Ceramic Monoliths Research Articles

Efficient Computation of Radiative Heat Recovery from Porous Ceramic Monoliths for Efficient Solar Thermochemical Fuel Production

Solar thermochemical hydrogen (STCH) produced by heat-driven water-splitting is a promising route for producing green hydrogen and other zero-emission synfuels. However, the efficiency of STCH must be dramatically increased for it to make an impact on decarbonization efforts. We have previously presented a novel Reactor Train System (RTS) for significantly increasing the efficiency of STCH by employing heat recovery from the redox material and efficient gas exchange processes. In this paper we present a higher-fidelity model for the RTS that accommodates the slow heat diffusion through the STCH redox material. For this purpose, a novel method is introduced for transient modelling of radiative heat in participating media. This method, called GREENER: Generalized Radiation Exchange Factors and Net Radiation, combines the accuracy of Monte Carlo Ray Tracing with the low computational cost of the P1 or Rosseland diffusion approximations. Along with STCH, GREENER has application for modelling volumetric solar receivers, high temperature heat recovery systems like heat exchangers and regenerators, and packed bed reactors. Using the GREENER method, the RTS counterflow radiative heat exchanger is shown to achieve heat recovery effectiveness greater than 70%. The performance of non-uniform porous redox morphologies is evaluated, and high-performing configurations are identified.

Effect of boron on phase, nanostructure, and thermal stability of polycarbosilane-derived SiC ceramics

The current study explores the formation, evolution, and thermal stability of polymer-derived SiBC at high temperatures. It focuses on the phase evolution of SiBC ceramics derived from the doping of boron in an allyl-containing polycarbosilane preceramic polymer after 1200 °C–1600 °C pyrolysis. Different SiBC ceramic monoliths have been obtained. Boron is incorporated into the carbon phase at lower pyrolysis temperatures but into both the carbon phase and the SiC lattice structure at high pyrolysis temperatures. B–C bonds form in SiBC and hinder the growth of graphitic carbon and SiC. Boron improves the densification and thermal stability of the SiBC ceramics. This work provides an improved understanding of boron effects in polymer-derived SiC nanostructures at high temperatures.

Mineral Fusion via Dehydration‐Induced Residual Stress: From Gels to Ceramic Monoliths

AbstractMan‐made ceramics generally undergo harsh manufacturing conditions (e.g., high‐temperature sintering). In contrast, mineral structures with superior mechanical strength are generated in organisms under mild biocompatible conditions. Herein, it is reported that ceramic objects can be directly produced and strengthened by drying purely inorganic gels (PIGs), mimicking the biological tactic of fabricating continuous monoliths from hydrated amorphous precursors. The overall process is easy and biocompatible in that solutions of common iron and molybdate salts are mixed to generate a PIG, consisting of 80 wt% liquid water and amorphous mineral nanoparticles (hydrated iron molybdate: FeMo2H7O11), which, upon drying under mild temperature, turns into a residual stress‐strengthened ceramic block that displays a high mechanical performance (with a hardness/elastic modulus of 1.7/17.5 GPa). Analogous to the well‐known Prince Rupert's drop reinforced by residual stress upon quenching, the uneven volume shrinkage from the outside inwards during dehydration builds up residual stress that enables amorphous mineral fusion (with the assistance of hydration water) and strengthening. Furthermore, a dramatic bandgap reduction is achieved in the dried objects due to local structural changes of the Fe atoms under residual stress. This PIG‐dehydration approach holds promise for green ceramic manufacturing and offers insights into biomineralization puzzles.

Fabrication of lightweight ceramics of complex geometries in freezing weather

Natural freezing weather is used to fabricate lightweight ceramic monoliths with aligned pores for the first time. A stable aqueous-based alumina slurry (16 vol%) was formulated and frozen at −10 to −25 °C in natural freezing environment. The thermally treated ceramic monoliths achieved ∼82–88 vol% porosity with short-range aligned pores. Finally, the unidirectional pores in the structure are achieved using a mold with thermal insulation properties. Natural freezing saves 300 kJ of energy per kg of alumina slurry. Mechanically stable lightweight porous ceramics with complex geometries can be designed without cryogenic fluids, refrigeration, or thermal baths. Implementing natural freezing in the porous ceramics industries, particularly in the Arctic region, will bring forward a sustainable approach by reducing energy consumption and CO2 emissions.

Polymer-Derived Silicon Oxycarbide/Graphene Oxide Porous Ceramic Monoliths Obtained from Pickering Emulsions: Application as Active Electrodes for Lithium-Ion Batteries

Polymer-Derived Silicon Oxycarbide/Graphene Oxide Porous Ceramic Monoliths Obtained from Pickering Emulsions: Application as Active Electrodes for Lithium-Ion Batteries

Numerical Study on NO Conversion Characteristics of Ceramic and Metallic Monoliths Under Steady-State External Heat Loss in Marine After-Treatment System

Numerical Study on NO Conversion Characteristics of Ceramic and Metallic Monoliths Under Steady-State External Heat Loss in Marine After-Treatment System

Direct synthesis of ultralight, elastic, high-temperature insulation N-doped TiO2 ceramic nanofibrous sponges via conjugate electrospinning.

The design of three-dimensional ceramic nanofibrous materials with high-temperature insulation and flame-retardant characteristics is of significant interest due to the effectively improved mechanical properties. However, achieving a pure ceramic monolith with ultra-low density, high elasticity and toughness remains a great challenge. Herein, a low-cost, scalable strategy to fabricate ultralight and mechanically robust N-doped TiO2 ceramic nanofibrous sponges with a continuous stratified structure by conjugate electrospinning is reported. Remarkably, the introduction of dopamine into the precursor nanofibers is engineered, which realizes the nitrogen doping to inhibit the TiO2 grain growth, endowing single nanofibers with a smoother, less defective surface. Besides, the self-polymerization process of dopamine allows the construction of bonding points between nanofibers and optimizes the distribution of inorganic micelles on polymer templates. Moreover, a rotating disk receiving device under different rotating speeds is designed to obtain N-doped TiO2 sponges with various interlamellar spacings, further affecting the maximum compressive deformation capacity. The resulting ceramic sponges, consisting of fluffy crosslinked nanofiber layers, possess low densities of 12-45 mg cm-3, which can quickly recover under a large strain of 80% and have only 9.2% plastic deformation after 100 compression cycles. In addition, the sponge also exhibits a temperature-invariant superelasticity at 25-800 °C and a low heat conductivity of 0.0285 W m-1 K-1, with an outstanding thermal insulation property, making it an ideal insulation material for high-temperature or harsh conditions.

Aging studies of Dual functional materials for CO2 direct air capture with in situ methanation under simulated ambient conditions: Ru thrifting for cost reduction

Dual function materials (DFMs) comprised of 0.25 %Ru, 6.1 %Na2O/γ-Al2O3//monolith were evaluated for about 250 hours time-on-stream (TOS) at various simulated ambient climate capture conditions followed by temperature swing methanation to 280 °C. This paper focuses on the impact of thrifting Ru to low levels and the impact on performance. Results showed both stable CO2 capture capacity and CH4 production with 0.25 % Ru DFM deposited on a ceramic monolith. The CO2 conversion to CH4 production was decreased slightly by the Ru decrease from 1 % to 0.25 %. The capture capacity decreased since a lower Ru content reduces the complete decomposition of the Na2CO3 precursor producing fewer active adsorption sites (“Na2O”). The deployment of a low Ru DFM monolith would significantly decrease the overall capital cost and give more potential for a large-scale direct air capture and methanation (DACM) application.

A Quasi-Dimensional Model of Heat Transfer between Multi-Concentric Monolith Structures

Metallic monolith structures are often used in compact reactor applications due to their superior heat transfer properties and lower pressure drop when compared to ceramic monoliths. Endothermic reactions like steam reforming depend heavily on externally supplied heat, making highly conductive supports especially useful. Simulations are invaluable for designing effective reactors with complex catalyst support structures but are conventionally resource-intensive. Additionally, few dedicated heat transfer experiments between monoliths exist in prior literature. To expand general knowledge of heat transfer between metal monolith structures, this work investigated heat exchange in concentric monoliths brazed to a common mantle. A computationally inexpensive quasi-dimensional model was developed and used to predict the heat exchange effectiveness and intrinsic heat transfer rate. The model used a discretized control volume approach and simplified geometries to reduce computational intensity. The model was calibrated against experimental data collected using a steady-state flow bench. After calibration, a parametric study was performed where monolith construction and flow conditions were varied. A parametric analysis showed that for identical catalyst space velocities and volumes, heat exchange effectiveness can be increased by 43.2% and heat transfer rates by 44.8% simply through increasing the surface area to volume ratio of the monolith. The described approach serves as an alternative framework for modeling catalytic heat exchangers without heavy computation and for quickly matching monolith geometries to their intended use and operating range.

High-strength, multifunctional and 3D printable mullite-based porous ceramics with a controllable shell-pore structure

The quest for lightweight and functional materials poses stringent requirements on mechanical performance of porous materials. However, the contradiction between high strength and elevated porosity of porous materials severely limits their application scenarios in emerging fields. Herein, high-strength multifunctional mullite-based porous ceramic monoliths were fabricated utilizing waste fly ash hollow microspheres (FAHMs) by the protein gelling technique. Owing to their unique shell-pore structure inspired by shell-protected biomaterials, the monoliths with porosity of 54.69%–70.02% exhibited a high compressive strength (32.3–42.9 ​MPa) which was 2–5 times that of mullite-based porous ceramics with similar density reported elsewhere. Moreover, their pore structure and properties could be tuned by regulation of the particle size and content of the FAHMs, and the resultant monoliths demonstrated superior integrated performances for multifunctional applications, such as broadband sound insulation, efficient thermal insulation, and high-temperature fire resistance (>1300 ​°C). On this basis, mullite-based porous ceramic lattices (porosity 68.28%–84.79%) with a hierarchical porous structure were successfully assembled by direct ink writing (DIW), which exhibited significantly higher compressive strength (3.02–10.77 ​MPa) than most other ceramic lattices with comparable densities. This unique shell-pore structure can be extended to other porous materials, and our strategy paves a new way for cost-effective, scalable and green production of multifunctional materials with well-defined microstructure.

Laboratory aging of a dual function material (DFM) washcoated monolith for varying ambient direct air capture of CO2 and in situ catalytic conversion to CH4

A DFM has been designed for direct air capture of CO2 and in situ catalytic methanation for sustainable natural gas production. It is composed of 1% Ru, 10% “Na2O”/γ-Al2O3//ceramic monolith, the latter with high open frontal area to reduce pressure drop when processing real air. Extended laboratory aging was conducted using simulated ambient capture conditions varying in temperature and humidity for over 100 cycles (450+ hours on stream). The continuous test protocol was designed to simulate some representative ambient conditions expected during advanced pilot plant testing. The capture step was followed by catalytic hydrogenation of CO2 to methane during a temperature swing to 300°C. Results demonstrated stable, repeatable CO2 capture and CH4 production with no evidence of sorbent or catalyst deactivation. These findings support the case for further advanced testing to substantiate scale up of this material for producing a useful fuel or feedstock while mitigating climate change.

Multifunctional Hierarchical Metamaterial for Thermal Insulation and Electromagnetic Interference Shielding at Elevated Temperatures.

The custom design of lightweight cellular materials is widely concerned due to effectively improved mechanical properties and functional applications. However, the strength attenuation and brittleness behavior hinder honeycomb structure design for the ceramic monolith. Herein, the ceramic matrix composite metamaterial (CCM) with a negative Poisson's ratio and high specific strength, exhibiting superelasticity, stability, and high compressive strength, is customized by combining centripetal freeze-casting and hierarchical structures. CCM maintains a negative Poisson's ratio response under compression with the lowest value reaching -0.16, and the relationship between CCM's specific modulus and density is E ∼ ρ1.3, which indicates the mechanical metamaterial characteristic of high specific strength. In addition to the extraordinary mechanical performance endowed by hierarchical structures, the CCM exhibits excellent thermal insulation and electromagnetic interference shielding properties, in which the thermal conductivity is 30.62 mW·m-1·K-1 and the electromagnetic interference (EMI) shielding efficiency (SE) reaches 40 dB at room temperature. The specific EMI shielding efficiency divided by thickness (SSE/t) of CCM can reach 9416 dB·cm2·g-1 at 700 °C due to its stability at elevated temperatures, which is 100 times higher than that of traditional ceramic matrix composites. Moreover, the designed hierarchical structure and metamaterial properties provide a potential scheme to implement cellular materials with collaborative optimization in structure and function.

Prediction strategy for the forming and stuffing of non-circular tube

The manufacturing of exhaust filter systems for cars typically comprises the forming of a tube and the later stuffing of the formed product with a ceramic monolith and an elastomer mat for filtration. It is shown, that for oval tubes the stuffing process leads to inhomogeneous deformation of the final product wherefore it must be considered when designing the tools for the forming step. The high number of iterations for the tool design can hence be reduced. Additionally, under certain conditions, the necessity of simulating the forming process is shown to no longer be given. The reason for this is that during the stuffing step, no plastic deformation is introduced in the tubes. Consequently, the forming history, including local strain and residual stress distributions, do not need to be explicitly considered. A simplified methodology is presented based on these findings, which can find the required cross-section geometry of the tube entering the stuffing process. The goal of the previous forming process therefore is to produce exactly that geometry, which can be done using conventional forming process planning approaches.

Co/SBA-16 coating supported on a 3D-printed ceramic monolith for peroxymonosulfate-activated degradation of Levofloxacin

This study reports a simple method for anchoring dispersed Co nanoparticles on SBA-16 mesoporous molecular sieve coating grown on the 3D-printed ceramic monolith (i.e., Co@SBA-16/ceramic). The monolithic ceramic carriers with a designable versatile geometric channel could improve the fluid flow and mass transfer but exhibited a smaller surface area and porosity. The SBA-16 mesoporous molecular sieve coating was loaded onto the surface of the monolithic carriers using a simple hydrothermal crystallization strategy, which can increase the surface area of the monolithic carriers and facilitate the loading of active metal sites. In contrast to the conventional impregnation loading method (Co-AG@SBA-16/ceramic), dispersed Co3O4 nanoparticles were obtained by directly introducing Co salts into the as-made SBA-16 coating (containing a template), accompanied by conversion of the Co precursor and removal of the template after calcination. These promoted catalysts were characterized by X-ray diffraction, scanning electron microscopy, high-resolution transmission electron microscopy, Brunauer–Emmett–Teller theory, and X-ray photoelectron spectroscopy. The developed Co@SBA-16/ceramic catalysts exhibited excellent catalytic performance for the continuous removal of levofloxacin (LVF) in fixed bed reactors. Co/MC@NC-900 catalyst exhibited a ∼ 78% degradation efficiency in 180 min compared to that of Co-AG@SBA-16/ceramic (17%) and Co/ceramic (0.7%). The improved catalytic activity and reusability of Co@SBA-16/ceramic was because of the better dispersion of the active site within the molecular sieve coating. Co@SBA-16/ceramic-1 exhibits much better catalytic activity, reusability and long-term stability than Co-AG@SBA-16/ceramic. After a 720 min continuous reaction, the LVF removal efficiency of Co@SBA-16/ceramic-1 in a 2 cm fixed-bed reactor was stable at 55%. Using chemical quenching experiments, electron paramagnetic resonance spectroscopy, and liquid chromatography–mass spectrometry, the possible LVF degradation mechanism and degradation pathways were proposed. This study provides novel PMS monolithic catalysts for the continuous and efficient degradation of organic pollutants.

Performance of Particulate and Structured Pt/TiO2-Based Catalysts for the WGS Reaction under Realistic High- and Low-Temperature Shift Conditions

The water–gas shift (WGS) activity of Pt/TiO2-based powdered and structured catalysts was investigated using realistic feed compositions that are relevant to the high-temperature shift (HTS) and low-temperature shift (LTS) reaction conditions. The promotion of the TiO2 support with small amounts of alkali- or alkaline earth-metals resulted in the enhancement of the WGS activity of 0.5%Pt/TiO2(X) catalysts (X = Na, Cs, Ca, Sr). The use of bimetallic (Pt–M)/TiO2 catalysts (M = Ru, Cr, Fe, Cu) can also shift the CO conversion curve toward lower temperatures, but this is accompanied by the production of relatively large amounts of unwanted CH4 at temperatures above ca. 300 °C. Among the powdered catalysts investigated, Pt/TiO2(Ca) exhibited the best performance under both HTS and LTS conditions. Therefore, this material was selected for the preparation of structured catalysts in the form of pellets as well as ceramic and metallic catalyst monoliths. The 0.5%Pt/TiO2(Ca) pellet catalyst exhibited comparable activity with that of a commercial WGS pellet catalyst, and its performance was further improved when the Pt loading was increased to 1.0 wt.%. Among the structured catalysts investigated, the best results were obtained for the sample coated on the metallic monolith, which exhibited excellent WGS performance in the 300–350 °C temperature range. In conclusion, proper selection of the catalyst structure and reaction parameters can shift the CO conversion curves toward sufficiently low temperatures, rendering the Pt/TiO2(Ca) catalyst suitable for practical applications.

CsxCo/Na-MOR Coating on Ceramic Monoliths for Co-Adsorption of Hydrocarbons Mixture and Selective Catalytic Reduction of NOx

In this work, ceramic monoliths were coated with powders based on exchanged Cs and/or Co cations in Na-mordenite (MOR) zeolite. SEM images showed that zeolite particles fill the macropores of cordierite walls and form a continuous layer of approximately 40 µm with good adherence. XPS analysis revealed that Co and Cs are present on the film surface solely as Co2+ and Cs+ at exchange positions in zeolite. The monolithic structures were evaluated for the butane-toluene co-adsorption and SCR of NOx with hydrocarbon mixture as the reducing agent. The presence of alkali metal cations in the zeolitic lattice favored the adsorption capacity of both hydrocarbons, while cobalt cations provoked a decrease in the adsorbed amounts due to its weak interaction with the HCs. Breakthrough curves of butane adsorption showed a roll-up phenomenon, associated with a competitive adsorption effect generated from toluene presence. In the desorption process, it was observed that adsorbed toluene hindered the butane diffusion through mordenite channels, which released at higher temperatures (above 250 °C). Cs2CoM and Cs7CoM monoliths were more active than the CoM monolith for NO-SCR. The presence of Cs cations close to Co cations increased the hydrocarbons concentration around active sites at high temperatures, according to TPD results, promoting the reduction activity of NO.

CFD SIMULATION OF A PILOT-SCALE REACTOR FOR THE REMOVAL OF VOLATILE ORGANIC COMPOUNDS (VOCS)

This work reports preliminary results on the fluid dynamic simulation using ANSYS CFD software of a pilot scale reactor experimentally tested for the removal of VOCs (toluene, ethylbenzene, methyl ethyl ketone and xylenes). The reactor is constructed from the modification of a commercial air stripper and has been successfully evaluated for the removal of VOCs using Mn, Ce and Pt based catalysts on ceramic monoliths (bentonite). By means of ANSYS CFD simulation it was possible to represent the flow in the reactor (validating with experimental data) and to simulate the flow in the monolith channels. This information will allow us to have a better understanding of the fluid dynamics in the catalysts and to simulate the reactions with different VOCs by combining ANSYS CFD with ChemKin-PRO.

10 - Translucency 0 f Zirconia and Hybrid Ceramic Monolithic Crowns

10 - Translucency 0 f Zirconia and Hybrid Ceramic Monolithic Crowns

Parametric and laboratory aging studies of direct CO2 air capture simulating ambient capture conditions and desorption of CO2 on supported alkaline adsorbents

Alkali and alkaline earth metal oxides dispersed on high surface area γ-alumina were studied for the selective adsorption of CO2 under simulated ambient direct air capture (DAC) and subsequent temperature programmed desorption. Thermogravimetric analysis showed Na2O/γ-Al2O3 had superior adsorption and desorption via temperature programed desorption (TPD) relative to other supported metal oxides. Parametric and laboratory aging studies were conducted under simulated direct air capture of 400 ppm CO2, reflecting seasonal and locational ambient temperature and humidity conditions. Initial studies were performed on granular carriers and subsequently on washcoated ceramic monoliths. Aging studies were conducted on sample compositions of 10% Na2O/γ-Al2O3 granules and 10% Na2O + PX-80 γ-Al2O3 washcoat, deposited on a cordierite automotive-catalytic converter type monolith designed for low pressure drop in high air flow rates. Both selective adsorption and desorption of CO2 showed high stability with no signs of deactivation after 400+ hours of cyclic testing under a wide variety of simulated ambient conditions.

3D printing of crack-free dense polymer-derived ceramic monoliths and lattice skeletons with improved thickness and mechanical performance

Previous research often failed to prepared polymer-derived SiOC ceramic components with dense and thick monoliths/skeletons based on additive manufacturing processes, due to the porosities and cracks generated during the pyrolysis process. Herein, we report a simple solution which combines the introduction of phenolic resin (PR) as an additive and the use of controlled strategy of pyrolysis, for the vat photopolymerization additively manufactured SiOC ceramics. As a result, crack-free dense monolith and lattice skeleton structural polymer-derived SiOC ceramics are successfully prepared despite the low ceramic yield of 19.3 wt% and large linear shrinkage of 50% generated after pyrolysis. The prepared dense monoliths possess a thickness of over 5 mm and the lattices show attainable maximum dense skeletons thickness of ~2 mm. The maximum dense thickness of the samples after pyrolysis is over 7 times that of other samples prepared based on additive manufacturing reported in the literature. As an indicator of dimensional retention, the specific dense thickness to ceramic yield ratio (T/Y) is deduced, resulting maximum values of 101.9 µm/(wt%) for lattice skeletons and 254.7 µm/(wt%) for monoliths. The former is even larger than that for dense monolith SiOC structures prepared by other conventional gel casting and isostatic pressing techniques with much higher ceramic yields of > 80 wt%, and is about 6.1 times the largest T/Y ratio (=16.7 µm/(wt%)) achievable in the AM-based works reported in the literature. This shows predominance of the current work over other types of polymer-derived ceramic structures prepared by additive manufacturing and even conventional methods. The lattice structures’ apparent density and specific strength reached 0.55 g/cm 3 and 6.6 × 10 4 N∙m/kg, respectively. The mechanical performance surpasses other structural polymer-derived ceramic structures with similar apparent density reported in the literature. Through the advanced characterization and analysis of material phase and morphology evolution during the pyrolysis process, the mechanism of defect-free densification is revealed. That is, the introduction of PR enables a highly smooth gas-releasing process due to the generation of ordered gas-releasing channels in the sample bodies during the pyrolysis process. As a result, the generation of cracks and defects was successfully prevented. Moreover, due to the high carbon residue of the PR, the samples containing 15 wt% PR in the preceramic state still possessed amorphous SiOC ceramics after pyrolysis at 1400 ℃, while 0 wt% PR samples showed SiC crystallization. Compared with similar materials reported, the ceramics prepared in this study exhibit enhanced structural and mechanical performance. The strategy investigated in the study can be a viable route for the additive manufacturing of high-performance crack-free and thick monolith and lattice skeleton SiOC ceramic structures based on vat photopolymerization.