25 μm thick Upilex films (registered UBE trademark) were carbonized, then graphitized at various temperatures up to 2800 °C and studied by optical and electron microscopies. While the graphitizing behavior of Kapton films is similar to that of anthracites, Upilex graphitization is erratic from one film to the other. The thickness of the better graphitizing Upilex films decreases as the anisotropy increases. Their graphitization occurs at a relatively low temperature (2100 °C), because the oxygen is entirely labile (no cross-linking). Non-graphitizing films are obtained when oxygen remains stable as the heat-treatment temperature (HTT) increases. They stay optically isotropic and microporous without flattening, and even show a limited swelling instead of a thinning. This behavior is attributed to the random mobility of the imide part of the molecule when carbonization starts.

The effect of gallium oxide on cristobalite formation in Pyrex borosilicate glass has been studied. XRD results show that with 20 vol.% gallium oxide, the precipitation of cristobalite at 800 °C is completely prevented. This result is further evidenced by the linear thermal expansion measurement, in which, in contrast to the system without a sufficient amount of gallium oxide (0–10 vol.%), the thermal expansion coefficient of the composite with 20 vol.% gallium oxide remains unchanged with sintering time at the temperature investigated and, moreover, is very close to the theoretically calculated value.

YBa2Cu3O7-x was molten and resolidified by a containerless process under free-fall conditions in a drop tube. The resulting samples revealed four different microstructures originating either from a “high-temperature melt” (Tm ≥ 1550 K) or from a “low-temperature melt” (1288 K ≤ Tm ≤ 1550 K). All structures exhibited very fine, homogeneously dispersed structural constituents. One of these microstructures is not compatible with actual equilibrium phase diagrams and implies the kinetic suppression of the nucleation of both the Y2BaCuO5- and the Y2O3-phase.

Equal amounts of carbon-12 methyl halides and carbon-13 methane, along with hydrogen, have been introduced into a hot-filament diamond CVD chamber. The isotopic ratios of the as-deposited diamond films on tantalum have been measured by Raman spectroscopy. It was found that methyl chloride yielded carbon-12 enriched diamond films, while the other methyl halides resulted in equal amounts of carbon-13 and carbon-12 in the films. Furthermore, the carbon-12 enrichment was more enhanced as the substrate temperature was lowered. Matrix-isolation FTIR analyses of the gas samples collected during the deposition indicated that there was no straightforward agreement between the 12C/13C ratios of the gas phase species, methane and acetylene, and that of the diamond films. The results imply the presence of a new chlorocarbon radical such as CH2Cl, which is postulated as a more effective growth species than the methyl radical.

The 27Al MAS-NMR spectra of alumina aerogels were determined. The spectra showed different profiles according to the supercritical methods used during drying. The alumina aerogel supercritically dried in a CO2 extractor (80 °C, 15.7 MPa) displayed a pentahedral-coordinated aluminum structure. On the other hand, the alumina aerogel supercritically dried in an autoclave (270 °C, 26.5 MPa) revealed no pentahedral-coordinated aluminum structure. The absence of pentahedral-coordinated aluminum was one factor for the lower temperature of transformation from the γ to the θ phase.

The present study was aimed at determining the rate of degradation of the transport critical current density Jc of ceramic YBCO stored in atmosphere, as a function of temperature. The transport critical current of ring-shaped samples was measured by the inductance technique. The samples were prepared by the standard method. The results show that annealing at 100 °C for over 500 h caused practically no degradation of Jc. Above 100 °C the rate of degradation increases rapidly with temperature.

Advances in the development of high Tc superconducting thick film components and devices for microwave, millimeterwave, and submillimeterwave applications have led to the optimization of laser patterning techniques. Plasma-sprayed superconducting thick films of YBaCuO materials on polycrystalline alumina were laser etched using an Nd: YAG laser (λ = 1.06 μm) in the Q-switched mode. Spatial uniformity of the surface elemental distribution of Y, Ba, Cu, and Al was observed in the underlying laser-etched area. An etch rate of 7.5 μm/scan was calculated at an optimized laser fluencc of 1.8 × 104 J/cm2 for a translation rate of 2.54 cm/s, having patterning widths ranging from 5–15 μm with a heat-affected zone of 3 μm. An absorption length of 18.3 μm for the Nd: YAG laser was determined to be suitable for patterning thick films (20–80 μm) for device fabrication. The results are further compared to CO2 (λ = 10.6 μm) laser etching for patterning (250 μm) thick films.

The equilibrium decomposition temperatures of Cu2Ln2O5 (Ln = Tb, Dy, Ho, Er, Tm, Yb, and Lu) compounds have been measured using a combined DTA-TGA apparatus under a flowing Ar + O2 gas mixture, in which the partial pressure of oxygen was controlled at 5.0 × 103 Pa. The Cu2Ln2O5 compounds yield Ln2O3 and Cu2O on decomposition. The decomposition temperature increases monotonically with the atomic number of the lanthanide element. This suggests that the stability of the Cu2Ln2O5 compounds with respect to the component binary oxides increases with decreasing radius of the Ln3+ ion.

The decagonal phase was studied by transmission and scanning electron microscopy in an Al62Cu24Co14 alloy annealed at 550–850 °C. The electron diffraction patterns of the decagonal phase exhibited weak quasiperiodic odd-n reflections in the [1-2100] zone axis corresponding to the equilibrated structure. The relative intensities of these reflections were significantly lower in the Al62Cu24Co14 than in the Al68Cu11Co21 decagonal phase. Diffuse scattering observed previously at the same positions can be related to a nonequilibrium state of the decagonal phase.

Al—Cu—Fe quasicrystalline alloys have been deformed by high-temperature creep between 680 and 740 °C. Deformations greater than 30% were achieved without cracking. Analysis of the data in the quasi-steady state regime reveals power law behavior with a stress exponent of 2.5. The activation energy for deformation was determined to be 640 ± 20 kJ/mole in the temperature region investigated. Transmission electron microscopy revealed lamellar defects which appear similar to twins.

Continuous microindentation tests performed on the electropolished surfaces of single crystal Fe (3 wt.% Si), known to have a thin passivation film, show a sharp discontinuity at a load of 1.8 mN. To this point, there was no apparent plastic deformation in the metal in that the loading and unloading curves exactly overlay each other. Stresses at the discontinuity were close to the theoretical strength of the metal. Elastic contact theories of Hertz and Love reproduced the elastic portion of the load-displacement curves. On removing the passivation film with a HCl solution, indentation tests yielded strengths nearly two orders of magnitude smaller. The strength recovered to near its initial value after the liquid evaporated and the passivation film re-formed.

In this brazing technique, at least one of the metal surfaces to be joined is coated with a powder-mixture of silicon and a potassium fluoroaluminate flux. Brazing of aluminum is carried out by heating at ∼600 °C in nitrogen gas. During heating, the flux melts and dissolves the oxide layers on the contacting surfaces, thus allowing the silicon to come into intimate contact with bare aluminum. At a temperature exceeding the Al–Si eutectic temperature of 577 °C, the silicon diffuses rapidly into the aluminum and generates in situ a layer of Al–Si liquid alloy of near-eutectic composition. The filler material then flows into the joint and forms a fillet. This brazing technique may be exploited with aluminum using intermediary elements other than Si, and may be used for joining a variety of metals.

The microstructures of YBa2Cu3O7−δ (YBCO) thin films grown on Si with Y-stabilized ZrO2 (YSZ) and Y2O3 buffer layers were characterized by means of high-resolution electron microscopy. At the Si–YSZ interface, a 2.5 nm thick layer of regrown amorphous SiOx is present. The layer is interrupted by crystalline regions, typically 5 to 10 nm wide and 10 to 50 nm apart. Close to the crystalline regions, {111} defects are present in the Si substrate. The typical defect observed is an extrinsic stacking fault plus a perfect dislocation close to the stacking fault which terminates extra {111} planes in the upper part of the Si. These defects are probably formed by condensation of Si self-interstitials created during oxide regrowth. Precipitates are present in the Si close to the Si–YSZ interface and indicate that in-diffusion of Zr has occurred. The YSZ–Y2O3 interface is atomically sharp and essentially planar and contains no second phases. Perfect misfit dislocations with Burgers vector 1/2〈110〉 are present at this interface along with unrelaxed elastic misfit stresses. The Y2O3–YBCO interface is atomically sharp and planar, but contains steps. (001) stacking faults are present in the YBCO above these steps; the faults are, however, healed a few unit cells away from the interface. By HREM analysis of ultrathin specimen areas, the atomic layer of the YBCO closest to the Y2O3 was found to be a barium-oxygen layer.

A compound with the stoichiometry of Y1Ba4Cu2CO3O5.5±δ is formed in the presence of CO2 or carbonate. Analysis techniques including oxygen overpressure, wet chemical analysis, and quenching experiments establish that this material is an oxycarbonate compound. Electrical measurements indicated no superconductive properties in the 10–298 K temperature range. The ease of formation of this compound causes it to commonly appear in synthesis in this region of the phase diagram and accounts for many of the conflicting reports of properties and solid solution formation. XRD shows evidence for the existence of some solid solution in this oxycarbonate. The compound Y1Ba4Cu3O8.5±δ, formed in the absence of CO2, and Y1Ba4Cu2CO3O5.5±δ, formed in the presence of CO2, are the only barium-rich phases seen to exist.

Glass-metal nanocomposites involving copper and nickel, respectively, have been synthesized in bulk form by hot pressing sol-gel derived silica-metal nanoparticle composite powders. The particle diameters range from 9 to 17.5 nm. The specimens exhibit the characteristic behavior of the metallic species in their nanocrystalline forms.

A computational model for laser-induced Wagner oxidation processes on a vanadium metal surface is described and compared with the experiment. It is found that for thin oxide layers, the oxide is nearly transparent and the metal temperature rapidly increases. For thicker layers, the oxide is nearly opaque and the metal temperature slowly decreases. The Wagner rate law is found to hold for thicker oxide layers, but not at the beginning of the process.

Single-crystal epitaxial films of cubic β(3C)–SiC(111) have been deposited on hexagonal α(6H)–SiC(0001) substrates oriented 3–4° toward [1120] at 1050–1250 °C via gas-source molecular beam epitaxy using disilane (Si2H6) and ethylene (C2H4). High-resolution transmission electron microscopy revealed that the nucleation and growth of the β(3C)–SiC regions occurred primarily on terraces between closely spaced steps because of reduced rates of surface migration at the low growth temperatures. Double positioning boundaries were observed at the intersections of these regions.

Pipes or hollow cylinders in the Bi-Sr-Ca-Cu-O system were found to be fabricated easily by inspiring or sucking the low viscosity melt into a cold silica glass tube. The outer part of the cast rod-like melt solidified, and the inner hot low-viscosity part of the rod melt was expired. The precursor pipes were reheated at 800 °C for 50 h in air, resulting in the formation of superconducting (Tc = 87 K) pipes which were of smooth surface without machining and high bending strength (100–150 MPa).

High Tc superconducting YBCO films have been prepared on Y2BaCuO5 (211) and ZrO2 substrates by screen printing and by the partial vacuum sintering method. The influence of reduced pressure and temperature in correlation with adherence, microstructure, and superconducting properties has been observed. This study was carried out under two different partial pressures, 1 and 45 mm. Films on Y2BaCuO5 substrates were found to have better superconducting properties as compared to the ZrO2 substrate.

Solid solutions of aluminum nitride (AlN) and silicon carbide (SiC), the only intermediate phases in their respective binary systems, have been grown at 1050 °C on α(6H)-SiC(0001) substrates cut 3–4° off-axis toward [11$\overline 1$0] using plasma-assisted, gas-source molecular beam epitaxy. A film having the approximate composition of (AlN)0.3(SiC)0.7, as determined by Auger spectrometry, was selected for additional study and is the focus of this note. High resolution transmission electron microscopy (HRTEM) revealed that the film was monocrystalline with the wurtzite (2H) crystal structure.