17 research outputs found
Stability of Tricalcium Silicate and Other Primary Phases in Portland Cement Clinker
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 1125ā1150 Ā°C in a temperatureātimeātransformation
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
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,
0.38ā0.63 with dry 400 ppmā1% 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 1ā4 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 ThermalāForce Coupling Conditions
The objective of this research was to develop a high-performance
flexible silica aerogel composite for thermal insulation under high-temperature
and thermalāforce 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 thermalāforce coupling conditions, and
thermal shock resistance. Thermal conductivities of the flexible silica
aerogel composite at 25ā1100 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 ThermalāForce Coupling Conditions
The objective of this research was to develop a high-performance
flexible silica aerogel composite for thermal insulation under high-temperature
and thermalāforce 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 thermalāforce coupling conditions, and
thermal shock resistance. Thermal conductivities of the flexible silica
aerogel composite at 25ā1100 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 lāLactide, ĪµāCaprolactone, and Methyl Methacrylate
Reaction of LnCl<sub>3</sub> (Ln = Y, Yb) with 2 equiv
of NaL<sup>2,6āipr2</sup><sub>Ph</sub> (L<sup>2,6āipr2</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>ā</sup>) afforded the chlorides (L<sup>2,6āipr2</sup><sub>Ph</sub>)<sub>2</sub>YCl (<b>1</b>) and (L<sup>2,6āipr2</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>2,6āipr2</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>2āMe</sup> (L<sup>2āMe</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>2āMe</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>2,6āipr2</sup><sub>Ph</sub> > L<sup>2āMe</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 āimmortalā nature and proved able
to quantitatively convert 10ā000 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> = 1.06ā1.11),
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 ā40 Ā°C with high activity, affording the PMMA
with 83.3% syndiotacticity
Hydration Mechanism of Reactive and Passive Dicalcium Silicate Polymorphs from Molecular Simulations
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
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>ā1</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
<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 20ā50Ā 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>ā1</sup> (equivalent to 1.4 Li per formula unit). A reversible capacity of 176.9 mAh g<sup>ā1</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
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 catalystās
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
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