Effect on crystallization

An increase in viscosity usually accompanies competition. Water molecules bound by the hydrocolloid are no longer effective as solvent molecules and the concentration of the solution is thereby increased. Increase in viscosity itself has a retarding effect on crystal growth. 

Temperature has a complex effect on crystallization rate. Initially, as the temperature falls below the equilibrium melting temperature, the crystallization rate increases because nucleation is favored. However, as the temperature continues to fall, the polymer s viscosity increases, which hampers crystallization. As a rule of thumb, a polymer crystallizes fastest at a temperature approximately mid-way between its glass transition temperature and its equilibrium melting temperature. 

Vijay Kumar R, Elgamiel R, Diamant Y, Gedanken A (2001) Sonochemical preparation and characterization of nanocrystalline copper oxide embedded in poly(vinyl alcohol) and Its effect on crystal growth of copper oxide. Langmuir 17(5) 1406-1410... 

As to the first route, we started in 1969 (1) in investigating unconventional transition metal complexes of the 5 and 4f block elements of periodic table, e.g., actinides and lanthanides as catalysts for the polymerization of dienes (butadiene and isoprene) with an extremely high cis content. Even a small increase of cistacticity in the vicinity of 100% has an important effect on crystallization and consequently on elastomer processability and properties (2). The f-block elements have unique electronic and stereochemical characteristics and give the possibility of a participation of the f-electrons in the metal ligand bond. 

In this part, we prepared and studied the Ag/Si02 catalyst by one-step and two-step sol-gel methods. The results show that the Ag/Si02 catalyst prepared here is one kind of bulk material which has a high surface area. The Ag/Si02 catalyst is made up with functional component of Ag or silver oxide in 20 to 30 nm and carrier Si02. Moreover, we found that the different preparation methods have great effect on crystal structure of the samples. The structure of the sample prepared by the one-step method is always a single crystal structure. And the structure of the sample prepared by the two-step method is always a mixed crystal structure. 

Figure 1,13 Expansion and/or compression effects on crystal structures (planar section). A = shared edge B = shared corner. From R. M. Hazen and L. W. Finger, Comparative Crystal Chemistry, copyright 1982 by John Wiley and Sons. Reprinted by permission of John Wiley Sons.

The commonest habits for hematite crystals are rhombohedral, platy and rounded (Fig. 4.19). The plates vary in thickness and can be round, hexagonal or of irregular shape. Under hydrothermal conditions, these three morphologies predominate successively as the temperature decreases (Rosier, 1983). The principal forms are given in Table 4.1. Hematite twins on the 001 and the 102 planes. The crystal structure of hematite has a less directional effect on crystal habit than does that of goethite and for this reason, the habit of hematite is readily modified. A variety of morphologies has been synthesized, but in most cases, the crystal faces that enclose the crystals have not been identified. 

Cornell, R.M. Giovanoli, R. (1988 a) Acid dissolution of akaganeite and lepidocrocite the effect on crystal morphology. Clays Clay Min. 36 385-390... 

Ozeki, S. Uehiyama, H. Katada, K. (1994) Hydrolysis of iron ions in chrysotile nanotubes a template effect on crystal growth. Langmuir 10 923-928... 

Foreign substances even in minute amounts may have other kinds of effects on crystallization They may inhibit or accelerate growth rate or change the shape of crystals, say from rounded to needlelike, or otherwise. One of the problems sometimes encountered with translating laboratory experience to full scale operation is that the synthetic liquors used in the laboratory may not contain the actually occurring impurities, and thus give quite different performance. Substances that modify crystal formation are very important industrially and many such materials have been the subject of patents. 

Instead of the seed zeolite crystals, a mixture of one part y-alumina ( 0.2 pm ) and three parts a-alumina ( ca. 1 im ) was used as seed material. Fortunately, a similar effect on the crystallization was observed, although about 2 times the quantity of the seed materials was necessary (5)). The metal pre-loaded y and a-alumina mixture was then tried as the seed material and confirmed the same effect on crystallization. In the case of 0.4 wt% Ru ( ) and 0.7 wt% Rh (12) in the catalyst product a longer catalyst life was obtained, i.e., 1.32 times and 1.65 times, respectively, without any significant change in the activity and selectivity compared with the non metal-loaded zeolite catalyst. 

Foley, J., Brady, J.P. 1984. Temperature-induced effects on crystallization behaviour, solid fat content and the firmness values of milk fat. J. Dairy Res. 51, 579-589. 

Studies on the addition of standard diacylglycerols demonstrated that their racemic purity had a significant influence on crystallisation behavior of milk fat triacylglycerols. Differences in the observed effects on crystallization... 

Effect on crystal packing Strong Distinctive Variable... 

Ultrasound-related variables and their effects on crystallization... 

Kishihara S, Wakiuchi N, Hosokawa T, Fujii S, and TamaM H. Clarification of sugar solution by ultrafiltration. Effect on crystallization... 

The nature of solvent has been found to have a profound effect on crystal habit of ibuprofen. Ibuprofen crystals precipitated from ethanol and acetone (solvents having high surface tension, dielectric constant, and less specific gravity) were thin, platy, and nearly circular-shaped, whereas those obtained from propylene... 

Impurities often have a profound effect on crystal habit. Adsorption of an impurity on faces of a crystal may retard the growth of certain crystal faces, and these will therefore become prominent in the final crystal, as described earlier (see Figure 2.7). For example, sodium chloride ... 

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