Anisotropic properties of highly textured porous alumina formed from platelets

Honda, Sawao; Hashimoto, Shinobu; Iwata, Syuya; Iwamoto, Yuji

doi:10.1016/j.ceramint.2015.09.090

Cited by 24 publications

(29 citation statements)

References 25 publications

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“…Textured ceramics have the potential to enhance adsorption and catalysis efficiency in porous filters [1], diffusion in solid-state batteries [2], cell growth and biointegration in implants [3], to serve as preforms for anisotropic reinforced composites with combined strength and toughness [4], transparency [5], and to create dense ceramics with outstanding mechanical, electromechanical and/or thermal properties [6][7][8][9][10]. Manufacturing methods of bulk textured porous or dense ceramics for those applications employ anisotropic porogens [3], directional freeze-casting [11], tape-casting [12], high magnetic fields [13] or unidirectional pressing combined with sintering [14,15]. However, the structuration achieved by those methods is generally determined by the specificities inherent to the processing method and cannot be easily controlled and tuned by the engineer.…”

Section: | Introductionmentioning

confidence: 99%

Porous textured ceramics with controlled grain size and orientation

Behera

Muhammad

Jiaxuan

et al. 2021

Journal of the European Ceramic Society

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Texture in dense or porous ceramics can enhance their functional and structural properties. Current methods for texturation employ anisotropic particles as starting powders and processes that drive their orientation into specific directions.Using ultra-low magnetic fields combined with slip casting, it is possible to purposely orient magnetically responsive particles in any direction. When those particles are suspended with nanoparticles, templated grain growth occurs during sintering to yield a textured ceramic. Yet, the final grains are usually micrometric, leading weak mechanical properties. Here, we explore how to tune the grain orientation size using magnetic slip casting and templated grain growth. Our strategy consists in changing the size of the anisotropic powders and ensuring that magnetic alignment and densification occurs. The obtained ceramics featured a large range of grain anisotropy, with submicrometric thickness and anisotropic properties. Textured ceramics with tunable grains dimensions and porosity are promising for filtering, biomedical or composite applications.

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Section: | Introductionmentioning

confidence: 99%

Porous textured ceramics with controlled grain size and orientation

Behera

Muhammad

Jiaxuan

et al. 2021

Journal of the European Ceramic Society

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“…13),15),17), 22) Yoshizawa, et al 15) investigated the mechanical properties of a textured alumina made by high-temperature deformation of normal-purity sintered alumina, where plate-like grains were aligned perpendicularly to the pressed direction, and found very high bending strength as well as extremely high fracture toughness when stress is applied in the alignment in one direction. They attributed the excellent fracture toughness to enhancement of the grain bridging effect by the large number of aligned plate-like grains and the full grain boundary fractures (or crack deflections) in the textured structure.…”

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confidence: 99%

“…p 0 is p of a standard material and standard ¡-alumina powder is used in this case. Since the peak intensity of (006) was small, the Lotgering factor f was calculated using the peak intensities from (116), (018), (1010) and (119) in addition to (006), as also pointed out by Honda et al 22) The f values from (A) and (B) were calculated to be 0.16 and 0.06, respectively. The f of (A) was almost three times higher than that of (B), which indicated that the alumina platelets of the surface layer were well aligned parallel to the surface.…”

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confidence: 99%

Fabrication and characterization of porous alumina with a surface layer composed of alumina platelet by direct-foaming method

Shimamura

Fukushima

Hotta

et al. 2017

J. Ceram. Soc. Japan

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Porous alumina with the surface layer was fabricated from an alumina platelet/novolac-HexaMethyleneTetramine (HMT) composite. HMT was used as a blowing agent as well as a curing one for the novolac binder. When the alumina platelet/novolac composite was heated with covering its surface with filter papers, a porous structure formed inside the composite due to blowing from HMT. On the other hand, the blowing gas near the surface was evolved outward through the filter paper, which resulted in the formation of the surface layer composed of the aligned alumina platelets. Effect of the surface layer on the mechanical strength was examined by three-point bending measurement. The bending strength of the obtained porous alumina increased by 94% compared to the porous alumina without the surface layer.©2017 The Ceramic Society of Japan. All rights reserved.Key-words : Alumina, Porous, Platelets [Received November 7, 2016; Accepted January 29, 2017] Porous ceramics have numerous industrial applications, including structural components, thermal insulators, absorbents, and filters, 1)6) due to a variety of specific properties, such as their heat and corrosion resistance, lightness, and low thermal conductivity. 7),8) Among these specific properties, the lightness is one of the most important properties in the porous ceramics. While increasing porosity reduces the weight, it also degrades mechanical strength, which is critically important where the porous ceramics is used as structural materials.We have previously proposed a direct-foaming approach for porous ceramics from ceramic/novolacHexaMethyleneTetramine (HMT) composite, 9),10) and using this approach we have fabricated porous alumina with the relatively dense surface layer. 11) In this study, HMT was used as a blowing agent and as a curing one for the novolac resin. A gas blown from HMT led to the formation of a porous structure in the alumina/ novolac composite with the expansion of the composite body, while it also resulted in swelling of the surface. This problem can be solved by covering the surface with a proper sheet and constraining the swelling using a mold during blowing. When using a plastic sheet for this purpose, coarse pores formed on the surface because the blowing gas accumulated around the surface, which led to degradation of mechanical strength. Instead, when employing a paper filter for the sheet, relatively dense layer was obtained since the blowing gas near the surface was released to the outside and to keep the surface flat, improving the mechanical strength 30% compared to that of porous alumina without the surface layer.It has been known that dense alumina with microstructure of aligned platelets exhibits excellent mechanical property when stress is applied in the alignment direction. 12)17) Therefore, if the surface layer composed of aligned alumina platelets parallel to the surface can be fabricated, then we can anticipate increase of the mechanical strength. However, to the best of our knowledge, there have been no studies on controlling mi...

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“…24-1165), indicating the accomplishment of α-alumina crystallisation. As a parameter indicating the grain orientation, the Lotgering factor of f [20] is calculated by…”

Section: Resultsmentioning

confidence: 99%

“…24‐1165), indicating the accomplishment of α ‐alumina crystallisation. As a parameter indicating the grain orientation, the Lotgering factor of f [20] is calculated by

\begin{matrix} right leftthickmathspace.5em \\ f = & (\sum I (00 l) / \sum I (h k l) - \sum I_{0} (00 l) / \sum I_{0} (h k l)) / \\ (1 - \sum I_{0} (00 l) / \sum I_{0} (h k l)), \end{matrix}

where ∑ I and ∑ I 0 are the sums of the diffraction peak intensities for α ‐alumina sample and standard α ‐alumina, respectively. Herein, the angular differences between planes of (116) and (018) and the basic plane of (006) for plate‐like α ‐alumina were small, and thus, these related planes of (116) and (018) were adopted for the calculation of ∑ I (00 l ) and the Lotgering factor f for SM and FISM after calcination at 1170°C is 0.0102 and 0.0134, respectively.…”

Section: Resultsmentioning

confidence: 99%

Synthesis of plate‐like α ‐alumina crystals by solid state reaction of fir immersed with slurry mixture of gibbsite and non‐fluorine morphological modifiers

Zhang

Wang

et al. 2019

Micro & Nano Letters

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Solid state reaction without fluorine addition was employed to synthesise plate-like α-alumina. Platelets of α-alumina with non-uniform thickness were obtained using slurry mixture (SM) comprised of gibbsite and morphological modifiers as starting materials. In comparison, α-alumina crystals were fabricated with a plate-like shape with uniform thickness after calcination of fir immersed with SM (FISM). The activation energies of phase transformation from γ-alumina to α-alumina for SM and FISM are determined by the Kissinger method as 109.8 and 132.9 kJ/mol, respectively. These results indicate the rearrangement of atomic stacking during transformation is accomplished with a relatively slow rate in an open space after the decomposition of fir template. The present study demonstrates a facile method to fabricate α-alumina platelets with extensive applications.

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Anisotropic properties of highly textured porous alumina formed from platelets

Cited by 24 publications

References 25 publications

Porous textured ceramics with controlled grain size and orientation

Porous textured ceramics with controlled grain size and orientation

Fabrication and characterization of porous alumina with a surface layer composed of alumina platelet by direct-foaming method

Synthesis of plate‐like α ‐alumina crystals by solid state reaction of fir immersed with slurry mixture of gibbsite and non‐fluorine morphological modifiers

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