Recrystallization effect

If the crude product melts lower, it contains too much tribromoaniline to permit satisfactory purification. Recrystallization effects no separation repeated fractional steam distillation is very slowly effective. 

Particle size distribution analyses in organic solvents may show dissolution and recrystallization effects when pigments with poor solvent fastness are measured. 

In Table 1, the surface free energies of several important oxides are listed. As may be seen in the table, the differences between the various Materials are remarkable. In single and multicomponent. Materials the tendency towards the lowest possible value of surface free energy is the reason for recrystallization effects and for sorption, phase separation, and segregation phenomena. Surface enrichment of the component with the lowest surface-tension value is generally observed. Calculations of the surface-tension and surface-enrichment effects were made for alloys (real... 

This indicates that the deformation of the crystal lattice as a result of pressing accelerates the recrystallization effects between a-Fe crystallites with the formation of larger crystals. At the very high tableting pressures (1700 MPa), the average size of the crystallites is comparable with the size of iron crystallites in the unpressed catalysts. This suggests that recrystallization process proceeding between differents crystallites is accompanied by the recrystallization inside a-Fe crystal with the formation of smaller crystals. 

In addition to these more or less common recrystallization effects, Kooli et al. [79-84] reported a precise method to recrystallize magadiite or kanemite resulting in new types of layer structures, named KLS and FLS. The transformation takes place in the presence of alkali cations, tetramethylammo-nium cations (hydroxides), water and 1,4-dioxane. Dioxane was found to be essential to formation of these unique structures (see also Sec. VI.A). 

The impact of particle size on the dissolution performance was also observed for amorphous ITZ Soluplus extrudates. Samples of defined sieve fractions as well as samples of the unmilled strands were compared (simulated gastric fluid, n=6). The results (Fig. 13.1 data not published) clearly showed that after 100 min, the API from milled particles with a mean particle size above 250 xm was fully dissolved, whereas the dissolution from finer particles was significantly slower and incomplete. The unmilled strands were steadily eroding resulting in almost 100 % dissolution after 330 min. For this formulation, coarser particles were more beneficial fhan finer grades, potentially as a result of polymer swelling or concurrent recrystallization effects. 

The change in properties extends beyond the static properties of the material. Under dynamic loading, the material behaves much more elastically and the tendency to destruction by hysteresis induced heating effects is reduced. On the other hand, because the polymer chains are stretched severely in the stress transfer process, there are much higher levels of bond breakage and recrystallization effects with typical fatigue failure performance. In the balance, the net result is a substantial improvement in the performance of the material in dynamic loading. 

The roles of alkali, alkali earth and rare earth metal oxides seem different from the structural promoters. These oxides are able to increase the specific activity per unit surface area, while decrease the heat-resisting and anti-toxic ability. Thus, they are called as electronic promoters. Because the diameter of K+ ions is quite large, it is not possibly for K to enter into the lattice of magnetite. After reduction, K2O diffuses to the surface of crystallite. The surface potassium is able to accumulate with various forms during reduction and operations, to accelerate the recrystallization effect, but due to the electron, negative alkali metals decrease the effusion work of iron atoms, and accelerate the adsorption of dinitrogen or desorption of ammonia and finally are able to increase the specific activity per unit surface area. 

Anionic polymerization of vinyl monomers can be effected with a variety of organometaUic compounds alkyllithium compounds are the most useful class (1,33—35). A variety of simple alkyllithium compounds are available commercially. Most simple alkyllithium compounds are soluble in hydrocarbon solvents such as hexane and cyclohexane and they can be prepared by reaction of the corresponding alkyl chlorides with lithium metal. Methyllithium [917-54-4] and phenyllithium [591-51-5] are available in diethyl ether and cyclohexane—ether solutions, respectively, because they are not soluble in hydrocarbon solvents vinyllithium [917-57-7] and allyllithium [3052-45-7] are also insoluble in hydrocarbon solutions and can only be prepared in ether solutions (38,39). Hydrocarbon-soluble alkyllithium initiators are used directiy to initiate polymerization of styrene and diene monomers quantitatively one unique aspect of hthium-based initiators in hydrocarbon solution is that elastomeric polydienes with high 1,4-microstmcture are obtained (1,24,33—37). Certain alkyllithium compounds can be purified by recrystallization (ethyllithium), sublimation (ethyllithium, /-butyUithium [594-19-4] isopropyllithium [2417-93-8] or distillation (j -butyUithium) (40,41). Unfortunately, / -butyUithium is noncrystaUine and too high boiling to be purified by distiUation (38). Since methyllithium and phenyllithium are crystalline soUds which are insoluble in hydrocarbon solution, they can be precipitated into these solutions and then redissolved in appropriate polar solvents (42,43). OrganometaUic compounds of other alkaU metals are insoluble in hydrocarbon solution and possess negligible vapor pressures as expected for salt-like compounds. 

Tungsten has Htde effect on recrystallization temperature or the high temperature properties of molybdenum. However, the Mo—30% W alloy is recognized as a standard commercial alloy for stirrers, pipes, and other equipment that is required to be in contact with molten zinc during processing of the metal and in galvanizing and die casting operations. 

The relative effectiveness of nucleating agents in a polymer can be determined by measuring recrystallization exotherms of samples molded at different temperatures (105). The effect of catalyst concentration and filler content has been determined on unsaturated polyesters by using dynamic thermal techniques (124). Effects of formulation change on the heat of mbber vulcanization can be determined by dsc pressurized cells may be needed to reduce volatilization during the cure process (125). 

The iodate is a poison potassium iodide, however, is used in foodstuffs. Thus the iodate must be completely removed frequently by a final reduction with carbon. After re-solution in water, further purification is carried out before recrystallization. Iron, barium, carbonate, and hydrogen sulfide are used to effect precipitation of sulfates and heavy metals. 

The principal impurities ia technical-grade bode acid are the by-product sulfates, <0.1 wt %, and vadous minor metallic impurities present in the borate ores. A bode acid titer is not an effective measure of purity because overdrying may result in partial conversion to metabotic acid and lead to B(0H)2 assays above 100%. High putity bode acid is prepared by recrystallization of technical-grade matedal. 

Effect of Thermal History. Many of the impurities present in commercial copper are in concentrations above the soHd solubihty at low (eg, 300°C) temperatures. Other impurities oxidize in oxygen-bearing copper to form stable oxides at lower temperatures. Hence, because the recrystallization kinetics are influenced primarily by solute atoms in the crystal lattice, the recrystallization temperature is extremely dependent on the thermal treatment prior to cold deformation. 

The checkers obtained erratic results in this step, possibly because of surface effects or trace impurities in the pressure vessel. In two other runs, only 16.8-18.8 g of crude product were obtained. In one case, high boiling oligomers were formed, but none of the desired product was produced. Impurities in the diene or dienophile did not appear to be the problem since runs which employed recrystallized 3-acetyl-2(3H)-oxazolone and redistilled 2,3-dimethyl butadiene also gave variable results. 

The product may be recrystallized from 1 2 acetic acid-water (about 8 ml./g.), but this process effects little improvement in melting point or color, even when activated carbon is used. 

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