Ceramic Honeycomb Research Articles

Additive manufacturing of yttrium-stabilized tetragonal zirconia: Progressive wall collapse, martensitic transformation, and energy dissipation in micro-honeycombs

For zirconia-based technical ceramics, the unique advantages of micro-architecture geometries combined with the potent mechanical and functional properties have been challenging to implement owing to additive manufacturing restrictions. In this work, we present a stereolithography-based additive manufacturing approach involving slurry development for yttrium-stabilized tetragonal zirconia polycrystals (Y-TZP), followed by printing using a custom-built large-area projection micro-stereolithography system. After post-processing, i.e., polymer burnout and sintering, 98% relative density is reached in the printed Y-TZP parts. Thanks to the good manufacturing quality, the bulk-scale Y-TZP micro-honeycombs are able to display typical stretch-dominated behavior in out-of-plane compression, showing elastic loading (Stage I) and protracted brittle failure of individual walls over a significant strain (Stage II). For a Y-TZP micro-honeycomb consisting of 5 × 4 hexagonal cells with a wall thickness of 300 μm and a cell diameter of 1.40 mm, the energy dissipation density is measured to be 9.45 J/g, substantially higher than other ceramic honeycombs and packings reported earlier. This energy dissipation capability is mostly attributed to the progressive wall collapse seen in Stage II deformation, in which the perimeter walls are preferentially fragmented relative to the interior walls. According to finite element analysis, this phenomenon is a result of the deviation from uniaxial compression and the presence of stress gradients in the perimeter walls. We also find evidence for stress-induced martensitic transformation in the Y-TZP micro-honeycomb after compression, which may be another contributor to the observed energy dissipation capability.

Numerical and Experimental Investigation of Pressure Drop in Periodic Open Cellular Structures for Intensification of Catalytic Processes

Periodic Open Cellular Structures are envisioned as potential enhanced catalyst substrates for heat and mass transfer-limited processes. To enable their rational design, in this study, we propose a combined numerical and experimental approach to assess the pressure drop in the tetrakaidekahedral and diamond lattices since generalized correlations are not present in the literature. Deviations are observed between the model predictions available in the literature, which are possibly due to the different methods of investigation, that is, numerical on ideal geometries and experimental on reproductions. To reconcile the two approaches and prevent discrepancies, careful attention is paid here to the quality of 3D-printed replicas for experimental investigation to obtain results representative of ideal lattices. Computational Fluid Dynamics simulations and experiments are then employed together to cross-validate the results and then to perform a parametric analysis of the effect of the morphological properties on the pressure drop. The effect of the cell size and the porosity are discussed, enabling the derivation of engineering correlations for the prediction of the pressure drop across the lattices within the range of 1 < Reds < 300. Finally, the performances of lattice materials are compared with those of conventional structured supports by evaluating the trade-off between the fluid–solid mass transfer rate and the pressure drop, which is crucial for several catalytic processes. Results show that the diamond lattice outperforms other cellular materials and can outperform ceramic honeycomb monoliths at low Reynolds numbers.

Heterogeneous Catalysis Mechanism

In this paper, two heterogeneous catalysis mechanisms are introduced, namely: Chemical Reaction Mode Cyclic Catalysis Mechanism-CRM and Electron Cyclic Donate-Accept Catalysis Mechanism-ECDAM or Electron Orbital Deformation-Recovery Cyclic Catalysis Mechanism -EODRM . Some difficulties encountered by CRM are listed. The author clearly points out that the CRM is not credible。This false theory has misled us for more than 100 years。&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; About&nbsp; ECDAM, the article also gives a brief description. The main point of ECDAM is that the catalysis phenomenon are physical rather than chemical phenomenon. The catalysts do not participate in chemical reactions, It's just contact，electron cyclic donate-accept or electron orbital deformation-recovery cycle.. The theory contains three viewpoints: &nbsp;1, There is a boundary between the catalyst and the poison. 2, The active of the catalyst or the degree of toxicity of the poison is closely related to the electronegative value of the catalyst or poison. 3, The active of catalyst is closely related to the chemical state of the catalyst.. The selectivity of catalyst is also related to electronegative or energy level. According to ECDAM, The author considers that there are several problems worth studying in production and scientific research. such as: alumina is a poison in the Fe ammonia synthesis catalyst. The Cordierite (2MgO·2Al2O3·5SiO2 ) ceramic honeycomb support is also a&nbsp; poison in automotive exhaust purification catalyst .The Cordierite ceramic honeycomb is&nbsp;retardant in wall flow filter for diesel vehicles. Activated carbon is a poison in the Ruthenium catalyst for ammonia synthesis. Alumina and activated carbon all are a poison to noble metal catalysts, and so on.

Development of ceramic honeycomb monolith from natural zeolite tested as adsorbent to remove methylene blue in aqueous media.

This work presents a ceramic monolith with a honeycomb structure obtained from a natural zeolite (clinoptilolite), bentonite, and alumina. The monolith obtained by extrusion had a cell density of 57 CPSI (cells per square inch), an open frontal area of 52% w/w, and a wall thickness of 0.9 mm. The raw materials and the natural zeolite ceramic monolith (NZCM) were characterized by X-ray diffraction, N2 adsorption-desorption at 77 K, CO2 adsorption at 273 K, mercury intrusion-extrusion, axial compression tests, resistance to leaching at acidic and basic pH, and point of zero charge. The NZCM presented an SBET = 31 m2∙g-1, a modal micropore size of 0.44 nm, a porosity of 39%, the compressive stress = 14 MPa, and a pHPZC = 7.5. The NZCM was used as an inexpensive and easy-to-handle adsorbent to remove methylene blue (MB) dye in batch studies of kinetics and adsorption isotherms. From modeling of adsorption kinetic data, the predominant phenomenon in this system was physisorption. The modeling of adsorption isotherm data shows that the material has homogeneous active sites. The adsorption occurs by monolayer formation, finding a maximum capacity removal rate of 27 mg MB per gram of NZCM. Compared to other structured materials, a high capacity for removing MB with the ceramic monolith was obtained along with good mechanical properties and resistance in acidic and alkaline environments.

Catalytic Ozonation of Aqueous 4-Methylquinoline by Fluorinated Ceramic Honeycomb

Catalytic Ozonation of Aqueous 4-Methylquinoline by Fluorinated Ceramic Honeycomb

Deactivation of Honeycomb Ceramic Metal Catalysts after Stability Tests in an Industrial Coal Combustion Reactor

Deactivation of Honeycomb Ceramic Metal Catalysts after Stability Tests in an Industrial Coal Combustion Reactor

Nickel Nanoparticles Embedded in Porous Carbon-Coated Honeycomb Ceramics: A Potential Monolithic Catalyst for Continuous Hydrogenation Reaction

Nickel Nanoparticles Embedded in Porous Carbon-Coated Honeycomb Ceramics: A Potential Monolithic Catalyst for Continuous Hydrogenation Reaction

Preparation and characterization of diesel particle filter (DPF) with hierarchical microstructure for catalytic combustion of soot

Mullite whiskers were prepared on the wall of cordierite honeycomb ceramics using the gas-phase growth method. Subsequently, Co/Ce0.75Zr0.25O2 catalyst was loaded on the mullite whiskers to form hierarchical microstructure by the sol-gel technology for catalytic combustion of soot. Scanning electron microscopy, energy dispersive X-ray spectroscopy, Fourier transform-infrared spectroscopy, X-ray diffraction and Transmission electron microscopy were used to characterize the structural morphology and phase compositions. The filtration capability can be improved by mullite whiskers growth on the wall of cordierite honeycomb ceramics, and the microstructural feature is similar to the pseudostratified ciliated epithelium on the tracheal cavity surface (one section of human respiratory system). The Co/Ce0.75Zr0.25O2 catalyst decreased the ignition temperature of soot particles oxidation, and the cycle stability experiment confirmed that Co/CZ@M/C sample has good structural stability and stable catalytic performance. The high-efficiency filtration and the low-temperature catalytic oxidation of soot particles are combined with the hierarchical microstructure of Co/CZ@M/C, which has potential application in the diesel particulate filter (DPF) field.

High strength and microwave-absorbing polymer-derived SiCN honeycomb ceramic prepared by 3D printing

The combination of 3D printing technology and polymer-derived ceramic route provides an attractive strategy to construct microwave-absorbing honeycomb with fine structure through flexible process. However, preparation of honeycomb ceramics with both excellent mechanical and microwave-absorbing properties is still challenging. Herein, SiCN honeycomb ceramic was fabricated by stereolithography from UV curable polymeric precursor consisting of polysilazane and multifunctional acrylates. By optimizing the multifunctional acrylates and its ratio, the decomposition of organic moiety and the ceramization process of precursor are matched, rendering the achieved ceramic with high compactness. The hardness and specific compressive strength of SiCN honeycomb ceramic reach as high as 14.3 GPa and 333.3 MPa/(g·cm3), respectively. Meanwhile, at low pyrolysis temperature, the copolymerized acrylate and polysilazane that formed during curing process was converted to free-carbon nanodamins in-situ, which endows SiCN honeycomb ceramic with the minimum reflection loss of –49.0 dB, namely microwave absorption rate over 99.99%.

Potassium titanate whiskers on the walls of cordierite honeycomb ceramics for soot catalytic combustion

In this paper, potassium titanate whiskers was prepared via the Molten salt synthesis on the surface of cordierite ceramics for the regeneration of diesel particulate filters (DPFs). SEM, EDS, XRD, FT-IR, TG-DSC and TPO were carried out to characterize the morphology, microstructure, growth mechanism and catalytic performance of the samples. Potassium titanate whiskers with diameter (100–500 nm) and length (about 3 μm) is tightly combined with the cordierite ceramic substrate. The catalyst performance investigation demonstrates that potassium titanate whiskers decrease the soot combustion temperature apparently. The soot combustion process was studied by thermal analysis tests, and the activation energy of the combustion reaction can be calculated using Freeman-Carroll method. The carbon oxidation activation energy is 14.009 kcal/mol, and the activation energy for the catalytic reaction with potassium titanate whiskers is 6.287 kcal/mol, it can be illustrated that potassium titanate whiskers/cordierite catalyst possess excellence performance for carbon catalytic combustion. The coarseness of the interface increased because potassium titanate whiskers grew on the cordierite substrate, and the trapping ability could improve. This unique microstructure has potential application in the DPF field.

Experimental study of combustion characteristics of lean LPG/air mixture in Porous Media Burner

ABSTRACT The performance of a porous media burner (PMB) is immensely dependent on the selection of porous material. Present experimental work investigates the impact of burner’s material on the thermal performance of lean LPG/air mixture. This includes the study of stable combustion limits on the surface of porous media, uniformity of temperature distribution in porous media during stationary combustion and damage of porous media. Experimental investigation shows that the high temperature zone of the burner filled with foam ceramic is closer to the burner inlet than that of the burner filled with honeycomb ceramics under the same inlet velocity. In addition, the temperature at the inlet of the burner filled with foam ceramics is higher than that of the burner filled with honeycomb ceramics under the same inlet velocity. What’s more, lean burn limit range of the burner filled with foam ceramic is broader than the burner filled with honeycomb ceramics. The axial temperature distribution of the burner filled with honeycomb ceramics is more significant fluctuation than that filled with foam ceramic and the burner filled with honeycomb ceramics is more prone to local heat concentration. Therefore, the fracture of honeycomb ceramics after experiments subjected to thermal stress is much more serious than that of foam ceramics. Overall performance assessment confirms that foam ceramics is a better choice over honeycomb ceramics for lean combustion of the mixture of LPG/air in the PMB.

Vacuum Balloon–A 350-Year-Old Dream

The centuries-old idea of a lighter-than-air vacuum balloon has not materialized yet as such structure needs to be both light enough to float in the air and strong enough to withstand atmospheric pressure. We propose a design of a rigid spherical sandwich shell and demonstrate that it can satisfy these stringent conditions with commercially available materials, such as boron carbide ceramic and aluminum alloy honeycomb. A finite element analysis was employed to demonstrate that buckling can be prevented in the proposed structure. Also discussed are other modes of failure and approaches to manufacturing.

Easily-synthesized and low-cost amine-functionalized silica sol-coated structured adsorbents for CO2 capture

One reason for the slow development of adsorption-based carbon capture technologies is the inefficient fabrication of adsorbents with both promising adsorption performance and granular strength. In this work, an easy, low-cost, and environmentally friendly one-pot method is proposed to prepare structured adsorbents for post-combustion CO2 capture. Different from the traditional method that uses powdered silica gel as the support, branched polyethyleneimine (PEI) was mixed with colloidal silica and was then coated onto a ceramic fiber honeycomb monolith. Scanning electron microscopy (SEM) provided evidence that the amine molecules dispersed uniformly onto the porous silica films after vacuum drying. The optimal adsorption temperature, humidity, and PEI loading of the adsorbents were then determined using isotherms, adsorption rate curves, and breakthrough curves. The results showed that the 50 wt% PEI-impregnated silica sol had the highest capacity (1.719 mmol/g), which was comparable to that prepared with silica gel powders. On this basis, the manufacturing process of the structured adsorbents was optimized by referring to the capacity, kinetics, and mechanical strength. In addition, the use of the 80 wt% PEI soaking solution to soak the ceramic fiber honeycomb twice was recommended. The structured adsorbents exhibited capacities up to 1.025 mmol/g in simulated flue gas and had very stable performance in humid conditions, showing little degradation after 50 adsorption/desorption cycles

Continuous dimethyl carbonate synthesis from CO2 and methanol over BixCe1\u2212xO\u03b4 monoliths: Effect of bismuth doping on population of oxygen vacancies, activity, and reaction pathway

We evaluated bismuth doped cerium oxide catalysts for the continuous synthesis of dimethyl carbonate (DMC) from methanol and carbon dioxide in the absence of a dehydrating agent. BixCe1−xOδ nanocomposites of various compositions (x = 0.06–0.24) were coated on a ceramic honeycomb and their structural and catalytic properties were examined. The incorporation of Bi species into the CeO2 lattice facilitated controlling of the surface population of oxygen vacancies, which is shown to play a crucial role in the mechanism of this reaction and is an important parameter for the design of ceria-based catalysts. The DMC production rate of the BixCe1−xOδ catalysts was found to be strongly enhanced with increasing Ov concentration. The concentration of oxygen vacancies exhibited a maximum for Bi0.12Ce0.88Oδ, which afforded the highest DMC production rate. Long-term tests showed stable activity and selectivity of this catalyst over 45 h on-stream at 140 °C and a gas-hourly space velocity of 2,880 mL·gcat−1·h−1. In-situ modulation excitation diffuse reflection Fourier transform infrared spectroscopy and first-principle calculations indicate that the DMC synthesis occurs through reaction of a bidentate carbonate intermediate with the activated methoxy (−OCH3) species. The activation of CO2 to form the bidentate carbonate intermediate on the oxygen vacancy sites is identified as highest energy barrier in the reaction pathway and thus is likely the rate-determining step.

Indentation resistance of brittle auxetic structures: Combining discrete representation and continuum model

This work investigates the indentation resistance of the auxetic/non-auxetic honeycomb ceramics layer by combining a discrete numerical representation and a continuum analytical model. The indentation depth of honeycombs with varying cell-wall angle and cell-wall thickness are measured. The indentation depth of auxetic honeycombs with negative Poisson’s ratio (NPR) is smaller than that of conventional ones in the premise of the same cell-wall thickness. But on the condition that the honeycombs possess the same relative density, there exists an inverse tendency. The corresponding mechanisms responsible for those trends are revealed. The stress intensity factor (SIF) is defined to characterize the stress singularity at the corner of the punch. The influence of NPR on the magnitudes of SIF is evaluated. A punch toughness concept is defined by a novel multi-scale method as the failure criterion of brittle honeycomb ceramics in indentation tests. The effects of NPR on the punch toughness of honeycombs are discussed. And the empirical formulas of punch toughness varying with the cell-wall thickness and the relative density are summarized. Finally, the NPR effects on the collinear punches problem are detected; the results show that the auxetic performance can significantly weaken the interaction between the punches.

Ceramic microchannel reactors with channel sizes less than 100 μm prepared by a mesh-assisted phase-inversion process

Microchannel reactors show fast mass transfer and heat transfer while limited active surface area, which can be greatly increased by reducing channel sizes. However, conventional extrusion makes honeycomb ceramics with channel sizes above 100 μm. This study has prepared ceramic microchannel reactors with channel sizes in the range of 1–100 μm by a one-step phase-inversion process, and channels are formed through the convection between coagulant and solvent. The effect of channel size on reaction performance was investigated by comparing two reactors with different channel sizes in dry reforming of methane. In addition, the microstructure of the reactors can be further tuned via sintering temperature to achieve high catalytic performance owing to the balanced active surface and mass transfer. Therefore, the microchannel reactors developed in this study represent a diagram-shift in the preparation of microchannel reactors by making channels with sizes less than 100 μm, which has potential applications in many catalytic reactions.

Development of a cordierite monolith reactor coated with CeO2-supported BaSrCo-based perovskite for chemical looping steam methane reforming

Perovskite oxide is a potential oxygen carrier for chemical looping steam methane reforming (CL-SMR). According to our previous study, CeO2-supported Ba1-xSrxCoO3-δ perovskite exhibited high oxygen capacity and good reactivity in CL-SMR. However, powder samples faced some difficulties in CL-SMR. In this study, a series of cordierite monolith reactors coated with Ba1-xSrxCoO3-δ/CeO2 were prepared for CL-SMR. The CL-SMR reaction performance of the monolith oxygen carriers was tested in a fixed bed, and the temperature and the flow field of the reaction process were simulated using the computational fluid dynamics model. Results showed that the introduction of honeycomb ceramics (cordierite) could effectively inhibit the methane pyrolysis and the carbon deposition in the later stage during the partial oxidation of methane and ensure that the H2/CO ratio of syngas was close to the theoretical value of 2. The gas velocity was uniform in the monolith reactors and only a maximum temperature difference of about 1.5 K appeared in the central region of monolith reactor during partial oxidation of methane. The novel cordierite monolith reactor coated with perovskite oxide provided a promising oxygen carrier choice for the industrial application of CL-SMR.

Research on impact resistance of ceramic matrix composites

The honeycomb structure has been used in the field of bulletproof materials, but there is little research on the impact resistance of ceramic honeycomb materials. In this res earch, ceramic matrix composite plates were prepared by using square-hole honeycomb ceramics and filling the honeycomb structure with second-phase reinforcing materials. Using LS-DYNA software to carry out numerical simulation analysis of the two groups of impact processes, to investigate the improvement effect of the composite material compared with the impact resistance of the honeycomb ceramic material, and at the same time, the 7.62 mm ballistic gun launcher was used to test the impact of composite plate and ceramic matrix on the honeycomb ceramic control target. The results show that the honeycomb ceramic material will break prematurely when it is impacted by the projectile at high speed, and the impact resistance is poor. The toughness of ceramic matrix composites filled with reinforcing materials is enhanced. Compared with honeycomb ceramic materials, the energy absorption efficiency of the composite material under the same thickness is increased by 115.6%, and the energy absorption density is increased by 52.3%, which improves the poor brittleness of ceramic materials.

Effect of sintering atmosphere on the crystallizations, porosity, and thermal expansion coefficient of cordierite honeycomb ceramics

High-porosity cordierite ceramics were sintered in two different atmospheres, that is, in air (oxidizing) or in double-enclosed crucibles (mildly reducing). Paste slurries of cordierite compositions mixed with organic binders and pore formers were extruded into honeycomb-type substrates to produce diesel particulate filters (DPFs). The present study was conducted to explore the effects of sintering atmosphere on pore size, crystallization, amorphous phase, and thermal expansion coefficient (CTE) of sintered DPF honeycombs. Crystal phases were quantitatively analyzed using the Rietveld refinement method using powder X-ray diffraction (XRD) data. Amorphous phases were quantified using the Rietveld-internal standard method, and their presence was qualitatively confirmed by high-resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SAED) analysis. The most notable features observed were a dramatic decrease in the pore-size distribution and an enhanced rate of cordierite/indialite phase crystallization when sintering was performed in a double-enclosed crucible. A relatively high concentration of carbon monoxide (CO) in the double-enclosed crucible reduced the liquid-phase viscosity. This low-viscosity liquid phase spread relatively easily on the surfaces of crystal phases and enhanced the crystallization rate owing to a relatively large liquid–solid contact area in the mildly reducing atmosphere. The higher CTEs of DPFs produced in air compared with those produced in enclosed crucibles are discussed in relation to the amounts of amorphous and crystal impurity phases and crystal texture.

Numerical study of the anti-penetration performance of sandwich composite armor containing ceramic honeycomb structures filled with aluminum alloy

The aim of this work was to study the anti-penetration effect of sandwich composite armor with ceramic honeycomb structures filled with aluminum alloy under the impact of high-speed projectiles. The finite element software ABAQUS was used to conduct numerical simulation research on the process of a standard 12.7-mm projectile penetrating sandwich composite armor. The armor-piercing projectile model was simplified as a rigid body. The numerical simulation models were applied to three different sandwich composite armor structures (A, B, and C), each with a total armor thickness of 25 mm. The penetration resistance of the three kinds of composite armor was studied. We obtained velocity curves for the rigid projectile penetrating the different structures. The failure forms and penetration resistance characteristics of the three composite armor structures adopted in this paper were analyzed. In addition, the velocity reduction ratio is proposed as an index to evaluate the penetration resistance performance of the armor. The simulation results revealed decreasing rates of projectile speed in the structures A, B, and C of 69.6%, 91.1%, and 100%, respectively. The third composite armor (structure C) designed here has excellent penetration resistance and can block the penetration of a high-speed (818m/s) rigid projectile. This study can provide some reference for the application of laminated armor material in anti-penetration protection structures.