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421.
Sonocrystallization implies the application of ultrasound radiation to control the nucleation and crystal growth depending on the actuation time and intensity. Its application allows to induce nucleation at lower supersaturations than required under standard conditions. Although extended in inorganic and organic crystallization, it has been scarcely explored in protein crystallization. Now, that industrial protein crystallization is gaining momentum, the interest on new ways to control protein nucleation and crystal growth is advancing. In this work we present the development of a novel ultrasound bioreactor to study its influence on protein crystallization in agarose gel. Gel media minimize convention currents and sedimentation, favoring a more homogeneous and stable conditions to study the effect of an externally generated low energy ultrasonic irradiation on protein crystallization avoiding other undesired effects such as temperature increase, introduction of surfaces which induce nucleation, destructive cavitation phenomena, etc. In-depth statistical analysis of the results has shown that the impact of ultrasound in gel media on crystal size populations are statistically significant and reproducible. 相似文献
422.
KTP crystals have been grown by two nucleation techniques namely spontaneous nucleation in flux medium and nucleation on Pt rod using K6P4O13 flux.10 °C/h, 7 °C/h, 0.8 °C/h, 0.4 °C/h and 0.2 °C/h cooling rates were applied for spontaneous nucleation and crystals up to 15 × 7 × 4 mm3 in size were grown. 1 °C/h and 0.8 °C/h cooling rates were also used for nucleation on Pt rod and crystals up to 8 × 6 × 3 mm3 in size were grown. The effect of cooling rate on size, morphology and optical quality of grown crystals by both techniques were studied. For nucleation on Pt rod upper and lower rotation rates limits and an optimum rotation rate were distinguished for each cooling rate. Quality of the grown crystals by both techniques was characterized by optical transmission analysis. 相似文献
423.
By performing 2D kinetic Monte Carlo simulations of colloidal crystallization we found that the boundaries of the crystalline nuclei are not only rough, as obtained by experimentalists, but fractal, whose value (df) we calculated. The corresponding boundary for the crystals, above the critical size (Nc), is also fractal but smoother. A knowledge of the particles coordinates during the crystallization process allows us to calculate the Nc, the line tension (γ) and the chemical potential difference (Δμ) between the two phases. However, different from the experimentalists procedure, we found that the boundary fractalities are needed to derive γ and Δμ. 相似文献
424.
Li-Li Zhou Rang-Su Liu Ze-An TianHai-Rong Liu Zhao-Yang HouPing Peng Xuan-Min ZhuQuan-Hui Liu 《Physica B: Condensed Matter》2012,407(2):240-245
The kinetic details of crystallization in supercooled liquid Pb during the isothermal relaxation process have been investigated by molecular dynamics simulations, and the microstructure evolution analyzed by the cluster-type index method (CTIM) and the tracing method. It has been found that, the dynamic features are consistently correlated with the microstructure evolution and the crystallization characteristics in the mean square displacement (MSD) and the non-Gaussian parameter (NGP): the β relaxation regime corresponds to the minor structural rearrangement because of the “cage effect”, and the atoms attempt to escape from the “cages”; the α relaxation regime is related to a more diffusive movement of atoms, and the appearance of the second plateau in MSD and the non-zero plateau in NGP corresponds to the completion of crystallization. In addition, three distinct stages of nucleation, growth of nuclei and coarsening of crystallites in the crystallization process have been clearly revealed. 相似文献
425.
Sanghwa Lee Taegeon Oh Boa Shin Chinkyo Kim Dong Ryeol Lee Hyun-Hwi Lee 《Journal of Crystal Growth》2010,312(14):2038-2043
GaN nanorods were grown on Si(1 1 1) substrates by using hydride vapor phase epitaxy, and the crystallographic characteristics associated with their preferred growth directions were investigated by utilizing synchrotron X-ray reciprocal space mapping in a grazing incidence geometry and scanning electron microscopy. Crystallographic analysis reveals that the nanorods containing both wurtzite and zinc blende phase tend to have narrower distribution of the preferred growth directions than those containing only wurtzite phase. This tendency is partly attributed to the subtle interplay between polytypism and the preferred growth directions of GaN nanorods. 相似文献
426.
V.P. Solntsev A.V. Davydov V.K. Malinovsky N.V. Surovtsev 《Journal of Crystal Growth》2010,312(20):2962-2966
Melting and crystallization scenarios of barium tetraborate BaB4O7 (BaO·2B2O3) are studied in situ by Raman spectroscopy. It is shown that the scenario depends on the temperature–time history of melt. Crystallization conditions of the beta modification of barium tetraborate (β-BaB4O7) from a stoichiometric glass structure BaO·2B2O3 were investigated. 相似文献
427.
F. Jones A. Oliviera G.M. Parkinson A.L. Rohl A. Stanley T. Upson 《Journal of Crystal Growth》2004,270(3-4):593-603
Calcium ions have been implicated in changing the precipitation of barium sulfate when organic additives are present, although whether it inhibits or promotes nucleation and/or growth has been disputed in the literature. We conducted a thorough investigation into the effect of calcium when additives are present and show that calcium cations do indeed promote nucleation of barium sulfate particles when compared to the appropriate control. This result is independent of the analytical method (conductivity or turbidity) used to assess precipitation. The nucleation promotion produces no change in the crystal morphology, thus morphology is not always a good indicator of nucleation or growth behavior. The extent of nucleation promotion depends on the functional group of the additive. 相似文献
428.
One frontier of measurement science is pushing the limit of what is measurable. Nanoelectrochemistry has transformed what is measurable at the nanoscale, elucidating reactivity of single atoms, molecules, and nanoparticles, one by one. The ability to interrogate physicochemical properties of single entities has elucidated new truths of nature that are otherwise averaged out during measurements over many entities (ensemble experiments). Single-entity experiments also give access to the ultimate sensitivity in measurement science: the specific detection of one single entity (not nanomolar quantities, not picomolar quantities—one single unit). One exciting subset of single-entity electrochemistry, and the topic of this review, is the study of reactions in nanoreactors of subfemtoliter (10?15 L) volumes with a particular focus on nanoparticle synthesis. 相似文献
429.
液滴外延技术不仅适用于晶格失配,也适用于晶格匹配材料系统,且易于制备低维半导体结构,如低密度量子点、环等.本文研究了液滴外延法在GaAs表面进行不同Al、Ga组分的量子点生长.在实验中用反射式高能电子衍射仪(Reflection High Energy Electron Diffraction, RHEED)对样品进行原位监控.通过控制Al、Ga液滴的沉积速率来控制液滴同时沉积在衬底上形成的组分.研究发现,随着Al组分的增加,量子点逐渐变得密集,润湿角变低.在Al组分增高超过0.5之后,出现了大小不一的量子点,且量子点密度出现指数型增长.对此进行研究分析,给出了一个经验公式,并就现象进行了解释. 相似文献
430.
Progesterone is known to exist under different crystallographic forms in the solid state. The thermodynamic stable form (I), melts at 129.2 °C (402.35 K) under atmospheric pressure. After melting and cooling a metastable form (II) can be obtained which melts at 122 °C (395.15 K). This uncommon behaviour can be explained with the theory of nucleation, only if heat capacity of the different forms are known. 相似文献