Thermal transformation of hydrated ferric oxide gel and preparation of ultrafine oxide

Rajendran, S.; Rao, V. Sitakara; Maiti, Himadri Sekhar

doi:10.1007/bf00543908

Cited by 14 publications

(5 citation statements)

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“…Naturally occurring and synthetic amorphous hydrated oxides of iron (III) subjected to thermal treatments in a variety of atmospheres have been well characterized (32)(33)(34)(35)(36). However, similar conditioning of thin passive oxide layers on iron has been little investigated (6,37).…”

Section: Discussionmentioning

confidence: 99%

Investigation of the Anodically Formed Passive Film on Iron by Secondary Ion Mass Spectroscopy

Murphy

Pou

Bockris

et al. 1984

J. Electrochem. Soc.

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This paper reports SIMS analysis of passive layers. Pure Fe disks are used in borate buffers of pH = 8.4. Preelectrolysis is carried out to remove trace impurities. Potential step control of the electrode is utilized. Two types of experiments are carried out. In one, passive layers are prepared and then exposed to chloride ions ~br various times. In the other, films are heated at various temperatures for preselected times. The passive layers subjected to these treatments are exposed to SIMS analysis. The distribution of OH-with depth, from SIMS analysis, shows an exponential-like decrease away from the electrode/solution interface for passive films exposed to 0.5M buffered chloride solutions for various times or heated at a given temperature for a predetermined period of time. The OH-peak heights at a fixed depth in passive layers decrease in a similar manner with increasing exposure time to chloride ions or with increasing annealing temperature for a given time period. C1-peak heights for films exposed to chloride ion-containing borate solutions increase rapidly for times up until breakdown, decrease sharply after breakdown, and then level off at times much longer than breakdown. O-peak heights decrease exponentially with depth for samples exposed to chloride ions and decrease linearly for specimens annealed at various temperatures for a number of different times. Corresponding Fe § peak height data display a linear decrease with depth for chloride-treated films and an almost constant value for layers subjected to thermal treatments. Positive SIMS O § peak heights increase sharply for thermally treated films over a surface region of approximately 7•, remain constant in the bulk regions, and decrease rapidly in the film]metal interfacial regions. Homogeneous films are indicated with a thickness of about 25~. Detailed mechanistic discussions of the two principal models of passivity show that the results are in greater agreement with the amorphous hydrated polymeric oxide model than with the crystalline oxide model, in which water is considered only in terms of adsorbed water on the surface of the passive film.) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 128.122.253.228 Downloaded on 2014-10-19 to IP

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Section: Discussionmentioning

confidence: 99%

Investigation of the Anodically Formed Passive Film on Iron by Secondary Ion Mass Spectroscopy

Murphy

Pou

Bockris

et al. 1984

J. Electrochem. Soc.

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“…Thermal characteristics of the hydrated ferric oxide gel prepared by the authors under a definite set of experimental conditions has been reported earlier [12]. The nature of the primary particle of the gel is found to be a-FeOOH, which crystallizes completely above 210~ and transformed to a-Fe203 with an exothermic peak at 315~…”

Section: Introductionmentioning

confidence: 56%

“…The first two exothermic peaks of ferric oxide gel are due to the crystallization of ~-FeOOH and the transformation of a-FeOOH to a-Fe203 [12]. Therefore, the decrease in intensity of these two peaks with increasing concentration of NiO for the samples FN1 to FN10 (Fig.…”

Section: Discussionmentioning

confidence: 93%

“…1) is due to the sudden increase of crystallite size within a relatively narrow range of temperature [12]. III of Fig.…”

Section: Discussionmentioning

confidence: 96%

“…Other experimental conditions were similar to those used for the preparation of nickel hydroxide and hydrated ferric oxide gel [12]. The concentration of the mixed metal ions in the solution was approximately 0.5 molar.…”

Section: Methodsmentioning

confidence: 99%

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Thermal transformations of iron(III)-nickel(II) mixed oxide gels

1984

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Iron-nickel mixed oxide gels have been prepared by a hydroxide co-precipitation technique and their thermal transformation has been studied by thermal analyses, X-ray diffraction and infra-red spectroscopy. Differential thermal analysis (DTA) of the hydrated ferric oxide gel indicates the presence of three exothermic peaks along with a broad endotherm. Addition of nickel oxide decreases the intensities of the exotherms and the peaks are completely absent in the samples containing more than 10 mol % of NiO. On the other hand these samples show the presence of three endothermic peaks. Thermal analysis of the sample containing 50 mol % of NiO indicates the formation of a precursor at around 185~ which changes to nickel ferrite at around 275 ~ C. This ferrite slowly crystallizes with a broad exotherm in the range 280 to 550 ~ C.

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Electrical Conductivity and Thermoelectric Power Studies of Iron (III)-Nickel (II) Mixed Oxides

Maiti¹,

Rajendran²,

Rao³

1984

Phys. Stat. Sol. (a)

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Thermal transformation of hydrated ferric oxide gel and preparation of ultrafine oxide

Cited by 14 publications

References 15 publications

Investigation of the Anodically Formed Passive Film on Iron by Secondary Ion Mass Spectroscopy

Investigation of the Anodically Formed Passive Film on Iron by Secondary Ion Mass Spectroscopy

Thermal transformations of iron(III)-nickel(II) mixed oxide gels

Electrical Conductivity and Thermoelectric Power Studies of Iron (III)-Nickel (II) Mixed Oxides

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