Crystal distortion

Sca.Ie nd Sta.in Controllers. Polyacrjiates (low molecular weight) and organic phosphonates, eg, (l-hydroxyethyhdene)diphosphonic acid, prevent or control precipitation of CaCO by acting as chelating agents (qv) or dispersants (qv) to prevent excessive formation of hard scale by promoting crystal distortion. 

Figure 3. The temperature dependence of the crystal distortion for VjSi, (0), derived from the data in Figure 2 [curves (a) and (c)], as discussed in reference 5. The dot-dashed curve shows the same distortion parameter for In-26.5 at%Tl derived from the data in Figure 1. The inset shows in detail the data below the super-c-nducting critical temperature, Tc. (From reference 5)...

Sludge conditioners are required. Originally these were based on starches and lignins, but modem carbonate cycle treatments use carbonate-polymer programs, where the polymer (such as a phos-phinocarboxylic acid) provides a combination of threshold effect, crystal distortion, and sludge dispersion to minimize scaling and prevent sludge deposition. 

A phosphate-sludge conditioner blend may be employed because the deposit control agent or sludge conditioner limits and controls crystal formation (threshold and crystal distortion effects) and ensures particle fluidization (dispersion effect). 

Phosphonates, especially aminotri(methylenephosphonic acid) (ATMP) and l-hydroxyethylidene-l,l-diphosphonic acid (HEDP). Organophosphonates have the ability to control both scaling and corrosion by a combination of chelation and crystal nuclei growth supression (threshold) mechanisms they also provide scale control by crystal distortion. 

Calcium carbonate crystal distortion or crystal modification,... 

Phosphonates exhibit all the properties of polyphosphates, such as threshold effect, crystal distortion, and sequestration, but are superior in their effectiveness. They provide good chelates for calcium, magnesium, iron, and copper and are commonly used where iron fouling is a problem. Their sequestering properties are generally superior to other common chelants, such as EDTA and NTA. 

Classical X-ray diffraction and scattering is carried out in the subarea of wide-angle X-ray scattering (WAXS). The corresponding scattering patterns yield information on the arrangement of polymer-chain segments (e.g., orientation of the amorphous phase, crystalline structure, size of crystals, crystal distortions, WAXS crystallinity). 

Asano, T Dzeick-Pickuth, A. and Zachman, H. G Influence of catalysts on the rate of crystallization and on the crystal distortions in poly(ethylene terephthalate), J. Mater. Sci., 24, 1967-1973 (1989). 

Some examples of direct measurement of the crystal distortion during the reaction by optical and electron microscopy, IR absorption, and x-ray diffraction have been reported (see references in Ref. 311). The observed (anisotropic) changes in lattice parameters have been used for calculating the kinetic parameters of the transformations. For some reactions, it was possible to follow by x-ray diffraction the change in lattice parameters and also in atomic coordinates, so the relaxation could be observed at atomic level. 

Crystal distortion in magnetic compounds. J. Appl. Phys. 31, 14 (1960). 

Ramirez et al (1970) discussed a metal-insulator transition as the temperature rises, which is first order with no crystal distortion. The essence of the model is—in our terminology—that a lower Hubbard band (or localized states) lies just below a conduction band. Then, as electrons are excited into the conduction band, their coupling with the moments lowers the Neel temperature. Thus the disordering of the spins with consequent increase of entropy is accelerated. Ramirez et al showed that a first-order transition to a degenerate gas in the conduction band, together with disordering of the moments, is possible. The entropy comes from the random direction of the moments, and the random positions of such atoms as have lost an electron. The results of Menth et al (1969) on the conductivity of SmB6 are discussed in these terms. 

Heat is the most common product of biological reaction. Heat measurement can avoid the color and turbidity interferences that are the concerns in photometry. Measurements by a calorimeter are cumbersome, but thermistors are simple to use. However, selectivity and drift need to be overcome in biosensor development. Changes in the density and surface properties of the molecules during biological reactions can be detected by the surface acoustic wave propagation or piezoelectric crystal distortion. Both techniques operate over a wide temperature range. Piezoelectric technique provides fast response and stable output. However, mass loading in liquid is a limitation of this method. 

As part of the overall scale-inhibiting threshold effect, the mechanism of crystal growth retardation is complemented by crystal distortion, whereby the crystal fails to successfully agglomerate into a larger crystalline scale. 

Phosphonates exhibit all the properties of polyphosphates, such as threshold effect, crystal distortion, and sequestration, but are superior in their effectiveness. 

The Rietveld refinements show that the crystalline structure contains microstrain that is mainly caused by the crystal distortion related to zirconium replacement. It is also found that cationic occupancy number in the crystalline structure is smaller than their normal value 0.02083 present in an ideal crystal, indicating that the crystalline structure is of cationic deficient. As far as the local environment of the cationic defect is concerned, the lattice oxygen ions around it are not fully bonded, which are mobile and more active under the reaction condition compared to the normal ones. Therefore, the creation of cationic defects in the structure is a possible origin of the unusual reducibility and high mobility of oxygen species from bulk to surface exhibited on the ceria-zircnia solids, that are reported by other groups [5, 6]. 

FIGURE 15.15. The transformation of (a) a CsCl-type structure to (b) an NaCl-type structure. This occurs at 465° C when the arrangement of ions found in CsCl crystals distorts to give the arrangement of ions found in NaCl crystals. A.H — 2.90 kJ mol and AF = 17% (Ref. 100). The filled circles represent Cs ions. 

By adequately varying the catalyst content, the temperature, time and the rate of crystallization, materials with a wide range of crystallinities, spherulitic morphologies, different crystal thickness and various levels of crystal distortions have been prepared. The influence of these structural parameters on the microhardness and the detection of specific changes after controlled crystallization are of special interest. 

An intensifying screen should not be used if it is important to record fine detail in the Laue spots, as in some studies of crystal distortion, since the presence of the screen will cause the spots to become more diffuse than they would ordinarily be. Each particle of the screen which is struck by x-rays emits light in all directions and therefore blackens the film outside the region blackened by the diffracted beam itself, as suggested in Fig. 5-5. This effect is aggravated by the fact that most x-ray film is double-coated, the two layers of emulsion being separated by an appreciable thickness of film base. Even when an intensifying screen is not used, double-coated film causes the size of a diffraction spot formed by an obliquely incident beam to... 

We will see later that Laue spots become smeared out if the reflecting crystal is distorted. Here, however, we are concerned with the shapes of spots obtained from perfect, undistorted crystals. These shapes are greatly influenced by the nature of the incident beam, i.e., by its convergence or divergence, and it is important to realize this fact, or Laue spots of unusual shape may be erroneously taken as evidence of crystal distortion. 

Copper-63 NMR/NQR spectra for CuS, from 4.2K up to ambient temperatures, show two distinct lines based on the abrupt change in the spectrum at 55K. This is ascribed to a structural phase transition for both the powder and the oriented CuS. A more recent study of powdered samples at temperatures as low as 1.5K under a magnetic field of 6.5 T revealed more detail. An intense resonance with satellites was observed at all temperatures up to the ambient. This peak consisted of two resonance lines above 60K and four lines below 50K. The splittings observed correspond to crystal distortions below 55K. The central peaks with satellites were assigned to the metallic Cu(l) and Cu(2) in the crystal structure of CuS, for which spin-lattice relaxation times of 4 ms and 55 ms, respectively, were measured at 15K. The authors suggest that the anomalously short Ti for Cu(l) is indicative of the metallic character in the plane formed by Cu(l)-S bonds. 

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