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1.
This work deals with the transient analysis of crystal size distribution (CSD) for imperfectly mixed draft tube baffled (DTB) and forced circulation (FC) crystallizers. The DTB and FC crystallizers are described by the Compartmental and Mixed models respectively. Monte Carlo (MC) scheme has been employed for simulation purposes. The simulation results have been compared with the available experimental data of BENNETT and VAN BUREN for continuous urea crystallizers. 相似文献
2.
Plots of crystal size distribution of the following crystallizer models are compared: an ideal continuous-flow MSMPR (mixed suspension, mixed product removal) crystallizer with a zero as well as non-zero initial crystal size, an MSMPR crystallizer with size dependent growth of crystals, an MSMPR crystallizer with missing fines, an MSMPR crystallizer with agglomerative growth, and a series of MSMPR crystallizers simulating a crystallizer with nonideal agitation. The shape of the individual size distribution curves can serve as a diagnostic criterion in determination of the most probable model of crystallization. 相似文献
3.
Silicon wafers which have a small misorientation from (111) become facetted, when they are etched beyond a critical HCl concentration. This facetting can be explained by the action of a second etch mechanism which directly attacks the surface between the steps. In this way enough new steps are generated to give a proper response to the desired etchrate. In BCF language: the spiral dissolution around a dislocation containing a screw component can become dominant over the etching process which occurs by a set of parallel steps, when beyond a critical HCl concentration the density of steps inside the shallow pit exceeds the density of the parallel steps due to the original misorientation. From the slope of the shallow pits at the critical HCl concentration a desorption energy for SiCl2 adatoms of around 60 kcal/mole could be calculated. 相似文献
4.
GaAs(100) and (111) oriented samples, treated by means of different chemical procedures, are studied by X-ray photoelectron spectroscopy (XPS). The thickness and composition of the residual oxide layers are estimated using the intensity ration of Ga 3d and As 3d core levels from the substrate and the oxide overlayers, respectively. Residual oxides containing As2 O3 and Ga2 O3 on GaAs surface are observed. The thickness of the oxide layers is found to range from 3Å to 15 Å. Optimal conditions for pre-epitaxial surface preparation of GaAs substrates are suggested. 相似文献
5.
S. V. Pasechnik D. V. Shmeliova A. V. Dubtsov V. G. Chigrinov Jiatong Sun 《Molecular Crystals and Liquid Crystals》2015,611(1):81-93
The modified method for shear viscosity measurements of nematic liquid crystals (NLC) oriented by surfaces is described. The main modification is concerned with usage of photoalignment technique for preparation of mono-domain samples with an orientation controlled by a polarization state of the secondary light irradiation. It provides the azimuthal rotation of a sample at any desirable angle. Thus different geometries of shear flows can be realized after filling the measuring cell with a liquid crystal. The method is experimentally approved at investigation of Poiseuille decay flows of 4-pentyl-4-cyanobiphenyl (5CB) through the channels with a rectangular cross section. The proposed construction of the cell with different surface treatment provides measurements of the three principal viscosities coefficients (Miesowicz’ viscosities) with additional usage of electric field. A small amount (less than 0.2 ml) of a liquid crystal needed for measurements and simple measuring procedure makes the method to be useful for rheological studies of newly synthesised liquid crystal materials. 相似文献
6.
L. Kramer 《Liquid Crystals Today》2013,22(3-4):17-18
Abstract This event marked the 10th anniversary of the first workshop on this topic in Bayreuth, which initiated a bi-annual series on pattern formation in complex systems which took place in Kitakyushu, Santa Fe, Copenhagen and Budapest. Some of the topics discussed are reported below (see also www.phy.uni-bayreuth.de/-ptlc/). 相似文献
7.
A. Iller G. Karczewski G. Karczewski G. Kolmhofer E. usakowska H. Sitter 《Crystal Research and Technology》1998,33(3):401-408
{211} polar surfaces of a Cd0.96Zn0.04Te chemically treated single crystal were investigated by Auger electron spectroscopy depth profiling. It was found that the use of a discriminatory “black-white” etchant causes the formation of a thick layer with cadmium having been severely depleted at both (211) A and (211) B faces. The thickness of this layer is larger by a factor of 2 for the matt black face then for the bright and reflecting face. AES investigation of chemical treatment influence on (100) CdTe epitaxial layer surface has been performed. It has been established that etching in Br/methanol solution removes S, Cl and O containing contaminants from the surface, but simultaneously forms a Cd-depleted layer. 相似文献
8.
A new highly flexible batch crystallizer control system and suite of software using a BBC model B microcomputer to programme the cooling rate and log data is described. The programs were tested satisfactorily with the cooling crystallization of potassium sulphate solutions. Both linear and controlled cooling increased the mean crystal size with lower coefficient of variation compared to natural cooling crystallization with a consequent improvement in filtrability characteristics. 相似文献
9.
The investigation of the element composition of TiCx layers depending on depth profiles shows that the samples stored on air are coated by a contamination layer of hydrocarbons. The subjacent layer consists of about 19 mole-% Ti, 26 mole-% C, 45 mole-% 0 and less than 5 mole-% of Cr and Fe. The change of the position of the C1s, 01s and Ti2p-lines depending on depth profiles allows us to draw conclusions from changes in the chemical bonding states of these elements. — A detailed profile analysis of the C1s-line shows five different bonding states of carbon (CyHx, TiCx, Fe3C, elemental C and 〉CO-compounds). The change of the O- and Ti-bonding states within the layer consists particularly in decreasing OH-bond as compared with oxide-bond and also of TiOx in comparison with TiCx. 相似文献
10.
This study demonstrates the application of metal-assisted and microwave-accelerated evaporative crystallization (MA-MAEC) technique to rapid crystallization of L-alanine on surface engineered silver nanostructures. In this regard, silver island films (SIFs) were modified with hexamethylenediamine (HMA), 1-undecanethiol (UDET), and 11-mercaptoundecanoic acid (MUDA), which introduced -NH(2), -CH(3) and -COOH functional groups to SIFs, respectively. L-Alanine was crystallized on these engineered surfaces and blank SIFs at room temperature and using MA-MAEC technique. Significant improvements in crystal size, shape, and quality were observed on HMA-, MUDA- and UDET-modified SIFs at room temperature (crystallization time = 144, 40 and 147 min, respectively) as compared to those crystals grown on blank SIFs. Using the MA-MAEC technique, the crystallization time of L-alanine on engineered surfaces were reduced to 17 sec for microwave power level 10 (i.e., duty cycle 100%) and 7 min for microwave power level 1 (duty cycle 10%). Raman spectroscopy and powder x-ray diffraction (XRD) measurements showed that L-Alanine crystals grown on engineered surfaces using MA-MAEC technique had identical characteristic peaks of L-alanine crystals grown using traditional evaporative crystallization. 相似文献
11.
The change in surface morphology of potassium nitrate and potassium alum has been studied in situ by means of scanning force microscopy. The supersaturation and undersaturation were varied in a cooling crystallizer under flow conditions. To keep the crystal growth rate of potassium nitrate low, the specific additive DOW FAX 3B2 had been used in different concentrations. The crystal growth rate of both systems could be determined and the growth and dissolution surface morphologies of potassium alum exhibited structures similar to those of microscopic measurements. 相似文献
12.
Jacques Cognard 《Molecular Crystals and Liquid Crystals》2013,570(9-10):331-342
Liquid crystal anchoring energy varies with the distance to the solid substrate in the interfacial layer. Experimental values correspond to a low anchorage as the liquid crystal slides on its interfacial layer. The question of whether it will be possible to observe low anchorage in a parallel alignment is raised. 相似文献
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14.
KDP晶体中包裹体形成机制的探讨 总被引:8,自引:8,他引:0
本文介绍了包裹体对KDP晶体质量的影响,并从两个方面探讨了KDP晶体生长过程中包裹体的形成机制.通过分析KDP晶体表面原子结构研究了不同杂质的吸附情况以及杂质对生长台阶的阻碍作用,通过分析晶体生长过程中流体动力学和质量输运条件的变化研究了旋转晶体的流体切应力和表面过饱和度,结果表明吸附杂质对生长台阶的阻碍和表面过饱和度的不均匀造成了生长台阶的弯曲和宏观台阶的形成,导致生长台阶形貌的不稳定是包裹体形成的重要原因. 相似文献
15.
S. Meyer A. L. Aseev A. G. Klimenko E. A. Klimenko S. I. Stenin 《Crystal Research and Technology》1975,10(3):247-257
A dislocation structure of Si layers crystallized from a floating grain on quartz glass and mullite ceramics substrates has been investigated by transmission electron microscopy (TEM) including the high-voltage one. The effect of the layer orientation on the crystallographic features of dislocation distribution and brittle fracture in Si-SiO2 system has been considered. The dislocation structure is proved to form mainly at temperatures lower than 0.8 of absolute melting temperature (Tm) of Si. Dislocation sources are located inside the crystallizable layer, and they are dislocations appearing from grain as well as the dislocation bundles near the interface. The cross slip of screws plays an essential role in dislocation multiplication. The difference of thermal expansion coefficients of the layer and substrate determines the finite dislocation density near the interface and in the bulk of the layer. 相似文献
16.
M. R. Philpott A Girlando W G. Golden W Knoll J. D. Swalen 《Molecular Crystals and Liquid Crystals》2013,570(1):335-351
The vibrational spectra of monolayer assemblies of cadmium arachidate on smooth and rough silver substrates were obtained by surface infrared and surface plasmon enhanced Raman spectroscopy. The assemblies were laid down by the Langmuir-Blodgett deposition technique. For Raman scattering the intensity of the incident light was enhanced by grating coupling to surface plasmon optical modes of the metal or to localized plasmon modes in the case of rough surfaces. It was found that the different vibrational frequency regions corresponding, for example, to C-C and C-H stretching modes, were enhanced by selecting different scattering angles for collecting the inelastically scattered light. The Raman spectra of monolayer assemblies in contact with silver islands showed evidence of conformational disorder, i.e., the alkyl chains of some molecules were not in the all-trans configuration. In contrast, the infrared spectra did not show evidence of similar disorder. These observations were explained by assuming that the infrared photons sensed the majority undistorted molecular species, while the Raman photons came from a distorted minority species located in regions where optical electromagnetic fields were enhanced by shape plasmon resonances of the rough silver surface. 相似文献
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18.
The observation of periodic bands and macroscopic deposits, when suspensions of silver and arsenious trisulphide are allowed to interact in a gel medium may be due to a chemical instability of autocatalytic reaction mechanism of colloid growth and nucleation. 相似文献
19.
G. Stergioudis 《Crystal Research and Technology》2006,41(10):1002-1004
Boronizing coatings were prepared by means of pack cementation technique. It was found that using the appropriate substrate and controlling parameters of the boribing process such as boron activity of the mixture, temperature and time of treatment, it is possible to obtain a structure predominantly consisting of the Fe2B phase. In the present study low alloy ferritic steels were chosen as substrates. Changing the boron carbide concentration in the mixture and the temperature and time of boronizing process the conditions of the boronizing were altered. As a result the formation of the Fe2B phase is enhanced. Characterization of the as‐borided steels is discussed based on X‐ray diffraction and Curie temperature measurements. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
20.
A. G. Petersyan G. O. Shirinyan K. L. Ovanesyan A. A. Avetisyan 《Crystal Research and Technology》1978,13(1):43-46
Formation of {110} and {211} type facets in rare-earth aluminium garnet crystals grown along different crystallographic directions is analyzed and it is shown that D/2R parameter (where D is the crystal diameter and R is the curvature radius of spherical growth interface) may be used to characterize the number of originating facets and their configuration in crystals. 相似文献