Nonequilibrium States of a Binary Mixture with Miscibility Gap in the Homogeneous One-Fluid-Phase Region: Study of the System 2,6-Dimethylpyridine/Water with Off-Critical Compositions Near its Lower Critical Point

1990 ◽  
Vol 94 (2) ◽  
pp. 145-150 ◽  
Author(s):  
W. Mayer ◽  
D. Woermann
Keyword(s):  
Binary Mixture ◽  
Critical Point ◽  
Fluid Phase ◽  
Phase Region ◽  
Miscibility Gap ◽  
Nonequilibrium States

Phase separation of binary mixtures induced by soft centrifugal fields

2021 ◽  
Author(s):  
Thomas Zemb ◽  
Rose Rosenberg ◽  
Stjepan Marčelja ◽  
Dirk Haffke ◽  
Jean-François Dufrêche ◽  
...  
Keyword(s):  
Phase Separation ◽  
Critical Point ◽  
Binary Mixtures ◽  
Liquid Mixture ◽  
Model System ◽  
Binary Liquid Mixture ◽  
Miscibility Gap ◽  
Critical Fluctuations ◽  
Binary Liquid

We use the model system ethanol–dodecane to demonstrate that giant critical fluctuations induced by easily accessible weak centrifugal fields as low as 2000g can be observed above the miscibility gap even far from the critical point of a binary liquid mixture.

Supercritical Adsorption

2005 ◽  
Author(s):  
Eldred H. Chimowitz
Keyword(s):  
Stationary Phase ◽  
Critical Point ◽  
Dynamic Models ◽  
Molecular Diffusion ◽  
Plug Flow ◽  
Fluid Phase ◽  
Commercial Application ◽  
Critical Systems ◽  
Mobile Phases ◽  
Column Dynamics

In this chapter, we discuss adsorption phenomena in supercritical systems, a situation that occurs in many application areas in chemical-process and materials engineering. An example of a commercial application in this area, which has achieved wide acceptance as a tool in analytical chemistry, is supercritical fluid chromatography (SFC). Not only is SFC a powerful technique for chemical analysis, but it also is a useful method for measuring transportive and thermodynamic properties in the near-critical systems. In the next section, we analyze adsorption-column dynamics using simple dynamic models, and describe how data from a chromatographic column can be used to estimate various thermodynamic and transport properties.We then proceed to discuss the effects of proximity to the critical point on adsorption behavior in these systems. The closer the system is to its critical point, the more interesting is its behavior. For very dilute solute systems, like those considered here, the energy balance is often ignored to a first approximation; this leads to a simple set of mass-balance equations defining transport for each species. These equations can be developed to various levels of complexity, depending upon the treatment of the adsorbent (stationary phase). The conceptual view of these phases can span a wide range of possibilities ranging from completely nonporous solids (fused structures) to porous materials with complicated ill-defined pore structures. Given these considerations, it is customary to make the following assumptions in the development of a simple model of adsorber-bed dynamics: . . .1. The stationary and mobile phases are continuous in the direction of the flow, with the fluid phase possessing a flat velocity profile (“plug” flow).. . . . . . 2. The porosity of the stationary phase is considered constant irrespective of pressure and temperature conditions (i.e., it is incompressible). . . . . . .3. The column is considered to be radially homogeneous, leading to a set of equations with one spatially independent variable, representing distance along the column axis. . . . . . . 4. The dispersion term in the model equation represents the combined effects of molecular diffusion and dispersion due to convective stirring in the bed. These effects are combined into an effective phenomenological dispersion coefficient, considered to be constant throughout the column. . . .

Scaling Near the Critical Point in Mixture

2005 ◽  
Author(s):  
Eldred H. Chimowitz
Keyword(s):  
Critical Point ◽  
Binary Systems ◽  
Critical Line ◽  
Phase Region ◽  
Unique Point ◽  
Pure Fluid ◽  
High Volatility ◽  
Two Phases ◽  
The One ◽  
Dew Line

The critical point of mixtures requires a more intricate set of conditions to hold than those at a pure-fluid critical point. In contrast to the pure-fluid case, in which the critical point occurs at a unique point, mixtures have additional thermodynamic degrees of freedom. They, therefore, possess a critical line which defines a locus of critical points for the mixture. At each point along this locus, the mixture exhibits a critical point with its own composition, temperature, and pressure. In this chapter we investigate the critical behavior of binary mixtures, since higher-order systems do not bring significant new considerations beyond those found in binaries. We deal first with mixtures at finite compositions along the critical locus, followed by consideration of the technologically important case involving dilute mixtures near the solvent’s critical point. Before taking up this discussion, however, we briefly describe some of the main topographic features of the critical line of systems of significant interest: those for which nonvolatile solutes are dissolved in a solvent near its critical point. The critical line divides the P–T plane into two distinctive regions. The area above the line is a one-phase region, while below this line, phase transitions can occur. For example, a mixture of overall composition xc will have a loop associated with it, like the one shown in figure 4.1, which just touches the critical line of the mixture at a unique point. The leg of the curve to the “left” of the critical point is referred to as the bubble line; while that to the right is termed the dew line. Phase equilibrium occurs between two phases at the point where the bubble line at one composition intersects the dew line; this requires two loops to be drawn of the sort shown in figure 4.1. A question naturally arises as to whether or not all binary systems exhibit continuous critical lines like that shown. In particular we are interested in the situation involving a nonvolatile solute dissolved in a supercritical fluid of high volatility.

Deposition of C60, C70 and C84 fullerene molecules, in benzene via a change of the fluid state, from a gas–liquid two phase region to the critical point

2011 ◽  
Vol 58 (3) ◽  
pp. 407-411 ◽  
Author(s):  
Takahiro Fukuda ◽  
Yoshihiro Katsube ◽  
Nami Watabe ◽  
Shunji Kurosu ◽  
Raymond L.D. Whitby ◽  
...  
Keyword(s):  
Critical Point ◽  
Phase Region ◽  
Two Phase ◽  
Fluid State

Morphology of Sintered Cr-Mo Porous Materials

2015 ◽  
Vol 825-826 ◽  
pp. 838-843
Author(s):  
Moritz Boehm ◽  
Thomas Schmoelzer ◽  
Reinhard Simon ◽  
Christian Gierl-Mayer
Keyword(s):  
Electron Microscopy ◽  
Solid Solution ◽  
Scanning Electron Microscopy ◽  
Linear Expansion ◽  
Solid Phase ◽  
Phase Region ◽  
Miscibility Gap ◽  
Liquidus Boundary ◽  
Different Temperatures ◽  
Scanning Electron

Chromium and molybdenum exhibit continuous solubility in the solid phase region at temperatures of 908°C and above [1]. At lower temperatures, the system exhibits a miscibility gap. Furthermore a congruent minimum in the liquidus boundary exists at 1854°C. Chromium and molybdenum powders with different particle morphologies were mixed and porous green parts were produced by pressing. Sintering experiments were performed at different temperatures and for different chromium to molybdenum ratios. To investigate the evolution of the microstructure, sintering was interrupted at different temperatures and points in time. The microstructure and morphology of the sintered parts was investigated by scanning electron microscopy as well as light optical microscopy. It was found that during sintering, a Cr-Mo solid solution is formed. Depending on the molybdenum content, this induces either shrinking or swelling of the porous parts. Samples exhibited a linear expansion of up to 10% and final porosities of up to 65%.

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