A MODEL FOR BAINITIC TRANSFORMATION KINETICS WITH PARABOLIC NUCLEATION RATE

Based on the assumptions of parabolic variation of nucleation rate versus time and transformation kinetics depending mainly on nucleation rate, a different model for bainitic transformation kinetics in hypoeutectoid steels was established. And this model was proved to be effective in the description of bainitic transformation by comparison with the result of conventional Avrami equation.

Nucleation Thermodynamics inside Micro/nanocavity

A thermodynamic approach at the nanometer scale was performed for the heterogeneous nucleation inside nanocavity, and an analytical expression of the critical energy of nucleation was evaluated considering a rough ball nucleus nucleating inside nanocavity. Compared with the case of the nucleation locating on planar or convex substrate, the critical energy of nucleation inside the concave substrate is the smallest. Based on the thermodynamic and kinetic analyses, at low supersaturation, the smaller the curvature radius of cavity and/or the smaller the contact angle, the smaller the critical energy of nucleation, and the larger the nucleation rate. At high supersaturation, the nucleation rate increases with increasing the contact angle and/or increasing the curvature radius of cavity. In this way, at the low supersaturation, the heterogeneous nucleation rate is larger than the homogeneous one, as the nucleation rate is mainly determined by the heterogeneous nucleation. At the high supersaturation, the heterogeneous nucleation rate is smaller than the homogeneous one, as the nucleation rate is mainly determined by the homogeneous nucleation.

Dissolution behavior,thermodynamic and kinetic analysis of malonamide by experimental measurement and molecular simulation

In this study,the solid structure,dissolution behavior,thermodynamic properties and nucleation kinetics of malonamide were explored.Firstly,the Hirshfeld surface analysis and molecular electrostatic potential surface were plotted to reveal the percentage contribution of various intermolecular contacts and location of the strongest hydrogen bond.Next,the solubility of malonamide in 12 solvents was determined by dynamic method at temperatures from 278.15 K to 318.15 K.Four thermodynamic models were applied to analyze solubility results.In addition,the thermodynamic properties were calculated to further analyze and discuss the dissolution behavior of malonamide.Moreover,the physicochemical properties of solvents were explored to express the solvent effects.The results illustrate“like dissolves like”,“mass transfer”and“solvent–solute interaction”rules play the synergistic effects on the dissolution process.The molecular dynamic simulation,including radial distribution function analysis and solvent free energy,was used to further explain the dissolution behavior.At last,the nucleation rate and effective interfacial energy in methanol solvent was measured and calculated to reveal the nucleation behaviour.

Effects of Small Biomolecules on Lysozyme Crystallization

To develop appropriate biocompatible nucleants,glutathione(GSH),glycine(Gly)and cysteine(Cys)were used as the biomolecular additives to study their effect on the regulation of lysozyme crystallization.Characterized by Fourier transform infrared spectroscopy,powder X-ray diffraction,circular dichroism,etc.,the results show that GSH can effectively promote protein crystallization under even lower concentrations of lysozyme by enhancing the nucleation rate,comparing with the additives of Gly and Cys,whereas lysozyme crystal structures produced in the presence of the biomolecular additives are similar to those in the absence of the additives.It shows in combination with molecular modeling that the stronger interactions between small biomolecular additives and the lysozyme LOOP accelerate the heterogeneous nucleation.It is suggested that such small biomolecules can be used as promising nucleants for promoting protein crystallization in the food and pharmaceutical industries.

CALCULATION OF TRANSFORMATION VOLUME FRACTION TO HQ590 HOT ROLLED STRIP STEEL DURING CONTINUOUS COOLING

On the basis of phase transformation kinetics, the transformation of γ→α,P,B have been investigated through considering the effect of deformation. The calculation methods of volume fraction have also been given. Comparing with common method, the simulated results are in more agreement with experiment results.

Molecular Dynamics Studies on the Kinetics of Phase Changes of Nanoparticles： Properties, Structures, and Crystal Nucleation of Copper Nanoparticle Cu453

Molecular dynamics （MD） computer simulations have been carried out to study the structures, properties and crystal nucleation of nanoparticles with 453 Cu atoms. Structure information was analyzed from the MD simulations, while properties of nanoparticles of Cu453, such as melting point, freezing temperature, heat capacity and mo- lar volumes, have been estimated. The face center cubic （FCC） phase and icosahedron （Ih） phase were observed during the quenching process, and nucleation rates of crystallization to FCC crystal of Cu453 at temperatures of 650, 700, 750, and 800 K were analyzed. Both classical nucleation theory （CNT） and diffuse interface theory （DIT） were used to interpret our observed nucleation rates. The free energy and diffuse interface thickness between the liquid and the FCC crystal phases were estimated by the CNT and DIT respectively, and the results show that the DIT does not work properly to the system.

The effect of CTAB on Na_2SO_4 nucleation in mixed Na_2SO_4/CTAB aerosols by FTIR-ATR technology

FTIR-ATR technology is used to study the efflorescence kinetic of Na2SO4 and mixed Na2SO4/CTAB aerosols.As the RH decreased linearly,the v3-SO42 band shifts from 1094 cm1 to 1132 cm1,suggesting the phase transition of Na2SO4 from solution to crystal phase（Ⅲ）.For pure Na2SO4 aerosols,the ERH is 75.1%RH,whereas the efflorescence point of mixed Na2SO4/CTAB aerosols（74.2%） is lower.By further analysis of IR differential spectra,the ratio of Na2SO4 crystals in mixed aerosols is only 62.7%and the heterogeneous nucleation rate of Na2SO4 in Na2SO4/CTAB mixed aerosols is lower than that in pure Na2SO4 aerosols.They showed that CTAB assembled into reversed micelle and part Na2SO4 droplets are in the core to form core-shell structure,and CTAB shell prevents core Na2SO4 solutions from crystallizing.However,the counter ion Br for CTAB reversed micelle can interact with Na＋ ions,which decreases the crystallization rate of free Na2SO4 droplets and ERH is delayed.

Molecular Dynamics Studies of the Kinetics of Phase Changes in Clusters IV:Crystal Nucleation from Molten (NaCl)_(256) and (NaCl)_(500) Clusters

Molecular dynamics computer simulation based on the Born-Mayer-Huggins potential function has been carried out to study the effects of cluster size and temperature on the nucleation rate of sodium chloride clusters in the temperature range of 580 K to 630 K. Clusters with 256 and 500 NaCl molecules have been studied and the results have been compared with those obtained from 108 molecule clusters. The melting point (MP) of the clusters were observed to increase with the size of the clusters and can be well described by a linear equation MP=1107(37)-1229(23)N -1/3 (N is the number of molecules in the cluster). The nucleation rate was found to decrease with increasing the cluster size or temperature. Various nucleation theories have been used to interpret the nucleation rates obtained from this molecular dynamics simulation. It is possible to use a constant diffuse interface thickness to interpret the nucleation rate from the diffuse interface theory in the temperature range of this study. However,the interfacial free energy estimated from classical nucleation theory and diffuse interface theory increases too fast with increasing the temperature while that from Gran-Gunton theory does not change with changing temperatures. The sizes of critical nuclei estimated from all the theories are smaller than those estimated from our simulations.

Microstructure Evolution of Primary γ′ Phase in Ni3Al-Based Superalloy

In this work,water cooling,air cooling(AC)and furnace cooling(FC)were applied to investigate the effect of cooling rate on microstructure evolution of primaryγ′in a newly designed Ni3Al-based alloy.The results showed that nucleation rate of primaryγ′increased with increasing cooling rate.In addition,higher cooling rate shortened growth period of primaryγ′,which made its morphology close to the initial precipitatedγ′.For AC and FC specimens,due to the lower cooling rate,primaryγ′possessed longer growth period and its morphology was mainly due to the evolution of lattice misfit betweenγand primaryγ′.Meanwhile,growth of primaryγ′depended on lattice misfit distribution between its corner and edge area.Moreover,primaryγ′morphologies of sphere,cube and concave cube with tip corners were illustrated by considering interaction between elemental diffusion and elastic strain energy.