Drift heterogeneity

Deviations from proportionality have three principal causes I, absorption and enhancement effects, placed together because they both involve absorption II, effects traceable to heterogeneity in the samples, principally surface effects and segregation III, instability, including drifts and fluctuations, in the spectrograph and in associated equipment. Class III deviations often increase with the complexity of the electronic circuitry. 

The existence of an azeotropic composition has some practical significance. By conducting a polymerization with the monomer feed ratio equal to the azeotropic composition, a high conversion batch copolymer can be prepared that has no compositional heterogeneity caused by drift in copolymer composition with conversion. Thus, the complex incremental addition protocols that arc otherwise required to achieve this end, are unnecessary. Composition equations and conditions for azeotropic compositions in ternary and quaternary eopolymerizations have also been defined.211,21... 

The alternating tendency of the copolymers is advantageous in that the polymerizations can be carried out to high conversions with little or no compositional drift. For random copolymerizations in which there is preferential incorporation of one monomer due to a mismatch in reactivity ratios, the compositional variations with conversion can be substantial. Such compositional heterogeneities in resist materials can lead to severe problems during image development. 

These equations show that the A and B fluxes are composed of both a drift term and a reaction term. The drift term stems from the electric field. The reaction term was already deduced in the kinetics of heterogeneous reactions. From Eqns. (8.78) and (8.79), we obtain the reaction product s rate of thickness increase to be... 

Cradun, R., Miller, D.J., Dulamita, N. and Jackson, J.E. (1996) Diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) applied in heterogeneous catalysis studies. Prog. Catal., 5, 55. 

The heterogenization of MAO-activated Nd(z 3-C3H5)3 dioxane on MAO-functionalized Si(>2 was reported by T. Riihmer et al. [307]. In situ DRIFT (= diffuse reflectance infrared Fourier transform) spectroscopy and TPRS (= temperature-programmed reaction spectroscopy) were employed... 

Ferri D, Kumar MS, Wirz R, et al. First steps in combining modulation excitation spectroscopy with synchronous dispersive EXAFS/DRIFTS/mass spectrometry for in situ time resolved study of heterogeneous catalysts. Phys Chem Chem Phys. 2010 12 5634. 

It is believed that the Kp data for the three homogeneous reactions (A, B, and C) are more reliable than those for the heterogeneous reaction (D) due to the need for a machine calibration constant which appears in the equilibrium expression for the latter. Ehlert et al. (2) determined this constant from vaporization experiments performed with silver contained in their Knudsen cell. Further support for this belief is provided by the large positive drift that arises in the 3rd law analysis of these Kp s. Also, it Is felt that the results otained from the flame-spectrophotometric studies (4, are somewhat more... 

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