Salt-gradient theory

This salt-gradient theory deserves further attention. It is possible that the concepts may be applicable to vapor explosions in different industries. 

One experiment which does not seem to fit into the network of the salt-gradient theory was that of Wright and Humberstone (1966), who impacted water on molten aluminum and obtained explosions. These results are at variance with those of Anderson and Armstrong, but the latter worked at 1 bar whereas the former used a vacuum environment. It might be possible that, under vacuum, it is much easier to achieve intimate contact between the aluminum and water and, under these conditions, there may be sufficient reaction between the aluminum and water to allow soluble aluminum salts to form. This salt layer could then form the superheated liquid which is heated to the homogeneous nucleation temperature and explodes. 

To study the range of possibilities the first molecular dynamics simulations of a DNA duplex tethered to a surface was performed [35,36] The technical aspects of simulations near surfaces are nontrivial, especially as concerns reliable boundary conditions [37], Molecular dynamics provides a more quantitative picture of the salt gradients and DNA structures near the surface responsible for changes in hybridization affinities and specificities than approximate (PB level mean field) theory and so may be used as a check on the simple analytical picture derived above. In addition simulation provides mechanistic clues which can form additional hypotheses for testing. 

Anion-exchange resins have been used (Wright and Schnitzer, 1960) in an attempt to fractionate soil humic substances. Some of the humic material is readily retained and a fractionation can be achieved by elution with a salt gradient and/or an alkaline reagent (usually NaCl and NaOH, respectively). In theory the anion-exchange technique should work well, but in practice the... 

A modified superheat theory was proposed by Shick to explain molten salt (smelt)-water thermal explosions in the paper industry (see Section IV). (Smelt temperatures are also above the critical point of water.) In Shick s concept, at the interface, salt difiuses into water and water into the salt to form a continuous concentration gradient between the salt and water phases. In addition, it was hypothesized that the salt solution on the water side had a significantly higher superheat-limit temperature and pressure than pure water. Thicker, hotter saltwater films could then be formed before the layer underwent homogeneous nucleation to form vapor. 

In the absence of gradients of salt concentration and temperature, flows of water and electric current in bentonite clay are coupled through a set of linear phenomenological equations, derived from the theory of irreversible thermodynamics (Katchalsky and Curran, 1967), making use of Onsager s Reciprocal Relations (Groenevelt, 1971) ... 

The observations discussed above may have implications for any system where water, dissolved salts and hydrophobic entities are present and there must be many. Currently the separation of hydrophobic proteins can be achieved using a hydrophobic chromatography column, by elution with salt solutions. There is no adequate theory for this process and present understanding is purely empirical. Suppose then, that while all salts reduce electrostatic forces, only those salts that reduce bubble coalescence also reduce the hydrophobic attraction. Further, these salts have a significant effect on the hydrophobic attraction only above their transition concentration. With this notion in mind the experimental results are explained. This then enables separations to be simplified, as the salt type and concentration gradient required are easily determined. 

Mobile phase parameters that have to be optimized include the salt type, concentration, gradient shape, pH, temperature, and possibly the addition of a surfactant or organic solvent [368-372]. The change in free energy on protein binding to the stationary phase is determined mainly by the contact surface area between the protein and stationary phase and by the salt type determined by its ability to increase the surface tension of aqueous solutions. Solvophobic theory predicts that in the absence of specific salt-protein interactions and at sufficient ionic strength the logarithm of the retention factor is linearly dependent on the surface tension of the mobile phase, which in turn, is a linear function of the salt concentration Eq. (4.13)... 

As mentioned in Sect. II.C.2, a small amount of electrolyte (as a water-soluble magnesium salt) was added to the emulsion as a corrosion inhibitor. This electrolyte could in theory balance the osmotic gradient and inhibit aging. However, the dehydration and desalting process was difficult to control and often the heavy crude oil ended up with larger amounts of brine that required larger amounts of electrolyte to offset the osmotic gradient... 

The thermoelectricity theory of thermophoresis has been proposed to explain these experimental results and to describe the effects of pH value and salt concentration and type [7]. This theory predicts that for particles suspended in an electrolyte solution under a temperature gradient, an additional thermoelectric force is generated to exert on the particles by induced electric field due to the thermodiffusion of positive and negative ions. 

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