The heterogeneous melts of isotactic polybutene-1 (iPB-1) containing Form I or Form II seeds with uniform size and random distribution were prepared by selective melting of melt crystallized and ...transformed samples, respectively. Compared with a reference blank melt, the remnant Form I or II seeds are able to significantly reduce the half-time of crystallization under isothermal conditions. Besides, the nucleation efficiency of Form II seeds is much higher than that of Form I seeds because of the lower lateral surface energy and highly lattice match. Furthermore, a great number of tiny spherulites with submicrometer radius nucleate and grow simultaneously, offers an opportunity to follow the development of spherulites at the very early stage. The analysis of the differential scanning calorimetry (DSC) curves confirms that the mass fraction for faster primary crystallization of heterogeneous melts is lower than that of blank melt, which clearly indicates that growth rate of spherulites is decreasing before impingement. The radius of spherulites was not much larger than the diffusion length provides the foundation for the observed non-linear growth of spherulites. This quantitative comparison of the crystallization kinetics of blank melt and heterogeneous melts can therefore be applied as a method to improve our understanding of nucleation and the diffusion-controlled growth of polymer.
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•The heterogeneous melts containing dispersed Form I and II seeds were prepared by selective melting of iPB-1 samples.•The analysis of faster primary crystallization behavior reveals the non-linear spherulites growth with predetermined seeds.•A method was proposed to improve our understanding of nucleation and the diffusion-controlled growth of polymer crystals.
•The puffing phenomenon is discussed in detail by categorizing it into three different modes.•The critical boundary conditions for the different phase transitions of the droplet are analyzed.•An ...improved vaporization model for the bi-component droplet is developed.•The boiling sub-models consider the effects of fuel viscosity and surface tension.•The model can quantitatively reproduce the bubble number and bubble size within the droplet.
With the increasing use of blended fuels, the vaporization process of mixed droplets imposes new requirements on classical droplet vaporization models, highlighting the urgent need for the development of a broadly applicable multi-component fuel droplet vaporization model. In this study, the boiling characteristics of n-heptane/n-hexadecane two-component mixed droplets with different physical properties were experimentally studied under wide ambient temperatures and initial mass fractions. The droplet boiling mainly involves two phenomena, i.e., puffing and micro-explosion. Based on the experimental observations, the puffing phenomenon is further refined and categorized into weak puffing, foam puffing, and strong puffing. Then, the analysis of the influence of initial conditions on the boiling modes was conducted. Furthermore, a droplet vaporization model was constructed according to the experimental data, which includes droplet evaporation, droplet boiling, and bubble point sub-models. The new model considers the effects of fuel viscosity and surface tension and makes improvements to the heterogeneous nucleation and bubble break-up sub-models, reducing the dependence on empirical parameters. The resistance terms were introduced in the heterogeneous nucleation sub-model to prevent the nucleation rate from reaching its upper limit. The relationship between the initial disturbance and the Ohnesorge number in the break-up sub-model was summarized. Based on the above improvements, an updated method for calculating the boiling mass rate was proposed. The results indicate that the vaporization model can effectively replicate droplet lifetime and diameter evolution under different mixing fractions and wide ambient temperatures.
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In this paper, in order to study the effect of oxides on the formation of complex TiN inclusions in 20CrMnTi steel, based on the two end quenching specimens with different components, the ...characteristics of complex TiN inclusions and oxides were observed and analyzed, and the formation mechanism of complex TiN inclusions was discussed. The results indicate the compositions of core oxides are regularly distributed in the MgAl2O4–TiOx composition line for different complex TiN inclusions, and the difference is the TiOx content. The complex TiN inclusions can be divided into two types, Type 1 and Type 2, based on the compositions of core oxides. For Type 1, TiOx content of core oxides are below 52%, while for Type 2, TiOx content of core oxides are over 52%. The core oxides of Type 1 have bigger size at the range of 1–3 µm, and lower nucleation capability for TiN inclusions. The core oxides of Type 2 have smaller size at the range of 0.5–2 µm, and higher nucleation capability for TiN inclusions. For Type 1, the MgAl2O4–TiOx oxides preexisting in molten steel are the heterogeneous nucleation cores of TiN inclusions during solidification. For Type 2, the tiny oxides newly formed during solidification are the nucleation cores of TiN inclusions. By controlling the characteristics of oxides, the characteristics of TiN inclusions can be controlled, which provides a new idea for the control of TiN inclusions in 20CrMnTi gear steel.
The modification effects of Sb on the morphologies of reinforcements Mg2Si and Mg2(Si,Sn) in Mg-4Si and Mg-5Sn-xSi(x = 1,4) alloys were investigated and the ideal adhesion works (Wad) between ...substrate (Mg3Sb2) and crystallization phases (Mg2Si, Mg2Sn and Mg2(Si,Sn)) were calculated using first principles calculations. The results indicate that the primary α-Mg matrix is significantly refined by the modification of Sb. For the eutectic mixture, the arm spacing of the intermetallics of Mg2Si or/and Mg2(Si,Sn) is decreased. For the primary Mg2Si or/and Mg2(Si,Sn) which in coarse angular bulk forms without any modification was rounded and distributed uniformly on the α-Mg matrix after modification. The primary Mg2Si in octahedrons morphology without modification grows in tetrakaidecahedron mode in Sb modified Mg-4%Si alloys. The clearly straight edges and the sharp corners of the primary Mg2Si become ambiguity, and tend to being spheroidized. Primary Mg2Si, Mg2Sn and Mg2(Si,Sn) were refined because Mg3Sb2 precipitated during solidification could act as their nuclei. When some Sn atoms replace equivalent Si from Mg2Si phase, the interfaces adhesion work (Wad) values between substrate and new crystal will increase. Moreover, the interface cohesive strength of Sb-Mg-Si(/Sn/Si-Sn) or Sb-Mg-Mg-Si(/Sn/Si-Sn) will be stronger than the others.
•Mg3Sb2 can act as the nucleus of primary Mg2(Si,Sn) phase.•When Sn replaces partial Si of Mg2Si, the Wad values of interfaces increase.•Sb-Mg-Si(/Sn/Si-Sn)/Sb-Mg-Mg-Si(/Sn/Si-Sn) layers have more cohesive strength.
The Y2O3/TiN interface of main complex inclusions in T4003 stainless steel with rare earth element Yttrium (Y) content of 0.014 wt% was studied. The chemical composition and morphology of composite ...inclusions were characterized by scanning electron microscope (SEM) and X-ray energy dispersive spectrometer (EDS), the formation process of Y2O3/TiN composite inclusions was calculated by the first-principles calculations of the Vienna Ab-initio Simulation Package (VASP). Compared with Fe matrix, TiN is more likely to grow in an uneven state, and tends to exist in stainless steel in the form of Y2O3(100)/TiN(110). The main reason for the stability of the interface system is that the p orbitals of the O atoms at the interface forms covalent bonds with the d orbitals of the Ti atoms. It provides a new idea for improving the properties of stainless steel effectively by using heterogeneous nucleation of inclusions in steel.
•A comprehensive review on heterogeneous sonocatalysts for treatment of organic pollutants.•Reviewed based on heterogeneous nucleation and photo-thermal catalytic mechanisms.•Mechanical stability and ...separation capacity of the catalyst were also considered.•New trend, ongoing challenges and possible solving strategies were involved.
Heterogeneous sonocatalysis, as an emerging advanced oxidation process (AOP), has shown immense potential in water treatment and been widely demonstrated to remove persistent organic compounds in the past decade. The present article aims to provide a comprehensive review on the development of a heterogeneous catalyst for enhancing the ultrasonic degradation rate of organic pollutants from a viewpoint of sonocatalytic mechanism. The rational design and fundamentals for preparing sonocatalysts are presented in the context of facilitating the heterogeneous nucleation and photo-thermal-catalytic effects as well as considering the mechanical stability and separation capacity of the heterogeneous catalyst. In addition, some new trends, ongoing challenges and possible methods to overcome these challenges are also highlighted and proposed.
In this study, we reveal the impact of the addition of TiC in the IN718 superalloys at both atomic and micron scales through density functional theory (DFT), molecular dynamics (MD), and experimental ...analysis. From the micro scales, the addition of TiC can effectively mitigate the segregation behavior of Nb and Mo atoms, promote heterogeneous nucleation, reduce grain size, and thus improve mechanical properties. From the atomic scales, the effect of alloying elements (Fe, Cr, Mo, Nb, Co) on the stability of the TiC/γ-Ni interface was investigated through first principles. Co-doping interface was more stable than other interfaces by MD calculations, followed by Cr and Fe-doping models. The heat of segregation results inferred that TiC can effectively mitigate the segregation behavior of Nb and Mo atoms in the TiC/γ-Ni interface, it is mutually verified with the experimental results. Furthermore, the interface energy values theoretically illustrated that TiC particles could promote the heterogeneous nucleation of γ-Ni, this behavior of TiC particles was verified by experiment results. This investigation results provide reference information in the study of ceramic particle reinforced alloys at atomic and micron scales.
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•The effect of TiC addition on the IN718 alloy was studied from the atomic scale/micron scale by DFT, MD, and experiment.•The Co- and Cr-doping in the Case Ⅳ model of the TiC/γ-Ni interface improved the interface bonding strength.•The Co-, Cr-, and Fe-doping models demonstrate a higher tensile strength through molecular dynamics calculations.•The values of interface energy of Fe-, Cr-, Nb-, Co-doping and Case Ⅳ interfaces can promote heterogeneous nucleation.•The addition of TiC is conducive to heterogeneous nucleation and improves the mechanical properties of the superalloy.
Poly (lacticacid) (PLA) fiber-reinforced poly (ε-caprolactone) (PCL) composite is used in a broad variety of biocompatible and biodegradable materials, while phase separation remains an obstacle to ...mechanical performance. In this work, the PLA fiber-reinforced PCL composite membranes were prepared by multi-spinneret blended electrospinning, followed various synergistic processes of strain and melt-recrystallization. In the composite, the micro-scaled electrospun PLA fibers, which accomplished glass transition and partial crystallization during the annealing processing, profoundly reinforce the PCL matrix. The orientation and crystallinity of PLA fibers as well as the interfacial bond are improved by the manipulations of strain and supercooling during the crystallization of PCL domains in the composite. As a result, the tensile performance of the composite is greatly improved, which exhibits a modulus of 6.146 GPa and strength of 32.85 MPa, respectively, achieving a high level of strength among the PCL/PLA composites. This work offers a new approach to the preparation of PLA fiber-reinforced PCL composites with outstanding tensile performances.
In the PLA fiber-reinforced PCL membranes, the orientation and crystallinity of PLA fibers, the interfacial bond got improved. Therefore, the tensile modulus and strength exhibited over 6 GPa and 30 MPa, respectively, which are over 100% higher than the unstretched samples. Display omitted
•Composites are prepared by multi-spinnerets electrospinning and followed synergistic processes of annealing and stretching.•Orientation and crystallization of PLA fibers, and interfacial bond contribute to the significantly improved tensile performance.•Microstructural information has been studied by the synchrotron SAXS/WAXS.
The calculated interfacial energy values of the Ti-terminated interface structures and the B-terminated interface structures depend on the B chemical potential μTislab-μTibulk.
The calculated ...interface energies of Ti-terminated “HCP”stacking structure and the B-terminated “HCP”stacking structure of Mg/TiB2 depend on the values of μTislab-μTibulk. In the steady state, in the range of -1.73eV⩽μTislab-μTibulk⩽0, the Ti-terminated “HCP”stacking interface structure is more stable. Under the condition of -3.26eV⩽μTislab-μTibulk⩽-1.73eV, the B-terminated “HCP” stacking interface structure is more stable. The interface energies of Mg/TiB2 interface is larger than 0.1 J/m2 in the whole range of Ti chemical potential, with corresponding interface energies of B-terminated“HCP”stacking structure of 1.83J/m2∼5.08J/m2, the interface energies of Ti-terminated“HCP”stacking interface of 1.65J/m2∼4.89J/m2, elucidating the poor nucleation of α-Mg grains on TiB2 particles from thermodynamical considerations.
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•The electronic structure, adhesion work, bonding properties and interface energies of Mg(0001)/TiB2(0001) interface were investigated by the first-principles calculations based on density functional theory (DFT).•The interface energy of Mg/TiB2 interface is much larger than that of α-Mg/Mg melt interface, indicating that TiB2 particles possess poor nucleation potency for α-Mg grains from thermodynamic considerations.
In order to explore the interfacial structure of Mg (0001)/TiB2 (0001) interface and understand the heterogeneous nucleation potential of α-Mg grains on TiB2 particles, the electronic structure, adhesion work, bonding properties and interface energy of Mg(0001)/TiB2(0001) interface were investigated by the first-principles calculations method based on density functional theory (DFT). The Mg (0001) slabs with five atomic layers and TiB2 (0001) slabs with 9 atomic layers were adopted for interfacial models. Mg (0001)/TiB2 (0001) models with different stacking positions (“OT” stacking sequence, “HCP” stacking sequence and “MT” stacking sequence) of different terminations (Ti- and B-) were investigated. Metallic/covalent mixed bonds and ion bonds were formed respectively when Mg atoms combined with Ti-terminated TiB2 surface and B-terminated TiB2 surface. The interface energy of Mg/TiB2 interface is much larger than that of α-Mg/Mg melt interface, indicating that TiB2 particles possess poor nucleation potency for α-Mg grains from thermodynamical considerations.
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Despite the wide occurrence of crystallization in the pharmaceutical industry, deep understanding and fine control of the process remain a tricky issue. Nevertheless, the successful ...manufacturing of finished pharmaceutical products, as well as the structural determination of biopharmaceuticals, depend on the size, form, shape and purity of the crystals. The ability of substrates with precise chemistry and topological features to induce nucleation has been thoroughly assessed during the recent years. This paper reviews the major advances and discoveries in controlling small molecule drug and protein crystallization by means of engineered surfaces. By designing superficial properties and morphology, it has been possible to tune the polymorph outcome, shorten the nucleation induction time, impose specific crystal shapes, control the crystal size and carry out crystallization at very low supersaturation levels. Such achievements underline the potential of surface-induced crystallization to provide an ideal platform for the study of the nucleation process and gain control over its stochastic nature.
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