Diffusivity pressure effect

Some Pressure Effects on Liquid Diffusion Coefficients and Equilibrium... 

Pressure effects The diffusion through liquids is governed by the number of defects or atomic-sized holes in the liquid. A high external pressme can reduce the concentration of holes and slow diffusion. Therefore, in a liquid, a diffusion-controlled rate constant also depends on the pressure. 

These theories fostered a great deal of experimental research to determine the effect of temperature and pressure on the flame velocity and thus to verify which of the theories were correct. In the thermal theory, the higher the ambient temperature, the higher is the final temperature and therefore the faster is the reaction rate and flame velocity. Similarly, in the diffusion theory, the higher the temperature, the greater is the dissociation, the greater is the concentration of radicals to diffuse back, and therefore the faster is the velocity. Consequently, data obtained from temperature and pressure effects did not give conclusive results. 

Detailed experimental studies on rock-forming minerals (see Chakraborty and Ganguly, 1991, and references therein) have shown that the pressure effect on elemental diffusivity cannot be neglected in petrologic studies, in which highly variable pressure regimes are commonly involved. 

A fourth factor is the flow rate of the eluent (mobile phase). A too high rate decreases resolution because there is no time for molecules to diffuse into the pores of the matrix. In contrast, a very slow migration of solvent decreases the resolution by remixing the components by diffusion. The effect of diffusion is minimized if the chromatography is done at low temperature. If short separation times are necessary, pre-packed columns, elevated pressure, or HPLC columns are indispensable. 

Temperature and Pressure Effect on Reaction Rate Coefficients and Diffusivities... 

The reaction rate constant and the diffusivity may depend weakly on pressure (see previous section). Because the temperature dependence is much more pronounced and temperature and pressure often co-vary, the temperature effect usually overwhelms the pressure effect. Therefore, there are various cooling rate indicators, but few direct decompression rate indicators have been developed based on geochemical kinetics. Rutherford and Hill (1993) developed a method to estimate the decompression (ascent) rate based on the width of the break-dovm rim of amphibole phenocryst due to dehydration. Indirectly, decompres-... 

Another m3d h arises from the intuition that pressure effect is opposite to the temperature effect. This is not true in kinetics. Therefore, kinetic constants (reaction rate constants, diffusion coefficients, etc.) almost always increase with increasing temperature, but they may decrease or increase with increasing pressure. Both positive and negative pressure dependences are well accounted for by the transition-state theory and are not strange. 

The same explanation applies to Fig 3, since on a per-unit-volume basis detonation energy increases as packing d increases, but this is eventually counteracted by incomplete reaction because of hindered oxidizer gas diffusion The effects of ambient pressure and temp (Figs 4 5) are primarily the consequence of reduced sensitivity and will be described later C Detonation Pressure Detonation pressures of Slurries are shown in Table 6, They appear to be quite normal 4 in that T in the equation P = p0D2 / T+l has values near 3. The range of T s in Table 6 is from 2.6 to 3.2... 

A diffuse pressure applied by the hydrophobic effect would compensate the strain thus engendered. Extension of this strategy may permit the use of self-assembly to construct other strained structures, which tend to have unusual and technologically interesting properties [35]. 

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