Supercritical water definition

Figure 12. Distributions of H-bonding angles 0 in liquid and supercritical water. Definitions of H-bonding angles 0 and < > are given on the inset.

The metallographic analysis of the reactors with the optical microscope shows not worth mentioning trace of corrosion in the high temperature section of the reactor The elemental analysis of the exposed surface revealed a layer reach in Ni and Fe oxides and depleted in Cr and Mo. These changes affect only a thin layer. In account to the long exposure time of more than 1000 h and the high (up to 0.2 mol/kg) HCl concentration, corrosion rates of alloy 625 in high temperature - low-density supercritical water solutions are definitely low. For such HCl and Oj solutions Ni-base alloys, similar to alloy 625, can be used. 

Several studies have been reported on the determination of the mean-force potential between aqueous ion pairs at ambient conditions, " yet little is known about the speciation in aqueous solutions at near-critical and supercritical conditions " which are typically encountered in technological processes where supercritical water is either the reaction medium or the energy carrier. In this section we analyze the association, equilibrium, and the kinetic (interconversion) rate constants for an infinitely dilute aqueous Na /CI" solution as described by a water-electrolyte model at several supercritical state conditions. In Section 3.3.1 we briefly describe the statistical mechanical formalism for the determination of the thermodynamic constants and the molecular dynamic determination via constraint dynamics. In Section 3.3.2 we discuss the actual kinetics of the inteicon-version between two ion pair configurations leading to the definition of the corresponding equilibrium constant. Finally, in Section 3.3.3 we discuss the outcome of the comparison between the association constants from simulation and... 

For subcritical systems, the activity of water is simply defined as the ratio of the vapor pressure of water over the solution of interest to the vapor pressure of pure water under identical conditions. However, for supercritical systems this definition is no longer useful or practical, because of the absence of a liquid phase. Irrstead, for supercritical water systems, which are esserrtially derrse gases, it is more convenierrt (and descriptive) to use the con-... 

Based on this definition, Cummings and collaborators [52,133,134] determined the radial dependence (with respect to a central water molecule or solute species) of the number of hydrogen-bonded water molecules, in ambient and supercritical SPC water, and the effect of the presence of different types of infinitely dilute solutes. An unexpected finding was the lack of any significant effect of the nature of the solute on... 

The sharp first peak and following deep minimum of gon(A ) for normal liquid water (at 1.8 A and 2.4 A, respectively) become much less pronounced under supercritical conditions (Fig. 7b). These two characteristic features of gon( ) observed in computer simulations, as well as experimentally (Soper et. al. 1997), are the basis of a simple geometric definition of a hydrogen bond, whereby the bond is assumed to exist between any pair of H2O molecules whose respective O and H atoms are separated by less than i HB = 2.4 A. Integration under gon(A ) up to the chosen threshold distance provides a convenient way to quantitatively estimate the average number of H-bonds in which an individual molecule participates under various thermodynamic conditions (e.g.,... 

Figure 10. Normalized intermolecular O -H distance-energy distribution functions for liquid (a) and supercritical (b) water. Arrows show the cutoff values of the H-bond definition. [Reproduced with permission from J Phys Chem A 1997,101, 9720-9727. 1997 American Chemical Society.]...

A radical polymerisation can be carried out with a range of polymerisation techniques. Those with only a single phase present in the system are bulk and solution polymerisations, involving the monomer, a solvent if present and the initiator. By definition, the formed polymer in a bulk or solution polymerisation remains soluble (either in the monomer or the solvent). A precipitation polymerisation is one in which the system starts as a bulk or solution polymerisation, but the polymer precipitates from the continuous phase to form polymer particles which are not swollen with monomer. A precipitation polymerisation when the polymer particles swell with monomer is called dispersion polymerisation apart from polymerisation in the continuous phase, the polymer particles have an additional locus of polymerisation, and the particles in these systems are colloidally stabilised. Precipitation polymerisation is often performed in an aqueous medium (e.g. acrylonitrile polymerisation in water). Dispersion polymerisation is usually performed in organic solvents that are poor solvents for the formed polymer (supercritical or liquid carbon dioxide may also be used as a continuous medium for dispersion polymerisation). 

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