As metastable

Iodine monochloride [7790-99-0] ICl, mol wt 162.38, 78.16% I, is a black crystalline soHd or a reddish brown Hquid. SoHd ICl exists ia two crystalline modifications the a-form, as stable mby-red needles, d = 3.86 g/mL and mp 27.3°C and as metastable brownish red platelets, d = 3.66 g/mL, mp 13.9°C and bp 100°C (dec). Iodine monochloride is used as a halogenation catalyst and as an analytical reagent (Wij s solution) to determine iodine values of fats and oils (see Fats and fatty oils). ICl is prepared by direct reaction of iodine and Hquid chlorine. Aqueous solutions ate obtained by treating a suspension of iodine ia moderately strong hydrochloric acid with chlorine gas or iodic acid (118,119). 

Zeohtes are formed under hydrothermal conditions, defined here in a broad sense to include 2eoHte crystalli2ation from aqueous systems containing various types of reactants. Most synthetic 2eoHtes are produced under nonequilihrium conditions, and must be considered as metastable phases in a thermodynamic sense. 

Chemical stabilization involves removing the concentration of surface hydroxyls and surface defects, such as metastable three-membered rings, below a critical level so that the surface is not stressed by rehydroxylation in use. Thermal stabilization involves reducing the surface area sufficiently to enable the material to be used at a given temperature without reversible stmctural changes. The mechanisms of thermal and chemical stabilization are interrelated because of the extreme effects that surface hydroxyls and chemisorbed water have on stmctural changes. Full densification of gels, such as the... 

Enols of simple ketones can be generated in high concentration as metastable species by special techniques. Vinyl alcohol, the enol of acetaldehyde, can be generated by very careful hydrolysis of any of several ortho ester derivatives in which the group RC02 is acetate acid or a chlorinated acetate acid. ... 

The fact that oxides can exist as metastable phases is illustrated by the Ni-HjO diagram (Fig. 1.18) in which the curves for the various oxides of nickel have been extrapolated into the acid region of Ni stability, and this diagram emphasises the fact that nickel can be passivated outside the region of thermodynamic stability of the oxides". 

States such as superheated liquid and supercooled vapour are known as metastable, they are not of themselves unstable, but become so on introduction of a small amount of the stable phase. 

The formation of arynes (8.26) as metastable intermediates in aromatic dediazo-niations was postulated by Stiles and Miller (1960) for the case of the 2-carboxy-benzenediazonium zwitterion (8.25) and by Cadogan and Hibbert (1964) for unsubstituted benzenediazonium salts. ... 

On the other hand, the large activation energy for the formation of sulfate from 8g and water makes it possible to prepare polysulfides as well as other reduced sulfur compounds as metastable products in aqueous solution at ambient conditions. 

Position A represents many cases of practical stability it does not represent the condition of minimum energy and is more accurately referred to as metastable, because it pertains to a condition of comparative rather than absolute stability. 

We have now derived the phase boundary between the two liquids. By analogy with our earlier examples, the two phases may exist as metastable states in a certain part of the p,T potential space. However, at some specific conditions the phases become mechanically unstable. These conditions correspond to the spinodal lines for the system. An analytical expression for the spinodals of the regular solution-type two-state model can be obtained by using the fact that the second derivative of the Gibbs energy with regards to xsi)B is zero at spinodal points. Hence,... 

Also, a rigorous treatment of isotope effects within the framework of QET reveals that the assumption /muZ/mD = hZZ d represents a simplification. [69] It is only valid for when the species studied populate a small internal energy distribution, e.g., as metastable ions do, whereas wide internal energy distributions, e.g., those of ions fragmenting in the ion source after 70 eV electron ionization, may cause erroneous results. This is because the fc(E) functions of isotopic reactions are not truly parallel, [76] but they fulfill this requirement over a small range of internal energies (Figs. 2.17 and 2.18)... 

Figure 2.14 Electrochemical phase diagram for chalcopyrite with elemental sulphur as metastable phase. Equilibrium lines (solid lines) correspond to dissolved species at 10 mol/L. Plotted points show the upper and lower limit potential of collectorless flotation of chalcopyrite reported from Sun (1990), Feng (1989) and Trahar (1984)...

Figure 2.18 rpH diagram for jamesonite in aqueous solutions with elemental sulphur as metastable phase. Equilibrium lines correspond to dissolved species at 10 moFL... 

From the Eqs. (3-1) to (3-13), the h-pH diagram of sodium sulphide solution is constructed with element sulphxir as metastable phase considering the presence of barrier (about 300kJ/mol) or overpotential (about 3.114 mV) of sulphide oxidation to sulphate and shown in Fig. 3.7. It is obvious that the lower limit of potential of sodium sulphide-induced collectorless flotation of pyrite, pyrrhotite and arsenopyrite at various pH agree well with the potential defined respectively by reactions of Eq. (3-9) producing elemental sulphur. The initial potential... 

The application of solid compounds with cluster units as sources for new molecular compounds, as well as for new polymers opens up an attractive field in chemistry. In view of the wealth of binary and ternary solid compounds, there is no end in sight. The wide range of materials should encourage many chemical groups to work much more in this direction. Especially fascinating is the possibility to form new modifications of the elements which as metastable systems could also have interesting chemical and physical properties. 

Formulations based on nanoreactants also known as metastable intermolecular composites (abbreviated as MIC and pronounced as Mick , also referred to as super-thermites or nano-energetic mixtures) were first reported by U.S. Los Alamos National Laboratory (LANL) and appear to be very attractive for a number of applications [103]. Some important MICs are illustrated here along with their properties. 

Heteromolecular -complexes of aromatic cation radicals have been designed from the complexation of aromatic cation radical with a different neutral aromatic donor but such ionic K-heterocomplexes were observed as metastable species in the gas phase or in freon matrices57 58. 

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