Third-generation silicon carbide (SiC) composites reinforced by SiC fibers (Hi-Nicalon S HNS and Tyranno SA3 SA3) are attractive for use in next generation reactors owing to their high strength and ...chemical inertness at high temperatures, as well as enhanced radiation tolerance under neutron irradiation environments. To optimize composite performance, the interfacial mechanical properties of chemical vapor–infiltrated (CVI) SiCf/SiC composites are investigated in this effort by using a slant interface micropillar compression testing procedure. The micropillar test specimens, containing an inclined pyrolytic carbon (PyC) interphase, are prepared using a focused ion beam. The novel microcompression testing successfully quantifies the debond shear strength and internal friction coefficient of micropillar test samples by using the Mohr-Coulomb formulation. According to four types of SiCf/SiC composite microcompression test results, interfacial properties and debond mechanisms are significantly affected by the PyC layer thickness, the local bonding mechanism of the PyC interphase on the SiC fiber surface, and the surface roughness of fibers. Regardless of PyC thicknesses, SA3-reinforced CVI SiCf/SiC composites are found to have much higher debond shear strengths than HNS-reinforced SiCf/SiC CVI composites. By using this micropillar compression technique alongside analytical methods, we uncover new understandings of PyC interface properties. Additionally, the micropillar test results obtained are correlated with macroscopic mechanical properties of neutron-irradiated CVI SiCf/SiC composites.
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Abstract
Invading microbial pathogens can be eliminated selectively by xenophagy. Ubiquitin-mediated autophagy receptors are phosphorylated by TANK-binding kinase 1 (TBK1) and recruited to ...ubiquitinated bacteria to facilitate autophagosome formation during xenophagy, but the molecular mechanism underlying TBK1 activation in response to microbial infection is not clear. Here, we show that bacterial infection increases Ca
2+
levels to activate TBK1 for xenophagy via the Ca
2+
-binding protein TBC1 domain family member 9 (TBC1D9). Mechanistically, the ubiquitin-binding region (UBR) and Ca
2+
-binding motif of TBC1D9 mediate its binding with ubiquitin-positive bacteria, and TBC1D9 knockout suppresses TBK1 activation and subsequent recruitment of the ULK1 complex. Treatment with a Ca
2+
chelator impairs TBC1D9–ubiquitin interactions and TBK1 activation during xenophagy. TBC1D9 is also recruited to damaged mitochondria through its UBR and Ca
2+
-binding motif, and is required for TBK1 activation during mitophagy. These results indicate that TBC1D9 controls TBK1 activation during xenophagy and mitophagy through Ca
2+
-dependent ubiquitin-recognition.
Zirconium carbide (ZrC) is a potential coating, oxygen-gettering, or inert matrix material for advanced high temperature reactor fuels. ZrC has demonstrated attractive properties for these fuel ...applications including excellent resistance against fission product corrosion and fission product retention capabilities. However, fabrication of ZrC results in a range of stable sub-stoichiometric and carbon-rich compositions with or without substantial microstructural inhomogeneity, textural anisotropy, and a phase separation, leading to variations in physical, chemical, thermal, and mechanical properties. The effects of neutron irradiation at elevated temperatures, currently only poorly understood, are believed to be substantially influenced by those compositional and microstructural features further adding complexity to understanding the key ZrC properties. This article provides a survey of properties data for ZrC, as required by the United States Department of Energy’s advanced fuel programs in support of the current efforts toward fuel performance modeling and providing guidance for future research on ZrC for fuel applications.
For the development of silicon carbide (SiC) materials for next-generation nuclear structural applications, degradation of material properties under intense neutron irradiation is a critical ...feasibility issue. This study evaluated the mechanical properties and microstructure of a chemical vapor infiltrated SiC matrix composite, reinforced with a multi-layer SiC/pyrolytic carbon–coated Hi-NicalonTM Type S SiC fiber, following neutron irradiation at 319 and 629 °C to ∼100 displacements per atom. Both the proportional limit stress and ultimate flexural strength were significantly degraded as a result of irradiation at both temperatures. After irradiation at 319 °C, the quasi-ductile fracture behavior of the nonirradiated composite became brittle, a result that was explained by a loss of functionality of the fiber/matrix interface associated with the disappearance of the interphase due to irradiation. The specimens irradiated at 629 °C showed increased apparent failure strain because the fiber/matrix interphase was weakened by irradiation-induced partial debonding.
Silicon carbide (SiC) continuous fiber-reinforced, SiC-matrix composites (SiC/SiC composites) are industrially available materials that are promising for applications in nuclear environments. The ...SiC/SiC composites consisting of near-stoichiometric SiC fibers, stoichiometric and fully crystalline SiC matrices, and the pyrocarbon (PyC) or multilayered PyC/SiC interphase between the fiber and the matrix are considered particularly resistant to very high radiation environments. This paper provides a summary compilation of the properties of these composites, specifically those with the chemically vapor-infiltrated (CVI) SiC matrices, including newly obtained results. The properties discussed are both in unirradiated condition and after neutron irradiation to intermediate fluence levels (most data are for <∼10 displacement per atom) at 300–1300°C.
The purpose of the present study is to clarify the phase stability of the corroded layer in reduced activation ferritic/martensitic steels under irradiation. The oxide film of F82H steel was ...subjected to ion irradiation using 2.8 MeV-Fe2+ at 573 K. For post-irradiation experiments, grazing incident X-ray diffraction (GIXRD) and Raman analysis were conducted to clarify the features of the oxide layer with the variation of the irradiation dose. The dominant phase of the oxide film was identified as FeCr2O4, which co-existed with up to ∼30% of the residual matrix phase. The fraction of the residual matrix decreased as the irradiation dose increased, the phase transformation from FeCr2O4 to Fe3O4 was confirmed. The hypothesis for the phase transformation of FeCr2O4 to Fe3O4 under irradiation was proposed based on the experimental results. Specifically, the FeCr2O4 phase is unstable under irradiation, and tends to become stable after absorbing Fe atoms from the residual matrix in the corrosion layer. As a result, the Fe concentration in the oxide layer increased under irradiation, the phase transformation of FeCr2O4 to Fe3O4 is presumed under irradiation. However, concerns about the mechanism of the instability of FeCr2O4 under irradiation, and better stability of Fe3O4 phase relative to FeCr2O4 phase have to be further considered to achieve a better understanding.
Group A Streptococcus (GAS) is one of the major human pathogens that can invade nonphagocytic cells. GAS internalized through endocytosis secretes the pore-forming toxin Streptolysin O (SLO) to ...escape into the cytoplasm. The cytosolic GAS is selectively captured by autophagic membranes (GAS-containing autophagosome-like vacuoles, GcAVs) and delivered to lysosomes for degradation. Macroautophagy (referred to as autophagy hereafter) is a highly conserved lysosome-mediated catabolic process, which is critical for cellular homeostasis. Autophagy also acts as an intracellular immune system. In this section, we describe how to identify GcAVs in infected cells using fluorescent microscopy.
Abstract
Xenophagy, a type of selective autophagy, is a bactericidal membrane trafficking that targets cytosolic bacterial pathogens, but the membrane homeostatic system to cope with bacterial ...infection in xenophagy is not known. Here, we show that the endosomal sorting complexes required for transport (ESCRT) machinery is needed to maintain homeostasis of xenophagolysosomes damaged by a bacterial toxin, which is regulated through the TOM1L2–Rab41 pathway that recruits AAA-ATPase VPS4. We screened Rab GTPases and identified Rab41 as critical for maintaining the acidification of xenophagolysosomes. Confocal microscopy revealed that ESCRT components were recruited to the entire xenophagolysosome, and this recruitment was inhibited by intrabody expression against bacterial cytolysin, indicating that ESCRT targets xenophagolysosomes in response to a bacterial toxin. Rab41 translocates to damaged autophagic membranes via adaptor protein TOM1L2 and recruits VPS4 to complete ESCRT-mediated membrane repair in a unique GTPase-independent manner. Finally, we demonstrate that the TOM1L2–Rab41 pathway-mediated ESCRT is critical for the efficient clearance of bacteria through xenophagy.
SiC/SiC composites are promising structural candidate materials for various nuclear applications over the wide temperature range of 300–1000 °C. Accordingly, irradiation tolerance over this wide ...temperature range needs to be understood to ensure the performance of these composites. In this study, neutron irradiation effects on dimensional stability and mechanical properties to high doses (11–44 dpa) at intermediate irradiation temperatures (˜600 °C) were evaluated for Hi-Nicalon Type-S or Tyranno-SA3 fiber–reinforced SiC matrix composites produced by chemical vapor infiltration. The influence of various fiber/matrix interfaces, such as a 50–120 nm thick pyrolytic carbon (PyC) monolayer interphase and 70–130 nm thick PyC with a subsequent PyC (˜20 nm)/SiC (˜100 nm) multilayer, was evaluated and compared with the previous results for a thin-layer PyC (˜20 nm)/SiC (˜100 nm) multilayer interphase. Four-point flexural tests were conducted to evaluate post-irradiation strength, and SEM and TEM were used to investigate microstructure. Regardless of the fiber type, monolayer composites showed considerable reduction of flexural properties after irradiation to 11–12 dpa at 450–500 °C; and neither type showed the deterioration identified at the same dose level at higher temperatures (>750 °C) in a previous study. After further irradiation to 44 dpa at 590–640 °C, the degradation was enhanced compared with conventional multilayer composites with a PyC thickness of ˜20 nm. Multilayer composites have shown comparatively good strength retention for irradiation to ˜40 dpa, with moderate mechanical property degradation beginning at 70–100 dpa. Irradiation-induced debonding at the F/M interface was found to be the major cause of deterioration of various composites.
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