Ultrafine-grained non-oxide ceramics were prepared by combining the synthesis technology for fine-grained starting powders and the rapid sintering technology for spark plasma sintering (SPS); the two technologies were combined for obtaining ceramics with improved heat and corrosion resistance and improved mechanical properties. Hollow spherical Ca-α SiAlON powders composed of nanosized particles were synthesized by carbothermal reduction–nitridation of a SiO₂–Al₂O₃–CaCO₃ powder mixture. Using the Ca-α SiAlON powder, dense Ca-α SiAlON nanoceramics and porous Ca-α SiAlON ceramics with excellent mechanical properties and high heat and corrosion resistance were fabricated by the SPS technique. Ultrafine-grained Si₃N₄ and SiC ceramics were prepared from fine-grained Si₃N₄ and SiC powders by SPS. The densification of cubic-BN-dispersed ceramics composites was achieved without the phase transformation of cubic BN to low-hardness hexagonal BN, at a moderate pressure by the SPS technique.

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We investigated the crystal growth of hydroxyapatite (HAp) from α-phase (α-TCP) and β-phase (β-TCP) tricalcium phosphates showing different solubility, under hydrothermal conditions. Samples of α-TCP and β-TCP were treated up to 72 h under hydrothermal conditions at 120°C. The α-TCP sample was completely transformed into HAp crystals within 1 h after the powder was exposed to hydrothermal conditions. In contrast, the β-TCP sample required more than 72 h to achieve complete transformation into HAp crystals. This difference in transformation behavior affected the morphology of the formed HAp crystals, which were observed to form plate- and rod-shaped crystals from α- and β-TCP, respectively. The high dissolution rate of α-TCP led to fine, plate-shaped crystals whose morphology was maintained up to 72 h once they formed. In comparison, the low dissolution rate of β-TCP allowed production of large, well-crystallized HAp crystals through the hydrothermal treatment conditions, even though the chemical composition of the reactant samples were the same. The morphology of the HAp crystals formed as a result of the hydrothermal conditions was controlled by selecting starting materials whose solubility affects an increase in the degree of supersaturation in the solution.

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This paper describes a novel experiment in which alumina was joined using polycarbosilane (PCS) and an aluminum foil. PCS was used to design the surface structure of alumina, and the aluminum foil enabled the formation of an area that included the alumina surface designed using PCS; this area could be joined to ceramic materials. A four-point bending test revealed that the flexural strength of both the silicon carbide (SiC) and the silicon oxide (SiO₂) pieces that were obtained from alumina whose surfaces were modified to SiC or SiO₂ increased, compared with the flexural strength of ceramics joined by alternative methods involving the use of organometallic polymers whose compositions are similar to SiC and SiO₂. Moreover, it was apparent that alumina was formed by the reaction of SiO₂ with aluminum. However, traces of Al and Si remained in the joining area in both the SiC and SiO₂ pieces.

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ZrB₂–ZrC–SiC composites were prepared by spark plasma sintering (SPS) at temperatures of 1750°C for 300 s under a pressure of 40 MPa. Densification, microstructural, mechanical properties and oxidation behavior of the composites were investigated. Fully dense ZrB₂–ZrC–SiC composites with a relative density of more than 99% were obtained at 1750°C for 300 s. Vickers hardness of ZrB₂–ZrC–SiC composites decreased with increasing ZrC content from 20 to 40 vol %, and composite containing 60 vol % ZrB₂, 20 vol % ZrC and SiC sintered at 1750°C for 300 s had the highest value of 21.1 GPa. The crack mode for the same composite was zigzag, and resulted in remarkable crack deflections and the highest fracture toughness value of 5.5 MPa·m^1/2. Oxidation of composites resulted in formation of protective layered oxide structures consisted of ZrO₂ and Si–O rich layer in the form of SiO₂ or SiO, and normalized mass change results increased with increasing oxidation temperature.

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The effect of additives on compressive strength and thermal conductivity of vermiculite-SiO₂ composites with a layered structure was investigated. Anisotropy in both properties was observed because of the layered structure produced by cellulose fibers. Both compressive strengths (58–123 MPa) and thermal conductivities (1.29–1.34 W/m·K) in the direction perpendicular to the pressing direction (T) were higher than those (22–68 MPa and 0.45–1.13 W/m·K) in the direction parallel to the pressing direction (S) in all samples. The compressive strength and thermal conductivity of the vermiculite-SiO₂ composite containing no additives were 54 MPa and 1.13 W/m·K when measured parallel to the pressing direction, respectively. In contrast, those of the composite containing 5 mass % TiO₂ and 5 mass % SiC were 68 MPa and 0.45 W/m·K when measured parallel to the pressing direction, respectively.

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Ca-α SiAlON powders were synthesized from a SiO₂–Al₂O₃–CaCO₃ powder mixture by reduction-nitridation with C₃H₈–NH₃ gas. Ca-α SiAlON with small amounts of AlN and β-SiAlON phases was produced at 1450°C for 120 min. Angular particles and agglomerated and bonded particles with irregular shapes were formed. In the product prepared at 1450°C without any holding time, Si₂N₂O was detected as an intermediate phase, in addition to the Ca-α SiAlON, β-SiAlON and AlN phases. A large number of agglomerated and bonded particles were observed.

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