In the three-dimensional molding of ceramics by direct ink writing, which is a type of material extrusion, extrudability and shape retention of the paste suspension are critical. In this study, we investigated the influence of varying fractions of the solid of paste suspensions on flowability and molding quality using ceramic clays with different mineral compositions. Stable molding was achieved by preparing the solid fraction based on the amount of plastic components in the ceramics clay, and by preparing the paste suspensions such that the apparent viscosity at a shear rate of 1000 s^－1 was between 10 and 40 Pa・s. When these moldings were fired, cracks and deformations were not observed in the sintered bodies. It was suggested that direct ink writing can fabricate three-dimensional ceramics-sintered bodies of various shapes.

　The morphology and powder properties of Si₃N₄ crystals obtained by nitriding high-purity Si powder in the temperature range of 1150℃ to 1450℃ under N₂–NH₃ atmosphere and further heat-treating porous Si₃N₄ ingots at 1550℃ and 1600℃ were investigated. At 1450℃, the fine needle crystals of Si₃N₄ were observed, but at 1550℃ and 1600℃, these were not observed. The value of the specific surface area and oxygen content of Si₃N₄ powders obtained from the porous Si₃N₄ ingot with fine needle crystals were both high, but these with no fine needle crystals were both low. These behavior of the specific surface and oxygen content of Si₃N₄ powders were presumed to be effected on the morphological changes of Si₃N₄ and decomposition of Si₂ON₂ generated by reaction Si₃N₄ and SiO₂ produced up to 1450℃ respectively.

　The sintering behaviors of ultrafine hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂; HAp) powders prepared by ultrasound irradiation were examined. Three kinds of ultrafine HAp powders having extremely high specific surface areas, i.e., 175, 194 and 237 m²・g^－1 (u–HAp(175), u–HAp(194) and u–HAp(237), respectively), were used as starting powders, together with commercial HAp powder (66 m²・g^－1 (c–HAp(66)). At the elevated temperatures, the temperature at which shrinkage started to occur was shifted toward lower value, as the specific surface area of the original powder increased. In any case, notable densification and microstructure developments occurred in the range of 900 to 1100℃, via the intra- and inter-agglomerate sintering of original particles. The relationship between porosity (P) and grain size (G) was expressed as GPⁿ=K (n and K, constants). The values of n and K decreased from 0.966 to 0.270 and 1.786 to 0.431, respectively, with increasing specific surface area of the original powder, indicating that the grain growth of sintered u–HAp(175), u–HAp(194) and u–HAp(237) bodies occurred slowly while the density approached full.

Ba-exchanged zeolite A (Ba-A) as a precursor of celsian, by grinding with various time, was investigated the changes of particle size and crystallinity, then thermal transformation processes of those ground specimens. The particle size and the crystallinity of Ba-A decreased with grinding time. Consequently, Ba-A became almost amorphous with grinding for 20 h. Ba-A, no-grinding sample, became an amorphous material at 300℃ with dehydration, and then generates a small amount of monocelsian in the amorphous material at 600℃, furthermore, hexacelsian formed in addition to the previously produced monocelsian at 1000℃. In contrast, in the amorphous sample ground for 20 h, mainly hexacelsian formed at temperatures above 1000℃. These results suggested that the structure in the amorphous induced by grinding was different from that in the thermal induced amorphous.

　Elution suppression treatment of heavy metals from municipal solid waste fly ash was applied by preparing geopolymer mixed Akadama soil as easily available volcanic soil. The solidified substances of Akadama soil mixed municipal solid waste incineration fly ash geopolymer were evaluated by the Japanese leaching test No. 13 defined by the Ministry of the Environment, tank leaching test, and compressive strength test. Quantitative values of As, Cd, Cr, Pb, Fe, Mn, Sr, and Zn in eluted solutions were quantified using inductively coupled plasma atomic emission spectrometry. The leaching amounts of heavy metals from Akadama soil-mixed fly ash geopolymer were suppressed as Cd not detected, 1/3 for Cr, 1/500 for Pb, 1/19 for Sr, and 1/23 for Zn, respectively, compared to those of raw fly ash. It is considered that soil-mixed fly ash geopolymer solidification can be applied as an effective treatment technique for elution suppression of heavy metals from the incinerator fly ash.