Gas-pressure sintering of β- and α-silicon nitride powders has been investigated at 1800-2000°C under 980 kPa N₂. The sintering behavior was detected by a dilatometer. Liquid phase sintering and grain growth of β powder is based on diffusion-controlled kinetics. The unimodal microstructure indicates a normal grain growth. With respect to β powder, there is an extra process for both sintering and grain growth of α powder. The nucleation of abnormal grains has been observed during phase transformation at the intermediate stage of sintering. At the final stage of sintering and grain growth, abnormal grains grow in the fine-grained matrix, resulting in in-situ reinforced microstructures. The grain growth behavior is to be discussed in relation to the driving force for grain growth. Finally, the control of microstructure is examined for in-situ reinforced microstructures and nano-ceramics.

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The historical understanding of polyphase silicon nitride, abbreviated throughout as SiN, has been a multidisciplinary effort that contributed to the sophistication of Ceramic Science over the last 50 years. This understanding and the development of SiN leading to significantly improved properties has been linked by uncovering relations between phase equilibrium, processing science, microstructural development and properties. The understanding of how to represent phase relations between Si₃N₄, other phases, eutectics and other important constituents in different Si-N-O-M systems was pioneered by Günter Petzow, his students, post-docs and co-workers at the Max-Planck-Institut fur Metallforschung in Stüttgart. It will be seen that this representation was one key to unlock the understanding of SiN properties as related to composition and its development into one of the modern ceramics of today. Major events and discoveries concerning these silicon nitride materials will be reviewed with reference major contributors to its science and technology.

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Heat resistant silicon nitride ceramics sintered with RE₂O₃ (RE: Sc, Y, and lanthanide) and those with RE₂Si₂O₇ as grain boundary phase were briefly reviewed. High-temperature strength and internal friction of silicon nitride ceramics with sintering additive of RE₄Si₂O₇N₂ composition (RE: La, Lu, Sc, and Yb) were measured to select candidates for evaluation of creep resistance. Following the results of high-temperature strength test and internal friction measurement, Yb and Lu were selected for sintering additive systems. Si₃N₄ powder with 2.4 mol% Yb₄Si₂O₇N₂ were gas-pressure hot-pressed at 1800°C for 1 h under 20 MPa in 1 MPa N₂ (YB). Si₃N₄ powder with 1.2 mol% (LU12) and 4.8 mol% (LU48) of Lu₂O₃ were gas-pressure hot-pressed at 1950°C for 1 h under 20 MPa in 1 MPa N₂. High temperature strength of LU12 was at its maximum among the three ceramics. Stress-strain curve of YB was linear at 1200°C, but at 1400°C it was non-linear. The Stress-strain curve of LU48 was non-linear at 1500°C. For LU12 the stress-strain curve was linear, and it was linear even at 1600°C, indicating that LU12 broke as a brittle fracture at 1600°C. LU12 had excellent oxidation resistance, and weight gain during the oxidation at 1500°C for 1000 h was 4 g/m². Creep resistance of LU48 was higher than that of YB. Creep life time of LU12 at 1500°C under tensile stress of 137 MPa exceeded 1678.5 h. Time-to-failure of LU12 was strongly stress sensitive.

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Based upon energetic considerations for every ceramic fabrication processing via solids as powders, liquids as solutions and melts, or gases including atoms and ions, it is concluded that solution processing has the least energy consumption when the shaped ceramics can be fabricated directly. The direct fabrication of ceramics in a solution by a single step process can be achieved via the interfacial reaction between a solid, substrate and reactant, and a solute specie in a solution. These soft processing and/or soft solution processing might prepare various ceramics films like BaTiO₃, SrTiO₃, CaWO₄, LiCoO₂, etc., at low temperatures, RT-150°C, without any post firing. The patterned ceramic films can also be fabricated directly in solutions when those interfacial reactions are locally activated and/or scanned. Another direct fabrication method, the ink-jet reaction method has been developed for the direct patterning of ceramics. The novel melt processings have been re-investigated for the direct fabrication of bulk ceramics particularly for the binary and ternary eutectic systems. Melt casting and annealing of the eutectic amorphous phase could produce nano-structured ceramics in HfO₂-Al₂O₃-GdAlO₃ and C₁₂A₇-CaYAlO₄ systems, etc. The importance of the powder-less processings, direct fabrications, of ceramics from solutions and/or melts has been demonstrated for the future sustainable society.

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This paper reviews typical and significant behaviours of the Sm₂Fe₁₇-N₂ system which is potentially of significance as a nitromagnetic material (metal nitride magnetic material). This paper is focusing on the processes of the N₂ absorption by the Sm₂Fe₁₇ and summarises results: (i) the crystal structure of Sm₂Fe₁₇N_x and the significance of N atoms as an interstitial in the alloy, (ii) thermodynamic properties and a partial phase diagram of the Sm₂Fe₁₇-N₂ system based on pressure-composition-temperature (PCT) measurements, and (iii) the mechanism of N₂ absorption by the Sm₂Fe₁₇ based on kinetic measurements and on catalytic behaviours on the alloy surface.

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Structural ceramics have been well known for their excellent mechanical properties and have obtained extensive applications in many fields. To explore the studies of the functional performances of structural ceramics have their wide developing space. To explore the studies of the functional performances of structural ceramics provides many opportunities for development. In this paper, I will introduce some examples for the electric, microwave absorbing, optic and other performances of structural ceramics in our laboratory.

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History of structural ceramics study has been examined specifically proceeded in NGK. At the early time of the age, structural ceramics had been selected to aim the potential candidate material for the variety of heat engine to achieve the better fuel efficiency. Many kinds of the sciences and technologies had been integrated to complete the material to commercial products. Later on the results of the heat engine components had been successfully transferred to semiconductor process equipment components and diesel particulate filter. In order to achieve the material properties goal, microstructure control philosophy had been kept as the principal how to optimize the character of the material to satisfy the necessary real world properties.

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Deposition experiments from aqueous solutions of zinc nitrate were performed in a bio-inspired way using biomolecules as directing agents. A global overview of the effect of various amino acids (8) and dipeptides (21) was done in term of structure and morphology of the obtained coating. The selection of certain biomolecules leads to the formation of smooth ZnO thin films. Variations of the amino acid chemical function and the sequence used within the peptides combination give rise to a wide variety of morphologies ranging from films to three dimensional nets. The data obtained from scanning electron microscopy and X-ray diffraction are discussed and correlated to the chemical properties of the biomolecules.

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Nanorods of wurtzite ZnS were synthesized by a hydrothermal method at 200°C and a co-precipitation method at room temperature in the presence of ethylenediamine (en) aqueous solutions. It was found that the wurtzite ZnS nanorods with uniform diameter around 80±20 nm, length about 300±100 nanometer appears at a proper concentration of en, unit [Zn] : [S] ratio, and an appropriate duration by the hydrothermal method. Much longer wurtzite ZnS nanorods with length from 300 to 2000 nm and diameter from 80 to 200 nm were obtained via the co-precipitation method. A very minor undecomposed ZnS•0.5en phase coexisted with the wurtzite ZnS nanorods in the co-precipitation method was identified and arguably thought to be due to the low temperature used. ZnO coated ZnS core-shell structures were successfully fabricated by annealing the ZnS nanorods in an oxygen flow at 650°C for 3-5 min. The coating of ZnO layer on ZnS nanorods results in a significant increase of photoluminescence (PL) intensity (30 times) at 490-500 nm visible regions for those of hydrothermal method and mild increase (double) for those of co-precipitation method.

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TiO₂ nanoparticles were synthesized by chemical vapor condensation (CVC) using titanium oxide acetylacetonate as a precursor in the temperature range of 800-1000°C. TEM observation revealed that TiO₂ nanoparticles 10-40 nm in diameter consisted of a hollow structure with shells 4-5 nm in thickness. From XRD results, it was found that TiO₂ nanopowders obtained at all temperatures consisted of a two-phase rutile and anatase mixture. The sequential decomposition of the metal acetylacetonate precursor observed in thermogravimetry (TG) analysis showed that formation of the hollow structure depends on the characteristics of the metal-organic precursor. In addition, it was found that the transmittance of TiO₂ hollow nanoparticles is lower than that of commercial nanopowders in the wavelength range of 400-800 nm by UV-visible spectrophotometry. However, the band gap energy of the TiO₂ hollow nanoparticles at about 3.0 eV is unchanged from other forms of TiO₂.

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The mechanical property and gas permeance of α-alumina (Al₂O₃) porous capillaries fabricated by a dry-wet spinning method were studied. Weibull analysis could be carried out on the fracture strength. Weibull modulus m and characteristic strength σ₀ decreased with an increasing porosity. The parameters of the capillaries agreed with the known value of the ordinary Al₂O₃ porous material. The helium (He) permeance for 77 capillaries at 298 K was 1.8×10^-5 mol m^-2 s^-1 Pa^-1 and deviation of the He permeances were in the narrow range from 1.5×10^-5 to 2.1×10^-5 mol m^-2 s^-1 Pa^-1. Permeances were proportionate to the exponential of porosity, and the dominant permeation mechanism was considered to be the Knudsen diffusion. The γ-alumina-coated porous α-Al₂O₃ capillary showed high H₂ permeance of 9.73×10^-6 mol m^-2 s^-1 Pa^-1 at 873 K. Therefore, the porous α-Al₂O₃ capillary in this study is a candidate for the support of hydrogen-permselective membrane at elevated temperatures.

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Structural transformations induced by high-energy ball-milling were studied in this work. It was found that amorphous Fe₉₀Zr₁₀ ribbons undergo crystallization into BCC α-Fe(Zr) under milling in a high-energy planetary ball-mill. Analyses of samples milled at different speeds suggested that the observed crystallization is a deformation-induced process rather than a thermally induced one. In addition, milling-induced structural transformations of CoSn and CoIn₂ intermetallics were studied. High-energy milling led to the decomposition of the CoSn phase into the high-temperature polymorph of Co₃Sn₂ and Sn(Co), whereas no evidence of the decomposition of CoIn₂ was found. These results may be attributed to high local stress during ball collisions which may make only those decomposition processes favorable, with which negative volume changes are associated.

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The thermodynamic assessment of the PZT system is carried out by the CALPHAD method. The thermodynamic properties of the phases are described using compound energy formalism (CEF) for the various solid phases and a solution model for the liquid. Three boundary systems PbO-ZrO₂, PbO-TiO₂ and ZrO₂-TiO₂ are reassessed based on the most recent experimental data, while the ternary PbO-TiO₂-ZrO₂ system is modelled for the first time. Calculated phase diagrams are compared with the experimental data.

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Thermodynamic modelling has been used to explain structural transformations during crystallization of amorphous Si-C-N polymer derived ceramics. Nanocrystalline SiC and nanocrystalline Si₃N₄ identified in ceramic microstructure have been regarded as metastable NASIC and NASIN phases of the Si-C-N system. Gibbs energies G(NASIC) and G(NASIN) have been derived considering an excess energy coupled with interfaces of nanocrystallites. The metastable phase equilibria including the nanocrystalline phases and the amorphous am-SICN phase have been analysed. Formation of NASIC and NASIN phases by eutectoid transformation of am-SICN phase and continuous growth of nanocrystallites have been ascertain as a possible way of crystallization. The resistance of Si₃N₄ against disintegration by reaction with carbon has been explained as a thermodynamic effect of nanocrystalline structure.

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Ceramic injection molding (CIM) is the most suitable shaping method for mass production of small ceramic components with complex shape in near net shape quality. Due to its high strength and fracture toughness zirconia toughened alumina (ZTA) is an interesting material for ceramic machine components and for biomedical applications. The ability to sinter ZTA to full density while retaining an extremely fine grained microstructure is the prerequisite to exploit the potential of the material. CIM components of ZTA which have much lower powder packing density and a lower homogeneity than e.g. isopressed or cast components normally show a very sluggish sintering behaviour even if very fine sub-μm or even nanosized powders are used. In this study a tailored pressureless sintering process for ZTA microcomponents was developed in order to be able to exploit the full technical and economic potential of the near-net-shape manufacturing process. Depending on the feedstock recipe a reduction in sintering temperature by more than 100 K was achieved and even higher densities reached than by conventional sintering. This leads to a refinement in microstructure and a reduction in alumina grain size by a factor of 2-3.

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Isothermal grain growth experiments have been conducted for undoped as well as cobalt oxide doped CeO₂ and Ce_0.8Gd_0.2O_1.9 (CGO20). Due to the solute drag effect of the dissolved gadolinium ions, the grain boundary mobility of CGO20 was significantly lower than that one of CeO₂. The addition of cobalt oxide increases the grain boundary mobility of CGO20. This increase is assigned to the formation of a characteristic cobalt oxide rich grain boundary film. In undoped and cobalt oxide doped CGO20, a transition from regular grain growth at high temperature in micron-sized grains to self-limited grain growth at low temperature in nanometer-sized grains occurs. As a consequence, highly stable microstructures result at lower temperatures. It is suggested that strain in amorphous grain boundary films becomes important for the self limited grain growth for very small grains at low temperatures.

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The critical average size of matrix BaTiO₃ grains for {111} twin-assisted abnormal grain growth in air was determined through the use of bi-layer samples of large BaTiO₃ grains with {111} twin lamellae and fine matrix grains of various sizes. Plates with large BaTiO₃ grains containing {111} twin lamellae were prepared by sintering 0.4 mol%-TiO₂-added BaTiO₃ powder compacts at 1250°C for 20 h in air. Additionally, plates with matrix grains having various grain sizes were prepared by sintering BaTiO₃ powder compacts at 1300°C for 0.5, 2, 8 and 48 h in H₂. Abnormal growth of the twin-containing large grains into matrix grains occurred for the matrix grain size of 4.1 μm and did not occur for that of 5.6 μm. It appears, therefore, that the critical size for abnormal grain growth is approximately 5 μm, which correspond to a critical driving force of 4.6 J/mol. The commonly observed abnormal grain growth during sintering of undoped BaTiO₃ in air is, hence, understood to result from much higher driving forces of fine powders than the critical value.

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Three-dimensional numerical simulation was performed to show that coarsening and grain growth was affected by particle arrangement in sintering of identical spheres. In the sintering of a row of three spheres the center particle with the coordination number of 2 coarsened, while particles on both sides with coordination number of 1 shrank and disappeared. The particles on both sides disappeared in a shorter time with increasing ratio of grain boundary energy γ_gb to surface energy γ_S. A new bond between two particles on both sides was created during sintering of three spheres with bond angle of 70°. This particle rearrangement changed the coordination number, and retarded the coarsening.

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The effects of α-Si₃N₄ powder, β-Si₃N₄ seed particles and sintering conditions on the texture development in Si₃N₄ ceramics, which were prepared by slip casting in a strong field of 12 T, followed by pressureless sintering. In the case of the replacement of the fine powder (UBE SN-E10) with the coarse powder (UBE SN-E05), no alignment of α-Si₃N₄ crystals was observed, but the alignment of β-Si₃N₄ crystals was observed in the green body, despite the low amount of β-Si₃N₄ (~1 wt%). This suggests that the grain alignment during slip casting is predominant by the grain alignment of the minor β-Si₃N₄ phase present in the α-Si₃N₄ raw powder, which is featured by the rod-like shape and less-agglomerated form. The alignment of both α-Si₃N₄ and β-Si₃N₄ crystals occurs by the c-axis of the crystals perpendicular to the magnetic field. The addition of 5 wt% β-Si₃N₄ particles leads to the enhanced grain orientation of the β-Si₃N₄ particles in the green body for both raw α-Si₃N₄ powders. It is shown that the crystallographic orientation of β-Si₃N₄ is enhanced by the substitution of SN-E10 for SN-E05 powder, the addition of β-Si₃N₄ particles and prolonged sintering, but the phase transformation of α to β may play a dominant role in the texture development in Si₃N₄ during sintering, compared to the grain growth after the complete phase transformation. Owing to the crystallographic orientation, the samples exhibited anisotropic shrinkage behavior during sintering and the anisotropy becomes strong with enhanced grain orientation. The present study suggests that the control of the alignment of β-Si₃N₄ is crucial for the texture development in Si₃N₄ by the magnetic field alignment.

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The potential of repeated-deformation processing using paraffin oil for the production of layered ceramic-matrix composites with ribbon-like microstructures is demonstrated. The examples given here include the alumina/zirconia, aluminium titanate/alumina, aluminium titanate/mullite, calcium phosphate/zirconia and barium titanate/Ni systems. Viscous ceramic- and metal-powder pastes containing 57 to 60 vol.% of solids were prepared using paraffin oil as the dispersing medium. These pastes were rolled into tapes, which were then stacked together to form starting bi-material laminates in an A-B-A or A-B sequence, and plastically deformed by repeated folding and rolling at room temperature. After a sufficiently large, true plastic deformation, composites with ribbon-like microstructures were successfully produced. These composites exhibited an almost isotropic sintering behaviour and attractive mechanical, thermal and/or electric properties.

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The present study reports on the preparation and structural characterization of dense NaNbO₃ ceramics with ultrafine grain size. Nanocrystalline raw powders obtained via microemulsion mediated synthesis were consolidated to green compacts, sinterforged to ceramic pellets with high density and ultra-fine microstructure and finally annealed under different thermal regimes in order to systematically increase the average grain size in the range from several hundreds of nm up to a few μm. Structural characterization of these materials included electron-microscopic observation and X-ray diffraction in combination with temperature tuning Raman-spectroscopy in order to detect both the global and local crystallographic symmetry in dependence of the grain size. The results show that ceramics with an average grain size from approximately 360 nm to 1-2 μm consist of a phase mixture of the anti-ferroelectric phase with the space group Pbcm, which is also observed for the conventional case of coarse NaNbO₃, and secondly of a new polar polymorph described by the space group Pmc2₁. The volume fraction of the second polar modification appears to increase with decreasing grain size suggesting an enhancement of the piezoelectric response of ultra-fine grained NaNbO₃ ceramics in comparison to coarse grained material of the same composition.

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Pure and Al³⁺ doped nano-hydroxyapatites (HA) were synthesized by a precipitation method to investigate their densification and thermal stability after the air sintering at 1100°C and 1300°C. Second phases were formed after increasing the Al³⁺ content from 2.5% to 7.5% in HA and increasing the sintering temperature from 1100°C to 1300°C. Al³⁺ addition into HA resulted in change in the hexagonal lattice parameters from the pure HA. When the sintering temperature was increased from 1100°C to 1300°C, densification was improved, which was verified by SEM micrographs. Al³⁺ addition resulted in smaller grain size after the sintering at 1300°C.

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Projected electrostatic and absorptive potential profiles across intergranular glassy films (IGFs) and interfaces between grains and glassy pockets in silicon nitride ceramics were obtained by reconstructing the electron exit face wave function from a series of defocused TEM images. The phase-object approximation (POA) was used for extracting the projected potential from the complex-valued exit-face wave function. The electrostatic as well as the absorptive potentials were scaled with respect to vacuum. For La₂O₃-MgO doped Si₃N₄, the potential profiles across the grain/glassy pocket interface and the IGF were observed to be very similar and give very strong evidence for the existence of a space charge layer at the interface.

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The oxygen self-diffusion behavior in deformed sapphire single crystals (α-Al₂O₃ sapphire) with a high density of unidirectional basal dislocations was examined in the temperature range of 1424-1636°C using ¹⁸O isotopes and secondary ion mass spectrometry-depth profiling techniques. The pipe and lattice diffusion kinetics were best described by r²D_p=4.6×10^-20 exp (-4.8[eV]/kT) [m⁴/s] and D_l=2.9×10^-1 exp (-5.5[eV]/kT) [m²/s], respectively. Both the magnitude of pre-exponential factor and activation energy for oxygen pipe diffusion were in good agreement with that of indirect measurements of pipe diffusion deduced from the annihilation of dislocation dipoles. The measured bulk diffusion coefficient is also in good agreement with previously reported data having activation energies ranged between 5.5-6.1 eV.

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The atomic structure of AlN(0001)/Al₂O₃(0001) interface, which is a model of a large lattice-mismatched film/substrate interface, was investigated by using static lattice calculations. Detailed analysis of the calculated structure revealed that the atomic relaxation behavior strongly depends on local atomic configurations of the interface. Interface distance became larger when Al atoms of AlN side and O atoms of Al₂O₃ side at the interface are in on-top configurations, while it became smaller when they are not in on-top configurations. The calculated structure qualitatively reproduced the experimental high-resolution transmission electron microscopy (HRTEM) image, which was obtained in our previous study. Such varieties of the atomic relaxation can be concluded to play one of the important roles for the formation of stable hetero-interface structures.

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Crystallographic orientation and phase identification on textured Ca-doped (ZnO)_mIn₂O₃ (m=3 and 4, denoted as Z_mIO) ceramics were investigated for better understanding and further improvement of the high-efficiency n-type thermoelectric oxide materials. Textured ceramics were prepared by the reactive-templated grain growth (RTGG) method, in which plate-like reactive seeds were exploited. A combination of electron backscatter diffraction pattern (EBSP) and energy dispersive X-ray spectrometry (EDS) techniques was utilized for analyzing the textured specimen parallel and perpendicular to the original sheet plane in detail. We revealed that in the specimen plate-like grains were aligned parallel to the sheet plane with the thickness direction parallel to the c-axis of each grain. Parallel aligned trigonal Z₃IO domains with a 60° misorientation angle were observed in a single grain. Coexisting trigonal Z₃IO and hexagonal Z₄IO phases were also observed in a single grain. These axis-sharing crystallites must be formed by the in situ topotactic conversion from a common hexagonal template crystal.

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X-ray analysis of the near-surface region of as-cut single-crystalline strontium titanate (001) wafers showed a reversible electric field-induced structure change at room temperature. To explain this phenomenon, a model is proposed which is based on the field-driven diffusional transport of oxygen and strontium along dislocation cores to the near-surface region and the growth of monolayer SrO precipitates by dislocation climb. Precipitate growth causes a lateral compressive stress in the near-surface region, which counteracts the diffusion of oxygen and strontium to the surface. By estimating the change of the Gibbs free energy due to precipitate formation, the lateral precipitate size and the resulting mean strain in the near-surface region is analyzed.

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An important fracture mechanics parameter governing path stability of growing cracks is the biaxiality ratio, i.e. the ratio of the T-stress and stress intensity factor. It is well known in general fracture mechanics that crack growth under positive biaxiality ratios is path-unstable. Any unavoidable mode-II loading must result in an increasing deviation from the initial straight crack plane. This holds for the most fracture mechanics test specimens used in tests on ceramic materials, for instance, edge-notched bending bars, CT, and DCB specimens. The theoretically predicted crack path stability is in disagreement with experimental findings reported in the literature on R-curve measurements, where R-curves were measured for crack lengths yielding high positive biaxiality ratios. Two possible reasons for this astonishing discrepancy between theory and experiments will be discussed.

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The first part of the paper deals with the computation of stress intensity factors for pyramidal indentation cracks with a ratio of crack length c to indentation half-diagonal a between 1 and 2. The residual stress field due to quasi-plastic deformation below the indenter is described by using the Hill model of an expanding sphere. It is found that the proportionality factor in the relation for K_Ic decreases with c/a→1 and confirms experimental results with nanoindents on sapphire and fused quartz. In the second part, the crack opening displacement of such cracks is determined.

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The R-curve behavior, spherical Hertzian contact damage and cyclic contact damage of a bearing grade Si₃N₄ ceramic reinforced with TiN particle dispersion are investigated and compared with the performance of a reference Si₃N₄ ceramic without TiN but with a similar microstructure. These ceramics were produced by firing powder compacts of Si₃N₄, Y₂O₃ and Al₂O₃, with and without additional AlN and TiO₂, at 1800°C for 2 h in 0.9 MPa N₂, followed by hot isostatic pressing at 1700°C. The ceramic without TiN has an R-curve with an initial value around 5.5 MPam^1/2, which slowly rises to 6.5 MPam^1/2 after a crack extension of 300 μm. In contrast, the Si₃N₄ ceramic with TiN particles has a higher initial K_R value but the R-curve remains relatively flat during subsequent crack growth. The latter ceramic exhibits a higher critical stress for permanent deformation and for ring-crack formation on the indented surfaces. It also demonstrates a better retention of the residual strength after single and repeated Hertzian indentation. The superior performance of the TiN-reinforced ceramic is attributed to the strengthening of grain boundary by TiN particles. Specifically, the resistance against contact and fatigue damage of this bearing grade Si₃N₄ is explained in terms of the effect of high grain boundary strength on the R-curve behavior, grain boundary microcracking, and the balance between crack shielding accumulation and degradation by grain boundary sliding during cyclic loading.

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A new biaxial tensile strength test (ball on three balls test, B3B-test) for brittle materials has been proposed by some of the authors several years ago. A disc-shaped plate is symmetrically supported by three balls at one plane and loaded by a fourth ball in the centre of the opposite plane. This new test has several advantages compared to conventional bending tests or other biaxial strength tests, especially the well defined load transfer geometry and a high tolerance against measurement uncertainties. This makes the testing of as-sintered (slightly buckled) specimens possible. In the past years the test has proved to be very practicable to test as-sintered disc specimens as well as as-sintered specimens which are shaped like a disc. Although discs are—in principle—easy to produce, in some cases it is more convenient to produce specimens having the shape of rectangular plates. Also many components have the shape of rectangular plates. Therefore, in this paper, the B3B-test is extended to test specimens which are that shape. An FE analysis of the stress fields in the specimens is performed and the maximum tensile stress amplitude and the effective volume in the specimens are determined. Specimens of different size and of several advanced ceramic materials were tested. It is shown that there exists a size effect on strength which can be explained in the framework of the Weibull theory. The B3B strength data determined on rectangular plate specimens fit to tests results determined on disc specimens and to conventional bending test results. The smallest tested specimen had a volume of some tenth of a cubic millimetre. To demonstrate the practicability of the method a strength distribution of an electroceramic component is determined by testing 494 individual rectangular B3B test specimens.

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Two different groups of Si₃N₄ based composites were prepared within the present study. The first group consisting of materials containing SiC nanoinclusions in Si₃N₄ matrix, the second one with the same SiC/Si₃N₄ composition containing different size of graphite particles. Wet volume abrasive wear of these two groups of materials was studied. Wear mechanisms of the first group is mainly transgranular fracture. The dominant wear mechanism of second group is changed with the increased load from transgranular to the intergranular. Significant role plays the weak graphite/matrix interface. The pull-out of SiC/Si₃N₄ grain agglomerates from this area deteriorates a possible lubrication effect of graphite during the test. No significant benefit of the application of graphite particles in respect to the wear behavior was observed in the present study.

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Silicon nitride ceramics are used under conditions were high strength, hardness and wear resistant is necessary. The increasing use of Si₃N₄-ceramics as ceramic ball bearings and valves in chemical apparatus demand an understanding of the relations between microstructure and corrosion behaviour of silicon nitride ceramics in different environments. The stability of the ceramics against corrosion in acids and bases is mostly controlled by the stability of the grain boundary. Therefore, the influence of different rare earth ions and the influence of the crystallisation of the grain boundary on the stability in sulphuric acid were investigated. The results showed that the nature of the rare earth has a minor influence on the corrosion behaviour. The stability against corrosion of the ceramics with amorphous grain boundaries is mostly controlled by the amount of the SiO₂ in the grain boundary. The crystallisation of the grain boundary can improve or not change the corrosion behaviour depending on the amount of crystalline grain boundary phases and the composition (stability) of the residual amorphous grain boundary phase. The results are discussed in the context with previous investigation and some systematisation of the corrosion behaviour of Si₃N₄ in acids and bases is given.

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12Ce-ZrO₂ based composites reinforced with the addition of 3Y-ZrO₂ as a second phase were fabricated by the pressureless sintering at 1400°C and subsequently post-HIP treatment at 1350°C. These 12Ce-ZrO₂ based composites with 3Y-ZrO₂ possessed the high strength over 1000 MPa and also maximum fracture toughness of 8 MPa•m^1/2. Furthermore, the significant inhibition of phase transformation of tetragonal to monoclinic phase under an aqueous hydrothermal condition at 150°C was obtained for these 12Ce-ZrO₂/3Y-ZrO₂ composites. Their microstructural observations and evaluation of some properties were carried out for these composites. Especially, their local structures of Ce-K, Y-K and Zr-K edges for these 12Ce-ZrO₂/3Y-ZrO₂ composites were examined by XAFS measurements.

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Magnetron sputtered (Ti_0.55, Al_0.45)N and (Ti_0.34, Al_0.66)N coatings are deposited onto cemented carbide substrates at 350°C. The crystal structure and microstructure of the deposited coatings are characterized by means of X-ray diffraction (XRD), electron probe microanalysis (EPMA), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Nanoindentation is employed to determine the microhardness of the coatings. The adhesion between the coating and substrate is investigated using scratch test. Measurement of flank wear is used to evaluate the wear resistance of the coatings. XRD examination indicates that both (Ti_0.55, Al_0.45)N and (Ti_0.34, Al_0.66)N coatings are of fcc structure. The atomic ratios of Al against Ti for the two coatings are approximately close to those of the alloy targets according to EPMA measurement. In accordance with SEM observation, the fractured cross-section of (Ti_0.55, Al_0.45)N coating is characterized by dense columnar grain structure with most of grains extending from the interface of coating and substrate to the surface. SEM and TEM investigations show that the (Ti_0.34, Al_0.66)N coating indicates the nano-crystalline feature without appearance of the columnar structure. (Ti_0.34, Al_0.66)N coating exhibits higher microhardness and wear resistance, but lower adhesion with the substrate than (Ti_0.55, Al_0.45)N coating.

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The c-axis oriented Zn_0.98Al_0.02O was prepared by a combination of high magnetic field and gelcasting techniques, and its thermoelectric properties were examined. Optimized gelcasting conditions made it possible to align the particles preferentially along the c-axis within a short exposure time in the high magnetic field. The particle orientation was not degraded and disturbed by the gelation and subsequent processing. The degree of orientation was increased after sintering at 1400°C. The c-axis oriented specimen along the ab-plane showed an enhanced the electrical conductivity compared with the non-oriented specimen. The differences in the Seebeck coefficients between oriented and non-oriented specimens were a very small. This study indicated that applying the magnetic alignment via gelcasting method provides effective and versatile techniques to fabricate large and dense grain oriented materials without hindering the thermoelectric properties.

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Fabrication and the electro-mechanical characteristics of fourteen types of piezoelectric micro bending actuators (PMBA) on silicon substrates using sol-gel multi-coated, thick PZT (Pb(Zr_0.52, Ti_0.48)O₃) films and MEMS processes were investigated. A PMBA was a piezoelectric body adhered to an elastic body. If an electrical field is applied to the z-axis, the piezoelectric body expands along the z-axis while contracting along the x- and y-axes. The elastic body was therefore deflected due to the generated bending moment. It was thought that PMBA might be used for designs of micro-fluidic devices and micro transducers. PMBA were fabricated using 2 μm-thick PZT films on Pt (350 nm)/SiO₂ (500 nm)/Si (300 μm) substrates with a MEMS process. Fourteen types of PMBA were fabricated with different sizes of silicon diaphragms, PZT films and top electrodes. When sizes of silicon diaphragms, PZT films, and Pt top electrodes with 3000 μm by 1389 μm, 4000 μm by 1000 μm, and 4000 μm by 980 μm were reduced down to 3000 μm by 194 μm, 4000 μm by 140 μm, and 4000 μm by 120 μm, respectively, the center displacements of PMBA were decreased from 0.70 μm to 0.13 μm at 5 Hz and 12 V_pp. At 5 V_pp and 10 kHz, in case of Sample 1 of Group 4, the center displacements were maintained in the range of 0.50 μm-0.56 μm up to 1.25 G cycles without remarkable degradation.

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Dense β-Si₃N₄ ceramics were prepared from the α-Si₃N₄ raw powder by sintering at 1900°C for 12 h at a nitrogen pressure of 1 MPa, using a mixture of Y₂O₃ and MgSiN₂ as the sintering additives. The effect of embedding conditions on the thermal conductivity of β-Si₃N₄ ceramics was investigated by changing the number of samples and the embedded fraction in BN packing powder with BN crucible. It was found that the embedment had no effect on the densification, but had an effect on the weight loss, crystalline secondary phase and microstructure. The thermal conductivity was found to increase linearly with the weight loss, but independent of the grain size. The complete embedment and the increased number of sintered samples tended to suppress the weight loss and thus lowered the thermal conductivity. The optimum condition led to a significant improvement in the thermal conductivity from 96 to 117 Wm^-1 K^-1. It is proposed that the enhanced thermal conductivity is attributed to the removal of lattice oxygen by the reaction Si₃N₄(s)+3 SiO₂(l)⇔6 SiO(g)+2N₂(g). In addition, the decreased amount of secondary phases also contributes to the thermal conductivity. This work suggests that the increased weight loss may also be an important strategy for enhancing the thermal conductivity of β-Si₃N₄ ceramics by controlling the sintering atmosphere.

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Small amount of Yb₂O₃ were added in Si₃N₄-Lu₂O₃-SiO₂ ceramics to improve their mechanical properties, and effect of the addition on gas-pressure sintering behavior and mechanical properties were investigated. The addition of small amount of Yb₂O₃ improved high temperature strength as well as fracture toughness, though the addition led to pore formation after gas-pressure sintering.

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In a recent paper by Omura et al.,¹⁾ wet jet milled α-alumina slurries exhibited distinctly different stability behavior compared to ball milled ones in terms of re-flocculation efficiency, rheological properties and packing density. The distinction was attributed to the different behavior of the same NH₄ ⁺ salt of poly(acrylic acid) in the two milling methods used. Force measurement via colloid probe method in the centrifuged supernatant of the milled slurries confirmed that the interaction distance between an alumina colloid probe and sapphire surface is about two times larger in wet jet milled slurry supernatant compared to the just ball milled one. This result confirmed that processing variables do affect the polyelectrolyte behavior in the slurry. The net force was always repulsive on approach in either supernatants.

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