In the combustion synthesis of TiC-Al2O3 composites from TiO2, Al, and C, different types of precursors, i.e., anatase and rutile TiO2, and graphite and carbon black were used. The measurements of combustion wave velocity showed that the reactivity was higher with graphite as a carbon source and anatase as a TiO2 source. This was also confirmed by analyzing the degree of conversion of reactants to products. For the precursors investigated, the wave propagation of the 3TiO2-4Al-3C system diluted by Al2O3 showed that the limit of wave propagation was more dependent on carbon source than on TiO2. The wave front of all the samples proceeded in unstable combustion mode. Temperature profiles in the reaction zone suggested that the heat-affected zone was broader in the case of graphite carbon source than carbon black. The microstructures and chemical composition of the products were also studied.

The effect of fiber orientation on the matrix plasticity and fracture behavior of SCS-6 fiber-reinforced Ti-15V-3Al-3Cr-3Sn composites was studied. The laminates used in this study were [0]6, [0/±45]s, and [90/±45]s. Three-point bending tests were conducted on chevron-notched specimens to determine the crack initiation energy, fracture toughness, and fracture strength as a function of notch length. The critical energy release rate was determined from the slope of the crack initiation energy versus notch length curve. The damage evolution and development of the matrix plastic deformation zone at the notch tip during the crack initiation and propagation as a function of fiber orientation were also determined. The relationships among the crack-tip matrix plastic deformation zone size, the critical energy release rate, and notch strength of the composites were discussed.

Pulsed-laser light was used to generate internal flaws in fused quartz. The size of the flaw produced was proportional to the amount of laser pulse energy above a threshold value of 2.5 mJ. Specimens of different flaw sizes were tested at room temperature under four-point bending. The bending strength decreased as the flaw size increased, and a Griffith relationship was established between the lateral flaw size and the critical stress at the flaw tip. Characteristic demarcation lines were observed on the fracture surfaces of specimens with a flaw size greater than 0.25 mm. It is suggested that the formation of the demarcation line is caused by a discontinuous change of stress intensity in the dynamic process of the crack propagation.

Infrared absorption measurements have been used to study the radiation response of various hydroxyl point defects present in natural quartz crystals in their unswept, Na-swept, and H-swept conditions for “low-H” and “high-H” samples with similar aluminum concentration. The irradiation was done at 77 K, 300 K, and finally again at 77 K in sequence. At low-temperature irradiation the Al-OH− bands equalize in their intensity-like H-swept or prior 300 K-irradiated cultured quartz. Among other major bands the alkali-related centers show a reduction in their strength at all stages of irradiation. Purely H-related centers show no steady-state room temperature effects; only the low-temperature irradiation reduces their band strength. The results have been discussed in terms of proton and alkali ion motion to shallow and deep traps and compared with cultured quartz.

Fine particles of a hydrogen storage alloy (LaNi3.8Co0.5Mn0.4Al0.3) were microencapsulated with a thin film of nickel of about 0.6 μm thickness. The microencapsulated alloy powders were used as an anode material in a sealed nickel/metal hydride battery. The battery characteristics were compared with those of a battery with a bare (uncoated) alloy anode. The battery using the bare alloy was less stable compared to the coated alloy due to the role of the coated nickel as an oxygen barrier for protecting the alloy surface from oxidation. In addition, charge-discharge characteristics were improved greatly by the nickel coating, especially at high rates and at low temperatures due to the role of nickel as a microcurrent collector. So the microencapsulation of the alloy powders improves the performances of the alloy electrode.

A method that determines the work done in shearing atom pairs straddling the slip plane, Φ, during emission of dislocations from a crack tip in an atomic model is presented. The model is based on an EAM-type potential for nickel. The dislocations are emitted as partials, and the disregistry, Δ, across the slip plane is found to be fit accurately by a simple arctan function of position for each partial. The width of the partials is also found to remain essentially constant as they are emitted and move away from the crack tip. Rice's unstable stacking energy is extracted from the Φ - Δ curves for the atom pairs along the slip plane and is observed to vary somewhat, particularly near the crack tip. In addition to the Φ (Δ) at points on the slip plane, the total work done on the entire slip plane is determined as a function of the dislocation position in the spirit of the Peierls approach. The derivative of this total work with respect to dislocation position leads to the lattice resistance, ŝr. The first partial dislocation to be emitted experiences a maximum in ŝr at about 0.2 nm from the crack tip, and several contributions to the overall resistance can be identified including the creation of a new surface at the tip as emission occurs, the creation of stacking fault as the dislocation glides away from the tip, and a small but discernible periodic component with a period related to the lattice. A string of hydrogen interstitials is introduced at various locations in the lattice and its effect on Δ, Φ - Δ curves along the slip plane, and the lattice resistance is examined. A substantial effect on the unstable stacking energy results as the dislocation passes an interstitial on the slip plane, but the effect of an interstitial on the resistance to dislocation emission expressed in terms of the maximum ŝr is small and then only if it is confined to a region very near the crack tip. The significance of these results is discussed together with some additional observations including dislocation pinning on the interstitials.

Chromium-carbon coatings have been deposited on various substrates by direct sputtering of a chromium carbide, Cr3C2, target in pure argon atmosphere. The composition of coatings determined by Rutherford backscattering spectroscopy and the deposition rate were investigated as functions of the sputtering gas pressure and self-bias voltage applied to substrates. The atom number ratio C/Cr in the coatings was equal to 0.7 regardless of the deposition conditions investigated. Oxygen and argon atoms were the major impurities incorporated in the amorphous coatings. Oxygen-free Cr-C coatings were prepared at low argon pressures or on substrates biased to a voltage in the range −100 to −320 V. The Cr-C coatings deposited on biased substrates contained less than 2 at. % of argon. The morphological features of Cr-C coatings examined by scanning electron microscopy were also dependent on the sputtering gas pressure and bias voltage of substrates. Fully dense structures were observed for coatings deposited at low argon pressures or on biased substrates. The electrical resistivity of Cr-C coatings was extremely dependent on the concentration of oxygen atoms incorporated in the coatings. Oxygen-free Cr-C coatings exhibited electrical resistivity values as low as 120 μΩ cm, i.e., less than twice the bulk resistivity of Cr3C2. The residual stresses in the coatings and microhardness of the deposited material were also investigated as functions of the deposition parameters. Tensile residual stresses were lower than 0.8 GPa, and the maximum microhardness of coatings was about 13000 MPa, i.e., similar to that of the bulk material.

Graphite fiber intercalation compounds were prepared by immersing graphitized thin vapor-grown carbon fibers (VGCF's) with diameters less than 0.5 μm into liquid bromine. The composition of Br2-intercalated VGCF was C70Br-C90Br. The powder resistivity of Br2-intercalated VGCF was estimated as 1/3 of pristine VGCF. An electroconductive plastic composite was prepared by mixing phenol resin with that of bromine intercalated VGCF as a conductive filler, and its electrical properties were investigated. The resistivity of a Br2-intercalated VGCF composite was 1.1 × 10−2 Ω · cm at room temperature, which is about 50% of pristine VGCF composite. Br2-intercalated VGCF-based composite had a high degree of stability against exposure at 150 °C in air and at 85 °C with 90% humidity for 500 h. Br2-intercalated VGCF-based plastic composites could be used as highly electroconductive materials.

Low temperature photoluminescence measurements were carried out on pseudomorphically strained InxGa1−xAs-Al0.28Ga0.72As ternary-on-ternary heterostructures grown by molecular beam epitaxy to investigate the change in the transition energy, linewidth, and intensity as a function of InGaAs well thickness at two different indium compositions, x = 0.10 and x = 0.15, respectively. Sharp exciton peaks as narrow as 4-6 meV were observed from the InGaAs wells grown at 530 °C with 1 min of growth interruption at the top and bottom heterointerfaces. The linewidth decreases as the well thickness is increased up to 300 Å. In addition, there are signs of linewidth broadening and sharp decrease in the photoluminescence intensity at higher well thicknesses that may indicate the onset of plastic relaxation. Relatively small variations in the transition energy were observed at well thicknesses that are up to ≍3 times the theoretical critical layer thickness calculated by the Matthews-Blakeslee model,10 suggesting that the small density of dislocations that may be present may not have a significant effect on the band structure of the well.

Polycrystalline diamond films may be produced by chemical vapor deposition (CVD) with morphologies ranging from multimicron crystallites with well-defined facets and texture to nanocrystalline “cauliflower” nodules. While previous efforts to connect diamond film “quality” to growth conditions focus on competitive growth of non-diamond phases, we propose that twinning is a major controlling factor. We use geometric arguments to define the conditions under which a given twin can outgrow and bury the “parent” face on which it originated. We then show how the full spectrum of diamond crystallite shapes and film morphologies can be explained in terms of penetration twins without reference to the actual mechanistics of diamond growth.

Diamond films grown on {100}, {111} boron-terminated, and nitrogen-terminated facets of cubic boron nitride (c-BN) single crystals were characterized by Raman spectroscopy, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The evolution of morphology and microstructure of the diamond films at different stages during the growth process were followed by SEM investigation. The results indicate that diamond growth proceeds by nucleation of oriented three-dimensional islands followed by their coalescence. Cross-sectional TEM specimens were prepared from thick (over 10 μm) continuous diamond films grown on {111} boron-terminated surfaces. Selected-area diffraction and high resolution TEM images show that the diamond film has a parallel orientation relationship with respect to the substrate. Characteristic defects, common to diamond films obtained by chemical vapor deposition on other substrates, are also discussed.

An interparticle glass matrix in ruthenium dioxide-based thick film resistors has been studied intensively by means of analytical and high resolution transmission electron microscopy. The ruthenium dioxide phase interacts with lead-borosilicate glass at high temperature by dissolving ruthenium ions and incorporating a small number of lead and aluminum ions on the surface. Ruthenium ions diffuse through the glass network at least over a distance of 1 μm during firing, but are accommodated in the glass structure by an amount only less than 7 at. % at room temperature. High resolution electron microscopy reveals numerous ruthenium-pyrochlore crystallites in high-lead glasses, but hardly any Ru-based clusters/crystallites in low-lead glasses, where lead-rich glass clusters due to glass immiscibility and reduced lead metal clusters are more commonly observed instead of ruthenium clusters. Lead oxide is prone to reduction both in high- and low-lead glasses upon irradiating with a high-energy incident electron beam. Comparison with gold-based resistor and estimation of average dispersion length of ruthenium clusters, 2 to 4 nm, prefer the model of electron hopping via ruthenium clusters/crystallites as a dominant conduction mechanism in thick film resistors.

Ferroelectric Pb[(Mg1/3Nb2/3)0.7Ti0.3]O3 (abbreviated PMNT) thin films were prepared on silicon substrates by rf magnetron sputtering deposition with PbO-enriched PMNT targets. The effects of electrode composition and thin film growth conditions were investigated with grazing-incidence x-ray diffraction, secondary ion mass spectrometry, and scanning electron microscopy. The dielectric property of perovskite films was also measured. The usage of a Pt/Ti electrode was observed to enhance the formation of perovskite PMNT films; in addition, the TiO2 rutile phase was formed at the interface between the PMNT film and Pt electrode due to the oxidation of out-diffused Ti atoms from the inner Ti electrode. It was then noticed that if a target containing a larger excess of PbO was used, a higher consumption of TiO2 occurred and more perovskite phase would be formed in the deposited films. Consequently, perovskite PMNT films having a uniform microstructure and satisfactory dielectric property close to the bulk value were obtained by rf magnetron sputtering deposition on the Pt/Ti/SiO2/Si substrate at 640 °C under appropriate working conditions.

A low cost, highly versatile electron backscattering diffraction system has been developed for an ElectroScan E3 Environmental Scanning Electron Microscope (ESEM). A P20 phosphor coated screen is placed in the microscope environment to image electron backscattering diffraction patterns (EBSP's). A CCD TV camera is used to view the patterns through a leaded glass port in the microscope specimen chamber. This system has a spatial resolution approaching 5 μm and yields analyzable patterns at pressures of up to 6 Torr. With minor modifications this system may be adapted to fit any scanning electron microscope. Comparison of analyses of the grain boundary misorientation of a Ni-16Cr-9Fe alloy with this system and by selected area channeling patterns (SACP's), performed in a standard SEM, yielded excellent agreement between the two techniques. Owing to the capability to perform on-line analysis of EBSP's, the EBSP technique required only half the time as the SACP technique. The capabilities of the system are illustrated in a study of the grain boundary character distribution of Ni-16Cr-9Fe following thermomechanical treatment.

Simultaneous measurements of thermal conductivity and diffusivity of ferroelectric polycrystalline samples of the KDP family type have been performed with the transient plane source (TPS) technique over the temperature range 88-300 K. The thermal conductivity behavior resembles that of the corresponding single crystals, but with values a factor of three lower. This decrease in thermal conductivity of the polycrystalline form is attributed to scattering mechanisms due to microstructural imperfections such as point defects, grain boundaries, etc. Values of porosity have been estimated using the dimensions of the unit cell deduced from the x-ray analysis and the apparent densities. The data indicate that the phase transition mechanisms (displacement type and order-disorder type) still dominate the conduction processes in spite of the presence of other scattering mechanisms due to the imperfection of the microstructure in the polycrystalline form of these materials.

One of the main problems found in the nuclear applications of graphite is its dimensional instability under irradiation, involving both swelling and shape changes. In order to understand better the mechanisms that give rise to these changes, highly oriented pyrolytic graphite was irradiated with 300 keV electrons at temperatures between 25 and 657 °C in a transmission electron microscope (TEM). Microscopic dimensional changes and structural disordering were studied in directions parallel and perpendicular to the graphite basal plane. Changes in the specimen length were investigated by measuring the distance between two markers on the specimen surface in TEM images. Changes in the lattice parameter and the crystalline structure were studied by a TEM diffraction technique. In agreement with reported results, large increases in the specimen length and the lattice parameter were observed along the c-axis direction, whereas a relatively small decrease was observed along the a-axis. In irradiation studies conducted at room temperature, it was found that the dimensional change saturates at high dose, at an elongation along the c-axis direction of about 300%. High resolution microscopy revealed that the microstructure had become nanocrystalline. Electron energy loss spectroscopy results showed that the volume change was recovered at this stage. These observations are discussed in terms of point defect evolution and its effects on the microstructure of irradiated graphite.

A unified kinetic and thermodynamic description of the glass transition in undercooled liquids at normal pressure is established. The following results are obtained for the first time: (1) The glass transition temperature Tg is determined to be in the range of Ts < Tg < Tn. Both Ts and Tn are material-dependent and each of them is characterized by a different Ω(T) = TΔslc(T)/Δslc(T) with Δhlc as the excess enthalpy and Δslc the excess entropy. (2) Being above Kauzmann's isentropic temperature, the lowest limit Ts is determined by Ω(Ts) = 1 −2/(3γ) with γ being the ratio between the total energy and the free energy of the liquid-crystal interface. (3) Although a glass preserves the entropy and enthalpy values of the liquid at Tg, the ratio Ω(Tg) is found to be bound by a Tg-independent material constant 1 −2/(3γ). (4) Tg increases linearly with the logarithm of the cooling rate and such a linear relationship is found to be not always valid. (5) The observed cooling-rate dependent glass transition at Tg is the kinetically modified reflection of an underlying cooling-rate independent transition at Ts, and the underlying transition at Ts is kinetically equivalent to the sudden and strong divergence of the structure relaxation time of the liquid. (6) It is shown that if the cooling rate exceeds a minimum value determined here as a function of temperature, the atoms of an undercooled liquid will not have sufficient time to rearrange themselves into the corresponding crystalline configuration; consequently, crystalline nucleation can be prevented. The results are supported by the available experimental evidence. A systematic test of the results on different systems is possible since the results are in terms of experimentally accessible quantities.