Oxide layers micrographs

In an optical micrograph of a commercially available nitinol stent s surface examined prior to implantation, surface craters can readily be discerned. These large surface defects are on the order of 1 to 10 p.m and are probably formed secondary to surface heating during laser cutting. As mentioned above, these defects link the macro and micro scales because crevices promote electrochemical corrosion as well as mechanical instability, each of which is linked to the other. Once implanted, as the nitinol is stressed and bent, the region around the pits experiences tremendous, disproportionate strain. It is here that the titanium oxide layer can fracture and expose the underlying surface to corrosion (9). 

Fig. 7 (a) Catechol derivatized tetracenes self-assemble on metal oxide surfaces such as aluminum oxide, (b) Schematic and (c) scanning electron micrographs of FET structures fabricated with a 5-nm aluminum oxide layer on top of a 5-nm thermally oxidized Si wafer to allow self-assembly of the derivatized tetracene between sub-100 nm Au source and drain electrodes, (d) /d-Eds characteristics of the assembled tetracene monolayer FET for a 40 nm channel length showing hole modulation and (inset) an atomic force microscope image of the FET channel... 

Fig. 9. A transmitted electron micrograph of an ultramicrotomed section of an aluminum-epoxy interphase. The highly ordered structure in the center is a 3.3 micron thick aluminum oxide layer present on the base metal. The featureless area is the epoxy matrix. The light areas within the oxide are fractures caused by the microtoming. The epoxy has however penetrated to the bottom of all of the 50 nm pores in the oxide...

Figure 11. High resolution TEM micrographs of oxide layers on stepped Si substrate a, native oxide b, 1000 thick oxide thermally grown on Si surface 3° off (111) toward [llO] (dry O2, 1000 °C), structural steps are clearly resolved and c, model of the stepped Si surface. (Adapted from Ref. 18.)...

Figure 1 represents a bright field TEM micrograph of a cross-section of the NiAI/ox-ide interface after the NiAl was oxidized in air at 950 °C for 0.1 h.The oxide scale was observed to be a 40 - 50 nm thick layer all along the NiAl surface. The scale contains many planar defects, possibly twin boundaries. Faceted 200 - 300 nm voids were observed with their facets parallel to (OOl)NiAl and (011 )Ni A1 planes. A thin oxide layer was found at the facetted metal surfaces of some of these voids. 

Figure 2-7. HREM images of clean lanthana (a), and the corresponding aged-in-air oxide (b). Micrograph (b) is consistent with the existence of a nucleus of hydroxide surrounded by a thin layer of heavily disordered hydroxycarbonate-like phase.

Figure 7.14 Optical micrograph showing an example of grain-boundary penetration by eutectic liquid in the Ni-S-O system following penetration of a preformed oxide layer by SO2 at 1000 °C.

As can be seen, the corrosion rates (as measured by corrosion current density) in biotic cases show an increase in comparison with the abiotic environment. Also, it can be seen from the SEM micrographs that while in abiotic environment the oxide layer on carbon steel is almost intact, it has been cracked and pitted (Figure 4.24c) in the biotic environments. These findings may strongly suggest that lOB are indeed very corrosive and thus must be taken care of when they exist in a system. 

Rgure 10.6 SEM micrographs used to measure oxidized layer thickness (a) 20% SiCw and (h) 30% SiCwL ... 

The microstructure and thickness of the oxide layers formed after exposure to atmospheric air at 1400 C was studied for both ZS and ZSC samples, which were cut and polished for observation in the SEM. Figure 6 shows a micrograph and compositional maps for a ZS sample annealed for 1 hour. The outer. Si and O rich layer can be concluded to be SiOi, while the intermediate layer, which is O rich and B poor, is Zr02. Similar conclusions can be drawn from Figure 7, which represents compositional maps for a ZSC sample annealed for 24h. Again, the outer layer is mainly composed of Si02, and an intermediate layer of ZrO separates the fonner layer and the bulk interior of the sample. 

Posttest exarrrirratiorts included deterrrrirration of weight loss and SEM/EDS exarrrirration of the steel surface. A typical SEM micrograph of the corroded surface is displayed in Fig. 55. The form of attack was observed to be scaling with sections where it was apparent that exfoliation had occurred (Fig. 55b), as observed in other studies. " The exfoliated material is almost certainly the outer layer, which from passivity theory forms via the hydrolysis of cations (Fe ) that are trarrsmitted as cation irrterstitials across the barrier oxide layer from the metal/barrier layer interface to the barrier layer/outer layer (solution in the pores of the outer layer) to... 

The SEM micrographs of the surface and fractured surface of the specimen after oxidation for 10 min are shown in Figure 26. The entire surface was covered with a dark glass layer the EDS analysis confirmed that the surface of the specimen was primarily composed of silicon and oxygen, which indicates a Si02-rich layer. A small quantity of zirconium was measured by EDS in the oxide layer, which revealed that a partial Zr02 phase was covered by the thin Si02-rich layer. 

Figure 27a displays a SEM micrograph of the surface of the specimen after oxidation for 25 min. The entire surface was covered with a dark SiO -rich layer and a white Zr02 phase was not detected, which revealed that the thickness of the Si02-rich layer increased as the oxidation time increased. Distinct pores were observed under high magnification, as shown in the insert in Figure 27a. These pores act as diffusion channels to the outer layer for gaseous products and as diffusion channels into the substrate for oxygen. Figure 27b includes a SEM micrograph of the fractured surface of the specimen, whose measured thickness of the oxide layer was 28 pm, after oxidation for 25 min. Compared with the fractured surfaces of the...

The bubbles tended to burst when the vapor pressure of the huhhles exceeded the sum of the ambient pressure and the tensile force of the oxide layer this condition resulted in the presence of pores on the surface of the oxidized specimen. Figure 28b displays a SEM micrograph of the fractured surface of the specimen after oxidation for 40 min, for which a thickness of 40 pm was measured for the oxide layer. The increased thickness of the oxide layer was attributed to the increased oxidation time and the presence of pores. The quantity of pores increased due to further active oxidation of the SiC phase. 

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