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Abstract: Silica sol is one of the frequently used binders in high‐temperature resisting fibrous porous ceramics, but in the drying process, it can diffuse with water and influence the uniformity of ceramics. To solve this diffusion problem and fabricate homogeneous fibrous porous ceramics, cationic starch was firstly introduced in mullite fibrous system. The effects of starch content and high‐temperature binder content on microstructure, physical, and mechanical properties were also investigated. The results indicate that starch consolidated mullite fibrous ceramics owned a homogeneous 3D skeleton structure, since the introduced starch can absorb both water and silica particles by gelatinization and ensure the even distribution of binders. Compared with the mullite fibrous ceramics fabricated without starch addition, starch consolidated ceramics owned better microstructure and higher interior compression strength. Furthermore, both the starch and silica sol content had great impact on the microstructure, density, porosity, thermal conductivity, and compressive strength of the fibrous ceramic. [ABSTRACT FROM AUTHOR]

Fine-grained mullite nanofibers derived from the diphasic mullite sol were successfully fabricated by electrospinning and subsequent pyrolysis at 1500°C. Polymethylsiloxane and aluminum tri-sec-butoxide were selected as the silicon and aluminum source to synthesize the diphasic sol. Results show that the weight loss of mullite precursor fibers in our work was about 60 wt.%, which is similar with that of fibers fabricated using the monophasic sol. This low weight loss was mainly attributed to the high ceramic yield of polymethylsiloxane and low introduced polyvinylpyrrolidone content, which ensures the integrity of fiber morphology during the sintering process. Mullite fibers with 216 nm average diameter were fabricated after sintered at 1500°C and the corresponding grain size was only ~100 nm, much smaller than that in mullite fibers derived from monophasic sols. Therefore, it can be predicated that mullite fibers in this work should possess a higher mechanical strength than those derived from monophasic sols when the sintering temperature was higher than 1400°C and therefore was an ideal starting materials for the fabrication of mullite nanofibrous ceramics used as the high-temperature thermal insulation materials. [ABSTRACT FROM AUTHOR]

The method of in situ synthesis of mullite whiskers by gas-phase deposition and reaction was applied to improve the compressive strength of the mullite fiber brick. During the preparation process, silica sol, Al(NO 3 ) 3 solution and NH 4 F solution were introduced into the fibrous brick in the form of ions or sol through vacuum impregnation and freeze drying, and the silica sol, Al(NO 3 ) 3 and NH 4 F served as the silica sources, aluminum source and catalyst, respectively. Effects of process parameters (concentration of impregnation solutions, holding time, sintering temperature) on compressive strength and elastic modulus of the fibrous brick during the in situ toughening process were analyzed. SEM and XRD analysis results demonstrated that the mullite whiskers were synthesized on the surface of mullite fibers based on the reaction of AlOF and SiF 4 . What is more, the whiskers on adjacent fibers intersected with each other and formed many unfixed lap-jointing points, resulting in the increase of compressive strength and elastic modulus. Although the density and thermal conductivity of the sample after the generation of mullite whiskers fabricated with the optimum process were 0.406 g/cm 3 and 0.1262 W/(m K), respectively, which were slightly higher than that of the raw fibrous brick (0.375 g/cm 3 density and 0.1069 W/(m K) thermal conductivity, respectively), the corresponding compressive strength and elastic modulus of the sample reinforced with the whiskers increased to 1.45 MPa and 42.03 MPa, respectively, which were much higher than that of the raw fibrous brick (0.39 MPa compressive strength and 6.5 MPa elastic modulus). [ABSTRACT FROM AUTHOR]

Various electrospun metal/SiOC (Ag/SiOC, Co/SiOC, and Cu/SiOC) composite fibers were synthesized via a carbon thermal reduction of four kinds of metal source (silver oxide nanoparticles, silver acetate, cobalt acetate, and copper trifluoro acetylacetonate). XRD results indicate that both common metal-organic metal precursors and seldom used metal oxide particles were successfully carbon thermally reduced to the corresponding metallic particles embedded in SiOC fibers, indicating that the range of metal source choices suitable for this method is quite broad. Further SEM and TEM analysis revealed that the shape and size of the formed metal particles were determined by the characteristics of the metal source in the electrospinning solution, which means these features of the metal particles can be adjusted by taking into account the solubility of the precursors in the chosen solvents. The prepared Ag/SiOC composite fibers possessed antibacterial activity for both Gram-negative E. coli bacteria and Gram-positive S. aureus bacteria and suitable permeability (~1 × 10 m), constituting a promising material for antibacterial filtration application. [ABSTRACT FROM AUTHOR]

ABSTRACT Silicon oxycarbide (SiOC) fibers with different chemical compositions were successfully fabricated by electrospinning a mixture of polyvinylpyrrolidone (PVP) and commercially available polymethylsilsesquioxane (MK) or polymethylphenylsilsesquioxane (H44) preceramic polymers, followed by cross-linking and pyrolysis at 1000°C in Argon. The influence of the processing procedure (solvent selection, cross-linking catalyst and additives) on the morphology of the produced fibers was investigated. For the MK/isopropanol system, the introduction of 20 vol% N,N-dimethylformamide (DMF) enabled to decrease the diameter of the as-spun fibers from 2.72 ± 0.12 μm to 1.65 ± 0.09 μm. For the H44/DMF systems, beads-free fibers were obtained by adding 50 vol% choloroform. After pyrolysis, the resultant SiOC fibers derived from MK and H44 resins possessed uniform morphology, with an average diameter of 0.97 ± 0.07 μm and 1.07 ± 0.08 μm, respectively. Due to their different chemical compositions, the MK-derived and H44-derived SiOC ceramic fibers could find different potential applications. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 39836. [ABSTRACT FROM AUTHOR]

To prepare a coating with a high emissivity and low solar absorption ratio on the surface of aluminum silicate fiber cloth, the sol-gel method was used with silica sol as a binder. In this study, the effects of two white fillers, titanium oxide and zirconia, on the substrate and radiation properties of coatings were compared after heat treatment at 800–1200 °C. The ZrO 2 -based coating had good stability after heat treatment at 800–1200 °C, and maintained its white color, exhibiting solar absorption ratio of approximately 0.14 and emissivity of 0.84. ZrO 2 -based coatings prevented harmful cracking, as observed for the TiO 2 -based coatings after heat treatment, because of the ZrO 2 phase transformation. The ZrO 2 -based coating did not have strong bonding with the substrate, and the substrate strength was improved by maintaining a weak bonding interface. Compared with the TiO 2 -based coatings, which exhibit reduced substrate strength above 1000 °C, the ZrO 2 -based coating was more suitable for the surface of flexible fiber cloths as a temperature-resistant coating with good development prospects. [ABSTRACT FROM AUTHOR]

To improve the oxidation inhibition of TaSi 2 -based high-emissivity coatings at high temperatures, TaSi 2 –SiC coating modified by SiB 6 was prepared on the surface of alumina fibre fabrics. The effects of the SiB 6 content on the surface appearance and emissivity of the coating were investigated, and the mechanical properties of the coated fabrics were compared. When the SiB 6 content in the coating was 2.5%, the borosilicate glass liquid phase generated by SiB 6 oxidation effectively prevented the oxidation of TaSi 2. The bond strength between the coatings and fibre fabric was 207 kPa after calcination at 1200 °C, which was 39% higher than that of the coated fabric without SiB 6. The emissivity of the TaSi 2 –SiC coating, modified by a SiB 6 content of 2.5%, reached above 0.92 after calcination at 1200 °C for 5 h. Therefore, the TaSi 2 –SiC high-emissivity coating modified by SiB 6 has good application prospects in the field of thermal protection. [ABSTRACT FROM AUTHOR]

A novel mullite fibers-based hierarchical heterostructure were fabricated using a sol–gel method. The porous performs were fabricated by mixing the mullite fibers with the aluminum borate xerogel which is derived from the gelation of Al(OC 4 H 9 ) 3 and boric acid. After calcination, the preforms with different mole ratio of Al/B, transformed into the composites with hierarchical structures of the aluminum borate nanowhiskers/mullite fiber and alumina plate/aluminum borate nanowhiskers/mullite fiber. The formed aluminum borate nanowhiskers showed a uniform distribution on the mullite fibers, and the growth process may follow a self-catalysis mechanism. The fabricated hierarchical mullite fiber-based products possessed low density of 0.448 g/cm 3 , low thermal conductivity of 0.132 W/mK, high specific surface area of 230.7 m 2 /g and excellent elastic property with high compression-resilience of 92.7%, and were promising flexible insulant materials for the application in high-temperature heat sealing field. [ABSTRACT FROM AUTHOR]

Aluminum silicate fiber fabric (ASFF) has been widely used in the outer surface of flexible insulation felt on the leeward side of aerospace vehicle. In order to improve the temperature resistance of ASFF, a kind of SiC–ZrC composite coating was prepared on the surface of fiber fabric via spraying method with SiC as emittance agent and ZrC as additive. The surface morphology and mechanical properties of the coating were studied. Compared with the single-component SiC coating, the composite coating could effectively avoid coating spalling and improve the surface integrity at high temperature. After thermal treatment at 1100 °C for 2 h, the interface bond strength of the composite coating/substrate was 52.41% higher than that of SiC coating/substrate. The tensile strength of fiber fabric with SiC–ZrC composite coating could reach 91.75 MPa, which was 101.76% higher than that of raw ASFF. Therefore, the SiC–ZrC coating could greatly improve the temperature resistance of ASFF, and has an attractive application prospect in the field of thermal protection system. [ABSTRACT FROM AUTHOR]

The anisotropy of compression response and energy absorption of fiber enforced porous ceramics by directional freeze-casting have been investigated to infer the failure mechanism. An enhanced porous ceramic structured with fiber-bridging-lamellar walls was synthesized by directionally freezing nano spherical alumina suspension with different fiction of alumina microfibers. Due to the anisotropic microstructure, the mechanical properties of the freeze-casting ceramics are closely related to the orientation of the applied stress. Different orientations of loads correspond to the different deformation mechanisms under the load. The compression experiments under different orientations were carried out, and the failure mechanism was judged by the energy absorption characteristics and compression response. In contrast to traditional freeze-casting ceramics, the scaffolds supported with fiber bridges have higher mechanical properties (up to 15 MPa in compressive strength and density up to 0.76 g/cm3), and their failure behavior tends to plastic fracture, which increases toughness and availability without decreasing porosity and pore size. [ABSTRACT FROM AUTHOR]

A heat resistance adhesive with wide operative temperature range for bonding alumina fiber fabric was developed by organic-inorganic modification. The polyvinyl alcohol modified by B 2 O 3 generated a complex cross-linked network connected by B–O–C bonds, which can enhance the bonding strength of adhesive after heat-treatment from RT to 400 °C. Moreover, the addition of B 4 C can enhance the bonding strength of adhesive after heat-treatment from 400 °C to 800 °C due to the formation of molten B 2 O 3 and borosilicate glass. Significantly, the appropriate addition of B 4 C can make the adhesive form a denser structure without transforming the fracture mode of the bonding joints, which is conducive to enhance the strength performance of bonding joints after sintered at 800 °C. On the contrary, the excessive addition of B 4 C will transform the fracture mode of the bonding joints into brittle fracture, which will degrade the strength performance of bonding joints. [ABSTRACT FROM AUTHOR]

Abstract Here we report a novel aerogel material assembled by the electrospun SiOC fibers with a hierarchical pore structure. The fibrous aerogels were successfully fabricated by the gel-casting and freeze-drying method using the SiOC fibers as the matrix and the silica sols as the binders. The effect of the SiOC fiber content and the silica sol content on the properties of the samples were investigated. The SiOC fibrous aerogels after calcined at 1000 °C exhibited low densities of 46.87–128.48 mg/cm3, low thermal conductivities of 0.0302–0.0440 W/m K, high compressive strengths of 18–167 kPa and relatively high specific surface areas of 12.48–34.87 m2/g. Such unique fibrous aerogel materials are foreseen as the promising high-temperature insulators, absorbents and supports. [ABSTRACT FROM AUTHOR]

TaSi 2 -MoSi 2 -borosilicate glass coatings with high emissivity were prepared on mullite fibrous ceramics via a slurry technique to enhance surficial thermal radiation and serve in the thermal protection systems for aircrafts. The effect of TaSi 2 dosages on the coatings' structure, phase composition, emissivity, thermal shock resistance and thermal endurance were investigated. The results show that all the coatings were flat and uniform, while the surface roughness and porosity increased with TaSi 2 dosages. Part of TaSi 2 was oxidized into Ta 2 O 5 during the coating preparation, and finally, the coating with TaSi 2 dosage of 45 wt% (C-45Ta) had the highest TaSi 2 content. Emissivity of the coatings increased with TaSi 2 contents. The total emissivity of C-45Ta was 0.855 in the range of 3–14.5 μm at 150 °C, while that of the coating without TaSi 2 (C-0Ta) was 0.809. However, compared with C-0Ta, C-45Ta showed worse thermal shock resistance because of its higher CTE mismatch with the substrate and higher porosity. The thermal endurance of C-45Ta was worse due to the limited oxidation resistance of TaSi 2 and the lower borosilicate glass content. [ABSTRACT FROM AUTHOR]

In order to prevent the embrittlement of high emissivity coating coated quartz fiber fabric applied in Thermal Protection System, LaPO 4 fiber coating was prepared on the fiber fabric by a repeated dip-sintering method using a liquid precursor. The formation process of La-monazite from the precursor was investigated, and on this basis, a high-temperature and short-time sintering schedule (1200 °C/60 s) was determined. Pure La-monazite fiber coating with a thickness of 80–300 nm was obtained, and cristobalite crystallization in the fibers was avoided. The La-monazite coated quartz fiber fabric retained the flexibility of the original quartz fiber fabric. By precoating La-monazite fiber coating, the quartz fiber fabric coated with SiC–SiO 2 high emissivity coating showed significantly increased ultimate bending deflection in three-point bending test, and fiber pull out and fabric distortion were observed at the fracture surface. • La-monazite fiber coating was prepared on quartz fabric by a dip-sintering method. • Repeated short-time sintering schedule at relatively high temperature was adopted. • Coating impurities and fabric crystallization/embrittlement were prevented. • High-temperature embrittlement of high emissivity coating coated fabric was relieved. [ABSTRACT FROM AUTHOR]

Abstract: Porous Si2N2O ceramics was synthesized by the tert-butyl alcohol-based gel-casting method at a relatively low temperature using Si3N4 and SiO2 powders as the starting materials and spodumene (LiAl(SiO3)2) as the sintering additive. Porous Si2N2O ceramics with relative high compressive strength (10.80MPa) and high porosity (65.5%) were successfully fabricated. The microstructure of porous Si2N2O after sintering at different sintering regimes was studied. The fibers observed in the pores can increase the compressive strength and the specific surface area of the sample. [Copyright &y& Elsevier]