Macroporous Ceramics Research Articles

The sound of porosity: Suitability of the impulse excitation technique (IET) to determine the Young's modulus of 2D macroporous ceramics

The presence of pores in a ceramic leads to a lower Young's modulus compared to dense material. For the development of porous ceramics with tailored elastic properties, an exact determination of the Young's modulus is required, especially for industrial applications. Therefore, we investigated the suitability of the non-destructive impulse excitation technique for measuring the dynamic Young's modulus of two-dimensional ceramics with low porosity (P < 19 %). For rectangular samples it was shown that the measurement results depend on the geometric pore position, as added pores outside the nodal lines of the fundamental flexural vibration had no influence on the result. Pores in the inner part of the sample led to a decrease of the Young's modulus that is in good agreement with empirical and analytical models. For the investigated interval of porosity range, the influence of pore size and geometric position on the reduction of the Young's modulus was determined.

Wet-ground calcium aluminate cement as a binder for directly-foamed high-temperature macroporous ceramics

Calcium aluminate cement (CAC) is broadly used as a binder for ceramic materials as it can provide suitable setting times, green mechanical strength and refractoriness. When applied to directly-foamed macroporous refractories, this binder can set the fresh foam before bubble coalescence, favouring higher porosity. Nevertheless, its large particles tend to thermodynamically stabilize bigger bubbles, resulting in samples with larger pores and broader cell size distribution, which is undesirable for high-temperature thermal insulation applications. An alternative to overcome this issue is CAC milling, which can be carried out in water by using sodium gluconate (SG) to produce a stable suspension of this binder. By using 1 wt% of SG, it was possible to grind the CAC in water for 6 h without hydration. When applied to macroporous samples, milled CAC provided faster setting kinetics and in situ formation of hibonite after firing. Additionally, smaller average pore size and higher cold crushing strength were attained when used for the production of ultrastable foam-derived refractories, whereas less significant changes were observed for samples based on surfactant-stabilized foams. The study also showed that the CaO/Al2O3 particle size ratio was an important feature to control the shrinkage/expansion effects after sintering, based on the morphological aspect of the resulting hibonite (CA6) phase.

Fabrication and characterization of macroporous alumina -nano tetragonal zirconia -nano spinel ceramic composites

In order to protect the environment, waste materials like bagasse have recently been recycled in the production of porous ceramics. For the synthesis of nano tetragonal zirconia (t-ZrO2) and nano spinel (MgAl2O4), a modified co-precipitation method is used. The phase composition, particle size, and surface area of the synthesized nanoparticles were examined using X-ray diffraction (XRD), scanning and transmission electron microscopy (SEM- TEM), and Brunauer-Emmett-Teller (BET) analyses, respectively. To prepare alumina – nano t-ZrO2 –nano spinel macroporous ceramics, nano t-ZrO2 was added from 0 to 30 wt% at the expense of nano spinel to calcined alumina (70 wt%). Bagasse ash (as a pore-forming agent) was added to the mixed compositions in weight percentages ranging from 0 to 15 wt%. All prepared samples were sintered at different temperatures (1350, 1450, and 1450 °C). The influence of nano t-ZrO2, bagasse ash, and sintering temperature on the phase composition, densification parameters, cold crushing strength (CCS), microstructure, and the distribution of pores in sintered samples was looked into. According to the results, the major phases observed in sintered samples are corundum, spinel, tetragonal zirconia, and monoclinic zirconia phase. The cold crushing strength of sintered samples increased with increasing nano tetragonal zirconia additions due to the tetragonal to the monoclinic toughening mechanism of t-zirconia. With increasing bagasse additions, the bulk density decreased from 2.66 g/cm3 to 1.49 g/cm3, while the apparent porosity increased from 30.2% to 56.04%. The microstructures and pore size distribution of the sintered samples show that the prepared porous ceramic samples have high crystallinity, with an average pore size between 2.51 μm and 3.32 μm.

Macroporous ceramics for the sustainable development goals (SDGs): Review

AbstractThe sustainable development goals (SDGs), including 17 goals and 169 targets, were adopted unanimously by the United Nations General Assembly in 2015. The aims are to end poverty, protect the planet, and ensure peace, health, and prosperity of all people over the world. Toward the SDGs, human beings must effectively utilize the global resources, such as (1) oceans, seas, rivers, lakes, and so forth that supply us with water and aquatic resources; (2) land, ground, and soil where we can raise agricultural crops and livestock; (3) forests and woods that provide us with lumber and paper and convert carbon dioxide to oxygen; and (4) fossil fuel and mineral resources, which are essential to our modern lives. The use of macroporous ceramics is definitely conducive to the solutions to achieve the SDGs, because it can help solve many of the related technical issues. This review addresses macroporous ceramics primarily for filtration and purification, agriculture and fisheries industry, thermal managements, sensing devices, and constructions, which contribute to achieving SDGs.

Enhanced mechanical strength and bactericidal activity of macro-porous Al2O3 ceramics through the introduction of Cu for membrane support application

Enhancing the mechanical strength of macro-porous ceramics and simultaneously endowing them with bactericidal activity are considered to be beneficial for their application as membrane support materials for water and wastewater treatment. In this study, Cu-containing Al 2 O 3 porous ceramics were prepared by powder mixing, cold pressing and subsequent sintering. The microstructures of as-fabricated ceramics consisted of large α-Al 2 O 3 particles as matrix, as well as inter-particle NaAlSiO 4 , CuAl 2 O 4 and CuO phase. With increased sintering temperature from 1430 to 1560 °C, the proportion of band-shaped CuO phase, which exhibited stronger binding tendency with Al 2 O 3 than NaAlSiO 4 , gradually increased, while that of particle-shaped CuAl 2 O 4 phase decreased. Increasing the Cu content from 2 to 8 wt% at a fixed sintering temperature of 1500 °C resulted in the presence of more band-shaped CuO phase in Al 2 O 3 matrix which tightly bonded Al 2 O 3 particles together. The increase of sintering temperature and Cu content could both lead to enhanced bending strength and reduced porosity, while the later factor showed stronger modulatory effects than the former one. Moreover, the bactericidal rates of Cu-containing Al 2 O 3 porous ceramics towards Escherichia coli ( E. coli ) and Staphylococcus aureus ( S. aureus ) were found to increase with increased Cu content in a Cu content-dependent manner. Together, the Cu-containing Al 2 O 3 porous ceramic added with 8 wt% Cu and sintered at 1500 °C exhibited the highest bending strength and strongest bactericidal activity, which could be a promising candidate material for membrane support application.

Facile processing of oriented macro-porous ceramics with high strength and low thermal conductivity

Unidirectionally oriented architectures demonstrate a notable efficiency in enhancing the properties of macro-porous materials, yet are difficult to construct in a time- and cost-effective fashion. Here a facile approach was exploited for fabricating oriented macro-porous ceramic materials by employing natural graphite flakes as a fugitive material and preferentially aligning the flakes within ceramic matrices using accumulative rolling technique. Flaky to near-ellipsoid shaped pores with a homogeneous distribution were created in macro-porous zirconia ceramics with their porosity and microstructural characteristics adjustable by controlling the additive amounts of graphite flakes. The resulting materials exhibited a good combination of properties with high compressive strength up to over 1.5 GPa, which exceeds those of most other porous zirconia ceramics with similar porosities, along with low thermal conductivity of 0.92–1.85 Wm−1·K−1. This study offers a simple means for developing new oriented macro-porous materials with enhanced properties, and may promote their application by allowing for easy mass production.

Chemically Bound Resorbable Ceramics as an Antibiotic Delivery System in the Treatment of Purulent–Septic Inflammation of Bone Tissue

Local drug delivery systems are an effective approach in the treatment of purulent–septic inflammation of bone tissue. Chemically bonded multiphase ceramics based on calcium-deficient carbonate-substituted hydroxyapatite combine resorbability, osteoconductivity, and the possibility of volumetric incorporation of antibiotics. Macroporosity is regulated by the concentration of polyethylene glycol granules introduced into the initial powder composition, followed by their extraction. The selected conditions for the consolidation of the ceramic matrix and the extraction of PEG granules retain the activity of vancomycin, which is confirmed by the results of microbiological studies. The concentration of vancomycin and the porosity affect the local concentration and release of the antibiotic. The incorporation method provides a prolonged release of the antibiotic for up to 31 days. In vivo experiments with bone implantation have shown that chemically bound macroporous ceramics with incorporated vancomycin are a therapeutically effective carrier of the substance during the healing of bone defects in conditions of surrounding purulent–septic inflammation, and can be considered as a carrier for local antibacterial therapy, at the site of implantation.

A review on gradient macroporous ceramic via powder-based direct foaming process

Macroporous ceramics are potentially applicable in a wide range of industrial applications. The porous structure of macroporous ceramics is designed depending on the application of macroporous ceramics. This paper reviews gradient macroporous ceramics fabricated via powder-based direct foaming to produce a relatively dense surface and a highly porous body. The fabrication process and the characterization of such ceramics are also considered. In terms of fabrication, an overview of the direct-foaming and foaming conditions to obtain a uniform porous structure is described. With regard to characterization, the unique structure of porous ceramics and effect of the denser surface on the bending strength are summarized through the results of microstructural observation and three-point bending strength measurements. The presence of the surface layer enables an improvement in the bending strength while maintaining high porosity. The fabrication processes reviewed herein are highly promising for reducing the weight of porous ceramics while enhancing their mechanical strength.

Effect of the Pore Size on the Biological Activity of \u03b2-Ca3(PO4)2-Based Resorbable Macroporous Ceramic Materials Obtained by Photopolymerization

The effect of the pore size of macroporous ceramic materials based on β-Ca3(PO4)2 on their biological activity was studied. The formation conditions of macroporous ceramics with a porosity of >50% and a specified pore size were determined. The effect of components of the light-curing emulsion on the pore size in the final macroporous ceramics was studied. The biocompatibility of β-Ca3(PO4)2-based macroporous ceramics was demonstrated in in vitro biomedical assays. The effect of pore size of macroporous ceramic materials on mesenchymal stromal cell proliferation and viability was established.

Stereolithography 3D printed calcium pyrophosphate macroporous ceramics for bone grafting

Macroporous calcium pyrophosphate ceramics with a pore size of 900 μm and a pore fraction of up to 65% demonstrating compressive strength of 5 ± 1 MPa were formed by DLP stereolithography 3D printing. Mixed sodium-calcium pyrophosphate CaNa2P2O7 was used as an eutectic additive in liquid phase sintering of the ceramics at 600–800 °C. Initial powder charge was selected from a mixture of Ca10(PO4)6(OH)2, Ca(H2PO4)2·H2O and NaH2PO4. The pH of the aqueous solution contacting with the manufactured pyrophosphate ceramics in the range (6–7.2) turns out to be acceptable for further biomedical tests as a bone grafting material.

Additive Manufacturing of Porous Ceramics With Foaming Agent

Abstract The macro-porous ceramics has promising durability and thermal insulation performance. As porous ceramics find more and more applications across many industries, a cost-effective and scalable additive manufacturing technique for fabricating macro-porous ceramics is highly desirable. Herein, we reported a facile additive manufacturing approach to fabricate porous ceramics and control the printed porosity. Several printable ceramic inks were prepared, and the foaming agent was added to generate gaseous bubbles in the ink, followed by the direct ink writing and the ambient-pressure and room-temperature drying to create the three-dimensional geometries. A set of experimental studies were performed to optimize the printing quality. The results revealed the optimal process parameters for printing the foamed ceramic ink with a high spatial resolution and fine surface quality. Varying the concentration of the foaming agent enables the controllability of the structural porosity. The maximum porosity can reach 85%, with a crack-free internal porous structure. The tensile tests showed that the printed macro-porous ceramics possessed enhanced durability with the addition of fiber. With a high-fidelity three-dimensional (3D) printing process and the precise controllability of the porosity, we showed that the printed samples exhibited a remarkably low thermal conductivity and durable mechanical strength.

Direct foaming of Al2O3-based macroporous ceramics containing pre-foamed colloidal alumina, calcite and CAC suspension

Adding pre-foamed colloidal alumina to ultrastable Al2O3-stabilised foams can be a path towards partially counteracting the firing shrinkage of these materials and producing macroporous ceramics with smaller pores. Nevertheless, this system still presents a long setting time and high sintering-induced shrinkage, which hinders the production of larger samples and reduces its porosity. In the present work, it was observed that adding calcium aluminate cement suspension (CACS) and CaCO3 (calcite) to the aforementioned system can speed up its solidification kinetics, improve its mechanical strength and reduce its shrinkage after firing, maintaining high porosity and smaller pore sizes. By using these raw materials, samples with an average pore size below 60 μm, total porosity above 70%, and a narrower pore size distribution were attained after thermal treatment at 1600 °C for 5h. Moreover, due to the in situ formation of calcium hexaluminate, their shrinkage after sintering was almost halved (from ~20% to 11%).

Direct foaming of macroporous ceramics containing colloidal alumina

Liquid foams containing Al2O3 nanoparticles were obtained after direct foaming of a colloidal alumina suspension with ammonium stearate. These systems were stable for at least 24 h and were comprised by small cells (<35 μm). Up to 10 wt% of these foams were added to an ultrastable Al2O3-stabilised one and resulted in macroporous samples with high total porosity (>70%). Their green mechanical strength was proportional to the amount of colloidal alumina added, but lower than a composition with calcium aluminate cement. When compared with compositions prepared with colloidal alumina suspension, the colloidal foams resulted in samples with a higher number of small pores (<30 μm) and lower linear shrinkage after firing at 1600 °C for 5 h (~9%). Thus, colloidal alumina foams can be used for processing macroporous refractory ceramics with smaller pores, lower dimensional changes after firing and higher porosity.

Формирование пористой керамики на основе Ca3(PO4)2 из фотоотверждаемых эмульсий

The fabrication method of macroporous ceramics based on Ca3(PO4)2 from photocured water-oil emulsions has been proposed. The conditions for obtaining porous ceramic structures with a pre-determined pore size in the range of 2—50 μm and their volume of more than 56% were determined. The main problems of this method are discussed, and the solution methods are proposed. The strength characteristics of the created porous ceramic structures are described.

Potentialities of Reaction Sintering in the Fabrication of High-Strength Macroporous Ceramics Based on Substituted Calcium Phosphate

Calcium alkali metal (potassium and sodium) double and triple phosphates have been synthesized in different ways. Was for the first time used reaction sintering to produce ceramics based on calcium alkali metal mixed phosphates and investigated the densification behavior of mixed phosphate-based multiphase materials during sintering by this method. Was presented the microstructure of polished surfaces of sintered samples differing in phase composition and determined the density of ceramics prepared using reaction mixtures differing in composition. The effect of reaction sintering on the porosity of the ceramics has been assessed. Using stereolithographic printing and reaction sintering, was produced macroporous mixed calcium phosphate-based ceramic implants. Their compressive strength has been determined to be 0.78 ± 0.21 MPa for two-phase samples and 1.02 ± 0.13 MPa for three-phase samples.

Calcium aluminate cement aqueous suspensions as binders for Al2O3-based particle stabilised foams

Macroporous refractory ceramics were prepared with Al2O3-based particle stabilised foams in which ceramic particles were partially hydrophobized with propionic acid or l-leucine. Calcium aluminate cement (CAC) as dry powder or stable aqueous suspension were added as binders. Cement addition resulted in solid foams whereby setting took place in less than 24 h. Highly porous samples were attained with leucine-based foams whereas the propionic-acid ones were not stable after CAC addition. For leucine-based foams, fired samples with homogeneous microstructures, both high porosity (~80%) and cold crushing strength (~30 MPa) were attained when CAC aqueous suspension was used instead of CAC dry powder. These results were associated to the better dispersion of cement particles in the foam structure when CAC liquid binder was used and pointed out the advantages of this suspension for producing solid macroporous ceramics based on particle-stabilised foams.

Synthesis of macroporous ceramic with enhanced sound absorption capability in low and medium frequency

We propose a novel hybrid method to produce macroporous ceramic with excellent sound absorption coefficient at medium and low frequency noise and multimodal pore size distribution. Macroporous ceramics with pore sizes from 100 nm to 2000 μm and apparent porosity in the range 85%–90% were fabricated by twice-foaming method and two pore-forming agents. These ceramics display a sound absorption coefficients from 0.11 to 0.99 in the sound-wave frequency range of 200–2000 Hz with sufficient connectivity rate above 99%. This ceramic represents a highly expected industrialization of properties for noise control and reduction at corrosive environments and high temperatures.

Colloidal forming of macroporous calcium pyrophosphate bioceramics in 3D-printed molds

A technique for colloidal forming of Ca2P2O7 macroporous bioceramics, based on low-pressure injection molding (LPIM) of a glycerol-water slip containing Ca2P2O7 and Ca(Н2PO4)2 into a plastic mold fabricated via FDM 3D-printing, was proposed. Chemical reaction between the solid phases of the water containing slip - Ca2P2O7 and Ca(Н2PO4)2, resulting in brushite (CaHPO4·2H2O) formation, led to consolidation of the casting and preserved its complex architecture in the course of mold burning-out. Macroporous ceramics of Kelvin structure (70% macropores with the sizes from 2 up to 4 mm), based on a pre-defined composition with 10 wt% Ca(PO3)2 and sintered in liquid-phase regime, demonstrated a compressive strength of 1.4 ± 0.1 MPa at a density of 22 ± 2%. In vitro tests on bioactivity in SBF solution, as well as on resorption of the ceramics in model solution of citric acid, were carried out.

Synthesis of Calcium Phosphate Powders in Nonaqueous Media for Stereolithography 3D Printing

Methods were presented to synthesize tricalcium phosphate Ca3(PO4)2 (TCP), calcium pyrophosphate Ca2P2O7 (CPP), and TCP/CPP composites in nonaqueous media in the temperature range 25–300°C. It was shown that solvo- and ionothermal synthesis methods can give phosphates of complex composition. The phase composition, micromorphology, and particle size distribution of the obtained powders and their evolution during synthesis were described. The synthesis at 110°C while slowly adding ammonium hydrophosphate to a solution of calcium ethylene glycolate in ethylene glycol gives a nanocrystalline β-TCP powder with an average size of aggregates of platy crystals of 150 nm and a distribution width of 50 nm. The morphological characteristics and sinterability of the powders synthesized in solutions in ethylene glycol make them suitable for producing macroporous ceramics by stereolithography 3D printing methods.

3D-Printed lightweight ceramics using capillary suspensions with incorporated nanoparticles

A new versatile route is reported to produce tailored porous sintering materials with high mechanical strength. A self-assembly mechanism deposits trace amounts of nanoparticles at contact areas between coarse ceramic particles prior to sintering, resulting in large and uniformly dense sintering bridges. This increases the porosity up to 75 % and simultaneously offers higher mechanical strength in comparison to similar materials even when weaker silica nanoparticles are introduced. This route is ideally suited for robocasting as well as conventional extrusion and, thus, can be used for rapid prototyping and mass production. We report the highest compressive strength-to-weight ratios for lightweight macroporous ceramics, covering an unrivaled density range while offering exceptional flexibility in tailorable microstructure. The strength is dominated by the silica bridges and identical strength is achieved for alumina and aluminosilicate structures. Finally, this route can be used to build hierarchical structures by point-welding particles while preserving inner surface area.