Interfaces in liquid-phase sintered Si₃N₄ materials were investigated employing both analytical and high-resolution transmission electron microscopy techniques (AEM, HREM). Owing to the sintering process that involves the addition of metal oxides to the Si₃N₄-starting powder, densified materials are composed of Si₃N₄-grains and amorphous as well as partly crystalline secondary phases. Most Si₃N₄ ceramics contain continuous, thin interlayers of residual glass along grain boundaries. HREM studies in conjunction with electron energy-loss spectroscopy (EELS) focused on the characterization of these grain-boundary films. A comparison between the diffuse dark field, the Fresnel fringe and the high-resolution lattice imaging technique revealed the latter technique to be most accurate in order to determine intergranular film width quantitatively. Depending on the interface composition, HREM imaging revealed conspicuous differences in film thickness. However, with a given batch composition each as sintered material is characterized by a constant film width within ±0.1nm. Crystallization of secondary phases can alter the interface chemistry and thus change intergranular film thickness. The latter result is in line with the variation of interfacial film widths before and after oxidation. Owing to cation outward diffusion, a thinning of the interlayer was observed. In contrast, with increasing impurity-cation concentration at the interface, first a thinning and furtheron a widening of the intergranular film was observed. Si₃N₄ materials with only SiO₂ present at interfaces showed a film thickness of 1.0nm, independent of glass volume fraction. Apart from cations, the influence of anion segregation at Si₃N₄-grain boundaries was studied. Fluorine was found to markedly affect the mechanical response of the material. Owing to a lowered cohesive interface strength, as a consequence of F-segregation at grain boundaries, intergranular fracture was predominantly monitored. Moreover, in comparison to undoped specimens, anion-doped samples revealed markedly higher creep rates, which are related to a decrease in the apparent grain-boundary viscosity, as elaborated from internal friction measurements.
In addition to the characterization of internal interfaces at room temperature, microstructures at high service temperatures were studied by rapid cooling Si₃N₄ materials from high temperatures. Quenching a MgO-doped Si₃N₄ from 1350°C produced no observable variation in the grain-boundary film thickness. A substantial increase and a non-uniform width of the amorphous films was, however, observed when rapidly cooling from temperatures of about 1420°C. Specimens quenched from higher temperatures or longer residence times above the eutectic temperature again revealed an equilibrium thickness that was slightly wider compared to the film widths observed in the material slowly cooled down to room temperature.
By studying a MgO-doped Si₃N₄ that was exposed for about 14, 000h to 1100°C, the question was addressed as to whether internal grain-boundary films are actually stable and can sustain a long-term exposure to high testing temperatures. It is shown that, apart from other microstructural changes induced during high-temperature exposure, the grain-boundary structure was fundamentally altered and depleted grain boundaries were formed. Moreover, the characteristics of interfaces, observed in Si₃N₄/SiC microstructures obtained by the pyrolysis and subsequent crystallization of organometallic precursors, are briefly discussed. Here, similar to the long-term exposure experiment, complex interface structures without the presence of continuous grain-boundary films were observed. In brief, the content of this

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The influence of the α to β phase transformation on the grain growth rate during liquid phase sintering of Si₃N₄ is theoretically discussed. When fine starting powders are used, the grain growth rate shows no significant difference between α-rich powders and β-rich powders, and rodlike coarse grains are generated irrespective of the crystal phase of powder. In contrast, the growth rate difference becomes more pronounced with increasing coarseness of the starting powders, the grain growth rate of β-rich powders decreases more rapidly than that of α-rich powder.

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Nitrate melts as fluxes are useful for the preparation of oxides. Oxidation atmosphere, supply of active raw material are expected. By using nitrate melts and their decomposition, high T_c superconducting YBa₂Cu₃O_x crystal was prepared at 690°C under a NO_x/O_x gas pressure of 0.1MPa. For comparison, a mixture of Y₂O₃, CuO and Ba(NO₃)₂ was heated at 690°C in air but YBa₂Cu₃O_x crystal was not formed.

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A new layered perovskite compound, NaLaTa₂O₇, was synthesized by ion-exchange reaction of the rubidium compound, RbLaTa₂O₇. The crystal structure of the compound was determined by the Rietveld analysis for powder X-ray diffraction pattern. The crystal structure is analogous to that of the corresponding niobate compound, NaLaNb₂O₇. This layered perovskite compound is a new member of the Dion-Jacobson series with n=2 for the general formula M[A_n-1B_nO_3n+1] (M=alkali metals).

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The formation process of porous glass supports in a SiO₂-ZrO₂-Na₂O system was investigated. The porous glass supports were prepared by impregnation of NaCl into a microspherical SiO₂-ZrO₂ gel, heating the mixture at temperatures ranging from 760 to 800°C, and washing it with water. Scanning electron microscope (SEM) observations indicated that porous glass skeletons were formed through sinering of the gel even before removal of NaCl, with the porosity of the gel partially retained. Heat treatment at a temperature higher than 760°C enhanced diffusion of sodium cations in the microspherical gel, which resulted in their homogeneous distribution. It was also confirmed that HCl was formed during reaction of the SiO₂-ZrO₂ gel and NaCl. Therefore, a liquid phase in a SiO₂-ZrO₂-Na₂O system was probably formed through ion exchange between sodium cations and protons of hydroxy groups on the SiO₂-ZrO₂ gel, and the gel was partially sintered to form the porous glass supports.

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The friction and wear properties of oil-retaining porous silicon carbide for sliding contact in air were investigated by using a pin-on-disk friction machine. The friction tests were carried out under the conditions of various sliding velocities (0.13 to 0.57m/s) and various combinations of oil-retaining porous silicon carbide and dense silicon carbide (pin/disk). In the dense SiC/oil-retaining porous SiC system, the lowest and most stable friction coefficient and the least wear were obtained independent of sliding velocity. This is due to the lubrication effect of the oil supplied from the oil-retaining porous SiC disk at the friction interface. The friction and wear mechanisms of these ceramics were classified into four modes depending on the relation between friction coefficient and specific wear amount and SEM observation of frictional surfaces.

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We investigated the deposition, reaction and growth of TiC whiskers from a K₂TiF₆+CH₄+Ar system on a graphite substrate at 1250-1400°C. The gaseous phase reaction between the formation of titanium fluoride and its thermal decomposition was important for the synthesis of TiC whiskers. TiC whiskers were considered to be formed through a series of thermal decomposition, reduction and carbonization reactions. Since there were no droplets on the tips of the TiC whiskers, and the tip shapes were similar regardless of the whisker length and at various temperature, the whiskers were considered to have grown by means of a vapor-solid (VS) growth mechanism.

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Oxidation behavior of porous SiC containing Fe was investigated using a quadrupole mass spectrometer by measuring the volume of evolved gases during oxidation at 1700K. This Fe-containing SiC was obtained by immersing the SiC in an acetone solution with an Fe(C₅H₇O₂)₃ concentration of 0.1M for 1-5min followed by calcination at 1173K. The weight gain and the total amount of gases evolved decreased with increasing Fe₂O₃ content. XRD intensity ratio of cristobalite to SiC was increased with increasing Fe₂O₃ content. These results indicate that the accelerated crystallization of amorphous silica to cristobalite and the retardation of the oxidation were caused by the added Fe.

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The thermal stability of Si-Ti-C-O fibers, STC (6H) and STC (6) prepared by the pyrolysis of polytitanocar-bosilane (PTC) was investigated. TEM study confirmed that STC (6H) contained larger β-SiC nanocrystals and higher crystalline free-carbon units than STC (6). During the exposure tests to high temperatures under Ar atmosphere, the crystallinity of the free carbon in STC (6H) further developed around β-SiC nanocrystals as if the free carbon formed nets for trapping β-SiC nanocrystals to prevent their direct contacts. STC (6H) showed slower gas-release and grain coarsening rates than STC (6). After being exposed at 1600°C for 60min, STC (6H) retained the tensile strength of as high as 0.6GPa, whereas STC (6) was too weak to handle for the tensile testing. The crystalline free-carbon had the excellent ability to retain the microstructural stability of Si-Ti-C-O fibers at high temperatures.

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Reaction bonded aluminum oxide (RBAO) is a promising oxide ceramic for engineering components due to its interesting characteristics, such as high green strength, low-to-zero shrinkage, and advanced mechanical properties. In the present work, the effect of Cyclic CIP on compaction of RBAO precursors and on properties of reaction sintered RBAO bodies was investigated. RBAO compacts were made by Cyclic CIP at 20 and 1000 cycles. A small number of cycles leads to RBAO compacts with homogeneous microstructure, however, further cycling results in degradation of the microstructure. After sintering, strength values of up to 690MPa were obtained for samples with 20 cycles. This is more than 20% above the standard material made by ordinary CIP. This shows that Cyclic CIP can be applied as a successful compaction technique to improve the mechanical properties of metal/ceramic powder mixtures like RBAO precursor powders.

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Stress relaxation in the glass bonded ferrites under various cooling conditions was studied. Warp of the glass bonded ferrites was released by holding at a suitable temperature during cooling. The extent of warping as a function of holding temperature gave a V-shaped curve whose maximum value was the same as that for warping without anneling. The temperature giving the minimum value was near the T_g of each glass under the condition that holding time was 0.5h. The stress relaxation process and slope of the V-shaped curve were discussed using the thermal expansion curves of the glass and the ferrite and the viscosity curve of the glass. A new method to decide the setting point using the V-shaped curve was also introduced.

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SiO₂:Sm²⁺ and SiO₂:Sm²⁺, Al glass films have been prepared by a co-sputtering method, using an RF magnetron sputtering apparatus. Heat treatment at 1273K in Ar gas increases the intensity of fluorescence spectrum due to Sm²⁺ ions. Also, the Sm concentration corresponding to a maximum fluorescence intensity becomes larger with the heat treatment. The heat treatment increases the number of isolated Sm²⁺ ions which contribute to the enhancement of fluorescence intensity.

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Thin-film microthermistors were prepared from Mn-Cu layered thin-films using a YAG laser. A Mn thin-film and a Cu thin-film were continuously deposited on quartz substrates by the vacuum deposition method, then the YAG laser beam was irradiated to the layered thin-films in air and scanned at various speeds. After the processing the resistance of the layered thin-films increased and their thermistor constant reached within the range of 2500 to 4000K. The resistance and thermistor constant were controlled by the laser scanning speed and the number of scanning times. The electrical properties were more stable for heat cycles when the laser beam was scanned at low speeds.

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The NO_x intercalation properties of La_2-xBa_xSrCu₂O_6-δ was investigated by thermal analysis (TGA-DTA) and X-ray photoelectron spectroscopy (XPS) analysis. The results of thermal analysis showed that the NO_x absorbability was increased by Ba substitution. The N1s XPS spectra suggested the surface adsorption of NO₂^- and NO₃^- groups corresponding to NO_x trapped by oxygen vacancies. The chemical shift of Cu2p XPS peak indicated the increasing hole concentrations at the level of O2p with NO_x intercalation. Also, the surface intercalation of NO₂ resulted the chemical shift of Ba3d and Sr3d XPS peaks.

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The influences of redox treatments on the mechanical and gas permeable properties of Ni-yttria stabilized zirconia (YSZ) cermets were investigated. The bending strength decreased successively with the continuous redox treatments. The porosity and the mean pore diameter increased by the first reduction, decreased to be close to the initial levels by the subsequent oxidation, and then again increased by the second reduction. With the oxidation treatment, the surface region of the cermet disk restored the tight microstructure consisting of well-packed grains, while the inside remained porous. This preferential oxidation in the surface region resulted in the negligibly small permeation of nitrogen gas, indicating a possibility of utilizing the cermets a shielding membrane against oxygen permeation. The oxygen gas shielding was experimentally confirmed to occur at around 500°C.

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A crystal structure model assembly program was developed, which designs starting models of Rietveld refinement, using chemical formulae, a number of formulae per unit cell, space group, cell parameters and X-ray powder diffraction data. The program moves co-ordinates of independent atoms in a unit cell by small degrees and calculates co-ordinates of all equivalent atoms using symmetry operation of a given space group. If all inter-atomic distances in a model are equal to or larger than the sum of each atomic radius, model data are stored. The program selects suitable starting models from stored models using the R-factor calculated from observed and theoretical Bragg intensities. The program was applied to several simple inorganic materials and good structure models were obtained.

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Oxidation behavior of an alumina composite containing 30vol% TiC whiskers has been studied at 800, 900 and 1000°C in air. Only rutile-type TiO₂ in addition to TiC and Al₂O₃ was observed after oxidation. The weight gain curve obeyed the parabolic law at each oxidation temperature, indicating that the oxidation was controlled by diffusion of oxygen in the matrix. An apparent activation energy for oxidation of this composite was around 127kJ/mol. The bending strength of the oxidized composite decreased gradually with oxidation time at any temperature. This can be explained by the following fact; the thickness of the oxidized layer and the size of oxidized grains increased with increase in oxidation temperature and time. A roughly linear relationship was observed between the thickness of oxidized layer and the weight gain.

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C₆₀ dissolved in toluene, benzene and carbon disulfide respectively, yielded a brown precipitate upon exposure to ultraviolet radiation. A thin film was deposited on a silicon substrate when dipped in each of the solutions. Further examination of this deposit revealed: (1) the substance to be amorphous by TEM observation; (2) No oxygen was detected by Auger electron spectroscopy; (3) Absorption peaks produced by FT-IR differed from those of pristine C₆₀, solid-state photopolymerized C₆₀ and high-pressure polymerized C₆₀; (4) The same substance was obtained for each of the three solvents; (5) The substance obtained is presumably a new photopolymerized C₆₀ solid.

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A perovskite La_0.59±0.01Li_0.27±0.01TiO_3.02±0.02 single crystal was grown by the floating zone method and its lithium ion conductivity was measured. The conductivity was found to be predominantly ionic. The ionic conductivities at 300K parallel and perpendicular to the c-axis are 5.8×10^-4 and 6.8×10^-4S·cm^-1, respectively. The anisotropy of the ionic conductivity corresponds to that of the structure, i.e., of the distribution of La ions. Furthermore, the ionic conductivity and activation energy for ion conduction are almost the same as those of a grain in polycrystalline samples, indicating that the evaluation of the ionic conductivity of polycrystalline samples was appropriate.

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