Crystallization disperse structures

A relatively simple but at the same time classical example illustrating the formation of crystallization disperse structure is hardening of gypsum semihydrate upon reacting with water as shown below [16] ... 

Crystallization disperse structures can also form in aqueous suspensions of other singlecomponent mineral binders. For instance, the hydration hardening of MgO results in the formation... 

X-Ray diffraction from single crystals is the most direct and powerful experimental tool available to determine molecular structures and intermolecular interactions at atomic resolution. Monochromatic CuKa radiation of wavelength (X) 1.5418 A is commonly used to collect the X-ray intensities diffracted by the electrons in the crystal. The structure amplitudes, whose squares are the intensities of the reflections, coupled with their appropriate phases, are the basic ingredients to locate atomic positions. Because phases cannot be experimentally recorded, the phase problem has to be resolved by one of the well-known techniques the heavy-atom method, the direct method, anomalous dispersion, and isomorphous replacement.1 Once approximate phases of some strong reflections are obtained, the electron-density maps computed by Fourier summation, which requires both amplitudes and phases, lead to a partial solution of the crystal structure. Phases based on this initial structure can be used to include previously omitted reflections so that in a couple of trials, the entire structure is traced at a high resolution. Difference Fourier maps at this stage are helpful to locate ions and solvent molecules. Subsequent refinement of the crystal structure by well-known least-squares methods ensures reliable atomic coordinates and thermal parameters. 

In all of this work there was little suggestion that the surface states of the palladium might behave differently from bulk states. Selwood (17) indicated that, from some sorption-magnetic susceptibility data for hydrogen sorbed on palladium which was finely dispersed on alumina gel, the ultimate sorption capacity was approximately at the ratio 2H/Pd. Trzebiatowsky and coworkers (25) deposited palladium on alumina gel in amounts ranging from 0.46 to 9.1% of gel weight. They found the palladium to be present in a normal crystal lattice structure, but its susceptibility was less than for the bulk metal. This suggested to the present authors that the first layer of palladium atoms laid down on the alumina gel underwent an interaction with the alumina, which has some of the properties of a semiconductor. Such behavior was definitely shown in this laboratory (22) in the studies on the sorption of NO by alumina gel. Much of this... 

Finally, the crystalline microstructure in many foods is not the only microstructural element of interest. Often crystal dispersions are found alongside other structures, such as air cells, fat globules, protein micelles, liquid crystals, and others. The interactions among these structural elements will be the focus of future studies in complex foods. 

Shear thinning of concentrated suspensions is typical for submicron particles dispersed in a low viscosity Newtonian fluid.At low shear strain rates. Brownian motion leads to a random distribution of the particles in the suspension, and particle collision will result in viscous behavior. At high shear strain rates, however, particles will arrange in layers, which can slide over each other in the direction of flow. This results in a reduced viscosity of the system in agreement with the principles of shear thinning. A pro-noimced apparent yield stress can be found for shear thinning suspensions, if the Brownian motion is suppressed by electrostatic repulsion forces, which result in three-dimensional crystal-like structures of the particles with low mobility. 

It was the aim of the present paper to show that crystallization in incompatible polymer blends can exhibit a lot of peculiar effects beside the classical well known physical and physico-chemical phenomena. The effects considered here, in particular, are due to the dispersion structure of such blends, and to the changes in the crystallization nucleation conditions which are such caused. They are important from a physical, a material scientific, and a technological point of view as well. 

The nature of plasticity is rupture and rearrangements of interatomic bonds which in crystalline objects involve peculiar mobile linear defects, referred to as dislocations. Temperature dependence of plasticity may significantly differ from that of Newtonian fluids. Under certain conditions (including the thermal ones) various molecular and ionic crystals, such as NaCl, AgCl, naphthalene, etc., reveal a behavior close to the plastic one. The values of x typically fall into the range between 10s and 109 N m 2. At the same time, plastic behavior is typical for various disperse structures, namely powders and pastes, including dry snow and sand. In this case the mechanism of plastic flow is a combination of acts involving the establishment and rupture of contacts between dispersed particles. Plastic object, in contrast to a liquid, maintains the acquired shape after removal of the stress. It is worth... 

ZnS toluene colloidal dispersions have been synthesized by an interphase interaction of toluene zinc oleate solution and aqueous solution of hydrogen sulfide. XRD analysis shows the crystal cubic structure of ZnS particles. According to TEM their size varies between 2 and 10 nm. The UV-vis absorption spectra indicate the prepared nanoparticles to have a narrow size distribution and show the maximum at 280 nm. PL intensity of nanoparticles could be enhanced with capping agents such as aromatic thiols and aromatic polymers. 

An isotropic pitch, when pyrolyzed at about 425°C was shown by Brooks and Taylor [230,231] to produce a liquid/crystal type structure containing domains of highly oriented molecules termed mesophase. Initially, the mesophase forms as a dispersion of ultra-fine... 

Preparation of Carvedilol Spherical Crystals Having Solid Dispersion Structure by the Emulsion Solvent Diffusion Method and Evaluation of Its in vitro Characteristics... 

Preparation of Carvedilol Spherical Crystals Having Solid Dispersion Structure... 

Figure 9 shows the UV-Visible absorption spectra of the Au particles dispersed films. In the spectrum of the film prepared by diermal decomposition, pl mon resonant peak around 550 nm was obviously observed. On the other hand, only a weak shoulder was observed for the H2S treated frlm. However, wh the frlm was heated at 200 , an increase in the peak intensity and blue shift in the peak position from 550 nm to 525 nm were observed with extending heating time as shown in Figure 10. Genially, heat treatment will cause ailargemait of pardde size. As a result, a red shift of die plasmon resonant absorption is expected. At the present time, the reason for the blue shift observed in this study is unknown. One possible explanation is that the Au particles generated by H2S treatment are disordered crystals with structure defects. Therefore, disorder-order transformation occurs further during die heating with volume reduction. Furdier studies of the relationship between the blue shift and thermal treatment are now in progress.

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