Applications of the scanning electron microscope to oxide surfaces

Castle, J. E.; Masterson, H.G.

doi:10.1108/eb006753

Cited by 4 publications

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“…Scanning electron microscopy (13) has provided micrographs of hematite platelets a few microns thick and about 1O~ across. These platelets grew in many orientations on mild steel in a 7-hr oxidation in 13% sodium hydroxide solution at 300~ and also by anodic polarization in sodium hydroxide solutions.…”

Section: Juzy Lg68mentioning

confidence: 99%

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Selected Area Electron Diffraction Study of Twinned α-Fe[sub 2]O[sub 3] Bladelike Platelet Growths on Iron

Tollman

Gulbransen

1968

J. Electrochem. Soc.

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The structure of α‐Fe2O3 bladelike platelets formed on iron at 450 °C in atmospheres containing both water vapor and a trace of oxygen was studied. Single crystal electron diffraction patterns show the blade axis to be false[true1¯true1¯20false] . The collection of all of the patterns indicates a structure of twinned crystals whose orientations are related by mirroring on the blade face plane, false(true1¯101false) . Arguments are presented in favor of a growth mechanism involving the diffusion of iron atoms or ions along the twin interface to the tip, where reaction occurs with oxygen.

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Section: Juzy Lg68mentioning

confidence: 99%

“…3, 4, and 5. The axis of the blades was found to be [710], i.e., [11][12][13][14][15][16][17][18][19][20] and [101] in the conventional structural hexagonal and rhombohedral systems, respectively. This axis is the fiber axis of the fiber texture patterns from surfaces with dense growths of blades.…”

mentioning

confidence: 99%

Selected Area Electron Diffraction Study of Twinned α-Fe[sub 2]O[sub 3] Bladelike Platelet Growths on Iron

Tollman

Gulbransen

1968

J. Electrochem. Soc.

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“…The SEM is ideal for examining and, with the probe attachment, analysing very thck breakaway oxide scales. A fracture section (Castle & Masterson, 1966) through breakaway oxide on Fe-I00/b chromium alloy (Fig. 4a) shows whiskers Fig.…”

Section: Methods For Thick Filmsmentioning

confidence: 99%

Metal oxide structure investigated using a variety of light‐ and electron‐microscopical techniques*

Fursey

1971

Journal of Microscopy

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SUMMARY Special techniques for examining the same specimen area of metal oxides with different instruments, for example light microscopy and scanning electron microscopy of identical features are described. Transmission electron microscopy and diffraction on stripped oxide films have been augmented by electron‐probe microanalysis both in a conventional microanalyser and in a combined electron‐microscope microanalyser EMMA‐4. Examples of scanning electron microscopy of oxidized sheet‐metal specimens and stripped films are given and probe analysis in the Stereoscan is illustrated. High‐voltage electron microscopy of oxide nodules reveals additional detail. Techniques for examining thick oxide scales are also described. The illustrations are taken from the oxidation of iron 10% chromium alloy at 500−600°C in air.

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“…Parabolic weight-gain kinetics are then restored and the cycle begins anew. There are many indications of such scale rupture effects in the literature (2,4,27,(21)(22)(23)(24)(25)(26)(27)(28)(29)(30).…”

Section: Table II Comparison Of Experimental Vs Calculated Kpmentioning

confidence: 99%

Effects of Scale Porosity, Second-Phase Oxides, and Doping in the High-Temperature Oxidation of Cobalt and Dilute Cobalt-Chromium Alloys

Billman

1972

J. Electrochem. Soc.

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The oxidation mechanisms of high-purity cobalt and dilute Co-Cr alloys have been investigated over a 950~176 temperature range in oxygen atmospheres of 10-760 Torr. The 99.999% cobalt exhibited parabotic oxlaation behavior for weight gains of up to 30 mg oxygen/em 2 rectangular specimen surface. Parabolic kinetics were interrupted when fissures developed in the oxide scale as a result of mechanical stresses at the metal/scale interface or through anisotropic decomposition along CoO grain boundaries. Molecular oxygen then short-circuited to the porous inner scaling layer in accelerated attack of fresh Co surfaces. Diffusion of Co 2+ through the CoO scale is considered to be the primary rate determining process during periods of steadystate oxidation. The effect of porosity at the metal/scale interface prior to perforation of the outer scaling layer is slight, but is believed to result in a small reduction of the oxidation rate due to a reduction in the CoO/Co contact surface through which cations enter the oxide. Co alloys containing 0.5, 3, 7, and 10 w/o (weight per cent) Cr also obey parabolic kinetics during formation of thinner scaling layers. Porosity and localized loss of scale adherence are aggravated by the presence of CoCr204 and Cr203 particles in the inner scaling layer to the extent that scale rupture mechanisms quickly obscure parabolic kinetics for chromium contents greater than 3 w/o at temperatures of 1150~ and above in 100 Torr oxygen. Under conditions where initial periods of steady-state parabolic oxidation were discernible on thermobalance curves, maximum reaction kinetics are associated with 1-2 w/o Cr additions (which approach the Cr 3+ solubility limit in CoO) as rationalized by Wagner's semiconductor valence theories.Previous oxidation studies of high-purity cobalt have been reported in the literature (1-8). Linear kinetics are observed during the growth of very thin oxide films, with a subsequent transition to parabolic growth kinetics for thicker oxide layers. At elevated temperatures CoO is a metal deficient, p-type semiconductor (9, 10) and the electrical conductivity of CoO at near atmospheric pressures, where singly charged cation vacancies supposedly predominate (9), is proportional to Po21/4 (9, 10). The self-diffusion of Co in CoO is reported to be proportional to Po2 lln, where n varies from values of ~-.4 at 10-8 atm to --3 at 1 atm oxygen over a 950~176 temperature range (11). The parabolic rate constant for the high-temperature oxidation of cobalt has also been reported to obey a Po21/n dependence where 4 > n > 3 (1-4). Parabolic oxidation of cobalt is rationalized according to the Wagner theory (12). Cobalt cations diffuse from the metal/oxide interface via cation vacancies in the oxide lattice to combine with oxygen at the oxide/gas interface and cation diffusion through the oxide is considered to be the rate-controlling process.Incremental additions of chromium have been reported to increase the Co-Cr alloy oxidation rate to a maximum value at approximately 10 w/o (weight pe...

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Applications of the scanning electron microscope to oxide surfaces

Cited by 4 publications

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Selected Area Electron Diffraction Study of Twinned α-Fe[sub 2]O[sub 3] Bladelike Platelet Growths on Iron

Selected Area Electron Diffraction Study of Twinned α-Fe[sub 2]O[sub 3] Bladelike Platelet Growths on Iron

Metal oxide structure investigated using a variety of light‐ and electron‐microscopical techniques*

Effects of Scale Porosity, Second-Phase Oxides, and Doping in the High-Temperature Oxidation of Cobalt and Dilute Cobalt-Chromium Alloys

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