Fluorphlogopite mica crystallites of dimensions in the range 0.5 to 24 µm were grown within silicate glass of suitable compositions by heat treatment at 1168 K. After an ion exchange treatment (K+ ⇆ Ag+) the specimens were subjected to an electrodeposition reaction. With the optimum concentration of K+ ions in the precursor glass, electrodeposition brought about the growth of silver nanowires about 0.5 nm diameter within the nanochannels of the fluorphlogopite mica structure. By applying a voltage pulse of 20 volts of duration 3 s, break junctions could be induced in the nanowires. A high dielectric constant of around 1.0 × 107was found in the resultant specimen. This was shown to be quantum mechanical in origin and arose due to the presence of metal filaments about 1280 nm in length. An asymmetric voltage–current characteristic was recorded at 114 K in the case of the specimen containing silver nanowires grown within the mica structure. This is believed to arise due to formation of a nanojunction between the metal nanowire and silver nanoparticles with diameters of less than 3 nm. The latter were earlier shown to behave as insulators

Dry sliding wear and friction tests of CrN coating on two types of aluminum alloy substrates, 6061 Al and 7075 Al, deposited by arc ion plating were performed with a ball-on-disk tribometer. The effects of normal load and the mechanical properties of the substrate on the friction coefficient and wear resistance of CrN coating were investigated. The worn surfaces were observed by scanning electron microscopy. The results show that surface microhardness of CrN-coated 7075 Al is higher than that of CrN-coated 6061 Al. With an increase in normal load, wear volume increases, while the friction coefficient decreases. The friction coefficient of CrN-coated 6061 Al is higher than that of CrN-coated 7075 Al, while the wear resistance of CrN-coated 6061 Al is lower than that of the CrN-coated 7075 Al. This indicates that the substrate mechanical properties have strong influence on the friction coefficient and wear of CrN coating. The main wear mechanism was fragments of CrN coating, caused by apparent plastic deformation of substrate during wear tests.

We report here the high-pressure synthesis of well-sintered millimeter-sized bulks of superhard BC2N and BC4N materials in the form of a nanocrystalline composite with diamond-like amorphous carbon grain boundaries. The nanostructured superhard B–C–N material bulks were synthesized under high P–T conditions from amorphous phases of the ball-milled molar mixtures. The synthetic B–C–N samples were characterized by synchrotron x-ray diffraction, high-resolution transmission electron microscope, electron energy-loss spectra, and indentation hardness measurements. These new high-pressure phases of B–C–N compound have extreme hardnesses, second only to diamond. Comparative studies of the high P–T synthetic products of BC2N, BC4N, and segregated phases of diamond + cBN composite confirm the existence of the single B–C–N ternary phases.

To improve the properties of the eutectic Sn–Ag lead-free solder alloy, various amounts of mixed rare-earth (RE) elements, mainly Ce and La, were added. The microstructure, wetting properties, melting behavior, mechanical properties, and creep behavior were studied. It was revealed that RE elements can refine the intermetallics, and with 0.5% RE addition, the RE-bearing phase can be detected in the microstructure of the slow-cooled alloy. The results of differential scanning calorimetry indicate that the melting points of the RE-doped alloys are slightly lower than that of the Sn–3.5Ag and have a eutectic peak. The wetting property and creep resistance of the Sn–3.5Ag–0.25RE alloy are better than those of the Sn–3.5Ag alloy. The creep properties were studied at the temperatures of 303, 348, and 393 K, at various stress levels between 8 and 34 MPa. The stress exponents of the Sn–3.5Ag and Sn–3.5Ag–0.25RE were obtained at these temperatures. Tensile, creep, and wetting properties were found to improve with the addition of RE elements. The improvement of creep resistance is due to the fine dispersion of intermetallics and the decrease in interface energy between matrix and intermetallics. The wettability improvement is mainly due to the accumulation of RE elements at the solder/flux interface, leading to the reduction of the interfacial tension between solder and flux.

Gallium–indium–oxide films (GaxIn2⊟xO3), where x = 0.0–1.1, were grown by low-pressure metalorganic chemical vapor deposition using the volatile metalorganic precursors In(dpm)3 and Ga(dpm)3 (dpm = 2,2,6,6-tetramethyl-3,5-heptanedionato). The films were smooth (root mean square roughness = 50–65 Å) with a homogeneously Ga-substituted, cubic In2O3 microstructure, randomly oriented on quartz or heteroepitaxial on (100) yttria-stabilized zirconia single-crystal substrates. The highest conductivity of the as-grown films was found at x = 0.12, with σ = 700 S/cm [n-type; carrier density = 8.1 × 1019 cm⊟3; mobility = 55.2 cm2/(V s); dσ/dT<0]. The optical transmission window of such films is considerably broader than that of Sn-doped In2O3, and the absolute transparency rival or exceeds that of the most transparent conductive oxides known. Reductive annealing, carried out at 400–425 C° in a flowing gas mixture of H2 (4%) and N2, resulted in increased conductivity (σ 1400 S/cm; n-type), carrier density (1.4 × 1020 cm⊟3), and mobility as high as 64.6 cm2/(V s), with little loss in optical transparency. No significant difference in carrier mobility or conductivity is observed between randomly oriented and heteroepitaxial films, arguing in combination with other data that carrier scattering effects at high-angle grain/domain boundaries play a minor role in the conductivity mechanism.

The mechanical properties of WC–SiC thin films deposited by dual radio frequency magnetron sputtering were investigated. The films were characterized by x-ray photoelectron spectroscopy, x-ray diffraction (XRD), and transmission electron microscopy (TEM) to evaluate the details of the microstructure and degree of amorphization. The results indicate that small additions of SiC (<25%) can significantly increase hardness compared to a pure WC film, but higher SiC contents do not strongly affect hardness. XRD studies show the SiC had a disordering effect. TEM results showed that WC films had coarse porous structure, but films with a low silicon carbide content (approximately 10 to 25 at%) had a denser nanocrystalline structure. Samples with greater than 25% SiC were amorphous. The initial hardness increase at lower SiC contents correlated well with the observed densification, but the transition to an amorphous structure did not strongly affect hardness.

Potassium tantalate powders were hydrothermally synthesized at 100 to 200 °C in 4 to 15 M aqueous KOH solutions. A defect pyrochlore, Kta2O5(OH). nH2O (n ≈ 1.4), was obtained at 4 M KOH, but at 7–12 M KOH, this pyrochlore was gradually replaced by a defect perovskite as the stable phase. At 15 M KOH, there was no intermediate pyrochlore, only a defect perovskite, 0.85Ta0.92O2.43(OH)0.57 0.15H2O. Synthesis at higher KOH concentrations led to greater incorporation of protons in the perovskite structures. The potassium vacancies required for charge compensation of incorporated protons could accommodate water molecules in the perovskite structure.

Nanocomposite powders of Ni–Al2O3 (5 and 10 vol% Ni) were prepared from porous alumina preforms with high specific area (100 m2 g?1) impregnated with nickel nitrate. Samples were obtained by reduction under a controlled oxygen partial pressure either directly or through an intermediate step, giving nickel aluminum spinel. In both cases, homogeneous dispersions of nickel particles in the alumina matrix were achieved. The Ni particle size ranged from 10 to 100 nm, depending on the preparation conditions and temperature.

Phase composition, degree of cation ordering, and dielectric properties of complex perovskites with general formula Ba(B' 1/3B"2/3)O3, where B′ = Mg, Zn, and Ni and B" = Nb and Ta, were analyzed. It was found that all the studied complex perovskites attained high degrees of 1:2 cation ordering at temperatures specific to each composition. A high temperature order–disorder phase transition in Ba(Zn1/3Nb2/3)O3 occurred below 1380 °C. Ba(Ni1/3Nb2/3)O3 (BNN) and Ba(Mg1/3Nb2/3)O3 (BMN) pervoskites remained 100% ordered at temperatures as high as 1500 and 1620 °C, respectively. It was found that in BMN and BNN extrinsic factors, such as the second phase (i.e., Ba3Nb5O15) and point defects, dominated the dielectric loss at microwave frequencies. Ba(Mg1/3Ta2/3)O3 (BMT) remained single phase up to 1630 °C. Above this temperature, the Ba3Ta5O15 second phase was detected. A decrease in the 1:2 cation ordering and increase of dielectric loss in BMT occurred at sintering temperatures above 1590 °C. It was also revealed by electron paramagnetic resonance that all samples studied contained a substantial amount of paramagnetic point defects. These defects contributed to extrinsic dielectric loss at microwave frequencies, thus degrading the Q factor.

Intercalation of EuCl3 TbCl3, and AlCl3 into graphite was carried out in the presence of chlorine. The observation of products by x-ray diffraction showed that the extent of chloride intercalation could be controlled through adjustment of the pressure of chlorine; increasing pressure tended to increase the extent of intercalation. In the case of EuCl3, the extent of intercalation varied to show a stage transition. In contrast, TbCl3 intercalation gave a mixture of stage 2 or stage 4 graphite intercalation compound (GIC) and remaining graphite, where the extent of intercalation is revealed by the ratio of GIC to graphite. With respect to AlCl3 intercalation, although the preparation of stage 1, 2, and 4 GICs was successful, stage 3 and 5 GICs could not be obtained.

Low thermal conductivity ceramics in the ZrO2–GdO1.5 system have potential in structural (refractories, thermal barrier coatings, thermal protection) and nuclear applications. To that end, the thermal conductivities of hot-pressed xGdO1.5 ·(1 – x)ZrO2 (where x = 0.05, 0.15, 0.31, 0.50, 0.62, 0.75, 0.89, and 1.00) solid solutions were measured, for the first time, as a function of temperature in the range 25 to 700 °C. On the ZrO2-rich side, the thermal conductivity first decreased rapidly with increasing concentration of GdO1.5 and then reached a plateau. On the GdO1.5-rich side, the decrease in the thermal conductivity with increasing concentration of ZrO2 was less pronounced. The thermal conductivity was less sensitive to the composition with increasing temperature. The thermal conductivity of pyrochlore Gd2Zr2O7 (x = 0.5) was higher than that of surrounding compositions at all temperatures. A semiempirical phonon-scattering theory was used to analyze the experimental thermal conductivity data. In the case of pure ZrO2 and GdO1.5, the dependence of the thermal conductivity to the absolute temperature (T) was less than 1/T. Therefore, the minimum thermal conductivity theory was applied, which better described the temperature dependence of the thermal conductivity of pure ZrO2 and GdO1.5. In the case of solid solutions, phonon scattering by cation mass fluctuations and additional scattering by oxygen vacancies on the ZrO2-rich side and by gadolinium vacancies on the GdO1.5-side seemed to account for the composition and temperature dependence of the thermal conductivity.

Combinatorial chemistry was applied to the optimization of red phosphors used for plasma display panels. Quaternary and ternary combinatorial libraries were developed for (Y, Gd, Lu, Sc)BO3 and (Y, Gd)(BO3 PO4) systems. Our combinatorial chemistry system consists of solution-based combinatorial synthesis and characterization, enabling the swift scanning of luminance and of Commission Internationale de l'Eclairage (CIE) chromaticity under vacuum ultraviolet light excitation. As a consequence of the combinatorial approach, several new candidates were found to show higher luminance than the commercially available red phosphor for plasma display panels.

Electrospun nanofibers have applications in the areas of filtration, composites, biomaterials, and electronics. Controlling the surface properties of these nanofibers is important for many applications. Nanofibers can also be used as unique substrates for observing the growth of deposited films and creating nanoscale structures. In this work, electrospun poly(meta-phenylene isophthalamide) (MPD-I) nanofibers were used as substrates for creating nanoscale structures out of carbon-based materials and metals. MPD-I was used because it can be electrospun into nanofibers with diameters smaller than 10 nm and it has good thermal stability. MPD-I nanofibers were coated with carbon, copper, and aluminum using plasma enhanced chemical vapor deposition and physical vapor deposition methods. Some of the aluminum-coated nanofibers were then converted into nanotubes. Transmission electron microscopy was used to determine the thickness, uniformity, and grain size of the coatings on the fibers and the nanotubes.

Combustion synthesis/micropyretic synthesis is a technique in which material synthesis is accomplished by the propagation of a combustion front across the sample. In some cases, the combustion front may propagate in an unstable mode where the propagation velocity and combustion temperature of the combustion front are altered periodically. In this study, the processing conditions leading to unstable combustion reaction were first studied theoretically. The boundary temperatures separating stable and unstable reactions were then determined. The numerical analysis showed that the combustion temperature and the propagation velocity changed periodically during unstable combustion. As the combustion reaction became unstable, the average propagation velocity and the oscillatory frequency of front propagation decreased. The products of unstable combustion synthesis possessed the banded structures, implying the occurrence of the unstable oscillatory propagation, as demonstrated experimentally. In this study, high activation energy combustion (Ti + 2B reaction) and low activation energy combustion (Ni + Al reaction) were both chosen to illustrate the effect of unstable combustion. It is the first time the experimental and numerical results were combined to investigate the temperature and propagation velocity variations during unstable combustion.

Optimum conditions for the synthesis of nonagglomerated BaTiO3 particles by salt-assisted spray pyrolysis (SASP) were investigated. The effect of particle residence time in the reactor and salt concentration on the crystallinity and surface morphology of BaTiO3 was examined by x-ray diffraction and scanning electron microscopy. Mixtures of a metal chloride or nitrate salt, dissolved in aqueous precursor solutions, were sprayed by an ultrasonic atomizer into a five-zone hot-wall reactor. By increasing the salt concentration or the particle residence time in the hot zone, the primary particle size was increased, and its surface texture was improved compared to BaTiO3 particles prepared by conventional spray pyrolysis. The SASP-prepared BaTiO3 crystal was transformed from cubic to tetragonal by simply increasing the salt concentration at constant temperature and residence time. Further thermal treatments such as calcination or annealing are not necessary to obtain nonagglomerated tetragonal BaTiO3 (200–500 nm) particles with a narrow size distribution. Increasing the carrier gas flow rate and decreasing the residence time in the hot zone resulted in cubic BaTiO3 particles about 20 nm in diameter.

Thermal decomposition of supersaturated single-phase body-centered cubic (bcc) Fe100−xZnx (5≤ x ≤65 at.%) solid solutions, processed via mechanical alloying of high-purity metal powders, was investigated using x-ray diffraction and differential scanning calorimetry (DSC). At elevated temperatures the metastable solid solution decomposed into a stable equilibrium aggregate consisting of the pure bcc Fe phase and an intermetallic compound Fe4Zn9. The decomposition temperature decreased with increasing Zn concentration. The enthalpy of decomposition for various Fe–Zn solid solutions measured by the DSC was in the range of 1.2–3.5 kJ/mol. The enthalpy of mixing of the as-milled solid solutions from elemental Fe and Zn powders was estimated to be 0.5–1.7 kJ/mol. In addition, the activation energies of decomposition for these solid solutions were determined on the basis of the Kissinger analysis, and their values appeared to be independent of the Zn concentration in the alloy, with an average of 147 ± 17 kJ/mol.

The effect of particle volume fraction fp on the light transmittance of glass particle-dispersed epoxy matrix composites with a particle volume fraction of fp = 0.0001 to 0.4 was studied. The particle size used was much larger than the wavelength of light in a visible wavelength. The transmitted laser beam scattering pattern and light transmittance of the composites were obtained, and the transmitted laser beam pattern showed a broadening, which increased with an increase in particle volume fraction. This behavior appeared more remarkable in particles with smaller diameters. The light transmittance of the composite was affected by the particle volume fraction fp and was divided into two characteristic regions according to fp. For fp < 0.01, the light transmittance was slightly affected by the incorporation of the particles, while the light transmittance of the composite with fp > 0.01 was strongly affected by fp and size of the glass particle dp. The effects of fp and dp on the light transmittance are explained by the introduction of a normalized total surface area 〈 S〉 A guideline to obtain higher light transmittance of the composite is discussed based on the parameter 〈S 〉.