Fractal slice model analysis for effective thermal conductivity and temperature distribution of porous crystal layer via layer crystallization

A fractal slice model was established based on the reported model to predict the effective thermal conductivity of a porous crystal layer via layer crystallization. The temperature distribution of the crystal layer was obtained by the fractal slice method. The simulation results agreed with the experimental data better than the other theoretical models. The results were helpful to enhance the thermal transport by mitigating the thermal resistance effectively.     

Impurity diffusion of 114In in Cu

Using the tracer-standard sectioning technique the impurity diffusion of indium in copper has been investigated in the temperature range from 798.1 to 1081.0°C. For the frequency factor and the activation energy, respectively, the following values were determined: D₀₂ = 1.87 cm² · s⁻¹; Q₂ = 2.034 eV. The results are compared with predictions of theoretical models of the impurity diffusion in metals.     

The effect of diluting crystallization droplets on protein crystallization in vapor diffusion method

In this study, effects of diluting either protein or crystallization agents in the droplets on the success rate of protein crystallization was investigated. Diluting the crystallization agent was found to increase the success rate of protein crystallization. Theoretical analysis showed that, concentration ranges of both protein and crystallization agent that can be scanned during the vapor diffusion process are wider with diluting the crystallization agent than that without dilution, resulting in more opportunities for the crystallization solution to be in the nucleation zone. On the other hand, diluting protein could lead to controversial results depending on the location of the initial concentration relative to that of the nucleation zone in the phase diagram. The method of diluting the crystallization agent is therefore proposed as an alternative modification to the conventional vapor diffusion method for obtaining more crystallization conditions in protein crystallization screening. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Concentration distribution in crystallization from solution under microgravity

Concentration distribution in crystallization from solution under microgravity is numerically studied. A quasi-steady state growth and dissolution in a 2D rectangular enclosure filled with sodium chlorate (NaClO₃) aqueous solution, in which one wall is the growth surface of the crystal and the opposite one is the dissolution surface, is considered. The solute transport process at the growth surface is described by the diffusion-reaction theory with finite interface kinetics coefficient. The results show that the concentration at the growth surface is supersaturated and the supersaturation distribution is of non-uniformity, i.e. the supersaturation in a region facing an incoming flow is high. On the other hand, the non-uniformity of supersaturation at the growth surface is closely related to the gravity level even under microgravity, it exponentially increases as the thermal Rayleigh number on behalf of the gravity level rises.     

Protein crystallization in low gravity by step gradient diffusion method.

Two-step crystallization experiments were conducted in low gravity employing a liquid-liquid diffusion method in an effort to eliminate problems associated with protein crystal growth under the supersaturating conditions required for nucleation. Experiments were performed in diffusion cells formed by the sliding of blocks on orbit. Step gradient diffusion experiments consisted of first exposing protein solutions in diffusion half-wells for brief periods to initiating buffer solutions of high precipitant concentrations to induce nucleation followed by expoure of the same protein solutions to solutions of lower precepitant concentration to promote growth of induced nuclei into crystals. To avoid convective disturbances that occur when solutions of discrepant densities are interfaced at normal gravity, crystallization of hen egg-white lysozyme and rabbit skeletal muscle aldolase by step gradient diffusion was investigated in low gravity on four NASA space shuttle flights. In general, the largest ctystals of both proteins formed at the highest initiating precipitant concentration used, which is consistent with nuclei formation upon brief exposure to high precipitant concentration, and that these nuclei are competent for sustained growth at lower precipitant concentration. The two-step approach dissociates nucleation events from crystal growth allowing parameters affecting nucleation kinetics such as time, precipitant concentration and temperature of nucleation to be varied separately from conditions used for post-nucleation growth.     

Impurity diffusion measurements of Bi in liquid Sn using stable density layering and the shear cell technique

To obtain reliable diffusion data on earth, impurity diffusion experiments of Bi in liquid Sn were performed using a stable density layering and the shear cell technique with a reservoir system to provide pressure on the liquid. The experiment type was diffusion of Bi from a SnBi3at.% (5 wt%) thick layer into Sn. The diffusion temperatures (diffusion times) were 300 °C (8 h), 500 °C (4.5 h) and 800 °C (2.5 h). At each temperature four parallel experiments were performed simultaneously in one shear cell cartridge. After the diffusion experiments, the Bi concentration profiles were measured by atom absorption spectroscopy. The diffusion coefficients were determined by fitting with the thick layer solution considering the correction method of the shear convection and the averaging effect. As a result, the concentration profiles had only small deviations and the diffusion coefficients agreed well among the four parallel experiments. The mean diffusion coefficient at 300 °C agreed well with data from the 1g-diffusion experiments in a magnetic field and with μg-data. It was also shown that this method can be applied also to interdiffusion experiments, in which the influence of Marangoni convection can be investigated by the variation of the pressure inside the capillary and artificial free surfaces on the liquid sample. The temperature dependence of the diffusion coefficient was empirically described as the nth power law (n ≈ 1.8) of T.     

The validity of the double layer model on the amorphous semiconductor surface including the bulk localized state within the gap

Under the two assumptions that the origin of surface states may be different from that of bulk localized states within the gap and the density of surface states is sufficiently high, the validity of the double layer model on the amorphous semiconductor surface is investigated in comparison with the case of a crystal. It is suggested that the criteria concerning the double layer should be determined by the relative value of the surface states to that of bulk localized states. The existence of the double layer can be confirmed when the bulk localized state density n(E_f) is smaller than 10¹⁹ cm^?3 eV^?1. When n(E_f) is high at about 10²⁰ cm^?3 eV^?1, surface states cannot be distinguished from the localized states within the gap. This double layer model is strongly supported by the results of previous experiments by others who have measured the dependence of the Schottky barrier height on the work function of metal and the dependence of the surface potential on the preparation conditions of a-SiH.     

Impact of agglomeration on crystalline product quality within the crystallization process chain

The quality of crystalline products, defined by e.g. purity or crystal size distribution (CSD), is primarily dominated by crystallization conditions but influenced by further downstream processes like solid‐liquid separation and drying also. Through uncontrolled agglomeration within the crystallization process chain the purity or CSD can be negatively affected. Therefore, in context of process optimization, missing knowledge of the impacts on the final product can lead to product batches out of specification. To increase the understanding of agglomeration and to provide insight into the relevance of holistic process optimization the agglomeration behavior of L‐alanine crystals is exemplarily quantified over the crystalline process chain. For the quantification the agglomeration degree (Ag) and the agglomeration degree distribution (AgD) are determined. The results show that the product quality achieved after crystallization is significantly affected by agglomeration during drying. Especially if washing after solid‐liquid separation is omitted, a broadening of the CSD is observed. Moreover, the evaluation by the AgD indicates that the final product can be ‐ despite similar characteristics of the CSD ‐ highly different. Consequently, it can be concluded that the characterization of the product quality by the CSD alone is insufficient and the quantification of agglomeration is essential for process optimization.     

Influence of various factors on the liquid/liquid diffusion crystallization of proteins

From a numerical simulation of pre-nucleation solute transport in the liquid/liquid diffusion crystallization of proteins, it is derived that there are various factors influencing the spatial and temporal distributions of supersaturation. They include the ratio of the length of the protein solution to that of the salt solution in a tube crystallizer, the initial concentrations of protein and salt, and the initial salt concentration in the protein solution. Their influences on the protein crystallization have been demonstrated by the corresponding experiments of gel crystal growth. It may be deduced that the experimental conditions for the liquid/liquid diffusion growth of protein crystals could be optimized under given conditions in order to develop the advantages of this method.     

Kinetic characteristics of the crystallization from model solutions of blood plasma

Crystallography Reports - The kinetic regularities of crystallization (growth order and constants) in a model solution of blood plasma have been investigated. The particular order and...     

Impact of amorphous Ge thin layer at the amorphous Si/Al interface on Al-induced crystallization

We investigated the impact of an amorphous Ge (a-Ge) thin layer inserted at the amorphous Si (a-Si)/Al interface on Al-induced crystallization. In situ observation of the growth process clarified that the nucleation rate is drastically reduced by insertion of a-Ge, which led to increase in the average size of crystal grains. This was interpreted as resulting from decrease in the driving force of crystallization, mainly due to the larger solubility of Ge in Al than that of Si in Al. The obtained films were SiGe alloys with lateral distribution of Ge content, and its origin is discussed based on the two-step nucleation process.     

A new model for the structure of chalcogenide glasses: The closed cluster model

A new model is proposed for the structure of low atomic coordination chalcogenide glasses. The closed clusters model is based on the various types of clusters, packed by van der Waals forces in a molecular-type packing. Arguments are given to support the new model, taken as example the typical chalcogenide glass As₂S₃.     

On the distribution coefficient of sulphur during the crystallization of GaP from nonstoichiometric gallium melts

GaP grown by the SSD technique was doped by sulphur in a wide concentration range. Using chemical, electrical and radiochemical methods the concentration and temperature dependence of the distribution coefficient k during this crystallization from the nonstoichiometric melt was determined. With the crystallization temperature at 1000°C for k a value 6.9 ± 1.4 was found independent on the sulphur quantity added. The distribution coefficient decreases clearly with increasing temperature.     

The distribution coefficient of zinc during the crystallization of GaP from nonstoichiometric gallium melts

Experiments were carried out to calculate by defining equations the distribution coefficient of zinc during the crystallization of GaP from the nonstoichiometric gallium melt. The TGS technique was applied to grow the crystals. Zinc detection was performed by the use of the radionuclide Zn⁶⁵ as a tracer. The distribution coefficient being of the order of 0.1 is dependent upon temperature and concentration. These relations are demonstrated by plots and discussed with special respect to the literature data.     

Sea water desalination by dynamic layer melt crystallization: Parametric study of the freezing and sweating steps

This work aims at developing a dynamic layer crystallizer operated batchwise, for freezing desalination of sea water. The experiments were performed with water/NaCl solutions and with samples of sea water from Nice, Rabat and Marseille. The pilot crystallizer consists of a cooled tube immersed in a cylindrical double jacketed tank. The solution is poured into the tank and the crystallization takes place on the external surface of the tube, by applying a cooling ramp in the tube. The solution is agitated by air bubbling. The whole process involves the freezing step, leading to the crystallization of the ice layer and the sweating step, which consists of purifying in depth the ice layer by melting the impure zones. A parametric study on the effect of the operating parameters has allowed quantifying the role of the different key parameters of the freezing and sweating steps. Three experiments allowed reaching salinities lower than 0.5 g/kg, satisfying the standards of drinking water. The duration of the whole process dropped to only 8 h (5 h for freezing and 3 h for sweating), with a yield of sweating equal to about 50%, provided severe conditions were applied for sweating. Higher yields required longer times. Overall, the results show the feasibility of the technique.     

Model of the radial distribution function of pores in a layer of porous aluminum oxide

An empirical formula is derived to describe the quasi-periodic structure of a layer of porous aluminum oxide obtained by anodization. The formula accounts for two mechanisms of the transition from the ordered state (2D crystal) to the amorphous state. The first mechanism infers that vacancy-type defects arise, but the crystal lattice remains undestroyed. The second mechanism describes the lattice destruction. The radial distribution function of the pores in porous aluminum oxide is obtained using the Bessel transform. Comparison with a real sample is performed.     

An analytical model to represent crystallization kinetics in materials with metastable phase formation

The aim of this article is to propose a simple analytical model that can describe the isothermal crystallization process in materials when the formation of a stable crystalline phase is preceded by the formation of a metastable phase. This model explains deviations from the well-known Johnson-Mehl-Avrami-Kolmogorov kinetics theory and predicts the three slopes in Avrami’s plot. The model predictions were compared with experimental results obtained from X-ray measurements in the chalcogenide glasses with composition of Ge₂Sb₂Te₅ (thin films) and in aqueous solutions of methylhydrazine monohydrate during isothermal phase transformations. In order to validate the proposed model to represent experimental results, a computer program was developed. This program uses experimental data from measurements of the total volume fraction at different times during isothermal transformations and fits the model parameters that best represent the kinetic behavior of the system.