Indentation-induced stress distribution and pressure effect on the resistivity of YSZ

International audienceIonic conductivities measured under GPa-order high pressure provide various information about ion hopping mechanisms such as the activation volume (ΔV). Traditionally, anvil cells have been used for high-pressure measurements. We previously reported a new method for high-pressure impedance measurements, up to a few GPa, employing an indentation-induced local stress field. In this method, both mechanical and electrical (Young's modulus and high pressure impedance) properties can be obtained simultaneously. However, in this method, high pressures are induced only around the tip of the indenter, and such stress distribution should be considered for the estimation of ΔV accurately. In the present study, employing a finite element method (FEM) calculation, the stress distribution around the tip of the indenter, and effects of such GPa-order high pressures on the O2− ion conduction of Y2O3-doped zirconia (YSZ) are shown

Void Formation/Elimination and Viscoelastic Response of Polyphenylsilsesquioxane Monolith

Polyphenylsilsesquioxane (PhSiO3/2) particles as an organic-inorganic hybrid were prepared using sol-gel method, and monolithic samples were obtained via a warm-pressing. The reaction mechanism of particles’ polymerization and transformation to the monolith under the warm-press were investigated using solid state 29Si nuclear magnetic resonance (NMR) spectrometer, thermal gravimetric-differential thermal analyzer (TG-DTA), mass spectrometer (MS) and scanning electron microscope (SEM). Transparent and void-free monoliths are successfully obtained by warm-pressing above 180 °C. Both the terminal –OH groups on particles’ surface and warm-pressing are necessary for preparation of void-free PhSiO3/2 monolith. From the load-displacement measurement at various temperatures, a viscoelastic deformation is seen for PhSiO3/2 monolith with voids. On the other hand, an elastic deformation is seen for void-free PhSiO3/2 monolith, and the void-free monolith shows much higher breakdown voltage

3-Methylcholanthrene-induced transforming growth factor-β-producing carcinomas, but not sarcomas, are refractory to regulatory T cell-depletion therapy

Regulatory T cell (Treg) is one of the major immunosuppressors in tumor-bearing hosts. Although Treg-depletion therapy has been shown to induce a complete cure in tumor-bearing mice, this is not always successful treatment. Using 3-methylcholanthrene (MCA)-induced primary mouse tumors, we examined the distinct regulation of Treg-mediated immunosuppression between carcinomas and sarcomas. We demonstrated that the numbers of Tregs were greatly increased in SCC-bearing mice compared with sarcoma-bearing mice. This appeared to be because SCC produced higher levels of active TGF-β, which is essential for inducing Tregs, compared with sarcoma. Moreover, SCC, but not sarcomas were refractory to Treg-depletion therapy by anti-CD25 mAb administration. The refractoriness of SCC against Treg-depletion therapy was due to the rapid recovery of Tregs in SCC-bearing mice compared with sarcoma-bearing mice. However, combination treatment of anti-TGF-β mAb with anti-CD25 mAb caused a significant reduction of Treg recovery and induced a complete cure in SCC-bearing mice. Thus, we first demonstrated the refractoriness of mouse carcinoma against Treg-depletion therapy using anti-CD25 mAb administration. We also proposed a novel Treg-blocking combination therapy using anti-CD25 mAb and anti-TGF-β mAb to induce a complete cure of tumor-bearing hosts

Synthesis of microporous amorphous silica from perhydropolysilazane chemically modified with alcohol derivatives

Perhydropolysilazane (PHPS) was chemical modified with alcohol derivative (ROH, R = CH3, i-C3H7, n-C5H11, n-C10H21) at the silicon (Si) of PHPS/ROH molar ratio of 4/1. The alkoxy group-functionalized PHPS was converted into amorphous silica powders by curing at 270°C to promote oxidative crosslinking, followed by pyrolysis at 600°C in air to complete the polymer/amorphous silica conversion. Thermogravimetric analysis in air of the 270°C-crosslinked PHPS showed an approximately 18%weight gain at 200 to 500°C. This weight gain was suppressed consistently with the number of carbon atoms of the alkoxy groups introduced to PHPS. Upon heating to 600°C, the PHPS modified with n-C5H11OH showed a total weight loss of 12%, and further weight loss of 31%was observed for the PHPS modified with n-C10H21OH. The nitrogen sorption analysis revealed that micropore volume of the polymer-derived amorphous silica increased consistently with the weight loss during the pyrolysis up to 600°C, and the amorphous silica derived from the PHPS modified with n-C10H21OH exhibited the highest micropore volume. Further increase in the micropore volume was achieved by increasing the Si/n-C10H21OH molar ratio from 4/1 to 2/1. The micropore volume and specific surface area of the resulting amorphous silica powders were 0.193 cm3/g and 370m2/g, respectively

Microporosity and CO2 Capture Properties of Amorphous Silicon Oxynitride Derived from Novel Polyalkoxysilsesquiazanes

Polyalkoxysilsesquiazanes ([ROSi(NH)1.5]n, ROSZ, R = Et, nPr, iPr, nBu, sBu, nHex, sHex, cHex, decahydronaphthyl (DHNp)) were synthesized by ammonolysis at −78 °C of alkoxytrichlorosilane (ROSiCl3), which was isolated by distillation as a reaction product of SiCl4 and ROH. The simultaneous thermogravimetric and mass spectrometry analyses of the ROSZs under helium revealed a common decomposition reaction, the cleavage of the oxygen–carbon bond of the RO group to evolve alkene as a main gaseous species formed in-situ, leading to the formation of microporous amorphous Si–O–N at 550 °C to 800 °C. The microporosity in terms of the peak of the pore size distribution curve located within the micropore size range (<2 nm) and the total micropore volume, as well as the specific surface area (SSA) of the Si–O–N, increased consistently with the molecular size estimated for the alkene formed in-situ during the pyrolysis. The CO2 capture capacity at 0 °C of the Si–O–N material increased consistently with its SSA, and an excellent CO2 capture capacity of 3.9 mmol·g−1 at 0 °C and CO2 1 atm was achieved for the Si–O–N derived from DHNpOSZ having an SSA of 750 m2·g−1. The CO2 capture properties were further discussed based on their temperature dependency, and a surface functional group of the Si–O–N formed in-situ during the polymer/ceramics thermal conversion

Synthesis of a Novel Polyethoxysilsesquiazane and Thermal Conversion into Ternary Silicon Oxynitride Ceramics with Enhanced Thermal Stability

A novel polyethoxysilsesquiazane ([EtOSi(NH)1.5]n, EtOSZ) was synthesized by ammonolysis at −78 °C of ethoxytrichlorosilane (EtOSiCl3), which was isolated by distillation as a reaction product of SiCl4 and EtOH. Attenuated total reflection-infra red (ATR-IR), 13C-, and 29Si-nuclear magnetic resonance (NMR) spectroscopic analyses of the ammonolysis product resulted in the detection of Si–NH–Si linkage and EtO group. The simultaneous thermogravimetric and mass spectrometry analyses of the EtOSZ under helium revealed cleavage of oxygen-carbon bond of the EtO group to evolve ethylene as a main gaseous species formed in-situ, which lead to the formation at 800 °C of quaternary amorphous Si–C–N with an extremely low carbon content (1.1 wt %) when compared to the theoretical EtOSZ (25.1 wt %). Subsequent heat treatment up to 1400 °C in N2 lead to the formation of X-ray amorphous ternary Si–O–N. Further heating to 1600 °C in N2 promoted crystallization and phase partitioning to afford Si2N2O nanocrystallites identified by the XRD and TEM analyses. The thermal stability up to 1400 °C of the amorphous state achieved for the ternary Si-O-N was further studied by chemical composition analysis, as well as X-ray photoelectron spectroscopy (XPS) and 29Si-NMR spectroscopic analyses, and the results were discussed aiming to develop a novel polymeric precursor for ternary amorphous Si–O–N ceramics with an enhanced thermal stability

Polymer-derived organoamine-functionalized amorphous silica materials for CO₂ capture

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