Al2O3–Al(OH)3-Based castable porous structures

Souza, A. D. V.; Sousa, Lucíola Lucena de; Fernandes, Leandro; Cardoso, Pedro Henrique Lopes; Salomão, R.

doi:10.1016/j.jeurceramsoc.2015.01.003

Cited by 34 publications

(36 citation statements)

References 24 publications

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“…At temperatures above 250°C, -Al 2 O 3 turns into boehmite and, at higher temperatures, into other transition phases of alumina. During this process, the significant density increase (from 2.8 g.cm -3 up to 3.5 g.cm -3 ) behaves as porogenic mechanism, also reported elsewhere [11]. The combination of these effects causes the enhancement of the average space amongst the HA and CaO particles, comparing to the CA and CaO ones.…”

Section: Resultssupporting

confidence: 76%

Production of porous ceramic materialusing different sources of alumina and calcia

et al. 2015

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Numerous papers and publications report the use of microporous calcium hexaluminate (CaO.6Al 2 O 3 ; CA 6 ) as a key raw material for high temperature insulating materials. This material has unique properties with respect to chemical purity and mineral composition. Another important property of CA 6 is its structure, which consists of platelet-shaped crystals that interlock. The free distance between the crystals defines the microporous structure. The low density in combination with the micropores hampers heat transfer by radiation at temperatures exceeding 1000 o C and results in a low thermal conductivity. Given the advantages presented by this material, it is necessary to understand the formation mechanism of CA 6 grains in order to better develop the potential applications of this material. CA 6 can be fabricated using organic binders to consolidate the Al 2 O 3 -CaCO 3 powder mixture and to provide green strength so that a green body can be formed and retains the desired shape before heating. However, these organic binders must be completely thermally decomposed so that they do not remain in the sintered body as carbon or ash. Moreover, the use of organic binders releases large volumes of gases such as carbon dioxide from the green body during heating. Therefore, an eco-friendly ceramic fabrication process has been developed that employs an inorganic binder (hydraulic alumina). The aim of the present work was to study the synthesis of porous calcium-hexaluminate ceramics using calcined alumina or hydraulic alumina combined with different sources of calcia (CaCO 3 and Ca(OH) 2 ) at different temperatures. The materials produced were characterized by X-ray diffraction, scanning electron microscopy, apparent porosity and mercury intrusion porosimetry. The materials produced by hydraulic alumina presented higher porosity and larger pores compared to those produced from calcined alumina.

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Section: Resultssupporting

confidence: 76%

Production of porous ceramic materialusing different sources of alumina and calcia

et al. 2015

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“…2f-g). Their relative density (RD, %) and the total porosity (TP, %) 15,50 were calculated using Equations 3 and 4…”

Section: Preparation and Characterization Of Mullite Samplesmentioning

confidence: 99%

“…Such a behavior is represented by the y = x function. In real cases, however, most commonly, the reduction of the mechanical properties caused by the introduction of porosity is far more intense due to the presence of tensile concentrators and lack of efficient sintering amongst particles 15,50 . The phases formed during thermal treatment were identified by X-ray diffraction (Rigaku, Rotaflex RV 200B, Japan, pulverized samples).…”

Section: Na Siomentioning

confidence: 99%

Preparation and Characterization of Mullite-Alumina Structures Formed "In Situ" from Calcined Alumina and Different Grades of Synthetic Amorphous Silica

Fernandes

Salomão

2018

Mat. Res.

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The in situ reaction between alumina and silica to obtain mullite (Al 6 Si 4 O 13 ) can be significantly affected by using synthetic amorphous silica (SAS) sources instead of crystalline ones (quartz and cristobalite). For instance, SASs promote early mullite formation (below 1300°C) and greater densification during sintering. This paper reports the "in situ" formation of mullite-alumina structures from fine calcined alumina (α-Al 2 O 3 ) and four grades of SAS of different particles' morphology, specific surface area and internal porosity. After sintering assisted by dilatometry (up to 1500°C), the samples' total porosity, density and flexural strength were measured. The relative density and strength levels of some of these structures were greater than or comparable to other studies in which similar compositions were sintered at higher temperatures (1600-1700°C). Their microstructure assessment indicated that the specific surface area and internal porosity of SAS particles showed a major influence in the development of these physical properties.

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“…The literature describes many combinations of ceramic phases (Al 2 O 3 , SiO 2 , ZrO 2 , MgAl 2 O 4 , SiC, amongst others) with organic particles (starch, casein, chitosan, alginate, polymer latexes, saw-dust) and foams (stabilized with surfactants and nanoparticles) [2,[4][5][6]. Particles of inorganic hydroxylated or carbonated compounds can also be used as pore generators [7][8][9] and offer important technological advantages: i) they can be easily added to many matrixes through standard equipment and additives; ii) during the forming step, the structure attained is less sensitive to variations in the environmental and application conditions; iii) they do not release toxic volatiles during the first heatup.…”

Section: Porous Ceramicsmentioning

confidence: 99%

“…The Al 2 O 3 -Al(OH) 3 system is the most explored example of this technique [2,4,5,8,9] and its mechanism of pore formation involves a two-step process, described as follows [2,5,8,9]. 1) Al(OH) 3 particles are consolidated with the Al 2 O 3 (D-Al 2 O 3 , from calcined alumina, for instance) ones by means of pressing or use of a binding agent.…”

Section: Porous Ceramicsmentioning

confidence: 99%

Development of densification-resistant castable porous structures from in situ mullite

Sousa

Souza

Fernandes

et al. 2015

Ceramics International

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Al2O3–Al(OH)3-Based castable porous structures

Cited by 34 publications

References 24 publications

Production of porous ceramic materialusing different sources of alumina and calcia

Production of porous ceramic materialusing different sources of alumina and calcia

Preparation and Characterization of Mullite-Alumina Structures Formed "In Situ" from Calcined Alumina and Different Grades of Synthetic Amorphous Silica

Development of densification-resistant castable porous structures from in situ mullite

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