The mechanism of formation of titanium nitride by the self-propagating high-temperature synthesis was investigated. Samples were quenched in liquid argon at different stages of the reaction and analyzed by x-ray diffraction and electron microprobe methods. A mechanism is proposed in which the propagation of the reaction wave results in the formation of a thin surface layer of TiN and an unsaturated solid solution. The layer then dissolves to form a solid solution of nitrogen in titanium and then re-forms with continued reaction. On the basis of phase equilibria and diffusion information, an analysis is made in which the feasibility of the proposal mechanism is demonstrated.

Spinning condition dependences of the microstructures of a pitch precursor fiber which is a raw material for carbon fiber preparation were studied in detail. The degree of preferred orientation of the molecules in a pitch precursor fiber along the fiber axis was higher when spinning was done at a lower mesophase pitch viscosity. An intermediate diameter gave the highest degree of preferred orientation. The degree of preferred orientation of the molecules in an extruded pitch rod was especially low. The crystallite size Lc(002) of the pitch precursor fiber also was varied by controlling the spinning conditions, and exhibited a good correlation with the degree of preferred orientation. Mesophase pitch at a higher temperature possessed a smaller Lc(002) and a larger d002. The small Lc(002) observed at high temperature was maintained by a rapid cooling to room temperature, but the large d002 relaxed to a small value at room temperature, even with rapid cooling. A qualitative model for the formation of a preferred orientation through spinning is proposed.

Thin carbon films grown from a low pressure methane-hydrogen gas mixture by microwave plasma enhanced CVD have been examined by electron microscopy. Previously reported transmission electron microscopy (TEM) of the diamond films has shown that the majority of diamond crystals have a very high defect density comprised of {111} twins, {111} stacking faults, and dislocations. In this study, high resolution electron microscopy (HREM) has been utilized to lattice image individual defects in these polycrystalline diamond films. Interpretation of the images from these defects is not trivial and reported image simulations have been utilized to understand further these defects. Fivefold multiply twinned particles have also been examined and it was found that the 7.5° misfit present in such particles has been accommodated at the twin boundaries rather than by elastic deformation. This creates a twin boundary coincident with a low angle grain boundary which has been termed a “tilted twin boundary”. The density of defects in these particles is generally high; however, a dramatic reduction in the defect density near the twin boundaries was observed. This defect reduction is significant because if its origin can be determined, this information may be useful in producing higher quality diamond films.

An experimental silicon-containing benzocyclobutene thermosetting resin from DOW has been evaluated for use as a plasma etch stop in packaging applications. The thermal and etch properties of this particular resin (DOW UX-13005.02L) make it suitable for use as an etch stop. Further, a model for in situ laser interferometry is proposed. By applying the model to the laser interferogram, the initial etch rate and amount of material removed before etching ceases may be determined.

Results of a study of compositional, optical, electrical, and structural properties of hydrogen amorphous silicon carbide (a-SiC:H) prepared, respectively, by glow-discharge (GD) and reactive sputtering (SP) techniques at power densities varying between 1.25 · 10−2 and 1.25 · 10−1 W · cm−2 for GD samples are presented. Measurements are reported on the composition, optical and IR spectroscopy, and on the temperature dependence of electrical conductivity. All experimental observations suggest that the power density only slightly affects the physical properties of GD silicon-rich samples, whereas those of the carbon-rich SP samples depend more strongly on this deposition parameter. Finally, it is shown that the GD technique can provide films with better characteristics, whereas samples of similar composition prepared by sputtering have higher compositional disorder and are more inhomogeneous.

Oxidation of IrAl alloys (50-50 at.%) was conducted at 1300 and 1600°C in air for different times. Due to the outward diffusion of Al atoms and subsequent oxidation, the formation of Al2O3 is accompanied with the generation of an Ir-rich phase in the vicinity areas. The oxidation zone is separated from the bulk IrAl alloy by a phase boundary. In the oxidation zones, alternating layers of Al2O3 and Ir-rich phase are produced at 1300°C, while irregularly intertwined; Al2O3 and Ir-rich phase are produced at 1600 °C. The discontinuous formation of Al2O3 gives rise to internal oxidation of the IrAl alloys. The thickness of the Al2O3 layer is in the range of tens of micrometer, and it grows thicker as its location gets farther away from the free surface. The formation of an Al2O3/Ir-rich phase layered structure is discussed based on the diffusion kinetics of O, Al, and Ir, the chemical reactivities of Al and Ir with respect to O, and the nucleation and growth kinetics of Al2O3.

Al2O3 and Si3N4 ceramics were joined to titanium alloy (TA6V) and niobium by active brazing. Chemical reactions between the Cu-40Ag-5Ti braze alloy and these materials were examined, and interfacial reaction products were characterized by scanning electron microscopy and electron probe microanalysis. Results indicate the importance of studying the microstructural features of the joints in order to understand better their effect on the mechanical properties of the interface.

The microstructures of five different diamond films formed by plasma-assisted chemical vapor deposition have been studied by transmission electron microscopy. The films were selected for study based on differences in their surface morphologies. The preferred orientations inferred from the symmetries of the crystals observed on the surfaces of these films were consistent with those measured by x-ray diffraction. A general characteristic of all of the diamond film microstructures was stacking faults and microtwins on {111} planes, but the densities and the distributions of the defects varied widely among the films. The observations of microstructure indicate that when a crystal grows so that {100} facets are formed, stacking faults and microtwins are confined to regions near its boundaries, and when a crystal grows so that {111} facets are formed, stacking faults and microtwins are distributed throughout its volume. Under some deposition conditions the defects are confined to bands in the crystal, and coincidence of these defect bands with small steps on the crystal facets suggests that the steps may be caused by the intersection of the bands with the surface.

Auger electron spectroscopy and low energy electron diffraction have been applied to the study of the structure and thermal stability of the Pt/β–SiC(001) interface. The morphology of the interface appears to be governed by the competition among surface diffusion, intermixing, and chemical reaction. An ultrathin Pt layer (8 Å thick) deposited on a substrate at low temperature is laterally uniform with some degree of intermixing across the interface. Brief anneals at 1000 °C result in aggregation of the Pt into islands interspersed with essentially bare SiC. Higher temperatures lead to reaction of the aggregated Pt to form Pt silicide and release free C. The reaction is signaled by characteristic changes in the Si LVV and C KLL Auger line shapes and by the appearance in LEED of a (2 ⊠ 2) pattern (believed to arise from ordered PtSi) and of diffraction rings from oriented polycrystalline graphite. Subsequent deposition of Si and annealing leads to regeneration of SiC by reaction with the free C. These results contrast with those for ultrathin Pt on Si(001) and on α-SiC(0001) which are dominated by the rapid indiffusion of Pt during annealing. A detailed model is presented for the growth and annealing dependence of the Pt/β–SiC(001) interface.

Microhardness measurements were carried out on ion implanted single crystal Y2O3 stabilized cubic ZrO2. Inert gas ions (Ne, Ar, Xe) and N, Si, Ti, and W were implanted up to fluences of 3 × 1017 ions/cm2. Implantation energies were selected to give equivalent ranges. Comparison of the Knoop microhardness values of ZrO2 implanted with various species over a range of fluences showed that the principal variable causing hardness changes is damage energy and not the ion fluence nor the ion species. For all implants studied, the hardness versus damage energy gives a unified plot. At low doses the hardness rises with increasing deposited damage energy to a value 15% higher than that of unimplanted zirconia. With additional damage the hardness drops to a value 15% lower than that of the unimplanted zirconia. Friction and wear measurements in a pin-on-disk assembly showed very different behavior for high dose versus unimplanted ZrO2. The unimplanted samples showed debris with an associated rise in friction. The implanted system showed much less debris and a constant value of friction even after 10 000 cycles.

We have deposited diamond films on Si〈111〉 using hot filament assisted chemical vapor deposition at low pressures ∼25 Torr. Diamond films deposited at different relative concentrations of methane (ranging from 0.25% to 2.0%) in methane-hydrogen mixtures have been characterized by Raman spectroscopy, scanning electron microscopy, and x-ray photoelectron spectroscopy. With varying methane concentration, Raman spectra show features characteristic of crystalline diamond, diamond-like carbon, and polycrystalline graphite. Scanning electron micrographs show densely packed diamond crystallites. SEM measurements made on diamond films grown as a function of time show that the median grain size of the diamond crystallites increases linearly with time during the initial phase of the growth. X-ray photoelectron spectroscopy reveals differences between the diamond sp3 covalent bonding and sp2 graphitic bonding as well as the extent of s-p hybridization as a function of methane concentration. The plasmon loss shoulder, characteristic of graphite, is absent from the spectrum of 0.25% methane concentration film. But it appears in the XPS spectra of films grown at higher concentrations.

We present an investigation of the influence of four dopant lithium concentrations on the electrical properties of CuO. X-ray measurements have revealed a single phase formed up to 4.2 at. % of Li, and a second phase formed, Li2CuO2, in the case of 10.5 at. % of Li concentration. The log(ρ/T) vs 1/T data are better represented by two straight lines than by one and show an initial strong decrease of the conduction activation energies for small contents of Li (<1.7 at. %), which becomes weak for larger contents. The change in slope observed in the resistivity measurements as a function of temperature has also been investigated by calorimetric measurements, revealing a specific heat anomaly which can be associated with the antiferromagnetic order transition.

We have studied the weight loss during sintering and the resulting phase constituents and dielectric properties of a series of compositions in the lead-rich region of the PbO:MgO:Nb2O5 phase diagram near the stoichiometric composition of Pb(Mg1/3Nb2/3)O3 (PMN). While a ternary system of PbTiO3–Pb(CO1/3Nb2/3)O3–PMN was used, only the PMN component was varied in composition. The observed weight loss was ascribed to PbO evaporation from the nonstoichiometric PMN component. It was found that the sintered PMN compositions at about 1000°C correspond to the stoichiometric composition with varying amounts of excess MgO. These sintered compositions can be calculated by taking the Nb ion as the controlling cation in forming the PMN unit cell, from which the excess MgO can be determined. The excess PbO in the starting compositions, above the amount needed to form the sintered compositions of Pb(Mg1/3Nb2/3)O3 plus excess MgO, serves as a densification aid during the sintering process. Subsequently, the excess PbO is lost through evaporation. The peak dielectric constant of these compositions varies between 12000 and 18500, with the highest value attained in the sintered composition corresponding to stoichiometric PMN plus 0.229 mole of excess MgO. The optimum processing conditions for this composition are also identified.

Procedures are described to deposit uniform layers of yttria and yttria-alumina prccursors on fine powders and whiskers of silicon nitride. The coatings were produced by aging at elevated temperatures aqueous systems containing the silicon nitride core particles, yttrium and aluminum nitrates, and urea. Optimum concentrations of the core particles, in relation to the reactants, were established to promote surface deposition of the oxide precursors. Polymeric dispersants were used effectively to prevent agglomeration of the solids during the microencapsulation process. The morphology of the powders was characterized using scanning and transmission electron microscopy. The mechanisms for the formation of the coated layers are discussed. A description is provided that allows qualitative assessment of the experimental factors that determine microencapsulation by a slurry method.

Small-angle x-ray and neutron scattering experiments were performed in several polymer-containing portland cement pastes with the same w/c ratio. The nature of the results is discussed in terms of the role of the polymer upon the properties of the materials. A comparison with other works seems to indicate that the capillary pores are strongly affected whereas the gel porosity remains unchanged by the polymer solutions.

The ferroelectric to paraelectric phase transition in lithium niobate is examined. The present study focuses on the microscopic mechanism for this phase transition. Literature reports that give insight into this mechanism are reviewed. Two alternate mechanisms for this second order transition have been discussed previously. The phase transition has been proposed to occur by either (a) cooperative displacement of Li ions or (b) statistical disordering of Li between two octahedral sites in the structure. The present study develops a general Landau expression for the second order phase transition. The spontaneous polarization of the lattice is used as an indicator of the extent of transformation. Then both displacement and disordering models are explored. These are compared with the observed spontaneous polarization data. It is concluded that the spontaneous polarization data are indicative of a Li disordering model, rather than a Li displacement model.

An indentation-bend failure-stress method was used for measurement of R-curves in a series of PSZ ceramics with varying peak toughness. Dilatational transformation-stress constraints are included in the residual-stress driving force contribution to the applied stress intensity factor. A power-law fit to the form of the R-curve simplifies the analysis. While the resulting curves show the expected form, measured toughness values are high relative to the expected peak toughness. Limitations and the range of applicability of the indentation-bend technique are discussed.

The anisotropic powder metallurgy of n-type Bi2Te2.85Se0.15 doped with bromines was studied by both x-ray diffraction and thermoelectric measurements. The statistical orientation of platelet-like grains in the samples was characterized using the orientation factor estimated by the Lotgering formula from (0,0,1) x-ray diffraction intensities. It is demonstrated that the orientation factor which is strongly influenced by the hot-pressing conditions and the particle size of the starting material has a strong effect on the thermoelectric properties of the samples in this system. This implies that the powder metallurgy has the additional freedom of controlling the thermoelectric properties in addition to the doping level in the grains.

Results of room-temperature optical studies on ∼10 micron thick, free-standing diamond films are reported. The films were grown on Si(100) substrates by hot filament-assisted chemical vapor deposition (CVD) from a methane/hydrogen mixture. The as-grown, free surface of the films exhibited a surface roughness of scale σ ∼ 0.2 to 5 microns, depending on the methane/hydrogen mixture, which introduces significant optical scattering loss for frequencies greater than 0.5 eV. Specular reflection and transmission spectra in the range 0.01–10 eV were collected. Below the threshold for interband adsorption near ∼5 eV, the films studied behaved approximately as thin parallel plates of refractive index 2.4, with the rough free surface leading to increasingly larger loss of specular transmission/reflection with decreasing wavelength. Structure in the mid-infrared transmission spectra was observed and attributed to disorder-induced one-phonon absorption, intrinsic multi-phonon absorption, and infrared active –C–H2 stretching modes. The strength of the C–H band was observed to increase with increasing methane pressure in the growth chamber. At 5.3 eV, the onset of interband absorption was observed, in good agreement with the value of the indirect bandgap in type IIa (intrinsic) diamond.

We describe an algorithm for computing the motion of a solid-liquid interface in 2D, which is applicable to geological pressure solution or to pressure sintering. The backward motion (toward the solid) of the interface is due to dissolution of the solid, and the forward motion (away from the solid) is due to the inverse process of reprecipitation. The interface velocity is assumed proportional to the difference between the solubility of the solid and the concentration of the solution. The former is dependent upon stress (the phenomenon of “pressure solution”), so our algorithm must also keep track of the stress. We use a Lagrangian grid, with constant-stress periodic boundary conditions. The method has been applied to porosity reduction in sandstone. It is applicable to other interface-following problems, such as freezing, if the motion is slow enough that heat transport is not rate-limiting.