Oxide formation rate

If a silicon electrode is anodically oxidized in an acidic electrolyte free of HF, the oxide thickness increases monotonically with anodization time. This is also true for alkaline electrolytes if the oxide formation rate exceeds the slow chemical dissolution of the anodic Si02. This monotonic behavior, however, is not necessarily associated with monotonic current-time or potential-time curves. 

Figure 9.66 Oxide formation rate of long-lived radionuclides as a function of rf power (a) and carrier gas flow rate (b) measured in a concrete matrix by LA-ICP-MS. (]. S. Becker, C. Pickhardt and H. j. Dietze, Int. f Mass Spectrom., 203, 283(2000). Reproduced by permission of Elsevier.)...

On the other hand, when dr dd < drjdd, the oxide formation rate is capable of keeping up with the change of the oxide film thickness due to the change of the dissolution rate. Current oscillation will not occur by a perturbation in the system. The variation in the occurrence of oscillation, oscillation amplitude, and frequency with respect to conditions can be further detailed by analyzing the two functions /-a -J AVId) and tb =/([F], pH, AV/d,... 

Lehmann and Baerns [18] have reported different reaction rate expressions based on a number of mechanisms to predict the hydrocarbon formation rate and carbon oxide formation rate in terms of PcH4 nd PQ2- None of the earlier studies included the dependence of R2 and Rj on Pc02- and co-workers [19] developed expressions for RcH4 function... 

Under steady state reaction conditions, the effects of CO2 on the methane coupling reaction over Li/MgO catalyst were quantitatively determined. Poisoning effects of CO2 on carbon oxide formation rate, C2 formation rate, and methane conversion were observed for all methane to oxygen ratios and all temperatures. However, C2 selectivity is relatively unaffected by CO2 partial pressure. The mechanism described here accounts for important elementary steps, especially the effects of carbon dioxide. Under the low conversion conditions used in this study, further oxidation of C2 products to CO and CO2 is assumed negligible. These reactions will become more important at high conversions. Rate expressions derived from the mechanism match well the experimental conversions and selectivities. 

The detailed variation in reaction rate with reactant pressures and surface composition has been examined at 200 and at 400 °C. The production of N 2 coincided quantitatively with the intensity of the AES N (390 V) peak the NO production rate correlated well with the intensity of the AES O (510 V) peak. At 200 °C the rate of nitrogen formation was first order in oxygen pressure but independent of NH3 pressure. Conversely at 400 °C the nitric oxide formation rate was first order in ammonia pressure above 4 x 10 Torr. Desorption experiments during the reaction proved the surface species were N atoms and O atoms respectively. 

FIGURE 12.6 Deactivation versus the amount of propene oxide produced during the propene epoxidation over 1 wt.% Au/Ti02. 0 propene oxide formation rate A water formation rate/10. [0.3 g of catalyst, 50 Nml/min gas feedrate (10% H2, O2, and propene), total pressure 1.1 bar(a).]... 

The increase of 0/Pts with increasing temperature is explained by the formation of subsurface Pt0x. The oxide formation rate is structure sensitive it forms at appreciable rates only for highly dispersed Pt such as that used in this study. 

The anisotropy of the oxide formation rate was used to convert the cross-sectional shape of macropores in (lOO)-oriented Si wafers from rounded square to circular upon an increase in their diameter via removal of the sacrificial Si02 layers (Trifonov et al. 2007). Figure 2 presents the results for a sample subjected to 11 cycles of oxidation in dry oxygen at 1,100 °C for 1 h. Note that the tendency toward pore rounding due to the oxidation rate anisotropy is enhanced by the oxidation retardation on the concave surface at square comers. 

Figures 18a and b. Dependence of carbon oxide formation rate on methane and oxygen partial pressures.

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