Porous SiC Ceramics Research Articles

Effect of SiC particle size on flexural strength of porous self-bonded SiC ceramics

Porous self-bonded silicon carbide (SBSC) ceramics were fabricated from SiC powders with various particle sizes (0.7 μm, 25 μm, 50 μm, 65 μm), plus Si, C and boron (as a sintering additive). The effects of submicron (0.7 μm) SiC particle incorporation into the SBSC and the SiC particle size (25 μm, 50 μm, 65 μm) on the flexural strength and porosity of the ceramics were investigated as a function of sintering temperature. Incorporating 0.7 μm SiC particles into the ceramic material containing 25 μm SiC particles increased the flexural strength by 3 times, from 11.7 MPa up to 35.5 MPa after sintering at 1800 °C. Simultaneously, the porosity was reduced by ∼5 %. Furthermore, the flexural strength of ceramic with 25 μm SiC particles was superior to that with 65 μm SiC particles. Generally, the flexural strength of the SBSC increased as, both, a function of submicron SiC particle incorporation along with relatively small micron-sized particles (25 μm) in the microstructure of the ceramic plus increased sintering temperature.

Fabrication of Gradient Porous SiC Ceramics with Directional Pores without Templates

Gradient porous pure SiC ceramics with directional SiC crystals and pores were fabricated by the high-temperature recrystallization process. In this work, silicon carbide decomposed to produce the gas mixture. The flow of gas mixture along the axial direction in the porous green body induces the surface ablation, rearrangement, and recrystallization of silicon carbide grains, which leads to the formation of the aligned columnar silicon carbide crystals and tubular pores in the axial direction. The different rates of the decomposition and recrystallization of SiC in different parts of samples resulted in the formation of the gradient porosity and pore size along the axial section of sample. Si3N4 powder was used as a pore-former, which promotes the formation of the gradient and interconnectivity of pores. With increasing Si3N4 contents, the total porosity and weight loss increase while the pores size and bending strength decrease. The total porosity of samples is 38–45%, and their bending strength is 33–38 MPa.

Manufacturing and characterization of porous SiC for flow channel inserts in dual-coolant blanket designs

SiC is the primary candidate for the flow channel inserts in dual-coolant blanket concepts. Porous SiC ceramics are attractive candidates for this non-structural application, since they can satisfy the required properties through a low cost manufacturing route, compared to SiC f/SiC. This work shows first results of the manufacturing of porous SiC ceramics prepared with different amounts of Y 2O 3 and Al 2O 3 as sintering additives. C powders were used as pore-formers by their burnout during oxidation after sintering. Comparison of microstructure, porosity, flexural strength, thermal and electrical conductivity and corrosion under Pb–15.7Li of porous SiC without and with sintering additives is presented. The addition of 2.5 wt.% of Y 2O 3 and Al 2O 3 improves the mechanical properties, and reduces the thermal and electrical conductivity down to reasonable values. Preliminary corrosion tests under Pb–15.7 Li at 500 °C show that the absence of a dense coating on porous SiC leads to poor corrosion behavior.

Bio-inspired porous SiC ceramics loaded with vancomycin for preventing MRSA infections

Implant-related infections are a serious complication in orthopaedic and dental surgery resulting in prolonged hospitalization, high medical costs and patient mortality. The development of porous implants loaded with antibiotics may enable a local delivery for preventing surface colonization and biofilm formation. A new generation of bio-derived porous ceramic material that mimics hierarchical structures from Nature was evaluated. Silicon carbide ceramics derived from Sapelli wood (bioSiC) were obtained by pyrolysis of Entandrophragma cylindricum wood followed by infiltration with molten silicon. This process renders disks that keep the bimodal pore size distribution (3 and 85μm) of the original material and are highly cytocompatible (BALB/3T3 cell line). The ability of the bio-ceramic to load the antimicrobial agent vancomycin was evaluated by immersion of disks in drug solutions covering a wide range of concentrations. The disks released at pH 7.4 an important amount of drug during the first 2 h (up to 11mg/g bioSiC) followed by a slower release, which is related to the presence of macro- and mesopores. Finally, the anti-biofilm effect against methicillin resistant Staphylococcus aureus was assessed and a considerable reduction (92%) of the bacterial film was observed. Results highlight the bioSiC potential as component of medicated medical devices.

Si 결합 다공성 탄화규소의 미세구조 및 통기도 특성 -카본 함량 변화 중심

The achievement of high gas permeability is a key factor in the development of porous SiC ceramics for applications of hot gas filter, vacuum chuck, and air spindle. However, few reports on the gas permeability of porous SiC ceramics can be found in the literature. In this paper, porous SiC ceramics were fabricated at temperatures ranging from 1600℃ to 1800℃ using the mixing powders of SiC, silicon, carbon and boron as starting materials. In some samples, expanded hollow microspheres as a pore former were used to make a cellular pore structure. It was possible to produce Si bonded SiC ceramics with porosities ranging from 42% to 55%. The maximum bending strength was 58㎫ for the carbon content of 0.2 wt% and sintering temperature of 1700℃. The increase of air permeability was accelerated by addition of hollow microsphere as a pore former.

Fabrication of porous SiC ceramics having pores shaped with Si grain templates

SiC porous ceramics were prepared by heating mixtures of Si powder and carbon black at 900 °C for 24 h in Na vapor. The grains of the Si powder were not only the source of Si for SiC but also served as templates for the pores in the SiC porous ceramics. Angular-shaped pores with sizes of 2–10, 10–150 and 50–150 μm were formed by angular Si grains with sizes of ≤10, ≤50 and ≤150 μm, respectively. The porosity of the SiC porous ceramics was around 55–59%. Spherical pores were also formed when spherical Si grains were used. A bending strength of 14 MPa was measured for the SiC porous ceramics prepared with the Si grains (≤50 μm).

Preparation of porous SiC ceramics by an infiltration technique

Abstract: The possibility of infiltration as a technique for synthesizing porous SiC ceramics was examined. SiC powder compacts were infiltrated with a liquid precursor which produced SiO2 during pyrolysis in air at a low temperature. Infiltrated SiO2 might act as a bond between the neighboring SiC particles at contacting points. The process parameters which control the rate of infiltration of liquid precursor to SiO2 into porous SiC powder compacts were studied. Results showed that the infiltration rate could be estimated by using weight gain measurements. Sintering infiltrated bodies at 1300 °C yielded specimens in which only silicon carbide and cristobalite were detected. The presence of cristobalite significantly controlled the porosity as also the mechanical properties. Reasonable flexural strengths (∼ 48 MPa) could be achieved at a porosity level of 26 vol.% with near uniform pore diameter of around 5 μm.

Effect of processing on the microstructure and crystalline phase composition of wood derived porous SiC ceramics

Pine ( Pinus silvestris) wood samples were dried and impregnated with a SiO 2 sol from a sol–gel process. The impregnation involved a two step process in a custom-made apparatus. Impregnated samples were dried and pyrolised at 500 °C under an oxygen-free atmosphere. SiC synthesis was performed in a high-temperature furnace in an argon atmosphere at a temperature of 1600 °C for 2, 4 and 8 h. The samples were investigated with X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM). The changes in the SiC synthesis time at the maximum temperature lead to changes in the microstructure and crystalline phase composition. An increase in the synthesis time opens up the possibility to produce mainly α-SiC crystalline modification containing porous SiC ceramics.

ChemInform Abstract: Reaction Sintering of Polycarbosilane-Impregnated Compact of Silicon Carbide Hollow Particles and the Resultant Thermoelectric Properties.

Porous SiC ceramics fabricated from hollow particles and polycarbosilane (PSC) are promising materials for high-temperature thermoelectric energy conversion. Reaction sintering of PCS-impregnated compacts of SiC hollow particles gave rise to porous microstructures with the hollow shape remaining. The repetition of the PCS-impregnation and sintering process resulted in only a slight increase in density but in a great improvement in thermoelectric properties.

Effect of bentonite addition on fabrication of reticulated porous SiC ceramics for liquid metal infiltration

SiC with different particles and a clay mineral bentonite (montmorillonite) were mixed in water to prepare ceramic slurry. The slurry was then infiltrated high porous polyurethane sponge. Excess slurry was squeezed out to adjust ceramic rate in the infiltrated body. The pore walls were coated with ceramic mix after the infiltrated body was dried. The polyurethane containing SiC particles and bentonite was fired in a box furnace to burn out the polyurethane from the body at 500 °C for 30 min. The remaining porous ceramic bodies were sintered at elevated temperatures to give strength. SiC particles with bentonite surface coating took polyurethane pore forms after firing the sponge. Bentonite was both used as binder for ceramic slurry at room temperatures and the sintering additives at elevated temperatures. Therefore, increasing bentonite addition gives higher strength to the resulting ceramic performs.

Preparation of porous SiC ceramics from waste cotton linter by reactive liquid Si infiltration technique

Porous carbon and porous silicon carbide with homogenous microstructure are prepared from cotton linter and phenolic resin through mold-stacking, solidification, carbonization and liquid Si infiltration process. SEM observation reveals that the irregular interconnected pores of carbon preparation were originated from the random arrangement of cotton linter fiber and different carbonization shrinkage. After the liquid Si infiltration process, the porous carbon was converted into dense SiC/Si composites. The porous SiC was formed during the Si-removing process at higher temperature. The result shows that open porosity of porous silicon carbide increases as Si-removing time increase, while the bending strength and the fracture toughness decrease.

Properties of Porous SiC Ceramics Prepared by Wood Template Method

Porous SiC samples were prepared with three types of wood (poplar, pine, big cone pine) by simply embedding the wood charcoal in a powder mixture of Si and SiO₂ at 1600 and 1700℃. The basic engineering properties such as density, porosity, pore size and distribution, and strength were characterized. The samples showed full conversion to mostly β-SiC with good retention of the cellular structure of the original wood. More rigid SiC struts were developed for 1700℃. They showed similar bulk density (0.5~0.6 g/㎤) and porosity (81~84%) irrespective of the type of wood. The poplar sample showed three pore sizes (1, 8, 60 ㎛) with a main size of 60 ㎛. The pine sample showed a single pore size (20 ㎛). The big cone pine sample showed two pore sizes (10, 80 ㎛) with a main size of 10 ㎛. The bend strength was 2.5 ㎫ for poplar, 5.7 ㎫ for pine, 2.8 ㎫ for big cone pine, indicating higher strength with pine.

TGA CHARACTERISTIC AND FABRICATION OF POROUS SiC CERAMICS

The long-range aim of this research is to develop porous ceramics with high strength, excellent thermal resistance and chemical stability at high temperature in environmental industry. The C f / SiC was made by hot pressing method with SiC powder whose particle size is 50nm and less on the average also Al 2 O 3, Y 2 O 3 and SiO 2 as additive. The carbon fibers of oxidation property are investigated by TGA for finding out decarburization point. As a result, decarburization point selected the specific temperature of TGA curve and the C f/ SiC composites occurred perfectly decarburization at carbon fibers so the clearly porous SiC ceramics were formed many holes of 3-5µm diameters through length direction by its reaction.

Processing of microcellular silicon carbide ceramics with a duplex pore structure

A novel processing route for producing microcellular SiC ceramics with a duplex pore structure has been developed using a polysiloxane, carbon black, SiC, Al 2O 3, Y 2O 3, and two kinds of pore former (expandable microspheres and PMMA spheres). The duplex pore structure consists of large pores derived from the expandable microspheres and small windows in the strut area that were replicated from the PMMA spheres. The presence of these small windows in the strut area improved the permeability of the porous ceramics. The gas permeability coefficients of porous SiC ceramics were 0.13 × 10 12 m 2 for the porous SiC without PMMA spheres, 0.47 × 10 12 m 2 for the porous SiC with 10 wt% PMMA spheres, and 0.82 × 10 12 m 2 for the porous SiC with 20 wt% PMMA.

Microstructural Evolution of porous biomorphous WC and SiC Ceramics

Microstructural Evolution of porous biomorphous WC and SiC Ceramics

Effect of Pore-Forming Processing on the Gas Permeability and Flexural Strength of Porous SiC Ceramics

The porous SiC ceramics were prepared by two methods of pore-forming. The gas permeability and flexural strength of the porous SiC ceramics prepared by different ways were investigated. The porous SiC ceramics prepared by particle stacking have evenly pore distrubution; the gas permeability was greatly increased with the particle size increasing while the porous SiC ceramics were kept a higher flexural strength. The pore-former also can be used to form large pores to increase the gas permieability. However, these unevenly distribution large pores lead to a deterioration in flexural strength.

Fabrication, Structure and Properties of Porous SiC Ceramics with High Porosity and High Strength

Porous SiC ceramics with high porosity and high strength were fabricated by gelcasting, with tert-butyl alcohol (TBA) as solvent, acrylamide (AM) as monomer, and in-situ reaction bonding with a-Al2O3 as sintering additive. SiC suspension with 10 vol% solid loading was successfully solidified by gel-casting to form high strength green body. The results showed that the compressive strength of the porous SiC ceramics increased with sintering temperature from 1300 to 1450°C, but porosity had little change, due to formation of more volume of cristobalite and mullite phases on the surface of SiC grains, accompanied by a large volume expansion effect. Very narrow single-peak distributions with about 2 mm median pore diameter could be found for the porous SiC ceramics. The porosity and compressive strength of the porous SiC ceramics sintered at 1450°C were 71.21 % and 12.14 MPa, respectively.

Engineering porosity in silicon carbide ceramics

Porosity and microstructure control of the strut are essential for tailoring the properties of porous SiC ceramics. This study examined four different strategies for engineering the porosity of SiC ceramics: adjusting the template content, processing parameters, filler content, and sintering additive content. The suggested strategies offer substantial flexibility for producing SiC ceramics with engineered porosity, whereby the total porosity can be controlled effectively from 35 to 95%. These results suggest that combinations of the proposed strategies will be useful for the manufacture of porous SiC ceramics with engineered porosity.

Effect of additive composition on porosity and flexural strength of porous self-bonded SiC ceramics

The effect of additive incorporation in porous self-bonded SiC (SBSC) ceramics fabricated from a mixture of coarse SiC powder (∼65 µm), Si and C is investigated here. Generally, it was found that the additive reduced the porosity and increased the flexural strength of the SBSC ceramic material. This was consistent with the presence of necking in the ceramic microstructure. The flexural strength of the material without additive (control sample) was ∼16–17 MPa and this was found to be enhanced up to ∼33 MPa using 2 wt % B and ∼38 MPa, using a mixture of 1 wt % Al + 1 wt % B. Thus, the porous SiC ceramic with Al–B additive (typical flexural strength ∼38 MPa at 42% porosity) is very promising, contrasting its mechanical properties with the cost-effectiveness of the raw materials.

Processing of porous silicon carbide with toughened strut microstructure

Porous SiC ceramics were fabricated by the carbothermal reduction of polysiloxane-derived SiOC containing hollow microspheres followed by sintering. The effect of the Al2O3–Y2O3–CaO (AYC) content on the microstructure and flexural strength of the porous SiC ceramics were investigated. The growth of large platelet α-SiC grains increased with increasing additive content due to enhanced grain growth and the β → α phase transformation of SiC. In situ toughened microstructures consisting of large platelet grains and fine equiaxed grains were obtained when 10 or 20 wt% AYC was added. The porosity generally decreased with increasing the additive content, whereas the flexural strength increased. The typical flexural strength of the porous SiC ceramics sintered with 10 wt% AYC was 61 MPa at a porosity of 44%.