Cyclic-oxidation behavior

Fig. 8. Effect of sulfur content on the cyclic oxidation behavior of NiAl. The as-received material contained 20ppmw S and the sulfur content of the hydrogen annealed material was calculated to be less than 1 ppmw.

F re 5-4. The effect of addition of yttrium (100-150 ppm) or desulfurizing pre-treatment (hydrogen anneal at 1280 C for 100h) on the 1150°C cyclic oxidation behavior of the cast, Ni-base superalloy Ren N5 (Smialek et al., 1994). 

Figure 5-20. (a) Long-term cyclic oxidation behavior of alloys 230, HR-120, and 800HT in air at 982 C (1 cycle = 30 days) and (b) corresponding variation in the surface chromium content of the three alloys as a function of exposure time (courtesy of Haynes International). 

In agreement with Eq. (5-29), Barrett and Lowell (1975) concluded from their study of the cyclic oxidation behavior of various commercial alloys at 1150 °C that the most critical factor in minimizing scale spallation is to keep the scale as thin as possible. They reported that Cr203-forming alloys with the most complex compositions tend to spall the most owing to the formation of thicker scale products. 

Barrett, C. A. (1997), 10,000-Hour Cyclic Oxidation Behavior at 982 °C 1800 °F) of 68 High-Temperature Co-, Fe-, and Ni-Base Alloys, Technical Memorandum 107394. Washington, DC National Aeronautics and Space Administration. 

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-... 

Barrett, C. A., The Effects of Cr, Co, Al, Mo and Ta on the Cyclic Oxidation Behavior of a Prototype Cast Ni-Base SuperaUoy Based on a 26 Composite Statistically Designed Experiment, in Conference on High Temperature Corrosion Energy Systems, Detroit, The Metallurgical Society/AIME, 1984, pp. 667-680. 

Ren C, He YD, Wang DR. Cyclic oxidation behavior and thermal barrier effect of YSZ-(Al203/YAG) double-layer TBCs prepared by the composite sol-gel method. Surface Coatings Technology. 2011 206 1461-1468. 

K. N. (2001), Cyclic Oxidation Behavior of Aluminide Coatings on the Co-Base Superalloy DZ40M , Surf. Coat. TechnoL,Vol. 145, pp. 75-79. 

Gleeson B and Harper M A (1998), The Long-Term, Cyclic-Oxidation Behavior of Selected Chromia-Forming Alloys, Oxid Met, 49, 373-399. 

Fig. 15. Compaiison of MoSi and othei intermetaUics and supeiaUoys (a), isothermal and (b), cyclic oxidation (1200°C) behavior (80).

Studies of the linear sweep and cyclic voltammetric behavior of N-methyl-ated xanthines 35 -37> reveals that they undergo electrochemical oxidation over a fairly wide pH range at the PGE (Table 1). All but three of the xanthines studied show just a single voltammetric oxidation peak, although it is prob-... 

Cyclic voltammetry, square-wave voltammetry, and controlled potential electrolysis were used to study the electrochemical oxidation behavior of niclosamide at a glassy carbon electrode. The number of electrons transferred, the wave characteristics, the diffusion coefficient and reversibility of the reactions were investigated. Following optimization of voltammetric parameters, pH, and reproducibility, a linear calibration curve over the range 1 x 10 6 to 1 x 10 4 mol/dm3 niclosamide was achieved. The detection limit was found to be 8 x 10 7 mol/dm3. This voltammetric method was applied for the determination of niclosamide in tablets [33]. 

Fig. 3 Cyclic voltammetric behavior of the Cu(ll) complex with [14]aneS4 (LBI) as a function of temperature in 80% methanol (by weight) illustrating the effect of Scheme 1 upon the electron-transfer behavior. At 25 °C (curve A) and at 0 °C (curve B) a reversible voltammogram is observed in which the cathodic peak (I) represents the reduction of equilibrated O and Q and the anodic peak (II) represents the oxidation of equilibrated P and R. As the temperature is lowered to —23 °C (curve C), a second oxidation peak (III) appears at a more positive potential representing the direct oxidation of R to...

Owing to its stability, solubility, and highly reproducible oxidation behavior, ferrocene has long been used as an electrochemical standard in nonaqueous solvents. Not surprisingly, the electron-donor or -acceptor properties of ring substituents in ferrocenes and other metallocenes have been repeatedly evaluated with electrochemical techniques. Measurements have been obtained using polarography,150 cyclic voltammetry (CV),151 chronopotentiometry,152 photoelectron spectroscopy, 53 and Fourier transform ion cyclotron resonance mass spectrometry.154 Extensive compilations of such data are available.155 156 Historically, variations of oxidation potentials have been discussed almost solely in terms of the... 

As an illustrative example of the influence of homogeneous reactions on the cyclic voltammetric behavior, the oxidation of an anion R to the corresponding short-... 

Figure 7-26 shows the cyclic voltammetric behavior of ferrocenylruthenocene 1 in acetonitrile solution [89]. It undergoes an initial, reversible, one-electron oxidation at a potential that is almost coincident with that of ferrocene, followed by two closely spaced, one-electron steps, with features of transient chemical reversibility. If one considers that ruthenocene undergoes an irreversible, single-step two electron oxidation, it appears that conjugation with ferrocene tends to stabilize the ruthenocenium cation fragments. This could be attributed to the steric hindrance afforded by the ferrocenyl fragment, which prevents rapid dimerization (followed by... 

Two successive C-S bond cleavages at the cation radical stage are suggested, the result of the first one being supposedly structure XXXVIII, which is followed by a homo-lytic dissociation to produce cation radical XXXIX. This can be oxidized to form XL. Product XXXIX was identified by comparison of its cyclic voltammetric behavior with that of tetrathioethylene, and by electron spin resonance (ESR) spectroscopy. 

The peptide fragments of metalloth-ioneins Lys-Cys-Thr-Cys-Cys-Ala [56-61] (FT) were studied by different electrochemical techniques. The cyclic voltammetric behavior of the peptide fragment in the presence of Cd(II) indicated two reversible electrochemical processes due to the oxidation of the mercury electrode in the presence of CdFT and reduction of CdFT complex, both from the dissolved and adsorbed state [105]. The influence of the experimental conditions on electroreduction of Cd-metallothioneins... 

Figure 3. (a) Comparison of cyclic oxidation (in static air) behavior of 4 alloys as indicated, (b) Influence of temperature of oxidation. 

The formation of a blocking film on an electrode surface will decrease the capacitance compared to that of the bare electrode, since the distance of closest approach of the counter ions, d, will be increased by the thickness of the layer [see (13.3.2) and Figure 14.5.5]. The extent of blocking by the monolayer and the presence of pinholes can be assessed in a number of ways (88). To obtain the aggregate area of the pinholes one can, for example, compare the sizes of voltammetric peaks for the bare and filmed electrode (such as those for the formation and reduction of an oxide layer on Au). To obtain the spatial distribution, one can deposit a metal like Cu, then strip the film and perform microscopy on the resulting surface. A frequently used procedure is to observe the chronoamperomet-ric or cyclic voltammetric behavior of an outer sphere species like Ru(NH3) in solution... 

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