Transport rate, additive consumption

Additives can be consumed at the cathode by incorporation into the deposit and/or by electrochemical reaction at the cathode or anode. Consumption of coumarin in the deposition of nickel from a Watts-type solution has been studied extensively. Thus, in this section we discuss the consumption of coumarin, which is used as a leveler and partial brightener. In a series of papers (33, 36), Rogers and Taylor, described the effects of coumarin on the electrodeposition of nickel. They found that the coumarin concentration decreases linearly with time at —960 mV (versus SCE and 485 to 223 rpm at a rotating-disk electrode, for plating times of 8 to 75 min. A rotating-disk electrode was used to achieve a uniform and known rate of transport of additive to the cathode. Rogers and Taylor found that the rate of coumarin consumption is a function of coumarin bulk concentration. Figure 10.16 shows that the rate of consumption... 

The effect of increasing temperature is to increase mass transport rates for all categories of diffusion. The obvious implication of more rapid mass transport for equilibrium-based interactions is more rapid sensor response. In addition, sensors based on the consumption of a reagent layer generally show enhanced sensitivity with increased temperature, because reaction rates and diffusion rates both exhibit a positive Arrhenius temperature dependence. 

The HTE characteristics that apply for gas-phase reactions (i.e., measurement under nondiffusion-limited conditions, equal distribution of gas flows and temperature, avoidance of crosscontamination, etc.) also apply for catalytic reactions in the liquid-phase. In addition, in liquid phase reactions mass-transport phenomena of the reactants are a vital point, especially if one of the reactants is a gas. It is worth spending some time to reflect on the topic of mass transfer related to liquid-gas-phase reactions. As we discussed before, for gas-phase catalysis, a crucial point is the measurement of catalysts under conditions where mass transport is not limiting the reaction and yields true microkinetic data. As an additional factor for mass transport in liquid-gas-phase reactions, the rate of reaction gas saturation of the liquid can also determine the kinetics of the reaction [81], In order to avoid mass-transport limitations with regard to gas/liquid mass transport, the transfer rate of the gas into the liquid (saturation of the liquid with gas) must be higher than the consumption of the reactant gas by the reaction. Otherwise, it is not possible to obtain true kinetic data of the catalytic reaction, which allow a comparison of the different catalyst candidates on a microkinetic basis, as only the gas uptake of the liquid will govern the result of the experiment (see Figure 11.32a). In three-phase reactions (gas-liquid-solid), the transport of the reactants to the surface of the solid (and the transport from the resulting products from this surface) will also... 

For dilute additive solutions, consumption can easily become limited by diffusion of the adsorbate to the interface. A particularly tractable situation occurs at the dilute limit of the Langmuir isotherm where C(- is proportional to the surface coverage, and in the limit of diffusion controlled adsorption CsoHd is directly proportional to the additive flux and thus the bulk electrolyte concentration. Such transport limited incorporation was reported in some radiotracer studies of thiourea incorporation in nickel and copper plating in the 1950-1960s [1-4, 17, 130, 131, 141-146], Consistently, a common observation was that the additive concentration in the solid was proportional to the additive concentration at the interface and inversely proportional to metal deposition rate, i, [1-4, 130, 131, 141, 142] such that ... 

In many cases it is preferential to use steam for heating and moistening this technique commonly results in a higher extrusion rate (capacity), increased die life, decreased power consumption, and improved quality of the extrudate. These characteristics are most reliably obtained if conditioning takes place in separate machines in which residence times of 5-30 minutes can be achieved. Figure 345 shows schematically the conditioner of such a system in which material is constantly moved with slowly rotating scrapers and transported from deck to deck while steam is injected and other additives, such as molasses or fat, are incorporated. 

The total mass flow of monomer, as measured by the monomer consumption, consists of two parts first, the monomer is consumed by the polymerization reaction and, second, the polymer formed (particles) will absorb additional monomer according to the apparent P/Pq value. The consumption of monomer is the driving force for the monomer transport which depends on the number of particles as well as the volume of the monomer swollen particles (or polymer Vp. In a reaction controlled system (at high agitation speed), the rate of polymerization increases with Vp and the particle concentration. 

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