Closed porosity ceramics and glasses

Abstract

In the last three decades, considerable effort has been devoted to obtain both open and closed porosity ceramics & glasses in order to benefit from unique combination of properties such as mechanical strength, thermal and chemical stability at low‐relative density. Most of these investigations were directed to the production and the analysis of the properties for open porosity materials, and regrettably quite a few compositions and manufacturing methods were documented for closed porosity ceramics & glasses in the scientific literature so far. This review focuses on the processing strategies, the properties and the applications of closed porosity ceramics & glasses with total porosity higher than 25%. The ones below such level are intentionally left out and the paper is set out to demonstrate the porous components with deliberately generated closed pores/cells. The processing strategies are categorized into five different groups, namely sacrificial templating, high‐temperature bonding of hollow structures, casting, direct foaming, and emulsions. The principles underlying these methods are given, with particular emphasis on the critical issues that affect the pore characteristics, mechanical, thermal and electrical properties of the produced components.

Preparation of a High Performance Electrocatalyst for Oxygen Reduction Reaction by Suppressing the Agglomeration of the Carbon Material with RbCl

“…[12] The Raman spectra of PON/C-"Rb" and PON/ C are compared in Figure S6, and both spectra contain D and G peaks centered at~1320 and 1597 cm À1 , indicating the presence of highly disordered and defective carbon materials. [13] The I D /I G value of PON/C-"Rb" is 1.44, which is slightly higher than that of PON/C (1.41), revealing a higher level of graphite in the former, [14] that leads to good electrical conductivity. The PON/C-"Rb" catalyst exhibits excellent hydrophilicity with a contact angle of~308, which is favorable for mass transfer in an aqueous electrolyte ( Figure S7).…”

Preparation and Characterization of Undoped and Chromia-Doped Porous Alumina Using Different-Sized Particles

“…The pore formers are commonly organic agents or salts such as wax spheres, naphthalene particles, poly methyl methacrylate, starch, NaCl, and ammonia bicarbonate (NH 4 HCO 3 ) [27][28][29][30]. The decomposition of pore formers may leave the undesired residual impurities in the nal product, hence the selection of pore-forming agents and the decomposition process should be carefully controlled [26,31]. Additionally, most of the pores achieved in the sacri cial template are open pores.…”

“…The sacri cial template method has been widely used due to its low-cost and simple process steps. This technique basically includes a dispersion of a sacri cial phase throughout the ceramic precursors, subsequently, compaction to form a green body, and nally decomposition of sacri cial agents to obtain the pores [25,26]. The pore formers are commonly organic agents or salts such as wax spheres, naphthalene particles, poly methyl methacrylate, starch, NaCl, and ammonia bicarbonate (NH 4 HCO 3 ) [27][28][29][30].…”

“…At the total porosity of 65%, the porous materials exhibited a compressive strength of 9.18 MPa. In order to attain the closed pores, it has been reported that a slurry or solution of ceramic precursors and sacri cial agents should be formed [26,[33][34][35][36]. Porous alumina with high closed porosity was fabricated by gel-casting of Al 2 O 3 powder and polyethylene, subsequently sintering at 1400 o C for 1h [37].…”

All-optical switching based on grating written photorefractive slab/fiber waveguide coupler

“…While porous materials are an important class of materials 51,52 , here the aim was to produce samples with highest relative density. According to spreadability test results, powder samples coded as S1, S2, S3, and S5 were chosen to determine the effects on final 3D printed cubes.…”