Active Nucleation Sites Research Articles

Alkalized MXene/carbon nanotube composite for stable Na metal anodes.

Ti3C2 MXenes are emerging 2D materials and have attracted increasing attention in sodium metal anode fabrication because of their high conductivity, multifunctional groups and excellent mechanical performances. However, the severe self-restacking of Ti3C2 MXenes is not conducive to dispersing Na+ and limits the function of regulating sodium deposition. Herein, an alkalized MXene/carbon nanotube (CNT) composite (named A-M-C) is introduced to regulate Na deposition behavior, which consists of Na3Ti5O12 microspheres, Ti3C2 MXene nanosheets and CNTs. Ti3C2 MXene nanosheets with large interlayer spaces and "sodiophilic" functional groups can provide abundant active sites for uniform nucleation and deposition of Na. Plenty of nanosheets are grown on the surface of the microsphere, thereby reducing the local current density, which can guide initial Na nucleation and promote Na dendrite-free growth. Furthermore, CNTs increase the electrical conductivity of the composite and achieve fast Na+ transport, improving the cycling stability of Na metal batteries. As a result, at a capacity of 1 mA h cm-2, the A-M-C electrode achieves a high average coulombic efficiency (CE) of 99.9% after 300 cycles at 2 mA cm-2. The symmetric cells of A-M-C/Na provide a long cycling life of more than 1400 h at 1 mA cm-2 with a minimal overpotential of 19 mV at an areal capacity of 1 mA h cm-2. The A-M-C/Na//NVP@C full cell presents a high coulombic efficiency of 98% with 100 mA g-1 in the first cycle. The strategy in this work provides new insights into fabricating novel MXene-based anode materials for dendrite-free sodium deposition.

A BF3-Doped MXene Dual-Layer Interphase for Reliable Lithium Metal Anode

The surface modification of lithium metal anode poses a promising way in reaching high energy-density batteries. Here we introduce a dual-layer interphase that consists of an in-situ formed lithium carboxylate organic layer and an ultra-thin BF3-doped monolayer Ti3C2 MXene on Li metal surface (Shang, Shovon, Wong, Niu. Advanced Materials, 35 (2023) 2210111). The honeycomb-structured organic layer increases the wetting of electrolyte due to the large surface area, leading to a thin solid electrolyte interface (SEI). While the BF3-doped monolayer MXene provides abundant active sites for lithium homogeneous nucleation and growth, resulting in about 50% reduced thickness of inorganic-rich components among the SEI layer. A low overpotential of less than 30 mV over 1000 h cycling in symmetric cells was received. The functional BF3 groups along with the excellent electronic conductivity and smooth surface of the MXene greatly reduce the lithium plating/stripping energy barrier, enabling a dendrite-free lithium metal anode. The battery paired with NMC811 exhibited a high initial Coulombic efficiency (CE) of 82.1%. A high capacity-retention of 175.4 mAh/g at 1.0 C was achieved after 350 cycles. After long 500 cycles, a reliable capacity was still remained while the cell with un-modified Li metal quickly dropped to below 74.2 mAh/g. In a pouch cell with a capacity of 475 mAh, the battery still exhibited a high discharge capacity of 165.6 mAh/g with a capacity retention of 90.2% after 200 cycles, while the cell with pure Li metal decreased to 80.5%. Keywords: Lithium metal electrode; Lithium ion battery; MXene; Doping

Electrochemical Nucleation and Growth: A Multimicroscopy Approach at the Same Scale

Electrodeposition is a critical electrochemical reaction with broad applications in technology. This demands a comprehensive understanding of the electrochemical nucleation and growth process (EN&G), and the different factors driving the formation of a new phase on a given substrate. Our understanding of the role of the substrate and the real nature of active sites still remains elusive due to the challenge of probing specific sites and bringing a statistical interpretation of the nucleation process. Moreover, conventional macroscopic approaches often record electrochemical magnitudes over large areas (cm2) which are then correlated with surface characterizations obtained from a vastly different scale (~μm2), correlations, which are not necessarily representative of the macroscopic surface. In order to establish meaningful and unambiguous correlations, it becomes necessary to employ techniques capable of surveying the surface with a high spatial-temporal resolution, such as scanning probe techniques, capable of recovering information in a scale closer to the growth of the new phase, i.e., local scale1. To address these challenges, we employed Scanning Electrochemical Cell Microscopy (SECCM), to study the EN&G of Cu on a glassy carbon substrate at a scale closer to the initial stages of the electrodeposition2. SECCM can be combined with other imaging methods such as scanning electron microscopy (SEM) to recover information from the deposited nanostructures at the same scale as the electrochemical response3. This so-called multimicroscopy approach allows us establishing direct correlations between the EN&G and the morphological, structural, and compositional features of the substrate and deposit. As a result, new insights that are not available with conventional macro-electrochemical analysis can be gained, such as the time-, potential-, and site-dependent nature of the EN&G process with a statistical perspective. This approach provides a new avenue for developing novel analysis strategies to understand the real nature of active sites for nucleation.References M. Bernal, D. Torres, S. S. Parapari, M. Čeh, K. Ž. Rožman, S. Šturm, and J. Ustarroz, Electrochim. Acta, 445, 142023 (2023).D. Torres, M. Bernal, A. Demaude, S. Hussain, L. Bar, P. Losada-Pérez, F. Reniers, and J. Ustarroz, J. Electrochem. Soc., 169, 102513 (2022).D. Torres, M. Bernal Lopez, and J. Ustarroz, Electrochemical nucleation and growth: A multimicroscopy Approach at the same scale, In preparation. (2023). Figure 1

Enhanced nucleate pool boiling heat transfer on CNTs-Cu nanoparticles-coated surfaces: Effects of sintering temperature and CNTs composition on pool boiling behavior

The present study involves the experimental investigation of pool boiling heat transfer characteristics on CNTs-Cu nanoparticles-coated heating surfaces. The advantages of coating the mixture of infinitesimal CNTs with Cu particles on the copper surface are to generate the active nucleation site density by porous structures and enhance the thermal conductivity of the heating surfaces. To explore the effects of sintering temperatures and CNTs composition on pool boiling behavior, we fabricated the boiling test sections under the sintering temperatures of 700, 750, and 800 °C for four different CNTs compositions of 0.0CNTs-100Cu, 0.2CNTs-99.8Cu, 0.3CNTs-99.7Cu, and 0.5CNTs-99.5Cu in wt.%. We first analyzed the surface morphologies, that is, the average pore size, porosity, and pore density, to characterize each tested sample. Pool boiling experiments were later conducted under atmospheric pressure using water to obtain the pool boiling curves and bubble dynamics for different sintering temperatures and CNTs composition. Based on the experimental analysis, nucleate boiling heat transfer enhancement was interpreted in relation to the sintering temperature with surface morphologies and CNTs composition in relation to improved pore density. Compared to the bare copper surface, the achieved maximum enhancement for boiling heat transfer coefficient and critical heat flux were 3.86 and 1.49, respectively, when a 0.5CNTs-Cu-coated surface sintered at 800 °C was applied.

Electrocrystallization and Morphology of Copper Coatings in the Presence of Organic Additives

Copper coatings with refined grains and smooth surface morphology were electrodeposited from electrolytes comprising a novel accelerator, the disodium salt of 4,4-dithiobenzene disulfonic acid (DBDA), with sodium chloride and polyethylene glycol (PEG) as inhibitors and 2-aminobenzothiazole (ABT) as a leveler. It was found that the morphology of the coatings strongly depends on the presence and type of additives. In the presence of only DBDA and NaCl, large crystallites are formed, whereas the addition of PEG and ABT significantly decreases their size, and the most fine-grained, smooth, and defect-free copper coating is formed with the combined use of all additives. To establish the correlation between the observed morphology and the kinetics of the additive-assisted copper electrocrystallization in the proposed electrolytes, the nucleation mechanism and its parameters were determined by transient electrochemical characterization. The extended nucleation model, which takes into account not only the copper deposition but also the electric double-layer charging and hydrogen reduction process, was used to establish the electrocrystallization kinetics in the presence of the additives. The results of such kinetic analyses can help to explain the morphological effect. By using the chronopotentiometry method, it was found that the addition of the disodium salt of 4,4-dithiobenzene disulfonic acid with chloride ions gives a catalytic effect, while the sequential introduction of polyethylene glycol and 2-aminobenzothiazole provides an increasing inhibitory effect. Voltamperometry and chronoamperometry tests showed that the process is controlled by the diffusion of ions to the growing three-dimensional cluster of a new phase. The introduction of additives into the electrolyte slows down the copper electroplating process at comparatively negative potentials and increases the probability of transition from instantaneous to progressive nucleation. Moreover, the rate of the process and the density of nucleation active sites increase (up to 2–3 times) with the addition of DBDA but decrease significantly (up to 5–8 times) in the presence of PEG and ABT, which additionally confirms their catalytic and inhibitory effects, respectively, and explains the significant smoothing effect on the morphology of the Cu-coatings.

Investigation of nucleate boiling and bubble dynamics at multiple nucleation sites in subcooled boiling flow

Accurate prediction of nucleate boiling heat transfer and phase change is crucial for subcooled boiling flow modeling. Among the nucleate boiling parameters, departure diameter, departure frequency, and active nucleation site density are considered the most important. To fulfill the modeling requirements, the present study established a comprehensive experimental database with simultaneous measurement of departure diameter, departure frequency, and active nucleation site density at multiple nucleation sites. The experimental data were collected in a vertical annular test section using a microscopic high-speed imaging system. Twenty-two experiments were performed at a system pressure of 150 kPa, liquid flow rate of 0.5 m/s, local subcooling ranging from 10 to 30 °C, and heat flux varying from 250 to 700 kW/m2. Stochastic characteristics of departure diameter and departure frequency at single and multiple nucleation sites were investigated. A correction approach was developed to minimize the impact of upstream bubbles on departure frequency measurement. The sample size of single-site measurement was determined based on the analysis of data dispersions. Large variations between nucleation sites were observed, indicating that single-site measurement is insufficient to characterize all nucleation bubbles. A parametric analysis of nucleate boiling parameters over operating conditions was performed based on the multi-site data. The experimental database generated in this study will be utilized for model evaluation and development in future research.

Asymmetric Domain Nucleation from Dislocation Core in Barium Titanate: Molecular Dynamics Simulation Using Machine‐Learning Potential through Active Learning

Barium titanate (BaTiO3) is a ferroelectric material without toxic elements, whose ferroelectric properties such as permittivity, coercive field, and spontaneous polarization are affected by the nucleation of domains of reversed polarization and the motion of domain walls. Dislocations can act as obstacles to domain‐wall migration or as active sites for domain nucleation. Thus, studies are conducted on the utilization of dislocations to improve the ferroelectric properties of BaTiO3. However, the atomistic mechanism of domain nucleation around the dislocation core is still unclear. In this article, a machine learning (ML) potential is developed to study the influence of dislocations on domain nucleation. The potential is trained using an active‐learning approach to ensure accuracy in the bulk properties of the ferroelectric and paraelectric phases, as well as in the dislocation core structures in BaTiO3. Molecular dynamics simulations using the ML potential show that the influence of dislocations on polarization reversal depends on the directional relationship between the external electric field and the dislocation. Furthermore, strong local polarizations exist surrounding the dislocation core, owing to vacancies in the core. These polarizations can act as both domain nucleation sites and obstacles for domain migration when ordered along the dislocation line.

Influence of smooth heater size on critical heat flux and heat transfer coefficient of saturated pool boiling heat transfer

In order to study the influence of smooth heater size on the performance of pool boiling heat transfer, saturated boiling experiments of FC-72 were conducted on eight sized smooth silicon chips (the test surfaces are denoted as S5 ∼ S30, and their dimensionless dimensions are in the range of Lh/Lc = 7 ∼ 42). The bubble dynamics during boiling were observed with a high-speed camera. The results indicated that in natural convection regime, the heat transfer coefficient decreases with increasing heater size at a given heat flux. Besides, the larger surfaces enter into the nucleate boiling regime earlier. In a fully developed nucleate boiling regime, S5 surface displays the optimal heat transfer performance. The reality is that no vapor columns are produced even in the high heat flux range due to its small bubble departure diameter and high bubble departure frequency. For S8 ∼ S15 surfaces, the wall temperatures increase continuously with the increase of heat flux, while S20 ∼ S30 surfaces present a trend of first keeping constant and then increasing. The active nucleation site densities on S15 ∼ S30 surfaces follow the law of Na = 0.45q2 in the whole nucleate boiling regime. By contrast, for S5 ∼ S12 surfaces, the nucleation site densities abide by this law only in a fully developed nucleate boiling regime. In addition, the departure diameter and departure frequency of bubbles increase with the increase of heat flux for all surfaces. It is observed that with the increase of smooth heater size, CHF presents a changing trend of first increasing (in range of Lh ≤ λD, λD is the most dangerous Taylor wavelength), then decreasing (in range of λD < Lh ≤ 3λD) and finally leveling off (in range of Lh > 3λD). Accordingly, the CHF value maximizes at the heater size Lh = λD. In the segment of decreased CHF, the decline rate of CHF in range of λD < Lh ≤ 2λD is larger than that in range of 2λD < Lh ≤ 3λD. Meanwhile, the influencing mechanisms of heater size on CHF were explained by consideration into bubble patterns and behavior.

Pool-boiling enhancement on periodic micro/nano ripple-structured surfaces fabricated by femtosecond laser

A study was conducted on whether periodic micro/nano ripple structures generated on metal surfaces using femtosecond laser processing could improve pool boiling heat transfer. Depending on the laser irradiation conditions on the metal surface, a surface structure with different geometrical characteristics is created. Changes in sample surface morphology caused by the laser irradiation intensity are examined using scanning electron microscopy and confocal laser microscopy. Pool boiling tests are conducted to compare three laser irradiation conditions fabricated samples and the bare copper surface. The working fluid is deionized water. The pool boiling curves of each sample surface were compared with each other. Visualization of bubble nucleation is performed using a high-speed camera. The superheat, bubble departure diameter, and bubble growth period of each sample are measured and compared at the onset of nucleate boiling (ONB). The most efficient periodic micro/nano ripple-structured surface reduces the superheat at the ONB by 6.13 °C in comparison with that at the bare Cu surface. The enhanced surface structure reduced the bubble departure diameter and renewal period by 60.5% and 55.6% in comparison with that of the smooth surface. Further, the structured surface showed 178.5% enhancement in heat transfer coefficient and 39.1% in critical heat flux, respectively. Thus, the combination of increased nucleate site density, high nucleation site activation, and a wicking effect in the periodic micro/nano ripple structure significantly improves the pool boiling heat transfer.

Mechanism underlying early hydration kinetics of carbonated recycled concrete fines-ordinary portland cement (CRCF-OPC) paste

Aiming to promote applications of carbonated recycled concrete fines (CRCF) as a low-carbon alternative to ordinary Portland cement (OPC), this study explored the effect of CRCF on the early hydration kinetics of OPC paste. The results show that CRCF is not only a highly active pozzolanic material but also an effective accelerator affecting the early hydration kinetics of OPC paste, thereby leading to an increased early compressive strength and a comparable 28-d compressive strength, even at a replacement ratio of 20%. Although the rheological properties and workability are negatively affected due to the high surface area and fine particle size of CRCF, the amorphous silica and silica-alumina gels and calcite present in CRCF facilitate initial ions dissolution and provide additional active nucleation sites for hydrates. As a result, the microstructure is densified due to the formation of additional C–S–H gels with high Si/Ca and Al/Ca ratios and carboaluminate phases, along with the inert filler effect of unreacted calcite particles. The incorporation of 20% CRCF to replace OPC can achieve a CO2 emissions reduction up to 25%. These indicate that the CRCF has a promising application scenario in transforming wasted concrete into high-value industrial products by CO2 activation.

Copper Oxide Decorated Carbon Nanofiber Skeleton for Dendrite‐Free Lithium‐Metal Anodes

AbstractLithium metal, possessing a high theoretical capacity, holds great promise as a desirable anode candidate for the next‐generation high energy density lithium batteries. However, the practical implementation of lithium metal faces significant challenges, including dendrite growth and volume expansion. Herein, a carbon nanofiber (CNF) three‐dimensional (3D) current collector was developed, complemented by the addition of copper oxide nanoparticles to the CNF framework, resulting in the creation of a lithiophilic 3D current collector known as CuO‐CNF. Subsequently, a 3D lithium metal composite anode (CuO‐CNF−Li) was fabricated through an electrochemical plating process. The utilization of a 3D structure based on carbon nanofibers provides sufficient space and a stable framework for lithium ion plating, effectively accommodating the substantial volume changes that occur during repetitive Li plating and stripping. The copper oxide nanoparticles loaded onto the CNF serve as active sites for lithium nucleation, facilitating an ordered and uniform plating/stripping process of lithium ions, thereby preventing dendrite formation. Consequently, the CuO‐CNF current collector enables dendrite‐free Li plating/stripping with an average Coulomb efficiency of up to 99 % and a low nucleation overpotential of only 15 mV. Moreover, symmetric cell tests demonstrated an extended lifespan of 2700 h at 2 mA cm−2 for the CuO‐CNF−Li composite anode.

Droplet boiling on micro-pillar array surface – Nucleate boiling regime

Despite spray cooling in the form of droplet boiling on a textured surface being a very promising phase-change heat dissipating method, the understanding of droplet/bubble two-phase dynamics in the nucleate boiling is extraordinarily limited. In this study, we report sessile droplet boiling on micro-pillar array surface in the nucleate boiling regime using a three-dimensional lattice Boltzmann model comprehensively. Effects of micro-pillar size on bubble behaviors inside droplet are discussed in detail, covering bubble nucleation, growth, coalescence, and rupture. For the micro-pillars with large side length or small spacing, nucleation sites are activated around micro-pillar top surface. The preferential activation location of nucleation sites is determined by temperature, confined space and fluid flow. In bubble growth stage, the variation of bubble radius with time follows the square root law, being consistent with previous experiments. Bubbles merge into a large central bubble beneath droplet for the short micro-pillars while into a vapor layer for the long micro-pillars. Emergence of large central bubble prolongs droplet lifetime but deteriorates heat transfer. In addition, increasing micro-pillar side length or decreasing micro-pillar height can delay activation of nucleation sites.

Numerical simulation of boiling behavior in vertical microchannels

High heat flux electronic devices put forward new requirements for heat dissipation, and boiling heat transfer technology is widely used because of its higher heat dissipation capacity. In this study, the volume of fluid method was employed, along with the incorporation of the Lee phase-change mass transfer model, to investigate two-phase flow and heat transfer in vertical upward rectangular microchannels. The heat flux was varied within the range of 10–40 kW/m2, while the mass flux was varied within the range of 200–600 kg/m2 s. With the increase in heat flux, bubble flow, slug flow, churn flow, and annular flow were found successively. A phase diagram was established to predict the flow pattern transition during the boiling process. When the flow pattern changes to the churn and the annular flow, the active nucleation site density increases obviously with the Boiling number (Bo). A new correlation was proposed for two-phase flow boiling heat transfer, suitable for vertical upward channels in microscale fluids. The friction factor obtained using the Darcy friction factor equation agrees well with the simulation results at a high-pressure drop. The instability in microchannels increases with the increase in heat flux, particularly in annular flow, resulting in more severe wall temperature fluctuations.

Enhanced mortar strength and resistance to seawater degradation in the presence of calcined coal-series kaolin

The hydration process of blended mortars and its resistance to seawater degradation in the presence of calcined coal-series kaolin (CCK) was investigated in this study. The TG tests were used to quantify the effect of calcination temperature on the chemical-bound water content of the blended pastes while the XRD tests were applied to analyze the main crystalline hydration phases of the blended pastes, which were further quantified using the Rietveld-XRD refinement. In addition, microcalorimetric tests were used to characterize the degree of hydration. The hydration process of the blended mortars was further investigated in detail via combining SEM and pozzolanic activity tests. Based on this, the resistance to seawater degradation of the blended mortars with added CCK were verified via the expansion and strength loss tests, and the mechanism was analyzed via the electric flux and the total Cl− content tests. The optimal percentage of CCK (12%) was determined via a linear weighted sum method. The CCK obtained at 800 °C had the highest pozzolanic activity, promoting hydration reactions to form new gels (C-S-H, C-A-H and C-A-S-H) at active nucleation sites in mortars. These further enhanced both the flexural and compressive strengths (the compressive strength reached ∼53.7 MPa) of the blended mortars. However, CCK reduced the generation of Mg(OH)2, AFt and Friedel’s salt, decreasing seawater degradation to the mortars. Therefore, this study provides a new strategy to prepare high-strength mortar with high resistance to seawater degradation.

Significance of interphase boundaries on activation of high-entropy alloys for room-temperature hydrogen storage

The ability of high-entropy alloys (HEAs) for hydrogen storage is a rather new topic in the hydrogen community. HEAs with the C14 Laves phase have shown a high potential to reversibly store hydrogen at room temperature, but most of these alloys require a high-temperature activation treatment. This study explores the role of interphase boundaries on the easy activation of HEAs at room temperature. Two chemically similar HEAs with single and dual phases, TiV1.5ZrCr0.5MnFeNi (C14 + 4 vol% BCC phases) and TiV1.5Zr1.5CrMnFeNi (single C14 phase), are designed and synthesized. While the dual-phase alloy readily absorbs hydrogen at room temperature without any activation treatment, the single-phase alloy requires a high-temperature activation. It is suggested that interphase boundaries not only provide pathways for easy hydrogen transport and activation of HEAs at room temperature but also act as active sites for heterogeneous nucleation of hydride. This study introduces interphase-boundary generation as an effective strategy to address the activation drawback of HEAs.

Deep learning-based approach to R-134a bubble detection and analysis for geothermal applications

This study utilized deep learning to analyse bubble images of R134a fluid produced on bare and novel oleophilic coated stainless steel heat exchanger plates to compare the heat transfer performance in terms of bubble parameters. This work was carried out as a part of the GeoHex project. The vapour bubbles of the boiling R134a fluid, produced on two types of heat exchanger plates, were captured with a high-speed camera during a boiling experiment. A deep learning algorithm based on the Mask R–CNN model was trained for bubble detection in the experimental videos. The algorithm achieved a bubble detection accuracy of 61.22% and 78.6% for the coated and uncoated plates, respectively. The lower accuracy for the coated plate could be attributed to the challenge of distinguishing bubbles from the complex coating pattern. The algorithm determined the number of detected bubbles, bubble sizes, and centroids per frame, tracking each bubble frame by frame. The tracking results were used to calculate the bubble parameters such as departure frequency, departure diameter, and active nucleation site density. The calculated departure diameter for both plates exhibited a difference of 3%, which corresponded closely to the experimental results showing a 4% variation in heat transfer coefficient, which was measured under identical experimental conditions utilizing the GeoHex rig. However, the calculated departure frequency and active nucleation site density exhibited a 17% disparity between the coated and uncoated plates, primarily stemming from the lower detection accuracy for the coated plate. Some limitations of the trained model were identified in accurately detecting very small, out of focus, and mutually occluded bubbles. Future research should focus on improving experimental rig designs to capture better side-view images and develop advanced machine learning or other techniques to address these limitations.

Advances in the use of carbonaceous scaffolds for constructing stable composite Li metal anodes

Compositing lithium metal anodes (LMAs) with carbon-based materials has been given much attention because of the latter's low density, high mechanical strength, stable electrochemical properties, and large specific surface area. Such a composite LMA stands out because of its ability to reduce the volume expansion, lower the local current density, and provide active nucleation sites for uniform Li+ plating. Recent research advances in carbon-based materials as scaffolds to make composite anodes are reviewed, including composites with pure metals and their alloys, and compositing strategies to improve anode stability.

Enhancement in pool boiling performance of GNP/Cu-Al2O3 nano-composite coated copper microporous surface

An experimental analysis of pool boiling is conducted on the GNP/Cu-Al2O3 (GNP-graphene nano particle) nanocomposite coated copper surfaces at atmospheric pressure using DI (distilled water) as boiling fluid. A two-step electro-deposition technique is used for fabrication of these micro/nano porous coated surfaces. A modified surface structure is formed due to this deposition and various surface morphology parameters such as surface structure, roughness, wettability are analysed. Results show the enhancement in BHTC (boiling heat transfer coefficient) and CHF (Critical heat flux) in nano composite coated surfaces compare to the bare copper surface. The maximum CHF of 2415 (kW/m2) and BHTC of 171.28 (kW/m2K) is found in the NCCS (nano-composite coated superhydrophilic) surfaces which are 122% and 239% more than the bare copper surfaces. The boiling performance is augmented mainly because of the improvement in roughness, wettability and also for the high thermal conductivity of the GNP/Cu- Al2O3 nano coating. Quantitative study of the bubble dynamics like active nucleation site density, bubble emission frequency, departure diameter of bubbleand their impact on heat transfer performance in the case of NCCS surfaces is performed with high-speed visualization.

Zeolite imidazolate framework composite membranes prepared on amine/tannic acid cross-linked polymeric hollow fiber substrates for enhanced gas separation

In this work, a continuous dense zeolite imidazolate framework (ZIF) composite membranes for enhanced gas separation were successfully prepared on diethylenetriamine (DETA) and tannic acid (TA) cross-linked polymeric hollow fiber substrates via the in-situ solvothermal method for the first time. With strong reactivity and small molecular volume, DETA connected various TA molecules and anchored TA molecules on the organic hollow fiber substrate to form a relatively tight spatial network. The modified polyvinylidene fluoride(PVDF) support contained abundant phenolic hydroxyl, carbonyl, and amine groups, providing a large number of active sites for heterogeneous nucleation and promoting the forming of continuous and non-defect MOF film. The synergistic effect between TA and DETA not only enhanced the stiffness and durability of the MOF composite membrane, but also improved the performance of membrane on gas separation. The morphology of the amine/TA modified to support and the MOFs composite membrane was analyzed by SEM, XRD, FTIR, XPS, etc. The fabricated TA-DETA-PVDF/ZIF-8 composite membrane with a continuously dense layer and unique structural stability displayed excellent H2 permeance of 1.01 × 10-7 mol·m−2 s−1 Pa−1 and competitive H2/N2 and H2/CH4 selectivity of 24.0 and 24.4, respectively.

Transparent glaze containing high-alumina glass frit: Batch-to-melt conversion

The use of high alumina (HA) glass frits in the production of transparent glazes is of potential technological interest due to their excellent mechanical properties. However, their strong tendency to crystallize limits their practical application. A transparent glaze was obtained by adding 30% by weight of the HA frit to a low-melting glaze fired at 1453 K for 30 min with a hardness between 5.92 GPa and 6.46 GPa. The crystallization and melting behavior of an HA frit mixed with a low-melting glaze model batch is investigated by studying the interaction between a compacted raw low-melting glaze placed on the polished surface of bulk HA glass. With increasing temperature, the low-melting glaze batch melts while CaAl2Si2O8 and MgAl2O4 crystallize in the HA frit. The melt surrounding the HA frit decreases the number of active nucleation sites weakening surface crystallization. In addition, the alkali cations in the melt tend to diffuse into the crystallized HA frit, reducing the viscosity of the layer surrounding the crystals, which accelerates their dissolution. The results provide information on the batch-to-melt conversion mechanism of high alumina content transparent glazes.