Rapid phase transitions metal

The field of gas-phase transition metal cluster chemistry has expanded rapidly due to the development of the laser vaporization source and the fast flow chemical reactor. The work from the three major laboratories have been reviewed. Many additional laboratories are developing cluster chemistry programs and will soon certainly make significant contributions. 

Events of this nature have been described by various terms, e.g., rapid phase transitions (RPTs), vapor explosions, explosive boiling, thermal explosions, and fuel-coolant interactions (FCIs). They have been reported in a number of industrial operations, e.g., when water contacts molten metal, molten salts, or cryogenic liquids such as liquefied natural gas (LNG). In the first two examples noted above, water is the more volatile liquid and explosively boils whereas, in the last example, the cryogenic liquid plays the role of the volatile boiling liquid and water is then the hot fluid. 

A thermal explosion is the metal industry s term for explosive boiling or rapid-phase transition. ... 

The combination of laser ionization and Fourier transform mass spectrometry (FTMS) has proved to be ideally suited for the study of gas-phase ion-molecule reactions involving metal ions (1-7). The laser source permits the generation of virtually any metal ion in the periodic table from a suitable metal target (8). The FTMS (9-14) stores these ions in an "electro-magnetic bottle" for times t)rpically on the order of msec to sec (hours are possible) permitting the study of their chemistry and photochemistry. These studies are further facilitated by the unusual ion and neutral manipulation capabilities of the FTMS which permit complex multistep processes to be monitored in an MS fashion (1-4). These capabilities have made laser ionization-FTMS a prominent method in what has been a rapidly growing arsenal of techniques for studying gas-phase transition-metal ion species. 

Anosovite (type 1) [12065-65-5] a-Ti,0, M = 223.0070 64.1 wt.% Ti 35.9 wt.% 0 (Oxides and hydroxides) Monoclinic a = 975.2 pm = 380.2 pm c = 944.2 pm =91.55 mC32 (Z= 4) S.G. C2/m Biaxial ( )= n.a. 4900 Habit needle-hke crystals. Color blue-dark. Diaphaneity opaque. Luster metallic. Streak black. Other properties melting point 1777 C It canbe prepared by the hydrogen reduction of solid TiO at temperature around 1300 C or by mixing indomtelly stoichiometric quantities of titanium metal and titanium dioxide in an electric arc furnace under argon atmo here. This oxide is dimorphic with a rapid phase transition from semiconductor to md al occuring at rou y 120 C... 

An example of an experiment in which LDL has been treated with 15-lipoxygenase and the oxidation monitored by the formation of conjugated diene is shown in Fig. 2.2. In the absence of transition metal, a rapid increase in absorbance occurs, with no lag phase, which ceases after a period of about 90 min under these conditions. If copper is added to promote LDL oxidation at this point, LDL treated with lipoxygenase oxidizes at a faster rate with a short lag phase when compared to the control. During this procedure there is only a minimal loss of a-tocopherol and so we may ascribe the shortened lag phase to the increase in lipid peroxides brought about by lipoxygenase treatment. A similar result was found when LDL was supplemented with preformed fatty acid hydroperoxides (O Leary eta/., 1992). 

The electrical conductivity of CoOP as a function of temperature is shown in Figure 6. Above room temperature the compound exhibits metallic behaviour but coincidental with the development of the superstructure the conductivity falls rapidly with decreasing temperature. Below 250 K CoOp behaves as a semiconductor with an activation energy of meV.74 The conduction has been shown to be frequency dependent below 250 K.75 Thermopower studies have also clearly demonstrated the changeover from metallic behaviour above 300 K. to semiconductor behaviour below 250 K.72 The behaviour of ZnOP is very similar to that of CoOp, with the phase transition from the Cccm to Pccn space group occurring at 278 K. Superstructure formation is complete by about 260 K.77... 

If a catalytic cycle should be maintained, oxygen diffusion out to the surface must be complemented by an inward diffusions of surface-activated oxygen resulting from accumulation of reduced metal centers required to activate gas-phase oxygen. Not all studies mentioned here ensured in their experiments that the conditions of lattice oxygen catalysis were such as to fulfill the conditions of cyclic reversibility [34, 51, 82,131,132] as opposed to stoichiometric and irreversible reduction [133] caused by a structural phase transition. As long as complex MMO oxides are being used and the extent of reduction is kept to levels where no bulk transformation can be detected this condition can be verified [20,99,118,121,134,135], The kinetics of re-oxidation of partly reduced oxide catalysts was found to be rapid [77, 78, 80, 82] and always faster than its reduction. 

In metal complexation, transition metals are added to the mobile phase to modulate selectivity. There are two approaches to the use of this technique. The first approach simply involves the introduction of a suitable metal ion, such as nickel(II), directly into the mobile phase. A solute ion that complexes rapidly with the transition metal will tend to be made more hydrophilic and will be eluted from the column more rapidly. Excellent efficiency and high selectivity have been achieved by that means.31... 

In the vicinity of a phase transition a rapid change of magnetic properties with the field intensity occurs. Consequently, a highly uniform magnetic field, comparable to the experimental conditions in the studies of the dHvA effect in metals, is required. 

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