Low Supersaturation Conditions Research Articles

Guiding Principles for the Design of a Chemical Vapor Deposition Process for Highly Crystalline Transition Metal Dichalcogenides

2D transition metal dichalcogenides (TMDs) for advanced logic transistor technologies are deposited by various modifications of the chemical vapor deposition (CVD) method using a wide variety of precursors. Being a major electrical performance limiter, the TMD crystal grain size strongly differs between the various CVD precursor chemistries from nano‐ to millimeter‐sized crystals. However, it remains unclear how the CVD precursor chemistry affects the nucleation density and resulting TMD crystal grain size. This work postulates guiding principles to design a CVD process for highly crystalline TMD deposition using a quantitative analytical model benchmarked against the literature. The TMD nucleation density reduces favorably under low supersaturation conditions where the metal precursor sorption on the starting surface is reversible and the corresponding metal precursor desorption rate exceeds the overall deposition rate. Such reversible precursor adsorption guarantees efficient long‐range gas‐phase lateral diffusion of precursor species in addition to short‐range surface diffusion, which vitally increases crystal grain size. The proposed model explains the large spread in experimentally observed TMD nucleation densities and crystal grain sizes for state‐of‐the‐art CVD chemistries. Ultimately, it empowers the reader to interpret and modulate precursor adsorption and diffusion reactions through designing CVD precursor chemistries.

Deterministic Formation and Growth of Dendritic Crystals of Attractive Colloids

AbstractDendrites are ubiquitous crystals produced in supersaturated solutions and supercooled melts, but considerably less is known about their formation and growth kinetics. Here, the key factors are explored that dictate dendrite formation and growth, utilizing experimental colloidal models in which the particles act as molecules with Mie potential. Depletion attraction is employed to colloids and manipulate their strength to control supersaturation. Dendrites are predominantly produced under conditions of low supersaturation, where the separation between crystals is large due to slow nucleation. The dendrites do not emerge directly from nuclei. Instead, isotropic grains, initially produced from nuclei, morph into polygons. Arms then sprout from the vertices of these polygons, eventually giving rise to dendrites. Triggering this polygon‐to‐dendrite transformation requires a high diffusional flux. This necessitates a prolonged diffusion time to maintain a steep concentration gradient in the surrounding environment even after the transformation from circular grains to polygons.

Development of Moisture Absorbent Ceramic-Coated Separators for Advanced Lithium-Ion Batteries

In the present human life, various electric devices and machines are worked by lithium-ion batteries (LIBs). The batteries have still remained challenges such as, the low cycling stability due to side reactions during charge-discharge cycling and the weak thermal stability at high temperatures. Accordingly, research on improving resistance to high temperatures and impregnability by coating ceramic particles and polymer binders on the surface of the separator is being conducted. The ceramic coating separator is manufactured by connecting small-sized inorganic particles to each other using a small amount of binder. The inorganic particles have high hydrophilicity and high specific surface area, so the ceramic separator has excellent wettability to the electrolyte. As a ceramic coating, alumina is currently commercialized, and a slurry is prepared by mixing a binder, etc., and then coated on a separator and then dried. LG Energy Solutions has commercialized a ceramic composite separator called SRS (Safety-reinforcing separator) and is applying it to batteries. By introducing a ceramic layer on the surface of a polyolefin-based separator, the heat resistance and mechanical strength of the separator have been greatly improved, and it has been widely used in high-capacity and large-sized batteries. when the temperature of the LIBs rises and the separator shrinks or ruptures, a large amount of lithium ions may move, making control difficult and creating a risk of explosion. Therefore, shutdown occurs, but a separator with good shape retention at high temperature is required. Accordingly, research on improving resistance to high temperatures by coating ceramic particles and a polymer binder on the surface of the separator is being conducted. In this work, Ceramic-coated separator membrane film was fabricated using aluminum fluoride (AlF3) materials for a powerful moisture (H2O) scavenger. Accordingly, research on improving high temperature resistance and impregnation property by coating ceramic particles and a polymer binder on the surface of the separator is in progress. First of all, a-AlF₃ nanorods with an average length of 1.882 μm and a diameter of 320 nm were synthesized under low supersaturation conditions. Then, PVdF-HFP [Poly(vinylidene fluoride-co-hexafluoropropylene)]-acetone solution was mixed and coated on a polypropylene membrane. The AlF₃-coated separator exhibited thermal shrinkage of 4%, 8%, and 18% at 130, 140, and 150°C, respectively, confirming that thermal stability was improved. In addition, as a result of the impregnation test, it was confirmed that the impregnation property of the coated separator was improved compared to the existing polypropylene separator. In addition, it was confirmed that the full cell manufactured using the a-AlF₃-coated membrane film has improved cycle stability and high-speed, high-capacity compared to the full cell manufactured using the existing non-coated separator.

Paths From Aerosol Particles to Activation and Cloud Droplets in Shallow Cumulus Clouds: The Roles of Entrainment and Supersaturation Fluctuations

AbstractThe activation of aerosol particles and its contribution to cloud droplet size distributions in shallow cumulus clouds are investigated by analyzing the cloud field simulation results using a Lagrangian cloud model coupled with large eddy simulation, which allows explicit simulations of the activation and tracking of each super‐droplet. Analysis is focused on the differences in activations for aerosol particles following central updraft from a cloud base (CB) and particles entrained above the cloud base (EA). Time series of various variables following individual particles confirm the distinctive nature of CB and EA activation. Strong supersaturation fluctuations induced by entrainment and turbulent mixing at cloud edges cause most EA particles to be deactivated soon after activation, substantially limiting their lifetime and growth relative to CB particles. Most net activation—the difference between activation and deactivation—occurs at the cloud base and vanishes aloft. Cloud droplet activation spectra follow the theoretical prediction at high supersaturation conditions, although the proportional constant is smaller because of particle deactivation. The spectra deviate from the theoretical prediction at low supersaturation conditions since they are affected by the transport of the CB particles activated elsewhere.

The role of protein contents in promoting wastewater phosphorus and bioenergy recovery during anaerobic digestion

Proteins present in domestic and industrial wastewater, yet their role in nutrient and energy recovery during anaerobic digestion (AD) has not been well understood. This study aimed to examine the impact of feedwater protein content on the calcium phosphate (CaP) precipitation under a low supersaturation condition and the methane production in an AD process. Four 1.0 L upflow anaerobic sludge blanket (UASB) reactors were fed with the synthetic feeds with different protein contents. The results showed that the amino acid degradation caused the pH elevation, triggering the CaP precipitation. A 25% bovine serum albumin (BSA) content in the feedwater helped shape a superior microbial community that contributed to a methanisation rate of 82.7%. The high prevalence of the phylum Synergistetes and the methanogen Methanosaeta suggested that methane was mainly produced through the acetate utilization.

Condensation Heat Transfer Correlation for Micro/Nanostructure Properties of Surfaces.

Condensation, which can be observed in nature as a phase change heat transfer phenomenon, is a critical phenomenon in industrial fields such as power generation, water desalination, and environmental control. Many existing studies have applied surfaces with different wettability by controlling the surface topology to enhance condensation heat transfer. However, the industrial applicability is close to zero due to the limited size and shape of surfaces and low supersaturation conditions. Here, we regulate the surface topology of large-area copper tubes, which are representative industrial metals. We fabricated four copper tubes with different surface structures. We analyzed the condensation phenomenon of the modified tube under specific supersaturation conditions by measuring the overall heat transfer coefficient. We analyzed the condensation phenomenon by measuring the condensation heat transfer coefficient. We have recognized that there is a difference between the maximum droplet radius and the droplet detaching frequency depending on the size and shape of the structure. We measured the contact angle and contact angle hysteresis to accurately analyze the droplet behavior on each surface. As a result, we show that there is a correlation between contact angle hysteresis (CAH) and the total heat transfer coefficient, indicating heat transfer performance. These findings can be applied when evaluating surfaces with excellent condensation heat transfer performance for use in real industrial environments, which can dramatically reduce time and cost.

Quantification of Nucleation Site Density as a Function of Surface Wettability on Smooth Surfaces

AbstractDew water is recognized as a valuable source of clean water for human consumption. Given the developing concerns over global water scarcity, great focus has been turned toward increasing the efficiency of existing dew harvesting methodologies. Droplet nucleation is a critical first stage in the condensation process – and therefore key to dew water harvesting. In this paper, the droplet nucleation site density (Ns) as a function of surface wettability on smooth thin polymer films is quantified. A custom‐built environment chamber, operated in low supersaturation conditions relevant to atmospheric water harvesting, allows strict experimental control over temperature and humidity. Droplet growth through coalescence is quantified, and an exponential increase in the rate of coalescence is seen as the test surface wettability increased. Ns declines exponentially as wettability decreases according to the fitted equation Ns = 1.1 × 1011e−0.043θ , where theta is the contact angle of the smooth surface, which can be used to predict Ns from a known contact angle, currently not available. The average distance between droplet centers is found to increase at a linear rate. This nucleation behavior is in line with those of droplets in a Rayleigh distribution.

A new CCN activation parameterization and its potential influences on aerosol indirect effects

Unactivated particles mixed in cloud condensation nuclei (CCN) measurements lead to inaccurate activation parameterization, thereby overestimating aerosol indirect effects in current models. Data from five CCN field campaigns in Eastern China are analyzed to identify unactivated particles. The lower temperature, lower aerosol hygroscopicity (κ), and the aerosol particle size distribution closer to that in the coast (compared to that in the continent) lead to a higher proportion of unactivated particles in CCN measurements; the underlying physical mechanisms are discussed. A correction for the CCN activation parameterization is essential for regions with the above characteristics. After removing the unactivated particles, it is found that the widely used Twomey power-law activation parameterization does not adequately fit the relationship between the corrected CCN concentration and the supersaturation; therefore, a new, better-fitting, two-parameter activation parameterization is proposed. A method is presented for estimating the parameters in the new parameterization according to the κ-Köhler theory, that is, the two parameters can be estimated as 59% and 66% of aerosol number concentration for continental regions (represented by Nanjing, 32.21°N, 118.70°E) and 69% and 79% of that for coastal regions (represented by Shenzhen, 22.48°N, 114.56°E), respectively. The new CCN activation parameterization significantly reduces the overestimation of CCN concentration at low supersaturation (SS) conditions, e.g., at SS = 0.1% in the five CCN campaigns, the overestimation is 77% to 102% for the classical power-law parameterization and only 6% to 13% for the new parameterization. As a result, the new parameterization may reduce the overestimation of aerosol indirect effects in models, especially at low supersaturation conditions.

Screw-Dislocation-Driven Hierarchical Superstructures of Ag-Ag2O-AgO Nanoparticles

Constructing multi-dimensional hierarchical superstructures has been, for a longtime, regarded as a promising strategy for modifying the physiochemical properties of nanomaterials. Guided by this rule, this work reports the synthesis of hierarchical superstructures of Ag-Ag2O-AgO nanoparticles (HSANs) using a convenient and surfactant-less photochemical method under 254 nm UV-irradiation. The formation of the HSANs superstructures is dominated by screw-dislocation-driven growth mechanism at low supersaturation condition. The structural evolution of the HSANs superstructures has been systematically investigated. The average size of the HSANs superstructures increased with prolonged 254 nm UV-irradiation. The step density on the superstructure surfaces also increased along with the 254 nm UV-irradiation time.

Dual-Electronic Nanomaterial (Synthetic Clay) for Effective Removal of Toxic Cationic and Oxyanionic Metal Ions from Water

A synthetic clay (Mg/Al-layered double hydroxides; LDH) was directly synthesized through a simple coprecipitation method under a low-supersaturation condition. The clay was applied to remove metal cations (Cd2+, Cu2+, Pb2+, Ni2+, and Cr3+) and oxyanions (MnO4– and Cr2O72–) from a single aqueous solution. The result demonstrated that LDH exhibited a poor porosity (its specific surface area and total pore volume: 23.2 m2/g and 0.161 cm3/g, respectively) and positively charged surface within solution pH from 3.0 to 12. The X-ray powder diffraction (XRD) data suggested that the basal spacing of LDH was 0.773 nm. The presence of active CO32– anions in the interlayer region of LDH that played an extremely important role in the adsorption process was identified by XRD and Fourier-transform infrared spectroscopy (FTIR). Energy-dispersive X-ray spectroscopy (SEM) analysis indicated that LDH possessed a surface morphology like a plate with a hexagonal shape. The adsorption isotherms of LDH towards various potentially toxic metals were conducted at 1.0 g/L, pHEquilibrium 5.0, 30°C, and 24 h. The Langmuir maximum adsorption capacity of LDH towards the target metals exhibited the following order: 1.299 mmol/g (for Ni2+ adsorption) > 0.880 mmol/g (Cd2+) > 0.701 mmol/g (Cr3+) > 0.657 mmol/g (Pb2+) > 0.601 mmol/g (Cu2+) > 0.589 mmol/g (Cr2O72–) > 0.522 mmol/g MnO4–. The synthetic clay can adsorb both cations and anions in the solution. Therefore, such LDH material can serve as a potential dual-electronic adsorbent for effectively eliminating various oxyanionic and cationic metal ions from water media.

Passive Anti-Flooding Superhydrophobic Surfaces.

Superhydrophobic (SHPo) surfaces can provide high condensation heat transfer due to facilitated droplet removal. However, such high performance has been limited to low supersaturation conditions due to surface flooding. Here, we quantify flooding resistance defined as the rate of increase in the fraction of water-filled cavities with respect to the supersaturation level. Based on the quantitative understanding of surface flooding, we suggest effective anti-flooding strategies through tailoring the nanoscale coating heterogeneity and structure length scale. Experimental verification is conducted using CuO nanostructures having different length scales combined with hydrophobic coatings with different nanoscale heterogeneities. The proposed anti-flooding SHPo can provide a ∼130% enhanced average heat transfer coefficient with ∼14% larger supersaturation range for droplet jumping compared to a previous CuO SHPo. The proposed anti-flooding parameter and the scalable SHPo will help develop high-performance condensers for real-world applications operating in a wide range of supersaturation levels.

A New Method for Distinguishing Unactivated Particles in Cloud Condensation Nuclei Measurements: Implications for Aerosol Indirect Effect Evaluation

AbstractAn ongoing challenge for cloud condensation nuclei (CCN) measurements is the inclusion of unactivated particles, which affects droplet activation parameterizations and aerosol indirect effects in models. For the first time, a reciprocal relationship between the critical diameter and critical supersaturation of activated droplets from the κ‐Köhler theory is derived to accurately count unactivated particles in CCN measurements. We conducted 4‐day continuous observations to simultaneously measure the number concentration of CCN (NCCN) and aerosol. The results show that as supersaturation (SS) decreases from 0.186% at 25 °C, the proportion of the unactivated particles in the CCN measurements increases, reaching 88% at SS of 0.07%. Owing to the NCCN overestimation caused by NCCN‐SS parameterizations with uncorrected NCCN, there is significant overestimation of aerosol indirect effects, especially under low SS conditions. After removing unactivated particles, NCCN‐SS parameterizations are adjusted accordingly, which can improve simulations of aerosol‐cloud‐radiation interactions in models.

Laboratory study of the heterogeneous ice nucleation on black-carbon-containing aerosol

Abstract. Soot and black carbon (BC) particles are generated in the incomplete combustion of fossil fuels, biomass, and biofuels. These airborne particles affect air quality, human health, aerosol–cloud interactions, precipitation formation, and climate. At present, the climate effects of BC particles are not well understood. Their role in cloud formation is obscured by their chemical and physical variability and by the internal mixing states of these particles with other compounds. Ice nucleation in field studies is often difficult to interpret. Nonetheless, most field studies seem to suggest that BC particles are not efficient ice-nucleating particles (INPs). On the other hand, laboratory measurements show that in some cases, BC particles can be highly active INPs under certain conditions. By working with well-characterized BC particles, our aim is to systematically establish the factors that govern the ice nucleation activity of BC. The current study focuses on laboratory measurements of the effectiveness of BC-containing aerosol in the formation of ice crystals in temperature and ice supersaturation conditions relevant to cirrus clouds. We examine ice nucleation on BC particles under water-subsaturated cirrus cloud conditions, commonly understood as deposition-mode ice nucleation. We study a series of well-characterized commercial carbon black particles with varying morphologies and surface chemistries as well as ethylene flame-generated combustion soot. The carbon black particles used in this study are proxies for atmospherically relevant BC aerosols. These samples were characterized by electron microscopy, mass spectrometry, and optical scattering measurements. Ice nucleation activity was systematically examined in temperature and saturation conditions in the ranges of 217≤T≤235 K and 1.0≤Sice≤1.5 and 0.59≤Swater≤0.98, respectively, using a SPectrometer for Ice Nuclei (SPIN) instrument, which is a continuous-flow diffusion chamber coupled with instrumentation to measure light scattering and polarization. To study the effect of coatings on INPs, the BC-containing particles were coated with organic acids found in the atmosphere, namely stearic acid, cis-pinonic acid, and oxalic acid. The results show significant variations in ice nucleation activity as a function of size, morphology, and surface chemistry of the BC particles. The measured ice nucleation activity dependencies on temperature, supersaturation conditions, and the physicochemical properties of the BC particles are consistent with an ice nucleation mechanism of pore condensation followed by freezing. Coatings and surface oxidation modify the initial formation efficiency of pristine ice crystals on BC-containing aerosol. Depending on the BC material and the coating, both inhibition and enhancement in INP activity were observed. Our measurements at low temperatures complement published data and highlight the capability of some BC particles to nucleate ice under low ice supersaturation conditions. These results are expected to help refine theories relating to soot INP activation in the atmosphere.

In Vitro Coral Biomineralization under Relevant Aragonite Supersaturation Conditions.

The biomineralization of corals occurs under conditions of high and low supersaturation with respect to aragonite, which corresponds to day- or night-time periods of their growth, respectively. Here, in vitro precipitation of aragonite in artificial seawater was investigated at a high supersaturation, allowing spontaneous nucleation and growth, as well as at low supersaturation conditions, which allowed only the crystal growth on the deliberately introduced aragonite seeds. In either chemical systems, soluble organic matrix (SOM) extracted from Balanophyllia europaea (light sensitive) or Leptopsammia pruvoti (light insensitive) was added. The analyses of the kinetic and thermodynamic data of aragonite precipitation and microscopic observations showed that, at high supersaturation, the SOMs increased the induction time, did not affect the growth rate and were incorporated within aggregates of nanoparticles. At low supersaturation, the SOMs affected the aggregation of overgrowing crystalline units and did not substantially change the growth rate. On the basis of the obtained results we can infer that at high supersaturation conditions the formation of nanoparticles, which is typically observed in the skeleton's early mineralization zone may occur, whereas at low supersaturation the overgrowth on prismatic seeds observed in the skeleton fiber zone is a predominant process. In conclusion, this research brings insight on coral skeletogenesis bridging physicochemical (supersaturation) and biological (role of SOM) models of coral biomineralization and provides a source of inspiration for the precipitation of composite materials under different conditions of supersaturation.

Effect of high lanthanum content and thermal treatment on mineralogical, textural, and structural properties of La-hydrotalcite-like compounds

Hydrotalcites and their respective mixed oxides are widely employed as catalysts and catalytic precursors on several industry processes. A series of La-hydrotalcite-like compounds (LaHT) synthesized by direct co-precipitation with ultrasonic homogenization under low supersaturation conditions and their respective oxides were studied by powder X-ray diffraction (XRD), infrared spectrometry (FTIR), and scanning electron microscopy with energy dispersive spectroscopy (SEM/EDS). The effect of thermal treatment (850 °C) and La3+ contents (55 ≤ La at.% ≤ 65) on the structure and texture of these minerals were investigated. Synthesis route was effective to produce LaHT as major mineral at all La samples. La carbonates and hydroxides were crystallized as accessory phases. At 850 °C, MgO-type oxides were crystallized as major phases.

Regularities of self-organization of technological conditions during plasma-arc synthesis of carbon nanotubes

The emerging concept of self-organization under conditions of plasma-surface interaction is reflected in the present analytical study of the processes and causes of carbon nanotube formation in anodic arc discharge. Based on the energy balance and the interelectrode mass transfer, we created a mathematical model of self-organization of technological conditions required for carbon nanotube synthesis. The self-organization regularities of such parameters as carbon concentration, relative supersaturation above the growth surface and the surface temperatures of both electrodes have been determined by the phase portrait method. Unique possibilities of self-organized processes have revealed the ways of maintaining required synthesis stationarity. It has been shown that extremely low supersaturation of deposited vapors, substance accumulation above the growth surface and exposure to plasma are important factors for carbon nanotube formation. The structure formation mechanism under conditions of self-organized low supersaturation has been discussed. The stated self-organization regularities are also expected to take place in other fields of plasma nanoscience.

SYNTHESIS OF HYDROTALCITE POWDER AND BEAD TO REMOVE ARSENATE

The affecting factors on the synthesis of hydrotalcite (HT) powder and bead for effective arsenate removal were investigated. HTs with a ratio of Mg:Al = 2:1 (MA) were synthesized by the co-precipitation method at 70 oC with reaction times of 1 and 120 -  300 min. The synthesis of MA with a reaction time of 1 min was done under high supersaturation condition, the others under low supersaturation conditions. The characteristics of MA were examined by X-ray diffraction (XRD), scanning electron microscopy, and nitrogen adsorption/desorption isotherms. According to the XRD patterns, pure HT was obtained for all tested conditions. With increasing reaction time from 1 to 300 min, the crystal size of MA increased from 4.9 to 11.3 μm, the surface area of MA increased from 9.3 to 71.4 m2/g. Batch-mode experiments showed that 1-min reaction time MA had the highest As(V) removal capacity. MA beads were separately synthesized using alginate and poly acrylamide (PAM) as binding agents. For alginate/MA, heat drying (110 oC) and freeze drying were applied to test the effect of these drying methods on the beads. The results showed that As(V) adsorption capacity of PAM/MA was the highest, closely followed by freeze drying/alginate/MA, much higher than that of heat drying/alginate/MA bead.   

Insight and Control of the Crystal Growth of Zeolitic Imidazolate Framework ZIF-67 by Atomic Force Microscopy and Mass Spectrometry

Combination of electrospray ionization mass spectrometry (ESI-MS) and in situ atomic force microscopy (AFM) are applied to provide the first nanoscopic study of the crystal growth of zeolitic imidazolate framework ZIF-67. ZIF-67 is found to form through a process of nucleation and spreading of metastable unenclosed substeps to form stable surface steps of the enclosed framework structure and demonstrates that isostructural MOFs, ZIF-67 and ZIF-8, undergo identical crystal growth mechanisms. The information on the crystal growth species obtained from the AFM experiments correlates well with the solution species identified by ESI-MS indicating that the species involved in the growth under low supersaturation conditions are methylimidazole/methylimidazolate, monomeric nonmethylimidazole/methylimidazolate complexed Co2+ ions and monomeric complexed [Co(methylimidazole/methylimidazolate)1-2] ions. Combination of the use of low supersaturation growth solutions and in situ AFM has also allowed the successful ext...

Step-free GaN surfaces grown by confined-area metal-organic vapor phase epitaxy

A two-step homoepitaxial growth process producing step-free surfaces on low dislocation density, Ga-polar ammonothermal GaN single crystals is described. Growth is conducted under very low supersaturation conditions where adatom incorporation occurs predominantly at step edges, and lateral growth is strongly preferred. The achievable step-free area is limited by the substrate dislocation density. For ammonothermal crystals with an average dislocation density of ∼1 × 104 cm−2, step-free mesas up to 200 × 200 μm2 in size are achieved. These remarkable surfaces create a unique opportunity to study the effect of steps on the properties and performance of semiconductor heterostructures.

Effect of hydration temperature on the structure reconstruction of MgAlY layered materials

This contribution investigates the obtaining of layered double hydroxides (LDHs) modified with different concentrations of yttrium and the effect of the yttrium concentration and temperature during the rehydration of the mixed oxides derived from these solids. Mg3Al(1−x)Yx-LDH (where x = 0.04–0.6) have been prepared using the standard coprecipitation method under low supersaturation conditions. After the calcination of these solids (460 °C, 18 h), the corresponding mixed oxides were obtained. The reconstruction of the layered structure was attempted by rehydration of the mixed oxides under two different conditions: (1) at 25 °C and (2) at 70 °C. All the aforementioned solids have been characterized by chemical analysis, X-ray diffraction, DRIFTS spectra, N2 adsorption–desorption isotherms, and determination of base sites. Their catalytic activity was tested in cyanoethylation of ethanol with acrylonitrile. The results obtained after the characterization and the catalytic activity tests were compared with those obtained for a standard hydrotalcite Mg3Al.