The relationship between grinding forces and the material's resistance to microfracture is investigated in abrasive machining of silicon nitride ceramics. Surface grinding is performed on two forms of silicon nitride with different microstructures, and the grinding forces are measured. In addition, single-point scratching is performed on polished surfaces to amplify the damage associated with the action of an individual abrasive particle in grinding. A thermal wave measurement technique is then used on the cross sections to characterize the density of subsurface microcracks associated with scratching. Compared to a fine-grain silicon nitride, the density of microcracks in a course-grain silicon nitride is significantly larger, while the grinding force is smaller. The smaller grinding force for the coarse-grain silicon nitride is attributed to the ease of local intergranular microfracture and grain dislodgement during grinding.

α-Fe2O3 thin films have been deposited on Si(111) substrates at high temperatures (600–800 °C) by the spray pyrolysis method. Four different iron(III) β-diketonates have been used as precursors in order to obtain polycrystalline films of good adherence, which have been characterized by x-ray diffraction, scanning electron microscopy, and magnetic measurements.

The microstructural variation and the interdiffusion of Pt (80 nm)/Ti (70 nm)/SiO2/Si during annealing in O2 were investigated using Auger electron spectroscopy, x-ray diffraction, transmission electron microscopy, and scanning electron microscopy. While the as-deposited and 400 °C annealed samples showed well-defined layer structures without any significant interfacial reaction, the degree of oxidation remarkably increased with increasing temperature above 500 °C. The PtTi alloy phase with Pmma structure (AuCd type) was observed from the 500 °C annealed sample. Drastic interdiffusion occurring above 600 °C changed the Pt/Ti bilayer into a very entangled structure. Some TiO2 phases were exposed to the ambient between Pt hillocks. In addition, a small amount of Pt-silicide was found near the TiOx/SiO2 interface.

The growth kinetics of cholesterol gallstones have been studied by growing crystals from melted gallstones. The resulting microstructures are spherulitic which is essentially the same as the structures seen in natural gallstones prior to melting. The cholesterol crystals when observed in hot stage microscopy emerge from a unique nucleation center growing radially in the [001] direction with constant rate. The DSC thermograph of a natural gallstone is initially similar to that of cholesterol monohydrate. Upon melting, cholesterol monohydrate changes to anhydrous cholesterol; both forms are crystalline and exhibit polymorphic transformations. Synthetic stones grown from cholesterol were anhydrous and have a phase change at temperatures close to human body temperature. Optical microscopy established that this phase transformation cracks the spherulitic crystals perpendicular to the fast growth direction. Thermal expansion measurements demonstrate that upon heating, the low density, low temperature phase is transformed to a high density phase. This phase transformation and repeated cracking may prove to be useful in destroying natural gallstones, while suppressing this transformation and its associated cracking might aid in securing other solid cholesterol deposits within the human body.

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.

Glass formation and structural properties of the unconventional lead cuprate glasses of compositions (CuO)x (PbO)100−x (mol %), are reported for the first time. X-ray diffraction and electron microscopic studies show that the glass formation occurs for x = 15-50 mol%. The compositional dependence of the density, molar volume, and glass transition temperature suggests that all glass compositions in this domain have the same topology and network connectivity. The glass structure is built up of [PbO4] tetrahedral units. On heat treatment above glass transition temperatures, the glasses crystallize to CuO and PbO. Electron Spin Resonance (ESR) spectra of the glass compositions consist of broad resonance lines.

The structure and electrical properties of multi-ion beam reactive sputter (MIBERS) deposited barium strontium titanate (BST) films were characterized in terms of Ba/Sr ratio, substrate temperature, annealing temperature and time, film thickness, doping concentration, and secondary low-energy oxygen ion bombardment. Films deposited onto unheated substrates, followed by annealing at 700 °C showed lower dielectric constant (<200), compared to a dielectric constant of about 560 for those deposited at elevated temperatures, probably due to reduced voids. Two types of microstructures (type I and type II) were observed depending on the incipient phase of the as-grown films, which also led to two types of time domain dielectric response, Curie-von Schweidler and Debye type, respectively. The current-voltage (I-V) characteristics of type II films doped with high donor concentration showed a bulk space-charge-limited conduction (SCLC) with discrete shallow traps embedded in a trap-distributed background at high electric fields. The I-V characteristics of bombarded films deposited at higher substrate temperatures showed promising results of lower leakage currents and trap densities.

Cross-sectional and plan-view transmission electron microscopy were used to characterize a BaTiO3 thin film deposited on a (100) MgO single-crystal substrate at 1000 °C. The major observations were as follows: interdiffusion between the film and substrate; a large number of antiphase boundaries in the BaTiO3; a two-phase microstructure in the film composed of perovskite BaTiO3 and a second nonperovskite phase, Ba2MgTi5O13 (2:1:5); and a well-defined orientation relationship between the 2 : 1 : 5 and BaTiO3 phases. We propose a mechanism for the formation of the 2 : 1 : 5 phase based on the similarities between the crystal structure of this phase and the structure of (210) antiphase boundaries in BaTiO3.

The playback efficiency of metal-in-gap (MIG) inductive read-write heads in magnetic recording devices is strongly influenced by wear of the air-bearing surface, metal core recession, and staining. In this study, stains were formed by sliding Co–Nb–Zr MIG tape heads against Co–γFe2O3 (oxide) and metal particle (MP) tapes in an accelerated mode. Optical and SEM imaging indicated that staining on a head run against the Co–γFe2O3 tape is thick and patchy, whereas on a head run against the MP tape, staining is in the form of a uniform film. Thickness variations of stains on the metal core formed by Co-γFe2O3 and MP tapes, measured using atomic force microscopy (AFM), were about 30–150 nm and 20 nm, respectively. Constituents of stains were analyzed by time-of-flight secondary ion mass spectrometry (TOF-SIMS), scanning Auger electron spectroscopy (AES), and micro-Fourier transform infrared (micro-FTIR) and micro-Raman spectroscopies. Stains formed on the head run against the Co-γFe2O3 tape consist of organic species with trace amounts of iron and oxygen (inorganic) constituents. On the other hand, stains formed on the head run against the MP tape consist of inorganic constituents of oxidized magnetic particles from the tape. In addition to organic species and iron from tapes, stains formed by either tape also exhibit wear debris from the metal core, ferrite core, and glass region of the head itself. In the case of heads run against both tapes, most of the staining was found to be on the metal core.

Mullite and zirconia-mullite ceramics have been prepared by coating alumina/zirconia particles with an amorphous silica layer. The effect of composition change of the amorphous silica layer by adding B2O3 was investigated. For the zirconia-free compositions, the addition of B2O3 remarkably accelerates the kinetics of the crystallization of the amorphous coating layer, the viscous sintering, and the mullitization. For the zirconia-containing ceramics, the addition of B2O3 enhanced the viscous sintering kinetics and delayed the decomposition of the transient zircon phase and the subsequent t- to m ZrO2 transition, thus resulting in a higher ratio of t- to m-ZrO2. The B2O3-containing zirconia-mullite composites exhibit the same level of fracture toughness (Kic) as the B2O3-free zirconia-mullite composites.

Cristobalite is known to precipitate out of borosilicate glass (Corning 7740) and a binary glass mixture of borosilicate glass and high silica glass when these glasses are heated to elevated temperatures. To prevent cristobalite from forming in these glass systems, a devitrification inhibitor needs to be found. Among oxides selected for testing, both Al2O3 and Ga2O3 are found to prevent cristobalite from forming in these glass systems.

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

Plan-view microstructures of two Co/Ru bilayers with a composition of [Co12ÅRu45Å]2 and [Co40ÅRu35Å]2 have been studied by conventional and high resolution electron microscopy. Large differences in electron diffraction and image contrast between the two bilayers were observed, which are recognized as the microstructural variations during the relaxation of large coherent planar strains when the Co layers wet coherently or semicoherently the Ru layers. For the [Co12ÅRu45Å]2 bilayer, the Co layers are unrelaxed from the Ru layers; only one set of electron diffraction patterns was observed, and the image consists of three types of contrasts which are closely related with either the generation and movement of misfit dislocations or large coherent strains. For the [Co40ÅRu35Å]2 bilayer, the Co layers are relaxed basically from the Ru layers; two sets of electron diffraction patterns with double diffraction spots were observed, and the image consists of small irregular areas with moiré fringe dots.

A modified Pechini process has been successfully developed for preparation of thin films of La1−zSrzCo1−yFeyO3−x (LSCF) on both dense and porous substrates. Results indicatc that the most important processing parameter is the ratio of the polymerization/complexation agent to metal ions. Ceramic films derived from solutions with a relatively low ratio of citric acid to metal ions are usually cracked, while films derived from solutions with a relatively high ratio are crack-free and uniform. The use of ethylenediamine as an additional chelating agent further improves film quality, especially the adhesion and uniformity of the films. A single coating of solution typically yields a ceramic film of thickness about 0.4 μm, and thicker films can be prepared by application of successive coatings. For deposition of thin-film membranes on a porous substrate, however, it is necessary to modify the surface of the porous substrate in order to prevent solution from infiltrating into the pores due to capillary force, and to prevent oxide films from cracking due to surface roughness. The application of an intermediate polymer film to the surfaces of porous substrates has effectively overcome the problems and has resulted in uniform, nonporous membranes of LSCF on porous substrates. Successful deposition of thin-film ceramic membranes on porous substrates is important to fabrication of various ionic and micro-ionic devices based on ceramic thin films.

The diffusion of water into silica glass is modeled to result from the diffusion of molecular water into the glass and its reaction with the silicon-oxygen network to form SiOH groups. Equations for this diffusion-reaction mechanism are presented and compared with experimental diffusion profiles. At temperatures above about 500 °C the reaction goes to equilibrium, but at lower temperatures it does not, leading to a time dependence of the concentration of surface-reacted OH groups and of their apparent diffusion coefficient. At higher temperatures, the OH groups are nearly immobile, but diffuse far enough to sample neighboring OH groups, leading to a bimolecular reverse reaction. At lower temperatures only OH pairs react, giving a first-order reaction. When water tagged with O18 diffuses into silica, the O18 exchanges with O16 in the silicon-oxygen network of the glass. This process is also controlled by the rate of diffusion of molecular water into the glass, and the rate of O18-O16 exchange. This diffusion-reaction mechanism gives a unified description of the diffusion of water in silica glass from 160 °C to 1200 °C at least.

Young's moduli of nanocrystalline Fe, Cu, Ni, and Cu-Ni alloys prepared by mechanical milling/alloying have been measured by the nanoindentation technique. The results indicate that Young's moduli of nanocrystalline Cu, Ni, and Cu–Ni alloys with a grain size ranging from 17 to 26 nm are similar to those of the corresponding polycrystals. The dependence of Young's modulus of nanocrystalline Fe on grain size corresponds well to a theoretical prediction, which suggests that the change in the Young and shear moduli of nanocrystalline materials, free of porosity, with a grain size larger than about 4 nm, should be very limited (<10%). It is likely that reported large decreases in the Young and shear moduli of nanocrystalline materials prepared by gas-condensation/vacuum consolidation result from a relatively large volume fraction of pores.

The synthesis of β-sialon has been carried out by heat treatment in nitrogen flow of Spanish coals or mineral graphite, both with a high content of mineral matter. The results were compared with those obtained with conventional clay/carbon mixtures. The coals and, especially, the mineral graphite produced a very high yield of β-sialon, with a faster reaction rate than the clay/carbon mixtures due to the more intimate contact among the reactants, with the additional advantage of forming much a lower proportion of vitreous phases. On the other hand, the results show that in the particular case of graphite, the use of high temperatures (even above 1450 °C) does not lead to changes in the crystalline phases of the product, allowing the synthesis to be carried out over a wider temperature range than that used for clay/carbon mixtures. The mechanical properties of the sintered artifacts obtained with the sialon synthesized from natural graphite are superior to those prepared from clay/carbon mixtures and comparable (or even superior) to commercial artifacts manufactured from much more expensive precursors.

Addendum: “Crystal growth, morphology, structure, and properties of HNaMP2O7 crystals where M = Co and Ni” [J. Mater. Res. 9, 1519 (1994)]

Solid lubricant films produced by cosputtering metals with MoS2 and by forming metal/MoS2 multilayers are being planned for use in the next generation of solid lubricated devices on spacecraft, including gimbal and sensor bearings, actuators, and sliding electrical contacts. The films exhibit increased densities and wear lives compared to films without additives, but the mechanism of density enhancement is not well understood. The extended x-ray absorption fine structure (EXAFS) technique is ideal for elucidating the structure of these poorly crystalline films. We analyzed MoS2 films cosputtered with 0, 2, and 10% Ni, as well as Ni/MoS2 and Au(Pd)/MoS2 multilayer films. The results obtained at the Mo-K absorption edge showed that the metal-containing films comprised predominantly the same nanocrystalline phases present in similar films without added metals: pure MoS2 and a MoS2−xOx phase. MoS2−xOx is isostructural with MoS2, with O atoms substituting for S atoms in the MoS2 crystal lattice. For all Ni-containing films, EXAFS data obtained at the Ni-K absorption edge showed that the Ni had not chemically reacted with the MoS2−xOx and MoS2, but formed a disordered NiOx phase. However, Ni-cosputtered films showed decreasing Mo-Mo bond lengths in the MoS2−xOx phase with increasing Ni content, probably due to preferential oxidation of Ni compared to MoS2. EXAFS of these Ni-cosputtcred films showed only a small decrease in short-range order with Ni content, while x-ray diffraction showed a concurrent large decrease in long-range order. The results indicate that film densification in Ni-cosputtered films is caused by NiOx formation at the edges of nucleating MoS2−xOx/MoS2 crystallites, limiting the crystallite size attainable within the films.

Local arrangements around Te atoms in TeO2-Li2O glasses with four different Li2O contents (15, 20, 25, and 30 mol %) are observed by Te K EXAFS spectroscopy and x-ray diffraction by making use of synchrotron radiation. EXAFS results based on the two-shell fitting method indicate that interatomic distances of Te-O in axial (ax) sites decrease from 0.208 to 0.197 nm with increasing Li2O contents, while distances between tellurium atom and oxygen atoms in equatorial (eq) sites change slightly from 0.190 to 0.188 nm. Total coordination numbers seem to decrease slightly with increasing Li2O contents. These results suggest the coordination states of tellurium atoms are changed from TeO4 trigonal bipyramids to TeO3+1 polyhedra and TeO3 trigonal pyramids. RDF results also suggest the change of coordination states of tellurium atoms. TeO3+1 polyhedra in glasses are considered to be connected at the vertices with Te-eq Oax-Te or Te-ax Oax-Te linkage as seen in crystalline α-Li2Te2O5.