An important, somewhat novel procedure for the bulk synthesis of finely divided crystalline BaTiO3 powder has been studied and is applicable to the synthesis of other compounds in the BaO-TiO2 system as well. An aqueous solution of Ba(NO3)2, TiO(NO3)2, and alanine is spray dried. A combustion reaction occurs when heating the product to 300 °C. The reaction converts the spray-dried mixture to BaTiO3. This BaTiO3 powder and its sinterability have been characterized by thermal analysis, XRD, SEM, dielectric, and particle size measurements. The powder resulting from the thermal runaway reaction is finely divided and sinters more readily than the conventionally prepared high purity BaTiO3.

Stoichiometric and 2 wt. % excess lead oxide containing lead magnesium niobate (PMN) ceramics have been prepared by partial oxalate route. Dielectric measurements with frequency showed a typical relaxor behavior for stoichiometric PMN, while PMN with excess PbO shows a scatter in the dielectric curves at all temperatures above Tc. Under the same processing conditions, the dielectric constant (Kmax) decreases drastically from 16,300 to 9500 at 1 KHz for PMN without and with excess PbO, respectively. Microstructure studies revealed a second phase (unreacted PbO) segregated in the grain boundaries for excess PbO samples. A careful analysis of the data on dielectric properties and phases present coupled with microstructural detail indicate that the second phase in the grain boundary has a pronounced effect on the dielectric properties and not the pyrochlore phase.

The influence of the key nucleation and grain growth parameters on (i) the evolution of the microstructure of the product phase (on a microscopic level) and (ii) the combustion synthesis process (on a macroscopic level) were investigated for the combustion synthesis process in the Nb-C system. This work is an integral part of the continuing effort1–3 to develop a more complete theoretical model for combustion synthesis processes in general. In particular, the nucleation and growth of the NbC(s) product phase from the supersaturated liquid Nb/C mixture that appears briefly during the combustion synthesis process was treated in a greater detail by using a decidedly more sophisticated treatment of the nucleation and growth process (as developed in the field of rapid solidification and welding). It was shown that the microstructure of the NbC(s) product phase, including the evolution of the grain size and the size distribution, and the development of the grain's morphology, as well as the combustion wave velocity, are significantly influenced by the total number density of the nucleation sites, nmax, that are present in the system. The grain size distribution was shown to possess a monosize distribution, since during the combustion synthesis process the rate of increase of the degree of local undercooling was very high so that the nucleation process took place (locally) during a very brief period of time. This work provides a sound basis for developing a better control of the microstructure, and for a better understanding and interpretation of the results of related experimental studies.

Ion-irradiation induces amorphization in many intermetallics and ceramics, but spinel (MgAl2O4) is considered a “radiation resistant” ceramic. Spinel was irradiated with 1.5 MeV Kr+ at 20 K and observed in situ by transmission electron microscopy (TEM). The spinel remained crystalline to a high dose of 1 × 1016 ions/cm2, without any evidence of amorphization. Another spinel was preimplanted with Ne (400 keV and 50 keV). The microstructure revealed a still crystalline material with 8 nm interstitial loops. After irradiation with 1.5 MeV Kr+ (20 K), amorphization, a result of cation disordering, initiated at a dose of 1.7 × 1015 ions/cm2. At a dose of 1 × 1016 ions/cm2, the spinel was partially amorphous and the remaining crystalline domains disordered. These results show that spinel can be disordered and that amorphization can be triggered by the introduction of stable defects, followed by ion irradiation at low temperature.

We studied the constrained-film sintering of a gold circuit paste used in microelectronic packaging applications. Optical techniques were developed to determine the shrinkage profiles of constrained and free films and stresses generated during sintering in the constrained films. Constrained films approximately 60 μm thick were made by multiple screen-printing of the gold paste on rigid alumina substrates, while the free films were obtained by peeling off portions of the gold films from the substrate after binder burnout. Constrained films for stress measurement were made by multiple screen-printing on an oxidized 25 μm thick silicon substrate. Sintering runs were done in a hot stage at temperatures between 650 °C and 900 °C. The densification rates were much lower in the constrained films than those in the free films. The in-plane tensile stresses in the constrained films, determined by wafer curvature measurement, rose rapidly to a maximum level of 510 kPa during the initial stage of sintering and then gradually decreased. The reduction in the sintering potential due to the hydrostatic stress is not large enough to completely account for the retarded densification in constrained films. SEM micrographs of the film microstructures after sintering showed no-significant difference in grain growth kinetics between the constrained and free films. However, the activation energy for densification was found to be very different between the two types of films, 90.1 ± 4.3 kJ/mole for the free film and 188.8 ± 6.7 kJ/mole for the constrained film. We suggest that the retarded densification kinetics in the constrained gold films is due to (i) the reduction in the sintering potential by the hydrostatic stress and (ii) a change in the dominant sintering mechanism from grain-boundary diffusion in the free films to lattice diffusion in the constrained films.

The microstructure and composition of TiN films, formed by ion beam enhanced deposition (IBED) with different energy (40 keV and 90 keV) xenon ion bombardment and by simple physical vapor deposition (hereafter S-PVD) without any ion beam enhancement, and the interfaces between TiN films and Si substrates have been studied by cross-sectional view analytical electron microscopy in this work. Both the IBED TiN films prepared by Xe+ bombardment with either 40 keV or 90 keV energy ions and the S-PVD TiN film consist of nanocrystals. The TEM observations in the S-PVD case reveal an amorphous layer and a mixed layer of TiN grains and amorphous material at the TiN/Si interface. The thicknesses of the amorphous layer and the mixed layer are about 210 nm and at least 40 nm, respectively. Upon 40 keV Xe+ bombardment, an amorphous Si transition layer of about 50 nm thickness is found at the TiN/Si interface, and the TiN grains close to the TiN/Si interface are of weak preferred orientation. Upon 90 keV Xe+ bombardment, amorphous TiN and Si layers are found with a total thickness of 80 nm at the TiN/Si interface, and the TiN grains near the TiN/Si interface are of preferred orientation [111]TiN ‖ [001]Si. The energy of xenon ion bombardment has a strong effect on the microstructural characteristics of TiN films and the interfaces between the TiN films and the Si substrates, as well as the size and the preferred orientation of TiN grains.

The effect of grain size on the elimination of an isolated pore was investigated both by the Monte Carlo simulations and by a scaling analysis. The Monte Carlo statistical mechanics model for sintering was constructed by mapping microstructures onto domains of vectors of different orientations as grains and domains of vacancies as pores. The most distinctive feature of the simulations is that we allow the vacancies to move. By incorporating the outer surfaces of the sample in the simulations, sintering takes place via vacancy diffusion from the pores to the outer sample surfaces. The simulations were performed in two dimensions. The results showed that the model is capable of displaying various sintering phenomena such as evaporation and condensation, rounding of a sharp corner, pore coalescence, thermal etching, neck formation, grain growth, and growth of large pores. For the elimination of an isolated pore, the most salient result is that the scaling law of the pore elimination time tp with respect to the pore diameter dp changes as pore size changes from larger than the grains to smaller than the grains. For example, in sample-size-fixed simulations, tp ∼ d3p for dp < G and tp ∼ d2p for dp > G with the crossover pore diameter dc increasing linearly with G where G is the average grain diameter. For sample-size-scaled simulations, tp ∼ d4p for dp < G and tp ∼ d3p for dp > G. That tp has different scaling laws in different grain-size regimes is a result of grain boundaries serving as diffusion channels in a fine-grain microstructure such as those considered in the simulations. A scaling analysis is provided to explain the scaling relationships among tp, dp, and G obtained in the simulations. The scaling analysis also shows that these scaling relationships are independent of the dimensionality. Thus, the results of the two-dimensional simulations should also apply in three dimensions.

Auger Electron Spectroscopy (AES) has been used to examine as-received and oxidized silicon carbide whiskers and their respective whisker/matrix interfaces after fabrication into SiC-whisker-reinforced alumina composites. As-received whisker surfaces exhibited a 2–3 nm-thick near-surface region that was C-rich. Oxygen was detected at the outer surface, but diminished to near zero within 25 nm of the surface. Oxidized whiskers had 60 nm-thick SiO2 surface layers, which was in agreement with the transmission electron microscopy observations. The whisker/matrix interfaces in both composites consisted of thin (<0.5 nm) layers of a C-Si-O noncrystalline material. The thick SiO2 layers on the oxidized whiskers were ejected from the interfaces during hot-pressing. It was concluded that (i) the higher toughness of the composite fabricated with as-received SiC whiskers may be related to the higher C and lower O in its SiCw/Al2O3 interfaces, and (ii) interface composition cannot be reliably predicted using the surface composition of free whiskers prior to fabrication.

Various polyimide films (Kapton, Upilex, Novax, and PPT) were carbonized and graphitized up to 3000 °C. They were studied by optical and electron microscopies. All films retaining oxygen as a cross linker over 1000 °C, i.e., Kapton, Upilex, and Novax, graphitize as anthracites (high rank coals) do. They get a long range statistical orientation parallel to the film plane with a nanotexture of flattened pores. Graphitization is both sudden and perfect above 2100 °C when the pore walls break. Since oxygen is released at 1000 °C, the film PPT behaves as a compact nonporous graphitizing carbon (orientation parallel to the film plane). Thermal graphitization is progressive and begins at a higher temperature.

A thermally stable copolymer of a polyimide and a dianiline terminated polydimethylsiloxane has been developed for use as a structural oxygen etch barrier material in high performance multilayer electronic wiring structures. We report on the preparation of the etch barrier material and on investigations of the etch stop and adhesion properties of this material. Studies on the effects of adhesion-promoting plasma treatments are supported by x-ray photoelectron spectroscopy (XPS) and Rutherford backscattering spectrometry (RBS) data. Before plasma treatment, it is observed that the siloxane component segregates to the surface. After either an O2 reactive ion etch treatment or H2O plasma exposure, the unusual XPS charging effects are interpreted as a surface layer containing two distinct phases: the etched polyimide fraction and a partial overlayer of a carbon containing SiO2

Thin films of polytetrafluoroethylene have been deposited on amorphous substrates by the pulsed-laser deposition technique. By transmission electron microscopy, the polymer films were shown to consist of both amorphous and crystalline components. The data for the crystalline component are consistent with it being highly ordered with the long helical molecular chains aligned parallel to the film substrate interface plane. The fraction of crystalline material in the films was found to be related to the substrate temperature during deposition with the maximum amount of crystalline material occurring when the substrate temperature was close to the melting temperature of the polymer.

The primary focus of this paper is on the axial compression behavior of high performance polymeric and carbon fibers. Seven test methods used for determining the compressive strength of single fibers have been reviewed. Various micromechanical models proposed in the literature to understand the compressive failure in single filaments and in other anisotropic systems have been discussed and analyzed. The results of various approaches to influence the compressive strength of polymeric fibers have been summarized. Possible reasons for the variation in the compressive strength of pitch and PAN-based carbon fibers have also been addressed.

“Effects of boron on the deformation behavior of Ni3Al” [J. Mater. Res. 9, 1742–1754 (1994)]