The surface area created during tensile deformation and fracture of the reactive metals Ti, Zr, Mg, and Al is probed by real-time measurements of chemisorptive electron emission (CSE) due to oxygen adsorption. CSE is sensitive to the number of fresh metal atoms exposed at the surface as a consequence of plastic deformation. At constant strain rate, Ti, Zr, and Mg all display exponential increases in CSE intensities during loading, reflecting exponential increases in surface area prior to fracture. In Ti and Zr, CSE begins at the onset of unstable necking. In contrast, CSE intensities from Al reflect a nearly constant rate of surface area production during deformation at constant strain rate. Calibration of the Ti CSE intensities per unit surface area allowed determination of the total surface area produced during deformation and fracture. Atomic force microscopy of the necked region in strained Ti samples shows dramatic increases in surface roughness, in near agreement with the CSE results. A model is presented to account for these observations. The utility of CSE measurements as a probe of deformation and ductile fracture is discussed.

Thin film coatings of (Ca0.6, Mg0.4)Zr4(PO4)6 (CMZP) on Si3N4, and SiC substrates, including porous SiC used in ceramic filters, were investigated using sol-gel and dip coating techniques. The coating thickness, ranging from 1 to 5 μm, was found to vary with the selected precursors and their concentrations in the solution. When applied to Si3N4 and SiC, CMZP coatings exhibit good thermal shock resistance and greatly improved alkali corrosion resistance. For porous silicon carbide, homogeneous, crack-free coatings were formed on both the outer surface and the interior sections of the pore walls. The CMZP coatings on Si3N4 and SiC exhibit good thermal shock resistance. The CMZP coating greatly improved the alkali corrosion resistance of Si3N4 and SiC.

Copper and diamond both have cubic crystal structures and similar lattice constants, making Cu an excellent candidate substrate for the heteroepitaxial growth of electronic device quality diamond. In this study a Cu substrate preparation method was developed to obtain large-area, free-standing polycrystalline diamond films. Concurrently, a statistically designed experiment was used to maximize the diamond film quality and resulted in (111) and (100) faceted films of quality comparable to or better than those grown on Si. The diamond films were analyzed by Raman spectroscopy, x-ray diffraction, and scanning electron microscopy.

Due to its interesting mechanical properties, silicon carbide is an excellent material for many applications. In this paper, we report on the mechanical properties of amorphous hydrogenated or hydrogen-free silicon carbide thin films deposited by using different deposition techniques, namely plasma enhanced chemical vapor deposition (PECVD), laser ablation deposition (LAD), and triode sputtering deposition (TSD). a-SixC1−x: H PECVD, a-SiC LAD, and a-SiC TSD thin films and corresponding free-standing membranes were mechanically investigated by using nanoindentation and bulge techniques, respectively. Hardness (H), Young's modulus (E), and Poisson's ratio (v) of the studied silicon carbide thin films were determined. It is shown that for hydrogenated a-SixC1−x: H PECVD films, both hardness and Young's modulus are dependent on the film composition. The nearly stoichiometric a-SiC: H films present higher H and E values than the Si-rich a-SixC1−x: H films. For hydrogen-free a-SiC films, the hardness and Young's modulus were as high as about 30 GPa and 240 GPa, respectively. Hydrogen-free a-SiC films present both hardness and Young's modulus values higher by about 50% than those of hydrogenated a-SiC: H PECVD films. By using the FTIR absorption spectroscopy, we estimated the Si-C bond densities (NSiC) from the Si-C stretching absorption band (centered around 780 cm−1), and were thus able to correlate the observed mechanical behavior of a-SiC films to their microstructure. We indeed point out a constant-plus-linear variation of the hardness and Young's modulus upon the Si-C bond density, over the NSiC investigated range [(4–18) × 1022 bond · cm−3], regardless of the film composition or the deposition technique.

Six CVD diamond thin films were examined by magic angle spinning (MAS) 13C nuclear magnetic resonance (NMR), Raman, and electron spin resonance spectroscopy. The use of film samples cut to the diameter of the magic-angle spinning rotor provided ease of spinning and the opportunity to obtain good signal-to-noise spectra in 4 to 16 h. MAS NMR linewidths exhibit a linear correlation with Raman linewidths and reflect the optical quality of the material. Residual MAS NMR linewidths most likely arise from a combination of crystal defect sites and paramagnetic effects.

Cu NMR spectra from cluster-assembled nanophase copper with an average grain size between 5 and 10 nm show a broadened peak, at the normal Knight-shifted frequency for copper metal, which arises from only the central 1/2 to −1/2 transition. The broadening of the central line is associated with a distribution of Knight shifts. A very broad background is observed on either side of that peak, associated with broadening due to internal electric field gradients. Pulsed NMR measurements of the central peak show that virtually all the copper signals are significantly broadened and have a spin-spin relaxation time longer than larger-grained copper samples. The strain within the grains is estimated to be 0.7%. Line shape measurements as a function of spin echo delay time show there are a number of copper sites with longer relaxation times which have a significantly larger broadening. Those sites are tentatively identified as being at or near a grain boundary or free surface. A small orientation effect is observed indicating an anisotropy within the samples. An isochronal anneal of one sample showed significant line narrowing after an anneal at 450 °C consistent with other nanophase metals which show grain growth above 40-50% of the absolute melting temperature. The dependence of NMR linewidth on average grain diameter is estimated.

The energetics of intermediate phases in the Ca2Fe2O5-CaTiO3 pseudobinary system was determined by high temperature solution calorimetry. The results suggest that both the intermediate compounds Ca3Fe2TiO8 and Ca4Fe2Ti2O11 are entropically stabilized because their enthalpies of formation are positive with respect to a mixture of Ca2Fe2O5 and CaTiO3. At high temperatures, the configurational entropy of the random distribution of Fe and Ti ions on the octahedral sites appears sufficient to stabilize the intermediate phases. The enthalpies of formation from the oxides at 1073 K of Ca2Fe2O5, Ca3Fe2TiO8, and Ca4Fe2Ti2O11 are −45.0 ± 3.8, −123.7 ± 8.0, and −192.7 ± 11.2 kJ/mol, respectively. Their enthalpies of formation from the elements at 298 K are −2139.8 ± 4.4, −3798.4 ± 8.6, and −5447.3 ± 12.2 kJ/mol, respectively.

The crystalline quality of a diamond film with two different preferential orientations (100) and (111), obtained in the same run by hot filament chemical deposition, has been studied. The quality of the film determined by Raman spectroscopy measurements was found to be nearly the same for both orientations. The second order Raman spectrum for diamond film was observed by using an infrared excitation.

The kinetics of silicon carbide (SiC) deposition, in a hot-wall chemical vapor deposition (CVD) reactor, were modeled by analyzing our own deposition rate data as well as reported results. In contrast to the previous attempts which used only the first order lumped reaction scheme, the present model incorporates both homogeneous gas phase and heterogeneous surface reactions. The SiC deposition process was modeled using the following reactions: (i) gas phase decomposition of methyltrichlorosilane (MTS) molecules into two major intermediates, one containing silicon and the other containing carbon, (ii) adsorption of the intermediates onto the surface sites of the growing film, and (iii) reaction of the adsorbed intermediates to form silicon carbide. The equilibrium constant for the gas phase decomposition process was divided into the forward and backward reaction constants as 2.0 × 1025 exp[(448.2 kJ/mol)/RT] and 1.1 × 1032 exp[(-416.2 kJ/mol)/RT], respectively. Equilibrium constants for the surface adsorption reactions of silicon-carrying and carbon-carrying intermediates are 0.5 × 1011 exp[(-21.6 kJ/mol)/RT] and 7.1 × 109 exp[(-33.1 kJ/mol)/RT], while the rate constant for the surface reaction of the intermediates is 4.6 × 105 exp[(-265.1 kJ/mol)/RT].

Polyxylylene thin films grown by chemical vapor deposition (CVD) have long been utilized for uniform, pinhole-free conformal coatings. Homopolymer films are highly crystalline and have a glass transition temperature around room temperature. We show room temperature copolymerization with previously untested comonomers during the CVD process. Samples were studied with wavelength dispersive analysis, FTIR, scanning variable angle ellipsometry, and x-ray diffraction. Copolymerizing chloro-p-xylylene with perfluoro-octyl methacrylate results in dielectric constants at optical frequencies as low as 2.19, compared to 2.68 for the homopolymer. Copolymerizing p-xylylene with 4-vinylbiphenyl resulted in films whose onset of weight loss in TGA measurements was 450 °C, compared to 270 °C for the homopolymer.

Studies of high-temperature alloys in the Ti-Sn system based on the intermetallic compound Ti3Sn have identified alloys that damp strongly both at low frequencies (0.1 to 10 Hz) and high frequencies (5 to 20 MHz). The low frequency damping behavior shows loss factors as high as 0.04 at room temperature and Young's moduli that rise with temperature from 40 °C to 100 °C for two alloys. Although the basic mechanism or mechanisms of energy dissipation are presently unknown, the alloys are notable for unusual shapes of microhardness indentations. The deformations imply that large reversible strains can occur at temperatures from 23 °C to 1150 °C.

The upper and lower bounds of the bulk, shear, and Young's moduli are calculated point-by-point along the radius of SCS-6 silicon carbide fibers using the Hashin-Shtrikman equations from considerations of the Auger spectra along the fiber radius. The calculated values are in agreement with measurements of the average Young modulus obtained over relatively large radial regions of the fiber using scanning acoustic microscopy (SAM). The validity of the Hashin-Shtrikman bounds calculations is enhanced by the agreement found between experimental SAM V(z) curves for fixed z along the fiber radius and the theoretical bounds of such curves obtained from the bounds of the calculated bulk and shear moduli.

The first direct electrical resistance measurements performed on a single carbon nanotube bundle from room temperature down to 0.3 K and in magnetic fields up to 14 T are reported. From the temperature dependence of the resistance above 2 K, it is shown that some nanotubes exhibit a semimetallic behavior akin to rolled graphene sheets with a similar band structure, except that the band overlap, Δ ≈ 3.7 meV, is about 10 times smaller than for crystalline graphite. In contrast to graphite which shows a constant low-temperature resistivity, the nanotubes exhibit a striking increase of the resistance followed by a broad maximum at very low temperatures. A magnetic field applied perpendicular to the sample axis decreases the resistance. Above 1 K, this behavior is consistent with the formation of Landau levels. At lower temperatures, the resistance shows an unexpected drop at a critical temperature which increases linearly with magnetic field. These striking features could be related to the unique quasi-one-dimensional structure of the carbon nanotubes.

Extruded NiAl and NiAlZr alloys often show discontinuous yielding on strain aging in compression at room temperature. Two sets of experiments were conducted to understand the reasons for this yield-point behavior. First, strain-aging experiments were carried out on NiAl alloys containing O to 0.1 at. % Zr. The specimens were all deformed in compression at room temperature at a nominal initial strain rate of 1.1 × 10−4S−1, and the effect of annealing at 700 and 1200 K on the stress-strain curves and the yield strength was studied after an initial prestrain. While annealing at 700 and 1200 K consistently reduced the yield strength of both NiAl and NiAlZr, the effects were quite different. In the case of NiAl, annealing at 1200 K did not result in discontinuous yielding, whereas it generally resulted in a sharp yield point for the Zr containing alloys. Second, the PUCOT (piezoelectric ultrasonic composite oscillator technique) was used to measure the dynamic Young modulus, breakaway strain amplitude, and damping for the alloys. Only small differences were observed in the values of Young's modulus, but the breakaway strain was at least a factor of 2 to 3 lower for NiAl than for NiAlZr. The experimentally determined values of damping were used in the Granato-Lücke model to estimate the binding energy for NiAl. While the binding energy values were found to be in agreement with the calculated values of dislocation kink nucleation and migration energies in this material, to within an order of magnitude, other effects, such as dislocation pinning by quenched-in vacancies, cannot be ruled out. The observations made in this study suggest that the yield-point behavior in NiAl may be due to several factors, such as difficulties in double kink nucleation, and single kink migration, as well as dislocation-vacancy interactions; whereas, the yield-point behavior in the Zr-alloyed material is due at least in part to dislocation-solute interaction.

The deformation characteristics of icosahedral Al70Pd21.5Mn8.5 have been investigated by high temperature creep experiments, and the resultant microstructures have been examined by transmission electron microscopy (TEM). From 730 to 780 °C, microstructural analysis revealed that the deformation is controlled by dislocation glide, with an activation energy of 210 ± 30 kJ/mole and a stress exponent of 1.2 ± 0.2. From 780 to 810 °C, microstructures were characteristic of deformation controlled by dislocation glide and climb. The activation energy and stress exponent were determined to be 1700 ± 80 kJ/mole and 2.9 ± 0.3, respectively. Hardness measurements also reflected an increase in dislocation density, as the hardness of the deformed samples was approximately 10% higher than the as-cast sample.

Diamond deposition was attempted on polyacrylonitrile (PAN) fiber and vapor grown carbon fiber (VGCF). PAN fibers were severely etched in a microwave plasma, whereas diamond was successfully deposited on VGCF. A diamond growth rate of 0.1 μm/h on VGCF was determined at a gas mixture of 99.9 sccm H2/0.1 sccm CH4 and a pressure of 30 Torr. It is proposed that diamond formation on VGCF occurs on not only the prism planes, but also the basal planes owing to the unique structure of VGCF. An explanation is proposed to explain diamond nucleation on the basal planes.

27Al MAS nmr spectra from alkoxide-derived Al2O3-BaO-CaO-TiO2-ZrO2 Synroc precursors were studied after isochronal annealing in air for 1 h at temperatures between 200 and 1300 °C. At temperatures below 1000 °C, some tetrahedral and a trace of 5-coordinated Al were observed together with a majority of octahedral Al. The amount of nonoctahedral Al reached a maximum at 400–700 °C, beyond which it diminished and disappeared; essentially, complete conversion to octahedral Al took place on full crystallization at 1200–1300 °C, with the Al being contained in barium hollandite and minor α-alumina. The hollandite nmr signal was absent in Synroc which was hot-pressed at 1200 °C/20 MPa, presumably because of coincorporation of paramagnetic Ti3+ in the hollandite phase, but a signal from α-alumina was observed. Samples containing simulated waste fission products gave results similar to their waste-free counterparts when calcined at 750 °C in 3.5% H2/N2 and when hot-pressed.

Dielectric polarizabilities for most of the ions in known perovskites scale with the ionic volume and the valence. These ionic dielectric polarizabilities and the ion additivity rule have been used to calculate molecular dielectric polarizabilities for perovskite substrate materials used for high-temperature superconductors. Using the ion additivity rule to predict possible low permittivity compositions seems to suggest that the constraints of the perovskite structure and stoichiometry, lattice match to high-temperature superconductors, and congruent melting required for bulk growth limit the compositions to ones unlikely to be superior to the currently available materials. The most limiting factor on the relative permittivity of the perovskites is probably the close-packed nature and lack of voids in the structure. However, in nonferroelectric perovskites, the polarizabilities derived from relative permittivity data using the Clausius-Mossotti relation are significantly less than the calculated values, with deviations that correlate with degree of cation compression. Use of cation compression to reduce the polarizability shows some promise for improving dielectric constants.

An attempt to unify the growth mechanisms and conditions for diamond formation is developed via the growth probability calculated by a barrier model between the two phases. From the distribution law of the equal growth probability lines plotted in a pressure-temperature (P-T) diagram, five regions of different growth methods and mechanisms were reasonably delineated. Many experimental results can be generalized and explained by our theory, and the unity of diamond growth mechanism was discussed over the wide region of the P-T condition.

The decomposition of congruent lithium niobate (LN) crystals proceeds by surface nucleation and growth of LiNb3O8 precipitates which exhibit an epitaxial orientation relationship. The same orientation relationship is observed on x-, y-, and z-cut LN substrates. The epitaxy arises from similarities between the two crystal structures and provides for an essentially continuous oxygen-ion framework from parent to product. On y-cut LN, the precipitates have a well-defined habit plane, and the interfacial misfit between the two structures is accommodated by a rectangular grid of misfit dislocations. The density, geometry, and imaging behavior of the misfit dislocations suggest that their Burgers vectors serve to accommodate the disregistry in the oxygen-ion framework. Based on these observations, it is concluded that the mechanism of formation of LiNb3O8 consists of preferential nucleation on the surface and subsequent growth, possibly by counterdiffusion of cations in a closed system where the oxygen-ion framework remains essentially fixed in space.