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The development of efficient and quick method to prepare structure-function integrative C/SiC composites is always a major challenge in this field. Herein, the thermal conductivity and bending strength of C/SiC composites were enhanced simultaneously via continuous high heat conductive channels constructed by continuous wave laser machining and pitch-based high thermal conductivity carbon fiber in thickness direction. Results revealed that the thermal conductivity of the modified C/SiC composites is three times higher than that of referential C/SiC composites due to its highly ordered heat conducive channel in the thickness direction. Importantly, the bending strength of modified C/SiC composites increased to 457 MPa. To better understand the enhance mechanism, the micro-structure for both the composites and heat conductive channel was systematically analyzed. The results demonstrated that the rivet effect of heat conductive channel and the formed two phases structure on the fibers dispersed partial of load and finally enhanced the property of the composites. In a word, this method holds a nice applicable future in constructing structure-function integrative C/SiC composites.

In this study, silicon carbide (SiC) composites reinforced with pitch-based carbon fibers and composed of heat transfer channels were fabricated by combining chemical vapor infiltration and reactive melting infiltration method. It was observed that the internal heat conduction skeleton of pitch-based carbon fibers was sequentially formed. The thermal conductivities from room temperature to 500 °C along through-thickness direction and in-plane direction were investigated. The results showed that Cpf/SiC composites with heat transfer channels possessed excellent thermal conductvity in two directions, and the thermal conductivity increased with increasing volume content of heat transfer channels. The thermal conductivity in through-thickness direction reached 38.89 W/(m·K), and that for in-plane direction reached 112.42 W/(m·K). Theoretical calculations were empolyed to study the temperature dependence of the Cpf/SiC composites. The variations in slope A′ and intercept B′ values of fitted curves were in good agreement with the experimental results. To verify the reliablilty of the theoretical model, the Cpf/SiC composites were heated at 1650 °C for 2 h and the thermal conductivity exhibited further improvement due to the formation of more perfect crystalline structure. Thermal conductivity through thickness direction improved to 43.49 W/(m·K), and that in in-plane direction improved to 142.49 W/(m·K), which could be identified by the theoretical model. Finally, the leading edge model was established by using ABAQUS finite element analysis software to evaluate the potential application of the composites. Owing to the outstanding thermal conductivity, the leading edge obtained by using Cpf/SiC composites in this study exhibited lower temperature gradient and a more uniform temperature distribution. Moreover, less thermal stress and displacement were generated during heating process.

Carbon/silicon carbide (C/SiC) composites are usually regarded as thermal protective system materials and widely applied in hypersonic vehicles or ramjet. However, poor thermal conductivity of C/SiC composites, leading to severe heat concentration and thermal stress during the high-speed operation of hypersonic vehicle, limits their broad-range of practical applications. Modification with high thermal conductive fillers is an optional method; however, controllable dispersion and orientation of the fillers to construct continuous and ordered heat conductive channel has been proven to be a challenging task. Herein, based on high thermal conductivity fibers, a three-dimensional micro-pipeline preform was developed for the preparation of structure–function integrated C/SiC composites. The technical feasibility of the method, the characteristics of microstructures, and the thermal conductivity and bending strength of the as-obtained composites were systematically studied. Results revealed that the thermal conductivities of as-obtained composites reached 150.2 and 46.7 W m−1 K−1 for in-plane and out-of-plane direction, respectively. The bending strength obtained herein is 264.4 MPa, which is lower than that of polyacrylonitrile C/SiC composites. However, the fine control over the component and microstructure or densification could provide a higher value in the future research. In sum, the proposed method provides a convenient and feasible approach to prepare high thermal conductive C/SiC composites.

Yttrium silicate was introduced into the matrix of SiCf/SiC composites via the slurry impregnation and reactive chemical vapor infiltration (RCVI) methods to improve the water and oxygen corrosion resistance of the modified composite materials. The effects of heat treatment on the modified matrix and strength of the composites were systematically investigated. The results showed that the modified matrix was composed of a mixture of yttrium monosilicate, yttrium disilicate, and silicon carbide. The modified yttrium silicate matrix (named Y-Si-O matrix) and the silicon carbide matrix were laminated and well combined. After heat treatment, the amount of Y-Si-O in the mixed matrix increased. The modified composites with yttrium silicate had a similar flexural strength as SiCf/SiC composites (∼400 MPa). After treated at 1000 °C – 1300 °C, the strength of the modified composites increased by 17 %–26 %. The highest strength was measured for composites treated at 1200 °C.

Poor interfacial bonding between diamond and matrices has limited industrial applications of diamond-containing composites. Herein, continuous and dense nanometer SiC coatings were deposited on both large size (200 μm) and small size (1.0 μm) diamond particles to improve the wettability of diamond and protect it from oxidation and graphitization. Coating procedure consisted of first pretreating diamond particles followed by chemical vapor deposition (CVD) using methyltrichlorosilane (MTS: CH3SiCl3) as a precursor. Effects of deposition temperature, time, and gas flowing rate on microstructures of SiC coatings were all studied. Results showed that diamond surfaces were fully coated by SiC with thicknesses of 30 nm and 20 nm for large and small size diamond particles, respectively. Meanwhile, onset oxidation temperatures of large and small SiC-coated diamond particles increased by 250 and 130 °C, showing greatly enhanced oxidation resistance than that of raw diamond particles. The compressive fracture strength (CFS) of SiC-coated diamond (200 μm) is 226 N, improved by 8.5% compared with that of the raw diamond (201 N). In sum, CVD method is promising for the preparation of homogeneous nanometer SiC coatings on diamond particles for its modification and further application in composites.

Electrical property of joints made with polymer-derived silicoaluminum carbonitride (SiAlCN) ceramics was investigated. SiAlCN ceramics were successfully joined using polycarbosilane precursor as joining medium at 1123 K and 250 kPa. The maximum tensile strength of obtained joints reached ~3 MPa, meeting strength requirement of sensor fabrication. DC and AC conductivity of joints were measured in temperature range of 373–823 K, and were shown to follow band tail hopping mechanism. Conductive behavior of joints was evaluated via comparison with free SiAlCN ceramics. Unique amorphous structures of SiAlCN substrate and joining layer played important role in overall electrical properties. Therefore, the prepared joints presented practical application in high-temperature sensors based on polymer-derived ceramics.

Thermal barrier coatings can improve the energy efficiency of industrial or aircraft gas turbines by increasing the operation temperature. In this study, new TBC materials, namely multicomponent rare-earth cerate (Sm0.2Eu0.2Tb0.2Dy0.2 Lu0.2)2Ce2O7 (5RC) and zirconocerate (Sm0.2Eu0.2Tb0.2Dy0.2Lu0.2)2ZrCeO7 (5RZC) ceramics were synthesized by solid-state reaction sintering. 5RC and 5RZC had a homogeneous rare-earth element distribution and a pure fluorite structure up to at least 1400 °C, hence, showing good phase stability. The coefficient of thermal expansion of 5RC appeared to have a linear increase, reaching 12.60 × 10−6 K–1 at 1200 °C without a sharp increase at low temperatures, as observed for several single-component rare earth cerates. The thermal conductivity was also reduced in multicomponent 5RC and 5RZC. Moreover, 5RZC exhibited a better sintering resistance than 5RC. The doped Zr reduces the volatilization of ceria and enhances the stability of 5RC. As conclusion, the multicomponent rare-earth cerates 5RC and 5RZC are potential thermal barrier coating materials.

In this work, high-entropy ceramics (Hf0.25 Zr0.25Ta0.25Nb0.25)C (HZTNC) and HZTNC doped with 20 vol% SiC (HZTNC-SiC) were fabricated by spark plasma sintering. Their oxidation behavior was investigated over the temperature range of 1300–1500 °C for up to 60 min. Both HZTNC and HZTNC-SiC exhibited good oxidation resistance, and their weight change as a function of oxidation time obeyed a parabolic law. Through XRD, microstructure observation, and elemental mapping analysis of the oxide layers, it was found that the formation of Nb2Zr6O17, Hf6Ta2O17, and (Ta, Nb)2O5 mixed-oxide layers effectively protected the matrix from further oxidation. Microcracks began to appear on the oxide layer of HZTNC at high temperatures after 60 min of oxidation. However, the addition of SiC in HZTNC suppressed these microcracks at high temperatures due to the active oxidation of SiC. Compared with the oxides formed on HZTNC, the additional formation of Hf(Zr)SiO4 on HZTNC-SiC could further improve its oxidation resistance over HZTNC ceramics.

Na3Zr2(SiO4)2(PO4), a typical solid-state electrolyte material, was fabricated at 700°C within seconds by flash-sintering. Under a direct-current electric field, the sodium oxides deposited on the cathode side due to the electrochemical reactions and thereby resulting in impurities (Na2ZrSi2O7 and m-ZrO2) within the bulks. The pure Na3Zr2(SiO4)2(PO4) bulks without the impurities could be sintered under alternative- current electric field, which exhibited comparable ion conductivity and activation energy to the reported data. This study demonstrated that flash-sintering can be used to synthesize and densify ceramics containing volatile composites. It may provide a new route to fabricate solid-state electrolytes in an efficient way.

Herein, we report the densification behavior of a typical electric ceramic, barium titanate (BaTiO3), and highlight the role of oxygen vacancies in rapid densification of BaTiO3 during flash sintering. The activation energies of flash- and conventional-densification processes are compared to reveal that the initiation of flash sintering is triggered by the accumulation of generated oxygen vacancies under the electric field. Furthermore, the densification kinetics of BaTiO3 and X-ray photoelectron spectroscopy of flash-sintered BaTiO3 infer that the ultrafast densification during the flash-sintering stage is dominated by the migration of electric field-generated defects coupled with defect-annihilation by take-in oxygen from the environment.

In this study, grooves were fabricated on the surface of fully dense polymer-derived SiAlCN ceramics. Industrial femtosecond laser source was used at wavelength of 1030 nm with pulse duration of 290 fs and repetition rate of 100 kHz. Moreover, comprehensive study was carried out to evaluate the influence of scan speed and energy fluence on grooves quality, including the heat-affected zone around the laser-machined grooves, microstructures of laser-irradiated surface, and cross-section morphology of grooves. A series of grooves with width in the range of 30–80 μm and depth below 280 μm was successfully fabricated using femtosecond laser pulse. Laser parameters were optimized to obtain grooves with satisfying surface quality. Furthermore, formation and disappearance of laser-induced periodic surface structures were systematically investigated. This study proposes fabrication of grooves on SiAlCN ceramics via laser processing, which provides precise method for fabrication of microstructure with fascinating properties.

In this work, high-entropy carbide (Hf0.2Ta0.2Zr0.2Ti0.2Nb0.2)C (HEC) ceramics doped with different concentrations of SiC were prepared by spark plasma sintering at 2000 °C in vacuum. Oxidation behavior of HEC ceramics was studied in 1300–1500 °C temperature range. The addition of SiC enhances oxidation resistance of HEC ceramics through the formation of Hf(Zr)SiO4 and Hf(Zr)TiO4 protective oxide layer, with 20 vol% SiC-doped ceramics exhibiting the best oxidation resistance. Outward diffusion of TiO is suggested to be rate-controlling process in the oxidation of SiC-doped HEC ceramics. Although the SiC does not affect oxidation mechanism of HEC ceramics, its presence leads to a delay in outward diffusion of transit elements including Nb and Ta during oxidation. Thus, oxidation resistance of HEC at high temperatures could be improved by the addition of SiC.

Polymer-derived ceramics (PDCs) are promising high-performance materials for various applications, yet their brittleness represents major drawback in their machining. Femtosecond laser pulse ablation is non-contact rapid processing method used in precision machining of PDCs. Herein, two laser parameters (laser energy fluence and rotational speed) were investigated to achieve laser–material interactions and machining characteristics via machine single circular lines, blind holes, and through-holes in polymer-derived SiAlCN ceramics. With the decrease in rotational speed, the morphology of single circular lines gradually roughened and heat-affected zone was produced. Varying ablation rates were obtained at different energy fluences. For blind holes, three different ablation regions were observed. As the energy fluence increased, blind holes gradually transformed into through-holes. Through-holes with near-cylindrical profiles and minimal collateral damage were obtained. Ablation debris deposited around through-holes were indicative of N release, breaking of Si–N and C–C bonds, and formation of SiOx. Laser ablation of PDCs led to the formation of laser-induced surface structures, bubble pits, stripe structures, molten materials, and sphere-like particles.

The amorphous and heterogeneous microstructures of polymer-derived ceramics (PDCs) make it challenging to uniformly polish them without the appearance of obvious polishing defects. In this study, the surface characteristics of polymer-derived silicoaluminum carbonitride (SiAlCN) ceramics were investigated after mechanical polishing and chemical–mechanical polishing (CMP). The results showed the generation of polishing defects including scratches, pits, and comet tails after mechanical polishing; nonetheless, the surface quality was largely improved after CMP, providing an ultra-smooth surface (Ra = ~0.25 nm). The evolution of the surface morphology was characterized in detail and X-ray photoelectron spectroscopy was used to analyze the characteristics of chemical bond before and after the CMP. The polishing slurry dominated the corrosion process during CMP, inducing the oxidation of the SiCxNy phase; nonetheless, the so-formed oxidation products and carbon phase were removed by mechanical action. The obtained ultra-high smooth surface can promote practical application in the field of PDCs-based sensors.

In last decade, rare-earth disilicates have been considered as candidate materials for top coat in multilayer environmental barrier coatings (EBCs). However, optimal coating material has not yet been found. Previous studies revealed that parabolic rate constant of thermally grown silica scale (silica-TGO) beneath EBCs played a key role in the durability of SiC matrix ceramic composites coated with EBCs. To determine optimal coating material, in this study, Lu2Si2O7 and Sc2Si2O7 coatings were first corroded under quasi-static water-vapor corrosion conditions. The evolution of silica-TGO beneath coatings was then examined in detail. Accordingly, parabolic rate constants of silica-TGO growth were calculated. Compared with parabolic rate constants of silica-TGO growth beneath barium-strontium aluminosilicate (BSAS), Yb2Si2O7, and Y2Si2O7-BSAS coatings in previous studies, Y2Si2O7-BSAS coating shows the lowest parabolic rate constant and growth rate of silica-TGO. Crystal structure of rare-earth disilicates was also studied. Results showed that bond lengths of Y–O and Si–O in Y2Si2O7 were short, indicating that it possessed low ionic oxygen permeability. This resulted in its low parabolic rate constant of silica-TGO growth. Therefore, Y2Si2O7 is the optimal material as top coat in multilayer EBCs.

ZrB 2 –SiC composite ceramics with different compositions (20 and 60 vol% ZrB 2 –SiC, 20ZS and 60 ZS, respectively) were prepared. Wear tests were conducted on the obtained ceramics in multiple distances using ball-on-flat tribotester. Volume loss and cross-sectional profiles of samples were measured by three–dimensional (3D) profilometer to study the onset of track wear damages. Pressure–depth curves and hardness were measured by indentation to investigate defects produced in the tribo-film by the debris. The debris of 20ZS was found to be joined to the tribo-film and accumulated with distance, shifting from microcrack (＜10,000 cycles) to abrasive wear (50,000 cycles). Compared to 20ZS, lower debris accumulation of 60ZS resulted in better wear resistance, leading to thinner and more stable non-substrate regions for this sample. These differences between both samples basically resulted from different particle sizes. Fine grains were easily pulled out in the experiment, resulting in abrasive wear of the specimen. While transgranular fracture of grains and the pinning led to larger grains with less debris, the damage mode remained transgranular fracture.

The mechanical and tribological performances of densified polymer-derived C-SiC nanocomposites containing in situ formed nano-carbon were studied. The hardness, elastic modulus, and fracture toughness of the nanocomposites decreased while increasing the carbon volume from 5% to 16%. Compared with monolithic SiC, all the nanocomposites showed higher toughness as a result of the crack deflection and bridging of the carbon phase. The wear mechanism included mechanical wear (micro-crack), abrasive wear, carbon lubrication, and humidity-driven tribochemical reactions. Wear resistance was found to be mainly controlled by both the hardness and the crystal size of SiC. 6%-DP, with the smallest SiC crystal size, showed the highest wear resistance among the samples studied though with a lower hardness herein. The small SiC crystal size was important in accelerating the formation of a tribo-oxidation-film and contributed to increase the fraction of transgranular fractures, both improving wear resistance.

A significant decrease in the thermal conductivity of SiC after irradiation has hindered its practical applications. To solve this problem, polymer-derived pure SiC and C-SiC composites were irradiated under 4 MeV Au2+ ions, and their thermal conductivity was evaluated. The time-domain thermoreflectance method was found to be effective and sensitive to obtain the thermal conductivity of the irradiated layer. In pure SiC, irradiation-induced complete amorphous SiC significantly decreased the thermal conductivity. However, in C-SiC composites, the heterogeneous interface between C and SiC probably increased the irradiation resistance, leaving residual crystallinity in both C and SiC phases and resulting in a higher thermal conductivity. The thermal conductivity of C-SiC composites was dominated by SiC matrix. The optimal thermal conductivity of SiC related composites after irradiation can be designed by controlling the distribution, size, content, interface, and degree of crystallinity of the two phases in the future.

ZrB 2 –SiC composite ceramics with varying compositions (6.4, 22.3, and 61.5 vol% ZrB 2 –SiC) were synthesized and spark plasma sintered (SPS) for 30 min under argon atmosphere. Ceramics showed relatively uniformly distributed phases with small spherical crystallized grains. Vickers hardness and fracture toughness of ceramics were measured, and scratch and tribological behaviors of sintered ceramic specimens were also investigated. According to experimental results, materials having different inter- and trans-granular fractures showed different wear loss, friction efficient, and tribofilm morphology. Ceramics chemically reacted with moisture while being tribotested, leading to the formation of a tribofilm on the bottom of wear track. Characteristics of silica/hydride silica revealed the formation of tribofilms with different morphologies, thereby implying that several key factors are involved in determining the efficiency of this process.

The piezo-dielectricity of a polymer-derived amorphous silicoaluminum oxycarbide ( a -SiAlCO) was studied. The material showed a relatively high dielectric constant and anomalous piezo-dielectricity characterized by a positive pressure coefficient as high as 0.10–0.25 MPa −1 . Further analyses indicated that this anomalous piezo-dielectricity resulted from an increase of polarizability with pressure. This phenomenon was ascribed to the unique self-formed bi-phasic (i.e., low-conductive ceramic and high-conductive free-carbon phases) structure of the SiAlCO material. The huge piezo-dielectric coefficient makes this material a very promising candidate for high-temperature sensing applications.

Polymer-derived SiC ceramics have been increasingly used in the field of nuclear energy. Herein, we synthetized polymer-derived SiCs with varying SiC/C heterogeneous interfacial properties by pyrolyzing the ceramics at different temperatures. Subsequently, we studied the effect of these interfacial properties on the irradiation behavior (i.e., volume swelling, amorphization, and mechanical properties) of the SiC ceramics. In the case of crystalline ceramics (pyrolyzed at 1150–1500 °C), the presence of a nano-crystalline graphite (NC-G) phase with sp3/sp2 hybridization ratios of 0.40–1.27 further enhanced the swelling resistance of nano-SiC by increasing the defect trapping capability of the interfaces. In contrast, amorphous ceramics (pyrolyzed at 900–1100 °C) showed low penetration depths and superior stabilities upon irradiation. These strong ion cascade blocking characteristics may result from the atomic short-range order of these materials. This approach allows optimum design of polymer-derived SiC with superior swelling resistance and stability under room-temperature irradiation.

In this paper, it is demonstrated that in an oxygen-enriched environment, the oxygen partial pressure affects the onset temperature of flash sintering of 3 mol% yttria-stabilized zirconia (3YSZ). Flash sintering experiments were performed with oxygen partial pressures in the range of 0.25–1 atm. The results indicate that the onset temperature increased by increasing oxygen partial pressure. According to the plots of the conductivity as a function of temperature, the oxygen partial pressure might affect the onset temperature, by changing the conductivity in the pre-flash stage. Combined to the analysis of the law of mass action, it was established that electron conduction might also represent a critical parameter during the pre-flash stage of flash sintering, excluding the oxygen vacancy conduction.

Polymer-derived ceramics (PDCs) are considered to be promising candidate materials for high-temperature sensor applications. Even though the PDCs have been studied for decades, the reliable PDC-based thin film sensors have not been produced, because ceramic films are too fragile to be handled without a substrate, but the huge shrinkage during polymer-to-ceramic conversion makes it difficult to fabricate PDC-based sensing elements on conventional substrates such as Al2O3. In this study, a thin polymer-derived ceramic double-layer thermistor was developed, using a layer with a lower resistivity as the sensing element and a layer with a higher resistivity as the substrate. The difficulty in PDC-based film sensing elements fabrication on a substrate was consequently resolved, because both the sensing elements and the substrate sustained a similar shrinkage during pyrolysis. The proposed double-layer thermistor was fabricated through step-growth photopolymerization and co-pyrolysis of two similar polymer precursors: commercially available polysilazane for the high-resistivity substrate and DVB-modified polysilazane for the low-resistivity sensing part. The DVB-modified polysilazane showed a similar shrinkage during pyrolysis, whereas the resistivity of the pyrolytic product was five orders of magnitude lower. The obtained thermistor exhibited a negative temperature coefficient in the temperature range from the room temperature to 650 °C, and the resistance of the thermistor decreased smoothly as the temperature increased. The resistance-to-voltage conversion was conducted with a voltage divider equipped with a fixed resistor and the output voltage was observed to increase smoothly along with temperature. The current sensor configuration based on PDCs was reported for the first time, and is much closer to applicable sensors.

In this paper, a pressure sensor made of polymer-derived SiAlOC ceramics is designed, fabricated and tested. The sensor package is composed of a SiAlOC sensor head and a serially connected divider resistor. The requirement of the divider resistor is to achieve maximum sensitivity. The results showed that the pressure sensor has high accuracy, stability, and repeatability to both unidirectional and bidirectional pressure variations. While the sensor is tested at room temperature, it has potential for high temperature applications due to the excellent high-temperature capability of the polymer-derived SiAlOC ceramic.

The electric behaviors of both free-carbon phase and ceramic phase in polymer-derived amorphous silicoaluminum oxycarbide were studied by impedance spectroscopy. The results revealed that the resistance of both ceramic phase and free-carbon phase are similar to each other and decreased with pyrolysis temperature. Meanwhile, the ceramic phase showed higher capacitance than the free-carbon phase. With increasing pyrolysis temperature, the capacitance of the ceramic phase drastically decreased, but that of the free-carbon phase remained similar. Each phase exhibited a relaxation process, which moved to higher frequency with increasing pyrolysis temperature. The results are correlated with the structural evolution of the two phases.

The piezoresistive behavior of polymer-derived amorphous SiAlCO ceramic is studied in a temperature range of 25–300 °C. It is shown that the material exhibits a giant gage factor of 7000–16,000, much higher than that for any reported high-temperature materials. The result also reveals that the material exhibits a positive temperature-dependent piezoresistive stress coefficient within the temperature range. The unusual piezoresistivity of the material was attributed to the structure of the SiAlCO, which consists of highly disordered graphene-like carbon nanoclusters dispersed within an amorphous matrix comprising of SiC x O4−x tetrahedra. The huge piezoresistivity, together with the processibility and low-cost, make the material very promising for high-temperature sensor applications.

The electric conductivity and microstructure of polymer-derived SiAlCO ceramic were studied. The conductivity increased drastically with increasing pyrolysis temperature and exhibited a typical Arrhenius dependence on pyrolysis temperature with the activation energy of ~7.15 eV. The microstructure was analyzed by XRD, Raman spectroscopy and XPS. Unlike previous reported PDCs, the increase in the conductivity of the SiAlCO cannot be explained by the structural changes of the free carbon phase. It is speculated that the increased conductivity is possibly due to the redistribution of C–O bonds within the free carbon phase.

To improve the poor membrane-forming ability of polymer containing sterically-protected organic cations with the excellent alkaline stability, a series of robust and crosslinked poly(2,6-dimethyl-1,4-phenylene oxide)s (PPO) anion exchange membranes (AEMs) with bulky and chemically stable imidazolium cations was prepared by quaternization with C1,C3,C4-substituted imidazole and crosslinking reaction via “thiol-ene” chemistry. Compared to the uncrosslinked counterpart, the crosslinked AEMs showed excellent film-forming properties with the highest of tensile strength of 53.2 MPa, probably owing to the increased entanglement interactions in polymer chains that may in turn result in the controlled the water uptake and dimensional stability of the AEMs. Moreover, by using two different crosslinkers, water uptake of the resulting AEMs could be effectively tuned. The crosslinked AEM had a water uptake of 12.8 wt% with the ion exchange capacity (IEC) of 1.27 meq./g when using a hydrophilic dithiol as the crosslinker, which was almost twice than that for the membrane with hydrophobic crosslinker AEM (water uptake was 6.6 wt%, IEC = 1.28 meq./g). The higher water uptake further contributed to high ionic transport with bromide conductivity of 11.2 mS/cm at 20 °C in water and 24.8 mS/cm at 80 °C. The excellent alkaline stability of these materials was demonstrated by the fact that, more than 90.4% of bromide conductivity and 60.5% of tensile strength was retained after 1000 h immersion in 1 M NaOH at 80 °C, due to the presence of crosslinked networks and alkali-resistant sterically-protected imidazolium. Furthermore, we compared the AEM fuel cell performance and durability of the membrane electrode assembly (MEA) using the crosslinked and uncrosslinked bulky imidazolium-functionalized PPO copolymers as ionomers in catalyst layers. A higher peak power density of 200 mW/cm2 at a current density of 475 mA/cm2 and improved short-term durability (20.5 h) under a constant current density of 200 mA/cm2 at 60 °C were obtained for the membrane electrode assembly with the crosslinked ionomer. These results suggest that crosslinking of anion conductive materials with stable sterically-protected organic cations is a facile and effective strategy to prepare the robust and alkaline stable AEMs for high-performance alkaline fuel cells.

Nonoxide SiCN hollow nanospheres were prepared from a block-copolymer comprising of a precursor block and a sacrificial block. The copolymer was first synthesized and then self-assembled into core-shell structured micelles with the sacrificial block forming the core and the precursor block forming the shell. The micelles were subsequently pyrolyzed at high temperatures to transform the shell into ceramics and to completely decompose the core to form a hole. The technique is probably applicable to other material systems.

This paper describes the use of polymer-derived SiAlCN (silicoaluminum carbonitride) ceramics (PDC) to fabricate a temperature sensor for high-temperature applications. A unique sensor head was designed and fabricated with Pt wires seamlessly embedded in as electrodes. Material characterization test demonstrates that the resistance of the senor head decreases monotonically with surrounding temperature, suggesting its readiness to be used for temperature measurement. In actual experiment (temperature up to 830 °C), the measurement of the PDC sensor demonstrates good repeatability to both unidirectional and bidirectional temperature variations for the total span of 10 h, and its measurement follows closely with the thermal couple measurement. These results demonstrated that the temperature sensors made of polymer-derived ceramics (PDC) have excellent accuracy and repeatability, and can be used in high temperature environment.