Mechanism of pore generation in calcium hexaluminate (CA6) ceramics formed in situ from calcined alumina and calcium carbonate aggregates

Salomão, R.; Ferreira, Vivian Lindmayer; Oliveira, I. R.; Souza, A. D. V.; Correr, Wagner Rafael

doi:10.1016/j.jeurceramsoc.2016.05.026

Cited by 79 publications

(29 citation statements)

References 38 publications

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“…The apparent peak of α‐Al 2 O 3 in the specimen without microsilica is doubtful if the stoichiometric proportion is taken into consideration. In a previous work, where press method is used for CA 6 specimen preparation with a stoichiometric ratio of CaCO 3 and Al 2 O 3 , negligible or no α‐Al 2 O 3 is found . The loose particle compacts are formed in this work due to the direct foaming method.…”

Section: Resultsmentioning

confidence: 55%

Fabrication of calcium hexaluminate‐based porous ceramic with microsilica addition

Xiang

et al. 2018

Int J Applied Ceramic Tech

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Calcium hexaluminate (CA 6 )-based porous ceramic was prepared with a-alumina powders and nanometer-sized calcium carbonate using a direct foaming technique with the addition of calcium aluminate cement and microsilica. The microsilica leads to the acceleration of CA 6 formation. Moreover, the shrinkage, densification, and elastic modulus at room temperature were enhanced with increasing microsilica content. But the hot elastic modulus showed obvious reduction between 1100°C and 1200°C if the microsilica content was over 0.5 wt%. Furthermore, a-Al 2 O 3 appeared in the specimens with and without microsilica after treatment at 1550°C, and the proportion of CA 6 grains having a high aspect ratio increased after microsilica addition.

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Section: Resultsmentioning

confidence: 55%

Fabrication of calcium hexaluminate‐based porous ceramic with microsilica addition

Xiang

et al. 2018

Int J Applied Ceramic Tech

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“…Therefore, the E drop at ~ 400 ºC is caused by Ca(OH)2 decomposition. It is also worth observing that the 5 % CAC composition presented the lowest mechanical strengthening after firing (Efinal -Einitial), which is most likely due to the formation of highly asymmetric platelet CA6 grains induced by using CaCO3 and Ca(OH)2 [24].…”

Section: Figurementioning

confidence: 99%

Al2O3–CaO macroporous ceramics containing hydrocalumite-like phases

Borges

Santos

Salvini

et al. 2020

Ceramics International

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A mechanism to explain the lower onset strengthening temperature induced by CaCO3 in alumina-based macroporous ceramics is proposed, which relies on hydrocalumite-like phase formation during processing. Close to 600 °C, such phases are decomposed to lime and mayenite (12CaO·7Al2O3), where the latter, due to its intrinsic nanoporosity and high thermal reactivity, generates bonds between the ceramic particles at ~700ºC, resulting in microstructure strengthening. Based on this premise, the authors concluded that other Ca 2+ sources could act similarly. Indeed, compositions containing Ca(OH)2 or CaO showed the same effect on the onset strengthening temperature, which reinforces the proposed mechanism. The results attained indicated that macroporous insulators could be thermally treated at lower temperatures, just to acquire enough mechanical strength for installation, finishing in-situ their firing process. Besides that, lower sintering temperatures could be used to produce macroporous ceramics that would be applied in low thermal demand environments, e.g. aluminum industries.

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“…Grain growth of CaAl 12 O 19 is anisotropic. Crystal nucleus preferentially grows along the basal plane to form a plate or tabular crystal [30,31]. As can be seen in Table 2, the lattice parameter a (b) of Sample D 0.1Gd was longer than that of Sample D, and the lattice parameter c of Sample D 0.1Gd was shorter than that of Sample D. However, compared with Sample D, lattice volume of Sample D 0.1Gd decreased.…”

Section: Resultsmentioning

confidence: 99%

“…The tensile stress at the grain boundary could be effectively mitigated by reducing calcium ingredient of glass phase. In addition, the thermal expansion coefficient of CaAl 12 O 19 is 8.0 × 10 −6 °C −1 [30], which is lower than that of Al 2 O 3 , and both could easily form compressive stress at grain boundary. All of these factors came together to improve the wear resistance of alumina ceramics.…”

Section: Discussionmentioning

confidence: 99%

Wear Resistance Mechanism of Alumina Ceramics Containing Gd2O3

et al. 2018

Materials

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Excellent wear resistance of alumina ceramics is a desirable quality for many products. The purpose of this work was to improve the wear resistance of 99% alumina ceramics in an Al2O3–Gd2O3–SiO2–CaO–MgO (AGSCM) system. The content of Gd2O3 varied from 0.01% to 1%. A test of wear rate was performed in a ball milling apparatus in a water environment according to the Chinese industry standard. The compositions and microstructure of this material, as well as the effect of bulk density on wear rate, were studied. The effect of Gd2O3 on phases, grain growth mode, and grain boundary cohesion was investigated. It was found that Gd2O3 could refine grain size, form compressive stress of the grain boundary, and promote the crystallization of CaAl12O19. The wear rate of this material was as low as 0.00052‰ (the Chinese industry standard wear rate is ≤0.15‰). The mechanisms for wear resistance of AGSCM ceramics were also determined.

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Mechanism of pore generation in calcium hexaluminate (CA6) ceramics formed in situ from calcined alumina and calcium carbonate aggregates

Cited by 79 publications

References 38 publications

Fabrication of calcium hexaluminate‐based porous ceramic with microsilica addition

Fabrication of calcium hexaluminate‐based porous ceramic with microsilica addition

Al2O3–CaO macroporous ceramics containing hydrocalumite-like phases

Wear Resistance Mechanism of Alumina Ceramics Containing Gd2O3

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