Surface Growth Mechanism Research Articles

Large eddy simulation of soot formation in a turbulent lifted flame with a discretized population balance and a reduced kinetic mechanism

This article presents simulations of a turbulent lifted flame using the large eddy simulation-transport probability density function-discretized population balance equation approach. This approach takes into account the interaction between turbulent reacting flow and soot particle formation. A reduced chemical kinetics mechanism including a series of polycyclic aromatic hydrocarbons (PAHs) species linked to soot formation is generated employing the approach of the directed relation graph error propagation and is tested on a perfectly stirred reactor under varying equivalent ratio conditions and premixed flames. The soot kinetics model includes the PAH-based nucleation and surface condensation, the hydrogen abstraction acetylene addition surface growth and oxidation mechanism, and the size-dependent aggregation. The soot morphology considers the surface area and other geometrical properties for both spherical primary particles and fractal aggregates. The simulation results show, in general, reasonably good agreement with experimental measurements in terms of lifted height, flame shape, flow-field velocity, the hydroxyl radical, and soot volume fraction. A discussion of micromixing and its modeling in the context of the Interaction by Exchange with the Mean model is also presented. To investigate the effect of the soot micromixing frequency factor on soot particles, an additional simulation is conducted where this factor is reduced by a factor of 10 for the soot particles. The maximum soot volume fraction is observed to increase slightly. However, compared with the impact of kinetics on soot modeling, this effect is a minor one.

Study of the Kinetics of Nucleation and Growth of Silver Nanoparticles: UV-Visible Spectroscopy vs. Atomic Force Microscopy and Transmission Electron Microscopy

Silver nanoparticles have been the subjects of research interest because of their unique properties and extensive use in modern-day applications. A variety of preparation techniques have been reported for their synthesis but among them mostly recognized is a modified version of the Turkevich citrate method. In this study, we also chose this method of silver nanoparticle synthesis. The synthesized nanoparticles were characterized first, traditionally with UV-Visible spectroscopy and then their sizes and shapes were identified employing Atomic Force Microscopy (AFM) and Transmission Electron Microscopy (TEM). From the UV-Vis data were extracted the rate constants for the nucleation ($$k_1$$) and growth ($$k_2$$) of the silver nanoparticles, and then these constants were further used to fit those obtained from AFM and TEM. Using the values of $$k_1$$ and $$k_2$$ independently in the two experimental methods validated and supported the well-acknowledged two-step mechanism of slow nucleation and fast autocatalytic surface growth.

Electrodeposition of Au Nanowires via Amine Ligand-Induced Active Surface Growth.

Amine ligands have been widely applied as morphology-directing reagents in nanostructure synthesis. In this work, we explored the application of the amine ligands in the active surface growth mechanism in place of the strong thiolated ligands. Despite being weaker compared to the thiols, amine ligands such as aniline were also shown to be capable of facilitating the template-less electrodeposition of Au nanowires (NWs) on the substrate via the active surface growth mechanism. Given the close binding difference between the amine-grafted substrate and the ligands, substrate functionalization becomes critically important for effective construction of the active surface and the growth of the nanowires. Additionally, the growth with the amine ligands took place at more positive reduction potentials and is less prone to splitting and bundle formation. A systematic generality study revealed that besides the aromatic amines, long-chain aliphatic amines were also capable of facilitating nanowire growth. Given the weak binding affinity of the amine ligands, the Au NWs are readily accessible for further processing to generate sophisticated one-dimensional structures. As a demonstration, tandem electrodeposition was performed to directly obtain coaxial core-shell Au@Pt NWs with adjustable length, diameter, and shell thickness.

Effect of Ge inclusion on surface morphologies and the growth mechanism of Cu2(Sn1-xGex)S3 films grown by the sulfurization of Ge/Cu/SnS precursors

The effects of the [Ge]/([Ge]+[Sn]): x ratio on the increase in the surface roughness and growth mechanism of Cu2Sn1-xGexS3 (CTGS) films were examined as a first step toward realizing high-efficiency CTGS solar cells. The surface roughness of the CTGS films did not change significantly up to 450 °C during the sulfurization of the Ge/Cu/SnS precursors, whereas that of the CTGS films increased beyond 500 °C. Further, Cu2GeS3 (CGS) and germanium sulfide (GeS) were observed via X-ray diffraction; these CGS and GeS compounds remained in the upper layer up to 540 °C, and CTGS was formed at 560 °C by the reaction with Cu2SnS3. The increased surface roughness in the CTGS films is attributed to the larger CTGS grain size that increases the x ratios of CTGS and the re-evaporation of vapor atoms (e.g., GeS) that generates a high vapor pressure on the surface of films by forming CGS and GeS compounds. These results confirm that the formation of CGS and GeS compounds, and the formation of dense grains in the CTGS films caused by the deposition of lower x ratios in the CTGS films are effective measures for improving the overall surface roughness.

Morphology, phase composition, surface roughness evolution and growth mechanism of hot-dip aluminum coating on Mo substrate

The Al-rich hot-dip aluminum composite coatings were synthesized on Mo surface by hot-dip aluminizing under different deposition processes. The aluminide coatings present a very smooth dense coating structure with a lower surface roughness and fine grain size, the average surface roughness (RSa) values are only 0.118–0.869 μm, and the corresponding surface area growth rate (Sdr) values are 3.85–80.19 %. Increasing the deposition temperature is beneficial for the transition of low melting point compounds of the coating surface to high melting point compounds, and extending the hot dip time is profit for the diffusion and enrichment of Al atoms on the coating surface. Besides, increasing the deposition temperature or time can also promote the growth of Al4Mo grains, thereby significantly increasing the coating thickness. When the deposition temperature is 750 °C, the thicknesses of Al4Mo and Al8Mo3 layers increases in a parabolic law with deposition time, and the Kp values both of them are 3.46 × 10−13 m2/s and 1.47 × 10−15 m2/s, respectively. The growth of the coating depends on the continuous diffusion of Al atoms towards the substrate direction, and the difference in chemical potential between Al atoms in each phase is the main driving force for coating growth.

Multi-scale soot formation simulation providing detailed particle morphology in a laminar coflow diffusion flame

The macroscopic simulation of soot production in flames by CFD approaches often assumes of spherical particles or considers ad-hoc formulas in order to take the particle fractal aggregates’ morphology into account. On the other hand, numerically simulated aggregates can be generated by Discrete Element Modeling (DEM) simulations at the nanoscopic scale. However, the change in thermodynamic conditions, surface growth, oxidation, and nucleation mechanisms are commonly neglected by this approach. This work combines these complementary approaches to investigate the detailed morphology of soot along 4 different particle trajectories in a diffusion flame. The proposed multi-scale approach shows remarkably larger and more compact aggregates near the wings of the flame as compared to the centerline, in agreement with previous experimental studies. This approach allows to analyse the particle polydispersity and morphological parameters beyond the fractal dimension, such as anisotropy coefficient and monomers overlapping coefficient. It becomes possible to reveal clear morphological signatures of soot formed along different streamlines in the flame. Finally, we have also observed a positive correlation between primary particle diameter and aggregate gyration diameter due to the predominance of surface reactions over aggregation. The proposed post-processing of CFD results based on DEM methods, bringing new information on soot morphology, is a proof of concept of a more accurate procedure for validating soot models used in CFD codes as compared to existing methods in the literature.

Re-evaluating cloud chamber constraints on depositional ice growth in cirrus clouds – Part 1: Model description and sensitivity tests

Abstract. Ice growth from vapor deposition is an important process for the evolution of cirrus clouds, but the physics of depositional ice growth at the low temperatures (<235 K) characteristic of the upper troposphere and lower stratosphere is not well understood. Surface attachment kinetics, generally parameterized as a deposition coefficient αD, control ice crystal habit and also may limit growth rates in certain cases, but significant discrepancies between experimental measurements have not been satisfactorily explained. Experiments on single ice crystals have previously indicated the deposition coefficient is a function of temperature and supersaturation, consistent with growth mechanisms controlled by the crystal's surface characteristics. Here we use observations from cloud chamber experiments in the Aerosol Interactions and Dynamics in the Atmosphere (AIDA) aerosol and cloud chamber to evaluate surface kinetic models in realistic cirrus conditions. These experiments have rapidly changing temperature, pressure, and ice supersaturation such that depositional ice growth may evolve from diffusion limited to surface kinetics limited over the course of a single experiment. In Part 1, we describe the adaptation of a Lagrangian parcel model with the Diffusion Surface Kinetics Ice Crystal Evolution (DiSKICE) model (Zhang and Harrington, 2014) to the AIDA chamber experiments. We compare the observed ice water content and saturation ratios to that derived under varying assumptions for ice surface growth mechanisms for experiments simulating ice clouds between 180 and 235 K and pressures between 150 and 300 hPa. We found that both heterogeneous and homogeneous nucleation experiments at higher temperatures (>205 K) could generally be modeled consistently with either a constant deposition coefficient or the DiSKICE model assuming growth on isometric crystals via abundant surface dislocations. Lower-temperature experiments showed more significant deviations from any depositional growth model, with different ice growth rates for heterogeneous and homogeneous nucleation experiments.

Growth mechanism, phase transition and optical properties of large-size and high-quality perovskite CH<sub>3</sub>NH<sub>3</sub>PbCl<sub>3</sub> single crystal

According to the phenomenon that the solubility of CH<sub>3</sub>NH<sub>3</sub>PbCl<sub>3</sub> decreases with the increase of temperature in different solvents, CH<sub>3</sub>NH<sub>3</sub>PbCl<sub>3</sub> perovskite single crystal with a maximum dimension of 11 mm × 11 mm × 2 mm is grown by introducing a high-quality seed crystal via the seed-induced inverse temperature crystallization method in this work. X-ray diffraction and Rietveld refinements show that the full widths at half maximum (FWHM) of CH<sub>3</sub>NH<sub>3</sub>PbCl<sub>3</sub> single crystal diffraction peaks are 0.1527°, 0.1353°, 0.2295° and 0.3452°, corresponding to the crystal plane indices of (100), (200), (300) and (400), respectively. And there are no miscellaneous peaks, indicating a good crystal quality. As a result, CH<sub>3</sub>NH<sub>3</sub>PbCl<sub>3</sub> single crystal is of cubic phase at room temperature, its space group belongs to <i>Pm</i><inline-formula><tex-math id="M3">\begin{document}$ \bar{3} $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20230097_M3.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20230097_M3.png"/></alternatives></inline-formula><i>m</i>, and the lattice constant is <i>a</i> = 0.56877 nm. The surface morphology and growth mechanism of CH<sub>3</sub>NH<sub>3</sub>PbCl<sub>3</sub> crystal are investigated by using a polarizing microscope. It is found that its growth mechanism follows the step horizontal growing mechanism of smooth interface, and its growth direction (that is, step movement direction) is along the outward normal direction of the step. The structural symmetry of CH<sub>3</sub>NH<sub>3</sub>PbCl<sub>3</sub> crystal is studied by variable temperature Raman spectroscopy, which reveals an orthogonal-tetragonal phase transition at 160 K. But the tetragonal phase structure is not stable, and its temperature range is very narrow. As temperature rises gradually, the tetragonal phase again transforms into a cubic phase (<i>Pm</i><inline-formula><tex-math id="M4">\begin{document}$\bar{3}$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20230097_M4.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20230097_M4.png"/></alternatives></inline-formula><i>m</i>). Results of UV-Vis-NIR absorption and photoluminescence spectra show that the absorption cutoff of CH<sub>3</sub>NH<sub>3</sub>PbCl<sub>3</sub> crystal is about 442 nm, and the photoluminescence peak is 450 nm. Thereupon, its band gap is obtained to be about 2.93 eV by a linear fit of Tauc formula, which is slightly higher than the theoretical value of 2.55 eV calculated by first principles simulation. We believe that it is related to the seed crystal, which is introduced into the crystal growth process as the core of heterogeneous nucleation and thus making the lattice more distorted. The lower the lattice symmetry of CH<sub>3</sub>NH<sub>3</sub>PbCl<sub>3</sub>, the larger the band gap is, that is, the lattice symmetry determines the degree of distortion for inorganic PbCl<sub>6</sub> octahedral frameworks, resulting in an increase of band gap for CH<sub>3</sub>NH<sub>3</sub>PbCl<sub>3</sub>.

Modeling soot formation in flames and reactors: Recent progress and current challenges

The study of soot has long been motivated by its adverse impacts on health and the environment. However, this combustion knowledge is also relevant to the production of carbon black and hydrogen via methane pyrolysis which are important commodities. Over the last decade, steady progress has been made in the development of detailed continuum models of soot formation in flames and reactors. Developing more comprehensive models has often been motivated by the need for predicting soot formation over a wider range of conditions (e.g., temperature, pressure, fuels). Measurements with novel experimental techniques have given us new insights into the chemistry, particle dynamics and optical properties of soot particles and even molecules and radicals forming them. Also, multi-scale modeling has enabled us to translate the detailed mechanisms of soot processes based on first principles into computationally efficient but accurate continuum models of soot formation in flames and reactors. However, important questions remain including (1) what is the mechanism of soot inception and surface growth, (2) which gas-phase species are involved in soot inception and surface growth (3) how surface growth and oxidation are affected by soot surface properties. Proposed models need to be evaluated against experimental data over a wide range of conditions to determine their predictive strength. These questions are critical for the accurate prediction of soot formation in flames and its emissions from engines. However, this knowledge can also be used to develop predictive process design and optimization tools for carbon black and other nanocarbon formation in reactors.

A numerical study on soot formation in methane-ethanol diffusion flames

• Soot volume fraction and particle number density increase with ethanol blending ratio. • The degree of soot enhancement decreases with further increase in ethanol blending ratio. • Effect of ethanol on soot concentration follows the order: chemical > dilution > thermal. • Thermal effect has a dominant influence on the flame temperature, but not on soot. • Ethanol addition promotes the HACA pathway and surface growth mechanism. Numerical simulation was carried out to investigate the effect of ethanol addition on the soot formation characteristics of methane diffusion flame. The ethanol blending ratio in methane ranged from 0 to 40 % in terms of the carbon contribution, ensuring a constant carbon flow rate for all cases. The sooting diffusion flames were modelled in an open-source environment, OpenFOAM, whereby-two different soot modelling approaches were attempted, including one detailed soot model and one semi-empirical soot model. Numerical results revealed that ethanol addition increased the soot volume fraction; however, further increase in the ethanol blending ratio (>20 %) reduced the relative enhancement of the soot concentration. Decoupling analysis was conducted to study the dilution, thermal, and chemical effects of ethanol separately. It was found that the dilution effect increased with the ethanol blending ratio. Also, the flame temperature was primarily affected by the thermal effect of ethanol. Despite these factors, the chemical effect of ethanol still played a dominant role in increasing soot formation. Analysis of the soot formation pathway revealed that ethanol addition promoted soot formation mainly through the acetylene addition reactions and polycyclic aromatic hydrocarbons (PAHs) addition reactions, which contributed to the hydrogen-abstraction-acetylene-addition (HACA) and surface growth mechanisms, respectively. Soot oxidation was enhanced with ethanol addition, which resulted in greater soot reduction; however, the overall effect of ethanol on soot formation remained positive.

Characteristics of diamond crystals from FeNiCo-C system with Ge doping under high pressure and high temperature

Various optical color centers in natural and synthetic diamond have attractive great attention of researched; to further investigate the effects of additive on diamond properties is of practical significance. In this work, diamond crystallization was investigated by temperature gradient growth method with Ge additive at a set pressure of 6.5 GPa and synthesis temperature ranging from 1290 to 1310 °C. Scanning electron microscope (SEM), and spectral characterization including Fourier transform infrared spectroscopy (FTIR) and photoluminescence (PL) spectra were used to investigate the surface growth mechanism of diamond. It was noticed that the visible inclusions gradually reduced in the as-grown diamond, accompanying with the increase of Ge additive in the synthesis cavity. The (111) surface of the synthesized diamond followed the layer growth pattern from the SEM results. According to the measured FTIR results, the nitrogen impurity concentration values of the synthesized diamond crystals decreased from 500 to 90 ppm, confirming that Ge showed its own ability to remove nitrogen impurity in the growth stage of diamond. Additionally, the nickel-related and nitrogen-related optical color centers of the obtained diamond were characterized by PL spectra. Characteristic peaks due to nickel-related optical color centers located at 515 or 535 nm, and Characteristic peaks attributing to nitrogen-related optical color centers located at 575 or 637 nm. We believe that the research is of great significance for the application of diamond in optical and quantum information science fields.

Morphology of Transition Metal Carbonate Cathode Precursors

Increasing the capacity of cathode materials used for lithium-ion batteries is desirable, as it ultimately enhances the energy density. Due to their lower cost and reversible cycling capacity of 250 – 300 mAh/g, Li- and Mn-rich LMR-NMC oxides are strong candidates as next generation cathodes used in lithium-ion batteries. Apart from the atomic structure, morphology of the cathode particles also influence their performance. LMR-NMC cathode particles are usually constructed through a two-step cathode fabrication process, which involves initial coprecipitation of the Mn-rich carbonate based cathode precursors, and later calcination of these precursors with a lithium salt at elevated temperatures. The secondary particles generally maintain their as precipitated precursor morphologies even after high temperature calcination. Even though the primary particles do change their size during calcination, the rate of oxidation and lithiation experienced by the transition metal precursors depend substantially on the primary particle morphology. Hence, it is critical to understand and control both the primary and secondary particle morphologies obtained after the coprecipitation process. In the present context, carbonate based NMC cathode precursors containing only Mn, only Ni and only Co, is precipitated, along with equal amount of the transition metals (Ni0.33Mn0.33Co0.33CO3), using conventional batch reactors. NH4HCO3 is used as the source of carbonate anions during the coprecipitation process, and the entire reaction is conducted at 50°C. The obtained particle morphologies for different transition metals are shown in Figure 1(a) as visualized using high resolution TEM techniques. Except MnCO3, all other transition metals demonstrate aggregated morphologies, which most probably form through surface growth mechanisms. Competition between growth rate and surface energies that leads to the formation of single crystalline particles for MnCO3, and particulate features for other transition metals, are demonstrated in Figure 1(b). Multiscale computational methodologies are developed to elucidate the impact of reaction kinetics and thermodynamics on determining the overall primary and secondary particle morphologies. Influence of transition metal content and ammonia concentration in determining the final particle size and size distribution will be discussed as part of this study. Figure 1

Alkynyl ligands-induced growth of ultrathin nanowires arrays

Ligands are almost essential in the synthesis of nanostructures. In this work, we introduce the alkynyl ligands into the synthesis of ultrathin gold (Au) nanowires arrays. The strong binding affinity of the alkynyl ligands enables one-dimensional (1D) growth via the active surface growth mechanism. The scope of the ligand generality was systematically investigated, and the alkynyl ligand-induced nanowire growth processes were compared and contrasted with those involving thiolated ligands. While strong ligands are usually difficult to dissociate from the nanostructure surface and therefore problematic for post-synthetic processing, the alkynyl ligands are readily dissociable, making the alkynyl ligand-stabilized Au nanowires potentially more modifiable and applicable. As a demonstration, direct palladium (Pd) deposition on the Au nanowires was successfully carried out without any ligand exchange process.

Dft Study of Soot Surface Growth Mechanism Over Carbene Active Site: From Initial Capture to Further Growth

Dft Study of Soot Surface Growth Mechanism Over Carbene Active Site: From Initial Capture to Further Growth

Pulsed‐UV illumination on graphene oxide: A new strategy in photocatalytic synthesis of electrocatalysts to control the structural and electrochemical properties

This study demonstrated the capability of a novel method in controlling the structural and electrochemical properties of electrocatalysts, utilizing a pulsed-ultraviolet (UV) setup for the synthesis procedure. A hand-made reactor provided a new set of parameters. The variation of UVon and UVoff periods resulted in samples with a range of different structures, compositions, and activities. Graphene/Pt was prepared with varying forms of illumination pulse, and its hydrogen oxidation and oxygen reduction reaction performances were evaluated. Controlling the reduction degree of Pt ions on partially reduced graphene oxide was achieved by manipulating the setup design. The results revealed a dominant growth and agglomeration phase of Pt particles, mostly with metallic states, by increasing both UVon and Uoff time spontaneously. Long UVon without adequate UVoff did not result in promising electrocatalytic activities. In other words, different structures, compositions, and activities of samples suggested that not just the illumination is the crucial factor, it is also the resting time or UVoff which determines the surface adsorption kinetics, nucleation sites, and growth mechanism of nanoparticles. Further chemical reduction by highly concentrated ascorbic acid was used to confirm the proposed mechanisms, which lead to samples even with more metallic Pt (Pt0).

Crystallization kinetics and photoluminescence studies on SiO2‐ZnGa2O4:Cr3+ glass ceramics

AbstractSiO2‐ZnGa2O4:Cr3+ glass ceramics were prepared by a sol‐gel method. The influence of TiO2 addition on the crystallization behavior and photoluminescence properties were investigated in detail. The nonisothermal crystallization kinetic studies based on Kissinger, Ozawa, and Matusita models were performed on the SiO2‐ZnGa2O4:Cr3+ glasses with different amount of TiO2. The introducing of TiO2 component as nucleant in the glasses can significantly reduce the crystallization activation energy. The results of the crystallization kinetic calculation and scanning electronic microscope observations indicated that the crystallization of ZnGa2O4:Cr3+ from the glass possessed a surface nucleation and growth mechanism. Near infrared emission of the glass ceramics was obtained under the excitation at 414 nm. The crystal field parameters around Cr3+ and excited state dynamics of Cr3+ were studied in detailed.

Molecular dynamics study of surface nucleation and growth mechanism in Cu-based CuPtPd ternary alloy system

This study report that a classical molecular dynamics (MD) simulation method has been performed to investigate the nucleation and growth mechanism from amorphous matrix of Cu-based CuPtPd ternary alloy system with different Pt and Pd addition at nano-scale. The Embedded Atom Method (EAM) utilizing the Sutton-Chen (SC) version is used to calculate interatomic interactions as a semi-empirical potential energy function. The crystallization stages have been examined by using computational method at different annealing temperatures using Johnson-Mehl-Avrami-Kolmogorov (JMAK) equations. The structural developments of systems are analysed with radial distribution function (RDF). Crystallized fractions (x) against annealing time have been calculated from the crystal-type bonded pairs based on Honeycutt-Andersen (HA) cluster analysis index. It is found that an increase in annealing temperature of systems plays important role for crystallization. In addition, the surface nucleation and one-dimensional growth are favourable for low Cu compositions in the CuPtPd system at low annealing temperatures. These findings shed new light on understanding the crystallization kinetics of CuPtPd system by using computer simulation method.

Preparation and Property Studies of Polyaniline Film for Flexible Counter Electrode of Dye‐Sensitized Solar Cells by Cyclic Voltammetry

AbstractIn this work, a polyaniline film was synthesized on the surface of ITO (indium tin oxide)–PET (polyethylene terephtalate) plastic substrate by cyclic voltammetry electrochemical method to prepare a transparent flexible counter electrode. Then, the surface growth mechanism of polyaniline film was analyzed, and the AC impedance and cyclic voltammetry curves were tested. The dye‐sensitized solar cell (DSSC) device was assembled for photocurrent density‐voltage curves (J‐V) test, and the photoelectric performance of the flexible polyaniline counter electrode was further discussed. All of the above tests were compared to electrochemically deposited Pt electrodes. The results show that the polyaniline has a larger specific surface area for the electrode, which is more conductive to the catalytic reduction of the iodide on the electrode. Moreover, its porous structure is more conductive to the diffusion and reaction of redox couples. Under the influence of dense layer and porous structure of polyaniline film, the cell performance of 25‐sweep‐segment polyaniline counter electrode is the best. Comparing with the conventional Pt electrode, the flexible counter electrode prepared by electrochemical synthesis not only has the same performance, but also reduces the cost by about 40 %, which is of great significance for promoting the application of DSSC.

Morphology prediction of 5,5′-bistetrazole-1,1′-diolate (BTO) crystal in solvents with different models using molecular dynamics simulation

For explaining in detail the influence of solvents on the morphology of 5,5′-bistetrazole-1,1′-diolate (BTO) crystal, molecular dynamics (MD) methods were used to simulate solution-crystal interface interactions, modified attachment energy (AE) model and occupancy model were used to predict the morphology of BTO. The simulation results demonstrated that the morphologically dominant growth surfaces of BTO in vacuum are (001), (110), (20–1) and (200), respectively. There has many intramolecular and intermolecular interactions exist with different strength in the crystal of BTO, and the atomic system is dominated by N···H/H···N contacts which are comprising 60.2%. Analysis of the crystal bond chain and crystal packing further explained the mechanism of crystal surface growth. The size of the BTO crystal face-solvent model and the number of solvent molecules was designed. The morphologies of BTO in different solvents with three models were displayed. Results of comparing the BTO crystal relative surface/volume ratio in different solvents indicated that the Diethyl Ether (DEE) solvent is more favorable for the spheroidization of BTO crystal in the study.

Impact of pressure-based HACA rates on soot formation in varying-pressure coflow laminar diffusion flames

There are several processes to occur in soot formation and destruction for which some in the growth regime require a better understanding. In this work, a consistent surface reactivity model, developed in recent years, has been implemented across various sooting laminar flames at varying pressures. The surface reactivity function proposed by Khosousi and Dworkin (2015) is employed in the present study. It is based on the temperature history of soot particles. As the functionally dependent model has been derived and validated for atmospheric pressure flames, there are discrepancies between simulation and experiment that can be observed as pressures vary. One reason for these discrepancies could be explained by the fact that chemical reaction rates for the soot growth mechanism at atmospheric combustion do not adequately characterize the kinetics at higher pressures. Based on a recently published study (Frenklach et al., 2019), the elementary reaction rates that compose the Hydogen-Addition-Carbon-Abstraction soot surface growth mechanism depend on pressure and an empirical pressure scaling factor to account for this pressure dependence has been introduced. It has been determined that after applying the new empirical pressure scaling factor for the soot growth mechanism, the performance of the functionally dependent surface reactivity model improves in the wing regions of the flame for pure-ethylene flames; however, there is minimal change on the wings for the nitrogen-diluted flames. Additionally, the quantity for soot concentration along the centerline of all flames is nearly independent of the surface reactivity model chosen and needs further investigation. For the flames investigated, it is concluded that pressure dependent HACA rates do not alleviate all discrepancies between the numerical and experimental results and that further work is required.