, such as high dynamic adsorption capacity and amine efficiency, excellent stability, and outstanding adaptation to the environment

    Flexible Silica Aerogel Composites for Thermal Insulation under High-Temperature and Thermalā€“Force Coupling Conditions

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    The objective of this research was to develop a high-performance flexible silica aerogel composite for thermal insulation under high-temperature and thermalā€“force coupling conditions. Based on synthesis of flexible silica aerogels with methyltrimethoxysilane as the precursor, flexible silica aerogel composites were developed by wet-impregnating ceramic fiber felt. Morphology, microstructure, chemical structure, hydrophobicity, and compression performance evolutions of the flexible silica aerogels and their composite counterparts with temperature revealed that the resulting flexible silica aerogel samples have excellent stability at 900 Ā°C. Flexible silica aerogel composites show 100 and 70% recovery with 50% strain after treatment at 500 and 900 Ā°C, respectively. Thermal insulation performance of the flexible silica aerogel composites was comprehensively studied from different aspects, including thermal conductivity, thermal shield behavior under high-temperature and thermalā€“force coupling conditions, and thermal shock resistance. Thermal conductivities of the flexible silica aerogel composite at 25ā€“1100 Ā°C are lower than those of most reported aerogel composites. Coupling of force under high temperature leads to degradation of thermal insulation performance, owing to deformation with compression. The synthesis method of the flexible silica aerogel is facile and inspiring, and the flexible silica aerogel composites have promising prospects in thermal insulation under high-temperature and thermal-stress coupling conditions, such as suppressing thermal runaway propagation of lithium-ion batteries

    Flexible Silica Aerogel Composites for Thermal Insulation under High-Temperature and Thermalā€“Force Coupling Conditions

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    The objective of this research was to develop a high-performance flexible silica aerogel composite for thermal insulation under high-temperature and thermalā€“force coupling conditions. Based on synthesis of flexible silica aerogels with methyltrimethoxysilane as the precursor, flexible silica aerogel composites were developed by wet-impregnating ceramic fiber felt. Morphology, microstructure, chemical structure, hydrophobicity, and compression performance evolutions of the flexible silica aerogels and their composite counterparts with temperature revealed that the resulting flexible silica aerogel samples have excellent stability at 900 Ā°C. Flexible silica aerogel composites show 100 and 70% recovery with 50% strain after treatment at 500 and 900 Ā°C, respectively. Thermal insulation performance of the flexible silica aerogel composites was comprehensively studied from different aspects, including thermal conductivity, thermal shield behavior under high-temperature and thermalā€“force coupling conditions, and thermal shock resistance. Thermal conductivities of the flexible silica aerogel composite at 25ā€“1100 Ā°C are lower than those of most reported aerogel composites. Coupling of force under high temperature leads to degradation of thermal insulation performance, owing to deformation with compression. The synthesis method of the flexible silica aerogel is facile and inspiring, and the flexible silica aerogel composites have promising prospects in thermal insulation under high-temperature and thermal-stress coupling conditions, such as suppressing thermal runaway propagation of lithium-ion batteries

    Bis(Ī²-diketiminate) Rare-Earth-Metal Borohydrides: Syntheses, Structures, and Catalysis for the Polymerizations of lā€‘Lactide, Īµā€‘Caprolactone, and Methyl Methacrylate

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    Reaction of LnCl<sub>3</sub> (Ln = Y, Yb) with 2 equiv of NaL<sup>2,6ā€‘ipr2</sup><sub>Ph</sub> (L<sup>2,6ā€‘ipr2</sup><sub>Ph</sub> = [(2,6-<sup><i>i</i></sup>Pr<sub>2</sub>C<sub>6</sub>H<sub>3</sub>)Ā­NCĀ­(Me)Ā­CHCĀ­(Me)Ā­NĀ­(C<sub>6</sub>H<sub>5</sub>)]<sup>āˆ’</sup>) afforded the chlorides (L<sup>2,6ā€‘ipr2</sup><sub>Ph</sub>)<sub>2</sub>YCl (<b>1</b>) and (L<sup>2,6ā€‘ipr2</sup><sub>Ph</sub>)<sub>2</sub>YbCl (<b>2</b>). Crystal structure analysis revealed <b>2</b> to be the unsolvated monomer. Treatment of the chlorides <b>1</b> and <b>2</b> with NaBH<sub>4</sub> in a 1/1 molar ratio in THF led to the preparation of the monoborohydrides (L<sup>2,6ā€‘ipr2</sup><sub>Ph</sub>)<sub>2</sub>LnBH<sub>4</sub> (Ln = Y (<b>3</b>), Yb (<b>4</b>)) in good yields. Reaction of LnCl<sub>3</sub> (Ln = Y, Yb) with 2 equiv of NaL<sup>2ā€‘Me</sup> (L<sup>2ā€‘Me</sup> = [NĀ­(2-MeC<sub>6</sub>H<sub>4</sub>)Ā­CĀ­(Me)]<sub>2</sub>CH<sup>ā€“</sup>) in THF, followed by treatment with 1 equiv of NaBH<sub>4</sub>, afforded the monoborohydrides (L<sup>2ā€‘Me</sup>)<sub>2</sub>LnBH<sub>4</sub> (Ln = Y (<b>5</b>), Yb (<b>6</b>)). Complexes <b>3</b>ā€“<b>6</b> were fully characterized, including X-ray crystal structure analyses. Complexes <b>3</b>ā€“<b>6</b> are isostructural. The central metal in each complex is ligated by two Ī²-diketiminate ligands and one Ī·<sup>3</sup>-BH<sub>4</sub><sup>ā€“</sup> group in a distorted trigonal bipyramid. Complexes <b>3</b>ā€“<b>6</b> were found to be highly active in the ring-opening polymerization of l-lactide (l-LA) and Īµ-caprolactone (Īµ-CL) to give polymers with relatively narrow molar mass distributions. The activity depends on both the central metal and the ligand (Y > Yb and L<sup>2,6ā€‘ipr2</sup><sub>Ph</sub> > L<sup>2ā€‘Me</sup>). The best control over the molar mass was found for complex <b>6</b>. The <i>M</i><sub>n</sub>(obsd) values (<i>M</i><sub>n</sub> = the number-average molar mass) of the resulting PCL are in good agreement with <i>M</i><sub>n</sub>(calcd), with a ratio of monomer to <b>6</b> of up to 1000. The polymerization kinetics of l-LA in THF at 20 Ā°C by complex <b>6</b> displays a first-order dependence on the monomer concentration. Notably, the binary <b>6</b>/<sup><i>i</i></sup>PrOH system exhibited an ā€œimmortalā€ nature and proved able to quantitatively convert 10ā€‰000 equiv of l-LA with up to 200 equiv of <sup><i>i</i></sup>PrOH per metal initiator. All the obtained PLAs showed monomodal, narrow distributions (<i>M</i><sub>w</sub>/<i>M</i><sub>n</sub> = 1.06ā€“1.11), with the <i>M</i><sub>n</sub> values decreasing proportionally with an increasing amount of <sup><i>i</i></sup>PrOH. Complex <b>4</b> can also initiate the polymerization of methyl methacrylate (MMA) at āˆ’40 Ā°C with high activity, affording the PMMA with 83.3% syndiotacticity

    Hydration Mechanism of Reactive and Passive Dicalcium Silicate Polymorphs from Molecular Simulations

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    Belite (C<sub>2</sub>S, Cī—»CaO, Sī—»SiO<sub>2</sub>) based cements are promising low-CO<sub>2</sub> substitutes of ordinary Portland cement. The main drawback is their low hydration rates, which makes them unpractical for construction. Yet more disconcerting is the different reactivity between polymorphs of belite: while Ī²-C<sub>2</sub>S reacts slowly with water, Ī³-C<sub>2</sub>S is almost inert. Due to the demand of improving C<sub>2</sub>S reactivity, in this work we aim to understand the hydration mechanism of belite polymorphs by density functional theory and molecular dynamics simulations methods. We calculated the low-index cleavage energies, and the thermodynamic equilibrium structures were constructed through Wulff shape constructing method. We built the adsorption energy surface (AES) maps and found out the transition state structures for (chemi)Ā­sorption of water molecules. Finally molecular dynamics were employed to simulate the reactions taking place during 2 ns at room temperature. We found that water dissociation consists of three steps, rotation, dissociation, and diffusion, with different energy barriers. Considering the AES, DFT energy barriers, and the molecular dynamics simulations, the number of reactive sites is the key aspect that controls hydration; even though water reacts preferentially in Ī³-C<sub>2</sub>S surfaces over in Ī²-C<sub>2</sub>S in terms of energy, a considerably lower number of reactive points in Ī³-C<sub>2</sub>S would limit the surface hydration and dissolution

    Developing Polymer Cathode Material for the Chloride Ion Battery

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    The chloride ion battery is an attractive rechargeable battery owing to its high theoretical energy density and sustainable components. An important challenge for research and development of chloride ion batteries lies in the innovation of the cathode materials. Here we report a nanostructured chloride ion-doped polymer, polypyrrole chloride, as a new type of potential cathode material for the chloride ion battery. The as-prepared polypyrrole chloride@carbon nanotubes (PPyCl@CNTs) cathode shows a high reversible capacity of 118 mAh g<sup>ā€“1</sup> and superior cycling stability. Reversible electrochemical reactions of the PPyCl@CNTs cathode based on the redox reactions of nitrogen species and chloride ion transfer are demonstrated. Our work may guide and offer electrode design principles for accelerating the development of rechargeable batteries with anion transfer

    Nanostructured cation disordered Li<sub>2</sub>FeTiO<sub>4</sub>/graphene composite as high capacity cathode for lithium-ion batteries

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    <p>Nanostructured Li<sub>2</sub>FeTiO<sub>4</sub>/graphene composite with a cation disordered rock salt structure (Fm-3Ā m) has been synthesised via a solgel process using graphene oxide (GO) as a template. The as-prepared Li<sub>2</sub>FeTiO<sub>4</sub> nanoparticles with a particle size of 20ā€“50Ā nm are uniformly distributed on the graphene substrate. The Li<sub>2</sub>FeTiO<sub>4</sub>/graphene cathode shows phase transformations of Fe<sup>2+</sup>/Fe<sup>3+</sup> and Fe<sup>3+</sup>/Fe<sup>4+</sup> in a wide potential range from 1.5 to 5.0Ā V and possesses a high discharge capacity of 218.6 mAh g<sup>āˆ’1</sup> (equivalent to 1.4 Li per formula unit). A reversible capacity of 176.9 mAh g<sup>āˆ’1</sup> is maintained after 50 cycles. High capacity retention rate at 1C after 200 cycles is obtained. The Li<sub>2</sub>FeTiO<sub>4</sub>/graphene should be of great interest as a potential cathode material for high-performance lithium-ion batteries.</p

    Asymmetric Nucleophilic Catalysis with an Octahedral Chiral-at-Metal Iridium(III) Complex

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    Herein, we report about the design, synthesis, and application of a nucleophilic octahedral chiral-only-at-metal iridiumĀ­(III) complex. We demonstrate that the enantiopure form of this complex serves as an efficient catalyst for the asymmetric Steglich rearrangement of <i>O</i>-acylated azlactones (up to 96% ee and 99% yield) and the related asymmetric Black rearrangement of <i>O</i>-acylated benzofuranones (up to 94% ee and 99% yield). We provide insight into the mechanisms of these two acyl migration reactions and the catalystā€™s manner of chiral recognition with crystal structures of the active catalyst and a catalysis intermediate analog, as well as with quantum chemical calculations based on them. Furthermore, we demonstrate that the presented catalyst also efficiently catalyzes the asymmetric reaction between aryl alkyl ketenes and 2-cyanopyrrole to give the corresponding Ī±-chiral <i>N</i>-acyl pyrroles (up to 95% ee and 99% yield)

    Magnesium Anode for Chloride Ion Batteries

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    A key advantage of chloride ion battery (CIB) is its possibility to use abundant electrode materials that are different from those in Li ion batteries. Mg anode is presented as such a material for the first time and Mg/C composite prepared by ball milling of Mg and carbon black powders or thermally decomposed MgH<sub>2</sub>/C composite has been tested as anode for CIB. The electrochemical performance of FeOCl/Mg and BiOCl/Mg was investigated, demonstrating the feasibility of using Mg as anode
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