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High-temperature diffusion studies

Comparisons with high temperature diffusion studies... [Pg.595]

The activation energies calculated for Rb, Cs and Sr in the present study (Table III and Figure 8) are considerably lower than those calculated for high temperature diffusion in both crystalline and glass silicates. This discrepancy in the latter case implies that the glass matrix may be significantly different in high and low temperature diffusion studies. [Pg.597]

At a very low temperature where an adatom jumps only occasionally, about one atomic jump in every few seconds, field ion microscope studies conclude that the surface diffusion of adatoms is consistent with a discrete nearest neighbor random walk. However, in molecular dynamic simulations of diffusion phenomena, which are carried out only for high temperature diffusions where atomic jumps are very rapid, i.e. an atomic... [Pg.224]

In general, electrochemical systems are heterogeneous and involve at least one (or both) of the fundamental processes - mass transport and an electron-transfer reaction. Moreover, electrochemical reactions involve charged species, so the rate of the electron-transfer reaction depends on the electric potential difference between the phases (e.g. between the electrode surface and the solution). The mass transport processes mainly include diffusion, conduction, and convection, and should be taken into account if the electron-transfer reaction properties are to be extracted from the experimental measurements. The proper control of the mass transport processes seems to be one of the main problems of high-temperature electrochemical studies. [Pg.726]

The softening at high temperatures is related to thermally activated creep processes which are the subject of the next section. Deviations from stoichiometry produce constitutional defects which enhance diffusion and lead to softening at high temperatures, whereas at low temperatures these defects are immobile and act as strengthening deformation obstacles. These different effects of deviations from stoichiometry at low and high temperatures were studied in detail for binary NiAl (Vandervoort etal., 1966). [Pg.55]

The intensity auto-correlation method has long been in use at high temperature to study dynamics in solutions [88]. Intensity fluctuations can arise from spectral jumps or changes, from rotational or translational diffusion with respect to the exciting beam, and from any process which can modulate the emitted intensity. Since correlation of single molecule fluorescence works at liquid helium temperature as well as at room temperature (see Section 2.1), it probably can cover the whole intermediate... [Pg.139]

Even though the recently developed flowthrough YSZ(Hg/HgO) electrode can now be used at temperatures up to 400 °C, substantial effort is still needed to provide accurate laboratory-scale pH measurements to these extreme temperatures and to develop a ru ed version of this electrode for industrial applications. In addition, reliable estimation of the diffusion and other undesirable potentials is a serious challenge in high-temperature electrochemical studies. [Pg.2718]

The diffusion of Ge on (lll)Si at high temperatures was studied experimentally by means of second-harmonic microscopy. The results could be described by ... [Pg.87]

Accumulatory pressure measurements have been used to study the kinetics of more complicated reactions. In the low temperature decomposition of ammonium perchlorate, the rate measurements depend on the constancy of composition of the non-condensable components of the product mixture [120], The kinetics of the high temperature decomposition [ 59] of this compound have been studied by accumulatory pressure measurements in the presence of an inert gas to suppress sublimation of the solid reactant. Reversible dissociations are not, however, appropriately studied in a closed system, where product readsorption and diffusion effects within the product layer may control, or exert perceptible influence on, the rate of gas release [121]. [Pg.19]

Armijo [1198] has discussed a number of features of the kinetics and mechanisms of spinel formation. Under suitable conditions, the rates of some high temperature spinel syntheses can be studied gravimetrically [1199]. Holt [1180] has been concerned with the role of oxygen diffusion in CoA1204 formation. [Pg.268]

Laminar flame speed is one of the fundamental properties characterizing the global combustion rate of a fuel/ oxidizer mixture. Therefore, it frequently serves as the reference quantity in the study of the phenomena involving premixed flames, such as flammability limits, flame stabilization, blowoff, blowout, extinction, and turbulent combustion. Furthermore, it contains the information on the reaction mechanism in the high-temperature regime, in the presence of diffusive transport. Hence, at the global level, laminar flame-speed data have been widely used to validate a proposed chemical reaction mechanism. [Pg.44]

The fractal behavior of diffusion trajectories of ions has been studied in the molten phase of Agl as well as in the a-phase. The Devalues for an MD system with 250 Ag and 250 I" at 900 K were calculated from Fig. 21 to be 2 and 2.17, respectively. The mean-square displacements are shown in Fig. 22 in comparison with those of the a-phase at 670 K. As results of supplementary MD simulations, these authors obtained Dj = 1 for Ag and D = 2.17 at 1000 K and Df = 2 for both ions at 2000 K. Thus, they have concluded that (1) at an extremely high temperature above the melting point, the system is in a completely liquid state, which leads to a... [Pg.166]


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