Special Issue "Advances in Functional Cellular Structures and Composites"

A special issue of Materials (ISSN 1996-1944). This special issue belongs to the section "Advanced Composites".

Deadline for manuscript submissions: closed (31 December 2020).

Special Issue Editors

Prof. Dr. Michael Scheffler
E-Mail Website
Guest Editor
Otto-von-Guericke University Magdeburg, Magdeburg, Germany
Interests: cellular ceramics manufacturing and functionalization; energy materials, ceramics from polymeric precursors; functional coatings
Dr. Tobias Fey
E-Mail Website
Guest Editor
Friedrich-Alexander-Universität Erlangen-Nürnberg, Germany
Frontier Research Institute for Materials Science, Nagoya Institute of Technology, Nagoya, Japan
Interests: periodic and nonperiodic cellular ceramics and composites, microstructure characterisation (esp. microtomography) and testing, simulation and modeling on µCT-derived microstructure models
Special Issues and Collections in MDPI journals
Dr. Ulf Betke
E-Mail Website
Guest Editor
Otto-von-Guericke University Magdeburg, Magdeburg, Germany
Interests: cellular ceramics manufacturing and functionalization; x-ray based material analyses; cellular adamantine compounds; Affiliation: Otto-von-Guericke University Magdeburg, Magdeburg, Germany

Special Issue Information

Dear Colleagues,

Activities in the development, manufacturing and application of cellular structures such as foams or 3D periodic materials made of ceramic, polymeric and metallic base materials are steadily growing. The combination of matter and porosity, which extends the properties of related materials, is exciting the interest in these materials for engineering and biomedical applications. These include, to mention just a few: the lightweight design of tools, machines and engines; fluid-dynamic applications, such as metal and gas filtration and environmental cleaning; the conversion of heat and matter in chemical and physicochemical applications; and hard tissue repair in prosthetics.

Apart from the base properties as defined by their material/structure combination, a surface and/or strut functionalization or a material combination may be necessary for a specific application. In order to highlight the most recent developments in this demanding field of materials science and materials processing, the focus of this Special Issue is on the functionalization of the outer and inner surfaces of cellular materials, e.g. by coating and infiltration. Work dealing with cellular composite materials, e.g. by reinforcement to improve the mechanical properties, is also welcome. We look forward to receiving your valuable contributions, regardless of whether your paper deals with ceramic, metallic, or polymeric cellular materials, or combinations thereof.

Prof. Dr. Michael Scheffler
Dr. Tobias Fey
Dr. Ulf Betke
Guest Editors

Manuscript Submission Information

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Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Materials is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2000 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • cellular materials
  • functionalization of cellular structures
  • composite materials

Published Papers (6 papers)

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Research

Open AccessArticle
Open-Cellular Alumina Foams with Hierarchical Strut Porosity by Ice Templating: A Thickening Agent Study
Materials 2021, 14(5), 1060; https://doi.org/10.3390/ma14051060 - 24 Feb 2021
Viewed by 280
Abstract
Alumina replica foams were manufactured by the Schwartzwalder sponge replication technique and were provided with an additional strut porosity by a freeze-drying/ice-templating step prior to thermal processing. A variety of thickeners in combination with different alumina solid loads in the dispersion used for [...] Read more.
Alumina replica foams were manufactured by the Schwartzwalder sponge replication technique and were provided with an additional strut porosity by a freeze-drying/ice-templating step prior to thermal processing. A variety of thickeners in combination with different alumina solid loads in the dispersion used for polyurethane foam template coating were studied. An additional strut porosity as generated by freeze-drying was found to be in the order of ~20%, and the spacings between the strut pores generated by ice-templating were in the range between 20 µm and 32 µm. In spite of the lamellar strut pore structure and a total porosity exceeding 90%, the compressive strength was found to be up to 1.3 MPa. Combining the replica process with freeze-drying proves to be a suitable method to enhance foams with respect to their surface area accessible for active coatings while preserving the advantageous flow properties of the cellular structure. A two-to-threefold object surface-to-object volume ratio of 55 to 77 mm−1 was achieved for samples with 30 vol% solid load compared to 26 mm−1 for non-freeze-dried samples. The freeze-drying technique allows the control of the proportion and properties of the introduced pores in an uncomplicated and predictable way by adjusting the process parameters. Nevertheless, the present article demonstrates that a suitable thickener in the dispersion used for the Schwartzwalder process is inevitable to obtain ceramic foams with sufficient mechanical strength due to the necessarily increased water content of the ceramic dispersion used for foam manufacturing. Full article
(This article belongs to the Special Issue Advances in Functional Cellular Structures and Composites)
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Open AccessArticle
Sodium Solid Electrolytes: NaxAlOy Bilayer-System Based on Macroporous Bulk Material and Dense Thin-Film
Materials 2021, 14(4), 854; https://doi.org/10.3390/ma14040854 - 10 Feb 2021
Viewed by 357
Abstract
A new preparation concept of a partially porous solid-state bilayer electrolyte (BE) for high-temperature sodium-ion batteries has been developed. The porous layer provides mechanical strength and is infiltrated with liquid and highly conductive NaAlCl4 salt, while the dense layer prevents short circuits. [...] Read more.
A new preparation concept of a partially porous solid-state bilayer electrolyte (BE) for high-temperature sodium-ion batteries has been developed. The porous layer provides mechanical strength and is infiltrated with liquid and highly conductive NaAlCl4 salt, while the dense layer prevents short circuits. Both layers consist, at least partially, of Na-β-alumina. The BEs are synthesized by a three-step procedure, including a sol-gel synthesis, the preparation of porous, calcined bulk material, and spin coating to deposit a dense layer. A detailed study is carried out to investigate the effect of polyethylene oxide (PEO) concentration on pore size and crystallization of the bulk material. The microstructure and crystallographic composition are verified for all steps via mercury intrusion, X-ray diffraction, and scanning electron microscopy. The porous bulk material exhibits an unprecedented open porosity for a NaxAlOy bilayer-system of ≤57% with a pore size of ≈200–300 nm and pore volume of ≤0.3 cm3∙g−1. It contains high shares of crystalline α-Al2O3 and Na-β-alumina. The BEs are characterized by impedance spectroscopy, which proved an increase of ionic conductivity with increasing porosity and increasing Na-β-alumina phase content in the bulk material. Ion conductivity of up to 0.10 S∙cm−1 at 300 °C is achieved. Full article
(This article belongs to the Special Issue Advances in Functional Cellular Structures and Composites)
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Open AccessArticle
Cellular Nickel-Yttria/Zirconia (Ni–YSZ) Cermet Foams: Manufacturing, Microstructure and Properties
Materials 2020, 13(11), 2437; https://doi.org/10.3390/ma13112437 - 26 May 2020
Viewed by 575
Abstract
Open-celled ceramic composite foams were prepared from NiO and yttria-stabilized zirconia (YSZ) powders by the polymer sponge replication (Schwartzwalder) technique using the respective aqueous dispersions. Mechanically stable NiO–YSZ foams with an average porosity of 93 vol.% were obtained. After chemical reduction of the [...] Read more.
Open-celled ceramic composite foams were prepared from NiO and yttria-stabilized zirconia (YSZ) powders by the polymer sponge replication (Schwartzwalder) technique using the respective aqueous dispersions. Mechanically stable NiO–YSZ foams with an average porosity of 93 vol.% were obtained. After chemical reduction of the NiO phase with hydrogen, cellular Ni–YSZ cermet structures were obtained. They are characterized by an electric conductivity up to 19∙103 S∙m−1 which can be adjusted by both, the Ni volume fraction, and the sintering/reduction procedure. The NiO–YSZ ceramic foams, as well as the cellular Ni–YSZ cermets prepared therefrom, were characterized with respect to their microstructure by scanning electron microscopy, confocal Raman microscopy and X-ray diffraction with Rietveld analysis. In addition, the compressive strength, the electric conductivity and the thermal conductivity were determined. The collected data were then correlated to the sample microstructure and porosity and were also applied for modelling of the mechanical and electric properties of the bulk Ni–YSZ strut material. Full article
(This article belongs to the Special Issue Advances in Functional Cellular Structures and Composites)
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Open AccessArticle
Injection Molding of 3-3 Hydroxyapatite Composites
Materials 2020, 13(8), 1907; https://doi.org/10.3390/ma13081907 - 17 Apr 2020
Cited by 3 | Viewed by 959
Abstract
The manufacturing of ideal implants requires fabrication processes enabling an adjustment of the shape, porosity and pore sizes to the patient-specific defect. To meet these criteria novel porous hydroxyapatite (HAp) implants were manufactured by combining ceramic injection molding (CIM) with sacrificial templating. Varied [...] Read more.
The manufacturing of ideal implants requires fabrication processes enabling an adjustment of the shape, porosity and pore sizes to the patient-specific defect. To meet these criteria novel porous hydroxyapatite (HAp) implants were manufactured by combining ceramic injection molding (CIM) with sacrificial templating. Varied amounts (Φ = 0–40 Vol%) of spherical pore formers with a size of 20 µm were added to a HAp-feedstock to generate well-defined porosities of 11.2–45.2 Vol% after thermal debinding and sintering. At pore former contents Φ ≥ 30 Vol% interconnected pore networks were formed. The investigated Young’s modulus and flexural strength decreased with increasing pore former content from 97.3 to 29.1 GPa and 69.0 to 13.0 MPa, agreeing well with a fitted power-law approach. Additionally, interpenetrating HAp/polymer composites were manufactured by infiltrating and afterwards curing of an urethane dimethacrylate-based (UDMA) monomer solution into the porous HAp ceramic preforms. The obtained stiffness (32–46 GPa) and Vickers hardness (1.2–2.1 GPa) of the HAp/UDMA composites were comparable to natural dentin, enamel and other polymer infiltrated ceramic network (PICN) materials. The combination of CIM and sacrificial templating facilitates a near-net shape manufacturing of complex shaped bone and dental implants, whose properties can be directly tailored by the amount, shape and size of the pore formers. Full article
(This article belongs to the Special Issue Advances in Functional Cellular Structures and Composites)
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Open AccessArticle
Phase Evolution, Filler-Matrix Interactions, and Piezoelectric Properties in Lead Zirconate Titanate (PZT)-Filled Polymer-Derived Ceramics (PDCs)
Materials 2020, 13(7), 1520; https://doi.org/10.3390/ma13071520 - 26 Mar 2020
Viewed by 652
Abstract
PZT-silsesquioxane-based 0-3 hybrid materials are prepared by mixing lead zirconate titanate (Pb(Zr,Ti)O3; PZT) powder with a [R-SiO3/2]n (R = H, CH3, CH=CH2, C6H5) silsequioxane preceramic polymer. A PZT load up [...] Read more.
PZT-silsesquioxane-based 0-3 hybrid materials are prepared by mixing lead zirconate titanate (Pb(Zr,Ti)O3; PZT) powder with a [R-SiO3/2]n (R = H, CH3, CH=CH2, C6H5) silsequioxane preceramic polymer. A PZT load up to 55 vol.% can be reached in the final composite. The piezoelectric and mechanical properties are investigated as a function of the filler content and are compared with theoretical models and reference samples made of the pure preceramic polymer or PZT filler. The piezoelectric response of the composites, as expressed by the relative permittivity and the piezoelectric coefficients d33 and g33, increases with an increasing PZT content. The bending strength of the composites ranges between 15 MPa and 31 MPa without a clear correlation to the filler content. The thermal conductivity increases significantly from 0.14 W∙m−1∙K−1 for the pure polymer-derived ceramic (PDC) matrix to 0.30 W∙m−1∙K−1 for a sample containing 55 vol.% PZT filler. From X-ray diffraction experiments (XRD), specific interactions between the filler and matrix are observed; the crystallization of the PDC matrix in the presence of the PZT filler is inhibited; conversely, the PDC matrix results in a pronounced decomposition of the filler compared to the pure PZT material. Full article
(This article belongs to the Special Issue Advances in Functional Cellular Structures and Composites)
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Open AccessArticle
Mechanical and Surface-Chemical Properties of Polymer Derived Ceramic Replica Foams
Materials 2019, 12(11), 1870; https://doi.org/10.3390/ma12111870 - 10 Jun 2019
Cited by 5 | Viewed by 1129
Abstract
Polymer derived ceramic foams were prepared with the replica method using filler free and filler loaded polysiloxane containing slurries for the impregnation of open celled polyurethane foams. A significant change in mechanical strength, porosity and surface energy, i.e., wettability after thermal treatment between [...] Read more.
Polymer derived ceramic foams were prepared with the replica method using filler free and filler loaded polysiloxane containing slurries for the impregnation of open celled polyurethane foams. A significant change in mechanical strength, porosity and surface energy, i.e., wettability after thermal treatment between 130 °C (crosslinking) and 1000 °C (pyrolysis) in argon atmosphere was observed. While low-temperature pyrolyzed foams are elastic and hydrophobic, foams pyrolyzed at high temperatures are brittle and hydrophilic, and they possess higher compression strength. Changes of these properties were correlated with the polymer-to-ceramic transformation. Full article
(This article belongs to the Special Issue Advances in Functional Cellular Structures and Composites)
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