Measured induction periods

Magnitudes of n have been empirically established for those kinetic expressions which have found most extensive application e.g. values of n for diffusion-limited equations are usually between 0.53 and 0.58, for the contracting area and volume relations are 1.08 and 1.04, respectively and for the Avrami—Erofe ev equation [eqn. (6)] are 2.00, 3.00 etc. The most significant problem in the use of this approach is in making an accurate allowance for any error in the measured induction period since variations in t [i.e. (f + f0)] can introduce large influences upon the initial shape of the plot. Care is needed in estimating the time required for the sample to reach reaction temperature, particularly in deceleratory reactions, and in considering the influences of an induction period and/or an initial preliminary reaction. 

IV, CCR and oxidation stability are three strictly co-related parameters. As a general rale, the reduction of IV (on the same feedstock) dramatically improves the oxidation stability. On the contrary the distillation step removes the main part of naturally occurring antioxidants. For this reason, even after hydrogenation the Rancimat induction time (as measured according to the EN 14112 standard) of the hydrogenated sample does not fulfill the EN 14214 requirement for oxidation stabihty (6 hours at 110°C), 4 hours being the measured induction period. 

At temperatures in the range 1500-1800 °K, N2, NF3 and F are important products and there is a small peak at mass 47, which suggests the presence of N2F2 molecules, N2F radicals or a combination of both148. There are measurable induction periods for both N2 and NF3. Both induction periods vary inversely... 

Application of the complexes 63 in the Mizoroki-Heck reaction did not reveal higher activity than the previously examined palladium(II) complexes. However, in the Suzuki-Miyaura reaction, a drastically increased activity was observed with complex 63. Catalysis starts without a measurable induction period at mild temperatures accompanied by an extraordinarily high turnover frequency (TOF) of 552 [mol product x mol Pd x h ] at the start of the reaction for the coupling of p-chlorotoluene and phenyl boronic acid [Eq. (48)]. ... 

This equation has been numerically integrated by Rice and his associates (4 ). The results of their rather tedious calculations are in good agreement with the experimental data which they have obtained for azomethane and ethyl azide explosions. These calculations, together with the measured induction periods and explosion conditions, allowed these authors to make reasonable estimates of ( , the heat of reaction. 

Another parameter often used to characterise nucleation is the induction time or period, t. This is defined as the time taken for the formation of crystals after creating a supersaturated solution. Hence, the measured induction period does depend upon the sensitivity of the recording technique. It is generally assumed that t is inversely proportional to the nucleation rate, i.e. 

Comparison of the measured induction periods in Figure 2 and those which can be predicted (e.g., after 750 hr) from Figure 3 makes it evident that both failure times are in statement with each other. 

The presence of seed crystals generally reduces the induction period, but does not necessarily eliminate it. Even if the system is seeded at time t = 0, a measurable induction period tmd may elapse before new crystals are detected. By definition, these are secondary nuclei and they may appear in several bursts throughout the latent period, making it difficult to attach any real significance to the induction time itself For these reasons it may be preferable to record the latent period as the more practical characteristic of the system. Factors that can influence the induction and latent periods and the rate of desupersaturation are temperature, agitation, heat effects during crystallization, seed size, seed surface area and the presence of impurities. 

Lancia, A., Musmarra, D. and Priciandaro, M. (1999) Measuring induction periods for CaS04 2H2O precipitation. AIChEJ, 45, 390 -397. 

Kinetic catalytic methods for determination of species can be classified in a manner similar to that of the kinetic noncatalytic methods described elsewhere in this encyclopedia (Table 1). Methods commonly used to measure induction periods are commented on in dealing with Landolt reactions below. 

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