Vapor sorption rate

The goals of the present study were to reexamine vapor sorption in a lightly crosslinked rubber, both as an unfilled sample and in samples containing two types of carbon black in varying amounts. Complications in the vapor sorption-rate curves motivated a more detailed study of the diffusion problems as the main area of concern. 

Significant reduction of the water vapor sorption rate the sorption rate for pure lysine at 80% relative humidity is 10.5% per day, whereas that of lysine with wheat bran is about 2.5% to 4% per day. 

The effect of physical aging on the crystallization state and water vapor sorption behavior of amorphous non-solvated trehalose was studied [91]. It was found that annealing the amorphous substance at temperatures below the glass transition temperature caused nucleation in the sample that served to decrease the onset temperature of crystallization upon subsequent heating. Physical aging caused a decrease in the rate and extent of water vapor adsorption at low relative humidities, but water sorption could serve to remove the effects of physical aging due to a volume expansion that took place in conjunction with the adsorption process. 

Van Campen et al. [31] developed models describing the rate of moisture uptake above RH0 that consider both the mass transport of water to the solid substance and the heat transfer away from the surface. For the special case of an environment consisting of pure water vapor (i.e., initial vacuum conditions), the Van Campen et al. model is greatly simplified since vapor diffusion need not be considered. Here, only the rate at which heat is transported away from the surface is assumed to be an important factor in limiting the sorption rate, W. For this special case, an expression was derived to express the rate of moisture uptake solely as a function of RHj, the relative humidity of the environment, and RH0. 

The experimental basis of sorption studies includes structural data (SANS, SAXS, USAXS), isopiestic vapor sorption isotherms,i and capillary isotherms, measured by the method of standard porosimetry. i 2-i44 Thermodynamic models for water uptake by vapor-equilibrated PEMs have been suggested by various groupThe models account for interfacial energies, elastic energies, and entropic contributions. They usually treat rate constants of interfacial water exchange and of bulk transport of water by diffusion and hydraulic permeation as empirical functions of temperature. 

We described elsewhere the Hg(0) vapor sorption of commercial CuS [10]. The relative rate of Hg(0) uptake for commercial grade cuS is 12.8 mmoles/day compared with 70 mmoles/day for CTAB mediated CuS. The sorption properties of the particle-size-mediated synthesized covellite, CuS, is likewise reflective of a redox process that results in the formation of cinnabar, HgS, and the copper(I) sulfide chalcocite, CU2S, according to Reaction (1) ... 

There are several advantages to the dynamic vapor sorption device. First, any humidity value can be dialed in, whereas salt solutions are not available for every humidity value and some are quite toxic. Second, since the weight is monitored as a function of time, it is clear when equilibrium is reached. The dynamic devices also give the sorption/desorption rates, although these can easily be misused (see the drying kinetics section later). The salt solution method, on... 

Adsorption of vapors on test chamber walls has been previously described by means of models including two or three rate constants for adsorption/desorption processes in the ease of dynamic experiments (Dunn et al., 1988 Colombo et al., 1993) and with three adsorption/desorption constants in the case of static experiments (Colombo et al., 1993). Two rate constants describe a reversible sink whereas three rate constants describe a reversible and an irreversible (i.e. leak type) sink. However, these models did not adequately describe the sorption process(es), especially in the case of long-term tests, as resulted from two observations (Colombo et al., 1993) (a) the model with three sorption rate constants (reversible + irreversible sink) provided a better description of the experimental data than the one-sink model and (b) desorption experiments following adsorption gave strong indications that the irreversible sink was in fact slowly rever-... 

Figure 4 illustrates the distribution curve of a compound through the sorbent bed and the capacitive breakthrough curve of the compound in the effluent. At the start of collation the compound is distributed through a sation of the sorbent as shown by curve 1. After continued collection this section becomes saturated , that is an equilibrium is established with incoming concentration Ci where the vapor sorption and desorption rates are equal. This is shown by curve 2. The sorption front has moved through the front section of the collection tube (L 2/3) and is being collected on the backup section. If collation continues, the... 

Vaporization is an activated process controlled by the Gibbs energy of water sorption, which determines (c (iJpem))- Condensation is a kinetic process with a rate proportional to the vapor pressure P" at the interface between PEM and flow chamber. The vaporization exchange rate constant has a physical meaning similar to the exchange current density in electrochemical kinetics, and P"- (c (t, Ipem)) — P" acts like an overpotential of the vaporization process. 

The extracted parameters are vital for rationalizing mechanisms and amounts of water fluxes in PEFCs. The model could be applied for the analysis of sorption data at varying PEM thickness and equilibrium water content. Experiments running at varying T would provide activation energies of the vaporization-exchange rate constant and bulk transport coefficients. Similar modeling tools can be developed for the study of water sorption and fluxes in catalyst layers. They can be extended, furthermore,... 

The assumptions in his model do not allow for the complexity of the moisture sorption isotherm and the sorption kinetics of fibers. Scientists presented two mathematical models to simulate the interaction between moisture sorption by fiber and moisture flux through the air spaces of a fabric. In the first model, they considered diffusion within the fiber to be so rapid that the fiber moisture content is always in equilibrium with the adjacent air. In the second model, they assumed that the sorption kinetics of the fiber follows Fickian diffusion. Their model neglected the effect of heat of sorption behavior of the fiber. Scientists developed a new sorption equation that takes into account the two-stage sorption kinetics of wool fibers, and incorporated this with more realistic boundary conditions to simulate the sorption behavior of wool fabrics. They assumed that water vapor uptake rate of fiber consists of a two components associated with the two stages of sorption identified by researchers. 

Second stage is much slower than the first, following an exponential relationship between the concentration gradient and the vapor flux [34]. The second stage sorption rate (R2) is related to the local temperature, humidity, and sorption history of the fiber at each point in the fabric, which is assumed to have the following form ... 

Volatilization. The susceptibility of a herbicide to loss through volatilization has received much attention, due in part to the realization that herbicides in the vapor phase may be transported large distances from the point of application. Volatilization losses can be as high as 80—90% of the total applied herbicide within several days of application. The processes that control the amount of herbicide volatilized are the evaporation of the herbicide from the solution or soHd phase into the air, and dispersal and dilution of the resulting vapor into the atmosphere (250). These processes are influenced by many factors including herbicide application rate, wind velocity, temperature, soil moisture content, and the compound s sorption to soil organic and mineral surfaces. Properties of the herbicide that influence volatility include vapor pressure, water solubility, and chemical stmcture (251). 

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