Al2O3 Ceramic Foam Research Articles

Efficient purification of scrap 1060 aluminum alloys contaminated with Fe and Si by super-gravity separation

1060 aluminum alloy has been used in high-volume commercial applications and correspondingly the mass of its downgraded recycling after contamination is huge, which is primarily due to the gradual accumulation of impurity elements such as Fe and Si. The separation of excess Fe is considered to be a key step towards the same-level recycling of aluminum alloy scrap with extremely economic and environmental benefits. A supergravity-induced technology was employed to purify the contaminating elements from molten aluminum scraps through Al2O3 CFF (Al2O3 ceramic foam filter). During the filtration process, the premature precipitation of Fe-rich phases and Si particles in the molten aluminum scraps were intercepted near the inner wall of Al2O3 CFF. Resultantly, the removal rate of Fe and Si reached 83.98 % and 49.67 %, respectively, at T = 690 ℃ and G= 30 via Al2O3 CFF of P = 80 ppi with H= 40 mm. A continuously supergravity-induced separation on industrial scale was further performed and the removal rate of Fe and Si were 83.5 % and 48.3 %, respectively.

Strong and tough laminated ceramics prepared from ceramic foams

Here, we present a novel strategy to prepare laminated ceramics by combining the ceramic foams and hot-pressing sintering. Al2O3 and ZrO2 ceramic foams prepared by the particle-stabilized foaming method was cut into thin slices and then directly laminated and hot-pressing sintered. Al2O3/ZrO2 laminated ceramics with various structures were prepared. Compared with the slices prepared by conventional process, ceramic foams can easily regulate the thickness of laminate to resemble the nacre-like structure. In addition, the grain in the ceramic foams have lower activity and shrinkage rate, thereby weakening the residual tensile internal stress caused by grain coarsening and differences in coefficient of thermal expansion. The effects of layer number and thickness ratio on residual stress and the structure-activity relationship between mechanical properties and microstructure were investigated. The fracture toughness, flexural strength, and work of fracture of the optimal Al2O3/ZrO2 laminated ceramics are 8.2 ± 1.3 MPa·m1/2, 356 ± 59 MPa, and 216 J·m−2, respectively.

Purification of primary aluminum liquid through supergravity-induced filtration

Fine particles in primary aluminum jeopardize the quality of aluminum production. Supergravity-induced filtration with an Al2O3 ceramic foam filter (Al2O3 CFF), used to purify primary aluminum, is proposed in this study. During the purification process, Al2O3 particles and Fe-rich phases prematurely precipitated around the Al2O3 particles, and were intercepted either on the surface of the Al2O3 CFF by being wrapped in alumina film or inside the filter. Furthermore, the premature precipitation of the intermetallic near the inner wall of the filter improved the capacity of the Al2O3 CFF to remove metallic impurities; the coarse filter walls acted as nucleation sites. After purification at 700 °C and a gravity coefficient of 80 with an Al2O3 CFF of P = 130 ppi and H = 20 mm, no Al2O3 particles were observed in the filtered aluminum, the removal ratio of Fe (RFe) reached 76%, and the loss percentage of Si (LSi) was 55%. Based on the optimized conditions obtained from the exploratory experiment, a continuous purification was further performed to complete the engineering scale purification of primary aluminum and obtain purified aluminum without Al2O3 particles, with 74% for RFe and 50% for LSi.

Explosion suppression effect and mechanism analysis of ceramic foam in the horizontal pipe

ABSTRACT Ceramic foams are potential materials for explosion suppression due to their complex three-dimensional porous structure and strong wave absorption capabilities. The ability of ceramic foams to suppress methane/air explosion was investigated in a large-scale horizontal pipe. The factors of pore size and thickness of the ceramic foam were taken into consideration, and the explosion overpressure and explosion energy were compared and discussed collectively. Furthermore, mechanisms for the suppression of ceramic foams were also analyzed. Results indicated that ceramic foam has a good quenching effect on explosions compared to the conditions in an empty pipe. It can effectively decrease the explosion overpressure and explosive energy, thus limiting the flame propagation owing to insufficient fuel supply. The tendency for maximum explosion overpressure and explosion energy varied significantly by changing the thickness and pore size. It is worth noting that the attenuation rate of the maximum overpressure is generally greater than 50%, and the Al2O3 ceramic foam showed a better suppression performance than SiC. Additionally, the inhibitory effect is most obvious at 15 mm-20ppi Al2O3 and 30 mm-30ppi SiC, where the maximum explosion overpressure was reduced to 0.11 MPa and 0.19 MPa. However, the reduction of explosive energy is the combined result of the thickness and size of the pores. Overall, 15 mm Al2O3 and 30 mm SiC were more advantageous in suppressing gas explosions. This work supports the mechanism for preventing and suppressing gas explosions while using ceramic foam, and it might serve as a technological reference for the construction of explosion-proof devices. It is essential to avoid and control explosions in gas pipelines, thereby successfully enhancing the safety guarantee in gas pipeline transportation and engineering applications.

Enhancement of partial oxidation reformer by the free-section addition for hydrogen production

Hydrogen production by the partial oxidation combustion in porous media provides an efficient utilization for renewable biogas. In this paper, the free section with lengths of 0, 5, 10, 15 mm were designed in the middle of two-section porous media respectively. The effects of free section addition on the temperature distribution and methane conversion were investigated to determine the optimal burner parameters at the operating conditions of different velocities and equivalence ratios. Results indicate that the highest temperature appeared in the free length of 10 mm but the maximum of H2 energy conversion efficiency was in that of 15 mm. For the Al2O3 ceramic foam of 20 PPI, the better heat recirculation and preheating effect were shown between the gas and solid. However, the productions of H2 and CO at the 10 PPI burner reached the highest. With the increasing of equivalence ratio from 1.4 to 1.8, the energy conversion efficiency of syngas rose from 41% to 61% with the 15 mm free length. The appropriate free section addition contributes to improving the reforming efficiency, which provides a new way for the burner design.

Near-zero-shrinkage Al2O3 ceramic foams with coral-like and hollow-sphere structures via selective laser sintering and reaction bonding

The large shrinkage that ceramics undergo during sintering is a severe challenge for high-performance porous ceramics. In this study, we report a powder-based selective laser sintering (SLS) approach to prepare Al2O3 ceramic foams with near-zero shrinkage, high porosity, and outstanding strength. The ceramic foams consist of specific coral-like and hollow-sphere structures derived from the raw Al2O3/Al composite powders via reaction bonding (RB). A near-zero shrinkage of 0.91 ± 0.15 % and a high porosity of 73.7 ± 0.2 % can be achieved based on the Kirkendall effect during the oxidation of Al particles. Meanwhile, the reinforced sintering necks and robust bond-bridge connections between hollow-sphere and coral-like structures result in a remarkable bending strength of 7.37 ± 0.37 MPa. This measured strength is more than six times higher than other fabricated samples from spherical Al2O3 powders, and the comprehensive performance of ceramic foams prepared by this novel SLS/RB strategy is exceptionally remarkable versus that via conventional forming methods.

Enhancement of ceramic foam modified hierarchical Al2O3@expanded graphite on thermal properties of 1-octadecanol phase change materials

Abstract The porous Al2O3 ceramic foam was composited with expanded graphite (EG) by calcination method to obtain Al2O3@EG composite with hierarchical pores. The specific surface area of Al2O3@EG composite was 2.3 times that of EG, which can better enhance the thermal conductivity and heat transfer performance of phase change materials (PCMs). The stable composite PCMs with high thermal conductivity and energy storage density were prepared via vacuum adsorbing 1-octadecanol (OD) in Al2O3@EG. The thermal conductivity of the modified OD containing 10 wt% Al2O3@EG was 4.5 times that of pure OD, while maintaining a high phase change enthalpy, approximately 200 kJ/kg. The results of SEM and EDS indicated that Al2O3 foam particles dispersed equably on the surface of EG without obvious agglomeration. The XRD and FTIR results revealed that OD, Al2O3 and EG were physically combined. The prepared OD/Al2O3@EG composite PCMs with high thermal conductivity and large energy storage density can be promising for low temperature heat storage, such as industrial heat recovery system, comfort applications in buildings and textiles, solar energy system, etc. This study provides an innovative idea for the application of porous ceramic foams in the field of solar energy storage PCMs modification.

Preparation of high-porosity Al2O3 ceramic foams via selective laser sintering of Al2O3 poly-hollow microspheres

In this paper, high-porosity Al2O3 ceramic foams called Al2O3 PHM ceramics were fabricated through selective laser sintering (SLS) via Al2O3 poly-hollow microspheres (Al2O3 PHMs). SLS parameters were optimized by an orthogonal experiment as to be laser power = 6 W, scanning speed = 1800 mm/s, and scanning space = 0.15 mm. The effect of sintering temperature on microstructure, shrinkage, porosity, phase composition, mechanical properties and pore size distribution of Al2O3 PHM ceramics were investigated. When sintering temperature increased, Al2O3 PHM ceramics contained only Al2O3 phase and were gradually densified. With the raise of sintering temperature, the porosity of Al2O3 PHM ceramics decreased gradually from 77.09% to 72.41%, but shrinkage in H direction and compressive strength of Al2O3 PHM ceramics increased from 6.63% and 0.18 MPa to 13.10% and 0.72 MPa, respectively. Sintering temperature had little effect on pore size distribution of Al2O3 PHM ceramics, which only declined from 24.2 to 21.4 μm with the increase of sintering temperature from 1600 to 1650 °C. This method can not only directly prepare ceramic foams with complex shapes, but also control properties of ceramic foams. It provides a simple preparation method for many kinds of ceramic foams with complex structure and high porosity by using PHMs with different composition.

Flame front stability of low calorific fuel gas combustion with preheated air in a porous burner

The flame front stabilization of low calorific fuel gas (LCFG) combustion with preheated air was investigated numerically in a burner filled with Al2O3 ceramic foams. A two-dimensional model was implemented to simulate the flame propagation process of methane–preheated air combustion at an extra-low equivalence ratio. In addition to the wall heat loss, the effects of the preheated air temperature were analyzed by focusing on the flame front inclination and propagation velocity. The flame front instability for room temperature air agreed well with the results of the corresponding experiments. The results show that an increase in the preheated air temperature helps to improve the flame stabilization, such as inhibiting flame front inclination, decreasing its propagation velocity, and increasing the maximum combustion temperature. A stable combustion flame can be realized for LCFG by preheating the air to a critical temperature, which decreases with increase in the equivalence ratio and decrease in the inlet velocity. The wall heat loss promotes the flame front inclination, whereas it has little effect on its propagation velocity for stable combustion. The results are conducive to clean combustion of LCFG in porous media, and helpful for the design and operation of porous burners.

Influence of Scattering Phase Function on Estimated Thermal Properties of Al2O3 Ceramic Foams

Open ceramic foams are usually constituted of three-dimensional networks with randomly interconnected solid struts and fluid within pores. The heat transport within this material can be understood as the coupling of conduction, convection as well as radiation. The cooperative control of different heat transfer mechanisms is critical to successful design and optimization of components working at high temperatures. An answer to this problem usually requires good knowledge and understanding of the corresponding thermal properties in a wide range of temperatures. In the present paper, an inverse identification method was developed to determine coupled thermal properties from transient thermal measurements at temperatures up to 900 K for full description of conduction/radiation heat transports of foam media with absorbing, emitting, and anisotropic scattering effects. The influence of postulated phase function on the identified equivalent extinction coefficient, scattering albedo, anisotropic scattering factor, and two-phase thermal conductivity was discussed for better understanding of thermal behavior within ceramic foams. The estimated thermal properties under each postulated phase function of the sample at transient temperature profiles were used to calculate equivalent thermal conductivities, which were then compared with the measured results at more than 1000 K. The accordance between them indicated that linear anisotropic scattering phase function demonstrates superiority in description of radiation behavior within Al2O3 ceramic foam.

Synthesis of monolithic alumina-silica hollow microspheres and their heat-shielding performance for adiabatic materials

Al2O3 ceramic foams-based composites were firstly synthesized to be used as the thermal insulation material which has excellent mechanical properties of the substrate material and better thermal properties of hollow microspheres. In this research, by doping TEOS, the monolithic hollow microspheres were prepared via a novel and effective synthesis route using propylene oxide as the gelation initiator to induce the gelation of aluminum chloride hexahydrate solution. The influence of TEOS on the morphology and high-temperature stability of the monolithic hollow microspheres was clarified in detail. Based on the optimized additive amount of TEOS, Al2O3 ceramic foams were introduced as the substrate material of alumina-silica hollow microspheres to fabricate the final Al2O3 ceramic foams-based composites. Benefited from this special structure, the Al2O3 ceramic foams-based composites displayed excellent mechanical properties and thermal properties. The samples changed less in appearance and did not show significant shrinkage after heat-treatment at 1200°C. The density, bending strength and thermal conductivity of the Al2O3 ceramic foams-based composite were 0.32g/cm3, 1.8MPa and 0.12W/mK, respectively.

Fabrication and Structure Characterization of Alumina-Aluminum Interpenetrating Phase Composites

Alumina-Aluminum composites with interpenetrating networks structure belong to advanced materials with potentially better properties when compared with composites reinforced by particles or fibers. The paper presents the experimental results of fabrication and structure characterization of Al matrix composites locally reinforced via Al2O3 ceramic foam. The composites were obtained using centrifugal infiltration of porous ceramics by liquid aluminum alloy. Both scanning electron microscopy (SEM + EDS) and x-ray tomography were used to determine the structure of foams and composites especially in reinforced areas. The quality of castings, degree of pore filling in ceramic foams by Al alloy, and microstructure in area of interface were assessed.

石墨型C<sub>3</sub>N<sub>4</sub>在泡沫陶瓷表面的原位负载及可见光催化空气净化应用

g-C3N4 is a metal-free visible light photocatalyst with wide promising application. In this work, an in situ approach of dissolution- recrystallization-thermal-treatment is developed for effective immobilization of g-C3N4 on the support using dicyandiamide as precursor. The immobilized g-C3N4 on Al2O3 ceramic foam was firm enough owing to the special physicochemical interaction between g-C3N4 and Al2O3. The g-C3N4 samples were analyzed by techniques. With a systematic investigation on the effects of different pyrolysis time on the microstructure and photocatalytic activity of g-C3N4, it was found that the immobilized g-C3N4 with a pyrolysis time of 4 h exhibited optimal NO removal ratio of 57.9%. The outstanding activity can be ascribed to the increased surface area and porosity and promoted charge separation. This work could provide an in situ immobilization approach based on the interaction between the photocatalyst and support, as well as the technical support and theoretical basis in practical application of g-C3N4 in air purification.

Wetting behavior of aluminium and filtration with Al2O3 and SiC ceramic foam filters

The wetting behavior between liquid aluminium and substrates made from industrial Al2O3 and SiC based ceramic foam filters (CFF) was investigated. The same CFF filters were also tested in plant scale filtration experiments. The wetting experiment results show that the SiC based filter material is better wetted by liquid aluminium than the Al2O3 based filter material. This indicates that the improved wetting of aluminium on a filter material is an advantage for molten metal to infiltrate the filter during priming. Also, better wetting of Al-filter might increase the removal efficiency of inclusions during filtration due to better contact between filter and metal. Non-wetted inclusions are easier to be removed.

Immobilization of polymeric g-C3N4 on structured ceramic foam for efficient visible light photocatalytic air purification with real indoor illumination.

The immobilization of a photocatalyst on a proper support is pivotal for practical environmental applications. In this work, graphitic carbon nitride (g-C3N4) as a rising visible light photocatalyst was first immobilized on structured Al2O3 ceramic foam by a novel in situ approach. Immobilized g-C3N4 was applied for photocatalytic removal of 600 ppb level NO in air under real indoor illumination of an energy-saving lamp. The photocatalytic activity of immobilized g-C3N4 was gradually improved as the pyrolysis temperature was increased from 450 to 600 °C. The optimized conditions for g-C3N4 immobilization on Al2O3 supports can be achieved at 600 °C for 2 h. The NO removal ratio could reach up to 77.1%, exceeding that of other types of well-known immobilized photocatalysts. Immobilized g-C3N4 was stable in activity and can be used repeatedly without deactivation. The immobilization of g-C3N4 on Al2O3 ceramic foam was found to be firm enough to overwhelm the continuous air flowing, which can be ascribed to the special chemical interaction between g-C3N4 and Al2O3. On the basis of the 5,5'-dimethyl-1-pirroline-N-oxide electron spin resonance (DMPO ESR) spin trapping and reaction intermediate monitoring, the active species produced from g-C3N4 under illumination were confirmed and the reaction mechanism of photocatalytic NO oxidation by g-C3N4 was revealed. The present work could provide new perspectives for promoting large-scale environmental applications of supported photocatalysts.

Effect of Composite Sintering Additive on Al<sub>2</sub>O<sub>3</sub> Ceramic Foam

In this study, the environment-friendly egg white protein was used as foaming agents and binders to fabricate Al2O3 ceramic foams, owing to its excellent foaming and binding properties. The CaO-SiO2-MgO-ZnO-TiO2-B2O3 composite sintering additive was added into Al2O3 ceramic foam to develop the mechanical performance of Al2O3 ceramic foam and facilitate sintering. The modified Al2O3 ceramic foam was investigated on porosity, density, compressive strength, pore morphology and grain size. The investigation revealed that: compared with ordinary Al2O3 ceramic foam, although the samples adding sintering additive had lower porosity, larger density and bigger grain, its compressive strength was significantly much stronger than samples without sintering additive. The XRD result indicated that samples adding sintering additive had spinel, anorthite and a small amount of mullite phase besides the main corundum phase. Adding sintering additive is a new way to develop the mechanical performance of Al2O3 ceramic foam and facilitate sintering which can help grain growth, thereby improving the mechanical properties of Al2O3 ceramic foam.

Effect of Multiple-Binders on Properties of Al<sub>2</sub>O<sub>3</sub>-Based Ceramic Foam Filter

In this paper，Al2O3ceramic foam filters prepared by polyurethane sponge impregnation.The effect of multiple binders on properties of ceramic foam was studied . The results show that using 90g dihydrogen phosphate and 30g under the CMC 1350°C sintered alumina matrix ceramic foam filters are the best performance. The compressive strength of the Al2O3-based foam ceramics prepared with optimal multiple-binder and sintered at 1350°C could reach up to 1.697MPa. At the same time,it is obtained through test that the thermal shock times of sintered samples reached 5 by staying at 1100°C for 10 min.

A novel method for preparation of interconnected pore-gradient ceramic foams by gelcasting

A novel approach was introduced to prepare pore-gradient Al2O3 ceramic foams with association of gelcasting process and polymer sphere template. This approach allows the design of pore connectivity and gradient height of ceramic foams by the appropriate selection of sphere sizes and numbers. The limitation of ceramic foams fabricated by polymeric sponge process on sponge carrier can be resolved by this approach. Epispastic polystyrene (EPS) spheres with different sizes were employed to array ordered templates. Influence of solid content and dispersant on the viscosity of Al2O3 slurry was studied. EPS spheres modified by oxygen plasma to increase the hydrophilicity of surfaces and influence of pre-removal of EPS template on the integrity of networks were investigated. Results showed that 55 vol.% Al2O3 slurries with 0.5 wt% dispersant kept good fluidity for casting and permeability in template. Water contact angle of EPS surface decreased from 95.2° to 20°. Some defects in green bodies such as edge-delamination and micropores disappeared after surface modification. The perfect structure and morphology of the ceramic foams were ascribed to the pre-removal of template by solvent. The hierarchical pore structure was fabricated with EPS spheres of 2.1, 2.6 and 3.2 mm diameters. Porosity and compressive strength of the pore-gradient Al2O3 ceramic foam were 68.5% and 3.06 MPa at 1,500 °C, respectively.

Removal of Inclusions from Aluminum Through Filtration

Filtration experiments were carried out using both an AlF3 slurry-coated and an uncoated Al2O3 ceramic foam filter to study the removal of nonmetallic inclusions and impurity elements. The results showed that the 30-ppi ceramic foam filter removed up to 85 pct inclusions from aluminum. Several pictures of two- and three-dimensional morphologies of both nonmetallic and intermetallics inclusions also have been presented. The following contributing mechanisms for the removal of nonmetallic inclusions in the deep-bed filtration mode are proposed: (1) collision with walls and interception effect and (2) the formation of both intermetallic and nonmetallic inclusion bridges during filtration. Fluid dynamics modeling of inclusion attachment to the filter walls showed that most inclusions, especially those with larger sizes, are entrapped at the upper part of the filter, whereas smaller inclusions are dispersed well throughout the filter. The calculated inclusions removal fractions for the 30-ppi filter showed that almost all inclusions >125 μm are removed, and inclusions ~5 μm in size are removed up to 85 pct. The interfacial energy between two collided same-size inclusions was calculated, indicating that a strong clustering of inclusions may result within the filter window. Magnesium impurities were removed up to 86 pct by the AlF3 slurry-coated filter. The filter acted in active filtration mode in addition to the contribution of the air oxidation of dissolved [Mg], which was calculated to be 13 pct. The total mass transfer coefficient of dissolved [Mg] to the reaction interface was calculated to be 1.15 × 10−6 m/s.