Time-dependent fracture of an alumina under long-term static and cyclic loading was investigated by four-and three-point flexure tests. Bend bars with two different sizes were prepared to evaluate the size effects on the failure time distribution. The resulting stress-life data were analyzed by two statistical time-dependent fracture theories which incorporate the statistics of strength and flaw size distribution with subcritical crack growth that leads to delayed fracture. The first model considers only the growth of a single major crack to a critical size while the second considers the size distribution of multiple flaws and their slow crack growth characteristics. Both models provided commonly acceptable description of the static and cyclic strength-probability-lifetime relationships for the experimental results from various specimen sizes and flexure modes.

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The change in the saturation magnetic moment of ferrite-glass mixtures has been investigated in relation to reactions at the interface between oxide glasses and ferrites. In mixtures of Mn-Zn ferrite and SiO₂-PbO or SiO₂-PbO-MO (M=Fe, Mn) glasses, it was established that as the temperature is increased above 500°C, the saturation magnetic moment decreases until reaching a minimum at about 800°C, but starts to increase again above 900°C. However, this pattern does not occur in mixtures containing SiO₂-PbO-ZnO and SiO₂-PbO-NiO glasses as the magnetic moment continues to decrease above 800°C. In contrast, the saturation magnetic moment of a mixture of Ni-Zn ferrite and SiO₂-PbO glass was found to slightly decrease at temperatures above 500°C but then start to increase above 800°C. However, the magnetic moment of a mixture of Ni-Zn ferrite and SiO₂-PbO-FeO_1.5 glass was seen to continuously increase at temperature up to the 1000°C limit of our investigations. In mixtures of SiO₂-PbO-MO (M=Mn, Ni, Zn) glasses the magnetic moment was stable up to temperatures of 900°C, but showed significant increase at 1.000°C. Conversely, the magnetic moment of a mixture containing SiO₂-PbO-ZnO glass only started to decrease at 1000°C.

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The products and kinetics of the reaction between Si₃N₄ and iron were studied at 1173 to 1573K under both nitrogen and argon. The following results were obtained:
(1) An Fe-Si solid solution was produced at low temperatures, which with an increase in temperature changed to iron silicides in the following order of occurrence: Fe₃Si, Fe₅Si₃ and FeSi.
(2) As the reaction proceeded, the lattice constant of the bcc crystal structure successively decreased throughout α-Fe, the Fe-Si solid solution and Fe₃Si.
(3) The incubation period was long at low temperatures, but shortened markedly with increasing temperature.
(4) The initial stage followed a linear rate of reaction. Below 1373K, the activation energies were 626kJ/mol under a nitrogen atmosphere and 477kJ/mol under argon atmosphere. The reaction rate is thought to be controlled by a chemical process. At 1373K and above, an activation energy of 106kJ/mol was obtained under both atmospheres. The rate is thought to be determined by the combination of gas-phase diffusion through interparticle pores and chemical reaction.
(5) On producing iron silicides, the reaction kinetics could be described by a parabolic rate law. The activation energy was estimated to be 217kJ/mol under an argon atmosphere. The reaction rate is thought to be determined by solid-state diffusion through the reaction layer. However, the parabolic rate law was unapplicable to the rate data produced under a nitrogen atmosphere, because of the approach to the reaction equilibrium.

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Interface reactions for TiAl/Al₂O₃ and TiAl/TiO₂ have been investigated by the present study and the reaction for Ti/Al₂O₃ and the oxidation reaction of TiAl obtained from the literatures have been analyzed by the use of chemical potential diagram of Ti-Al-O system, The layer sequences for these interface reactions are summarized as follows.
(1) TiAl/Al₂O₃ at 1273K: No essential reaction occurred.
(2) TiAl/Al₂O₃ at 1373K; TiAl(O)/Ti₃Al(O)/Al₂O₃
(3) Ti/Al₂O₃ at 1373K for a thick sample by Choi et al.: Ti/Ti₃Al(O)/TiAl(O)/Al₂O₃
(4) Ti/Al₂O₃ at 1373K for a thin sample by Choi et al.: Ti₂O/Ti₃Al(O)/Al₂O₃
(5) Ti/Al₂O₃ at 1273K by Hatakeyama et al.: Ti/Ti₃Al(O)/TiAl(O)/Al₂O₃
(6) Oxidation of Ti-42at% Al at 1273K by Hatakeyama et al.: TiAl/Al₂O₃/Al₂O₃+TiO₂/TiO₂
(7) Oxidation of Ti-36.3at% Al at 1173K by Shida and Anada: TiAl/Ti₃Al(O)/Al₂O₃+TiO₂/Al₂O₃/TiO₂
These reaction paths have been reasonably elucidated by the use of chemical potential diagram of Ti-Al-O system, which was constructed using the data of Gibbs energy of formation of the compounds composed of Ti, Al and O.

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The potential use of Ba(Zr, Ti)O₃ (BZT) thin films as a decoupling capacitor for a multi chip module (MCM) has been examined. The crystal structure of BZT thin films on Pt(100)/MgO(100) and MgO(100) deposited from Ba(Zr_0.2Ti_0.8)O₃ powder targets had a perovskite structure and were strongly (100) oriented. The crystal structure of BZT thin films on Pt(111) was different from that of Pt(100)/MgO(100) and MgO(100) substrates. The degree of (100) orientation on Pt(111)/SiO₂/Si increased with increasing deposition temperature. A maximum dielectric constant of 150 was obtained at 600°C deposition. The loss tangent, leakage current and temperature dependence of capacitance of these BZT thin films were very small.

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Friction and wear tests of sintered α-SiC were conducted from room temperature to 1200°C both in air and vacuum. The coefficient of friction was larger in air than that in vacuum but was almost independent of the temperature. The specific wear loss generally increased with an increase of temperature. However, a substantial decrease in wear loss was observed at the highest temperature for lower contact pressure tests where a thick layer of small particles was formed on the friction surface. Silicon oxide was identified in wear debris particles particularly collected from high-temperature tests. It suggests that oxidation, which is accelerated at high temperatures, generally promotes material removal, resulting in a higher wear loss. However, the wear loss could decrease when oxide-containing particles form a thick surface layer.

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C₆₀-based thin films were prepared on Si(111) and quartz substrates as well as on a stainless steel rod (frictional specimen) by vacuum evaporation and rf ion plating methods. Their structures and friction properties were elucidated by Rraman and UV-VIS absorption spectra and by a pendulum type friction machine, respectively. The ion-plated films were composed of C₆₀ and its decomposition product (amorphous carbon: a-C) and the C₆₀/a-C ratio could be controlled by the rf power applied to generate the plasma. An ion-plated film containing C₆₀ was especially useful for preserving a low friction for a long time.

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Microstructure and mechanical properties of the self-composed Si₃N₄-TiN ceramics prepared from Si, TiC and TiO₂ mixed powder compacts were studied. Si₃N₄ matrix and TiN particles were formed during the sintering process of the ceramics. The results were compared with the reaction bonded Si₃N₄-TiN ceramics prepared from Si and TiN mixed powder compacts. The TiN particles in the self-composed Si₃N₄-TiN ceramics were finely and homogeneously distributed in comparison with those in the reaction bonded Si₃N₄-TiN ceramics. The fracture toughness was 5.0MPa·m^1/2 in Si₃N₄ ceramics, which incresed with addition of TiN particles. Fracture toughness of 6.3 and 5.9MPa·m^1/2 were obtained at 20vol% TiN for the self-composed Si₃N₄-TiN ceramics and the reaction bonded Si₃N₄-TiN ceramics, respectively. The incresed fracture toughness is probably due to the thermal expansion coefficient difference between the Si₃N₄ and TiN. The fracture strength was 930MPa in Si₃N₄ ceramics and it was retained up to 20vol% TiN in the self-composed Si₃N₄-TiN ceramics, whereas in the reaction bonded Si₃N₄-TiN ceramics the fracture strength was 350MPa at 20vol% TiN, only 40% of the initial value. This is possibly attributed to the difference in the distribution of TiN particles between two-ceramics.

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High uniformity of light output is required for scintillators utilized in detectors for high resolution X-ray CT. It was found that the uniformity of light output of Gd₂O₂S: Pr ceramics scintillator decreased with nonuniformity in B content in the sintered body. The B content depends on the particle size; raw material powders with smaller particle size contain higher B content. It was thought that the nonuniformity in B content in the sintered body was caused by the difference in the content of the fractions of smaller particles at each part of the compaction body.

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Conditions of slurry preparation and granule production processes influence the properties of granules produced from the slurry. In this study, alumina slurries of different amounts of dispersant (from 0.1 to 0.8mass%) were prepared to change the dispersion state. Granules were prepared from these slurries by using a spray-dryer to obtain granules of different microstructures. The relationship between microstructure of granules and green bodies compacted from the granules is discussed. As the amount of dispersant decreases, granules become weak and fragile, but uniform. The granules with high amounts of dispersant are strong, tough, and difficult to break. Uniaxially pressed green bodies from granules with high addition of dispersant, i.e., strong granules, contain defects such as granule traces and crescent-shaped irregular distribution of density. The defects come from the original shape of granules.

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Pseudo-single crystals of 3mol% R₂O₃-ZrO₂ (R=Yb, Y, Dy, Gd, Eu and Sm) were unidirectionally compressed in the range of 100 to 1000MPa at 700°C to examine the effect of additive cation on ferroelastic domain switching. The critical stress linearly increased with increasing radius of additive cation. The crystal lattice that solutionized larger additive cation dilated extensively, and was compressed heavily by adjacent lattices. This lattice compression seemed to prevent domain switching. On the other hand, as the critical stress was proportional to the elastic strain energy stored in the crystal lattice, this implies that the activation energy of domain switching increased by the elastic strain energy.

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Chemical reactions of diborane (B₂H₆), disilane (Si₂H₆), phosphine (PH₃) and hydrogen selenide (H₂Se) with copper (II) oxide (CuO) at room temperature were investigated. P₂H₆ and Si₂H₆ were chemically adsorbed on CuO surface and formed B-O bond and Si-O bond, respectively. The adsorbed species on the CuO surface prevented the hydrides from diffusing into the inner part of CuO. On the other hand, PH₃ and H₂Se reacted with CuO forming H₂O and Cu₃P and CuSe, respectively. In these cases oxygen atoms were removed from CuO particles as water molecules, and the reaction proceeded to the inner part of CuO particles. The reactions of hydride gases with CuO are divided into two types: the surface reaction and bulk reaction types, depending on the enthalpy of formation of the oxide per oxygen atom which is supposed to be produced by the reaction.

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Fine ceramics, especially Si₄N₄ ceramics, are promising as structural materials. In using Si₄N₄ ceramics as structural parts, it is important to develop more economical machining of the ceramics with low damage for finished surface. This paper presents feasibility of the Ultra-High-Speed (wheel speed: 60-180m/s) and low damage grinding process for Si₄N₄ ceramics with the newly developed metal-bonded wheel. Grindability was evaluated by grinding force, specific grinding energy and material strength after processing in the Ultra-High-Speed cylindrical grinding of Si₄N₄ ceramics by using the metal-bonded diamond wheel with homogeneously controlled distribution of grain cutting edges. Main results are summarized as follows: High efficiency grinding of a stock removal rate of Z′=50mm³/mm·s was achieved at a wheel speed higher than 60m/s, and 10-20% strength degradation was observed by grinding at a stock removal rate of Z′=50mm³/mm·s vis-á-vis to mateial strength before processing. These results indicate the experimental achivement of high efficiency and low damage processing. The point of this study is the small wheel depth of cut necessary for low damage grinding was achieved by increasing the wheel speed at an even high material removal rate. The metal-bonded wheel with homogeneously controlled distribution of grain cutting edges was used to decrease damage for finished surface.

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Using Cranz-Schardin camera, measurement of terminal velocity for thermally tempered glass has been attempted. Tempered 3.5mm-thick glass plates with three different levels of surface residual compressive stresses were used. It has been shown that the terminal velocity of fully tempered glass is 1.500×10³m/s, and that a linear relation exists between the terminal velocity and the suface compressive stress.

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The enthalpy changes for the formation reaction, ΔH, of the superconducting related oxide Bi₂Sr₂(Ca_xY_1-x)Cu₂O_y system from the simple oxides, Bi₂O₃, SrO, CaO, Y₂O₃ and CuO, were determined by the solution calorimetric method using a perchloric acid solution containing 1×10^-4mol iron (II) perchlorate hexahydrate. The standard enthalpies of formation, Δ_fH°, of the Bi₂Sr₂(Ca_xY_1-x)Cu₂O_y system were calculated from the ΔH and Δ_fH° values of the simple oxides. The enthalpy changes for the formation reaction in terms of mole of atoms, ΔH_R, were calculated by dividing ΔH by v, the number of atoms in a formula unit. On the basis of enthalpy, discussion was developed on the relation between the chemical stability of the complex oxide, the superconducting region and structure change. The enthalpy change for the formatin reaction, |ΔH_R|, of the Bi₂Sr₂(Ca_xY_1-x)Cu₂O_y system increased with increasing Ca substitution, x, and indicated a thermodynamic stability from the view point of enthalpy. The heats of solution of each sample composition, which was annealed at various temperatures, and oxygen partial pressures and oxygen contents, were measured. The enthalpy changes for the formation reaction, |ΔH_R|, were increased with increasing oxygen content for each composition and indicated thermodynamic stability.

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Effect of Al₂O₃ on high temperature strength of silicon nitride with Yb₄Si₂O₇N₂ was investigated. A silicon nitride was fabricated by hot-pressing powder mixture including 87.4mass% Si₃N₄, 12.1mass% Yb₂O₃ and 0.5mass% Al₂O₃. For reference, silicon nitride without Al₂O₃ addition was fabricated from powder mixture including 0.5mass% SiO₂ instead of Al₂O₃. Sinterability of silicon nitride with Al₂O₃ was higher than that of silicon nitride without Al₂O₃. Room temperature strength of the materials with Al₂O₃ was higher than that of the materials without Al₂O₃. Average strength at 1200 and 1350°C of both materials were almost same. The strength at 1500°C of the material with Al₂O₃ was slightly lower than that of the material without Al₂O₃. Creep resistance of the material with Al₂O₃ was lower than that of the materials without Al₂O₃.

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Volume and grain boundary diffusions of silver as an electrode material in PLZT were studied by means of a secondary ion mass spectrometry (SIMS). The volume diffusion coefficients (D_v) are described by an Arrhenius law as follows: D_v=0.12exp{-(258±25)(kJ·mol^-1)/RT}(cm²·s^-1). Distribution of silver ions in PLZT ceramics was observed by imaging of SIMS, and indicated that grain boundaries act as the high diffusivity path for silver element in PLZT. The temperature dependence of grain boundary diffusion coefficients (D_gb) was formulated as follows: D_gb=43.50exp{-(236±46)(kJ·mol^-1)/RT}(cm²·s^-1). The intergranular fracture is considered to be associated with the grain boundary diffusion of silver. At higher temperature, a reaction layer was remarkable near the interface between PLZT and electrode. Silver electrode reacted with PLZT, and then the reaction layer formed, as follows: PLZT+Ag→PLT+ZrO₂+(PbO+Ag) (PLT: (Pb, La)TiO₃). It is clear that the grain boundary diffusion of silver strongly effects to the mechanical and chemical strength and plays an important role in the reaction between Ag electrode and PLZT ceramics.

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An investigation has been made on the local structure and the gel to crystalline conversion mechanism in BaTiO₃ monolithic gels derived from hydrolysis of concentrated Ba, Ti alkoxide precursor solutions with a Ba/Ti molar ratio of 1.00 during aging at 30°C by means of XRD, Ba L_III-edge EXAFS, Ti K-edge XANES, and ICP. The results indicate that local structures of amorphous monolithic gels obtained immediately after gelation consisted of Ba-TiO₆ clusters coordinated with alkoxyl or hydroxyl ligands as a structural unit, which underwent condensation polymerization by corner-sharing of TiO₆ octahedra to form a three-dimensional gel-network. The conversion of gel to crystalline barium titanate nano-particles during aging at 30°C can be explained by a model that the crystalline phase directly forms from the amorphous phase without dissolution, deposition and diffusion of the reactant species nor generation of intermediate phases.

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Processing and some properties of 28.6mass% Shirasu/71.4mass% alumina light weight composites were studied to develop the dielectric constant and hermeticity required high performance microelectronic ceramic substrates. Colloidal processing was applied to obtain homogeneous and dense compact of Shirasu (or Shirasuballoons) and alumina. Mixed suspension of pulverized Shirasu particles (diameter of 8.2μm) or Shirasuballoons (15μm), and alumina particles (0.5μm) were prepared by adding an appropriate amount of polyelectrolyte. The green compacts were sintered at 1800-1500°C for 1h in air. The flexural strength of Shirasu/alumina composites sintered at 1400°C showed maximum value. Relative dielectric constant of the Shirasu/alumina composites was lower than that of the sintered monolithic alumina, which was interpreted by a modified Maxwell's equation. Mullite formation was confirmed for the Shirasu/alumina composites sintered at 1500°C by X-ray diffractometer.

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Synthesis of β-SiAlON whiskers from pyrophyllite was investigated and the growth of the whiskers was explained by VLS (vapor-liquid-solid) mechanism. During heating, Fe₂O₃ in pyrophyllite was reduced by carbon derived from resin to Fe which further reacted with C to form an alloy (Fe_xC_y). When the temperature was above the melting point of the alloy (about 1153°C), the alloy would become a liquid droplet under the influence of surface tension. Once the droplet was formed, the gases such as Si(g), SiO(g), Al(g), Al₂O(g) and N₂(g) would dissolve into the droplet. When the liquid droplet became supersaturated with the gases, the whiskers would grow by precipitation of β-SiAlON from the liquid.

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The fracture behavior of a silicon nitride layered composite with alternating dense and porous layers was investigated under varying span-to-depth ratio in bending tests. Although the load-deflection curves always indicated a linear behavior, delamination cracks were often observed in central porous layers. During four-point bending, a complicated fracture mode and local stepwise crack extension were observed. In the high span-to-depth ratio region, the fracture stress was almost constant and a fracture origin was always confirmed in the dense layer on the tensile surface. As for three-point bending, the fracture was originated in the dense layer on the tensile surface by tensile stress followed by delamination.

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