Oxygen dissolution rate

Lopes De Figueiredo, M. M. and P. H. Calderbank, "The Scale-Up of Aerated Mixing Vessels for Specified Oxygen Dissolution Rates," Chem. Eng. Sci. 34 (1979) 1333-1338. 

Figueiredo, M.M.L.d., and Calderbank, P.H. (1979), The scale-up of aerated mixing vessels for specified oxygen dissolution rates, Chemical Engineering Science, 34 1333-1338. 

Damjanovic A, Bockris JO M. 1966. The rate constants for oxygen dissolution on bare and oxide-covered platinum. Electrochim Acta 11 376-377. 

The scheme in Fig. 5.5 indicates that the ligand, for example, oxalate, is adsorbed very fast in comparison to the dissolution reaction thus, adsorption equilibrium may be assumed. The surface chelate formed is able to weaken the original Al-oxygen bonds on the surface of the crystal lattice. The detachment of the oxalato-aluminum species is the slow and rate-determining step the initial sites are completely regenerated subsequent to the detachment step provided that the concentrations of the reactants are kept constant, steady state conditions with regard to the oxide surface species are established (Table 5.1). If, furthermore, the system is far from dissolution equilibrium, the back reaction can be neglected, and constant dissolution rates occur. 

The dissolution of quartz is accelerated by bi- or multidentate ligands such as oxalate or citrate at neutral pH-values. The effect is due to surface complex formation of these ligands to the Si02-surface (Bennett, 1991). In the higher pH-range the dissolution of quartz is increased by alkali cations (Bennett, 1991). Most likely these cations can form inner-spheric complexes with the =SiO groups. Such a complex formation is accompanied by a deprotonation of the oxygen atoms in the surface lattice (see Examples 2.4 and 5.1). This increase in C H leads to an increase in dissolution rate (see Fig. 5.9c). 

Fig. 5. Plot showing the effect of radiation field intensity on U02 dissolution rate (data extracted from Christensen Sunder 1996). Dissolution rates were obtained by electrochemical measurements. A significant enhancement in the reaction rate is observed with dose and in the presence of oxygen.

Eq. (9.32) predicts that the the mass-transfer coefficient for the oxygen dissolution in water 25°C in a mixing vessel is 4.58 x lO m/s, regardless of the power consumption and gas-flow rate as illustrated in the previous example problem. Lopes De Figueiredo and Calderbank (1978) reported later that the value of kL varies from 7.3 x 10"4 to 3.4 x 1CT3 m/s, depending on the power dissipation by impeller per unit volume (Pm/v) as... 

W. H. Casey and H. R. Westrich, Control of dissolution rates of orthosilicate minerals by divalent metal-oxygen bonds, Nature 355 157 (1992). 

In the presence of oxidizing species (such as dissolved oxygen), some metals and alloys spontaneously passivate and thus exhibit no active region in the polarization curve, as shown in Fig. 6. The oxidizer adds an additional cathodic reaction to the Evans diagram and causes the intersection of the total anodic and total cathodic lines to occur in the passive region (i.e., Ecmi is above Ew). The polarization curve shows none of the characteristics of an active-passive transition. The open circuit dissolution rate under these conditions is the passive current density, which is often on the order of 0.1 j.A/cm2 or less. The increased costs involved in using CRAs can be justified by their low dissolution rate under such oxidizing conditions. A comparison of dissolution rates for a material with the same anodic Tafel slope, E0, and i0 demonstrates a reduction in corrosion rate... 

Oxide dissolution in aqueous electrolytes involves transfer of metal and oxygen ions to the solution. Since O2- ions cannot be transferred into the solution, protonation must precede the ion transfer reaction, which leads to strongly pH-dependent dissolution rates [37], The cation and oxygen transfer reactions may be regarded as statistically independent with... 

Activation control of an overall dissolution rate can, of course, reside in the reduction process, in the oxidation process, in a mixture of both, or in a mixture including some transport control. The reduction process is usually more influential in determining the overall rate. Thus, in the absence of transport control, the kinetics of the electrode process for reduction of hydrated protons, or water molecules, or dissolved molecular oxygen plays the major role in metal dissolution kinetics. Indeed the literature confirms the conclusion that many of the systems seen in experiment or in practice are diffusion controlled that most of the rest are under mixed diffusion and activation control and that those with some activation control... 

The kinetics of the reaction of germanium with dissolved oxygen can be related to the surface structure. Thus it was found (2) that the dissolution rates for the three principal low-index planes vary in the order of the densities of dangling bonds as shown in Fig. 4 and Table I. It was speculated that the intermediates Ge-OH and Ge-C H are formed on the surface during dissolution. Orientation effects have also been observed in fast etching media (4), although high rates usually mask relatively small differences due to orientation. 

Fig. 5. Specific effects of halogen ions on the dissolution rate of Ge in oxygen-saturated solutions of potassium salts at 30°C and pH 6. The anion molarities have been corrected for additions of die corresponding acids in pH adjustments. The experimental points for KC1 are omitted for clarity (2).

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