Advanced Materials Research Vols. 11-12

Abstract: To improve fracture strength and fracture toughness in ceramic materials, we focused our attention on an intra-type structure of nanocomposites. We proposed new processing method for fabricating intra-type nanocomposites. In this work, Al2O3/Ni nanocomposites were fabricated using a soaking method and sintered by PECS(Pulse Electric Current Sintering) method. We also estimated seed effects on this system. Seeded nanocomposites showed high fracture strength and higher fracture toughness than non-seeded nanocomposites and monolithic alumina. The fracture strength of the seeded nanocomposites was more than 800MPa in all sintering temperature range. The maximum value of the fracture toughness was 5.5 MPa⋅m1/2 for the specimen sintered at 1350°C. The sintered specimens with high fracture strength and high fracture toughness were annealed from 800°C to 1000°C for 0 to 10 min. The specimen annealed at 800°C for 5 min showed the highest fracture toughness of 7.6 MPa⋅m1/2. This value is two times higher than that of the monolithic alumina.

Abstract: The filling of multi-walled carbon nanotubes with metallic silver nanowires via wet chemistry method was investigated. The carbon nanotubes were filled with long continuous silver nanowires. The carbon nanotubes were almost opened and cut after being treated with concentrated nitric acid. Silver nitrate solution filled carbon nanotubes by capillarity. Carbon nanotubes were filled with silver nanowires after calcinations by hydrogen. The diameters of silver nanowires were in the range of 20-40 nm, and lengths of 100 nm - 10 μm. We studied the micromorphology of the silver nanowires filled in carbon nanotubes by transmission electron microscopy (TEM) and X-ray diffraction (XRD). Based on the experimental results, a formation mechanism of the Ag nanowire-filled carbon nanotubes was proposed.

Abstract: Gold nanoparticles were prepared by NaBH4 reduction method, and homogeneous SiO2 were coated on gold nanoparticles and assembled into densely-packed 3-dimensional arrays by the layer-by-layer self-assembly (LBL) technique. Every layer of films exhibited densely packed 2-dimensional arrays of Au@SiO2 composite nanoparticles and the film thickness was controllable through the number of deposition cycles. These multilayer films exhibited high volume fraction of gold nanoparticles (0.047). The imaginary part of the third-order nonlinear optical susceptibility (Imχ(3)) with different deposition layer have been investigated by femtosecond pump and probe spectroscopy. The Imχ(3) value is about (-8.7±3.3)×10-11 esu and almost not dependent with the layer numbers which indicates every layer of our films has the same structural and optical properties.

Abstract: Highly-densified Fe cluster-assembled films were obtained at room temperature by an energetic cluster deposition. Fe clusters were produced using a plasma-gas-condensation (PGC)-type cluster deposition apparatus with a high cluster productivity. Ionized clusters in a cluster beam were electrically accelerated and directly deposited onto a substrate together with neutral clusters from the same cluster source. By increasing the impact energy of the ionized clusters up to about 1 eV/atom, the obtained cluster-assemblies have packing fractions higher than 0.8 without any serious size change, and result in a soft magnetic behavior up to a frequency range of few hundred MHz.

Abstract: Nanometric SnOx cluster-assembled films prepared by a plasma-gas-condensation cluster deposition apparatus have been examined by transmission electron microscopy (TEM) and electrical resistance. TEM observation showed that those clusters were almost spherical and size-monodispersive with a mean cluster size of 10 nm. The high-resolution TEM images indicated that the films were composed of randomly oriented nanocrystallites and that their surface roughness retained the traces of the original SnOx clusters. The electrical resistance of the SnOx cluster-assembled film decreased with decreasing partial O2 gas pressure. This result suggests that the intergranular potential barriers were responsible for the resisitvity variation. The activation energy estimated from the temperature-dependent resistivity was 0.75 eV for 330 K < T < 410 K under the partial O2 gas pressure of 0.02 MPa.

Abstract: BaTiO3 and SrTiO3 ultrafine powders are synthesized from sodium hydrogen titanate nanowires using hydrothermal route. Their preparation and purity depend strongly on the pH value of reaction system (the amount of added alkaline). Under the reaction condition of strong alkaline, the BaTiO3 phase can be obtained, but the SrTiO3 phase can not be easily prepared. Without the addition of any alkaline, the pure SrTiO3 phase can be synthesized. Reaction time also affects on the purity of BaTiO3 phase. Below 15 h of reaction time at reaction temperature 180°C, pure BaTiO3 phase can not be prepared. SEM measurement results show that the average diameter of BaTiO3 powders is about 200 nm and that of SrTiO3 submicrorods is about 300 nm. Their Raman spectra further demonstrate that the prepared products are BaTiO3 and SrTiO3 phases.

Abstract: A compact angle-resolved secondary ion mass spectrometer (AR-SIMS) with a special geometrical configuration, composing of a differentially pumped micro-beam ion-gun, a tiltable sample stage and a time-of-flight (TOF) mass spectrometer was applied to measure angular distribution (AD) of secondary ions ejected from VN by oblique 3 keV Ar+ sputtering at room temperature. AD of V+ was almost identical with that of N+, strongly suggesting that Gibbsian segregation did not take place during sputtering. Since the angular dependence of VN+/V+ and V2 +/V+ intensity ratios was independent of that of N+ and V+ intensities, VN+ and V2 + dimer ions were generated via the “as such” direct emission process.

Abstract: Magnetic material CoFe2O4 was prepared via layered precursor method. Magnetic nanosized photocatalyst TiO2/SiO2/CoFe2O4 was synthesized by hydrolysis titanium bis- ammonium lactato dihydroxide into photoactive TiO2 onto silica-modified CoFe2O4. Based on XRD, FT-IR, VSM analysis and catalytic evaluation, as-synthesized magnetic photocatalyst possess core-shell structure and exhibits evident photodegradation activity for methyl orange.

Abstract: Sialite is an ecological cementitious material that can be polymerized at normal temperature and under normal pressure. According to the nature’s rules of transformation from pozzolana to rock, rock mineralogical theories, geochemical theories and materials design theories, coordinate rule and compatibility principle, large amount of industrial solid wastes are made to produce sialite, which not only can achieve the reuse of the industrial solid wastes, but also can solve the problem of lack of original resources in cement industry. On the bases of the sialite technology theory background and the study evolve of laboratory and the applied projects, the significance of the sialite technology is expatiated.

Abstract: A novel organic and inorganic hybrid aerogel of RF/SiO2 is synthesized by one-step method of sol-gel polycondensation reaction using resorcinol-formaldehyde and tetramethoxysilane (TMOS) in ethanol solution, followed by supercritical drying with petroleum ether. The influence of the ratio of raw material on the structure and properties of samples was studied by high resolution electron microscope (HREM), nitrogen adsorption-desorption and infrared ray technology (IR). The results showed that the network structures of RF/SiO2 hybrid aerogels were constituted by an intercross framework of RF and SiO2. The hybrid aerogels can be tuned in bulk density from 0.098 g/cm3 to 0.062 g/cm3 according to the ratio of raw materials. The data of nitrogen adsorption-desorption showed that BET specific surface area was changed from 254 cm2/g to 545 cm2/g, and the pore size of aerogels was in the wide range of 2-10 nm. The investigation of IR spectrum analysis exhibited that there were no chemical bonds formed between SiO2 and RF aerogel.