The thermally induced transformation of pseudoboehmite gels—a comparison of the effects of corundum seeding and iron doping

Nofz, Marianne; Stößer, Reinhard; Scholz, Gudrun; Dörfel, I.; Schultze, D.

doi:10.1016/j.jeurceramsoc.2004.04.014

Cited by 27 publications

(53 citation statements)

References 21 publications

(23 reference statements)

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“…Hence it appears that the presence of Mn somehow influences the alumina transitions meaning that the transitions occur at lower temperatures. It was also shown that Fe species can act similarly and induce the alumina transition [38]. It can also be noted the temperature of the alumina transition namely its θ → α transition is lowered by the introduction of α-alumina seeds that act as heterogeneous nucleation sites [39].…”

Section: X-ray Diffraction (Xrd)mentioning

confidence: 96%

On the initial deactivation of MnxOy–Al2O3 sorbents for high temperature removal of H2S from producer gas

Chytil

Kure

Lødeng

et al. 2015

Fuel Processing Technology

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Section: X-ray Diffraction (Xrd)mentioning

confidence: 96%

On the initial deactivation of MnxOy–Al2O3 sorbents for high temperature removal of H2S from producer gas

Chytil

Kure

Lødeng

et al. 2015

Fuel Processing Technology

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“…This means that a spontaneous crystallization of the non or only weakly activated parts of the matrix is more probable than a nucleation via Fe 3+ species being different from Fe 2 O 3 . The corresponding ESR spectrum yields here the typical habit of α-Al 2 O 3 : Fe 3+ spectra [1,2], but with very broad lines. With respect to the overall Fe concentration this indicates an incorporation of the Fe 3+ ions in the temperature range of the phase transition to give α-Al 2 O 3 .…”

Section: Resultsmentioning

confidence: 76%

“…Whilst in the sample (b) in Scheme 1 only ESR signals could be detected, which indicate for Fe 3+ ions incorporated into highly distorted Al-O phases [1][2][3], sample (c) shows the first steps of local corundum formation, α-Al 2 O 3 : Fe 3+ [3], whereas sample (d) yields the typical X-band spectrum of α-Al 2 O 3 : Fe 3+ with signals at g = 13; 5.2 and 2. This means that 95.5% of the iron was inserted into the AlO x matrix as trivalent iron ions.…”

Section: Resultsmentioning

confidence: 98%

“…The AlO(OH) xerogels have been synthesized as described previously [1] and mechanically activated by using a Pulverisette 7 (Fritsch, Germany). The "high energy ball milling" procedure has been applied to pure or mixed samples of 2 g per milling beaker utilizing 5 milling balls (beaker and balls made from silicon nitride).…”

Section: Methodsmentioning

confidence: 99%

“…We started with the sol-gel process [1] and ended up at the phase transition to α-Al 2 O 3 [1][2][3] at temperatures below 1,000 • C. The quality of the coatings and the transition temperatures can be influenced by doping (e.g. with Fe 3+ species) as well as by mechanical activation ("high energy ball milling") of the corresponding xerogels.…”

mentioning

confidence: 99%

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The fate of Fe3+ ions in the system {AlO(OH)-xerogel/Fe-compounds} after mechanical activation and different thermal treatments studied by Mössbauer, ESR spectroscopy and thermal analysis

2009

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Co-milling of AlO(OH) xerogels with various iron(III) compounds such as α-Fe 2 O 3 or K 3 [Fe(CN) 6 ] has been used for mechanochemical activation leading to Fe/Al oxide phases in coexistence with the activated main component. The results obtained allow a deeper insight into the chemical processes occurring during activation, doping, and thermal treatment in atmospheres of different chemical activity (H 2 O; N 2 ; O 2 /N 2 ; H 2 /N 2 ). Evidence will be given for Fe 3+ species being able to form suitable crystallization germs and to lower the crystallization temperature. One can distinguish between the incorporation of Fe 3+ ions into the alumina matrix at the crystallite growth (e.g. on Fe 2 O 3 -like seeds) and the incorporation of Fe 3+ ions during the last steps of crystallization. These last-mentioned Fe 3+ ions are provided by coexisting Fe/Al oxide phases. In contrast to alumina matrices equilibrated at high temperatures (e.g. at 1,200-1,500 • C), the matrices formed in situ are able to incorporate Fe 3+ ions by diffusion at temperatures of ∼900-1,100 • C in a short time regime.

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Alumina Thin Films

Nofz¹

2016

Handbook of Sol-Gel Science and Technology

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This chapter gives an overview over preparation, properties, and applications of alumina thin films. The preparation of polymeric and colloidal alumina sols and their deposition on diverse substrate materials with different geometries are described first. Consideration of properties (surface tension, particle size, viscosity, aging of the sols, and their optimization by using certain additives) is included, too. A description of posttreatments of the coatings, which initiate phase transformations and also determine their microstructure, completes the part on coating preparation. Data on adhesion, thickness, surface roughness, and mechanical, textural as well as optical properties of alumina thin films are provided in a further paragraph. In a third main part, experience concerning possible applications, such as (i) membranes for catalysis, separation, and filtration, (ii) barrier layers against electrochemical and high-temperature corrosion or interdiffusion of ions between different phases, (iii) mechanical protection, (iv) sensor construction, (v) improvement of optical properties, as well as (vi) achieving water repellency, is summarized.

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The thermally induced transformation of pseudoboehmite gels—a comparison of the effects of corundum seeding and iron doping

Cited by 27 publications

References 21 publications

On the initial deactivation of MnxOy–Al2O3 sorbents for high temperature removal of H2S from producer gas

On the initial deactivation of MnxOy–Al2O3 sorbents for high temperature removal of H2S from producer gas

The fate of Fe3+ ions in the system {AlO(OH)-xerogel/Fe-compounds} after mechanical activation and different thermal treatments studied by Mössbauer, ESR spectroscopy and thermal analysis

Alumina Thin Films

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