Advanced Materials Research Vols. 123-125

Abstract: This presentation deals with the aggregation characteristics of Cu and Ag nanoparticles in presence of starch as the polymer stabilizer. Uncontrolled aggregation of the destabilized nanoparticles offers problem for applications based on surface plasmon activity. Polymer or small molecule surfactants are used to control nature of aggregation of nanoparticles produced by chemical reduction synthesis routes. Different growth models such as diffusion limited cluster aggregation (DLCA), reaction limited cluster aggregation (RLCA) proposed to explain the formation of fractal colloidal aggregates do not account for aggregate formation in presence of polymer or small molecule surfactants. We shall be discussing the role of starch on the aggregation characteristics of copper and silver nanoparticles formed by chemical reduction in aqueous conditions. The effect of NaOH concentration and consequently the pH on such aggregation kinetics during such synthesis is delineated. We use small angle x-ray scattering (SAXS) to quantitatively understand different aspects of aggregation behavior.

Abstract: This paper presents the elastic buckling behavior of nonlocal micro- and nano- Timoshenko rods/tubes based on Eringen’s nonlocal elasticity theory. The critical buckling loads are obtained using the theorem of minimum total potential energy and Chebyshev polynomial functions. The present method, which uses Rayleigh–Ritz technique in this paper, provides an efficient and extremely accurate buckling solution. Numerical results for a variety of some micro- and nano-rods/tubes with various boundary conditions are given and compared with the available results wherever possible. Through the comparison of the results and the appropriate discussion, the knowledge of the level of capability of the developed method is promoted. The small scale effects on the buckling loads of rods/tubes are determined and discussed.

Abstract: A set of Y-shaped carbon nanofibers obtained from ethanol flames is reported. The set of Y-shaped carbon nanofibers includes four types of morphologies. No catalyst particles could be found at the junction of Y-shaped carbon nanofibers. The growth mechanism of the multiple Y-junction carbon nanofibers is discussed.

Abstract: Combustion method is a simple method to synthesize carbon nanotubes(CNTs), which employs flames of carbon-contained reactant to synthesize CNTs. It has been proved that combustion method is an effective method to synthesize carbon nanotubes and carbon nanofibers. In this paper, we reported the synthesis of CNTs by using ethanol catalytic combustion with an additive of thiophene, which employed ethanol as carbon source and fuel, nitrate as catalyst precursor, stainless steel as substrate, and thiophene as accelerant. Compared with previous reports on the synthesis of CNTs by ethanol catalytic combustion, great yield of CNTs were obtained with adding thiophene in ethanol. The reproducibility of the synthesis of CNTs in the case of adding thiophene in ethanol was greatly improved.

Abstract: La1.6Ln0.4Zr2O7 (Ln= La, Nd, Dy, Er) nanocrystals were prepared by stearic acid combustion method. The samples were characterized by powder X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) nitrogen adsorption, transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM). The photocatalytic activity of La1.6Ln0.4Zr2O7 was evaluated by the photocatalytic degradation of methyl orange. The order of the photocatalytic activity was as following: La1.6Er0.4Zr2O7>La1.6Dy0.4Zr2O7> La1.6Nd0.4Zr2O7> La2Zr2O7. La1.6Dy0.4Zr2O7 showed that the best photocatalytic activity and the reason may be related to the big magnetic moment of Er3+. It may be considered largely to be caused by the partly occupied Ln4f levels. Since the solid samples have the same structure, the reason that La1.6Er0.4Zr2O7 shows the highest reactivity may be related to lowest Ln4f level of Er3+.

Abstract: The rapid sintering of nanostuctured SiC hard materials was investigated with high-frequency induction heating sintering process. The advantage of this process is that it allows very quick densification to near theoretical density and prohibition of grain growth in nanostuctured materials. A dense nanostructured SiC hard material was produced with simultaneous application of 500 MPa pressure and induced current within 2 minutes. The effect of the ball milling times on the sintering behavior, grain size and mechanical properties of binderless SiC was investigated.

Abstract: The majority of concrete used nowadays is based on matrixes formed by hydrating Portland cement. Latest developments in nanosciences introduced a new generation of nano-sized materials possessing often remarkable mechanical and physical properties. These materials can be also used to improve or alter the characteristics of the binder matrixes based on Portland cement. The results showed that mechanical properties such as compressive and flexural strength can be increased by up to 50% by addition of for example 0.23wt% of carbon nanotubes. Carbon nanotubes and carbon nanofibres and/or nanosilica appeared to improve also the frost resistance. Other properties, such as autogenous shrinkage decreased significantly after addition of carbon nanofibres. Nanosilica enabled an immense densification of the hydrated binder matrix, which in turn improved for instance the durability and mechanical properties.

Abstract: Si/Cu100xZrx (x= 0~38.1) bilayer recording thin films were deposited on nature oxidized silicon wafer, and glass substrate by magnetron sputtering. The ZnS-SiO2 films were used as protective layers. We have studied the thermal property, optical property, and crystallization mechanism of the Si/Cu100-xZrx bilayer thin films. The optical contrasts of the Si/Cu100-xZrx (x= 0~38.1) bilayer films under 405 nm wavelength are all larger than 15%, and it reaches a high value of 40%, as x= 38.1. This indicates that the Si/Cu100-xZrx (x= 0~38.1) bilayer films are suitable for blue laser optical recording.

Abstract: The NiO-Au composite films with Au contents of 0 to 33.7 at.% are deposited on glass substrates. The high electrical resistivity (ρ) of Au-doped NiO films with Au contents below 1.0 at.% is difficlut to measure by four point probe. The ρ value could be reduced to 30.4 Ω-cm as Au content of 1.4 at.% is added into NiO film. It is reduced significantly to 0.375 Ω-cm as Au content is increased to 13.6 at.%. Further increasing the Au content to 33.7 at.%, the ρ value of NiO film is further decreased to 4 x 10-4 Ω-cm. On the other hand, the transmittance of Au doped NiO films also decreases with increasing Au contents. The transmittance for pure NiO film is as high as 96 %. As the Au contents of 1.4, 13.6, and 33.7 % are added into NiO film, they are decreased drastically to 45 %, 20 %, and 9 % respectively. The XRD patterns of Au-doped NiO films with Au content below 9.6 at.% only appear NiO peaks and their (200) peaks shift slightly to low angle as Au content is increased. When Au content is added to above 9.6 at.%, the NiO crystalline become worse. In addition, further increasing the Au content to above 13.6 at.%, the (111) peak of Au also appears in XRD patterns. This indicating that the Au atoms instead of part of Ni atoms results in the enlargement of NiO lattice for Au-doped NiO film with lower Au contents, but large amount of Au atoms are precipitated from the NiO lattice when the content of Au in the NiO film is increased to above 13.6 at.%.

Abstract: Palladium (Pd) nanoparticles were incorporated into free-standing polymer films, where isotactic polypropylene (iPP) was used, by a one-step dry process involving simultaneous vaporization, absorption and reduction schemes of palladium(II) bis(acetylacetonate), Pd(acac)2 at 180oC, used as a precursor. iPP film was exposed to the sublimed Pd(acac)2 vapor in a glass vessel with nitrogen atmosphere heated at 180oC. The exposing time was 30 min and the Pd nanoparticle contents in polymer films were estimated from ash contents in a sample of about 5 mg by pyrolysis of the films at 800 oC for 1 h in an electric furnace of the TGA apparatus under dry argon atmosphere. The sensitivity of the TGA apparatus was 0.2 mg, and thus the minimum content to be measured was 0.004 wt% of a 5 mg sample. The reduced Pd nanoparticles were observed by transmission electron microscope (TEM), and it was found that metal nanoparticles were selectively loaded into the amorphous regions between the lamellae of crystalline polymers having higher melting temperatures than the processing temperature (180 oC). In order to measure the thermal degradation rate, TGA data measured by the heating rates of 5, 10, 15 and 20 oC /min at the nitrogen atmosphere of 200 ml/min. The TGA data was introduced to the Ozawa equation and the degradation activation energy was calculated according to the degradation ratio.