Al2O3 Foam Research Articles

Experimental characterization of Al2O3 foam based on high temperature thermal response experiments

Alumina foam has potential application value in aerospace, solar energy, and other fields. This study proposes a combined radiative-conductive heat transfer model, in which the thermal conductivity and extinction coefficient are temperature-dependent, and the radiation transfer equation is solved by the Monte Carlo method. A self-designed setup is used to measure the high temperature thermal response experiments of alumina foams in 10PPI, 20PPI, and 40PPI. Combined with the genetic algorithm, the thermal conductivity, extinction coefficient, albedo and asymmetry factor of scattering are solved. According to the inversion results, the extinction coefficient of materials with a high pore density is more sensitive to temperature than those with a lower pore density. The thermal conductivity of high pore density materials is greater than that of low pore density materials. The thermal conductivity and extinction coefficient slightly remain basically unchanged as atmospheric pressure increases.

Microstructure evolution and mechanical properties of Al2O3 foams via laser powder bed fusion from Al particles

Microstructure evolution and mechanical properties of Al2O3 foams via laser powder bed fusion from Al particles

Fabrication and characterization of alumina and zirconia-toughened alumina porous structures

In the present study, alumina (Al2O3) and zirconia-toughened alumina (ZTA) porous structures (foams) were manufactured using the space holder technique. Al2O3 and ZTA foams with varying porosities from 20% to 69% were fabricated by adding different sizes (10, 20, and 40 μm) and different volume % of polystyrene beads (space holders) to Al2O3 and ZTA powders. All the fabricated foams were investigated under static conditions to assess the compressive behavior. It is observed that the compressive strength of these foams strongly depends on porosity, pore size, pore size distribution and pore wall thickness. Among all fabricated foams, Al2O3 foams with 20 vol% beads of 10 μm size showed a higher compressive strength of 700 MPa with low porosity (21%) and a higher pore wall thickness (2.8 μm). It is also observed that the pore wall thickness decreased with the increase in beads size and the volume % of the beads, resulting in a low compressive strength value of 8 MPa with a lower pore wall thickness of 1.75 μm at 80 vol% of 40 μm beads. All the foams, irrespective of pore size, showed a typical ceramic failure phenomenon up to 70 vol% of beads; after that, the failure behavior changed to complete open-cell fracture.

A novel process to high‐strength and controlled‐shrinkage Al2O3 foams with open‐cell by Al powder hollowing technology

AbstractCeramic foams with open‐cell structures have attracted extensive attention due to their unique structure and superior properties. But these materials often exhibit the weakness of high sintered shrinkage and low strength at high porosity levels. In this work, novel ceramic foams with open‐cell structures have been obtained using Al powder by combining direct foaming and gelation freezing (DF–GF). The foams are assembled by hollow Al2O3 particles resulting from the Kirkendall effect, in which expanded particles overcome the shrinkage of sintering. The influence of sintering temperature on the microstructure and properties of foams are investigated. The Al2O3 foams show near‐zero‐shrinkage at 1773 K after undergoing the process of first expansion and then shrinkage. Compared to other conventional open‐cell foam, this foam displays relatively high compressive strength of 0.35–2.19 MPa at high porosity levels of 89.45%–94.45%, attributed to hierarchical pore structure and reaction bonding between Al and O2. This method from pore structure design provides a novel route for the preparation of controlled shrinkage and high‐compressive strength alumina foam with open‐cell toward potential application.

Catalytic Pt/Al2O3 Monolithic Foam for Ethanol Reforming Fabricated by the Competitive Impregnation Method.

Here, the synthesis of Pt/Al2O3 catalysts on a monolithic foam employing the competitive impregnation method is presented. NO3 - was used as a competitive adsorbate at different concentrations in order to delay the adsorption of Pt, minimizing the formation of Pt concentration gradients throughout the monolith. The catalysts' characterization includes the BET, H2-pulse titration, SEM, XRD and XPS techniques. The catalytic activity evaluation was performed under partial oxidation and autothermal reforming of ethanol in a short contact time reactor. The competitive impregnation method was able to produce better dispersion of the Pt particles through the Al2O3 foams. XPS analysis indicated the catalytic activity of the samples, by the presence of metallic Pt and Pt oxides (PtO and PtO2) in the internal regions of the monoliths. Compared to other Pt catalysts reported in the literature, the catalyst produced by the competitive impregnation method was revealed to be selective toward H2. Overall, the results showed that the competitive impregnation method employing NO3 - as the co-adsorbate is a promising technique to synthesize well dispersed Pt catalysts over α-Al2O3 foams.

Applicability of methane foam stabilized via Nanoparticles for enhanced oil recovery from carbonate porous media at various temperatures

Over the 60 years of primary production from carbonate oil reservoirs in the middle east, approximately 30 % of initial oil in place has been recovered in this area and the rest requires appropriate enhanced oil recovery (EOR) methods for production. Since there are huge gas resources in this area, applications of gas-based EOR methods especially those with methane gas should be the top priority. Therefore, the objective of this study is to experimentally determine and compare the influences of stabled methane foams via aluminum oxide (Al2O3), titanium dioxide (TiO2), zinc oxide (ZnO), and silica (SiO2) nanoparticles (NPs) for EOR from a limestone porous medium at 25, 50 and 85 °C. For this goal, 0.1 wt% Sodium dodecyl sulfate (SDS) was dissolved in NaCl solution 0.5 wt% and then the above-mentioned nanopowders at concentrations from 0.005 to 0.1 wt% were added. Methane at a flow rate of 250 ml/min was injected into the suspensions and the stability of produced foams was defined by measuring the half-life time. Once an optimum concentration of each NP type was found, that foam was chosen to be flooded to the limestone porous medium for EOR purposes. The optimum NP content in terms of foam stability at all temperatures was achieved at 0.01 wt% for SiO2 and ZnO NPs and 0.05 wt% for TiO2 and Al2O3 NPs. Half-life time values of methane foams in the presence of NPs were averagely found to be 16 and 3 times higher than those of the base foam at 25 and 85 °C, respectively. TiO2, Al2O3, ZnO, and SiO2 NPs in order were the best additives for foam stability at all temperatures. In addition, at 85 °C, the incremental oil recovery amounts from the limestone porous medium by TiO2, Al2O3, ZnO, and SiO2 NPs-methane foams were achieved 20.4, 18.9, 17.6, and 16.1 %, respectively, which were 6 to 10 % higher than foam flood tests without NPs. Overall, it can be concluded that NPs methane foam flooding is a promising method for EOR from carbonate porous media in the middle east area.

Alumina doped Fe2O3 foams by freeze-casting for redox cycling applications

Hydrogen is the next energy vector for a decarbonization society but industrial production is still methane-based. The Steam Iron Process (SIP) could provide a carbon-free production and safety storage option. Here, we show that a Fe2O3-3 wt% of Al2O3 foams created by freeze-casting withstand 10 redox cycles at different temperatures with no reduction in performance or pore shrinking. The use of stearic acid as a dispersant agent/binder produces the porous structure enhancement of the foam and promotes the early reduction of the hematite phase during foam sintering. The Al2O3 incorporation was detected as a solid solution in the Fe2O3 phase at the particle surface. This result is relevant as correlated the positive values of the zeta potential observed. Freeze-casted foams could improve long-term redox performances combining a unique tailored interconnected pore structure with a specific chemical composition.

Enhancing the active site accessibility of cobalt-silica catalysts for improved Fenton-like performance

The narrow pore channels of cobalt-silica (CoSi) catalyst generated by conventional sol–gel process limited the active site accessibility. In this work, mesoporous CoSi catalysts containing highly dispersed Co sites were synthesized by a facile sol–gel derived soft-templating technique and tested for the Fenton-like oxidation of dyes and antibiotics. By controlling the concentration of triblock polymer Pluronic F127 template, the textural and chemical properties of CoSi catalysts were fine-tuned to improve the accessibility of their active sites. The CoSi catalyst achieved ∼ 96% removal of acid orange 7 (AO7) within 15 min using a low catalyst loading (50 mg L−1) and H2O2 dosage (11 mM) at pH of 7–8. Moreover, thin-film CoSi coated on Al2O3 foam, as a monolithic catalyst prepared by the washcoating method, maintained high oxidation activity (∼99% removal for AO7) over 10 days, demonstrating excellent operational stability and process intensification for practical wastewater treatment applications.

Catalytic Removal of NOx on Ceramic Foam-Supported ZnO and TiO2 Nanorods Ornamented with W and V Oxides

Energy consumption steadily increases and energy production is associated with many environmental risks, e.g., generating the largest share of greenhouse gas emissions. The primary gas pollution concern is CO2, CH4, and nitrogen oxides (NOx). Environmental catalysis plays a pivotal role in NOx mitigation (DeNOx). This study investigated, for the first time, a collection of ceramic foams as potential catalyst support for selective catalytic NOx reduction (SCR). Ceramic foams could be an attractive support option for NOx removal. However, we should functionalize the surface of raw foams for such applications. A library of ceramic SiC, Al2O3, and ZrO2 foams ornamented with nanorod ZnO and TiO2 as W and V oxide support was obtained for the first time. We characterized the surface layer coating structure using the XPS, XRF and SEM, and TEM microscopy to optimize the W to V molar ratio and examine NO2 mitigation as the SCR model, which was tested only very rarely. Comparing TiO2 and ZnO systems reveals that the SCR conversion on ZnO appeared superior vs. the conversion on TiO2, while the SiC-supported catalysts were less efficient than Al2O3 and ZrO2-supported catalysts. The energy bands in optical spectra correlate with the observed activity rank.

Investigations of Thermal Conductivity and Radiation Properties of Al2o3 Foam Materials Based on High Temperature Thermal Response Experiments

Investigations of Thermal Conductivity and Radiation Properties of Al2o3 Foam Materials Based on High Temperature Thermal Response Experiments

Inversion of Thermal Conductivity and Radiation Properties of Al2o3 Foam Materials Based on High Temperature Thermal Response Experiments

Inversion of Thermal Conductivity and Radiation Properties of Al2o3 Foam Materials Based on High Temperature Thermal Response Experiments

Porous reticular CuO/ZnO/CeO2/ZrO2 catalyst derived from polyacrylic acid hydrogel system on Al2O3 foam ceramic support for methanol steam reforming microreactor

A hydrophilic polyacrylic acid hydrogel was formed in the millimeter-sized pores of Al2O3 foam ceramic by the polymerization of acrylic acid, and a large amount of nitrates precursor solution was adsorbed by the hydrogel via vacuum impregnation. A porous reticular CuO/ZnO/CeO2/ZrO2 catalyst with fine and uniform particles was obtained after 500 °C calcination. The ceramic loaded with pristine PAA hydrogel and loaded with absorbed hydrogel after 300 °C and 500 °C calcination were characterized to illustrate the formation mechanism of catalyst structure. The ceramic after 500 °C calcination was applied in a microreactor as catalyst support for methanol steam reforming to investigate the catalytic performance. Results showed that the porous reticular catalyst reduced the size of the catalytic channels and increased the number of effective catalytic channels simultaneously, resulting in a 100% methanol conversion rate, 0.288 mol/h H2 yield at 300 °C and an inlet methanol flow rate of 0.096 mol/h.

Microstructural and mechanical properties of Al2O3 and ZTA foams prepared by thermo-foaming technique

Alumina and zirconia toughened alumina foams were fabricated through a thermo-foaming method using varying amounts of powder to sucrose weight ratio. All the fabricated foams were characterized for their compressive strength, bending strength, and fracture toughness under static loading conditions. The compressive strength increases with an increase in a weight ratio from 0.4 to 1.2. The maximum compressive strength values were found to be 1.9 MPa, and 1.8 MPa for alumina and zirconia toughened alumina foams, respectively. Further increase in powder to sucrose weight ratio led to a decrease in the compressive strength due to the partial collapse of the cell walls during the foaming process. The 3-point bend test results revealed an improvement of bending strength and fracture toughness values of zirconia toughened alumina foams compared to alumina foam, which can be attributed to the transformation toughening mechanism.

Determination of the representative volume-of-interest (REVOI) in ceramic replica foams

The investigations on ceramic foams with porous, heterogeneous microstructure are based on the standards and dimensions for dense materials due to the lack of alternatives. It is known that variations in pore size, shape and porosity have a significant effect on the physical properties, however, the considered sample volume is treated here as a secondary interest. To determine the representative volume-of-interest (REVOI), image data from micro tomography measurements of 30,45 and 60 ppi (pore per inch) Al2O3 foams were used. The REVOI is the minimum volume that comprehensively represents the microstructure and can thus be considered a unit volume. The Minkowski functionals allow an invariant microstructure description by single value using stereology approaches. Based on these values of defined volume sets, the REVOI was determined as a novelty in microstructure characterization. Additional analysis of the pore sizes in the 3D volume and determination of tortuosity and permeability at the previously defined volumes allowed validation of the REVOI.

Innovative iron oxide foams for the removal of micropollutants by Catalytic Wet Peroxide Oxidation: Assessment of long-term operation under continuous mode

This work aims to develop highly stable iron oxide foams for the continuous Catalytic Wet Peroxide Oxidation (CWPO) of micropollutants in a structured fixed-bed reactor. Homogeneity and adhesion of the active phase were achieved by adjusting the preparation methodology. Three structured catalysts based on Al2O3, SiC and ZrO2 foams were obtained with Fe content of 2.5%, 2.1% and 0.90% wt., respectively. The catalytic foams were tested in the CWPO of a mixture of three pharmaceuticals (metronidazole (MNZ), sulfamethoxazole (SMX) and carbamazepine (CBZ)), with a concentration of 100 µg L−1 each. The catalysts resulted active and stable up to 200h of CWPO carried out at ambient conditions, with the exception of Fe/ZrO2, which showed a progressive deactivation due to the iron leaching from the solid. An increase in space time led to an enhanced performance achieving remarkable conversion levels of 73%, 83% and 90% for MNZ, SMX and CBZ, respectively. The effect of H2O2 dose was also evaluated revealing the development of competing side reactions for supra-stoichiometric dosages. Moreover, the scavenging effect of the water matrix was assessed operating in presence of humic acid as representative natural organic matter (NOM). In this case, the conversion levels for SMX and CBZ resulted alike to the ones obtained for ultrapure water and only a slight decrease in MNZ removal rate was detected. After 400h of usage at different steady-state conditions, the outstanding catalytic performance of Fe/Al2O3 and Fe/SiC was sustained in the long-term operation.

In Situ Reduction of a CuO/ZnO/CeO2/ZrO2 Catalyst Washcoat Supported on Al2O3 Foam Ceramic by Glycerol for Methanol Steam Reforming in a Microreactor

A CuO/ZnO/CeO2/ZrO2 catalyst slurry was prepared by mixing the catalyst powder, a polyvinyl alcohol aqueous solution, and glycerol. The slurry was coated on a Al2O3 foam ceramic support via a dip-c...

One-step growth of CuO/ZnO/CeO2/ZrO2 nanoflowers catalyst by hydrothermal method on Al2O3 support for methanol steam reforming in a microreactor

CuO/ZnO/CeO2/ZrO2 nanoflowers catalyst was grown on an Al2O3 foam ceramic by a one-step hydrothermal process, while a naked Al2O3 foam ceramic and an Al2O3 foam ceramic grown with ZnO nanorods that directly impregnated into the catalyst precursor solution were also fabricated simultaneously. The morphology, composition, redox property and specific surface area of catalysts on the three ceramics were investigated in detail. The catalyst-loaded ceramics were used as catalyst supports in a microreactor to study the catalytic performance for methanol steam reforming. Results showed that the microreactor with Al2O3 support grown with nanoflowers catalyst achieved 99.8% methanol conversion rate, 0.16 mol/h H2 flow rate at 310 °C, and an inlet methanol flow rate of 0.048 mol/h. Moreover, the microreactor exhibited 92% methanol conversion rate after 30 h continuous reaction.

Ultrastrong Hierarchical Porous Materials via Colloidal Assembly and Oxidation of Metal Particles

AbstractPorous materials are useful as lightweight structures, bone substitutes, and thermal insulators, but exhibit poor mechanical properties compared to their dense counterparts. Biological materials such as bone and bamboo are able to circumvent this trade‐off between porosity and mechanical performance by combining pores at multiple length scales. Inspired by these biological architectures, a manufacturing platform that allows for the fabrication of Al2O3 foams and Al2O3/Al composites with hierarchical porosity and enhanced mechanical properties is developed. Macroscale pores are formed through the assembly of aluminum particles around templating air bubbles in wet foams, whereas the thermal oxidation of the metal particles above 800 °C generates porosity at the micrometer scale. After elucidating the mechanism of pore formation under different sintering conditions at the microscale, the mechanical performance of the resulting hierarchical foams using compression experiments and finite element simulations is evaluated. Porous materials manufactured via this simple approach are found to reach unparalleled mechanical properties with near‐zero sintering shrinkage and minimum loss in mechanical strength. The ability to produce macroscopic objects with ultrahigh strength at porosities up to 95% makes this an attractive manufacturing technology for the fabrication of high‐performance lightweight structures or advanced thermal and acoustic insulators.

3D printing of dense and porous TiO2 structures

Direct foam writing allows the fabrication of highly porous and hierarchical ceramic structures with high specific mechanical properties. This manufacturing technique, however, has mainly used stabilized Al2O3 foam inks. In this work, we pressent a novel foam ink based on TiO2. This ink uses polyvinyl alcohol (PVA) as a binder and a small amount of zinc as a frothing agent. We used this ink to produce cylindrical foam samples via direct foam writing. The foams had a porosity of up to 65% and a mean pore size of 180 μm, which is significantly larger than previously reported for direct foam writing with Al2O3. The foams were tested in compression and were found to have an elastic modulus of 0.5 GPa and a compressive strength of 12–18 MPa. These mechanical properties are similar to those of porous ceramics produced by conventional manufacturing routes. Therefore, this work represents a step forward by broadening the direct foam writing process to a wider range of porous ceramics.

Titania-Coated Alumina Foam Photocatalyst for Memantine Degradation Derived by Replica Method and Sol-Gel Reaction.

In the present work, alumina (Al2O3) foam was prepared by the replica method where a polyurethane (PU) foam (30 pores per inch (ppi)) template was impregnated with a 60 wt.% Al2O3 suspension. Sintered Al2O3 foam was used as substrate for the deposition of sol-gel derived titania (TiO2) film using dip coating. For the preparation of TiO2 sol, titanium(IV) isopropoxide (Ti-iPrOH) was used as the precursor. The common problem of qualification and quantification of a crystalline coating on a highly porous 3D substrate with an uneven surface was addressed using a combination of different structural characterization methods. Using Powder X-ray Diffraction (PXRD) and synchrotron Grazing Incidence X-ray Diffraction (GIXRD) on bulk and powdered Al2O3 foam and TiO2-coated Al2O3 foam samples, it was determined Al2O3 foam crystallizes to corundum and coating to anatase, which was also confirmed by Fourier Transformed Infrared Spectroscopy (FTIR). Scanning Electron Microscopy with Energy Dispersive X-ray Spectroscopy (SEM/EDS) revealed the structural and microstructural properties of the substrate and coating. Differential Thermal Analysis (DTA) and Thermogravimetric Analysis (TGA) were used to clarify the evolution of the porous microstructure. The Al2O3-TiO2 composite was evaluated as a photocatalyst candidate for the degradation of the micropollutant medication memantine. The degradation rate was monitored using a light-emitting diode (LED) lamp operating at electromagnetic (EM) wavelength of 365 nm. The photocatalytic activity of sol-gel-derived TiO2 film immobilized on the Al2O3 foam was compared with commercially available TiO2 nanoparticles, P25-Degussa, in the form of a suspension. The levels of memantine were monitored by High-Performance Liquid Chromatography–Tandem Mass Spectrometry (HPLC–MS/MS). The efficiency and rate of the memantine photodegradation by suspended TiO2 nanoparticles is higher than the TiO2-coated Al2O3 foam. But, from the practical point of view, TiO2-coated Al2O3 foam is more appropriate as a valuable photocatalytic composite material.