Particle heterogeneous

The final one is to nucleate particles heterogeneously only on the support surfaces, not homogeneously independently from the surfaces, as shown in Figure 4. 

Maillard F, Savinova E, Simonov PA, Zaikovskii VI, Stimming U. 2004b. Infrared spectroscopic study of CO adsorption and electrooxidation on carbon-supported Pt nanoparticles Inter-particle versus intra-particle heterogeneity. J Phys Chem B 108 17893-17904. 

Fig. 21. Three steady states in a catalyst bed. Pt catalyst diluted with inert particles (heterogeneous mixing).

We consider now a class of models that introduce particle heterogeneity through random rate coefficients. In this conceptualization, the particles are assumed different due to variability in such characteristics as age, size, molecular conformation, or chemical composition. The hazard rates h are now considered to be random variables that vary influenced by extraneous sources of fluctuation... 

Ingredient Segregation Avoided Powders such as hypromellose and titanium dioxide exhibit dramatically different particle size distribution and density. Such particle heterogeneity may result in constituent segregation inducing film imperfections or color deviations on tablets. 

The particles are heterogeneous by definition. As with singlepolymer particles, heterogeneities in density can arise as a result of the mechanism of particle formation. Usually a polymer has a different density to the liquid monomer from which it is derived, and in most emulsion polymerisation processes to produce reasonably concentrated dispersions, propagation is dominated by arrival at the particle surface of oligomeric radicals which can lead to non-homogeneous shrinking within the particle. 

When the volatile matter has left the particles, heterogeneous reactions, such as gasification with CO2 and H2O and char combustion, begin. Char combustion is a slower process than gas combustion and demands a higher temperature (> 800°C) to be complete. As long as oxygen is present combustion dominates, since gasification is slow. 

Widegren JA, Finke RG (2003) A review of the problem of distinguishing true homogeneous catalysis from soluble or other metal-particle heterogeneous catalysis under reducing conditions. J Mol Catal A Chem 198 317... 

For the two-particle heterogeneous model the source term in the bulk gas phase equation is given as the sum of the conventional particle-bulk phase mass transfer terms for both the catalyst and C02-acceptor particles. The net source term is thus defined by ... 

Fig. 11.8. Comparison in dry hydrogen mole fraction with pseudo-homogeneous model (----),one-particle heterogeneous model ( —) and two-particle heterogeneous model (-----) at t = 200 s, standard conditions. Reprinted with permission...

Catalysis. Many reactions are catalyzed, i.e., increased in rate, by a compound in solution (homogeneous catalysis) or a group at the surface of a particle (heterogeneous catalysis), where the catalyst is not consumed itself. Examples are various hydrolyzing reactions, like the ester hydrolysis mentioned above, that are catalyzed by H+ as well as OH ions. In such a case the reaction rate greatly depends on pH, though the ions themselves do not appear as reactants in the overall reaction scheme. Ubiquitous in natural foods are enzyme-catalyzed reactions. The simplest case leads to Michaelis-Menten kinetics, but several complications may arise. 

This book presents coverage of the dynamics, preparation, application and physico-chemical properties of polymer solutions and colloids. It also covers the adsorption characteristics at and the adhesion properties of polymer surfaces. It is written by 23 contemporary experts within their field. Main headings include Structural ordering in polymer solutions Influence of surface Structure on polymer surface behaviour Advances in preparations and appUcations of polymeric microspheres Latex particle heterogeneity origins, detection, and consequences Electrokinetic behaviour of polymer colloids Interaction of polymer latices with other inorganic colloids Thermodynamic and kinetic aspects of bridging flocculation Metal complexation in polymer systems Adsorption of quaternary ammonium compounds art polymer surfaces Adsorption onto polytetrafluoroethylene from aqueous solutions Adsorption from polymer mixtures at the interface with solids Polymer adsorption at oxide surface Preparation of oxide-coated cellulose fibre The evaluation of acid-base properties of polymer surfaces by wettability measurements. Each chapter is well referenced. 

Fig. 4 General approach for distinguishing between a metal-particle heterogeneous catalyst and a metal-complex homogeneous catalyst as described by Finke.

A nucleation process is generally described assuming the initial formation of the voids to be in accordance with the classical nucleation theory. It can be assumed that nucleation occurs between resin and fiber or resin and added particle (heterogeneous nucleation) or within the resin itself (homogeneous nucleation). 

Applications of the TCR have included single phase liquid reactions reactions between inunisdble liquids dispersion of solids in liquids aystaUisations polymerisations electrochemistry fermentation photochanical reactions emulsion polymerisation synthesis of silica particles heterogeneous catalytic reactions and liquid-liquid extractions. 

The Fan-Tsuchiya equation with constant values of Pm estimated from Eq. (12) predicts reasonably well the general trend of bubble rise velocity variation in liquid-solid suspensions as shown in Figs. 8 and 9. However, a detailed match between the experimental results and predictions appears to be difficult to attain by assigning a constant value of p for each condition. A more elaborate analysis is required to account for the effect of bubble size on interactions of the bubble with the surrounding medium (non-Newtonian approach) or with individual particles (heterogeneous approach). 

Synthetic strategy Magnetically separable nano-material-catalyzed oxidative cyclization Catalyst Manganese ferrite (MnFe204) nano-particles (heterogeneous and magnetically separable)... 

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