Ceramic Honeycomb Research Articles

Thermal Properties of Cu–Al–Ge Alloy PCM for Improving Thermal Energy Storage of Current CSP

Metallic phase change material was proposed and examined at melting/eutectic temperatures less than 600 °C for latent heat storage in concentrated solar power. The PCM alloy can potentially charge/discharge thermal energy as a sensible/latent heat at the temperature range of 414-527 °C. The working temperatures of PCM alloy are in operation temperatures of current molten-salt based CSP plant. In this study, thermal response testing of PCM alloy and sensible/latent storage unit that PCM alloy was loaded in a ceramic honeycomb were prepared in a laboratory scale. The thermal charging/discharging performance of PCM alloy and sensible/latent storage unit were experimentally examined and compared. The storage unit provided thermal release/absorption behaviour at close to temperatures of the thermodynamic equilibrium state.

Size shrinkage and compressive behaviour of Al2O3 honeycomb structures fabricated via Digital Light Processing technology

Al2O3 ceramic have excellent chemical inertness, superior heat resistance, and excellent corrosion resistance, so they are considered ideal materials for manufacturing high-performance components such as thermal end devices in aerospace, heat dissipation panels in electronic communication, and exhaust filters in the automotive industry. Digital Light Processing (DLP) is a useful technology to fabricate complex Al2O3 ceramic components. However, the size shrinkage effect of DLP-fabricated components need to be investigated deeply before its further application. In this work, we utilized DLP technology to fabricate Al2O3 ceramic honeycomb structures and systematically investigated their microstructure, size shrinkage, and mechanical properties. Our findings revealed that the Al2O3 ceramic grains exhibit flake-like structures with an average diameter of 1–2 μm, and the ceramic particles are tightly bonded. The shrinkage rates in the X and Y axes were 7.54 % and 7.42 %, respectively, while the Z-axis exhibited a more significant shrinkage of 13.04 %. This anisotropic shrinkage in different direction was attributed to accumulation of the interlayer bonding under gravity action during debinding and sintering process. The compressive stress-strain curve of the honeycomb structures demonstrated a typical brittle compressive behavior, including elastic, stress plateau, and brittle fracture stages. The honeycomb structures exhibited an elastic modulus of 54.49 ± 1.22 MPa and a compressive strength of 10.22 ± 0.42 MPa. The fracture analysis indicated that the fractures region of honeycomb structures initiated at the corners of the honeycomb structures, indicating their easy-broken compared to the walls. These findings provide valuable guidance for the high-precision and high-performance manufacturing of complex Al2O3 ceramic components.

Cordierite ceramic membrane preparation using gas solid reaction growth for nanoparticles filtration

Mullite whiskers have been successfully grown on the surface of cordierite honeycomb ceramics by the gas-phase growth method. The cilia-like structure can significantly improve the filtration precision. The acicular mullite whiskers grew on the cordierite present nanometer-sized (200–300 nm) diameters and micrometer-sized (1–2 μm) lengths. Owing to mullite whiskers growth on surface of pores, the morphology of pores is changed and the microstructure change will lead to filtration precision increasing. The composites with the largest ratio of length/diameter mullite whiskers possess the highest filtration precision, which can reach 122.42 nm, 255.00 nm and 458.67 nm in intercepting different particle size of nano-SiO2, respectively. Moreover, the bending strength of the cordierites were enhanced due to the generation of mullite whiskers, these generated whiskers intersected with each other forming many unfixed lap-jointing points. The porous ceramics membrane with the unique microstructure has great potential application in gas-solid separation field and liquid-solid separation field.

Hydraulic pressure resistance of the ceramic resin composite buoyancy materials based on cylindrical tube configuration

Due to high modulus, high strength and low water absorption of the 99.5% alumina ceramic, the tubular ceramic resin composite (TCRC) has been designed and fabricated, which can provide a potential option for the deep-sea buoyancy materials. The reliability and applicability of TCRC under hydrostatic pressure are systematically discussed by means of theory, experiment and simulation. Circumferential instability and strength failure are two possible failure modes of the TCRC through theoretical analysis. The study indicates that the load-bearing capacity of TCRC decreases with the increase of the number of vertical/horizontal tube arrays m, the ratio of the inner to outer radius r/Rc of the ceramic tube or the ratio of the length to the outer radius L/Rc of the ceramic tube. Conversely, the load-bearing capacity of TCRC increases with the increase in the modulus of matrix phase Er. In addition, TCRC with parameters of “r/R-0.93/0.91-3X3-L40-E3.18” has excellent performance through experimental verification. That is, the core density and hydrostatic strength of the TCRC are 0.67 g/cm3 and 150.6 MPa, respectively. Better stated, our designed buoyancy material can be applied in the deep-sea environment of 12000m, which is the deepest spot on the ocean floor ever explored. The excellent performance of TCRC verifies the feasibility of ceramic circular honeycomb configuration in the application of hydrostatic pressure environment. Meanwhile, the buoyancy materials used in different water depths can be designed by changing the L/Rc or r/Rc of the round tube in circular honeycomb.

Transient heat transfer analysis of a sandwich panel with a cracked honeycomb core

Sandwich structures with ceramic honeycomb cores are extensively employed in thermal protection systems owing to their exceptional ability to resist high temperatures. This work aims at exploring the effect of cracking on the transient thermal process of the sandwich panel subject to impulsive and cyclic thermal loadings. Both the conventional and re-entrant hexagonal alumina honeycombs are considered for the core material. By the integral transform method, combined with singular integral equations, the transient temperatures of the whole sandwich panel are determined from the semi-analytical solution. The straightforward temperature difference of the crack face’s midpoints is exploited to characterize the heat intensification near the crack. Parametric investigations are carried out for the internal cell angle, the relative density, crack length, crack position, and thickness of face sheets, which provides a better understanding of the honeycomb materials working in thermal protection systems.

Low-Temperature Catalytic Oxidation of Volatile Organic Compounds (VOCs) using Transition Metal Mixed Oxide Catalysts

This paper discusses the modification of MnOx by doping various metals, such as Cu, supported on cordierite honeycomb ceramics, which were easily synthesized by using the impregnation method. The physicochemical properties were comprehensively featured via the BET, XRD, SEM-EDX and H2-TPR techniques. Activity results suggested that the introduction of doping metals significantly enhanced the catalytic performance of Cu1Mn2Ox compared to single metal oxides. Furthermore, in the catalytic oxidation of benzene and toluene, the monolithic Cu1Mn2Ox catalyst demonstrates the best catalytic performance. It was able to completely oxidize the two compounds at 275oC with a reaction velocity (WHSV) of about 18,000 mL/(g•hr) and pollutant concentrations of 7000 ppm and 12000 ppm, respectively. The formation of a Cu-Mn solid solution with spinel Cooper-Manganese structure was thought to be the cause of the excellent catalytic performance of monolithic Cu1Mn2Ox. This resulted in an increase in the amount of adsorbed oxygen species on the surface and a high lattice oxygen mobility. This can improve catalyst reducibility and oxygen species activity, as demonstrated by significantly higher dehydrogenation temperatures of Cu-Mn composite oxides through H2-TPR. Meanwhile, the monolithic Cu1Mn2Ox catalyst showed good stability in 16 hours of testing and cycle ability test and showed great potential in practical application.

Effects of unit cell parameters on the thermal shock resistance of auxetic honeycomb sandwich structures: Combining discrete and continuum model

The influence of unit cell geometric parameters on the thermal fracture behavior and thermal shock resistance of honeycomb ceramics sandwich structures is revealed for the first time. The present study establishes a continuum model for the thermal fracture of sandwich structures, and a discrete numerical representation model for the equivalent fracture toughness of honeycombs, respectively. A novel evaluation approach for the thermal shock resistance of porous material structures has been provided by combining the two models. The effects of temperature dependence, face sheet thickness, honeycomb orientation and honeycomb geometrical parameters on thermal shock resistance are studied. Results indicate that changing the inclined angle of honeycomb can effectively increase the critical thermal shock temperature rise. Auxetic honeycomb sandwich structures with the inclined angle of −9° can reach the peak of the critical temperature rise. The results would contribute to the application of honeycomb sandwich structures in thermal protection systems.

Four-channel catalytic micro-reactor based on alumina hollow fiber membrane for efficient catalytic oxidation of CO

The traditional automotive catalytic converter using commercial ceramic honeycomb carriers has many problems such as high back pressure, low engine efficiency, and high usage of precious metals. This study proposes a four-channel catalytic micro-reactor based on alumina hollow fiber membrane, which uses phase inversion method for structural molding and regulation. Due to the advantages of its carrier, it can achieve lower ignition temperature under low noble metal loading. With Pd/CeO2 at a loading rate of 2.3% (mass), the result showed that the reaction ignition temperature is even less than 160 °C, which is more than 90 °C lower than the data of commercial ceramic substrates under similar catalyst loading and airspeed conditions. The technology in turn significantly reduces the energy consumption of the reaction. And stability tests were conducted under constant conditions for 1000 hours, which proved that this catalytic converter has high catalytic efficiency and stability, providing prospects for the design of innovative catalytic converters in the future.

Vat photopolymerization of silicon carbide strengthened alumina ceramic composites with honeycomb structure for heat insulation and oil/water separation

In this study, the effects of different silicon carbide (SiC) particle sizes on the viscosity and curing behavior of alumina (Al2O3) ceramic suspensions were thoroughly investigated. The findings revealed that increasing the size of SiC particles led to a noticeable decrease in the viscosity of the suspension. The Al2O3 ceramic suspension with 0.6 μm SiC powder demonstrated a shallower cure depth and wider excess width compared to the suspension with 1.0 μm SiC powder. Sintering tests demonstrated that the properties of the SiC–Al2O3 ceramics improved at higher sintering temperatures. Moreover, a high-performance honeycomb ceramic was successfully designed and fabricated with a porosity and compressive strength of 30.8 % and 188 MPa, respectively. Finally, the SiC–Al2O3 honeycomb ceramics were effectively applied in heat insulation and oil-water separation applications, demonstrating their remarkable capabilities.

Assessment of mechanical performance of Al2O3 ceramic honeycomb sandwich structures produced with SLA 3D-printing regarding unpolymerized slurry removal strategy

Al2O3 ceramic honeycomb sandwich bars with a hexagonal core were manufactured through SLA 3D-printing to analyze the impact of hole placement, designed for the removal of uncured slurry, on the bending strength of the samples. Several holes were placed specifically on the samples in the design in two different ways. In the initial design, the holes were placed on the honeycomb sandwich structure’s upper and lower face-sheets. In the second design, the holes were positioned in the direction of the sample thickness, in the lateral walls. The moment of inertia values for the honeycomb structures were calculated with the help of experimental elastic modulus results, and true bending strength was determined according to these results. Nominal strength values were found using the common three-point bending formula. The true bending strength value of Al2O3 with lateral holes was 73% higher than Al2O3 with holes on face-sheets, while the nominal bending strength was 79% higher. Al2O3 samples with holes on face-sheets exhibited a significantly higher failure index compared with both the bulk samples and the Al2O3 samples with lateral holes. The holes on the face-sheets reduced the cross-sectional area of the tensile surface and contributed to an increase in stresses due to the stress concentration effect. The Al2O3 samples with lateral holes provided a great advantage of specific strength, reaching an average value of 65% above the specific strength of the bulk samples.

Quench-induced Cu-ZnO catalyst for hydrogen production from methanol steam reforming

Methanol steam reforming (MSR) is considered as a promising approach to provide hydrogen for proton-exchange membrane fuel cells. However, it is challenging to develop effective and durable Cu-based catalysts. Herein, Cu-ZnO catalysts are prepared by facile quenching of ZnO in copper nitrate solution followed by reduction to obtain the desired metal loading and induce the doping of surface metal heteroatoms for producing more vacancies. Catalysts enriched with oxygen vacancies can efficiently activate H2O and rapidly transform C-containing intermediates, resulting in higher methanol conversion and lower CO selectivity. As a result, the quenched optimal catalyst achieves 100 % methanol conversion and 0.05 % CO selectivity at 280 ℃, exhibiting the excellent catalytic performance in MSR reaction. In practical applications, structured catalysts are more attractive for large-scale catalytic reactions owing to the low pressure drop and high utilization efficiency. Therefore, ZnO-Cu3 catalyst is coated on cordierite honeycomb ceramics with 100 % methanol conversion and 0.04 % CO selectivity at 280 ℃. After 100 h of the reaction, the structured catalyst remains ∼ 92.3 % with CO selectivity varying from 0.02 to 0.06 %, demonstrating the good catalytic stability in the long-term experiment. In addition, the evolution of reactants and intermediates on the catalyst surface are briefly described by FTIR spectra. This study offers a novel and efficient approach to obtain highly active and durable catalysts with great potential for industrial-scale preparation and application.

Foamy ceramic filters and new possibilities of their applications

Peculiarities of sintering of foamy ceramic filters based on submicron aluminum oxide powders with additions of titanium oxide and manganese dioxide nanopowders are considered. The processes of removal of polymeric and binder paraffin material during sintering have been studied. The physical and mechanical properties of the obtained porous permeable filters with a foamy structure were analyzed in details. At a sintering temperature in an air atmosphere of 1350 °C, sufficiently high physical and mechanical properties were obtained, which made it possible to use the developed filters as catalyst carriers for vehicle exhaust gases. Bench comparative tests have shown that ceramic filters with a foamed structure are promising catalysts for afterburning car exhaust gases instead of ceramic honeycomb blocks of catalyst carriers. The developed technology allows reducing the sintering temperature of porous foam ceramic filters to 1350 °C and replacing expensive high-temperature ceramic heaters with cheaper nickel-chromium ones.

Fabrication of cobalt (II, III) oxide @nitrogen doped carbon/honeycomb ceramics with porous structure for room-temperature formaldehyde oxidation

The content of surface cobalt active sites and oxygen vacancy (VO) is vital to the catalytic performance of Co3O4 catalysts. Herein, a robust Co3O4@N doped C supported on honeycomb ceramics (Co3O4@NC-HC) catalyst with porous structure was prepared by an impregnation-calcination method using ZIF-67 as the precursor. The N2 calcining atmosphere and relatively closed environment are beneficial for the formation of more pyridine N, Co3+ surface active sites, and VO, which favors formaldehyde (HCHO) or O2 adsorption and activation. The higher content of NC in Co3O4@NC-HC than in Co3O4@NC-HC-open and Co3O4@NC-HC-air can disperse Co-containing catalysts better and promote electron transfer. The Co3O4@NC-HC catalysts exhibited excellent activity and stability for HCHO oxidation at room temperature. The 1.0 Co3O4@NC-HC sample with theoretical 7.7 wt% showed the maximum efficiency (96.5 %) for HCHO removal. The related catalytic mechanisms over Co3O4@NC/HC for HCHO oxidation were posed.

Numerical study of flame inclination instability in a packed bed with extra lean methane/air intake by an adaptive multi-scale model

The common numerical method to simulate the evolution of flame instability during filtration combustion mainly includes volume average method and pore scale simulation. However, they are not satisfying in computation accuracy and cost respectively. In this paper, a self-developed adaptive multi-scale model is built to study the inclination instability of the flame front in a packed bed with honeycomb ceramics. The perturbations on the distribution of the intake parameters and physical properties of fillings in the packed bed lead to the flame inclination. The influences of the amplitude and range of the perturbations on the flame inclination development are investigated. The development mechanism of flame inclination is analyzed by method of flow competition (MFC) theory. The results show that the increase of the flame inclination angle will enhance the transversal heat transfer. Subsequently, the radiation and conduction fluxes restrain the increase of the flame inclination. Under the same level of perturbation amplitude, the result shows that the influence sequences of the four factors for the flame inclination are as follows: fillings porosity, feed flow rate, fillings heat capacity, and feed concentration. In addition, larger amplitude of perturbation leads to higher maximum flame inclination angle. However, the perturbation range has little influence on the development of flame inclination angle. Finally, the flame inclination is restrained successfully through adding new perturbation of intake parameters or elimination of initial perturbation. The above.studies are quite meaningful to the stable operation and wide application of porous media combustion technology in the utilization of low calorific value gas energy.

Development of a sunlight-driven thermoacoustic engine for solar energy harvesting

Solar-powered thermoacoustic engine (TAE) is a promising technology for harvesting solar energy. In this study, a prototype of triple quarter-wavelength standing-wave TAEs with different total lengths (0.195 m, 0.235 m, and 0.275 m) driven by sunlight collected by three Fresnel lenses (diameter 0.36 m) is constructed and tested. Experimental results show that when the ceramic honeycomb is heated by the sunlight, the triple TAEs resonate at steady state at the fundamental frequencies of 312 Hz, 366 Hz and 435 Hz, respectively. These values are in reasonable agreement with those predicted by the reduced-order network model. For the TAE operating at 366 Hz, acoustic oscillations with a sound pressure level of 140 dB are measured at the TAE outlet, and the acoustic power generation in the ceramic honeycomb is estimated to be 0.135 W. The potential applications of the proposed sunlight-driven TAEs are then envisaged. This work demonstrates the feasibility of converting solar energy into acoustic power using thermoacoustic technology, providing great guidance for prospective studies on the development of solar-driven thermoacoustic electric generators and refrigerators.

Outlet-coated ceramic honeycomb bodies and methods of manufacturing same

Outlet-coated ceramic honeycomb bodies and methods of manufacturing same

Continuous near-complete photocatalytic degradation of toluene by V/N-doped TiO2 loaded on honeycomb ceramics under UV irradiation

Photocatalytic degradation of volatile organic compounds (VOCs) is a significant applying aspect of photocatalysis. Both the modulation of photocatalysts and the rational dispersion of them on supports are key for solar-driven VOC degradation. Conventional batch-type photoreactors have low efficiency while continuous-flow photoreactors suffer from the problem of incomplete removal of VOCs. Herein, aiming for continuous and complete degradation of toluene gas as the target contaminant, continuous-flow photocatalytic degradation reactors were made by adhering the vanadium and nitrogen codoped TiO2 on honeycomb ceramics (V/N-TiO2@HC) by a simple sol-gel method. In such a reactor, the rich ordered pores in the HC accelerate mass transport of toluene, and the introduction of V/N dopants narrows the bandgap and widens the light absorption range of TiO2, together resulting in continuous and nearly-complete photocatalytic degradation of toluene. The unique and stable structure of HC allows the photocatalysts to be reused. The degradation rate of toluene gas can reach 97.8%, and after 24 rounds of photocatalytic degradation, there is still a degradation rate of 96.7%. The impacts of loading times and gaseous flow rate on the photocatalytic performance of V/N-TiO2@HC are studied in detail. Our study provides a practical solution for the continuous and complete photocatalytic degradation of VOCs and opens a new application field for HC.

Retracted: The Adsorption of VOCs by Honeycomb Ceramics Loaded with Molecular Sieves

Retracted: The Adsorption of VOCs by Honeycomb Ceramics Loaded with Molecular Sieves

Enhanced mechanical properties of R–SiC honeycomb ceramics with in situ AlN–SiC solid solution

Recrystallized SiC (R–SiC) honeycomb ceramics were prepared using Al4SiC4 as additives through a two–step sintering process, consisting of pre–nitridation treatment at 1800 °C for 180 min, followed by heat treatment for 60 min at temperatures ranging from 2000 to 2200 °C. The influences of firing temperature on phase compositions, microstructures, porosity, and mechanical properties of honeycomb ceramics were evaluated. The results revealed that AlN, SiC, and C were formed in situ after nitriding at 1800 °C. As the subsequent heat treatment temperature increased from 2000 to 2200 °C, the sublimation rate of submicron SiC increased, as well as AlN solid solubility. AlN diffused into SiC lattice and formed the SiC–AlN solid solution, which accelerated the conversion of 6H–SiC to 4H–SiC. According to first–principles calculations, the formation of solid solution contributed to the sintering process, which performed through the reduction of the surface energy of the grains. In addition, the pore size of specimens increased with elevating the heating temperature, and the distribution transitioned from unimodal to bimodal. Simultaneously, AlN and C activated the SiC lattice and facilitated mass transfer rate. The SiC sintering necks were well–developed at 2200 °C, resulting in the optimized overall performance of SiC honeycomb ceramics with a porosity of 52.7% and compressive strength of 17.98 MPa.

Energy-Reduced Fabrication of Light-Frame Ceramic Honeycombs by Replication of Additive Manufactured Templates.

Ceramic components require very high energy consumption due to synthesis, shaping, and thermal treatment. However, this study suggests that combining the sol-gel process, replica technology, and stereolithography has the potential to produce highly complex geometries with energy savings in each process step. We fabricated light-frame honeycombs of Al2O3, Ba0.85Ca0.15Zr0.1Ti0.9O3 (BCZT), and BaTiO3 (BT) using 3D-printed templates with varying structural angles between -30° and 30° and investigated their mechanical and piezoelectric properties. The Al2O3 honeycombs showed a maximum strength of approximately 6 MPa, while the BCZT and BaTiO3 honeycombs achieved a d33 above 180 pC/N. Additionally, the BCZT powder was prepared via a sol-gel process, and the impact of the calcination temperature on phase purity was analyzed. The results suggest that there is a large energy-saving potential for the synthesis of BCZT powder. Overall, this study provides valuable insights into the fabrication of complex ceramic structures with improved energy efficiency and enhancement of performance.