Nucleation Growth Processes Research Articles

Dual‐Functional Quantum Dot Seeding Growth of High‐Quality Air‐Processed CsPbI2Br Film for Carbon‐Based Perovskite Solar Cells

The high‐quality perovskite film is a prerequisite for high‐performance optoelectronic devices. Herein, CdSe colloidal quantum dots (QDs) serve as crystallization seeds for the first time to modulate the nucleation and crystal growth processes simultaneously of the CsPbI2Br film in the ambient environment. As additives, CdSe QDs help promote the nucleation process in the initial stage of perovskite formation. In addition, it is revealed that the surface ligands of QDs also have an essential influence on the subsequent crystal growth of the perovskite film. The bifunctional ligands on the surface of QDs are beneficial in delaying the growth process of perovskite due to the free functional groups at the ends. The CsPbI2Br film prepared with bifunctional organic ligand‐capped CdSe QD additives shows better crystallinity than that of the inorganic ligand‐based one due to the dual function of these kinds of QDs in not only promoting nucleation but also retarding crystal growth of CsPbI2Br crystals. As a result, the high‐quality CsPbI2Br film with a low defect state density is prepared in the ambient environment. The optimized efficiency of the assembled hole‐conductor‐free carbon‐based perovskite solar cells (C‐PSCs) is increased from 12.73% to 14.49%, which is one of the best results for all‐inorganic C‐PSCs.

Effect of ion-exchangeable calcium on carbonaceous particulate matter formation during coal pyrolysis

This work investigated the effect of ion-exchangeable calcium on the mass yield, size distribution and structural properties of carbonaceous particulate matter from coal pyrolysis. The raw, acid washed and calcium-exchanged coal samples were pyrolyzed in a flat-flame burner at 1600 K. The particulate matter was collected with a three-stage dilution sampler. Then, the particle size distributions were measured by a low pressure impactor (DLPI+) and a scan mobility particle sizer (SMPS). The results show that, with the addition of ion-exchangeable calcium, the soot yield reduces, and the size growth of soot particles is inhibited. Transmission electron microscopy (TEM) analysis shows that ion-exchangeable calcium diminishes the sizes of disordered cores in soot primary particles, accelerates the graphitization of soot and makes the soot aggregates more compact. The chemical structures derived from Raman spectroscopy and Fourier transform infrared spectroscopy (FTIR) indicate that the graphitization degree of the soot is first enhanced and then inhibited with increasing calcium loading amount. Additionally, the inorganic species in the size-segregated soot particles were characterized. The fractions of calcium and sodium in soot show opposite trend with particle size. Unlike Na, which nucleates before soot inception, Ca tends to participate in both the soot nucleation and surface growth processes, and is enriched at larger particle size.

Wellposedness of a DNA replication model based on a nucleation-growth process

<p style='text-indent:20px;'>In this paper, we analyze a nonlinear equation modeling the mechanical replication of the DNA molecule based on a Kolmogorov-Jhonson-Mehl-Avrami (KJMA) type model inspired on the mathematical analogy between the DNA replication process and the crystal growth. There are two different regions on the DNA molecule deep into a duplication process, the connected regions where the base pairs have been already duplicated, called eyes or islands and the regions not yet duplicated, called holes. The Cauchy problem associated with this model will be analyzed, where some dependences and nonlinearities on the replication velocity and the origins of replication are introduced.</p>

Inhibitory effect of novel green polymer (Aspartic-citric acid) on the process of nucleation during gypsum scale formation

The presence of metal salts in the process fluid in industries leads to scale deposition over the heating or cooling surfaces and causes an significant increase in the overall process and product cost of the product. This further reduces the efficacy of the equipment and the quality of the product is compromised. Hence, in order to avoid this various conventional additives containing nitrogen, phosphorous and sulphur are used as antiscaling agents due to their superior scale inhibition properties. However, excessive use of these antiscalants has created an imbalance in the ecosystem. Hence, there is a necessity to look for more reliable compounds that are as equally efficient as the conventional ones and are eco-friendly, biodegradable and cost effective. In the present study, homo and hetero polymers of aspartic acid and citric acid have been synthesized using condensation method and their antiscaling properties against gypsum deposition is been evaluated. Characterization of the synthesized polymers and deposited scale was performed by FTIR, GPC, SEM and XRD. The polymer showing the highest efficiency in the preliminary screening test was further evaluated to study its effect on the process of nucleation and crystal growth. The synthesized polymers were found to be efficient in inhibiting the scale deposition process at additive concentration as low as 3 ppm. The presence of additive (PAS-co-CA2) increased the induction time, surface free energy of formation, critical nuclei size and number of molecules per critical nuclei. Hence, rate of nucleation was reduced. Molecular weight and functional groups were the crucial factors in determining the scale inhibition properties of the polymer. The process of crystal formation and deposition was significantly retarded in presence of the additive with a change in the crystal morphology of the deposited crystals.

The study on the impinging freezing of the supercooled droplet containing the atmosphere aerosol

The aerosols have significant effect on the nucleation of supercooled droplet in the atmosphere. In this paper, the impinging freezing and static isothermal freezing experiments of the supercooled droplet were conducted to investigate the effect of potassium feldspar (K-feldspar), as the representative of aerosols, on the impinging freezing process. The results show that the impingement has more effect than K-feldspar on the freezing of supercooled droplet on the cold substrate. However, the K-feldspar can increase the impinging freezing probability of supercooled droplet further, and the higher the concentration of K-feldspar, the greater the influence. The freezing probability model in the static freezing and impinging freezing was established. Significantly, these freezing probability curves of K-feldspar suspension are exponential function and linearly proportional to the concentration approximately.However,the K-feldspar has little effect on the nucleation time during the impinging freezing. Moreover, by comparing the impinging freezing process, not only the nucleation but also the ice growth could be affected by the K-feldspar, leading to different final freezing morphology. The horizontal growth rate of ice could be increased by 3–10% because of K-feldspar, and the higher the temperature, the more the increase. Finally, according to the nucleation and ice growth process, the spreading ratio model was established and could predict the spreading ratio on various substrates. Spreading ratio of K-feldspar suspension is higher than pure droplet.

MOFs the movie: Molecule to nuclei evolution during metal-organic framework formation

The chemical and structural diversity of Metal-Organic Frameworks (MOFs) makes them an exciting class of materials as a scientific playground to potentially address a variety of applications, yet this diversity poses a daunting challenge to fully understanding their fundamental principles. Scientists from Netherlands and Belgium have captured MOFs in motion through a complementary set of simple yet informative <i>in situ</i> spectroscopy to promote an in-depth visualization of the nucleation growth process. Not only does this work elucidate guiding theories for MOF synthesis, but it also paints a picture of complex nucleation dynamics for those seeking to strengthen their foundational knowledge.

Effects of the electric field on soot formation in combustion: A coupled charged particle PBE-CFD framework

In this article, a coupled PBE-CFD framework has been proposed to study counterflow non-premixed flames and soot formation under an external electric field. This framework integrates the population balance equation (PBE) for nanoparticle dynamics into an in-house CFD solver for the multicomponent reactive flows. Different electric properties have been considered in this model. An ion mechanism used in both fuel-rich and fuel-lean combustion is combined with a detailed chemistry for neutral gaseous species and small-size aromatics to retain the full chemistry. In order to model soot particles carrying charges and the movement of the reacting fluid medium in the electric field, a second PBE for the production and transport of charges on soot particles is introduced for the first time and incorporated into the original PBE for the number density of particles. Also, the electric force for the gas mixture is included in the momentum equations. The electric drift velocities for ions and soot particles are also considered in the transport equations of ions and the PBE of soot particles, respectively. The simulations have shown that the presence of the electric field modifies the stagnation plane of the counterflow flames and reduces the soot formation in both rich-fuel and lean-fuel conditions in agreement with experimental observations. The application of the soot particle charging model, accompanied by a proper electric correction factor on the nanoparticle processes of nucleation and surface growth, significantly improves the stability of the flame structure. The introduction of the electric correction factor reveals that the suppression of soot formation in an electric field is mainly caused by the inhibited chemical reactions of the PAH nucleation and particle surface growth, which is more important than the electric drift of the charged particles. Reducing the critical size of the particle charging process enhances the electric drift of nascent soot, thus lessening its subsequent evolution.

High-temperature tensile and creep behaviour of Inconel 625 superalloy sheet and its associated deformation-failure micromechanisms

Thermal tensile and creep properties provide important information for selecting the suitable service conditions for metal materials. In this study, the effects of temperature on the tensile and creep properties, microstructure evolution, and deformation mechanisms of thermal-rolled Inconel 625 sheets were systematically investigated at 650 and 750 °C. The results showed that type B + C serrations dominated the tensile deformation at 650 °C. As the tensile temperature increased to 750 °C, type C serrations occurred in the early stages of the deformation and gradually transformed to type B serrations with the increase of the strain level. The microscopic observations through transmission electron microscopy (TEM) indicated that type B and C serrations were related to the carbon atom–moving dislocation interactions and nucleation–growth process of twin deformation, respectively. Moreover, the creep tests at 650 °C exhibited a better creep resistance than that at 750 °C. The results from the electron backscatter diffraction and TEM indicated combined grain boundary sliding and dislocation slipping as the main creep mechanisms at 650 °C. Moreover, the creep stress can accelerate the precipitation of the γ″ phases at 650 °C, which plays an important role in improving creep resistance, thereby improving the efficiency in strengthening Ni-based alloys. In addition, δ phase precipitation occurred during creep loading at 750 °C. The δ phases/matrix interfaces can act as nucleation sites to initiate dynamic recrystallization, which greatly affects the reduction of the work hardening rate and consequently, decreasing the creep resistance at 750 °C.

Synthesis of pure zeolite X from coal slime

Coal slime, a solid waste from coal separating plant, was still underutilized with leaving disposal problems. In fact, high silica and aluminum oxide content inside this material opened a possibility to become a potential zeolites precursor. Zeolite X was synthesized from HuangLing mining coal slime. After the coal slime was treated by calcination, acid leaching for removing iron and alkali fusion, the residue was used to prepare zeolite X by hydrothermal synthesis method. The crystallization mechanism was studied. The influence factors on crystallinity were investigated, including n(SiO2/Al2O3) (mole ratio), n(Na2O/SiO2) and n(H2O/Na2O). X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to characterize the nucleation and crystal growth processes. High purity of zeolite X was prepared by the optimizing process condition, and had complete crystal shape with uniform particle size. The BET surface area of self-governing zeolite X reached 645.55 m2/g.

Simulation and experimental study of dynamic recrystallization process during friction stir vibration welding of magnesium alloys

A two-dimensional cellular automaton (CA) model was utilized to analyze the effect of mechanical vibration on microstructure evolution of AZ91 alloy during friction stir welding (FSW). The simulated results, namely grain topology, grain size distribution, average grain size, and also the dynamic recrystallization (DRX) fraction were compared with measured data. The adequate comparability between FEM and experimental data shows that the CA method can be applied to the analysis of the microstructure progression during the friction stir welding of AZ91 alloy. It is concluded that the dislocation density during the friction stir vibration welding (FSVW) is higher than that in the FSW process and the process of nucleation and grain growth is faster for samples during FSVW compared to FSW. The grain size modification and DRX phenomenon with various vibration frequencies were also simulated in detail during FSVW. It is found that vibration makes nucleation start earlier and decreases the proportion of the incubation period and the percentage of recrystallization as vibration frequency improves.

Investigation on the flow limitation during copper electroplating of polyurethane foam

The electroplating method was employed to precipitate ionic Cu on the polymeric foam substrate. To compare the effective parameters in the foam electroplating process, open-cell polyurethane foams with different pore sizes 30, 35, 40, and 70 ppi (pore per inch) were used. To attain the desired conductivity in polymeric foams, graphite was selected as a pre-coating material. Both direct current and pulsed current were used for electroplating samples. The results show that by reducing the pore size of the foams, significant changes in the ions' hydrodynamic behavior and forces from the electromagnetic field occur. These factors cause the trend of a coating rate to decrease. The magnitude of these changes in the sample with 70 ppi is more severe than in the other samples. It was seen that the precipitated Cu on the foam through the pulsed current electroplating method was smoother than its counterpart produced by a direct current electroplating method. Flower-shaped precipitations were observed in SEM images showing the nucleation and grain growth process. A physical model has described the precipitation mechanism according to the limiting diffusion current (LDC).

Effects of ammonia addition on soot formation in ethylene laminar premixed flames

This paper presents particle size distributions and chemical compositions of soot measured using a Scanning Mobility Particle Sizer (SMPS) and a Fourier-Transform Ion Cyclotron Resonance Mass Spectrometer (FT-ICR-MS), respectively, in flames of ethylene-oxygen and ethylene-oxygen doped with ammonia. The inhibitory effect of ammonia addition on soot formation in ethylene flames, as well as the influence on soot particle size are discussed. The results of particle size distributions showed that doping with ammonia decreases soot particle size and the volume fraction of soot particles. In this work, the flames were carefully studied under similar temperature conditions, so all observed changes could be attributed to chemical effects. The results of FTICR-MS analysis showed that polycyclic aromatic hydrocarbons (PAHs) were the main compositions in both pure ethylene and ammonia doped ethylene flames. Nitrogen-containing PAHs (N-PAHs) did not contribute significantly to soot nucleation or mass growth processes. Chemical kinetic analysis revealed that CN species generated in ethylene-ammonia flames removed carbon from participating in soot precursor formation, thereby reducing soot formation.

Removal of trace amount impurities in glycolytic monomer of polyethylene terephthalate by recrystallization

Chemical recycling is a promising way to achieve the closed-loop recycling for polyethylene terephthalate (PET). During this process, the post-consumer PET is depolymerized into bis(2-hydroxyethyl) terephthalate (BHET) through glycolysis and BHET can be polymerized again to produce recycled PET (rPET). However, since the applications of rPET is greatly limited to the color, recycling of PET fibers is challenged by the residual of colored impurities. In this study, a modified recrystallization process using ethyl acetate (EA) as the solvent was employed for the removal of colored impurities from the BHET. The process showed a decoloring rate of over 97.5% for the model colored impurities, performing better than the reported physical adsorption processes. Since almost no disperse dye was precipitated during the nucleation and crystal growth process due to the high solubility in EA, only a small amount of colored impurities adsorbed on the surface of crystals, leading to an excellent decolorization performance and post-consumer EA could be easily recycled through evaporation followed by condensation. Besides the model colored BHET, raw BHET obtained from the depolymerization of dark PET fibers was also purified by this modified recrystallization. By applying a composite purification strategy combining EA-based recrystallization and activated carbon adsorption, the whiteness (L*) of BHET greatly increased from around 65 to over 95 (L*=100 for pure white) and the whiteness of rPET produced from purified BHET (L*=86.21) was greatly improved compared with that from raw BHET (L*=44.01), showing the possibility of achieving the closed-loop recycling of dark PET fibers.

The Impact of Ionic Surfactants on the Crystallisation of Glycine Polymorphs

AbstractThe glycine polymorphs have provided a rich and challenging tapestry for crystal growth and polymorphism studies. In this new contribution we report some preliminary studies of the impact of two ionic surfactants on the morphologies and the competitive crystallisation of the α and γ polymorphs. We find both selective growth inhibition and acceleration combined with fascinating crystal aggregates. The role of both monomeric and micellar forms of the surfactants are explored and discussed in terms of nucleation and crystal growth processes.

Modelling of nucleation – Isotropic surface growth for finite platelet-like particles

This article concerns the realistic modelling of gas–solid reactions ubiquitous in industrial reactors. A simplistic deterministic model describing the stochastic isotropic nucleation-growth process in a powder of platelets has been strongly improved. Comparisons with a rigorous Monte-Carlo (MC) method that was used as a benchmark show that for realistic platelets, the current deterministic approach can strongly overestimate the reaction rate and underestimate the reaction duration because it considers the platelet surface to be infinite. A new deterministic model considering the finite dimensions of the platelets was developed and leads to the same results as MC simulations. Virtual experimental data were generated with this new model. Kinetic parameters were then optimised using the old and new deterministic method. The optimal curves obtained under the infinite platelet hypothesis are far from the measurements. This paper underscores that chemical kinetic parameters are only reliable if the underlying theoretical model is sound.

Microstructure and properties of sustainable cement-based materials using combustion treated rice husk ash

Improving the performance of cement-based product using agricultural waste is one of the major challenges for developing sustainable construction materials, and rice husk ash from the recycling of rice husk, could be a great candidate to partially replace cement from this perspective. This study explored the hydration kinetics of cement-based materials (w/b ratio of 0.5) that incorporated with combustion treated rice husk ash (CRHA) through isothermal calorimeter test with the adoption of Krstulović and Dabić model, while the mechanical and water absorption properties were also examined. Silica fume (SF) severed as SCM reference, and the dosage of the two additives ranged between 5% and 20% (by weight). The microstructure of the binary binding system was investigated with the aid of X-ray diffractometer (XRD), Thermogravimetry analysis /Differential thermogravimetry (TG/DTG), Mercury injection porosimeter (MIP) and Scanning Electron Microscopy (SEM). It was found that both CRHA and SF additions accelerated the hydration process, reflecting by the increased reaction rate constants (KNG and KI) correspondingly in nucleation and crystal growth process (NG) and in interaction at phase boundaries reaction process (I), while KD in diffusion process (D) remained stable. The strength enhancement effect of blending CRHA started to show at early age of 3 d on mortars, and the compressive strength of CRHA blended mortars all exceeded that of SF blended mortars with the same replacement ratio at 28 d. Meanwhile, the permeability was declined for samples containing increased dosages of CRHA (15–20%). The superior properties from the addition of CRHA were mainly attributed to the significant consumption of Ca(OH)2 and the pore structure refinement arised from CRHA. Furthermore, the connection between hydration heat release and water absorption at different temperatures was assessed to confirm the beneficial role of using increased dosages of CRHA in thermal cracking control.

Frosting behavior of louvered-fin and tube heat exchanger after surface treatment: Experimental analysis

In heat pump systems, frost creates insulation, restricts airflow, and induces stress that can have serious negative effects on the heat exchanger. Hydrophobic surface treatment is a low-cost, efficient, passive defrosting method that has attracted widespread research attention. In this study, the hydrophobic-modification surfaces of louvered-fin heat exchanger (HEX) in heat pump systems were investigated at microscopic and macroscopic scales, respectively. Frosting and defrosting experiments were conducted on evaporators with hydrophobic surfaces on an automotive performance test bench to provide novel information regarding the hydrophobic louvered-fin HEX. The nucleation growth process of modified fins in the microscopic state was studied under classical nucleation theory and electron polarization theory. The experiments show that the refrigerant flow rate of the bare HEX is drastically reduced at 35 min, leading to a sharp decay in heat pump system performance. The air pressure drop in the HEX at this time is 140 Pa. The time taken to reach this air pressure drop for the coated HEX is 153 min, which indicates that the hydrophobic surface has excellent anti-frost performance. We also find that subcooling acts as an intrinsic driving force for nucleation. The nucleation work increases by 77.8% as the bare HEX moves from the surface temperature region of −20 °C to the −15 °C region. The nucleation work on the hydrophobic surface increases by 255% at −20 °C compared to the bare surface. The theoretical analyses of surface elemental composition, non-bonded electron polarization, and crystal perturbation are consistent with the experimental results.

Spatiotemporally super-resolved dendrites nucleation and early-stage growth dynamics in Zinc-ion batteries

Safety and lifespan problems caused by the zinc dendrite formation continue to impede the application of zinc-based batteries. To address this severe issue, it is crucial to fully understand the nanoscale nucleation and early-stage dendrite growth process. However, the key dynamic process can hardly be resolved at the nanoscopic level under ambient working conditions with the current in situ / operando methods. Here, we develop a highly sensitive, super-resolution operando imaging approach for directly investigating the initial electroplating process in the zinc-air battery system. With this approach, millisecond/nanometer-resolution observation is achieved, providing nucleation rate, growth heterogeneity, and direction information at the single zinc nuclei level, and revealing nanoscopic details of early-stage dendrite growth. The spatiotemporally super-resolved observation elucidates that dynamic change in the local electrochemical environment is the key factor for the formation of the zinc dendrites. This novel straightforward approach can enable a deep understanding of the electrochemical interfacial issues and facilitate problem solving in diverse battery systems. Super-resolution operando imaging of zinc initial electroplating process Millisecond/nanometer resolution observation of single zinc nuclei formation Zinc nucleation rate, growth heterogeneity, and direction obtained Super-resolved early-stage dendrites formation and role of zinc depletion In-depth understanding of initial electroplating dynamics is crucial for designing/developing safer batteries. Here, Ye et al. develop a super-resolution microscopy with nanoscale and millisecond resolution, that enables the direct imaging and analysis of highly dynamic zinc nucleation and early-stage dendrite growth under ambient conditions. This new approach can be used for probing key interfacial electrochemical issues in diverse battery systems.

Nucleation and Post-Nucleation Growth in Diffusion-Controlled and Hydrodynamic Theory of Solidification

Two-step nucleation and subsequent growth processes were investigated in the framework of the single mode phase-field crystal model combined with diffusive dynamics (corresponding to colloid suspensions) and hydrodynamical density relaxation (simple liquids). It is found that independently of dynamics, nucleation starts with the formation of solid precursor clusters that consist of domains with noncrystalline ordering (ringlike projections are seen from certain angles), and regions that have amorphous structure. Using the average bond order parameter q¯6, we distinguished amorphous, medium range crystallike order (MRCO), and crystalline local orders. We show that crystallization to the stable body-centered cubic phase is preceded by the formation of a mixture of amorphous and MRCO structures. We have determined the time dependence of the phase composition of the forming solid state. We also investigated the time/size dependence of the growth rate for solidification. The bond order analysis indicates similar structural transitions during solidification in the case of diffusive and hydrodynamic density relaxation.

Intraoral low-temperature degradation of monolithic zirconia dental prostheses: Results of a prospective clinical study with ex vivo monitoring

ObjectiveTo investigate the intraoral development and kinetics of low-temperature degradation (LTD) in second-generation 3 mol.% yttria-doped tetragonal zirconia polycrystal (3Y-TZP) monolithic prostheses, as well as the influence of masticatory mechanical stress and glaze layer on it. MethodsA total of 101 posterior tooth elements were included in a prospective clinical study, which included ex vivo LTD monitoring (at baseline, 6 months, 1 year, and 2 years) using Raman spectroscopy (n = 2640 monoclinic phase measurement points per evaluation time) and SEM. Four types of areas (1–2 mm2 surface, 6 on molars, and 4 on premolars) were analyzed on each element surface: occlusal, axial, glazed, or unglazed. Raman depth mapping and high-resolution SEM were performed on the selected samples. ResultsLTD developed in 3Y-TZP monolithic restorations 6 months after intraoral placement and progressed with time. After two years, the tetragonal-to-monoclinic transformation was non-uniform, with the presence of localized clusters of transformed grains. In axial areas, the grain aspect was typical of the classical nucleation-growth process reported for LTD, which progresses from the surface to a depth of several tens of microns. However, in occlusal areas, tribological stress generated surface crushing and grain pull-out from the clusters, which induced an underestimation of the aging process when the evaluation was limited to monoclinic phase quantification. Glazing cannot be considered a protection against LTD. SignificanceIf LTD occurs in dental prostheses in the same way as in orthopedic prostheses, its clinical impact is unknown and needs to be further studied.