Properties Of Porous SiC Ceramics Research Articles

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.

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.

Microstructure and properties of porous SiC ceramics with AlN–RE2O3 (RE = Sc, Y, Lu) additives

The intrinsic microstructure and crystalline phases of porous SiC ceramics with 5 vol% AlN–RE2O3 (RE = Sc, Y, Lu) additives were characterized by high-resolution transmission microscopy with energy-dispersive spectroscopy and X-ray diffraction. The homophase (SiC/SiC) and heterophase (SiC/junction) boundaries were found to be clean; that is, amorphous films were not observed in the specimens. In addition, ScN, YN, and LuN were formed as secondary phases. The flexural strength and thermal conductivity of the ceramics were successfully tuned using different additive compositions. The flexural strength of the ceramics improved by a factor of ~3, from 11.7 MPa for the specimen containing Y2O3 to 34.2 MPa for that containing Sc2O3, owing to the formation of a wide necking area between SiC grains. For the same reason, the thermal conductivity improved by ~56%, from 9.2 W·m−1·K−1 for the specimen containing Lu2O3 to 14.4 W·m−1·K−1 for that containing Sc2O3.

Effect of carbon content on electrical, thermal, and mechanical properties of porous SiC ceramics with B4C and C additives

The electrical, thermal, and mechanical properties of porous SiC ceramics with B4C-C additives were investigated as functions of C content and sintering temperature. The electrical resistivity of porous SiC ceramics decreased with increases in C content and sintering temperature. A minimal electrical resistivity of 4.6 × 10−2 Ω·cm was obtained in porous SiC ceramics with 1 wt% B4C and 10 wt% C. The thermal conductivity and flexural strength increased with increasing sintering temperature and showed maxima at 4 wt% C addition when sintered at 2000 °C and 2100 °C. The thermal conductivity and flexural strength of porous SiC ceramics can be tuned independently from the porosity by controlling C content and sintering temperature. Typical electrical resistivity, thermal conductivity, and flexural strength of porous SiC ceramics with 1 wt% B4C-4 wt% C sintered at 2100 °C were 1.3 × 10−1 Ω·cm, 76.0 W/(m·K), and 110.3 MPa, respectively.

Influence of sintering atmosphere and BN additives on microstructure and properties of porous SiC ceramics

The effects of the boron nitride (BN) content on the electrical, thermal, and mechanical properties of porous SiC ceramics were investigated in N2 and Ar atmospheres. The electrical resistivity was predominantly controlled by the sintering atmosphere and secondarily by the BN concentration, whereas the thermal conductivity and flexural strength were more susceptible to changes in the porosity and necking area between the SiC grains. The electrical resistivities of argon-sintered porous SiC ceramics (6.3 × 105 – 1.6 × 106 Ω·cm) were seven orders of magnitude higher than those of nitrogen-sintered porous SiC ceramics (1.5 × 10−1 – 6.0 × 10−1 Ω·cm). The thermal conductivity and flexural strength of the argon-sintered porous SiC ceramics increased from 8.4–11.6 W·m−1 K−1 and from 9.3–28.2 MPa, respectively, with an increase in the BN content from 0 to 1.5 vol%, which was attributed to the increase in necking area and the decrease in porosity.

Effects of dopants on electrical, thermal, and mechanical properties of porous SiC ceramics

Nitrogen-, vanadium-, aluminum-, boron-, and scandium-doped porous SiC ceramics were fabricated to investigate the effects of dopants on electrical, thermal, and mechanical properties of porous SiC ceramics. The electrical resistivity of a nitrogen-doped porous SiC ceramic was 2.1 × 10−1 Ω cm four orders of magnitude lower than that of an undoped porous SiC ceramic (1.2 × 103 Ω cm). A B-doped porous SiC ceramic exhibited the highest thermal conductivity (16.6 W/(m K)) and flexural strength (25.9 MPa), whereas a Sc-doped porous SiC ceramic exhibited the lowest thermal conductivity (7.7 W/(m K)) and flexural strength (10.5 MPa) among the doped porous SiC ceramics. The electrical resistivity was strongly influenced by the doping, whereas the thermal and mechanical properties were dependent primarily on the necking area between SiC grains. The results suggest that the electrical conductivities of porous SiC ceramics can be successfully tuned independently of the thermal conductivity by a suitable doping.

Effects of initial particle size on mechanical, thermal, and electrical properties of porous SiC ceramics

The effects of initial particle size and sintering atmosphere on the compressive strength and thermal and electrical conductivities of porous SiC ceramics, fabricated using α-SiC and polycarbosilane (PCS), were investigated in the porosity range of 40–54%. Generally, the mechanical strength and thermal conductivity of a porous SiC ceramic decrease as the porosity increases. However, in this study, both the compressive strength (10.7–17.4 MPa) and thermal conductivity (0.55–0.79 W/(m·K)) of porous SiC ceramics increased as the porosity increased from 40 to 54% because of the decreased pore size (1013–218 nm) and increased bonding area per unit volume as the starting particle size decreased (35–1 μm). The influence of sintering atmosphere on the compressive strength and thermal conductivity of the porous SiC ceramics was negligible, whereas the porous SiC ceramics sintered in N2 atmosphere exhibited 4–10 times higher electrical conductivities than those of the samples sintered in Ar atmosphere, which can be attributed to N doping in the PCS-derived β-SiC. These results suggest that the mechanical, thermal, and electrical properties of porous SiC ceramics can be independently tuned to a certain extent by judiciously selecting the starting particle size and sintering atmosphere. The compressive strength, thermal and electrical conductivities, and porosity of the porous SiC ceramic processed with 35 μm particles in the N2 atmosphere were 10.7 MPa, 0.58 W/(m·K), 2.2 × 10−3 Ω−1 cm−1, and 40.3%, respectively.

Effects of carbon and silicon on electrical, thermal, and mechanical properties of porous silicon carbide ceramics

The properties of porous SiC ceramics were investigated as a function of Si/C content. The addition of C to SiC decreased the electrical resistivity, thermal conductivity, and compressive strength of the porous SiC ceramics for an increase in C content from 0 to 50 wt%. In contrast, the addition of Si to SiC increased both electrical resistivity and compressive strength and decreased thermal conductivity for an increase in Si content from 0 to 30 wt%. The addition of 5 wt% C increased the electrical conductivity, compressive strength, and thermal conductivity of porous SiC ceramics because of the partial densification of SiC by the removal of silica via carbothermal reduction. The current results suggest that both the electrical and thermal conductivities of porous SiC ceramics can be adjusted in the range of 9.0 × 10−2 –3.9 × 101 Ω cm and 1.3–31.4 W/(m·K), respectively, by controlling the Si or C content.

Microstructure and mechanical properties of porous SiC ceramics by carbothermal reduction and subsequent recrystallization sintering

ABSTRACT Porous SiC ceramics were prepared by a new approach combination of carbothermal reduction and subsequent recrystallization sintering. Firstly, micro-sized SiC particles were used as the skeleton, and SiC spherical nanocrystals were in-situ synthesized by the vapor-solid reaction between carbon nanoparticles and silicon monoxide vapor. The shape and diameter of SiC nanocrystals are related to the pristine carbon nanoparticles, showing a shape memory effect. After recrystallization sintering, high purity α-SiC porous ceramics with tailored necking area were obtained by the evaporation-condensation of SiC nanocrystals. A linear relation was revealed between the flexural strength and the value of d/d0 of porous recrystallized SiC (RSiC) ceramics (the neck diameter to coarse micron-sized grains diameter ratio). The necking area and d/d0 value increased with the SiC nanocrystals content, due to the higher saturated vapor pressure resulted in high mass mobility to neck area of SiC nanoparticles. As a result, a remarkable value of d/d0 ~ 99% and outstanding flexural strength of 75.7 MPa could be achieved for the porous RSiC ceramics with ~42% porosity by adding 20 wt.% nano-sized SiC sintered at 1950°C for 2 h.

In-situ reaction bonding to obtain porous SiC membrane supports with excellent mechanical and permeable performance

In order to develop filter material that can be used for high-temperature gas cleaning, porous SiC ceramic membrane support was fabricated by in situ reaction bonding. Pressureless sintering was carried out in the temperature range of 1280–1480 °C in air. Green bodies were formed by uniaxially pressing coarse SiC particles (150–180 μm) as a skeleton, fine SiC particles and ρ-Al2O3 powder as bonding additives, basic magnesium carbonate as sintering aid and polyvinyl alcohol (PVA) as binder. Effects of sintering temperature and ρ-Al2O3 content on mechanical performance and physical properties of porous SiC ceramics were systematically investigated. Results revealed that interconnected pores of support were mainly formed due to the packing of SiC coarse particles. Mullite (3Al2O3·2SiO2) was formed due to in-situ reaction between cristobalite obtained by SiC surface oxidation and α-Al2O3 converted from ρ-Al2O3 at higher temperatures. SiC particles were strongly bonded by mullite and oxidation-derived SiO2, which resulted in highly porous SiC membrane support with excellent mechanical properties. Open porosity of samples decreased with an increase in sintering temperature and ρ-Al2O3 content. In addition, flexural strength initially increased up to threshold limit, followed by gradual decrease. The sample with 9 wt. % ρ-Al2O3 exhibited the highest flexural strength after sintering at 1430 °C for 3 h. As-prepared SiC support with 9 wt. % ρ-Al2O3 demonstrated flexural strength of 25.1 MPa and air permeability of 4.8 × 10−12 m2. Moreover, as-prepared support exhibited excellent resistance to cyclic thermal shock, which indicates that these supports can be used for high-temperature flue gas cleaning under normal pressure.

Microstructure and Properties of Porous SiC Ceramics Modified by CVI‐SiC Nanowires

Sintered porous SiC ceramics are modified with SiC nanowires prepared via chemical vapor infiltration (CVI). SiC nanowires are successfully grown within sintered porous SiC ceramics following vapor–liquid–solid growth. The diameter of the SiC nanowires is in the range of 200 nm–1 μm, and first decreases with increasing input gas ratio (α = 50, 60, 70, and 80) and increases thereafter. The diameter of the nanowires decreases from the surface to the interior areas of the porous SiC ceramics. SiC nanowires effectively improve the mechanical properties of the porous SiC ceramics, and sample Ni‐50 has the highest flexural strength of 33.91 MPa and fracture toughness of 0.79 MPa · m1/2, which increases by 90.4% and 49.1% compared to an unmodified sample, respectively. Additionally, the presence of SiC nanowires leads to porous SiC ceramics with altered porosity and microstructure, and higher thermal conductivity. The porous SiC ceramics modified by CVI SiC nanowires satisfy the requirements of gas filtration applications and the pressure drop increases with decreasing apparent porosity. The porous SiC ceramics modified with CVI SiC nanowire has higher permeability than those resulting from the introduction of CVI‐SiC matrix or CVD‐SiC coating into porous SiC ceramics.

Fabrication and microstructure of liquid sintered porous SiC ceramics through spark plasma sintering

6H-SiC porous SiC ceramics accompanied by the formation of large clubbed and tabular grains were successfully fabricated at 1800 °C under an applied pressure of 50 MPa for 5 min by spark plasma sintering technique without introducing any pore-creating agent. The phase composition, microstructure and properties of porous SiC ceramics were investigated. The measured porosity of the specimens was 35.7% and the mean pore size varied in the range of 0.3–3 μm. The sintered specimen had a strength of 103 MPa, a fracture toughness of 2.89 MPam1/2, and a density of 1.85 g/cm3. The mechanisms of porous structure and grain growth were elucidated.

Properties of Porous SiC Ceramics Processed by Gelation and Consolidation of Boehmite Coated SiC Suspensions

ABSTRACTSiC powder was dispersed in various concentrations of boehmite sol. The boehmite coated SiC powder was characterized by zeta potential measurement, TEM and FT-IR analyses. Mullite bonded porous SiC ceramics were fabricated by sintering boehmite coated SiC powder compact via a pressureless sintering in air at 1300oC and were characterized by XPS, XRD, SEM analyses. The sintered ceramics have an interconnected open porous network with near uniform pore diameter. Rod shaped mullite crystals were observed in the neck region that bonded the SiC particles together. Effect of boehmite sol concentration on phase composition, microstructure, flexural strength, porosity and pore size distribution was studied. The ceramics synthesized from 30 wt% boehmite sol coated SiC powder contained 26 wt% mullite with ∼30 vol% porosity.

Strong effect of atmosphere on the microstructure and microwave absorption properties of porous SiC ceramics

Excellent microwave absorption properties of porous SiC ceramics were successfully synthesized using SiC/camphene slurries with various polycarbosilane (PCS) contents related to the SiC powder. The compositions of the nanowires (NWs) growth in the pore channels of porous SiC ceramics strongly depended on the pyrolysis atmosphere, with N2-generating Si3N4 NWs and Ar SiC NWs. With the increase of PCS content, the minimum reflection coefficient (RC) of porous SiC ceramics decreased from −7.6dB to −67.4dB in Ar and from −10.9dB to −24.7dB in N2, respectively. The effective absorption bandwidth (EAB) of porous SiC ceramics could be up to 8.1GHz in Ar and 4.5GHz in N2. The enhanced microwave absorption properties of porous SiC ceramics could be attributed to the formation of SiC nano-crystalline, nanosized carbon and the NWs, which would increase the amount of boundaries and defects, leading to the electronic dipole polarization and interfacial scattering.

Microstructure and properties of porous SiC ceramics by LPCVI technique regulation

A new gradient pore structure in porous SiC ceramics was fabricated by low pressure chemical vapor infiltration (LPCVI). Effects of deposition duration on the mechanical properties and permeability ...

Porous SiC ceramics fabricated by quick freeze casting and solid state sintering

Porous SiC ceramics with uniform microstructure were fabricated by quick freezing in liquid nitrogen and solid state sintering. Poly (vinyl alcohol) (PVA) was added as binder and pore morphology controller in this work. The microstructure and mechanical properties of porous SiC ceramics could be controlled by the composition of the aqueous slurries. Both solid content of the slurries and PVA content impacted on the pore structures and mechanical properties of the porous SiC ceramics. The solid content of slurries and PVA content varied from 60 to 67.5wt% and 2–6wt%, respectively. Besides, the grain morphology of ceramics was also tailored by changing the sintering temperature from 2050 to 2150°C. Porous SiC ceramics with an average porosity of 42.72%, flexural strength of 59.28MPa were obtained at 2150°C from 67.5wt% slurries with 2wt% PVA.

Processing and properties of porous SiC ceramics prepared by yttrium aluminum garnet infiltration

AbstractOxide bonded porous SiC ceramics were synthesized by infiltrating a liquid precursor of yttrium aluminum garnet into porous powder compact of SiC followed by sintering at 1300‐1500°C in air. Infiltration rate was estimated using weight gain by the liquid precursor sol into porous SiC powder compact as a function of time and was explained by Darcy's and Ficks's laws. The effects of SiC particle sizes and sintering temperatures on the formation of bonding phases, microstructure, SiC oxidation degree, flexural strength, porosity, and pore size distribution of porous SiC ceramics were studied. Various crystalline oxide phases were detected by XRD analysis. Depending on the starting SiC powder sizes and sintering temperatures, the porosity of the final ceramics varied nearly in the range of ~29‐41 vol. % with the variation of average pore diameter between ~5 and 30 μm. Flexural strength varied from 41 to 8 MPa depending on porosity. The effect of corrosion on oxide bond phases was investigated in strong acidic and basic medium at 90°C. The ceramics showed better corrosion resistance in acidic medium compared to basic medium. In basic medium, significant reduction in flexural strength (~42%) was arisen.

Effects of Additives Content on the Properties of Porous SiC Ceramics

The porous silicon carbide ceramics were fabricated by adding a variety of low melting point oxides in this paper. The additives were mullite, magnesium oxide, calcium oxide, and vanadium oxide. Effects of the additives content on the properties of porous silicon carbide ceramics were studied. The results showed that, when the additives content was greater than 2.8%, the apparent porosity, the bending strength, the permeability and the pore size were in an inversely proportional relationship with the additives content, while the content was less than 2.8%, proportional relationship was observed. When the additives content reached 2.8%, the porous SiC ceramics showed the best performances.

Effect of V2O5 addition on the properties of reaction-bonded porous SiC ceramics

Mullite-bonded porous SiC ceramics were prepared with and without V2O5 addition in air by an in situ reaction bonding technique. This process is based on the oxidation of SiC and the mullitization between oxidation-derived SiO2 and Al2O3. The effects of V2O5 addition on the phase composition, microstructure, open porosity, flexural strength and pore size distribution of porous SiC ceramics were investigated. With the addition of V2O5, the mechanical properties of porous SiC ceramics were improved. It was found that the V2O5 addition strongly promoted the phase transformation towards mullite and reduced the temperature of mullitization by nearly 400°C. When 4wt% V2O5 was added, a high strength of 30.11MPa was achieved at an open porosity of 42.1%.