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In this study, metal-modified silicon oxycarbides ceramics (SiOC/M, M = Fe, Al, and Zr) were fabricated, and the thermal stability of the SiOC/M (M = Fe, Al, and Zr) ceramics was investigated under the water-vapor- argon hybrid atmosphere. The phase and microstructural analysis showed that the thermal stability was in the order of SiOC/Zr ＞ SiOC/Al > SiOC/Fe. The SiOC/Zr and SiOC/Al ceramics possessed better thermal stability than SiOC/Fe ceramics, because they formed metallic oxides (ZrO 2 , mullite, or sillimanite). Additionally, the water-vapor-argon hybrid atmosphere increases the defects within the carbon clusters of SiOC/M ceramics and refines the lateral size of the nanocrystalline carbon. Understanding thermal stability and microstructural evolutions of metal-dropped polymer derived ceramics provided a new method for achieving high-temperature ceramics for application in an extreme environment. [ABSTRACT FROM AUTHOR]

3D-carbon fiber felts reinforced ceramic-based composites are considered as valuable structural materials due to their excellent high-temperature mechanical performance, low density and low thermal conductivity. In order to enhance the mechanical properties of the carbon fiber reinforced silicon oxycarbide (SiOC) ceramics, in-situ growth of SiCnws on the surface of carbon fiber via a simple precursor impregnation and pyrolysis method was proposed. As a result, nanoscale SiC nanowires and microscale carbon fiber felts reinforced SiOC ceramics were successfully fabricated. The results showed that the compressive strength of the composite increased by 369% and 173% after two PIP process in x/y and z directions, respectively. The enhanced compressive strength could be ascribed to the brittle fracture of SiCnws and CFs, and crack deflection. [ABSTRACT FROM AUTHOR]

We propose a novel hybrid method to produce macroporous ceramic with excellent sound absorption coefficient at medium and low frequency noise and multimodal pore size distribution. Macroporous ceramics with pore sizes from 100 nm to 2000 μm and apparent porosity in the range 85%–90% were fabricated by twice-foaming method and two pore-forming agents. These ceramics display a sound absorption coefficients from 0.11 to 0.99 in the sound-wave frequency range of 200–2000 Hz with sufficient connectivity rate above 99%. This ceramic represents a highly expected industrialization of properties for noise control and reduction at corrosive environments and high temperatures. [ABSTRACT FROM AUTHOR]

Abstract A kind of heterostructural SiC nanowires/SiOC composite ceramic is obtained by directly pyrolysis of mixture of poly(methylhydrosiloxane) (PMHS) and 2, 4, 6, 8-tetramethyl-2, 4, 6, 8-tetravinylcyclotetrasiloxane (TMTV) polysiloxane. The mechanical of in-situ growth SiC nanowires is mainly attributed to the initial phase separation of SiOC ceramic and subsequent solid-phase reaction of SiO and C phases. Due to the formation of SiC nanowires in amorphous SiOC ceramic, the interfaces of the SiOC particles are raising, which leads to the escalation of interfacial scattering. Thus, the absorption properties are promoted by the electronic dipole polarization and interfacial scattering. Results show that the minimal reflection coefficient (RC min) of hybrid SiC nanowires/SiOC ceramic decreases with the increasing annealed temperature, and reaches − 10 dB at 13 GHz at the thickness of 3.8 mm when the heat-temperature gets to 1400 °C. [ABSTRACT FROM AUTHOR]

Abstract Critical flaw size of structural ceramics is generally less than 100 μm and is therefore too small to be reliably evaluated. In this study, micro-sized flaws (as small as 10 µm) were introduced via femtosecond laser for the first time, and the critical flaw sizes of ZrB 2 and ZrB 2 -SiC-Graphite ceramics (12.9 µm and 36.1 µm, respectively) were accurately evaluated by linear extrapolation in double logarithmic coordinates. The critical flaw sizes calculated from the indentation fracture toughness (14.3 µm and 34.3 µm for ZrB 2 and ZrB 2 -SiC-Graphite ceramics, respectively) agreed well with the experimental results, while significant overestimation would occur by using fracture toughness values measured by means of single-edge notched beam, single-edge V-notched beam and single-edge precracked beam methods, which was mainly due to the fact that the notches in these three tests had the depth scale nearly two orders of magnitude higher than those of the inherent flaws. [ABSTRACT FROM AUTHOR]

Novel hybrid thermal protection material (TPM), consisting of TaSi 2 -based coating on carbon-bonded fiber (CBCF) composites and mullite fiber insulation tiles, is investigated using a plasma wind tunnel. Mullite fiber insulation tile is ceramically bonded to coated-CBCF composites. Results show that surface temperatures range from 400 °C°C to 1200 °C°C at low heat flux and dynamic pressure. However, at high heat flux and dynamic pressure, the surface temperature rapidly reaches 1400 °C°C, and the damage to the TaSi 2 -based coating is also observed. The cold-wall temperature of the hybrid structure remains at room temperature during ablation. In addition, TPM is invalid because of the consumption of the TaSi 2 -based coating. [ABSTRACT FROM AUTHOR]

Silicon oxycarbide (SiOC) ceramic aerogels in mesopores range have been fabricated by pyrolyzing polycarbosilane aerogels in nitrogen (N 2 ) atmosphere. The reactants, poly(methylhydrosiloxane) and 2, 4, 6, 8-tetramethyl-2, 4, 6, 8-tetravinylcyclotetrasiloxane have been heated in the presence of hydrochloroplatinic acid. As-prepared SiOC preceramic aerogel has specific surface area of 299 m 2 /g at room temperature, and decomposes during pyrolysis. Structural evolution of the aerogels as a function of heat-treatment temperature has been investigated by Fourier transform infrared spectrophotometer, X-ray diffraction analysis, transmission electron microscopy and X-ray photoelectron spectroscopy. Results indicate that tetrahedral Si–O–C network underwent four structural changes during thermal treatment from room temperature to 1600 °C. [ABSTRACT FROM AUTHOR]

This paper presents a double-layered coating system consisting of MoSi 2 ceramic reinforced with SiC whiskers and a MoSi 2 -TaSi 2 ceramic coating reinforced with SiC whiskers. This system improves oxidation resistance of carbon-bonded carbon fiber (CBCF) composites. Double-layer coating was about 160 µm in thickness and no interfaces or cracks between the layer and matrix were observed. Isothermal oxidation tests revealed that as-prepared coating presented excellent oxidation resistance, which could protect CBCF composites at 1500 °C for 160 min with 0.02% weight loss, whereas weight loss of single MoSi 2 ceramic coating reinforced with SiC whiskers reached 0.08%. High-temperature resistance barrier of the glassy phase and Ta 2 O 5 had a positive effect on improving the oxidation resistance of double-layer coating. [ABSTRACT FROM AUTHOR]

Continuous carbon fiber (CF) reinforced ceramic composites have been extensively studied owing to their excellent resistance to thermal shock, low density, and low thermal conductivity. However, the weak oxidation resistance of these composites has considerably limited their applications in some aerobic environments. Herein, high-emissivity silicon-carbide (SiC)-based ceramic coating was fabricated on SiOC/CF matrix using a facile vacuum impregnation technology and brush method. The coating reinforced with in-situ grown SiC nanowires could protect the SiOC/CF matrix, and the CFs were not oxidized after 60 min oxidation at 1500 °C. [ABSTRACT FROM AUTHOR]

Presently, the formation of oxide films on the surface of Ti-based bipolar plates results in decreased electrical conductivity. This limitation frequently curtails the operational lifespan of proton exchange membrane fuel cells (PEMFCs). In this study, we engineered Ti alloy bipolar plate materials using an elemental screening process and validated their performance through experimentation. The elemental screening results identified eight elements, specifically Ni, Cr, Mo, Ta, W, Fe, Co, and Zn, as promising candidates for bipolar plate materials. Among these, Mo exhibited a pronounced affinity for incorporation into the TiO 2 oxide film. Conductivity measurements of passivated bipolar plates indicated that the Ti–Mo alloy displayed excellent electrical conductivity (1.699 × 1020 Ω m−1). Notably, the introduction of Mo (with an energy level of 1.64 eV) significantly reduced the band gap of the oxide film. Importantly, even after continuous potential oxidation for 10,000 s, the interfacial contact resistance (ICR) of Ti-0.35Mo (9.80 mΩ cm2) remained below the threshold set by the American DOE standard (ICR <10 mΩ cm2). Consequently, this research successfully devised a bipolar plate material utilizing a Ti–Mo alloy and proposed an innovative strategy for improving the conductivity of oxide films in bipolar plate materials via an elemental screening approach. [ABSTRACT FROM AUTHOR]

Crack initiation and propagation of ZrB 2 -SiC-Graphite (ZSG) sharp leading edges (SLEs) subjected to thermal shock were systematically evaluated by the water spraying method followed by a crack dyeing treatment. Distinct differences in the crack patterns among different test conditions were observed, and the cracking behavior of ZSG SLEs (including crack initiation time, crack number and critical failure temperature) was revealed to be strongly dependent on both the cooling rate and the microstructure. The crack propagation during thermal shock could be considered as a quasistatic process (crack speed was lower than 1 cm/s) that needed to be driven by continuous cooling. [ABSTRACT FROM AUTHOR]

As a typical kind of multiple flaws, collinear flaws are particularly detrimental to the mechanical properties of ceramics. Here, two identical collinear micron-sized flaws with controllable length and spacing were successfully fabricated in ZrB 2 -20 vol% SiC (ZS) ceramic using femtosecond laser, and the effect of flaw length and spacing on flexural strength as well as fracture behavior (i.e., load-displacement curve and fractography) of ZS ceramic were investigated. The flexural strength almost remained constant when the flaw spacing was less than the critical value, which strongly depended on the flaw length, then increased gradually with increasing flaw spacing and reached a plateau. If the ratio between flaw spacing and flaw length was small enough, flaws would tend to coalescence first before fracture, owing to the strong interaction between flaws. If the ratio was too large, the center of the mirror area in fracture surface would be offset. [ABSTRACT FROM AUTHOR]

Manganese dioxide (MnO 2) has been widely utilized in the electromagnetic wave (EMW) absorption field because it exhibits numerous crystal types including α-MnO 2 , β-MnO 2 , γ-MnO 2 , and δ-MnO 2 , and is environmentally friendly. To enhance the EMW absorption performance of this material, we combined the precipitation method and calcination process to obtain γ-MnO 2 microspheres, and developed a core-shell structure of γ-MnO 2 @SiO 2 and γ-MnO 2 @SiO 2 @TiO 2 microspheres via the sol-gel process. Based on the synergistic effects between the core-shell structure and dielectric loss, γ-MnO 2 @SiO 2 with a thickness of 2.85 mm achieved the minimum reflection loss of −60.2 dB, demonstrating that these microspheres are excellent candidates for EMW absorbers. [ABSTRACT FROM AUTHOR]

Herein, the SiC nanowires were successfully fabricated via chemical vapor infiltration (CVI) into carbon fiber felts (CFs) and then the SiOC/SiCnws/CFs composites were synthesized by precursor infiltration and pyrolysis (PIP) processes. Results indicated that the lightweight composites possessed enhanced mechanical performance, low thermal conductivity, and excellent electromagnetic wave absorption properties. Detailedly, the compressive strength reached to 22.0 MPa and 9.6 MPa after two PIP processes cycles in z and x/y directions, respectively. Meanwhile, the composites exhibited tailored electromagnetic wave absorption performance with the effective absorption bandwidth of 3.06 GHz, and the minimum reflection loss (RL min) was -48.2 dB with a thickness of 3.6 mm. The present work has a guidance to prepare and design multifunction properties for application in harsh environment. [ABSTRACT FROM AUTHOR]

A new idea to improve the performance of porous sound absorbing ceramics is introduced in this study. By in-situ growth of magnesium borate whiskers in the prepared porous sound-absorbing ceramic matrix, the sound absorption coefficient of middle and low frequency is increased by 28.9% and the compressive strength is increased by 5 times. Because the ceramic system has high thermal stability and good chemical stability, this method provides a new possibility for the wide application of porous sound absorbing ceramics in sound absorbing field. [ABSTRACT FROM AUTHOR]

A novel Fe ion doped silicon oxycarbide (SiFeOC) ceramic was prepared by solvothermal method using methyltrim ethoxysilane, dimethyl dimethoxy silicane, and ferric nitrate as raw materials. Compared with pure SiOC ceramic, the incorporation of Fe ion into SiOC ceramic significantly enhanced phase separation of the SiOC network. Transmission electron microscopy and X-ray diffraction analysis showed that the SiFeOC ceramics were made up of amorphous SiOC, SiC and Fe 3 Si phases after pyrolysis at 1573 K. The anti-oxidation capabilities of such nanocomposites were also investigated at medium temperatures. Results showed that SiFeOC ceramics had better oxidation resistance properties than pure SiOC ceramics, and the phase compositions of those samples were also analyzed after the oxidation test process. This work provides a guidance to fabricate metal-modified SiOC ceramics with desired structures. [ABSTRACT FROM AUTHOR]