Solubility and diffusion

The amount of gas dissolved in a liquid is directly proportional to the partial pressure of the gas in equilibrium with the liquid. 

The rate of diffusion of a gas is inversely proportional to the square root of its molecular weight. 

The rate of diffusion of a gas across a membrane is proportional to the membrane area (A) and the concentration gradient (C, - C2) across the membrane and inversely proportional to its thickness (D). 

The ratio of the amount of substance present in equal volume phases of blood and gas in a closed system at equilibrium and at standard temperature and pressure. 

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A further problem is possible if the reinforcements are very small. Coarsening of the particles or whiskers may occur driven by Ostwald ripening, in which large particles grow through diffusional transport at the expense of smaller ones. This can be minimized by choosing matrices in which the reinforcement elements have very low solid solubilities and diffusion coefficients. Platelets, however, have been shown to be more resistant to coarsening than particles or whiskers. 

Process Description Gas-separation membranes separate gases from other gases. Some gas filters, which remove hquids or sohds from gases, are microfiltration membranes. Gas membranes generally work because individual gases differ in their solubility and diffusivity through nonporous polymers. A few membranes operate by sieving, Knudsen flow, or chemical complexation. 

Of particular interest in the usage of polymers is the permeability of a gas, vapour or liquid through a film. Permeation is a three-part process and involves solution of small molecules in polymer, migration or diffusion through the polymer according to the concentration gradient, and emergence of the small particle at the outer surface. Hence permeability is the product of solubility and diffusion and it is possible to write, where the solubility obeys Henry s law,... 

An antiozonant should have adequate solubility and diffusivity characteristics. Since ozone attack is a surface phenomenon, the antiozonant must migrate to the surface of the rubber to provide protection. Poor solubility in rubber may result in excessive bloom. 

Titanium and most of its alloys readily absorb and evolve hydrogen due to high solubility and diffusion mobihty of hydrogen at moderate temperatures. 

When a polymer film is exposed to a gas or vapour at one side and to vacuum or low pressure at the other, the mechanism generally accepted for the penetrant transport is an activated solution-diffusion model. The gas dissolved in the film surface diffuses through the film by a series of activated steps and evaporates at the lower pressure side. It is clear that both solubility and diffusivity are involved and that the polymer molecular and morphological features will affect the penetrant transport behaviour. Some of the chemical and morphological modification that have been observed for some epoxy-water systems to induce changes of the solubility and diffusivity will be briefly reviewed. 

In mbber-mbber blends, maldistribution of curatives such as sulfur, accelerator, and activator due to their difference in solubility and diffusivity leads to uneven distribution. Blending strategies such as adding the accelerators to each mbber followed by blending the two mixed batches has been found to be more effective than blending the curatives into both mbbers in a single step. Selection of... 

Unlike a plastic blend where the properties largely depend on the properties of the individual component and the compatibUizer used, those of a rubber blend depend on the solubility and diffusivity of the curatives, reaction rates, scorch time, etc. Figure 11.16 gives relative cure rate and scorch time for a number of accelerators. Hence, in designing a rubber blend, aU these parameters have to be taken into consideration in order to obtain good properties along with good processability. 

The more permeable component is called the fast gas, so it is the one enriched in the permeate stream. Permeabihly through polymers is the product of solubility and diffusivity. The diffusivity of a gas in a membrane is inversely proportional to its kinetic diameter, a value determined from zeolite cage exclusion data (see Table 20-26 after Breck, Zeolite Molecular Sieves, Wiley New York, 1974, p. 636). Tables 20-27, 20-28, and 20-29 provide units conversion factors useful for calculations related to gas-separation membrane systems. 

The nature of the extractant affects the extraction in both the solubility and diffusion limiting cases. 

By inspection, the flux is directly proportional to the solubility to the first power and directly proportional to the diffusion coefficient to the two-thirds power. If, for example, the proposed study involves mass transport measurements for series of compounds in which the solubility and diffusion coefficient change incrementally, then the flux is expected to follow this relationship when the viscosity and stirring rate are held constant. This model allows the investigator to simulate the flux under a variety of conditions, which may be useful in planning experiments or in estimating the impact of complexation, self-association, and other physicochemical phenomena on mass transport. 

Solubility and Diffusion at High Temperatures a. Permeation and Solubility Data... 

Midazolam is water soluble and diffuses rapidly into the CNS but has a very short half-life (0.8 hours). It must be given by continuous infusion. There is increasing interest in using it buccally and intramuscularly when IV access cannot be obtained readily. 

Neither is it connected with oxygen solubility and diffusion, since oxygen solubility in deformed polymers decreases by 5-10 times, and diffusion coefficient lessens significantly. 

The electrolyte composition affects the performance and endurance of MCFCs in several ways. Higher ionic conductivities, and hence lower ohmic polarization, are achieved with Li-rich electrolytes because of the relative high ionic conductivity of Li2C03 compared to that of Na2C03 and K2CO3. However, gas solubility and diffusivity are lower, and corrosion is more rapid in Li2C03. 

In dense membranes, no pore space is available for diffusion. Transport in these membranes is achieved by the solution diffusion mechanism. Gases are to a certain extent soluble in the membrane matrix and dissolve. Due to a concentration gradient the dissolved species diffuses through the matrix. Due to differences in solubility and diffusivity of gases in the membrane, separation occurs. The selectivities of these separations can be very high, but the permeability is typically quite low, in comparison to that in porous membranes, primarily due to the low values of diffusion coefficients in the solid membrane phase. 

The major respiratory factors in the control of ozone uptake are the morphology (including the mucus layer), the respiratory flow, the physical and chemical properties of mucus, and the physical and chemical properties of ozone. The next two sections discuss models of the morphology and the air and mucus flow. The physical and chemical properties of bronchial secretions have been reviewed by Barton and Lourenco and Charman et al. The relevant physical and chemical properties of ozone, are its solubility and diffusivity in mucus and water and its reaction-rate constants in water, mucus, and tissue. 

To maximize the current limit that could be shunted by redox additives so that the occurrence of such irreversible processes due to overflowing current could be more efficiently suppressed, the redox additive apparently should be present in the electrolyte at high concentrations, and both its oxidized and reduced forms should be very mobile species. Where the criteria for selecting potential redox additives are concerned, these requirements can be translated into higher solubility in nonaqueous media and lower molecular weight. In addition to solubility and diffusion coefficients, the following requirements should also be met by the potential redox additives (1) the formal potential of the redox couple [R]/[0] should be lower than the onset potential for major decom-... 

Versteeg, G.F. andvanSwaaij, P.M. Solubility and diffusivity of acid gases (CO2, N2O) in aqueous alkanolamine solutions, / Chem. Eng. Data, 33(l) 29-34, 1988. 

Carroll M.R. and Stolper E.M. (1991) Argon solubility and diffusion in silica glass implications for the solution behavior of molecular gases. Geochim. Cosmochim. Acta 55, 211-225. 

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