Nickel is deposited over pristine, surface-treated, and brominated P-100 carbon fibers using cementation and electroplating techniques. The fibers are brominated by bromine vapor for 48 h and then desorbed at 200 °C in air for 12 h. The anodic oxidation treatment is performed by etching fibers electrochemically in a dilute sodium electrolyte for 3 min or by immersing fibers in nitric acid for 72 h. Electroplated-coated fibers show better tensile properties than cementation-coated fibers. Tin-lead alloy composites reinforced by nickel-coated fibers (which are pristine, anodically oxidized, and brominated) are fabricated by squeeze casting. The composites containing coated carbon fibers with bromination or surface treatment have higher tensile and shear strength than the ones containing coated pristine carbon fibers. In addition, the composite containing coated carbon fibers with brominalion shows the best performance in the tensile properties.

In this paper, a one-step, combustion synthesis-based process for fabricating Al2O3 fiber-reinforced Ni3Al is described. The process uses relatively low temperatures and pressures, and can be used to prepare relatively large, dense, near-net-shape articles that possess either simple or relatively complicated shapes. This process can be used to incorporate continuous, aligned fibers into the Ni3Al matrix material in such a way that the fibers are not damaged either mechanically (due to relatively small loads applied during the process) or chemically (due to the very short time at which the sample remains at elevated tempertures during the process). (Chopped fibers, as well as equiaxed particles or whiskers, could also be similarly incorporated using this process.) This combustion synthesis process is a relatively simple one-requiring only relatively low temperatures and pressures, as well as relatively low-cost starting materials-which suggests that its scale-up beyond the laboratory scale would be particularly straightforward.

Paste development and evolution of microstructure, microchemistry, and mechanical properties of macro-defect-free composites were investigated. Mixing torque plots from a Banbury mixer showed a “window of processibility” within which an optimum polymer-particle network structure formed. This processing window can be controlled by mixing rate and temperature. Network development during paste formation governed the flexural strength and microstructure of the cured material. Electron microscopy studies of the composites corresponding to various points along the mixing torque curve revealed a matrix formation-destruction process that was linked to the mixing activity and the mechano-chemistry of the system. Microchemical evolution in the composite was studied by EDS. These studies suggested that a combined convection and diffusion mechanism was responsible for the migration of Al3+ and Ca2+ ions into the different regions of the microstructure. Increasing concentrations of these elements in the polymer regions stiffened the matrix, leading to complete degradation on further mixing.

Thin films of ZrO2-Al2O3 were grown on cubic-Zr(Y)O2 substrates by a liquid precursor route. Phase formation and epitaxy of these films was studied as a function of heat-treatment temperature and time. The following sequence of phases was observed in these thin films: Precursor → t-(Zr,Al)O2 → t-(Zr,Al)O2 + γ-(Al,Zr)2O3 → m-ZrO2 + α-Al2O3 Observations strongly suggest that the epitaxial process initiated before the metastable, single phase t-(Zr, Al)O2 partitioned to t-(Zr, Al)O2 + γ-(Al, Zr)2O3. Observations at 1400 °C show that, after the γ to α transformation, α-Al2O3, grains develop an elongated, prismatic morphology and an epitaxial relation with the underlying and surrounding m-ZrO2. The phase that is chemically and structurally similar to the substrate, in this case t-(Zr,Al)O2, or m-ZrO2, forms an epitaxial layer between the substrate and isolated, prismatic grains of heteroepitaxial α-Al2O3.

We have studied effects of hydrogen on texture in diamond films grown by hot filament assisted chemical vapor deposition by utilizing x-ray diffraction (XRD). We present results for the relative intensities of the XRD peaks originating from the (111). (220), and (400) crystallographic planes as functions of CH4/H2 makeup during growth and post-growth H2 treatment of the films. The texture of the films can be controlled by varying composition of the CH4/H2 mixture during growth and also by subjecting films to hydrogen treatment. The complementary characterization of these films by XRD, Raman spectroscopy, and positron annihilation techniques exemplifies a correlation among film texture, diamond contcnt, and dcnsity of the microvoids in the films.

For crystal structures of oxides with tetrahedral coordination polyhedra, the average number of tetrahedra participating in the sharing of a corner, i.e., Zoltai's tetrahedral sharing coefficient, provides a measure of the degree of polymerization of the tetrahedra. By contouring oxide phase diagrams with Zoltai's tetrahedral sharing coefficient, crystal structure systematics can be conveniently displayed and correlated with other physical and thermochemical properties. The advantages of this analysis are (i) a structural map guides exploration for new compounds, (ii) possible structures for existing compounds that are not known are suggested, (iii) the internal consistency of the chemistry of specific compounds is tested by structural constraints, (iv) the physical behavior and properties of a family of compounds in a chemical system can be correlated with the degree of polymerization of the tetrahedra, and (v) the analysis lends itself to computer programming, in that contour templates of tetrahedral sharing coefficients for different types of oxide systems can be easily determined and overlaid on traditional phase diagrams. Shortcomings to this approach are that the tetrahedral sharing coefficient does not define a unique tetrahedral anion topology, ambiguities arise if some of the oxygen atoms are not part of the tetrahedral anion, and many chemical systems contain oxides where one or more of the tetrahedral cations adopt other coordination geometries.

Epitaxial thin films of LiNbO3 were prepared by the sol-gel method on (0001)-sapphire, (0001)-LiTaO3 and (0001)-5% MgO-doped LiNbO3, substrates. The precursor films crystallized with the highly preferred orientation on all substrates. When sapphire substrates, which have large discrepancies in the lattice constant and thermal expansion percentage with the film were used, the resulting films showed a low crystallinity after heat treatment at 500 °C and grain growth at 650 °C. On the other hand, when using LiTaO3 and 5% MgO-doped LiNbO3 substrates, with smaller discrepancies, the formed films, after heat treatment at 500 °C, showed better crystallinity with the smooth surface.

Barium titanate powder and heteroepitaxial thin films were successfully produced by hydrothermal routes at ambient pressure and temperatures less than 100 °C. This processing method provides a simple low temperature route for producing epitaxied barium titanate thin films on single-crystal SrTiO3 substrates and powders which could also be extended to other systems. A dissolution/reprecipitation growth mechanism also was proposed for the formation of barium titanate by this route using previously published aqueous stability diagrams. Repeated hydrothermal treatments improved film thickness and surface coverage at the expense of increased surface roughness.

The microstructural variation and the interdiffusion of Pt (80 nm)/Ti (70 nm)/SiO2/Si during annealing in O2 were investigated using Auger electron spectroscopy, x-ray diffraction, transmission electron microscopy, and scanning electron microscopy. While the as-deposited and 400 °C annealed samples showed well-defined layer structures without any significant interfacial reaction, the degree of oxidation remarkably increased with increasing temperature above 500 °C. The PtTi alloy phase with Pmma structure (AuCd type) was observed from the 500 °C annealed sample. Drastic interdiffusion occurring above 600 °C changed the Pt/Ti bilayer into a very entangled structure. Some TiO2 phases were exposed to the ambient between Pt hillocks. In addition, a small amount of Pt-silicide was found near the TiOx/SiO2 interface.

The playback efficiency of metal-in-gap (MIG) inductive read-write heads in magnetic recording devices is strongly influenced by wear of the air-bearing surface, metal core recession, and staining. In this study, stains were formed by sliding Co–Nb–Zr MIG tape heads against Co–γFe2O3 (oxide) and metal particle (MP) tapes in an accelerated mode. Optical and SEM imaging indicated that staining on a head run against the Co–γFe2O3 tape is thick and patchy, whereas on a head run against the MP tape, staining is in the form of a uniform film. Thickness variations of stains on the metal core formed by Co-γFe2O3 and MP tapes, measured using atomic force microscopy (AFM), were about 30–150 nm and 20 nm, respectively. Constituents of stains were analyzed by time-of-flight secondary ion mass spectrometry (TOF-SIMS), scanning Auger electron spectroscopy (AES), and micro-Fourier transform infrared (micro-FTIR) and micro-Raman spectroscopies. Stains formed on the head run against the Co-γFe2O3 tape consist of organic species with trace amounts of iron and oxygen (inorganic) constituents. On the other hand, stains formed on the head run against the MP tape consist of inorganic constituents of oxidized magnetic particles from the tape. In addition to organic species and iron from tapes, stains formed by either tape also exhibit wear debris from the metal core, ferrite core, and glass region of the head itself. In the case of heads run against both tapes, most of the staining was found to be on the metal core.

A new class of molecular composites of carbon black and an electronically conducting polymer, namely polypyrrole, has been synthesized by chemically polymerizing pyrrole in an aqueous dispersion of carbon black. The carbon black content of these composites can be varied from ∼5% to ∼85% (by weight). The surface area and density of these composites were compared to corresponding mixtures of carbon black and polypyrrole. The influence of carbon black on the efficiency of polymerization of pyrrole is described. The effect of carbon black content on the electronic conductivity of the composite has been mapped, and compared with the corresponding behavior of a mixture of carbon black and polyvinylchloride. The influence of the parent black characteristics (porosity, void volume, surface area) on the electronic conductivity of the resultant composite has been probed by comparing the behavior of composites derived from six commercial and experimental blacks. The temperature dependence of the composites has been studied as a function of the carbon black content. Finally, the application of these new materials is an environmental remediation scenario is demonstrated for Cr(vi) as a model pollutant.

Verneuil sapphire was purified of Cr3+ by containerless melting and processing at ca. 2550 K in argon, dry air, and pure oxygen. Recovered material was examined by laser induced fluorescence and Raman spectroscopy. The Cr3+ fluorescence intensity decreased in processed specimens at rates proportional to the chromium concentration and p(O2)0.21. The initial chromium concentration was ca. 5 ppm and decreased by factors of ca. 50, 3000, and 2 × 105 after processing for 300 s in argon, air, and oxygen, respectively. Evidence is presented that the Cr3+ was removed predominantly as CrO2(g) and not by conversion to other oxidation states of chromium in the condensed phase.

A series of computer experiments has been conducted in order to study the combined combustion synthesis-densification process, in which a mechanical load is applied to a sample as it undergoes a combustion synthesis process. The current work is an extension of a theoretical model of the combustion synthesis process that was developed previously.1,2 In this work, the appropriate constitutive equations for sample deformation have been incorporated, in order to account for the pore-volume change that may take place when the mechanical load is applied, thus densifying the sample. It was shown that the brief appearance of a liquid phase in the combustion wave front provides an important opportunity for densification when the self-propagating combustion synthesis process is conducted in conjunction with an applied mechanical load. That is, the concomitant decrease in the (local) total volume fraction of the solid phases—due to the elementary melting and dissolution processes that also occur (locally)—effectively lowered the (local) apparent yield strength of the sample, thus allowing for the compaction and densification of the sample (i.e., locally). Results indicated that the mechanical load should be applied at the instant at which the sample is ignited, in order to ensure that articles whose density is uniform throughout the sample can be fabricated. This work provided a more detailed and quantitative understanding of this unique process for preparing dense articles by the self-propagating combustion synthesis process, that is, when it is conducted in conjunction with an applied mechanical load.

The sintering of glass powder compacts was studied by dilatometer in the (25 - x) Na2O–xK2O–75SiO2 glass system. The dilatometrically determined sintering temperature (Tsin) at constant heating rate decreases and the shrinkage at isothermal sintering increases when Na2O is replaced by K2O up to the mole fraction of K2O/(Na2O + K2O) = 0.5. This is due to the decrease in viscosity and means that sintering can be possibly accelereted by introduction of mixed alkali oxides in this system. According to calculation using the VFT-equation, the viscosity value at Tsin is almost independent of glass composition. From these results it may be supposed that the dilatometrically determined sintering begin temperature (Tsin) can be a characteristic point for the sintering of glass.