Examination of oxide scales in the SEM using backscattered electron images

Price, C.W.; Wright, I.G.; Wallwork, G. R.

doi:10.1007/bf02669385

Cited by 9 publications

(7 citation statements)

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“…Therefore, three different samples with added SiO 2 or Sb 2 O 3 , which are widely used additives for ZnO varistors, as well as both Sb 2 O 3 and SiO 2 added simultaneously to the basic varistor were prepared and the form of the Bi 2 O 3 deposit on the surface of grain boundary fracture of ZnO was investigated. It was confirmed using EDS that all additives added further to the basic varistor coexisted with Bi at grain boundaries or triple points . Moreover, it has been reported that the size of a ZnO grain becomes smaller by the addition of Sb 2 O 3 .…”

Section: Resultsmentioning

confidence: 76%

“…It has been reported that the orientation of ZnO grains was prominently changed by adding 0.01 mol% Sb 2 O 3 to the basic varistor (see Fig. ) . The XRD patterns from the pressurized and side surfaces of Sample 5 are shown in Fig.…”

Section: Resultsmentioning

confidence: 88%

“…), and Sb 2 Zn 7 O 12 ‐type spinel particles, which makes Sb 2 O 3 the main ingredient (see Fig. ; hereafter spinel‐type particles); these are typical phases in ZnO varistors . The thin bismuth oxide layer at the grain boundaries is necessary to form a potential barrier for improving the varistor properties .…”

Section: Resultsmentioning

confidence: 99%

“…On the other hand, a high‐contrast compositional image can be easily obtained using the back‐scattered electron (BSE) mode in SEM, although a BSE detector does not allow quantitative analysis. This is because the emission efficiency of BSEs increases with increasing atomic number and the difference in back‐scattered electrons for each element is converted into a high‐contrast compositional image . Moreover, the resolution of a BSE detector is higher than that of EDS because the area of fluorescent X‐rays generated by electron irradiation is more widespread than that of BSEs.…”

Section: Introductionmentioning

confidence: 99%

“…This is because the emission efficiency of BSEs increases with increasing atomic number and the difference in back-scattered electrons for each element is converted into a high-contrast compositional image. 12 Moreover, the resolution of a BSE detector is higher than that of EDS because the area of fluorescent X-rays generated by electron irradiation is more widespread than that of BSEs. In a previous study, the microstructure of a polished surface of a ZnO varistor was observed macroscopically using a BSE detector with SEM.…”

Section: Introductionmentioning

confidence: 99%

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Relation Between Grain Boundary Structure and Electrical Degradation in Zinc Oxide Varistors

2012

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The electrical characteristics of zinc oxide (ZnO) varistors are closely correlated with the state of impurities, such as Bi2O3, at grain boundaries. To clarify the distributions of these impurities, the fracture surface of a Bi–Mn–Co–Sb–Si‐added ZnO varistor was observed and characterized using scanning electron microscopy, energy dispersive X‐ray spectrometry, and back‐scattered electron detection. It was found that depositing Bi2O3 as an additive yielded two different shapes, spot like and sheetlike, on the surface of the grain boundary fracture for the Bi–Mn–Co–Sb–Si‐added ZnO varistor. By the dissolution of SiO2 in Bi2O3, the surface tension of Bi2O3 decreased and the sheetlike Bi2O3 deposit increased, whereas the spot like Bi2O3 deposit decreased. Moreover, when the sample was annealed at 700°C, a compound of Bi and excess Zn formed a uniform thin deposit or moved to triple points, since the surface free energy (surface tension) decreased. The main factor responsible for the improvement in resistance to electrical degradation by the addition of SiO2 or by annealing is the increase in the surface area of the ZnO grains by the sheetlike deposit of Bi2O3, since this deposit hinders the movement of oxide ions or Zn2+ ions across the grain boundaries under an applied voltage.

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Section: Resultsmentioning

confidence: 76%

Section: Resultsmentioning

confidence: 88%

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Relation Between Grain Boundary Structure and Electrical Degradation in Zinc Oxide Varistors

2012

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Growth mechanisms of oxide scales on ODS alloys in the temperature range 1000–1100°C

Quadakkers

1990

Materials & Corrosion

118

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After a short overview of the production, microstructure and mechanical properties of nickel-and iron-based Oxide Dispersion Strengthened (ODS) alloys, the oxidation properties of this class of materials is extensively discussed. The excellent oxidation resistance of ODS alloys is illustrated by comparing their behaviour with conventional chromia and alumina forming wrought alloys of the same base composition.ODS alloys exhibit improved scale adherence, decreased oxide growth rates, enhanced selective oxidation and decreased oxide grain size compared to corresponding non-ODS alloys. It is shown, that these experimental observations can be explained by a change in oxide growth mechanism. The presence of the oxide dispersion reduces cation diffusion in the scale, causing the oxides on the ODS alloys to grow mainly by oxygen grain boundary transport. As oxilde grain size increases with time, the oxide growth kinetics obey a sub-parabolic time dependence especially in the case of the alumina forming iron-based ODS alloy.Die vorliegende Arbeit gibt zunachst eine kurze Ubersicht uber Herstellung, Mikrogefiige und mechanische Eigenschaften von oxiddispersionsverfestigten (ODS-)Legierungen auf Nickel-und Eisenbasis. AnschlieBend werden die Oxidationseigenschaften dieser Werkstoffgruppe ausfuhrlich diskutiert. Die hervorragende Oxidationsbestandigkeit von ODS-Legierungen wird aufgezeigt durch Vergleich derer Eigenschaften mit denen von konventionellen chrom-und aluminiumoxidbildenden Legierungen gleicher Basiszusammensetzung.Oxidschichten auf ODS-Legierungen unterscheiden sich von dcnen auf konventionellen, dispersionsfreien Legierungen insbesondere durch bessere Haftung, reduziertes Wachstum, verbesserte selektive Oxidation und feineres Korn. Es wird gezeigt , dal3 diese experimentellen Ergebnisse durch eine Anderung der Schichtwachstumsmechanismen gedeutet werden k8nnen. Die Oxiddispersionen bewirken eine Reduzierung dcs Kationentransports in der Deckschicht, so dal3 die Oxidschichtcn auf den ODS-Legierungen nahezu ausschliel3lich durch Sauerstofftransport iiber Oxidkorngrenzen wachsen. Da die OxidkorngroRe mit zunehmender Oxidationszeit zunimmt, gehorcht die Schichtwachstumskinetik, insbesondere bei den aluminiumoxidbildenden Eisenbasislegierungen, einem subparabolischen Zeitgesetz. Introductionlmreased efficiency of processes in chemical engineering and energy conversion can in many cases only be achieved if the process temperatures are increased. This requirement necessarily leads to the demand for metallic materials which allow the design of plant or engine components operating at high temperatures, often at high stresses in corrosive environments. Oxide dispersion strengthened (ODS) alloys are due to their unique combination of superior high temperature creep and corrosion resistance poitentially suitable construction materials for components which are subjected to hostile service conditions [1]. Especially in cases where component life is limited by corrosive attack, ODS alloys offer the possibility for significan...

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The Effect of Yttria Dispersions on the Growth Mechanisms and Morphology of Chromia and Alumina Scales

Quadakkers

Holzbrecher

Briefs

et al. 1989

The Role of Active Elements in the Oxidation Behaviour of High Temperature Metals and Alloys

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Examination of oxide scales in the SEM using backscattered electron images

Cited by 9 publications

References 4 publications

Relation Between Grain Boundary Structure and Electrical Degradation in Zinc Oxide Varistors

Relation Between Grain Boundary Structure and Electrical Degradation in Zinc Oxide Varistors

Growth mechanisms of oxide scales on ODS alloys in the temperature range 1000–1100°C

The Effect of Yttria Dispersions on the Growth Mechanisms and Morphology of Chromia and Alumina Scales

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