A Comparison of Al(OH)3 and Mg(OH)2 as Inorganic Porogenic Agents for Alumina

Salomão, R.; Souza, A. D. V.; Cardoso, Pedro Henrique Lopes

doi:10.1007/bf03401122

Cited by 7 publications

(5 citation statements)

References 26 publications

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“…Such materials combine the high refractoriness of ceramics, the low thermal diffusivity and conductivity of porous structures, and the straightforward processing and energy saving of castable suspensions [4,5]. Due to this, several recent studies evaluated porous structures based on α-Al 2 O 3 [1, 4−8], magnesium aluminate spinel (MgAl 2 O 4 ) [9,10], calcium hexaluminate (CaAl 12 O 19 ) [11−13] and mullite (Al 9 Si 4 O 13 ) [14−18] prepared using aqueous suspensions and in-situ solid-state reactions.…”

Section: Binders For Microporous Castable Ceramics: General Aspectsmentioning

confidence: 99%

Designing Colloidal Silica-Bonded Porous Structures of In-situ Mullite for Thermal Insulation

Spera

Fernandes

Sakihama

et al. 2020

Interceram. - Int. Ceram. Rev.

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Colloidal silica (CS) is a promising raw material for refractory castable ceramics. It consists of stable suspensions of synthetic amorphous silica nanoparticles that behave simultaneously as liquid medium and binder for ceramic particles and as a porogenic agent and highly reactive source of silica to promote in-situ reactions. The setting mechanism of CS balances two opposite effects. Adding more CS to a suspension increases the bonding potential for gelling reactions and strengthening; on the other hand, it also introduces more water into the system, enhancing pore content. Such effects can be advantageously employed in the preparation of porous structures from aqueous suspensions and applied as high-temperature thermal insulators. The present study addresses the production of porous structures of in-situ mullite attained from aqueous suspensions of highly porous transition alumina particles bonded with colloidal silica. Different grades of CS and transition aluminas were combined to present suitable workability (flowability and gelling time) and to generate stoichiometric mullite or mullite-alumina porous structures after sintering.

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Section: Binders For Microporous Castable Ceramics: General Aspectsmentioning

confidence: 99%

Designing Colloidal Silica-Bonded Porous Structures of In-situ Mullite for Thermal Insulation

Spera

Fernandes

Sakihama

et al. 2020

Interceram. - Int. Ceram. Rev.

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“…On the other hand, for systems that are thermally treated after curing and drying (such as high-temperature thermal insulators, e.g. ), a significant gain of strength is expected after sintering and the high total porosity levels would be a technological advantage [26][27][28]31].…”

Section: Samples Cured Under Rotation and Under Isostaticmentioning

confidence: 99%

“…is last aspect has been recently used as an advantageous way to produce porous ceramics. Aqueous suspensions of calcined alumina or silica (dense matrixes), several inorganic porogenic agents (hydrotalcite [8], Al(OH) 3 [9,10], Mg(OH) 2 [27], and CaCO 3 [28]) and hydratable alumina were produced and directly cast using hydraulic binders (hydratable alumina, mainly). In these systems, the total porosity levels attained after curing and drying (50-120°C, 45-60%) were close to the volumetric amount of water initially added during mixing (40-55%).…”

Section: Introductionmentioning

confidence: 99%

Porogenic Behavior of Water in High‐Alumina Castable Structures

Salomão

2018

Advances in Materials Science and Engineering

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Direct casting is a processing method that can produce large parts of complex geometry. It uses dispersions of ceramic particles in water and a hydraulic binder for consolidation. Studies on castable structures have reported the generation of a significant fraction of pores due to the presence of water. This effect occurs because drying preserves part of the interparticle pores originally occupied by water. The fraction of pores obtained in these cases can reach levels higher than 50%, affecting the properties of the structure. However, the porogenic behavior of water in these materials was not investigated in depth. In this work, aqueous suspensions of calcined alumina and hydratable alumina (hydraulic binder) of different water contents (40–60 vol.%) were prepared in a paddler mixer. For compositions of lower (5–35 vol.%) or higher (66–80 vol.%) water amounts, casting and curing steps were assisted by external pressure and a rotating device, respectively, to produce homogeneous microstructures. The total porosity after drying was similar to the initial volumetric content of water in the compositions when side effects, such as sedimentation and air entrapment, were prevented. Below water content of 25 vol.%, particles packing flaws became the main pore generator and the hydroxylation reaction of the binder no longer occurred effectively.

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“…The Bar Resonance (BR) technique [15] has been used to evaluate Young's modulus ( ) variations during curing and drying of MgO-based castable refractories, which indirectly highlights MgO hydration and the mechanical damage caused by the reaction [11,16,17]. Additionally, the Impulse Excitation Technique (IET) [18] was applied to measure the damping caused by microstructural modifications of refractory castables after thermal shocks [19] and the Young's modulus of alumina castables [20].…”

Section: Introductionmentioning

confidence: 99%

Digital image correlation applied to in situ evaluation of surface cracks upon curing of MgO-containing refractory castables

Sciuti

Hild

Pandolfelli

et al. 2021

Journal of the European Ceramic Society

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MgO particles are added to high-alumina castables to provide in situ spinel formation at high temperatures. However, the MgO hydration upon curing may damage the material because of localized volumetric expansion. Usually, the damage is evaluated by the ex situ overall measurement of Young's modulus changes during processing via Impulse Excitation Techniques. In this paper, an experimental setup was designed to use Digital Image Correlation (DIC) as an in situ alternative to evaluate the damage. Tomographic scans highlighted that all cracks initiated on the sample surfaces, and propagated in the bulk in an intergranular mode. Crack initiation and growth were assessed, for different temperatures, via Surface Crack Density (SCD) measurements, and Mean Crack Opening Displacement (MCOD) fields. They provided important insights into heterogeneous expansion phenomena and crack network quantification; for example, the SCD flattened out while the overall damage was still increasing. The results attested the usefulness of DIC for in-situ quantification of ceramics cracking during the processing.

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A Comparison of Al(OH)3 and Mg(OH)2 as Inorganic Porogenic Agents for Alumina

Cited by 7 publications

References 26 publications

Designing Colloidal Silica-Bonded Porous Structures of In-situ Mullite for Thermal Insulation

Designing Colloidal Silica-Bonded Porous Structures of In-situ Mullite for Thermal Insulation

Porogenic Behavior of Water in High‐Alumina Castable Structures

Digital image correlation applied to in situ evaluation of surface cracks upon curing of MgO-containing refractory castables

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