Heteropolytungstates in which one of the positions normally occupied by a tungsten cation is occupied instead by an iron cation are shown to be catalysts for the electroreduction of H202. The rate constant governing the reduction of H202 by H20FellSiW1103g6" was measured by stopped flow as 9 X 102 M"1 s"1. A catalytic mechanism involving an Fe(IV) intermediate generated from the reaction between the Fe(III) form of the heteropolytungstate anion and hydroxyl radicals is presented. The Fe(IV) intermediate can react with itself to produce H202 and the Fe(lll) form of the heteropolytungstate. Alternatively, the Fe(IV) intermediate can consume additional H202 by oxidizing it to 02. Competition between these two reaction pathways accounts for the nonintegral stoichiometry observed under some experimental conditions during the electroreduction of H202 catalyzed by H20FellSiW1]03g6". Pulse-radiolysis experiments were employed to detect the Fe(IV) intermediate, to evaluate rate constants for the reactions in which it is formed and decomposed, and to measure the rate of reduction of the Fe(III) form of the heteropolytungstate by Of.
Poly(urethane/isocyanurate) is a major resin used in the structural reaction injection molding (SRIM) process. In this study, the kinetics and viscosity changes of a poly(urethane/isocyanurate) resin were investigated by the adiabatic temperature/viscosity rise method and differential scanning calorimetry. The effect of the catalyst concentration and the volume ratio of isocyanate to polyol was investigated. It is found that isocyanate trimerization depends on the diffusion effect resulted from the urethane formation. A kinetic model including the diffusion effect is developed, which is able to predict the experimental results. The reaction induced viscosity rise depends on the concentration and the molecular weight of the formed polymer. The measured adiabatic viscosity rise correlates well with the calculated molecular weight growth using the recursive method.
The injection/compression liquid composite molding (LCM) process is simulated by using the control/volume finite element method (CV/FEM). The flow in the runner and the fiber‐free areas is simplified by using an equivalent permeability approach. Several molding experiments were conducted using a tub‐shaped mold and the structural reaction injection molding (SRIM) process for a poly(urethane/isocyanurate) matrix and a glass fiber preform. Good agreement is found between the experimental results and the simulation.
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