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• Silica fibers/SiC nanowires/Silica aerogel (SFs/SiCNWs/SA) composites were prepared by papermaking, chemical vapor infiltration (CVI) and sol-gel method. • SiCNWs were distribution evenly and weave to form networks inside aerogel composites based on CVI method. • SFs/SiCNWs/SA exhibited layered and mesoporous structure to improve thermal insulation performance. • SiCNWs blocked heat radiation at high-temperature to improve to thermal insulation performance at high-temperature. • SFs/SiCNWs/SA exhibited remarkable thermal conductivity(0.017 W/(m K) at 25 ℃, 0.019 W/(m K) at 200 ℃, 0.029 W/(m K) at 400 ℃, 0.034 W/(m K) at 600 ℃ and 0.094 W/(m K) at 1000 ℃). Due to excellent thermal insulation performance at room temperature and ultralow density, silica aerogels are candidates for thermal insulation. However, at high temperatures, the thermal insulation property of silica aerogels decreased greatly caused by transparency to heat radiation. Opacifiers introduced into silica sol can block heat radiation yet destroy the uniformity of aerogels. Herein, we designed and prepared a silica aerogel composite with oriented and layered silica fibers (SFs), SiC nanowires (SiC NWs), and silica aerogels, which were prepared by papermaking, chemical vapor infiltration (CVI), and sol-gel respectively. Firstly, oriented and layered SFs made still air a wall to block heat transfer by the solid phase. Secondly, SiC NWs were grown in situ on the surface of SFs evenly to weave into the network, and the network reduced the gaseous thermal conductivity by dividing cracks in SFs/SiC NWs /SA. Thirdly, SiC NWs weakened the heat transfer by radiation at high temperatures. Therefore, SFs/SiC NWs /SA presented remarkable thermal insulation (0.017 W (m K)–1 at 25 °C, 0.0287 W (m K)–1 at 500 °C, and 0.094 W (m K)–1 at 1000 °C). Besides, SFs/SiC NWs /SA exhibited remarkable thermal stability (no size transform after being heat treated at 1000 °C for 1800 s) and tensile strength (0.75 MPa). These integrated properties made SFs/SiC NWs /SA a promising candidate for highly efficient thermal insulators. [ABSTRACT FROM AUTHOR]

Aerogels have an impressive thermal insulation performance at room temperature. However, with high infrared transmittance, pure aerogels have no advantages in thermal insulation at high temperature. Opacifiers can reduce infrared transmittance to make a low thermal conductivity with sacrifice of that at room temperature. Herein, VO2powders undergoing reversible insulator to metal transition at 67.8 °C as opacifier with temperature-switch were introduced into silica aerogel composites to prepare aerogel reinforced by VO2@SiO2fibers paper (AVSP). At 25 °C, insulator VO2made little contribution to thermal conductivity (0.025 W/(m·K)) so that it was close to aerogel reinforced by pure SiO2fibers papers without opacifier (0.023 W/(m·K)). When temperature rose to 500 °C, metal VO2made thermal conductivity of AVSP (0.051 W/(m·K)) much lower than that of aerogel reinforced by pure SiO2fibers papers without opacifier (0.076 W/(m·K)). Meanwhile, SiO2fibers papers with three-dimensional network structure improved flexibility of aerogel. The tensile strength of AVSP was 2.1 MPa with density of 0.186 g/cm3. With 152° contact angle and flame resistance, AVSP showed a great potential in high temperature thermal insulation in a nonplanar condition. Thereby, this work provides a novel strategy to improve thermal insulation property at high temperature with little contribution to that at room temperature.

In the present study, the unique three-dimensional graphene coated nickel (Ni/C) foam reinforced silicon carbide (Ni/C@SiC) composites were first obtained via the precursor impregnation and pyrolysis (PIP) processes. The microstructure images indicated that the SiC fillers were successfully prepared in the skeleton pores of the Ni/C foam. The influence of the PIP cycles on the microwave absorption performances was researched, and the results indicated that after the primary PIP process, Ni/C@SiC–I possessed the optimal microwave absorbing performance with a minimum reflection loss(RL) of −25.87 dB at 5.28 GHz and 5.00 mm. Besides, the RLvalues could be below −10.00 dB from 5.88 GHz to 7.74 GHz when the corresponding matching thickness was 3.85 mm. However, the microwave absorption properties of Ni/C@SiC-II and Ni/C@SiC-III were tremendously degraded as the PIP times increased. At last, the electromagnetic parameter, dielectric loss, attenuation constant as well as impedance matching coefficient were further investigated to analyze the absorbing mechanism, which opened a new path for the certain scientific evaluation of the absorbing materials and had extremely important to the defence technology.

Alumina-silica composite coatings were prepared on the surface of graphite paper by chemical vapor deposition using Al[Cl.sub.3]/Si[Cl.sub.4]/[H.sub.2]/C[O.sub.2] as precursor in the temperature range of 300 to 550[degrees]C. X-ray diffraction (XRD) [...]

The threshold voltage modulation of carbon nanotube thin-film transistors (TFTs) and flexible three-dimensional (3D) integration circuits has become hot research topics for carbon-based electronics. In this paper, a doping-free gate electrode technology is introduced to significantly modulate the threshold voltage of polymer-sorted semiconducting single-walled carbon nanotube (sc-SWCNT) TFTs in combination with the highly effective gate-controlling ability of solid-state electrolyte thin films as the dielectrics. A systematic investigation was conducted on the impact of printed silver, evaporated silver, and evaporated aluminum (Al) gate electrodes on the threshold voltage of flexible printed bottom-gate and top-gate SWCNT TFTs. The results indicate that the SWCNT TFTs with Al gate electrodes exhibit enhancement-mode characteristics with excellent electrical properties, such as the negative threshold voltages (−0.6 V), high Ion/Ioff(up to 106), low subthreshold swing (61.4 mV · dec−1), and small hysteresis. It is attributed to either the formation of lower work function thin films (Al2O3) at the electrode/dielectric layer interfaces through the natural oxidation of the Al bottom-gate electrodes or the dipole reaction of the Al top-gate electrodes from X-ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS) data. In addition, 3D complementary metal-oxide-semiconductor (CMOS) inverters with common gate electrodes were constructed using the resulting enhancement-mode P-type SWCNT TFTs and matched N-type SWCNT TFTs, which shows high voltage gain (34), rail-to-rail output and high noise margins (80.04%, VDD= −1 V) as well good mechanical flexibility at low operation voltages. It demonstrates that SWCNT TFTs have great advantages for building large-scale 3D flexible integrated circuits.

In this study, silicon carbide (SiC) coating was prepared by CVD using MTS-H2-Ar as precursors on graphite substrate in the temperature range of 1100–1300℃. The morphology of SiC coatings was observed by SEM, and the phase composition, preferred orientation, grain size and crystallinity of the SiC coating were analyzed by XRD. It was found that the rate of deposition was increased with increasing temperature under low temperature range and then was nearly consistent over 1200℃. It indicated that the structure changed from smooth featureless to highly faceted structures. The β-SiC was obtained at four different deposition temperatures. An increasing crystallinity and grain size were observed with increasing temperature. Hardness and Young’s modulus also increased with increasing temperature. It can be concluded that crystallinity has an important influence on both hardness and Young's modulus, while grain size has a greater influence on hardness but a smaller influence on Young's modulus.

In this study, the air permeability of ultrafine glass fiber felts (UGFFs) as a function of bulk density and thickness was predicted by three analysis methods including linear fitting, polynomial fitting, and an artificial neural network (ANN). A 36-set database was obtained by the measurements of samples produced by the fame blowing process. It was shown that the ANN structure with six neurons in the hidden layer was optimal. The ANN model showed much better quality of predicting the permeation rate compared with linear fitting and polynomial fitting, which was evaluated by three important parameters, namely mean relative error (MRE), mean squared error (MSE), and correlation coefficient (R). The prediction diagrams applying the ANN model also matched the theoretical analysis very well, which verified the advantages and practicability of ANN.

Porous three-dimensional SiC/melamine-derived carbon foam (3D-SiC/MDCF) composite with an original open pore structure was fabricated by the heat treatment of the commercial melamine foam (MF), carbonization of the stable MF, and chemical vapor deposition of the ultra-thin SiC coating. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) were employed to detect the microstructure and morphology of the as-prepared composites. The results indicated that the 3D-SiC/MDCF composites with the coating structure were prepared successfully. The obtained minimum reflection loss was -29.50 dB when the frequency and absorption thickness were 11.36 GHz and 1.75 mm, respectively. Further, a novel strategy was put forward to state that the best microwave absorption property with a thin thickness of 1.65 mm was gained, where the minimum reflection loss was -24.51 dB and the frequency bandwidth was 3.08 GHz. The excellent electromagnetic wave absorption ability resulted from the specific cladding structure, which could change the raw dielectric property to acquire excellent impedance matching. This present work had a certain extend reference meaning for the potential applications of the lightweight wave absorption materials with target functionalities.

Melamine foam (MF), a promising development in light materials, finds application in construction, agriculture, aviation, transportation, electronic message, and other fields due to its excellent thermal insulation performance, sound absorption and noise reduction capabilities, safety and health benefits, as well as easy processing. However, its own shortcomings such as hardness, poor toughness, fragility, and slag removal greatly limit its application scope. In this review, a survey of the literature from two aspects of toughening of melamine resin and regulation of MF pore structure are reviewed to explore the research progress of toughening modification of MF. The principle, merit, and demerit of different modification methods are analyzed. In addition, owing to the extensive literature available, this article also summarizes the representative achievements of the nanotechnology modification of MF derivatives (carbon foam and carbon aerogel). Eventually, based on an assessment of current application status for both MF and its derivatives while considering existing challenges in their modification processes using nanotechnology approaches, we discuss future prospects for their application.

With the development of nanotechnology, nano-biomaterials have shown good development prospects in gene therapy. Cationic lipids include a group of amphiphiles that exhibit positive charge which interacts with negatively charged DNA/RNA leading to the formation of complexes containing condensed gene materials. Cationic liposomes complexed with gene materials are promising non-viral carriers for gene therapy. As an environmentally ionized cationic lipid, N-[1-(2,3-dioleyloxy)propyl]-N,N,N-trimethylammonium chloride (DOTMA) shows positive charge at low pH with moderate pKa value due to the headgroup of tertiary amine. It makes 1,2-dioleyloxy-N,N-dimethyl-3- aminopropane (DODMA) very effective in encapsulating nucleic acids during synthesis by temporarily reducing pH. Thus, lipid nanoparticles with DODMA can have neutral or low zeta potential at physiological pH. These remarkable structure-dependent properties have far reaching application potential in gene therapy. This review summarizes the synthesis methods and structure characteristics of DODMA and derivatives, and illustrates their applications in gene delivery.

Ablation is an erosive phenomenon with removal of material by a combination of thermo-mechanical, thermo-chemical, and thermo-physical factors with high temperature, pressure, and velocity of combustion flame. Materials with outstanding thermo-mechanical and thermo-chemical properties are required for future high-temperature components. C/SiC is a kind of great potential high-temperature structural material in aeronautics and astronautics with low specific weight, high specific strength, good thermal stability, oxidation resistance and excellent resistance to ablation. In this paper, the ablation phenomenon and mechanisms were summarized adequately. The ablated surface of C/SiC composites could be divided into three regions from center to external. In general, the higher the density, the lower the ablation rate; the lower the ablation temperature and less time, the lower the ablation rate, and the preparation methods also had a great influence on the ablation property. Thermo-physical and thermo-mechanical attacks were the main ablation behavior in the center region; oxidation was the main ablation behavior in the transition region and the border oxidation region.

Inspired by biological microvascular systems, microchannel embedded fiber reinforced polymer composites were developed to enhance the performance and reliability of aerospace composite structures by inducing self-healing, self-sensing and active-cooling capabilities. However, the creation of hollow channel network within composites largely depends upon the manufacturing technique, which not only influences the properties of channel and host structure, but also limits its use for a specific application. The aim of this study is to introduce a cost-effective, novel processing approach to produce microchannel embedded carbon-epoxy composites for a broader range of applications. The proposed approach essentially comprises of two steps of composite molding. In the first step, microchannels are first generated on the surface of a composite laminate during composite molding and later this composite laminate with microchannels is bonded with the other composite laminate in situ second step composite molding. The efficiency of the composite-composite joining was assessed through interlaminar shear and flexural testing. By applying this approach, carbon-epoxy composites embedded with microchannels of simple and complex shape, varying diameters and varying paths were fabricated, which can be potentially used in structural health monitoring, self-healing, lightweight heat exchanger, biological and chemical microreactors applications.

In this work, the SiC ceramics were fabricated by stereolithography (SLA) combined with reactive melt infiltration (RMI), and the microstructure and mechanical properties of SiC ceramics were optimized by adjusting the solid content and impregnating phenolic resin. The bulk density and bending strength of SiC ceramics were positively correlated with the proportion of SiC content. The SiC phase content was increased from 48.10% to 61.42% with the solid content increased from 30 vol% to 45 vol%. When the solid content was 40 vol%, the bulk density and bending strength of SiC ceramics attained the highest value of 2.85 g/cm3and 234.8 MPa. Meanwhile, the pyrolysis shrinkage of SiC ceramics along the non-additive direction and the additive direction was 4.83% and 1.21%, respectively. This research has successfully demonstrated the direct correlation of microstructure and content of SiC with the performance parameters of SiC ceramics fabricated by SLA.

The advent of nanotechnology has provided unprecedented opportunities for nanomedicine. Electrospun nanofibers have some astounding features such as high loading capacity, extremely large surface area and porosity, high encapsulation efficiency, ease of modification, combination of diverse therapies, low cost and great benefits. These remarkable structure-dependent properties have far reaching application potential in cancer diagnosis and therapy such as ultra-sensitive sensing systems for point-of-care cancer detection, targeted cancer cell capture, and functional and smart anticancer drug delivery systems. This review summarizes the principal mechanism of electrospun nanofibers and a variety of modified electrospun nanofibers, illustrates their application in biosensors for cancer detection, and enumerates their application in implantable drug delivery for cancer therapy.

The purpose of this work was to grow SiC as binder to adhere diamond particles to graphite substrate by low pressure chemical vapor deposition (LPCVD) at 1100 °C and 100 Pa using methyltrichlorosilane (MTS: CH 3 SiCl 3 ) as precursor. The composite coatings on graphite substrates were analyzed by various techniques. Results show that a dense SiC coating with a cloud-cluster shape was formed both on the diamond particles and the substrate after deposition. The thermal stress (290.6 MPa) strengthened the interfacial bonding between the diamond particle and the SiC coating, which is advantageous for the purpose of adhering diamond particles to graphite substrate. The applied load of sliding wear test was found to affect not only the friction coefficient, but also the wear surface morphology. With increasing loads, the asperity penetration was high and the friction coefficient decreased. [ABSTRACT FROM AUTHOR]

Oxidation resistance coatings of Ir–40 at.% Zr and Ir were produced onto Mo substrates by double glow plasma technology. The oxidation resistances of the coatings were evaluated at high temperature. Ir–Zr coating consisted of two layers: the primary layer close to the substrate was composed of dense columnar grains and the second layer was composed of dense grains of nanometric size. The mass gain of Ir coating above 800 °C was about 1.35% due to the formation of solid IrO2. The mass loss of Ir coating was about 5.3% due to the formation of gaseous oxide IrO3 when being held at 1227 °C for 30 min. The substrate was protected more effectively by multilayer than monolayer coating of Ir in oxidizing environment. The Ir–Zr coating was well bonded to the substrate after oxidation at 800 °C. After oxidation at 1000 °C, the Ir–Zr coating was poorly bonded to the substrate. The oxidation resistance of Ir–Zr coating was poor due to high content of Zr. [ABSTRACT FROM AUTHOR]

Abstract(SiO2)f/SiO2composites reinforced with three-dimensional (3D) six-directional preform were fabricated by the silicasol-infiltration-sintering method. The nominal fiber volume fraction was 47%. To characterize the mechanical properties of the composites, mechanical testing was carried out under various loading conditions, including tensile, flexural, and shear loading. The composite exhibited highly nonlinear stress-strain behavior under all the three types of loading. The results indicated that the 3D six-directional braided (SiO2)f/SiO2composites exhibited superior flexural properties and good shear resistant as compared with other types of preform (2.5D and 3D four-directional)-reinforced (SiO2)f/SiO2composites. 3D six-directional braided (SiO2)f/SiO2composite exhibited graceful failure behavior under loading. The addition of 5th and 6th yarns resulted in controlled fracture and hence these 3D six-directional braided composites could possibly be suitable for thermal structure components.

AbstractThis research paper establishes the relationship between fabric parameters and fiber volume fraction through analyzing the representative unit cell of the 2.5D shallow straight-joint preform. The effect of fabric parameters on the fiber volume fraction by theoretical study is also investigated. The 2.5D shallow straight-joint fabric was manufactured by quartz fiber to verify the fiber volume fraction by theoretical and experimental study. The errors between predicted and measured results is only 2.12% and 1.13%. It was also found that as warp density and linear yarn density of yarn decrease and fabric thickness increases, the overall fiber volume fraction and weft yarn fiber volume fraction increase, but warp yarn fiber volume fraction decreases. Weft yarn has greater influence on fiber volume fraction of fabric than warp yarn in the structure of shallow straight-joint.

AbstractSilica composites (2.5D quartz fibers-reinforced) were prepared by the silicasol-infiltration-sintering method. The fiber volume fraction was 50.5%. The composites were sintered in a temperature range of 400∼450°C. Mechanical properties of the composites were determined by pc-controlled electronic universal testing machines. The microstructure of the composite was observed by scanning electron microscopy (SEM). The density of the composite was 1.77 g/cm3. The flexural strength and the shear strength of the composites were 50.35 MPa and 22.41 MPa, respectively. The stress-deflection curves exhibited mostly nonlinear behavior; the failure was not catastrophic. Some fibers pull-out indicated that the composite had part toughness. However, abundant fibers fractured in the same plane revealed that the composite presented serious brittleness. The fracture mechanism of the composite was a mixture of ductile and brittle modes.

Water difference: Using H2O as the reaction medium in a conventional hydrothermal synthesis gives two nonporous materials with dense dia frameworks, dia(Zn) and dia(Co), from 2‐methylimidazole and M(OAc)2(M=Zn, Co; see structures, left). However, separation of the H2O and a solid mixture of the same starting materials in a steam‐assisted conversion gives open‐framework porous materials, ZIF‐8 and ZIF‐67 (right).

Abstract: Dense and adherent Ir coating was obtained on the surface of the Mo substrate by double glow plasma, which had a deposition chamber and two cathodes. Argon gas was used as the working gas. The bias voltage of Ir target and Mo substrate were −800 and −300 V, respectively. The chamber pressure was 35 Pa. Microstructure of the Ir coating was observed by scanning electron microscopy. The Ir coating had a polycrystalline structure with preferential growth orientation of (220) crystal plane. The deposition rate was ~3.5 μm/h. The good adhesion resulted from the buffer layer between the Mo substrate and the Ir coating. The buffer layer, a combined Ir and Mo, was formed at the beginning of the deposition. The Mo concentration distributed gradiently along the depth of the buffer layer.