Porous SiC Ceramics Research Articles

Preparation of biomorphic porous SiC and SiO2 ceramics by sol infiltration into biotemplate followed by controlled sintering

Preparation of biomorphic porous SiC and SiO2 ceramics by sol infiltration into biotemplate followed by controlled sintering

High‐temperature behavior and self‐enhancing mechanisms of oxide‐bonded SiC porous ceramics

AbstractOxide‐bonded SiC porous ceramics (SCPCs), synthesized via reaction bonding, exhibit significant potential for high‐temperature applications. However, incorporating sintering aids inevitably results in a considerable quantity of amorphous glass phase within SCPCs, thereby introducing risks to their high‐temperature mechanical performance. In this study, we employ in‐situ characterization techniques to investigate the high‐temperature behavior of SCPCs. Our findings reveal that SCPCs demonstrate remarkable high‐temperature self‐enhancing properties, with a critical bending strength at 800°C. Beyond this temperature, the strength declines sharply. Intriguingly, the critical bending strength is 36.6% greater than at ambient temperature. Moreover, elevated temperatures enhance the elastic modulus and promote the transition of SCPCs from multilinear to nonelastic fracture. The neck phase, which imparts strength to the SCPCs, is composed of four distinct layers along the depth direction: silicate glass, oxygen‐containing, silicon‐rich, and SiC region, as revealed by FIB‐TEM. The transformation from α to β‐cristobalite in the oxygen‐containing region improves the thermal expansion match with SiC, thereby mitigating local stress concentration. Furthermore, the compressive stress within the neck region intensifies with increasing temperatures, thereby inhibiting crack propagation. This work provides a basis for the high‐temperature applications of SCPCs.

Structural control and mechanical properties optimization of porous SiC foams with three-dimensional network structure

In this paper, a new process for preparing porous SiC foam with three-dimensional network structure is presented. A certain thickness of SiC coating is deposited on the surface of ultra-light carbon skeleton by CVD process, so as to achieve effective control of its structure and mechanical properties. The effects of CVD deposition time on the density, porosity and skeleton thickness rates of SiC foams were explored. By increasing the CVD deposition time, the structure of SiC foams can be effectively regulated, and the mechanical properties of SiC foams can be significantly improved. The porosity of the prepared SiC foam can be adjusted in a wide range (26.9%∼94.68%). When the density of SiC foam increases from 0.67 g/cm3 to 2.36 g/cm3, its bending strength increases from 27.4 MPa to 136.9 MPa, which is significantly improved. After high temperature oxidation treatment (800–1200 °C), the mechanical properties of SiC foam will be further improved. However, when the oxidation temperature reaches 1400 °C, its mechanical properties will be reduced. This research provides a new idea for the preparation of high-performance porous SiC ceramics, and lays a foundation for its structural design, manufacture and application.

Effect of Binder Content on Properties of Cordierite-Mullite Porous Ceramics

In this paper, 70-80 mesh SiC particles were used as the base, and 2.5%MgO was added on the basis of quartz, kaolin and potassium feldspar as the binder. Meanwhile, graphite and activated carbon were added as pore-making agents for SiC porous ceramic supports. At the same time, the amount of binder added was changed under the condition of keeping SiC: pore-making agent 8:1 unchanged. The effects of binder content on flexural strength, filtration pressure drop and porosity of porous SiC ceramics were investigated. The results indicated that the comprehensive properties of SiC porous ceramics can be improved by adding proper amount of MgO. When the content of MgO in the binder was controlled at 2.5% and the amount of binder was 6%, the comprehensive performance of the sample was the best under the conditions of 1300 °C, holding time for 90 minutes and forming pressure of 4/10MPa, respectively. In this case, the flexural strength was 48mpa, the porosity was 25% and the filtration pressure drop was good.

Temporal Pattern of Microcracking in Impact–Damaged Porous SiC Ceramics

Temporal Pattern of Microcracking in Impact–Damaged Porous SiC Ceramics

Effect of La2O3 adding on Properties of SiC Porous Ceramic Support

In this paper, 80-90 grains of SiC as the main raw material, doped La2O3 into the binder composed of potassium feldspar, kaolinite and quartz, and then graphite and activated carbon as pore-making agents to prepare silicon carbide porous ceramic carrier. The effects of doped La2O3 content on the bending strength, porosity and filtration pressure drop of porous SiC ceramics were studied. The results show that the formation of mullite phase and the bending strength of SiC porous ceramics can be improved by adding proper amount of La2O3. Under the sintering temperature of 1300°C for 90 minutes, when the content of La2O3 in the binder is 2.5wt%, the comprehensive performance is the best, the porosity is 21.5%, the bending strength is 53.5MPa, and the filtration pressure drop is low.

Porous SiC ceramic obtained by spark plasma sintering of preceramic paper: Microstructure, mechanical properties and gas permeability

This paper describes the fabrication and characterization of porous SiC ceramics derived from highly-filled preceramic papers. The SiC ceramics were obtained by spark plasma sintering of stacked preceramic papers at temperatures of 2100 and 2200 °C under pressures of 5–60 MPa for 10 min. The microstructure and phase composition were analyzed by scanning electron microscopy and X-ray diffraction, respectively. Gas permeation tests were performed using hydrogen permeation cell at room temperature. It is revealed that the porosity of sintered SiC can be varied from 9 to 45 % depending on the sintering parameters. The shrinkage of the materials during spark plasma sintering occurs in four stages. The linear shrinkage value of the material increases from 7 to 47 % at 2100 °C and from 20 to 50 % for the samples sintered at 2100 and 2200 °C, respectively. Correlation dependencies between porosity and mechanical properties of the fabricated SiC were established. The obtained porous SiC ceramics exhibit high bending strength of 165 MPa and gas permeation flux of 78 molH2/m2/s at the porosity of 36 % that make it suitable for ceramic-based membranes.

High strength mullite-bond SiC porous ceramics fabricated by digital light processing

High strength mullite-bond SiC porous ceramics fabricated by digital light processing

Direct ink writing of hierarchical porous SiC ceramics as catalyst support for hydrogen production

Due to the tunable porosity at multiple scales, hierarchical porous ceramics feature large specific surface area and excellent heat and mass transfer performance, which can effectively improve the catalytic reaction performance. This paper presents a method to fabricate SiC scaffolds with regular and hierarchical pore structures by direct ink writing (DIW) combined with sacrificial template technology, which can be used as methanol steam reforming (MSR) microreactor catalyst supports. Through printing along a defined path, primary pores with a regular pore structure were created. After sintering, the sacrificial template was removed and secondary pores appeared. Four different types of hierarchical porous SiC scaffolds were successfully prepared and the pore structure, total porosity, linear shrinkage and compressive strength of these scaffolds were investigated. The catalyst coating was then loaded onto the scaffold, and the microstructure characterization showed that the pore structure would not be damaged and blocked. Finally, the hydrogen production experiments were carried out on the MSR microreactor, and the results showed that the support with larger and denser secondary pores had the best fluid flow and hydrogen production characteristics. At the temperature of 280 °C and the gas hourly space velocity (GHSV) of 30000 ml g−1 h−1, the methanol conversion and hydrogen production of the best support can reach 90.95 % and 44.96 ml/min, respectively.

In-situ mullite whisker reinforced SiC porous ceramics with whiskers and bonding layers synchronously growing: Using CaF2 as a temperature-controlled whisker formation switch

Mullite-bonded SiC porous ceramics are of potential in hot gas infiltration while the insufficient mechanical performance limits its application. In-situ mullite whisker reinforcement is a potential solution but the formation temperature mismatch between mullite whisker and bonding layer is a challenge. In that case, mullite whiskers massively form ahead of the bonding layer excessively consuming alumina leading to poor bonding layers between SiC particles and thus, the mechanical performance. Herein, the mismatch was solved by using CaF2 as a temperature-controlled reaction switch. As a result, both the bonding layer and whisker synchronously formed. The material showed significant reinforcement effects, and exhibited a flexural strength of 124.8 MPa and a fracture toughness of 1.53 MPa·m1/2 with an open porosity of 36.6 vol%, realizing a breakthrough in the mechanical performance. Interestingly, an increase in oxygen vacancy concentration with the sintering temperature was first reported, which may benefit the whisker growth.

Tuning the electrical, thermal, and mechanical properties of porous SiC ceramics using metal carbides

The effect of addition of various metal carbides on the electrical, thermal, and mechanical properties of porous SiC ceramics was investigated. The results showed a decrease in the electrical resistivity from 1.2 × 102 to 1.3 × 10-3 Ω‧cm and thermal conductivity from 14.2 to 3.6W.m-1K-1 whereas the compressive strength increased from 12.7 to 21.1–81.1MPa at ~60.2% porosity. The decrease in electrical resistivity and thermal conductivity was caused by the introduction of conductive carbides and multiple heterophase interfaces, respectively, in the porous ceramics. The electrical and thermal conductivities and compressive strength of porous SiC-based ceramics, processed with a SiC-B4C-VC-ZrC-NbC composition, were 8.0 × 102 Ω-1‧cm-1, 3.6W‧m-1K-1, and 58.0MPa, respectively. Therefore, it is proven that the electrical, thermal, and mechanical properties of porous SiC ceramics can be tuned over a wide range by adding a suitable combination of metal carbides.

Effects of pore size on electrical and thermal properties of porous SiC ceramics

AbstractPorous SiC ceramics with three different pore sizes (∼7, ∼45, and ∼98 μm) and two different porosities (∼54% and ∼63%) were prepared to investigate the effects of pore size on electrical and thermal properties of the porous ceramics. With an increase in pore size from ∼7 to ∼98 μm at the same porosity (∼54%), the electrical and thermal conductivities of the porous ceramics increased from ∼1.01 to ∼2.30 Ω−1·cm−1 and ∼14.3 to ∼26.2 W·m−1K−1, respectively. Similar trends have been obtained in the ceramics with ∼63% porosity. The porous SiC ceramic with larger pore size has smaller pore/strut interface area at the same porosity, which leads to less carrier scattering and phonon‐pore scattering at the pore/strut interfaces, resulting in higher electrical and thermal conductivities, respectively. These results suggest that the electrical and thermal properties of porous SiC ceramics can be successfully tuned by adjusting the pore size and porosity depending on the application.

Study of the effect of the morphology of initial powders on the structural and dimensional characteristics of SiC-based porous ceramic materials

The realization of the necessary energy-efficient technological solutions for the production of highly porous SiC-ceramic materials requires appropriate research. The results of developing energy-efficient one-step methods for the synthesis of porous SiC-based ceramics and studying the characteristics of the obtained ceramics are presented. The effect of the morphology of initial powders on the synthesized product is considered. Ultrafine silicon carbide powders of two types, identical in characteristic particle size, but quite different in the surface morphology, were used as fillers in the synthesis of experimental samples of porous ceramics. The first one was obtained by the traditional furnace method (SiCf), the second one was synthesized by the technology of self-propagating high-temperature synthesis (SiCshs). It is shown that the particle morphology of initial powder components determines the structural parameters and characteristics of synthesized porous ceramics. The pore space parameters (average pore size, specific surface area, equivalent hydraulic diameter, permeability, etc.) can vary significantly. Porous ceramic materials synthesized on the basis of SiCf have an open porosity of 47%, high liquid permeability (up to 2 mDarcy), overwhelming dominance of α-SiC phase, and a narrow pore distribution with an average pore size of about 1 μm. High open porosity (more than 58 %), highly developed nanostructured pore space surface with an area of more than 12 m2/g, and wider pore size distribution (average pore size — 140 nm) are observed in porous ceramic materials based on SiCshs. The obtained results can be used to improve energy-efficient synthesis technologies and methods for predicting the properties of highly porous SiC-based ceramic materials. This will make it possible to create highly porous SiC ceramics within a priory predicted limits of effective applicability for the processes of ultrafiltration or catalysis.

Effects of chemical corrosion and thermal shock on the properties of mullite- and cordierite-bonded porous SiC ceramics prepared using waste fly ash

Effects of chemical corrosion and thermal shock on the properties of mullite- and cordierite-bonded porous SiC ceramics prepared using waste fly ash

Silicon carbide ceramic membrane support sintered at 800 °C with low-temperature sintering aid

Silicon carbide ceramic membranes have been widely used in the treatment of various corrosive and high temperature wastewaters. However, SiC is a compound with strong covalent bond, thus the sintering temperature and then the energy consumption during sintering of SiC ceramics is high, which inhibits the scale-up manufacturing of SiC ceramic membranes. Here, a silicon carbide ceramic membrane support was prepared at 800 °C with a low melting-point glaze as the sintering aid. The glaze infiltrated the SiC skeleton during sintering, and gave rise to high fracture strength of the porous ceramics. With the content increase of sintering aid from 10 wt% to 30 wt%, the pore-formation mechanism of the ceramic membrane support transformed from SiC particles packing to SiC aggregations packing, leading to the increase in pore size and decrease in porosity. The permeance and selectivity of the support was investigated via pure-water and oil-in-water emulsion tests. Due to the high hydrophilicity, the pure-water flux increased from 32 L/(m2·h) to 87 L/(m2·h) while the oil rejection decreased from 99.0% to 93.1% with the increase of trans-membrane pressure. This work provides a feasible route for the preparation of SiC porous ceramics with low energy consumption.

Study on transpiration cooling performance of SiC porous ceramics

Ceramic matrix composites are desirable for applications in the thermal protection system of hypersonic flight vehicles due to their excellent oxidation resistance. However, the service temperature exceeds the melting point of the components with a small curvature radius. Among the active cooling techniques, transpiration cooling has been proven to be a promising thermal protection method for hypersonic vehicles. In this study, SiC porous ceramics with different geometrical shapes and open porosities are fabricated using the polymer infiltration and pyrolysis route and sacrificial template method. Theoretical analysis and experimental investigation are performed to explore the feasibility of transpiration cooling with various coolants for SiC porous ceramics. The results confirm that the specific heat capacity is a key parameter that affects the cooling efficiency when a gas is used as the coolant. The effects of the material’s porosity, the attack angle, and the heat flux on the transpiration cooling performance with nitrogen are experimentally tested, and the highest cooling efficiency exceeded 80%. Meanwhile, the SiC porous ceramics displayed superior adaptive and self-pumping transpiration cooling performance when in a quartz lamp heating environment for about 10 min. The cooling mechanisms with a water phase change are also analyzed in detail. This study offers the possibility of developing thermal protection materials that could be used in active thermal protection techniques.

Microstructures, Mechanical Properties and Electromagnetic Wave Absorption Performance of Porous SiC Ceramics by Direct Foaming Combined with Direct-Ink-Writing-Based 3D Printing.

Direct-ink-writing (DIW)-based 3D-printing technology combined with the direct-foaming method provides a new strategy for the fabrication of porous materials. We herein report a novel method of preparing porous SiC ceramics using the DIW process and investigate their mechanical and wave absorption properties. We investigated the effects of nozzle diameter on the macroscopic shape and microstructure of the DIW SiC green bodies. Subsequently, the influences of the sintering temperature on the mechanical properties and electromagnetic (EM) wave absorption performance of the final porous SiC-sintered ceramics were also studied. The results showed that the nozzle diameter played an important role in maintaining the structure of the SiC green part. The printed products contained large amounts of closed pores with diameters of approximately 100-200 μm. As the sintering temperature increased, the porosity of porous SiC-sintered ceramics decreased while the compressive strength increased. The maximum open porosity and compressive strength were 65.4% and 7.9 MPa, respectively. The minimum reflection loss (RL) was -48.9 dB, and the maximum effective absorption bandwidth (EAB) value was 3.7 GHz. Notably, porous SiC ceramics after sintering at 1650 °C could meet the application requirements with a compressive strength of 7.9 MPa, a minimum RL of -27.1 dB, and an EAB value of 3.4 GHz. This study demonstrated the potential of direct foaming combined with DIW-based 3D printing to prepare porous SiC ceramics for high strength and excellent EM wave absorption applications.

Effect of SiO2 Adding on Properties of SiC Porous Ceramic Support

In this paper, The binders were prepared with different proportions of potassium feldspar, kaolin and quartz. In order to optimized the performance of SiC porous ceramics, the influence of binders with different content of SiO2 on the bending strength, filtration pressure drop and stomatal rate of porous ceramics were explored. The results show that doping of 10wt% SiO2 in the binder can improve the mechanics performances of SiC porous ceramics. Samples prepared by thermal insulation for 90 minutes at 1300°C had the best comprehensive performance when the adhesive contained 10wt% SiO2. At this time, the porosity was 25.52%, the bending strength was 47.15 MPa, and the filtration pressure drop was comparatively low.

Permeability and corrosion resistance of porous SiOC‐bonded SiC ceramics prepared by the preceramic polymer

AbstractPorous SiC ceramics have been used in high temperature flue gas filtration fields because of their excellent properties such as high strength, high temperature resistance, corrosion resistance, and long service time. This work reports the porous SiOC‐bonded SiC ceramics prepared at low temperature. The properties of porous SiC ceramics were first investigated with silicone resin content from 10 to 25 wt%, and then the effects of different pore‐forming agent contents on the behaviors of porous SiC ceramics were discussed by adjusting poly (methyl methacrylate) PMMA microbeads from 5 to 20 wt%. The prepared porous SiC ceramics showed apparent porosity from 17.3% to 57.7%, compressive strength from 6 to 216 MPa, and Darcy permeability k1 ranging from 7.02 × 10−14 to 1.45 × 10−12 m2. The corrosion behavior of porous SiC ceramics was investigated in acidic and alkaline media. The porous SiC ceramics showed better corrosion resistance in acidic solutions.

Fabrication of SiC Porous Ceramics by Foaming Method

In this work, hierarchically porous SiC ceramics were prepared via the foaming method. Porous ceramics with tunable, uniform, and bimodal pore structures were successfully fabricated in a facile way. The formation mechanisms of the 1st and 2nd modal macropores are the H2O2 foaming process and SiC particle overlap, respectively. The effect of pore-foaming agent amount, foaming temperature, and surfactant was investigated. According to the results, with increasing H2O2 amount, the porosity, pore size, and interconnectivity of the 1st modal pores increased, whereas bulk density and strength decreased. The porosity increased while the strength decreased as the foaming temperature increased. Surfactants increased pore interconnectivity and porosity. When the foaming temperature was 85 °C, and the addition of H2O2 was 5 wt.%, the porosity, bulk density, flexural strength, and compressive strength were 56.32%, 2.8301 g/cm3, 11.94 MPa, and 24.32 MPa, respectively. Moreover, SiC porous ceramics exhibited excellent corrosion resistance to acids and alkalis.