A new family of lithography-based modeld experiments has been developed that permits the introduction of micron-scale controlled-geometry defects at interfaces. These microdesigned interfaces can be used to study various aspects of microstructural evolution during sintering. In addition, they can be applied to studies of mechanical behavior of porous materials and ceramic-metal composites. Research utilizing such microdesigned interfaces is reviewed, and numerous potential applications of the technique are suggested.

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CuCl-doped Na₂O-B₂O₃-SiO₂ glasses were successfully obtained by the conventional melt-quenching method. Complete glassy bodies were obtainable up 2mol% CuCl. The CuCl microcrystals grew by heat-treatment at 450° or 500°C, and the mean radius of the microcrystals was proportional to one third power of heating duration. The exciton peaks were observable even at room temperature and the temperature dependence of the peak shift implied the significant influence of volume effect. Homogeneous and inhomogeneous widths of the exciton peaks were evaluated from the temperature dependence of Z₃ peak line width. The large inhomogeneous distribution seems to result from random structure of the matrix glasses and large microcrystal size distribution.

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To improve the properties of zirconia-toughened-alumi-na (ZTA) ceramics, a technique which involves hydrolysis of Zr(OC₃H₇)₄ in an Al₂O₃ slurry to form an Al₂O₃ powder with uniformly distributed ZrO₂ is described. The addition of TiO₂ within its solubility limit in ZTA enhanced the sinterability of the ZTA powder. A relative density of 98% for ZTA bodies can be obtained by firing at 1500°C for 2h. It is shown that the presence of TiO₂ promotes the grain growth of Al₂O₃ and ZrO₂, and contributes to the retention of tetragonal-ZrO₂ in the sintered ZTA body.

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The effects of dopant on the electrical conductivity of sintered SiC were investigated. SiC specimens containing B₄C, AlB₂, and BN were fired in the temperature range of 1900°-2050°C. The frequency dependence AC conductivity and temperature dependence of DC conductivity were measured. The electrical conductivity of B₄C or BN doped specimens sintered at below 1960°C was several orders of magnitude higher than that of specimens sintered at above 1970°C. On the other hand, the electrical conductivity of specimens doped AlB₂ depended slightly on the sintering temperature. The electrical conductivity of the specimens fired below 1960°C was independent of the frequency and the measurement temperature. On the other hand, the electrical conductivity of specimens fired above 1970°C depended on the frequency and temperature. The electrical conductivity of specimens fired at 2050°C depended strongly on the frequency and the temperature regardless of the dopant. The electrical conductivity of BN doped SiC depended strongly on the frequency and measurement temperature. On the other hand, the electrical conductivity of AlB₂ doped SiC depended slightly on the frequency and temperature. The experimental results were discussed using the energy band models and the equivalent circuits.

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This study was undertaken to obtain kaolinite from serpentinite by treating with AlCl₃ solution under various hydrothermal conditions. The serpentinite used as a starting material was from Hidaka district, Kochi Pref. Magnetite included was removed by wet magnetic separation after crushing under 280mesh. Then, 0.4g of the purified serpentinite was sealed in an ample together with AlCl₃ solution and heated in an autoclave above 150°C. When this material was treated with 0.5-1.0mol/l AlCl₃ solution at 200° and 245°C for 48h boehmite and/or Al₂₄O₁₁(OH)₄₄Cl₆ were formed together with kaolinite. Treatment with 0.5mol/l AlCl₃ solution yielded only boehmite in addition to kaolinite. To prevent the formation of boehmite, mixed solutions of AlCl₃ and HCl were used. When the concentrations of AlCl₃ and HCl were 0.5 and 0.3mol/l, respectively, white kaolinite with low crystallinity was obtained at 245°C for 48h or 200°C for 65h. It was found that metallic elements except Si was exracted completely from the starting material into the solutions. About 98% of Si in the starting material was converted to kaolinite. The experimental results indicate that the transformation from serpentine to kaolinite proceeds at low reaction temperature in a short duration. This is presumably because the kaolinization of serpentine proceeds topotaxially as a consequence of virtually indentical crystal structure of serpentine and kaolinite.

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Titanium nitride (TiN) ceramics without additives were fabricated by the hot-pressing (HP), and their mechanical and electrical properties were investigated. Hot-pressing was performed at various sintering parameters such as sintering temperature (1800°-2250°C), sintering time (30-180min), pressing pressure (2-14MPa) and ambient gas (Ar) pressure (vacuum-10atm). Densification was promoted at higher temperature, higher pressing pressure and longer sintering time. The TiN ceramics fabricated by hot-pressing at 2100°C×60min under the pressing pressure of 14MPa in the normal ambient gas pressure showed the representative properties: bulk density; 5050kgm^-3 (relative density 92.8%), Vickers microhardness; 8.52GPa, flexural strength; 265MPa, static modulus (Young's modulus); 387GPa, dynamic modulus; 459GPa, and volume resistivity; 0.360μΩ·m. These properties were affected especially by the ambient gas pressure during hot-pressing. The TiN ceramics prepared in vacuum showed 30-40% augmentation, on the average, in hardness, flexural strength, Young's modulus and resistivity, compared with those prepared under normal (1atm) and higher pressures (5, 10atm). TiN ceramics with high mechanical properties were obtained by sintering in vacuum.

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The effect of grain size on creep in mullite ceramics containing 71, 72 and 74wt%Al₂O₃ (71A, 72A, and 74A, respectively) has been studied. It is shown that a glass phase existed around grain boundary triple points for 72A, whereas it did not exist for 74A from the observation by transmission electron microscope. Stress exponents n's for creep deformation were 1.1-1.2, 1.2-1.3 and 1.3-1.5, and grain size exponents m's were 2.4, 2.0 and 1.2 for 71A, 72A and 74A, respectively. It was assumed that the creep deformation was controlled by grain boundary sliding accommodated by cavitation for 74A, diffusion in glass phase at grain boundaries for 71A and their combined mechanism for 72A.

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The fatigue behavior of gas pressure sintered silicon nitride ceramics at room temperature in air was investigated. Cyclic and static fatigue tests were carried out for smooth specimens and precracked specimens. Precracks were introduced by indentation at the center of the tension side surfaces. All the testing was conducted by the 3-point bending method. Smooth specimens showed no significant enhancement of the subcritical crack growth by cycling. On the other hand, enhanced fatigue was observed for precracked specimens. In addition, it is suggested that the fatigue behavior depends on the size of the precracks. Cyclic fatigue behavior was not influenced by residual stress introduced by Vickers indentation.

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The influence of chain length and molecular structure of alcoholic solvents on the hydrolysis behavior of zirconium tetra butoxide ‹ZBu› and morphology of product particles was investigated. ZBu dissolved in alcoholic solvents except methanol. Monodispersed zirconia particles with submicron size were obtained in the range of water to ZBu molar ratio of 1.6-2.5 in ethanol and 2.1-2.2 in propanol. In contrast, in alcohols with longer chain lengths than butanol, a mixture of agglomerates and large spherical particles was obtained. The formation of the mixture was related to induction time and hydrolysis rate of ZBu. On the other hand, an increase in the number of carbon branches in butanol increases the amount of agglomerates.

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Superconducting YBa₂Cu₄O₈ (1-2-4) films were prepared by the dipping-pyrolysis process, and effects of heat-treatment conditions and partial-substitution of Y for Ca on the product films were investigated by XRD, SEM and resistance measurement. Films of the 1-2-4 phase with T_{c, zero}=70K and 55K were prepared by direct heat-treatment of (Y₂O₃-BaCO₃-CuO) precursor films (Y:Ba:Cu=1:2:4 in molar ratio) in O₂ at 780°C for 24-72h followed by slow-cooling and quenching, respectively. Both the films showed metallic behavior above the transition temperatures, indicating the formation of the 1-2-4 phase. On the other hand, once a mixture of YBa₂Cu₃O₇ (1-2-3) and CuO was formed by the heat-treatment at 820°C, p(O₂)=10^-3atm; or at 700°C, p(O₂)=10^-2-10^-4atm, conversion into the 1-2-4 phase was very difficult after the subsequent heat treatment within the stability region (780°C, p(O₂)=1atm) of the 1-2-4 phase. The Y_1-xCa_x Ba₂Cu₄O₈ (x=0.05 and 0.1) films exhibited higher Tc, onset values, however, the film of x=0.1 was found to contain only small fraction of the 1-2-4 phase. Moreover, when the Ca-containing precursor films were fired in an atmosphere with p(O₂) of 10^-3-10^-4atm at 700°C, the product films gave an XRD pattern of (1-2-3)+(1-2-4) mixture.

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Sintered bodies of Fe₄N were prepared by way of a hot-press, followed by firing in an atmosphere containing NH₃ and H₂ gases. After the hot-press, Fe₄N was not sintered and impurities of an iron oxide and a paramagnetic compound coexisted. The sintered bodies were obtained by firing the hot-pressed bodies in the atmosphere. It was found that, in firing, Fe₄N was reduced and sintered above the decomposition temperature (approx. 670°C) and then the sintered bodies were rapidly renitrified in the atmosphere to Fe₄N through open pores in cooling. X-ray diffraction and Mössbauer spectra showed that the sintered bodies were Fe₄N single phase.

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In order to produce SiCl₄ efficiently from active SiO₂ in rice hulls, rice hull ash, combustion waste of rice hull, was chlorinated under the coexistence of alkaline and alkaline earth additives such as potassium compounds in the temperature range of 600° to 1000°C. These additives changed to chlorides under the condition of chlorination. Potassium compounds accelerated the chlorination of the rice hull ash. Other alkaline and alkaline earth compounds such as lithium, sodium, magnesium and calcium inhibited the chlorination. The acceleration effect of potassium in the chlorination of SiO₂ was explained by assuming that the diffusion of K⁺ ion in SiO₂ lattice caused the distortion of SiO₂ lattice and the chlorinating species such as chlorinated carbon were easy to diffuse in SiO₂ lattice. The inhibitory efffect of other elements was interpreted in terms of the absence of SiO₂ lattice distortion, since the ionic radii of these elements are smaller than that of K⁺. It is also inferred that the melts of these chlorides covered the contact points of SiO₂ and C.

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Improved K_IC values of monolithic Si₃N₄ ceramics will be expected by growing-in a matrix of microcrystals of β-phase Si₃N₄-an appreciable amount of extensively large, rod-shape crystals of the same phase. It is anticipated that the large grains should play as crack impediments like whiskers mixed in composite ceramics. The test materials prepared by changing firing conditions had such well-grown crystals of different sizes, ranging from 2 to 10 microns in diameter. The fracture toughness (measured by the SEPB method) increases up to 11.3MPa·m^1/2 with the increase in the grain size. Prominent crack bridging along the fracture surface behind the propagating crack tip is found to be the possible toughening mechanism.

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The initial stage growth of a metallized layer of silicon-nitride ceramics was investigated by the Vapor-diffusion method. The metallization was carried out using manganese powder as a vapor source under a dynamic vacuum condition from 1073 to 1273K up to 129.6ks. The metallization process was found to be divided in to two reaction stages. At the initial stage a two layer structure was found; the surface layer of Mn₆Si and alpha-Mn(Si), and the bottom layer of MnSiN₂ and oxide additives. The thickness of the bottom layer increased rapidly at the onset of the initial stage. This change in layer thickness is due to the reaction of Si₃N₄ ceramics with manganese gas molecules supplied directly through opening and pores in the growing surface layers. After the initial transition period, the surface layer became compact, and a middle layer, a mixture of alpha-Mn(Si), Mn₆Si and oxide additives, was newly formed by decomposition of the bottom layer. Consequently, the thickness of the bottom layer decrese. Thereafter, it remained almost constant at 6.0μm at 1173K, 4.8μm at 1223K and 4.0μm at 1273K. Under steady state condition, it was found that the growth of the surface layer and bottom plus middle layer obeyed the parabolic rate law, respectively.

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The effect of alumina content on the electrical and thermal properties of substrates consisting of tetragonal zirconia polycrystals and various volume fractions of Al₂O₃ was studied. The substrates were fabricated by the doctorblade casting, using an Al₂O₃ powder and coprecipitated zirconia powders with compositions 4 mol% YO_1.5-4mol%CeO₂-ZrO₂ and 3mol%Y₂O₃-ZrO₂, and their surface roughness and microstructure were investigated. The average surface roughness (R_a) of the substrates was smaller than 0.1μm. The dielectric constant (ε), dielectric loss tangent (tanδ) and thermal expansion coefficient of the substrates decreased with increasing alumina content. The volume resistivity of the substrates was not sensitive to the alumina content in the range of 33.9 to 69.8vol%. It depended on the volume resistivity of TZP.

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Indium-tin-oxide (ITO) films were prepared by the chemical spray pyrolysis method using InCl₃⋅6H₂O and SnCl₄⋅xH₂O (x=3-5) as starting materials. The film with a minimum resistivity of 1.23×10^-3Ω·cm was obtained for tin doping, Sn/In=5at%. Resistivity of 50nm thick films showed hysteresis phenomena in heat cycles repeated at temperatures between 100° and 500°C in O₂ and Ar gases. The hysteresis results were discussed in terms of desorption of H₂O from In₂O₃-H₂O complexes, superposing desorption of adsorbed O₂ from the films.

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Single crystals of a new compound NaGaTi₅O₁₂ were synthesized by the flux method. This crystal always occurred in coexistence with Na_1-xTi_xGa_5-xO₈ crystals. The best crystal was obtained by slow-cooling after keeping at 1350°C for 10h using a mixture of 35mol% crystal composition of (Mo₂O)₁(Ga₂O₃)₁(TiO₂)₁ and 65mol% flux composition of (Na₂O)₁(MoO₃)_1.5 as a compositional condition in the flux melt. This crystal structure consists of peculiar framework with one-dimensional tunnel structure of a new type which is a monoclinic system with a=15.202(Å), b=3.732(Å), c=9.317(Å) and β=122.04°. This compound was identified as a high temperature phase of Na-Ga-freudenbergite (Na_0.7Ga_0.7Ti_3.3O₃) which transformed at 1238°C, and melted at 1336°C.

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The addition effect of alkali-earth metal oxides to the mother glass of alkali durable porous glass has been experimentally examined, and following results were obtained. The composition of the mother glass employed in this report was 57.2SiO₂⋅22.8B₂O₃⋅5.7Na₂O⋅9.2RO(R=Mg, Ca, Sr, Ba)⋅3.2ZrO₂⋅1.9Al₂O₃ (mol%). (1) The addition effect of alkali-earth metal oxides on the phase separation rate of mother glass was largest for MgO, followed by, in the decreasing order, CaO, SrO and BaO. (2) The addition effect of alkali-earth metal oxides on ZrO₂ content in the skeleton of porous glass is not obvious now, but it may be closely associated with the phase separation rate of mother glass. (3) The addition of alkali-earth metal oxide was effective for retaining ZrO₂ in the skeleton of porous glass.

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