Cyclic oxidation kinetics

Fig. 2. Schematic diagrams showing the cracking and spalling of an oxide layer, which often occurs on cooling from the oxidation temperature and comparing the isothermal and cyclic oxidation kinetics.

Fig. 5. Plot of mass change versus time indicating the effect of sulfur content on the cyclic oxidation kinetics of two single-crystal, nickel-base superalloys at 1100°C [12].

Fig. 7. Cyclic oxidation kinetics of NiAl, containing various oxide dispersions, in air at 1200"C [25].

Fig. 22. Oxide map showing the regions of Cr and A1 contents which form external alumina scales in air at various temperatures (left) and cyclic oxidation kinetics forTi-Cr-Al alloys over a range of compositions for exposures in air at 1000°C (right).

Cockeram and Rapp have evaluated the kinetics of silicide coatings on Ti [103] and have used a halide-activated pack-cementation method to form boron- and germanium-doped silicide coatings on orthorhombic alloy substrates [104]. The coatings greatly decreased the cyclic oxidation kinetics and microhardness measurements did not indicate diffusion of oxygen into the substrate. 

Figure 5.39 Cyclic oxidation kinetics for several Fe-Cr-Al alloys exposed at 1100°C.

Figure 10.23 (a) Cyclic oxidation kinetics of a sputtered Ti-Cr-Al coating on y-TiAl at 900 °C and (b) a cross-section of the coating after exposure. 

Figure 8.9 Cyclic oxidation kinetics (expressed in terms of specific mass change versus number of cycles) for a normal-S and a low-S superalloy in dry air and air...

D. Poquillon and D. Monceau. Application of a Simple Statistical Spalling Model for the Analysis of High-Temperature, Cyclic-Oxidation Kinetics Data. Oxidation of Metals, 59(3/4) 409 31, 2003. 

Cyclic oxidation kinetics of Ti3SiC2 oxidized at 1100°C in air. The inset shows a cross-sectionai micrograph of a sampie after 360 cycies. 

Kroutil, W., and Faber, K. 1998. Deracemization of compounds possessing a sec-alcohol or -amino group through a cyclic oxidation-reduction sequence a kinetic treatment. Tetrahedron Asymm., 9(16), 2901-2913. 

In some cases a measure of the reaction kinetics is not as useful as a measure of the useful life under a given set of experimental conditions. Cyclic oxidation tests using weight-change versus time measurements and visual examination of exposed specimens can be useful to determine times beyond which protective scales, such as alumina, are no longer formed on alloy test coupons. 

Temperature-programmed oxidation (TPO) is an equally valuable technique for investigating the oxidation kinetics and mechanisms of reduced materials. The cyclic application of TPR and TPO provides information on the redox behavior of catalytic materials, for example, of catalysts for selective catalytic oxidations. 

Based on this concept, electrochemical oxidative kinetic resolution of cyclic diol, aminoalcohol, or aminoaldehyde efficiently proceeded to afford optically active compounds (Scheme 11) [17]. 

Although not studied in detail, the cyclic oxidation behavior of MoSi2 (when not susceptible to pesting) seems fairly good (reviews by Doychak (1994) andTortorelli and DeVan (1996)). As shown in Fig. 6-43, oxidation rates at 4(X) and 450 °C are considerably less than at 500 °C, at which temperature linear kinetics (rate constant of 0.013 mg cm" h" ) are observed after an incubation period (Meschter, 1992). Increasing the temperature to 550-600 C re-... 

Figure 7-25. Cyclic oxidation weight change kinetics for several silica forming materials exposed in air at 1300 °C in 5 h cycles (Jacobson and Opila, 1999).

Oxidative kinetic resolution of a racemic mixture of cyclic 4-hydroxyisoleucine by an l-AAO originating from Crotalus... 

At least two other sources of background currents have been identified (6). These currents, which have been labeled kinetic and induced , arise only in the presence of the substance being electrolysed and, therefore, cannot be determined by experiments on the supporting electrolyte alone. The kinetic current is the result of a cyclic oxidation or reduction of the solvent by some chemical interaction with the products of the primary electrolysis process. In some cases this current may be potential dependent and could be minimized by proper choice of the potential of the working electrode. The situation is complicated by the fact that this kinetic current will vary during the course of the electrolysis and will also be a function of the total amount of material being electrolysed. 

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