The ac electrical behavior of yttria doped with a zirconia concentration ranging from 0.15 to 20 mole % is investigated in the temperature range of 800 to 1300 °C. The ac electrical data, obtained in the range from 5 Hz to 13 MHz, indicated two distinct relaxations when analyzed in the impedance plane. These relaxations are attributed to lumped grains and trapping within grain boundaries, including possible electrode/sample effects. The admittance plane analysis revealed a semicircular relaxation in the low-frequency region, indicating identical response to that of the low-frequency relaxation of the impedance plane. The incorporation of zirconia into yttria is found to lower the activation energy of conduction in the grains and enhance ionic contribution to the overall electrical conduction. The PO2 studies and transference number measurements near atmospheric region indicate that p-type conduction dominates for the lightly doped yttria. An ionic contribution to the conduction processes becomes significant in heavily doped samples at/near atmospheric PO2.

We have used a combination of techniques to examine modifications in the structural characteristics of carbon nanofibers produced from the interaction of cobalt and copper-cobalt powders with ethylene at temperatures over the range 425 to 700 °C. The nanofibers generated from the interaction of cobalt with ethylene at 600 °C were found to be highly crystalline in nature. Incorporation of as little as 2% copper into the cobalt created a major modification in the conformation of the solid carbon deposit, which was composed of multiple nanofiber limbs emanating from a single catalyst particle, and in this state the carbon structures tended to be disordered. As the composition of the bimetallic was progressively changed to the point where copper became the major component, there was a significant increase in the degree of crystalline perfection of the nanofibers even though they maintained their multidirectional form. The transformation in structural characteristics of the carbon nanofibers is rationalized, according to a concept wherein the crystalline order of the deposit is related to the wetting properties of the bimetallic particles with graphite.

Nanocrystalline copper powder was produced by a NaBH4 reduction of CuCl in a simple solution phase room temperature reaction. Uniaxial hot pressing in a closed tungsten die was used to compact powder into dense specimens. Samples were analyzed by x-ray diffraction, precision densitometry, electron microscopy, energy dispersive x-ray analysis, and selected area diffraction. Mechanical properties of the consolidated samples were determined by microhardness measurements, three-point bending of rectangular specimens, and compression tests. Yield strength measured for nanocrystalline Cu in the present work was over two times that reported in literature for Cu with comparable grain size and over five times that of conventional Cu. Restricted grain growth observed in the hot-pressed samples and improved mechanical properties are attributed to the presence of boron. A unique method of obtaining homogeneous in situ nanosized reinforcements to strengthen the grain boundaries in nanocrystalline materials is identified.

Nanocrystalline copper produced by a solution-phase chemistry approach and compacted by hot pressing was subjected to room temperature deformation. Uniaxial compression and rolling were used to deform the samples to °90% reduction in thickness. Samples were subjected to several heat treatments to study microstructure and property evolution as a function of heat treatment. Thermal response of the as-pressed and deformed nanocrystalline Cu was also studied by differential scanning calorimetry. Optical metallography, scanning and transmission electron microscopy, and selected area diffraction were used to characterize microstructures after heat treatments. Samples exhibited an endotherm upon heating at 322 °C which was reversible upon cooling. This was attributed to either dissolution and formation of Cu–B precipitates or the diffusion of B from the grain boundaries to the bulk and back to the grain boundaries. Exaggerated recrystallization occurs in the temperature range of 399–422 °C. Samples maintained high dislocation density, deformation bands, and fine grain size up to 322 °C. Beyond the recrystallization temperature, grains grew at a faster rate to submicron or micron levels. The strain hardening observed in the samples of the present study is attributed to the presence of boron. Two mechanisms are suggested for the role of B: (i) segregation of B to the grain boundaries leading to strengthening of grain boundaries, and (ii) formation of Cu–B nanoprecipitates leading to precipitation strengthening.

A new method was developed to determine the eutectoid temperature, Ac1, of carbon steel during laser surface hardening. In the method a three-dimensional heat flow model with temperature-dependent physical properties was set up and solved for the temperature distribution employing a finite element method (FEM). Workpieces were heat-treated to produce a melted and hardened zone by a single pass of a continuous-wave TEM00 CO2 laser beam. The depth profile of the melted zone was used as a calibrator to solve the uncertainty imposed by the unknown surface absorptivity. Obtained was an Ac1 of, on average, 770 °C, a superheat of 47 °C compared to the equilibrium Ac1 of 723 °C. Furthermore, the numerical model was also employed to predict the hardened depth, and the results show that, for a depth of more than 100 μm, the eutectoid temperature 770 °C leads to a depth about 10% smaller than that predicted at 723 °C. The use of the temperature-dependent physical properties is critical; an error up to 80% could result if constant physical properties are used.

We report the microwave dielectric properties of composites made of nickel-coated graphite fibers in two different types of silicone polymers. The influence of matrix viscosity on the fiber alignment, fiber filamentation in the composites, and how those affect the permittivity and loss tangent of the composite are discussed. The dependence of the permittivity and loss of the composites on the permittivity and loss of the matrix will also be compared.

A nanocrystalline α–Fe2O3 particle/oligomer hybrid can be synthesized by polymerization of iron (III) 3-allylacetylacetonate (IAA) followed by in situ hydrolysis. The polymerization of IAA was dependent upon the polymerization temperature and solvent. GPC measurement showed that the polymerization degree of the IAA oligomer ranged from ∼3 to ∼6. The magnetic particle/oligomer hybrid was synthesized by hydrolysis of the IAA oligomer under a neutral or alkaline condition. Crystalline particles from 10 to 40 nm were finely dispersed in the oligomeric matrix, depending upon the hydrolysis conditions. The nanocrystalline particles below 10 nm in diameter were identified to be α−Fe2O3 by electron diffraction. The nanosized α−Fe2O3/oligomer hybrid was found to show superparamagnetic behavior.

Selsing's formula for radial tension at the particle-matrix interface is extended into a general formula which includes the effects of the amount of dispersed particles. A relationship is derived between individual volumes of strained unit cells in the crystal lattices of the particles and of the surrounding matrix. These relationships are used to predict the effect of the particles (2H−TiB2, 2H−ZrB2, and t−WB) on their unit cells and on the unit cell of the surrounding 6H–SiC matrix. The precision of these predictions was 7.1% or better. Hence, in principle, it is possible to investigate the distributions of residual bulk stress/strain. Estimates of characterizing values of the three composite systems are attempted on the rough basis of the elastic constants of the SiC matrix, confirming the physical validity of this approach as a first approximation. Further, the residual bulk strain energies of the particles and the matrix are discussed in connection with the elastic term involved in the fracture energy of such composites.

A glass of 47.5BaO · 47.5B2O3 · 5Al2O3 (in mol%) having a shorter optical absorption edge (∼236 nm) and suitable glass formation was selected as the mother glass for studying the surface crystallization of β−BaB2O4 · β−BaB2O4 was not the main surface crystallized phase when only a conventional heat treatment was applied. Crystallization of β−BaB2O4 was stimulated due to ultrasonic surface treatment with an ethanol suspension of β−BaB2O4 particles and subsequent heat treatment. After the ultrasonic treatment, β−BaB2O4 was the main crystallized phase. Transparent and dense β−BaB2O4 thin films/glass showed second harmonic generation. The tensor components of the second-order nonlinear optical susceptibility were estimated.

In 1993, a new beryllium bearing bulk metallic glass with the nominal composition Zr41.25Ti13.75Cu12.5Ni10Be22.5 was discovered at Caltech. This metallic glass can be cast as cylindrical rods as large as 16 mm in diameter, which permitted specimens to be fabricated with geometries suitable for dynamic testing. For the first time, the dynamic compressive yield behavior of a metallic glass was characterized at strain rates of 102 to 104/s by using the split Hopkinson pressure bar. A high-speed infrared thermal detector was also used to determine if adiabatic heating occurred during dynamic deformation of the metallic glass. From these tests it appears that the yield stress of the metallic glass is insensitive to strain rate and no adiabatic heating occurs before yielding.

The magnetic softness of nanocrystalline materials prepared from amorphous precursors is attributed to the average of the local magnetocrystalline anisotropy of the individual crystallites. In the present paper we have studied the effective magnetic anisotropy of Fe-based nanocrystalline samples with different microstructures. These microstructures were produced by using different heating rates when crystallizing the precursor material by means of continuous heating treatments. From the results of our study of the magnetic properties of the samples, carried out from the measurement of the bias field dependence of the transverse susceptibility, it was possible to discern the occurrence of intergranular coupling and to evaluate the typical dimensions of the coupled units. Since these dimensions were larger than the characteristic length of the microstructure, we suggest that the enhancement of the soft properties is linked to the decrease of the microstructure-magnetization interactions originating in large units of coupled magnetic moments.

Optically clear monolithic (OCM) gels of mesoporous aluminosilicates (average pore diameter 3.6 nm) and alumina (6 nm) have been prepared by slow hydrolysis-polycondensation of alkoxides and converted into OCM mesoporous glasses by heating. In order to change the properties, different ways of modifying the pore size and structure are proposed. We show that addition of boron oxide reduces the average pore diameter. A higher effect can be obtained by addition of a surfactant. In this case the mesoporous matrix becomes microporous (d < 2 nm). Another way of modifying the pore structure consists of introducing nanoprecipitates inside the porosity by an impregnation process. Modifications of the porous structure are different in alumina and aluminosilicates.

The mechanical properties of many polymers are known to change as they absorb water. This fact has been used to monitor the absorption of water into the surface layers of an epoxy adhesive with a depth sensing indentation system. Two methods have been demonstrated. The sample can be immersed in water for a period of time and then removed and tested in air. Alternatively, the sample can be tested in in situ. In the second method the transport of water through the adhesive can clearly be seen in hardness/depth profiles. Hardness, elastic modulus, and creep strain of the adhesive change with time until a stable value is reached, which corresponds to full plasticization of the adhesive to the influence depth of the indenter. The initial mechanical properties of the epoxy are mostly recovered on drying.

We present the derivation of the elastic Green's function for an anisotropic bimaterial in a state of plane strain. A Fourier transform method is used to calculate the Green's function. A discontinuity in displacement is permitted across the interface between the two solids. This provides a useful functional form for parameterizing damage along an interface. We show several examples for the form of the displacement discontinuity and calculate the displacement Green's function for each. The Green's function derived here is applicable to a variety of interface problems between two different anisotropic solids or for two similar solids at different orientations.