Factors affecting crystallization rate

Why do we get differences in crystal shape or habit This may be a matter of directional rates of growth. Factors affecting directional rates will then affect the habit. Directional rates of growth can be illustrated with a relatively simple crystal structure, that of sodium chloride. 

We have proposed a fluidized bed type process, which can be applied to phosphate removal from wastewater containing phosphate 2-23 mg/jg as P.By the results of experiments using equipment of capacity l-4m3 /day, factors such as supersaturation, recirculation ratio and space velocity were recognized to affect crystallization rate or phosphate removal efficiency. By mathematical analysis, we could obtain the characteristic equation for fluidized bed process, to agree well with experimental results. 

We have proposed fluidized bed process and by the results of experiments, factors such as supersaturation, recirculation ratio and space velocity affected crystallization rate or phosphate removal efficiency, and experimental results agreed well with calculated values from characteristic equation. 

One of the main factors affecting crystallization in solution systems is the water content, or total solids content. This determines supersaturation and the subsequent rate kinetics as tempera-... 

Adsorption Kinetics. In zeoHte adsorption processes the adsorbates migrate into the zeoHte crystals. First, transport must occur between crystals contained in a compact or peUet, and second, diffusion must occur within the crystals. Diffusion coefficients are measured by various methods, including the measurement of adsorption rates and the deterniination of jump times as derived from nmr results. Factors affecting kinetics and diffusion include channel geometry and dimensions molecular size, shape, and polarity zeoHte cation distribution and charge temperature adsorbate concentration impurity molecules and crystal-surface defects. 

Decompositions may be exothermic or endothermic. Solids that decompose without melting upon heating are mostly such that can give rise to gaseous products. When a gas is made, the rate can be affected by the diffusional resistance of the product zone. Particle size is a factor. Aging of a solid can result in crystallization of the surface that has been found to affect the rate of reaction. Annealing reduces strains and slows any decomposition rates. The decompositions of some fine powders follow a first-order law. In other cases, the decomposed fraction x is in accordance with the Avrami-Erofeyev equation (cited by Galwey, Chemistry of Solids, Chapman Hall, 1967)... 

The rate (or kinetics) and form of a corrosion reaction will be affected by a variety of factors associated with the metal and the metal surface (which can range from a planar outer surface to the surface within pits or fine cracks), and the environment. Thus heterogeneities in a metal (see Section 1.3) may have a marked effect on the kinetics of a reaction without affecting the thermodynamics of the system there is no reason to believe that a perfect single crystal of pure zinc completely free from lattic defects (a hypothetical concept) would not corrode when immersed in hydrochloric acid, but it would probably corrode at a significantly slower rate than polycrystalline pure zinc, although there is no thermodynamic difference between these two forms of zinc. Furthermore, although heavy metal impurities in zinc will affect the rate of reaction they cannot alter the final position of equilibrium. 

Strain hardening effect, 20 224 Straining efficiency, 77 340 Strain rate, 73 473 Strain recovery rate (Rr), in testing shape-memory polymers, 22 361 Strain sensors, 77 150, 151-152 Strain tensor, for noncentrosymmetry pont group crystals, 77 93-94 Strain versus time curve factors affecting, 73 473 material and microstructure effect on, 73 473-474... 

In electrolytic systems the crystallization solvent type will affect the degree of solute ionization. This is an important factor in the rate of nucleation and can be successfully utilized for polymorphic control [11]. 

Pilati, F., Toselli, M., Messori, M., Manzoni, C., Turturro, A. E. and Gat-tiglia, E. G., On specific factors affecting the crystallization of PET the role of carboxyl terminal groups and residual catalysts on the crystallization rate, Polymer, 38, 4469 (1997). 

At present, there remains complexity to make clear the relation between j values and its affecting factors, however, the procedures presented in this paper was found to be useful to inspect the characteristics of some industrial continuous crystallizers and to estimate the crystallization rate parameters from their CSD data. 

We have now proposed fluidized bed type process, which can be applied to wastewater, containing from 2 to 23 mg/jg phosphate as P. This report reveals fundamental studies on factors affecting phosphate removal and crystallization rate in the fluidized bed process. 

In this experiment, tap water with added phosphate was used as influent. Concentration of phosphate was adjusted to an adequate range from 2 to 23 mg/jg. Calcium chloride and sodium hydroxide solution were added to maintain calcium concentration from 70 to 100 mg/jg and pH of the effluent from 9.0 to 9.5. Using this equipment, we performed experiments to obtain efficiency of phosphate removal, relationship between phosphate concentration, and crystallization rate and factors affecting phoshate removal. 

It should be noted that there may be other possible factors affecting the normal growth rate of crystal faces. 

Nickerson, T. A. 1956. Lactose crystallization in ice cream. II. Factors affecting rate and quantity. J. Dairy Sci. 39, 1342-1350. 

In view of the importance of macroscopic structure, further studies of liquid crystal formation seem desirable. Certainly, the rates of liquid crystal nucleation and growth are of interest in some applications—in emulsions and foams, for example, where formation of liquid crystal by nonequilibrium processes is an important stabilizing factor—and in detergency, where liquid crystal formation is one means of dirt removal. As noted previously and as indicated by the work of Tiddy and Wheeler (45), for example, rates of formation and dissolution of liquid crystals can be very slow, with weeks or months required to achieve equilibrium. Work which would clarify when and why phase transformation is fast or slow would be of value. Another topic of possible interest is whether the presence of an interface which orients amphiphilic molecules can affect the rate of liquid crystal formation at, for example, the surfaces of drops in an emulsion. 

Other experiments showed that both selectivity and product distribution could be drastically affected by changes in the electrode potentials [70]. Similarly, surface roughness and pretreatment were also factors affecting methane production [41]. In addition, when the effect of crystal structure was examined, the rate of methane production in a C02-saturated 0.5 M KHC03 electrolyte was shown to be highest on Cu(lll), followed by Cu(110) and Cu(100) [41]. 

Another factor that necessitates a close control is the gel composition because a series of other structures like zeolites X, Y or Beta can easily crystallize from similar systems "Table II and Figure 1". The H20/Si02 ratio is also important to control. For higher initial water contents the crystallization rate of ZSM-20 considerably decreases. In very diluted systems, zeolite Y is more readily formed, although with a rather low rate due to the smaller Na+ concentrations in such a system (331. Furthermore, the water content also affects the pH, the supersaturation conditions and the rate of hydrolysis of Si(OEt)4 and hence the further condensation of the resulting (Si(OH)4)n species(46). 

As is clear from the above discussion, reduction of surface-located Fe(III) (which may or may not lead to oxide dissolution) is associated in most instances with oxidation of the electron donor at the particle surface and many of the same factors that influence the rate of reductive dissolution will also affect the rate of donor oxidation. Leland and Bard [138] found that the rate constants of photooxidation of oxalate and sulfite varied by about two orders of magnitude with different Fe(III) oxides and concluded that this appears to be due to differences in crystal and surface structure rather than to differences in surface area, hydrodynamic diameter or band gap . 

Many industrial processes require accurate environmental control. Examples include chemical reactions and processes that are affected by atmospheric conditions biochemical reactions quality, uniformity, and standardization of certain products factors such as rate of crystallization and size of crystals product moisture content or regain deliquescence, lumping, and caking of hygroscopic materials expansion and contraction of macliines and products physical, chemical, and biological cleanliness effects of static electricity odors and fumes conditions in storage and packaging quality of painted and lacquered finishes simulation of stratosphere or space conditions and productivity and comf ort of workers. Controlled atmospheric conditions are... 

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