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

The decomposition of alite (C₃S) 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 1125–1150 °C in a temperature–time–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 C₃A and C₄AF contents. The recrystallization of C₃A was temperature-dependent, especially above 1000 °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 °C with dry and humid 400 ppm CO2, respectively. The amine efficiency of AFSAG24 with low CO2 concentrations, 0.38–0.63 with dry 400 ppm−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 1–4 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 Thermal–Force Coupling Conditions

The objective of this research was to develop a high-performance flexible silica aerogel composite for thermal insulation under high-temperature and thermal–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 °C. Flexible silica aerogel composites show 100 and 70% recovery with 50% strain after treatment at 500 and 900 °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 thermal–force coupling conditions, and thermal shock resistance. Thermal conductivities of the flexible silica aerogel composite at 25–1100 °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 Thermal–Force Coupling Conditions

The objective of this research was to develop a high-performance flexible silica aerogel composite for thermal insulation under high-temperature and thermal–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 °C. Flexible silica aerogel composites show 100 and 70% recovery with 50% strain after treatment at 500 and 900 °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 thermal–force coupling conditions, and thermal shock resistance. Thermal conductivities of the flexible silica aerogel composite at 25–1100 °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

Development of Regular Hydrophobic Silica Aerogel Microspheres for Efficient Oil Adsorption

The objective of this research was to develop new hydrophobic silica aerogel microspheres (HSAMs) with water glass and hexmethyldisilazane for oil adsorption. The effects of the hexmethyldisilazane concentration and drying method on the structure and organic liquid adsorption capacity were investigated. The hexmethyldisilazane concentration of the modification solution did not influence the microstructure and pore structure in a noteworthy manner, which depended more on the drying method. Vacuum drying led to more volume shrinkage of the silica gel microsphere (SGM) than supercritical CO2 drying, thus resulting in a larger apparent density, lower pore volume, narrower pore size distribution, and more compact network. Owing to the large pore volume and pore size, the HSAMs synthesized via supercritical CO2 drying had a larger organic liquid adsorption capacity. The adsorption capacities of the HSAMs with pore volumes of 4.04–6.44 cm3/g for colza oil, vacuum pump oil, and hexane are up to 18.3, 18.9, and 11.8 g/g, respectively, higher than for their state-of-the-art counterparts. The new sorbent preparation method is facile, cost-effective, safe, and ecofriendly, and the resulting HSAMs are exceptional in capacity, stability, and regenerability

Bis(β-diketiminate) Rare-Earth-Metal Borohydrides: Syntheses, Structures, and Catalysis for the Polymerizations of l‑Lactide, ε‑Caprolactone, and Methyl Methacrylate

Reaction of LnCl₃ (Ln = Y, Yb) with 2 equiv of NaL^2,6‑ipr2_Ph (L^2,6‑ipr2_Ph = [(2,6-^<i>i</i>Pr₂C₆H₃)­NC­(Me)­CHC­(Me)­N­(C₆H₅)]⁻) afforded the chlorides (L^2,6‑ipr2_Ph)₂YCl (<b>1</b>) and (L^2,6‑ipr2_Ph)₂YbCl (<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 NaBH₄ in a 1/1 molar ratio in THF led to the preparation of the monoborohydrides (L^2,6‑ipr2_Ph)₂LnBH₄ (Ln = Y (<b>3</b>), Yb (<b>4</b>)) in good yields. Reaction of LnCl₃ (Ln = Y, Yb) with 2 equiv of NaL^2‑Me (L^2‑Me = [N­(2-MeC₆H₄)­C­(Me)]₂CH^–) in THF, followed by treatment with 1 equiv of NaBH₄, afforded the monoborohydrides (L^2‑Me)₂LnBH₄ (Ln = Y (<b>5</b>), Yb (<b>6</b>)). Complexes <b>3</b>–<b>6</b> were fully characterized, including X-ray crystal structure analyses. Complexes <b>3</b>–<b>6</b> are isostructural. The central metal in each complex is ligated by two β-diketiminate ligands and one η³-BH₄^– group in a distorted trigonal bipyramid. Complexes <b>3</b>–<b>6</b> were found to be highly active in the ring-opening polymerization of l-lactide (l-LA) and ε-caprolactone (ε-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^2,6‑ipr2_Ph > L^2‑Me). The best control over the molar mass was found for complex <b>6</b>. The <i>M</i>_n(obsd) values (<i>M</i>_n = the number-average molar mass) of the resulting PCL are in good agreement with <i>M</i>_n(calcd), with a ratio of monomer to <b>6</b> of up to 1000. The polymerization kinetics of l-LA in THF at 20 °C by complex <b>6</b> displays a first-order dependence on the monomer concentration. Notably, the binary <b>6</b>/^<i>i</i>PrOH system exhibited an “immortal” nature and proved able to quantitatively convert 10 000 equiv of l-LA with up to 200 equiv of ^<i>i</i>PrOH per metal initiator. All the obtained PLAs showed monomodal, narrow distributions (<i>M</i>_w/<i>M</i>_n = 1.06–1.11), with the <i>M</i>_n values decreasing proportionally with an increasing amount of ^<i>i</i>PrOH. Complex <b>4</b> can also initiate the polymerization of methyl methacrylate (MMA) at −40 °C with high activity, affording the PMMA with 83.3% syndiotacticity

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

Belite (C₂S, CCaO, SSiO₂) based cements are promising low-CO₂ 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 β-C₂S reacts slowly with water, γ-C₂S is almost inert. Due to the demand of improving C₂S 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)­sorption 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 γ-C₂S surfaces over in β-C₂S in terms of energy, a considerably lower number of reactive points in γ-C₂S would limit the surface hydration and dissolution

Nanostructured cation disordered Li₂FeTiO₄/graphene composite as high capacity cathode for lithium-ion batteries

<p>Nanostructured Li₂FeTiO₄/graphene composite with a cation disordered rock salt structure (Fm-3 m) has been synthesised via a solgel process using graphene oxide (GO) as a template. The as-prepared Li₂FeTiO₄ nanoparticles with a particle size of 20–50 nm are uniformly distributed on the graphene substrate. The Li₂FeTiO₄/graphene cathode shows phase transformations of Fe²⁺/Fe³⁺ and Fe³⁺/Fe⁴⁺ in a wide potential range from 1.5 to 5.0 V and possesses a high discharge capacity of 218.6 mAh g⁻¹ (equivalent to 1.4 Li per formula unit). A reversible capacity of 176.9 mAh g⁻¹ is maintained after 50 cycles. High capacity retention rate at 1C after 200 cycles is obtained. The Li₂FeTiO₄/graphene should be of great interest as a potential cathode material for high-performance lithium-ion batteries.</p

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^–1 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