Sawao Honda

Characterization of Zeolite in Zeolite-Geopolymer Hybrid Bulk Materials Derived from Kaolinitic Clays

Zeolite-geopolymer hybrid materials have been formed when kaolin was used as a starting material. Their characteristics are of interest because they can have a wide pore size distribution with micro- and meso-pores due to the zeolite and geopolymer, respectively. In this study, Zeolite-geopolymer hybrid bulk materials were fabricated using four kinds of kaolinitic clays (a halloysite and three kinds of kaolinite). The kaolinitic clays were first calcined at 700 °C for 3 h to transform into the amorphous aluminosilicate phases. Alkali-activation treatment of the metakaolin yielded bulk materials with different amounts and types of zeolite and different compressive strength. This study investigated the effects of the initial kaolinitic clays on the amount and types of zeolite in the resultant geopolymers as well as the strength of the bulk materials. The kaolinitic clays and their metakaolin were characterized by XRD analysis, chemical composition, crystallite size, 29Si and 27Al MAS NMR analysis, and specific surface area measurements. The correlation between the amount of zeolite formed and the compressive strength of the resultant hybrid bulk materials, previously reported by other researchers was not positively observed. In the studied systems, the effects of Si/Al and crystalline size were observed. When the atomic ratio of Si/Al in the starting kaolinitic clays increased, the compressive strength of the hybrid bulk materials increased. The crystallite size of the zeolite in the hybrid bulk materials increased with decreasing compressive strength of the hybrid bulk materials.

Influence of MgO on microstructure and properties of mullite–Mo composites fabricated by pulse electric current sintering

Abstract Mullite–Mo (10 vol.%) composites and monolithic mullite were fabricated using a pulse electric current sintering technique. Both monolith and composites of mullite were sintered up to theoretical density at 1500°C within few minutes. MgO of 0.25 wt.% was added as a sintering aid to both the mullite and composites. Addition of MgO significantly increased the bending strength of the monolithic mullite and mullite/10 vol.% Mo composites to 441 and 634 MPa respectively. The apparent increase in the bending strength of the composites was attributed to the combinational effect of Mo and MgO present in the composites. The fracture toughness of the composites also increased from 2 to 3.9 MPa.m 0.5 for the mullite/10 vol.% Mo composites, which was nearly twice that of the mullite. Crack-bridging and frontal process-zone elongation were expected to be the toughening mechanisms operated in these composites. The addition of Mo having high thermal diffusivity slightly increased the thermal diffusivity of the composites, because the 10 vol.% Mo particles were well dispersed and discontinuous in the matrix. Elongated mullite grains were observed for the composites without MgO, whereas the composites with MgO have a controlled microstructure.

A Facile Surfactant-Assisted Reflux Method for the Synthesis of Single-Crystalline Sb2Te3 Nanostructures with Enhanced Thermoelectric Performance

Antimony telluride (Sb2Te3) and its based alloys are of importance to p-type semiconductors for thermoelectric applications near room temperature. Herein, we report a simple, low-energy intensive, and scalable surfactant-assisted reflux method for the synthesis of Sb2Te3 nanoparticles in the solvent ethylene glycol (EG) at low temperatures (120-180 °C). The formation mechanism of platelike Sb2Te3 nanoparticles is proposed. Also, it is found that the size, shape, and chemical composition of the products could be controlled by the introduction of organic surfactants (CTAB, PVP, etc.) or inorganic salts (EDTA-Na2, NaOH, etc.). Additionally, the collected Sb2Te3 nanoparticles were further fabricated into nanostructured pellets using cold-compaction and annealing techniques. Low resistivity [(7.37-19.4) × 10(-6) Ω m], moderate Seebeck coefficient (103-141 μV K(-1)), and high power factor (10-16 × 10(-4) W m(-1) K(-2)) have been achieved in our Sb2Te3-nanostructured bulk materials. The relatively low thermal conductivity (1.32-1.55 W m(-1) K(-1)) is attained in the nanobulk made of PVP-modified nanoparticles, and values of ZT in the range of 0.24-0.37 are realized at temperatures ranging from 50 to 200 °C. Our researches set forth a new avenue in promoting practical applications of Sb2Te3-based thermoelectric power generation or cooling devices.

Sintering and Characterization of Zr2Al3C5 Monolith

Zr2Al3C5 has been successfully synthesized via solid state reaction between Al, ZrC and carbon powder at 1600 in vacuum. This complex carbide has very strong bond between metal atoms and carbon atoms. Thus, this material has a potential to be utilized as structural materials. Some properties of Zr2Al3C5 powder from solid-state reaction in vacuum had been tested. It was found that this powder was completely oxidized in air at 900 1 h, and can be hydrated in moist air. These drawbacks might come from the high reactivity of the powder due to synthesis in vacuum. Zr2Al3C5 powder from solid state reaction in vacuum was sintered at various temperatures from 1500 to 2000 under vacuum with pulse electric current sintering (PECS) and pressureless sintering. Zr2Al3C5 started to sinter at 1500 and got partially dense from 1700. Physical properties and mechanical properties of this material were investigated and discussed.

Compressive deformation behavior of Al-doped β-SiC at elevated temperature

Abstract Compression tests were performed on Al-doped β-SiC fabricated by hot-pressing using pyrolyzed polycarbosilane at 2123–2223 K in He. An amorphous phase was clearly seen at the grain boundaries in as-sintered specimens. The stress exponents were from 1.1 to 1.4 in the temperature range 2123–2223 K. Strain hardening was observed under all experimental conditions. The phase transformation from β to α was not observed even after the compression tests. The amorphous phase at grain boundaries was vaporized from specimen surfaces during testing. The deformation behavior was influenced by the dynamic change of grain-boundary structure.

H + emission under room temperature and non-vacuum atmosphere from a sol–gel-derived nanoporous emitter

A high proton-conducting P2O5-SiO2 nanoporous glass rod was prepared via sol–gel technique, and its tip was sharpened by a meniscus-etching method. The glass rod shows proton conductivity of 1 × 10−3 at room temperature after absorption of water molecules. A palm-sized proton gun was prepared by utilizing the glass rod as a H+ emitter. A high voltage (~2.5 kV) was applied between the tip of glass rod and an extraction electrode, and a high ionic current was successfully observed even under non-vacuum atmosphere at room temperature. Protonation reaction for polyaniline was confirmed from the structural changes of C=N in quinone to protonated C–N+. New applications of proton implantation will be expected especially in bioscience and medical technology.Graphical Abstract

Detoxification of Asbestos and Asbestos-Containing Cement Board

Mechanical destruction of acicular asbestos has been carried out as a process for decontamination. The dehydration reaction of asbestos occurred at 600°C and has been completed for 2 h at that temperature. This dehydration reaction of asbestos led to weakening of the mechanical properties of asbestos. After grinding, the microstructure of asbestos appeared no acicular shape. Further, this technique could be applied to asbestos-containing cement board. The spent cement board has about 10-20 mass% of asbestos (chrysotile: Mg3Si2O5(OH)4) and 5 mm thickness was used. After heating at 600°C for 2 h and grinding, the microstructure of the sample also appeared no acicular shape. Thus it was cleared that heating at 600°C and then grinding treatment for asbestos (chrysotile) has a grate important effect of mechanical and chemical destruction of asbestos in both cases of free asbestos and asbestos-containing cement board.

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.

Development of H + emission gun using a proton conducting glass fiber

H+ emission from the sharpening glass fiber was successfully observed. Here, ion current density and chemical functionalization via ion irradiation are presented.