We discuss the oxidation of carbon nanotubes and how it is affected by structure and geometry. While graphite is known to oxidize primarily at defects to create etch pits, nanotubes have additional structural features such as high curvature, helicity, and contain five and seven membered rings which modify the initiation and propagation of oxidation. Oxidation does not necessarily start at the tip of the tubes, and there are pronounced differential oxidation rates between layers which depend on the helicity of the individual shells.

Films of Yba2Cu3O7−δ (YBCO) were grown on (001), exact and vicinal (110), and (111) SrTiO3 single crystal substrates by pulsed laser deposition, and evaluated by x-ray diffraction and scanning force microscopy (AFM). It was observed that the YBCO was always epitaxially aligned to the substrate with the [001] (c-axis) parallel to a substrate cube axis direction. For the exact (001), (110), and (111) surfaces, there were one, two, and three orientations, respectively. For the vicinal (110) surfaces, however, there was usually only one discernible c-axis orientation, corresponding to a single {013} film surface orientation. The reduction of the (110) surface twofold symmetry by use of a vicinal substrate thus allowed controlled growth of a YBCO single crystal with an inclined c-axis orientation.

The present authors have already reported that barium oxide is the most effective catalyst for the conversion of waste polystyrene into styrene including both monomer and dimer. Around 85 wt.% of waste polystyrene was converted into styrene when it was degraded at 623 K in the presence of barium oxide as catalyst. In this paper, the preparation and the thermal degradation of polystyrene films with dispersed catalyst are described for a design of recyclable plastics for better environment. More than 85 wt.% of the films was degraded into styrene at 623 K without addition of other catalytic compounds. Techniques for foaming the films using either nitrogen or carbon dioxide are discussed. It was found that the polystyrene foams with dispersed catalyst are well converted into styrene when they are simply degraded at 673 K.

Several kinds of Cu polycrystals with dispersed SiO2 particles of different volume fractions were tensile tested at high temperatures from 473 K to 1023 K. All of the alloys showed clear intermediate-temperature embrittlement (ITE). Although the temperature of minimum elongation was almost the same in all the alloys, temperature dependence of fracture strain depended strongly on the SiO2 volume fraction: (1) At a fixed temperature, the fracture strain tended to first decrease with increase in SiO2 volume fraction, showed minimum in an alloy with certain volume fraction, and increased again with increase in volume fraction. (2) With increase in SiO2 volume fraction, the temperature range of ITE became narrower and sharper. These results were reasonably understood by considering the occurrence of stress concentration at grain-boundary particles induced by grain-boundary sliding (GBS) and occurrence of dynamic recrystallization and stress relaxation by Cu/SiO2 interfacial diffusion.

A technique for microstructural control of excimer laser-annealed silicon thin films on SiO2 substrates has been developed. By using single-crystal photolithographically etched silicon seed wafers in intimate contact with the silicon films, we have shown that it is possible to spatially control nucleation. Transmission electron micrographs show the resultant microstructure to consist of large (∼1 µm) grain structures in the area surrounding the seed contact, with distinct organization not previously observed. A theoretical discussion is presented to explain the observed phenomena. Also, results from a numerical simulation are given which outline the effects of the seed wafer on the resultant microstructure of the laser-annealed film, as compared to nonseeded areas.

Kinetics of congruent ordering in Cu3Au at 350 °C was investigated by means of a three-dimensional atom probe. This instrument, called a Tomographic Atom Probe (TAP), enables atomic resolution images of a small volume (10 × 10 × 100 nm3) of the material reconstructed in the three dimensions of space. The time evolution of ordered domains at 350 °C shows that a t1/2 law is followed as soon as 5 min. For this aging time, the nucleus diameter is close to 1.7 nm. This scaling law was observed even before domains came into contact (t = 50 min). Competitive growth was observed to start as soon as 5 min. The number density was observed to decrease rapidly up to t = 50 min. A slower decrease was observed when domains begin to impinge. Experimental conditions and requirements as well as advantages of TAP as compared to HREM for the study of ordering are discussed in detail.

A fully dense nanocrystalline compact of the Ti–47Al–3Cr (at. %) alloy was produced by mechanical alloying and hot isostatic pressing at 725 °C. Microstructure characteristics and grain growth behavior of this compact were studied after annealing for up to 800 h in the temperature range of 725 to 1200 °C, using analytical transmission electron microscopy techniques. The temperature and time dependencies of the grain sizes and the grain size distributions were determined. The grain growth occurred, with a timeand temperature-invariant single-peak grain size distribution (when normalized by the mean grain size), which was consistent with normal grain growth. The experimentally measured grain growth exponent decreased from 10 to 4.6 when the temperature was increased. The grain growth kinetics was described by a single thermally activated rate process limited by a permanent pinning force on the grain boundaries. The microhardness decreased on annealing and followed the Hall–Petch relationship with the parameters Hυo = 5.8 GPa and KH = 1.6 MPa m0.5.

In this paper, nanometer-sized CdO organosol was prepared by using microemulsion methods. Its electronic structure and optical properties are characterized through UV-visible light absorption, photoluminescence, and Z-scan techniques. Some newfeatures were observed. Fluorescence and nonlinear optical responses are mainly related to surface trapped states.

Titania gels in liquid media crystallized from amorphous to anatase at temperatures as low as 120 °C, while the onset of crystallization in air was 370 °C. The crystallization rate in water was much faster than in methanol and n-hexane, and the crystallite size of anatase prepared in water was larger than of those prepared in organic solvents. The crystallized powders were capable of efficient hydrogen evolution following band gap irradiation in the presence of a sacrificial hole acceptor such as methanol. The photocatalytic activity of powder crystallized in methanol was superior to those prepared in water and air.

High angle boundaries in Ba1−xKxBiO3 are superconductor-insulator-superconductor (SIS) Josephson tunnel junctions of a quality unequaled among the high temperature superconducting oxides. Electron microscopy of 24° [001] tilt boundaries reveals nominally symmetric and straight boundaries of aperiodic structure with reappearing structural units. Low {hk0} atomistic facets are predominant. A segregation layer of only 1 nm thick is identified straddling the boundary. This layer which forms naturally is insulating, pin-hole free, and surprisingly robust with a breakdown voltage which exceeds 1 × 106 V/cm, yet thin enough to allow quasiparticle tunneling, yielding reliable gap energies for theoretical comparison.

The plume generated by ablation of hydroxyapatite targets under ArF excimer laser irradiation has been investigated by means of fast intensified charge coupled device (CCD) imaging and optical emission spectroscopy. Results have shown that the plume splits into two plasma clouds as it expands. Time and spatial resolved spectra have revealed that under the experiment conditions emission is mostly due to calcium neutral atoms and calcium oxide molecular radicals. Imaging of the plume with the aid of bandpass filters has demonstrated that the emissive species in the larger and faster plasma cloud are calcium neutral atoms whereas in the smaller and slower one are calcium oxide molecular radicals.

Two nonequilibrium processes (melt-spinning and ball-milling) were successfully employed to synthesize Al1−xPbx (x = 5, 10, 20, 30 wt. %) nanocomposites with distinct microstructures. In the melt-spun (MS) Al–Pb alloys, the nanometer-sized Pb particles are uniformly distributed in the micrometer-grained Al matrix and have an orientational relationship with the matrix, while in the ball-milled (BM) samples, both Pb and Al components are refined with prolonged milling time, forming nanocomposites with Pb particles homogeneously dispersed into the Al matrix. The minimum particle size of Pb in the milled samples linearly increases with the Pb content. The microhardness of the BM Al–Pb samples is much larger than that of the MS samples, which mainly results from strengthening effects of the nanometer scale Al grains following the Hall–Petch relationship. The microhardness for both BM and MS Al–Pb samples varies with the Pb content, and maximum hardness for both samples exists when Pb content is about 5 wt. %, indicating that small amounts of Pb, in the form of nanoparticles, may strengthen the Al matrix.

ZnO ceramics used as varistors are prepared with cobalt oxide as an essential additive to improve nonohmic properties. Because some of its effects during the liquid-phase sintering remain unexplained, we characterize the liquid-phase formation temperatures and phase reactions in the system ZnO–PrO1.5–CoO. Using differential thermal analysis (DTA) during sintering, we detect new thermal phenomena. An addition of cobalt oxide to ZnO–PrO1.5 mixtures (ZnO–5 mol% PrO1.5–10 mol% CoO) significantly decreases the liquid-phase formation temperature to 1272 ± 5 °C, which is about 110 °C lower compared to those in the ZnO–PrO1.5 system. Characterization of ceramics quenched during sintering allows us to describe an isoplethal section with PrO1.5 contents of 5 mol% and solubility limit of Co in ZnO.

Using a scanning laser microscope and mercury porosi-meter, we evaluate the effects of an excellent car-coating treatment on resistance to environmental corrosion after aging for three years. The treatment maintains the clear surface. The effect can be explained mainly by the contact angle of sessile drops.

The present investigation deals with the electrical response of doped SnO2 to improve the selectivity for liquid petroleum gas (LPG) in the presence of CO and CH4, by utilizing noble metal sensitizers such as Pd, Pt, and Rh. SnO2 with the addition of Pd (1.5 wt. %) or Pt (1.5 wt. %) sintered at 800 °C which have shown high sensitivity toward LPG with no cross interference of CO and CH4 at an operating temperature of 350 °C. The results suggest the possibility of utilizing the sensor for the detection of this hydrocarbon gaseous mixture. X-ray diffraction studies have been carried out to evaluate the crystallite size as a function of sintering temperature; x-ray photoelectron spectroscopy studies have been carried out to define the possible chemical species involved in the gas-solid interaction and the sensitivity enhancing mechanism of the SnO2/Pd sensor element toward LPG.

The structure model for HgTlBa2CuOx was proposed from high-resolution electron microscopy using residual indices. Averaged digital high-resolution image of the HgTlBa2CuOx showed the existence of separated Hg layers and oxygen vacancies in the double (Hg, Tl) layers. Image calculations based on the proposed structure model of HgTlBa2CuO5 agreed well with the observation, and showed low residual values. The present result indicates the stability of the (Hg, Tl) double layer structure would be due to the formation of oxygen vacancies in the Hg layers.

The local critical current (Ic) at 77 K measured at the mm scale in a 60 mm long sample of YBa2Cu3O7−δ prepared by a melting zone process is correlated to the microstructure. Lower values of Ic (<20 A) were obtained in a part of the sample which optical microscope examination showed to be generally polycrystalline. In contrast, the rest of the sample, consisting mostly of large textured domains, gave values for Ic of 120 A and above. Transmission electron microscope observations revealed that the textured domains contain internal boundaries. Depending on the scale of observation, the misorientation angles across the boundaries could vary from a few tenths of a degree up to a few degrees. This seems characteristic for boundaries in textured material which allow strong coupling of the superconducting current across themselves.

The surface composition of MA 956 superalloy both as-received and after four exposure times at 1100 °C has been investigated by energy dispersive x-ray spectrometry (EDX) and x-ray photoelectron spectroscopy (XPS). The passive layer of the as-received sample is mainly formed by Cr- and Fe-oxides. Heat treatment leads to the formation of an alumina layer on which small nodules grow. XPS spectra evidence the presence of titanium and yttrium oxides at the surface of the heat-treated samples, suggesting Y and Ti outward diffusion through the alumina layer. Iron and chromium oxides at the topmost surface layers are observed only for short heat-treatment times.

Hydroxy double salts (HDS's) comprise a class of layered materials that are similar to layered double hydroxides (LDH's) and show a comparable intracrystalline reactivity. Their anion exchange reactions occur with preincorporated anions in the hydroxide layer and with anions bound as gegenions of the positively charged layers, respectively. In this study, nitrate and acetate anions of HDS's were exchanged with anionic monoand di-carboxylic acids, and we confirmed that interlayer spacing of HDS's increased depending on the size of mono- and di-carboxylic acids. Moreover, we have prepared photofunctional materials by exchange reaction with azobenzene-p-carboxylic acid and 4–4′-azobenzenedicarboxylic acid.

It was found in a previous work that the Al–Si alloy could spontaneously infiltrate into carbon preforms in air. In this study, the initiation stage of the infiltration process was investigated in detail through two different infiltration experiments. In one experiment, carbon preforms were fully dipped into an alloy bath that was exposed to air, and in the other experiment a carbon preform was only partially dipped into an alloy bath that was protected with a flowing Ar or N2 gas. Experimental results have suggested that the initiation of infiltration is controlled by the pressure of oxidizing gases such as O2 or CO at the infiltration front and is not affected by the presence or absence of N2 gas. The critical pressure of oxidizing gases is estimated to be on the order of 10−4 atm for systems investigated in our experiments. An effective way to reduce the O2 or CO pressure is to flush a preform with nonoxidizing gases during or before infiltration, or to use an active metal to reduce the O2 pressure and thus the corresponding CO pressure.