Electrical conductivity of cementitious materials with a wide range of chemical compositions has been studied during the first 24 h of hydration. Relationships between heat of hydration and electrical conductivity curves are discussed. Results are tentatively explained in terms of some physical and chemical parameters. Further evidence that the electrical conductivity of hydrating cement pastes is related to the hydration mechanisms operating in these systems was obtained. The order in which the cations of inorganic admixtures (chlorides and hydroxides) were found to increase the peak and rate of development of the electrical conductivity is the same order that they have been found to increase the heat liberated upon hydration of systems containing these admixtures.

We prepared and characterized PbO–MgO–Nb2O5 ceramics near the Pb(Mg⅓Nb⅔)O3 stoichiometric composition. We examined microstructures, sintering behavior, and phase compositions in this system and prepared several new compositions, which have a single phase perovskite structure and a high dielectric constant (28000), by low sintering temperature (950–1020 °C). These compositions have a high electrical resistivity (1013 ohm-cm), which is about 1000 times higher than those of Pb(Fe½Nb½)O3 and Pb(Fe⅔W⅓)O3 based ceramics. The new compositions can be readily prepared into a single phase perovskite without a detectable amount of pyrochlore second phase by a simple method of mixing and calcining the constituent oxide and carbonate powders. Our dielectric measurements and XRD data establish the correlation between the decrease in dielectric constant and the presence of pyrochlore second phase. The effects of PbTiO3 dopant were quantitatively measured and our data showed that at a low (10 mole %) PbTiO3 concentration, the Curie temperature increases 6.6 °C for every mole % PbTiO3 dopant in the new compositions. The dielectric constant increases from 18000 in the undoped composition to 27 100 and 29000 by a PbTiO3 dopant concentration of 5% and 10%, respectively. The maximum dissipation factor also decreases from 0.10 in the undoped composition to 0.055 in the 10% PbTiO3 doped composition. The electrical resistivity, ρ, decreases with the PbTiO3 dopant concentration, t, following the ρ = ρ0 exp (–t/t0) relation where ρ0 ≍ (9.6 ± 0.2) × 1012 Ωcm and t0 ≃ 0.044.

Infrared absorption spectra have been used to characterize OH− and OD− ions at the surface and the bulk of undoped CaO, lithium doped CaO, and SrO crystals. Diffusion of deuterons from D2O vapor into these crystals was performed at elevated temperatures. Diffusion coefficients were obtained to be D (CaO) = 3 ⊠ 10−6 cm2/sec at 1773 K and D (SrO) = 4 ⊠ 10−7 cm2/sec at 1523 K. For the doped CaO crystal with lithium concentration of 310 ppm, the diffusion coefficient was measured to be D (CaO:Li) = 4 ⊠ 10−7 cm2/sec at 1473 K and the activation energy in the Arrhenius equation was estimated to be 1.7 eV.

The Young's modulus of silica aerogels is measured, using the three point flexural technique. Various parameters have been investigated, such as the concentration of silicon compounds as well as the catalyting conditions used to develop the initial alcogel and the heat treatment performed to densify the material. The elastic behavior of aerogels depends on the conditions of gel preparation, and the Young's modulus is shown to obey the power dependence E ≃ ρ3.7. This scaling exponent is compared to the percolation model predictions. On the other hand, the elastic behavior of different sets of aerogels is related to the spatial arrangement of the particles pointed out by fractal features.

Silicon-29 NMR is used to study the structural intermediates in tetramethyl and tetraethyl orthosilicate (TMOS and TEOS) low pH sol-gel reactions. Differences in the number of compact ring structures are related to differences in gel times. Reactions are followed at various silicon: water: acid molar ratios.

We studied the effects of 15 dopants on the dielectric properties of the Pb1–x–yMgxNb2yO1+4y perovskite system. The investigated dopants are Ba, Ag, La, Bi, and Nd, which substitute in the Pb sublattice, and Co, Ni, Zn, Mn, Cr, Dy, Al, Fe, Zr, and Ti, which substitute in the sublattice occupied by Mg and Nb. While the dielectric constants of Pb1−x–yMgxNb2yO1+4y) are not affected by Al, Zr, and Ni dopants, their dielectric constants are increased by Ti dopant and decreased by other dopants. The rates of change in the Curie temperatures of Pb1–x–y MgxNb2yO1+4y with different dopant concentrations were quantitatively measured. The relative effectiveness of these dopants in altering the Curie temperature is correlated to the bond strengths between oxygen and the dopants in either the Pb sublattice or the Mg/Nb sublattice. The effects of these dopants on the dissipation factors and electrical resistivities were investigated. Cobalt and manganese oxides were identified as the most effective dopants in reducing the dissipation factor and lanthanum and barium oxides are effective in increasing the resistivity. We have also observed that zinc oxide promotes densification and reduces the temperature coefficient of capacitance in these compositions. Ternary and quaternary systems based on selected combinations of these dopants were prepared and characterized. Compositions in the Pb(Zn⅓Nb⅔)O3 + Pb(Co⅓Nb⅔O3 + PbTiO3 + Pb1–x–yMgxNb2yO1+4y quaternary systems were shown to be promising candidates for capacitor applications. Furthermore, multilayer capacitors of these promising compositions were fabricated and they were shown to have favorable device properties.

The passivation characteristics of various insulators are evaluated for the β–SiC surface. It is found that wet thermal oxides yield minimum electrical defects at the oxide-SiC interface. Dry thermal oxide results in too much charge either at the oxide-SiC interface or in the bulk. It is also shown that anodic aluminum oxide seems to possess suitable electrical properties for the fabrication of MOS structures on SiC, whereas the CVD silicon nitride proved to be the worst.

In current processes of diamond growth, the substrate temperature is in general around 600–900 °C. In the case of diamond-like carbon, the substrate temperature is lower, around 25–200 °C. There are many superior properties of diamond compared with diamond-like carbon; however, the high temperature requirement to grow diamond precludes many technologically important substrate materials such as zinc sulfide for an infrared window or electronic devices on which protective diamond layers are to be coated. The present approach is a hot filament DC glow discharge of hydrocarbon gases. A graphite hot filament cathode is inserted in a discharge cylinder tube anode. The discharge voltage is in the range of 50 to 250 volts at a methane gas pressure of about 100 microns. A negative biased voltage of 100 volts is applied between the cathode and the substrate. A magnetic field of 1 kG is applied near the cathode-anode assembly. At a substrate temperature of 200–400 °C, the deposited film on silicon crystal is confirmed by an electron diffraction pattern to consist of microcrystalline diamond.

Raman spectra are reported for consolidated nanophase TiO2 particles in their as-compacted state and after annealing at a variety of temperatures up to 1273 K. The Raman-active bands normally observed for the rutile form of TiO2 were present in as-compacted samples having average grain sizes in the range from about 10 to 100 nm. However, significant broadening of these bands was found, which was uncorrelated with initial grain size, but not necessarily with other synthesis-related factors. This broadening decreased upon isochronal annealing at elevated temperatures in air. Based upon these observations, it is concluded that nanophase TiO2 in the as-consolidated state contains significant defect concentrations within the rutile grains and that these intragrain defects and the grain-boundary regions as well have local atomic structures with the rutile symmetry, albeit with some short-range displacements. Some sporadic sample regions containing small amounts (<5%) of the anatase form of TiO2 were also found; these traces of anatase transformed to rutile upon annealing in air at temperatures above 883 K.

The fluoride anion has been shown to be one of the most effective catalysts in accelerating the polycondensation of alkoxide-derived silica gels. A detailed pore analysis study has been employed to investigate the effect of NaF on the pore structure of the resulting xerogels and its evolution during thermal heat treatment up to 800 °C. Addition of NaF to tetramethylorthosilicate-sols leads to an increase in average pore size, and the pore size distribution becomes narrower. By changing the fluoride concentration and the heating temperature, the surface properties of the xerogels can be tuned over a wide range. The possible application of the F− anion catalyzed sol gel process to prepare porous host materials for the studies of fluids in restricted geometries is also discussed.

Electrodeposition from molten-salt systems has been studied extensively as a method of producing both polycrystalline and single-crystalline materials. In this work, the thermodynamic aspects of the electrodeposition process are examined in a number of cases in which the molten-salt system behaves effectively as an oxygen-transporting medium, with particular reference to the thermodynamic properties of the melt. It is demonstrated how information gained from the construction of the appropriate isothermal phase diagram may be used to control and/or rationalize the behavior found in a given melt system on electrolysis.

A new method of producing alumina powder is described. Aluminum basic acetate is first synthesized from alkoxide precursor. The chemical reactions which control the precipitation of this salt are followed, using IR spectroscopy. Alumina powder is obtained by further thermal decomposition, and the thermal evolution of the precipitate is studied.

Molecular dynamics simulations (MD) employing multibody potentials were used to simulate sodium trisilicate glass (Na2O·3SiO2). A multibody term has been added to a pair potential in order to incorporate the bond directionality which is expected for the partially covalent silicate structure. The structure of the glass was analyzed and results were compared to those found using two-body potentials and molecular statics, as well as to experimental results found using x-ray diffraction, XPS, NMR, and EXAFS. Current results compared favorably to experiment and showed improvement over results obtained using two-body potentials. Nearest neighbor distances and coordination numbers agreed well with published data. Although two-body potentials normally show overcoordinated silicon (>4.3) and broad O–Si–O tetrahedral angle distributions, in this study all silicon exhibited tetrahedral coordination (4.0) and the O–Si–O bond angle distribution was markedly sharpened. The number of nonbridging oxygens was shown to be nearly equal to the number of sodium ions present, and a reasonable distribution of Qc species was found. The overall structure closely resembled the modified network structure of glass proposed experimentally, with silicon tetrahedra remaining intact and sodium ions breaking up the network through the creation of nonbridging oxygens.

Iridium oxide films deposited on Ti-alloy stimulation electrode wires by rf sputtering exhibit markedly different surface morphologies and redox capacities in response to variations in applied substrate bias potential. Films deposited with a −20 volt bias were relatively smooth and featureless whereas those sputtered with a +20 volt bias were comprised of closely packed 1 micron long platelets. Intermediate substrate biases revealed a gradual progression from the smooth surface to one sparsely populated with particles to a morphology comprised of tightly packed platelets. The electrochemical properties of the films are strongly dependent on the substrate bias employed during deposition. As the DC bias was increased from −20 volts to +20 volts the anodic and cathodic charge capacities determined by cyclic voltammetry decreased linearly from 36 to 12 mC/cm2.

The growth mechanism for small precipitates of Al2O3 formed by internal oxidation in the Nb–Al2O3 interface is studied in detail. The observations show that the Nb (001)/Al2O3 (00.1) interface is almost atomically flat and that there are no interface compounds. We suggest that the final layer on the Al2O3 side of this interface consists of oxygen atoms. The effects of image forces on misfit dislocations are found to result in a standoff distance between dislocation cores and the interface, in good agreement with the recent theory. The implications of this for the strength of metal-ceramic bonding are discussed.

A new Monte Carlo simulation procedure is developed for the initial stages of sintering of randomly packed particles. This simulation takes into account the possibility of crack initiation due to the stresses generated by the sintering particles and can accommodate both localized stresses and stress propagation. This procedure is used to investigate the sintering of two-dimensional aggregates of copper particles, and the results are compared with the results of model experiments available in the literature. The two-dimensional simulations presented here lead to shrinkage in area, decreases in perimeter, and particle rearrangements that are physically consistent with the expected behavior and experimental results. The proposed procedure can be extended to accommodate more complex features of sintering and to account for the material-dependent effects of stresses. It can also be used as a probe of sintering of bulk materials with random microstructure and to identify and design model experiments.

Alkali metal ion exchange isotherms at a total ionic strength of 0.001 M were determined at 25 °C on a 1.13 nm anomalous [Al3+ + Na+]-substituted tobermorite with the formula, Ca5Na0.75Al0.9Si5.1O16(OH)2 · 6.03H2O. The Kielland plots of Na+/K+, Na+/Rb+, and Na+/Cs+ exchange reactions showed straight lines. The slopes were steeper for Cs+ and Rb+ exchange reactions, as compared to K+ exchange. The cation-exchange selectivity for alkali metals was found to increase as follows: Cs+>Rb+>K+>Na+. A new evaluation method of the separation factor (αMN/KMd/KNd,Kd: distribution coefficient) for a combination of two cations at infinite dilution was proposed in terms of the selectivity coefficient (KMNa) which can be easily determined from the Kielland plot. An extremely large separation factor for Cs (αCsNa = 112) was found at infinite dilution. These basic studies of cation exchange selectivity are of relevance in cation separation and purification and nuclear waste disposal.

In the present work we characterize sputtered iridium oxide films (SIROF) by differential scanning calorimetry (DSC), x-ray, and impedance spectroscopies. We show that a crystallization transition occurs at ca, 230 °C, and suggest a bilayer model for the sputtered film. The transition results in a crystalline mixture of iridium metal and iridium oxide; this suggests a decomposition-crystallization process of the type 2Ir2O3 ⇉ Ir + 3IrO2. In the bilayer model proposed by us, the layer closer to the substrate would reflect the combined influence of the sputtering conditions and of the substrate, while the properties of the second layer depend on the sputtering conditions alone. The bilayer structure is supported by results obtained by impedance spectroscopy.

A periodically inhomogeneous medium is constructed by stacking up unit cells made of (identical) structurally chiral slabs. Each structurally chiral slab is comprised of a certain number of identical biaxially anisotropic plates, the consecutive optic axes describing either a right- or a left-handed spiral. The characteristic matrix of the unit cell is obtained and used with the Floquet-Lyapunov theorem to obtain the electromagnetic fields in the periodic medium. When the unit cell thickness is very small compared to the principal wavelengths in the biaxial plates, the periodically inhomogeneous biaxial medium is shown to be equivalent to a homogeneous biaxial medium, the two optic axes of the equivalent medium being dependent on the handedness of the periodic medium.

Barium aluminosilicate glasses are being investigated as matrix materials in high-temperature ceramic composites for structural applications. Kinetics of crystallization of two refractory glass compositions in the barium aluminosilicate system have been studied by differential thermal analysis (DTA), x-ray diffraction (XRD), and scanning electron microscopy (SEM). From variable heating rate DTA, the crystallization activation energies for glass compositions (wt. %) 10BaO–38Al2O3–51SiO2–1MoO3 (glass A) and 39BaO–25Al2O3–35SiO2–1MoO3 (glass B) were determined to be 553 and 558 kJ/mol, respectively. On thermal treatment, the crystalline phases in glasses A and B were identified as mullite (3Al2O3 · 2SiO2) and hexacelsian (BaO · Al2O3 · 2SiO2), respectively. Hexacelsian is a high-temperature polymorph which is metastable below 1590 °C. It undergoes structural transformation into the orthorhombic form at ∼300 °C accompanied by a large volume change which is undesirable for structural applications. A process needs to be developed where stable monoclinic celsian, rather than hexacelsian, precipitates out as the crystal phase in glass B.