Solution crystallization temperature

PVB) 100,000 (PCL) 35,000 Vulcan XC-72 conductive carbon black (5 vol%) CB roll-mixed blend films from THF solutions crystallization temperature of 41°C As above and also with fullerene (5 vol%)... 

Sodium Xylenesulfonate, 50% solution) Crystallizing Temperature 30c Assay 50%... 

Sodium Toluenesulfonate, 40% solution) Crystallizing Temperature 10C Assay 40%... 

Sodium Cumenesulfonate, 45% Solution) Crystallizing Temperature 25C Assay 45%... 

Ammonium Xylenesulfonate, 40% Solution) Crystallizing Temperature OC Assay 40%... 

Fig. 13.16 Plotof time in minutes for 10% of the transformation to occur, ro.i, as a function of molecular weight for fraction of linear polyethylene crystallizing from dilute n-hexadecane solution. Crystallization temperatures are indicated. (From Chu (29))...

Above the solution treatment temperature (ca 1250°C), the alloy is single phase with a bcc crystal stmcture. During cooling to ca 750—850°C, the sohd solution decomposes spinodally into two other bcc phases a and lattice parameter composition. The matrix a-phase is rich in Ni and Al and weakly magnetic as compared with which is rich in Fe and Co. The a -phase tends to be rod-like in the (100) dkection and ca 10 nm in diameter and ca 100 nm long. As the temperature is decreased, segregation of the elements becomes mote pronounced and the difference between the saturation polarizations of the two phases increases. 

The ammonium perchlorate solution is spray-dried to the desired crystal size at air temperatures below 150°C and crystal temperatures of about 110°C. This procedure provides a pure product having a controlled grain size. Prior mechanical and thermal treatment affects the isothermal... 

Barium acetate [543-80-6] Ba(C2H202)2, crystallines from an aqueous solution of acetic acid and barium carbonate or barium hydroxide. The level of hydration depends on crystallization temperature. At <24.7°C the trihydrate, density 2.02 g/mL is formed from 24.7 to 41 °C barium acetate monohydrate [5908-64-5] density 2.19 g/mL precipitates and above 41 °C the anhydrous salt, density 2.47 g/mL results. The monohydrate becomes anhydrous at 110°C. At 20°C, 76 g of the monohydrate dissolves in 100 g of water. Barium acetate is used in printing fabrics, lubricating grease, and as a catalyst for organic reactions. 

Several features of the hypothetical system in Eigure 2 can be used to illustrate proper selection of crystallizer operating conditions and limitations placed on the operation by system properties. Suppose a saturated solution at temperature is fed to a crystallizer operating at temperature T. Because the feed is saturated, the weight fraction of in the feed is given as shown in Eigure 2. The maximum crystal production rate from such a process depends on the value of and is given by... 

Purification of a chemical species by solidification from a liquid mixture can be termed either solution crystallization or ciystallization from the melt. The distinction between these two operations is somewhat subtle. The term melt crystallization has been defined as the separation of components of a binaiy mixture without addition of solvent, but this definition is somewhat restrictive. In solution crystallization a diluent solvent is added to the mixture the solution is then directly or indirec tly cooled, and/or solvent is evaporated to effect ciystallization. The solid phase is formed and maintained somewhat below its pure-component freezing-point temperature. In melt ciystallization no diluent solvent is added to the reaction mixture, and the solid phase is formed by cooling of the melt. Product is frequently maintained near or above its pure-component freezing point in the refining sec tion of the apparatus. 

Anhydrous caustic soda (NaOH) is available but its use is generally not considered practical in water and wastewater treatment applications. Consequently, only liquid caustic soda is discussed here. Liquid caustic soda is generally shipped at two concentrations, 50 percent and 73 percent NaOH. The densities of the solutions as shipped are 12.76 Ib/gal for the 50 percent solution and 14.18 Ib/gal for the 73 percent solution. These solutions contain 6.38 Ib/gal NaOH and 10.34 Ib/gal NaOH, respectively. The crystallization temperature is 53 F for the 50 percent solution and 165 F for the 73 percent solution. The molecular weight of NaOH is 40. The pH of a 1 percent solution of caustic soda is 12.9. 

The term solubility thus denotes the extent to which different substances, in whatever state of aggregation, are miscible in each other. The constituent of the resulting solution present in large excess is known as the solvent, the other constituent being the solute. The power of a solvent is usually expressed as the mass of solute that can be dissolved in a given mass of pure solvent at one specified temperature. The solution s temperature coefficient of solubility is another important factor and determines the crystal yield if the coefficient is positive then an increase in temperature will increase solute solubility and so solution saturation. An ideal solution is one in which interactions between solute and solvent molecules are identical with that between the solute molecules and the solvent molecules themselves. A truly ideal solution, however, is unlikely to exist so the concept is only used as a reference condition. 

For PVDF, several experiments have shown that at room temperature the p form is thermodynamically the most stable, while the ot form is kinetically the most advantageous. For instance, by solution crystallization (casting from polar hexamethylphosphamide solutions) p form, y form and a form crystals are obtained for low, intermediate and high evaporation rates, respectively [15, 66]. 

As can be seen from Fig. 6, liquid-liquid demixing clearly precedes crystallization in case Cl. Moreover, crystallization in this case occurs at a higher temperature than in cases C2 and C3. Apparently, the crystallization takes place in the dense disordered phase (which has a higher melting temperature than the more dilute solution Fig. 5). In case C2, the crystallization temperature is close to the expected critical point of liquid-liquid demixing, but higher than in case C3. This suggests that even pre-critical density fluctuations enhance the rate of crystal nucleation. 

Polymorphism and solvatomorphism are not, of course, limited to small molecules, and such phenomena can be observed in protein crystals as well. Two polymorphic forms of aprotinin have been identified, and the solubility of these studied in a variety of aqueous media [84], The needle polymorph was found to exhibit increased solubility with increased temperature (i.e., an endothermic heat of solution), while the solubility of the bipyramid form decreased by with increasing temperature (i.e., an exothermic heat of solution). The solubility curves crossed at 25 °C for a pH of 4.75, and hence one could obtain the desired crystal form through a judicious selection of crystallization temperature. 

The triselenadiborolanes 3,5-R2-l,2,4,3,5-Se3B2 R=Et (33), Pr readily formed coordination adducts with two equivalents of pyridine, 3,5-dime-thylpyridine, and 3-chloropyridine.168 With one equivalent of base, only one of the B atoms became coordinated, and surprisingly, the system was not fluxional at room temperature.168 The addition of two equivalents of pyrazole to 33 (Scheme 7) resulted in a brown suspension and a yellow solution. Crystals of a B2N4Se2-bicyclo[2.2.2]octane were formed upon cooling this solution to —80 °C. With bulkier pyrazole derivatives (phenyl-pyrazole), the B2N4Se-bicyclo[2.2.1] heptanes were formed.169... 

Reagent selection, solvent, and choice of solution reaction conditions serve to define the nature of the solution precursor species that are formed and that will be used for him deposition. The characteristics of these solution species serve to define him processing characteristics, including aspects such as cracking tendency,50 organic burn-out temperature,48 and for crystalline films, crystallization temperature.49,51... 

In some instances, this approach has proven successful, with comparatively low crystallization temperatures being observed. For example, Eichorst and Payne in the synthesis of LiNb03 noted crystallization temperatures of 400-500 °C for a mixed-metal alkoxide precursor.111 In other instances, these attempts have proven less successful. Numerous attempts have been made to synthesize Pb-Zr and Pb-Ti precursors, each with the 1 1 cation stoichiometry of the desired PbZr03 and PbTi03 compounds.83,84 Unfortunately, 1 1 stoichiometric ratio compounds have not always been obtained, with crystalline compounds of other stoichiometries precipitating from the solution, as illustrated in Fig. 2.11.83 This figure shows the crystal structure of PbTi2[p(4)—... 

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