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Mechanical behavior, oxide scales

D. L. Douglass, Exfoliation and the mechanical behavior of scales. In Oxidation of Metals and Alloys, ed. D. L. Douglass, Metals Park, OH, ASM, 1971. [Pg.160]

Long-term exposure of composites to oxidative environments can have deleterious effects on short-term mechanical behavior, such as resistance to crack initiation. This is particularly true in the case where the composite oxidizes to form an oxide surface scale. Although such reactions can be beneficial in limiting oxidation reactions, when the composite is subsequently cooled to room temperature, the reaction product can be a source of flaws and increase the composite s susceptibility to crack initiation. The following example illustrates this point. [Pg.284]

Hydrogen permeation tests on ferritic stainless steels indicated that hydrogen can diffuse through the alloys, though the permeation was drastically decreased by formation of chromia scale on the alloys. - The mechanisms by which the presence of hydrogen or protons at the air side affects the oxide scale structure and growth are not clearly understood at this time. Several mechanisms have been proposed to tentatively explain the observed anomalous oxidation behavior. ... [Pg.238]

Example 1 Swan and O Meara " compared the creep for Si3N4 with and without SiC whisker reinforcements. Creep mechanisms, phase content, whisker distribution, grain boundary crystallinity, and oxidation behavior were studied using TEM and X-ray diffraction (XRD). Figure 10.4 shows a TEM micrograph of an oxide scale on a whisker. The oxide scale contained Si2N20 and other crystalline phases in an amorphous layer. No improvement was found for the creep behavior of the composite over the unreinforced Si3N4. [Pg.193]

If n = 1/2, a parabolic behavior of nonporous, adherent, and protective scale develops by diffusion mechanism. Thus, 1 < PB < 2 and Ae mechanism of sc growth is related to metal cations diffusing through the oxide scale to react with oxygen at the oxide-gas interface. [Pg.319]

As already mentioned, mechanical scale failure takes place when a critical stress level Of. is reached. This critical stress level can be converted into a critical strain fij. by simply dividing the stress by the Young s modulus Ox if it is assumed that elastic behavior dominates in scale failure. Strain values are better suited for discussion than stress values, as they can easily be determined by experiments. Therefore the following discussion, which is covered in more detail in the literature (Schiitze, 1995), will be based on critical strain values for failure of the oxide scales. Generally, two failure cases are conceivable depending on the stress situa-... [Pg.97]

The electrode processes on the voltammetric and the preparative electrolysis time scales may be quite different. The oxidation of enaminone 1 with the hydroxy group in the ortho position under the controlled potential electrolysis gave bichromone 2 in 68% yield (Scheme 4.) with the consumption of 2.4 F/mol [21], The RDE voltammogram of the solution of 1 in CH3CN-O.I mol/1 Et4C104 showed one wave whose current function, ii/co C, was constant with rotation rates in the range from 1(X) to 2700 rpm and showed one-electron behavior by comparison to the values of the current function with that obtained for ferrocene. The LSV analysis was undertaken in order to explain the mechanism of the reaction which involves several steps (e-c-dimerization-p-deamina-tion). The variation of Ep/2 with log v was 30.1 1.8 mV and variation of Ep/2 with logC was zero. Thus, our kinetic data obtained from LSV compare favorably with the theoretical value, 29.6 mV at 298 K, for a first order rate low [15]. This observation ruled out the dimerization of radical cation, for... [Pg.94]

The complexity of the system implies that many phenomena are not directly explainable by the basic theories of semiconductor electrochemistry. The basic theories are developed for idealized situations, but the electrode behavior of a specific system is almost always deviated from the idealized situations in many different ways. Also, the complex details of each phenomenon are associated with all the processes at the silicon/electrolyte interface from a macro scale to the atomic scale such that the rich details are lost when simplifications are made in developing theories. Additionally, most theories are developed based on the data that are from a limited domain in the multidimensional space of numerous variables. As a result, in general such theories are valid only within this domain of the variable space but are inconsistent with the data outside this domain. In fact, the specific theories developed by different research groups on the various phenomena of silicon electrodes are often inconsistent with each other. In this respect, this book had the opportunity to have the space and scope to assemble the data and to review the discrete theories in a global perspective. In a number of cases, this exercise resulted in more complete physical schemes for the mechanisms of the electrode phenomena, such as current oscillation, growth of anodic oxide, anisotropic etching, and formation of porous silicon. [Pg.442]


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See also in sourсe #XX -- [ Pg.135 ]




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Mechanical behavior

Oxidation behavior

Oxidative behavior

Oxide scales scale

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