In this paper, experimental and simulated data for the diffusion of water across Nafion membranes as a function of the water activity gradient are presented. The gradient in the activity of water across the membrane was varied by changing the flow rate and pressure of nitrogen gas on one side of the membrane. The other side of the membrane was equilibrated with liquid water. It was found that the model predictions are very sensitive to the value of the diffusion coefficient of water in Nafion. Using the Fickian diffusion coefficient extracted from self-diffusion measurements reported in the literature, the model simulations matched experimental data with less than 5% error over a wide range of operating conditions.

In this paper, diffusion and electro-osmotic drag of water across Nafion® membranes in the presence of HCl are characterized. For all the measurements, one side of the Nafion membrane was in contact with liquid water and the other side with gaseous anhydrous HCl. To characterize diffusion of water, the open-circuit flux of water across a catalyst-coated Nafion 115 membrane was measured as a function of HCl flow rate and temperature at a constant cell pressure of 1 atm. Due to the nature of varying driving force for diffusion as a function of HCl flow rate, the experimental data was analyzed in conjunction with a mathematical model. The mathematical model accounts for condensation of water and is used to calculate the concentration of liquid hydrochloric acid in contact with the membrane. The mathematical model presented here is general and can be applied to the characterization of water transport across Nafion membranes in the presence of any gas that is soluble in water. In the case of HCl, at low inlet flow rates ͑Ͻ1500 cm 3 /min, STP͒, the diffusion of water across the membrane is primarily governed by the diffusional limitations of HCl in the condensed phase. At high flow rates ͑Ͼ3000 cm 3 /min, STP͒, the flux of water is a constant and depends on the saturation solubility of HCl in the condensed liquid phase. To measure the electro-osmotic drag parameter, the net flux of water across the membrane was measured as a function of the applied current density at high HCl flow rates ͑i.e., uniform water flux͒. At 80°C, it was found that 3.8 mol of water per mole of protons are transported from the anode to the cathode.

Two fundamentally different procedures of metal oxide production, which provide nanometer‐sized oxide particles, are described here. Earthalkaline oxides, e.g., are produced by chemical gas phase deposition with MeO molecules (Me = Ca, Mg) and clusters being directly deposited after gas phase reaction between Me atomes and O2 molecules. The procedure also allows the dotation of MgO with a second component such as CaO and vice versa. In order to obtain information on surface properties like reactivity and surface composition, OH groups as probe species are produced on the surface of the resulting particles. The respective chemisorption as well as thermal desorption of OH groups are monitored by FT‐IR spectroscopy. X‐ray powder diffraction provides information on the bulk composition and bulk structure. Cu2O, on the other hand, is produced by deposition of Cu metal from the vapour and subsequent oxidation of the resulting solid particles, which are then characterized by X‐ray powder diffraction and UV/VIS spectroscopy.

synopsisThe physicochemical high-temperature reactions of a nadic methyl anhydride-crosslinked novolac epoxy resin were investigated by means of differential thermal analysis, thermogravimetric analysis, and by other analytical procedures. The thermogravimetric study revealed that decomposition involving weight lm occurred in two stages. Chemical analysis showed that the major gaseous products formed during weight loss were Zmethylcyclopentadiene, carbon dioxide, and carbon monoxide. The formation of a fine mist of solid particles was observed during the second stage of degradation. Changing various experimental parameters affected the degradation processes. The kinetics of degradation were also investigated. The method of Freeman and Carroll was used to find that a eero-order rate law was followed at the beginning of both first and second stages of reaction. The activation energy associated with the major portion of the first stage of weight loss was 15 kcal/mole. There was good agreement between the observed reaction rates and the reaction rates calculated from a theoretical model which depended on desorption as the rate-controlling step. The activation energy for the beginning of the second stage of weight loss was 24 kcal/mole. By using DTA, the heat of exothermal reaction during this latter phase of decomposition was evaluated as 65 cal/g.

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