SiC/SiC mini-composites with multilayer ZrSiO4 interphase: Room-temperature properties and toughening mechanism

SiC/SiC mini-composites reinforced with SiC fibers coated with different numbers of ZrSiO₄ sublayers prepared via a non-hydrolytic sol-gel process were fabricated. The tensile strength and work of fracture of the prepared SiC/SiC mini-composites were determined, and the relationship between their mechanical properties and fracture morphologies was discussed. The toughening mechanism and the variation tendency of their mechanical properties were further elaborated by analyzing the interfacial debonding morphologies of the SiC/SiC mini-composites with 1 and 4 layers of ZrSiO₄ interphase as well as the results of prior studies. A relatively rare phenomenon—the delamination of the multilayer ZrSiO₄ interphase in the SiC/SiC mini-composites but not on the SiC fibers—was observed, which clearly demonstrated the weak bonding between the ZrSiO₄ sublayers in the SiC/SiC mini-composites. The ZrSiO₄ sublayer delamination mechanism was then explained based on the high-magnification morphologies found in and beside the ZrSiO₄ interphase.     

A progressive damage model for ceramic matrix mini-composites with thick interphases

Toughness enhancement in ceramic matrix composites (CMCs) with brittle matrix and fiber phases is often accomplished by introducing a weak finite-thickness interphase between the fiber and matrix. The current work presents a progressive damage model to predict the tensile response of single tow CMCs (mini-composite) representative of a unidirectional composite at the microscale. Implementation of a 3-phase shear-lag model for a geometrically accurate representation of the underlying microstructure in CMCs with finite thickness interphase has been highlighted. A probabilistic progressive modeling approach has been adopted, accounting for multiple matrix cracking, interfacial debonding, and fiber failure in 3-phase mini-composites. The predicted tensile response of CMCs from the progressive damage modeling approach agrees with experimental results obtained for C/BN/SiC mini-composites validating the approach.     

SiC/SiC mini-composites with yttrium disilicate fiber coatings: Oxidation in steam

Solutions of YPO₄ were used to precipitate YPO₄ on pre-oxidized Hi-Nicalon-S SiC fibers. Tows of the coated fibers were then infiltrated with a preceramic polymer loaded with SiC particles to form mini-composites. During pyrolysis of the matrix, SiO₂ and YPO₄ on the fibers reacted and formed a Y₂Si₂O₇ fiber matrix interphase. Mini-composites were exposed to steam at 1000 °C for 10, 50, and 100 h, tensile tested, and the effect of oxidation in steam on the functionality of the Y₂Si₂O₇ fiber coating was investigated. The minicomposites oxidized at 1000 °C for 10 h retained 100 % of their unoxidized strength, and those oxidized for 50 and 100 h retained 92 % and 90 % of unoxidized strength, respectively. Strength retention and fiber pullout in both unoxidized and oxidized minicomposites suggests that the Y₂Si₂O₇ interphase was effective in maintaining a weak fiber-matrix interface.     

Mechanical properties and strengthening mechanism of SiCf/SiC mini-composites modified by SiC nanowires

The effects of the SiC nanowires (SiCNWs) and PyC interface layers on the mechanical and anti-oxidation properties of SiC fiber (SiC_f)/SiC composites were investigated. To achieve this, the PyC layer was coated on the SiC_f using a chemical vapour infiltration (CVI) method. Then, SiCNWs were successfully coated on the surface of SiC_f/PyC using the electrophoretic deposition method. Finally, a thin PyC layer was coated on the surface of SiC_f/PyC/SiCNWs. Three mini-composites, SiC_f/PyC/SiC, SiC_f/PyC/SiCNWs/SiC, and SiC_f/PyC/SiCNWs/PyC/SiC, were fabricated using the typical precursor infiltration and pyrolysis method. The morphologies of the samples were examined using scanning electron microscopy and energy dispersive X-ray spectrometry. Tensile and single-fibre push-out tests were carried out to investigate the mechanical performance and interfacial shear strength of the composites before and after oxidization at 1200 °C. The results revealed that the SiC_f/PyC/SiCNWs/SiC composites showed the best mechanical and anti-oxidation performance among all the composites investigated. The strengthening and toughening is mainly achieved by SiCNWs optimization of the interfacial bonding strength of the composite and its own nano-toughening. On the basis of the results, the effects of SiCNWs on the oxidation process and retardation mechanism of the SiC_f/SiC mini-composites were investigated.     

Drosophila melanogaster Uncoupling Protein-4A (UCP4A) Catalyzes a Unidirectional Transport of Aspartate

Uncoupling proteins (UCPs) form a distinct subfamily of the mitochondrial carrier family (MCF) SLC25. Four UCPs, DmUCP4A-C and DmUCP5, have been identified in Drosophila melanogaster on the basis of their sequence homology with mammalian UCP4 and UCP5. In a Parkinson’s disease model, DmUCP4A showed a protective role against mitochondrial dysfunction, by increasing mitochondrial membrane potential and ATP synthesis. To date, DmUCP4A is still an orphan of a biochemical function, although its possible involvement in mitochondrial uncoupling has been ruled out. Here, we show that DmUCP4A expressed in bacteria and reconstituted in phospholipid vesicles catalyzes a unidirectional transport of aspartate, which is saturable and inhibited by mercurials and other mitochondrial carrier inhibitors to various degrees. Swelling experiments carried out in yeast mitochondria have demonstrated that the unidirectional transport of aspartate catalyzed by DmUCP4 is not proton-coupled. The biochemical function of DmUCP4A has been further confirmed in a yeast cell model, in which growth has required an efflux of aspartate from mitochondria. Notably, DmUCP4A is the first UCP4 homolog from any species to be biochemically characterized. In Drosophila melanogaster, DmUCP4A could be involved in the transport of aspartate from mitochondria to the cytosol, in which it could be used for protein and nucleotide synthesis, as well as in the biosynthesis of ß-alanine and N-acetylaspartate, which play key roles in signal transmission in the central nervous system.     

Tailoring Unidirectional Water-Penetration Janus Fabric with Surface Electrospun Deposition

This paper provides a new method to fabricate an integrated Janus fabric that has excellent unidirectional water-penetration property. Based on commercial polyester fabric that is pretreated with CaCl₂ solution, polyvinyl alcohol/sodium alginate (PVA/SA) solution is deposited directly on the fabric via electrospinning and in situ chelated with Ca²⁺ contained in the fabric. The in situ formed PVA/SA gel coating not only transfers the surface of polyester fabric from hydrophobic to hydrophilic but also retains original porous structure of polyester fabric. As the water droplet contacts with unelectrospun side of modified polyester fabric (M-PET) pretreated with 10 wt% CaCl₂, it penetrates through the M-PET within 1 s from unelectrospun side to electrospun side after application, and disappears on unelectrospun side within 2 s, and in turn, droplet spreads out on electrospun side of M-PET within 2 s after application and no penetration occurs. The M-PET pretreated with CaCl₂ solution has outstanding antistatic property, vapor, and air permeability. The impact of ratio (v/v) of the PVA and SA solution and the concentration of CaCl₂ pretreating solution on properties of the M-PET are investigated.     

Residual Stresses in Unidirectional Composites with Closely Spaced Fibers

Many of the composites utilized in current applications are consolidated at high temperatures. After cooldown to room temperature, the differences in the expansions of the constituent materials may lead to very high residual stresses. Since failure is driven by critical rather than average states, the local stress field becomes essential in evaluating any composite before it is tested under service conditions. The present study describes an analytical solution for the local residual field of a composite with fibers that are closely spaced. The geometry under consideration involves three fibers with their centers located at the vertices of an equilateral triangle. This arrangement corresponds to the generic element of the hexagonal array, an arguably natural fiber distribution. It was found that when the interfaces are perfectly bonded and the three fibers are very close to each other, tensile radial stresses may develop in the constrained matrix region. The analysis can be generalized for any number of fibers at the vertices of a regular polygon.     

海藻酸钠冷冻干燥制备环保型直通孔多孔氧化铝陶瓷(英文)

将海藻酸钠、氧化铝混合制成的浆料定向冷冻,使水定向结冰成孔,再对坯体进行冷冻干燥,使冰升华留下的孔隙结构得以保存,制备具有直通孔结构氧化铝多孔陶瓷。气孔率为66.7%的多孔氧化铝陶瓷具有比传统氧化铝泡沫陶瓷高10倍的渗透率。利用固相体积含量25%的浆料制备的多孔陶瓷抗压强度达到16.03 MPa。通过在原料中加入天然无毒的海藻酸钠作为黏结剂,不仅使整个工艺过程和原料都环境友好,而且使干燥后的坯体具有一定强度,可以满足搬运和机加工的要求。通过控制浆料的黏度和流动性以及分散剂加入量,获得均匀的孔隙结构。此外,还研究了固相含量、烧结温度对气孔率、压缩强度及渗透率等性能的影响。随着固相含量从30%降低到20%,样品的气孔率从61%提高了到72%,而压缩强度从16.03 MPa下降到3.42 MPa,渗透率从0.19×10–11 m2提高到4.51×10–11 m2。随着烧结温度从1 300℃提高到1 500℃,材料的气孔率从69.72%下降到67.02%,而压缩强度从4.45 MPa提高到18.66 MPa,渗透率从4.51×10–11 m2下降到4.09×10–11 m2。     

Heterogeneous material joining of sapphire and TC4 alloy with a functionally graded interface

The natural high brittleness of sapphire leads to its poor machinability, which limits its application shape and size. The connection between sapphire and metal provides a new method to prepare large-size sapphire components and complex structural parts. In this study, sapphire and TC4 alloy were joined by spark plasma sintering (SPS) diffusion technology with Al₂O₃-Ti as interlayer fillers. The effects of filler composition, sintering temperature, microstructure, and phase distribution on the strength of the joint were explored. The results showed that sapphire and TC4 could be well connected by SPS with Al₂O₃-Ti fillers. The microstructure of the joint showed no obvious defect or element enrichment. The optimized shear strength of sapphire/interlayer(Al₂O₃-Ti)/TC4 joint reached 121 MPa, and the fracture path mode was sapphire-interlayer-TC4, indicating the strong bonding between the heterogeneous materials. The sapphire/interlayer(Al₂O₃-Ti)/TC4 structure could relieve the residual stress caused by the difference in the thermal expansion coefficient in direct connection between sapphire and TC4.     

Mucoadhesive Electrospun Nanofiber-Based Hybrid System with Controlled and Unidirectional Release of Desmopressin

The sublingual mucosa is an attractive route for drug delivery, although challenged by a continuous flow of saliva that leads to a loss of drug by swallowing. It is of great benefit that drugs absorbed across the sublingual mucosa avoid exposure to the harsh environment of the gastro-intestinal lumen; this is especially beneficial for drugs of low physicochemical stability such as therapeutic peptides. In this study, a two-layered hybrid drug delivery system was developed for the sublingual delivery of the therapeutic peptide desmopressin. It consisted of peptide-loaded mucoadhesive electrospun chitosan/polyethylene oxide-based nanofibers (mean diameter of 183 ± 20 nm) and a saliva-repelling backing film to promote unidirectional release towards the mucosa. Desmopressin was released from the nanofiber-based hybrid system (approximately 80% of the loaded peptide was released within 45 min) in a unidirectional manner in vitro. Importantly, the nanofiber–film hybrid system protected the peptide from wash-out, as demonstrated in an ex vivo flow retention model with porcine sublingual mucosal tissue. Approximately 90% of the loaded desmopressin was retained at the surface of the ex vivo porcine sublingual mucosa after 15 min of exposure to flow rates representing salivary flow.     

High heterogeneous compatibility of HfB2-SiC ceramic and Zr-4 alloy with in-situ assembled interface

HfB₂-based ceramics, such as HfB₂-SiC, are promising materials of neutron control rods. Under nuclear conditions, the interfacial compatibility between the HfB₂-SiC control rod and the guide tube (made of Zr-4 alloy) is critical in the operation. The present study demonstrated the high compatibility of the two heterogeneous materials even at 1400 °C. The formation of an in-situ assembled triple diffusion layer with stable phases and dense structures largely improved the interface compatibility. In addition, the as-produced phases with unique microstructures were organized at the interface. ZrSi formed typical columnar crystals with strong [001] fiber texture, which extended in the direction favorable to the interface. ZrB₂ grains grew as needle shapes and entered the Zr-4 alloy substrate. These unique morphologies clearly revealed an interface with strong stability and high compatibility. The results provide the basis for the application of HfB₂-based ceramics in nuclear infrastructures.     

Interaction of acridine-calix[4]arene with DNA at the electrified liquid|liquid interface

The behaviour of an acridine-functionalised calix[4]arene at the interface between two immiscible electrolyte solutions (ITIES) is reported. Molecular modelling showed that the acridine-calix[4]arene has regions of significant net positive charge spread throughout the protonated acridine moieties, consistent with it being able to function as an anion ionophore. The presence of this compound in the organic phase facilitated the transfer of aqueous phase electrolyte ions. Upon addition of double stranded DNA to the aqueous phase, the transfer of electrolyte anions was diminished, due to DNA binding to the acridine moiety at the ITIES. The behaviour provides a basis for DNA hybridization detection using electrochemistry at the ITIES.     

Processing of carbon-fiber reinforced (SiC + ZrC) mini-composites by soft-solution approach and their characterization

Carbon-fiber reinforced (SiC + ZrC) mini-composites have been prepared via soft-solution process using inorganic precursors. In this process, water-soluble compounds have been used to act as precursor materials to impregnate the fiber tow. Thermal analysis provided the temperature range for the pyrolysis to convert the precursors into the desired (SiC + ZrC) matrix. X-ray diffraction of the composites confirmed the phase formation and the crystallite size of these phases were in the range of 25–40 nm. Cross-sectional microstructures of the composites have shown the matrix formation around each individual fiber. The mechanical properties revealed that the tensile strength and fracture energy of the composites pyrolyzed at 1600 °C were significantly higher with typical composite failure behavior, as compared to those pyrolyzed at 1700 °C. The statistical size effects of the tensile strength were investigated on the basis of the Weibull statistics.     

Hydraulic and Thermal Regulation of Coke Batteries with Unidirectional Gas Input and Product Output

The problems arising in the operation of coke battery 3 at Rourkela Steel Plant (India) are considered. The design of coke battery 3 is described. It has an Otto system; the capacity of a single coking chamber is 21.6 m³. Hybrid heating is employed, and heating gas is supplied to the bottom of the chamber. A method is proposed for hydraulic regulation of the coke battery with unidirectional heating-gas input and product output.     

Failure Modes of a Unidirectional Ultra-High-Modulus Carbon-Fiber Carbon-Matrix Composite

The objective of this study was to observe the effects of various microstructural features on the in situ , room-temperature tensile fracture behavior of an ultra-high-modulus, unidirectional carbon/carbon (C/C) composite as a function of processing heat-treatment temperature (HTT) over the range of 1100° to 2750°C. An in situ SEM flexural stage was used to observe the interactions between the advancing crack tip and the microstructural features in the frontal process zone. Following the lowest HTT of 1100°C, failure is dominated by the well-bonded brittle matrix; a tortuous crack path in the E130 fibers appears to contribute to a relatively high utilization of fiber strength in spite of this brittle-matrix failure. Approximate calculations of the interfacial shear stress that might be generated by matrix shrinkage during pyrolysis of the polymer to carbon were compared to approximations of crack-tip interfacial shear stresses (IFSS) using the Cook-Gordon approach. The results suggest that the strong bonding in the 1100°C HTT composite cannot be accounted for by friction alone, and, therefore, chemical bonding or some type of fiber-matrix mechanical interlocking must be involved. Higher HTTs lead to progressive weakening of the fiber-matrix interface, and, with heat treatment to 2150°C, multiple matrix cracking (MMC) is observed. Using the crack-spacing model of Aveston, Cooper, and Kelly (ACK), an IFSS of 1 MPa is estimated for the MMC case. Attempts to calculate the matrix failure strain using the ACK formulation led to a large overprediction of the failure strain, although a number of the parameters used in the calculation are known only very approximately. Heat treatments to 2400° and 2750°C led to longitudinal intramatrix cohesive failure; at 2750°C, this damage is extensive and results in composites with strength utilizations approaching those of dry fiber bundles.     

Preparation of High-Strength Calcium Phosphate Glass-Ceramics by Unidirectional Crystallization

Unidirectionally crystallized CaO-P₂O₅ glass-ceramics were produced by reheating glass rods between 450° and 580°C (glass transition temperature ∼500°C) under a temperature gradient of 30°C/cm. These glass-ceramics exhibit high bending strength (∼650MN/m²) and toughness. Sample preparation is described and compared with conventional unidirectional solidification of melts. The characteristic mechanical properties are discussed in terms of the texture of the glass-ceramics.     

Unidirectional arrays of vertically standing graphenes in reactive plasmas

The possibility for the switch-over of the growth mode from a continuous network to unidirectional arrays of well-separated, self-organized, vertically oriented graphene nanosheets has been demonstrated using a unique, yet simple plasma-based approach. The process enables highly reproducible, catalyst-free synthesis of arrays of graphene nanosheets with reactive open graphitic edges facing upwards. Effective control over the nanosheet length, number density, and the degree of alignment along the electric field direction is achieved by a simple variation of the substrate bias. These results are of interest for environment-friendly fabrication of next-generation nanodevices based on three-dimensional, ordered self-organized nanoarrays of active nanostructures with very large surface areas and aspect ratios, highly reactive edges, and controlled density on the substrate. Our simple and versatile plasma-based approach paves the way for direct integration of such nanoarrays directly into the Si-based nanodevice platform.     

Li2O-doped MgAl2O4 nanopowders: Energetics of interface segregation

Manufacturing nanoceramics is challenging owing to the instability of the grain size resulting from the high driving force toward growth associated with the interfaces. Nanometric ceramics of some oxides have exceptional mechanical and optical properties, eg, magnesium aluminate spinel (MgAl₂O₄). The production of these fully conformed ceramics requires a precursor powder, which generally contains sintering-promoting additives. Li salts are typically used as sintering promoters for MgAl₂O₄, but the interface stability associated with the segregation of the additive is poorly understood. In this study, MgAl₂O₄ samples containing 0-2.86 mol% Li ions were synthesized via a simultaneous-precipitation method in an ethylic medium and subsequently calcined at 800°C in air. The nanopowders exhibited only the MgAl₂O₄ phase, and the crystallite size was determined by the Li₂O concentration. The crystallite size was changed via the chemical modification of the interfaces by the segregation of Li ions. The solubility in the bulk material was very low at the fabrication temperature, and small amounts of Li ions saturated the bulk material and segregated to the grain boundaries (GBs), significantly stabilizing the grain–grain interface compared with the surface. The resulting powder was then aggregated further owing to the initial stage of sintering. The surface excess obtained via the selective lixiviation method confirmed that the segregation to the GBs was greater than that to the surface. Energetics calculations confirmed these results, indicating a high enthalpy of segregation at the GBs () compared with that at the surfaces (). The enthalpy of segregation together with the interface excess allowed us to estimate the reduction in the interface energy with Li⁺ segregation of 0.8% to the surface and 11.2% to the GBs. The Li⁺ segregation to the surfaces started by Al³⁺ substitution, and for powders with ≥1.8 mol% Li ions, Mg⁺² was preferentially substituted at the surfaces.     

A 2D image-based multiphysics model for lifetime evaluation and failure scenario analysis of self-healing ceramic-matrix mini-composites under a tensile load

We propose a multi-physics numerical model for a self-healing ceramic matrix mini-composite under tensile load. Crack averaged PDEs are proposed for the transport of oxygen and of all the chemical species involved in the healing process and studied in the dimensionless form to perform the most appropriate discretization choices concerning time integration, and boundary conditions. Concerning the fibres’ degradation, a slow crack growth model explicitly dependent on the environmental parameters is calibrated using a particular exact solution and integrated numerically in the general case. The tow failure results from the statistical distribution of the fibres’ initial strength, the slow crack growth kinetics, and the load transfer following fibres breakage. The lifetime prediction capabilities of the model, as well as the effect of temperature, spatial variation of the statistical distribution of fibres strength, and applied load, are investigated highlighting the influence of the diffusion/reaction processes (healing) on the fibre breakage scenarios.