Crystallization rate coefficient

Crystallization rate coefficient Differential scanning calorimetry Differential thermogravimetry Modulus of elasticity Cooling rate... 

Co-Pak corona packaging (National Can s pro- CRC crystallization rate coefficient... 

Differential scanning calorimetry was used to study the non-isothermal crystallization behavior of blends of poly(phenylene sulfide) (PPS) with the thermotropic liquid-crystalline copoly(ester amide) Vectra-B950 (VB) [126], The PPS crystallization temperature and the crystallization rate coefficient increased significantly when 2-50% VB was added. The Ozawa equation was shown to be valid for neat PPS as well as for the blends. The values of the Avrami exponents matched well against those determined previously using isothermal analysis, and they are independent of the concentration of VB. 

Crystallization rate coefficient Crystallization rate parameter Dibenzylidene sorbitol Total volume of growing crystals Radial crystallization rate Preexponential factor in growth rate High density polyethylene Rate of nucleation Avrami constant... 

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. 

This deceleratory reaction obeyed the parabolic law [eqn. (10)] attributed to diffusion control in one dimension, normal to the main crystal face. E and A values (92—145 kJ mole-1 and 109—10,s s-1, respectively) for reaction at 490—520 K varied significantly with prevailing water vapour pressure and a plot of rate coefficient against PH2o (most unusually) showed a double minimum. These workers [1269] also studied the decomposition of Pb2Cl2C03 at 565—615 K, which also obeyed the parabolic law at 565 K in nitrogen but at higher temperatures obeyed the Jander equation [eqn. (14)]. Values of E and A systematically increased... 

Crystalline polyimide powders, 304 Crystalline transition temperature. See Melting temperature (Tm) Crystallization rate, for processing semicrystalline polymers, 44 CTE. See Coefficient of thermal expansion (CTE)... 

A comparative study [10] is made for crystal-growth kinetics of Na2HP04 in SCISR and a fluidized bed crystallizer (FBC). The details of the latter cem be found in [11]. Experiments are carried out at rigorously controlled super-saturations without nucleation. The overall growth rate coefficient, K, are determined from the measured values for the initial mean diameter, t/po, masses of seed crystals before and after growth. The results show that the values for K measured in ISC are systematically greater than those in FBC by 15 to 20%, as can be seen in Table 2. On the other hand, the values for the overall active energy measured in ISC and FBC are essentially the same. 

Comparison of crystal growth rate coefficients measured in ISC and FBC... 

The main processing options open to the crystallizer designer are the solubility gap (transition temperature, acid content), the operating temperature and the values of the rate coefficients (affected by Impurities) and crystal surface areas (eg. altering crystal content). The computer model generated In this study allows these effects to be evaluated. 

Geochemical kinetics is stiU in its infancy, and much research is necessary. One task is the accumulation of kinetic data, such as experimental determination of reaction rate laws and rate coefficients for homogeneous reactions, diffusion coefficients of various components in various phases under various conditions (temperature, pressure, fluid compositions, and phase compositions), interface reaction rates as a function of supersaturation, crystal growth and dissolution rates, and bubble growth and dissolution rates. These data are critical to geological applications of kinetics. Data collection requires increasingly more sophisticated experimental apparatus and analytical instruments, and often new progresses arise from new instrumentation or methods. 

On the other hand, as an implication, the equation for the diffusion rate based on Pick s law includes the assumption of the solute concentration in the liquid bulk being completely uniform, which is actually difficult to realize and thus may yield a deviation from reality. The poorer the micromixing, the larger would be the deviation. Therefore the crystal-growth rate coefficients measured in different devices with different micromixing conditions may be different from each other. 

Further, substituting Eq. (12-8) into Eq. (12-3), integrating the resulting equation between t - 0 and t = tf and rearranging yields the expression for the overall crystal-growth rate coefficient as... 

To ensure that all the overall crystal-growth rate coefficients are measured under the conditions without nucleation, the metastable region of the solution has to be determined first and therefore the solubility and super solubility need to be measured. 

For comparison, the experiments for measuring the overall crystal-growth rate coefficient are carried out in an impinging stream crystallizer (ISC) and a fluidized bed crystallizer (FBC). 

The values measured in the ISC for the overall crystal-growth rate coefficient of Na2HP04 are listed in Table 12.2. As can be seen, the reproducibility of the data is in a reasonable range and that of most data is very good. 

Overall crystal-growth rate coefficient of Na2HP04 in SCISR... 

Except for a few questionable data, the values for the observed active energy measured in the two crystallizers of different types, EiS and EFB, show little difference and can be considered to be more or less identical. On the other hand, the values measured in the impinging stream crystallizer for the overall crystal-growth rate coefficient, KIS, are obviously and systematically larger than those in the fluidized bed crystallizer, A pe. Therefore it can be affirmed without the need for further analysis that, with the observed frequency factors, there must... 

In the ranges of the operating conditions tested, the overall crystal- growth rate coefficient of Na2HP04 measured in ISC, Vs. is higher systematically than that measured in FBC, Vu. by 15 to 20%, while the reaction rate constant of ethyl acetate saponification measured in the SCISR, Vs. is larger systematically than that measured in the STR, Vt> by about 20%. 

In this equation c [mol l-1], Ds (9) [m2s-1], vi [ms-1] and R [mol l-1s-1] respectively are the ion concentration in the water, the diffusion coefficient of the ions in the moisture, velocity of the moisture flow and and the crystallization rate. Expression 2 makes clear that during a drying experiment there is a competition between advection, which forces ions to move to the top of the sample and thereby causes accumulation, and diffusion, which levels off any accumulation. It has been shown that the following Peclet number determines the behaviour of the system ([6]) ... 

FR may vary considerably from face to face in the same crystal. Consequently, mean values of FR or F0 are of interest in the design of crystallization apparatus, whereas experimental studies with single crystals may measure mass transfer rates at specifically oriented surfaces. McCabe and Smith (M3) suggest a procedure for estimating the contribution of individual surface rate coefficients to mean values and a method for calculating the increase in linear crystal dimensions from the latter. 

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