Author
Takaaki Nagaoka
Other affiliations: Industrial Research Institute
Bio: Takaaki Nagaoka is an academic researcher from National Institute of Advanced Industrial Science and Technology. The author has contributed to research in topics: Sintering & Ceramic. The author has an hindex of 13, co-authored 60 publications receiving 685 citations. Previous affiliations of Takaaki Nagaoka include Industrial Research Institute.
Topics: Sintering, Ceramic, Green body, Microstructure, Silicon nitride
Papers
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TL;DR: In this paper, the effect of seeding on microstructure development and mechanical properties of silicon nitride was investigated by the use of morphologically regulated rodlike β-Si3N4 singlecrystal particles with a diameter of 1 μm and a length of 4 μm as seed crystals.
Abstract: The effect of seeding on microstructure development and mechanical properties of silicon nitride was investigated by the use of morphologically regulated rodlike β-Si3N4 singlecrystal particles with a diameter of 1 μm and a length of 4 μm as seed crystals. Silicon nitride with a bimodal microstructure was fabricated under a relatively low nitrogen gas pressure of 0.9 MPa owing to the epitaxial growth of β-silicon nitride from the seed particles. Grain growth from seeds followed the empirical equation Dn–D0n=kt, with growth exponents of 3 and 5 for the c-axis direction and the a-axis direction, respectively, being analogous to the kinetics of matrix grain growth. By seeding morphologically regulated particles, fracture toughness of silicon nitride was improved from 6.3 to 8.4–8.7 MPa·m1/2, retaining high strength levels of about 1 GPa.
226 citations
TL;DR: In this paper, SiC joints were reaction joined in the temperature range of 1450-1800°C using TiB 2 -based composites starting from four types of joining materials, namely Ti-BN, Ti-B 4 C 4 C,Ti-BN-Al, and Ti B 4 C-Si.
Abstract: SiC ceramics were reaction joined in the temperature range of 1450–1800 °C using TiB 2 -based composites starting from four types of joining materials, namely Ti–BN, Ti–B 4 C, Ti–BN–Al and Ti–B 4 C–Si. XRD analysis and microstructure examination were carried out on SiC joints. It is found that the former two joining materials do not yield good bond for SiC ceramics at temperatures up to 1600 °C. However, Ti–BN–Al system results in the connection of SiC substrates at 1450 °C by the formation of TiB 2 –AlN composite. Furthermore, nearly dense SiC joints with crack-free interface have been produced from Ti–BN–Al and Ti–B 4 C–Si systems at 1800 °C, i.e. joints TBNA80 and TBCS80, whose average bending strengths are measured to be 65 MPa and 142 MPa, respectively. The joining mechanisms involved are also discussed.
34 citations
TL;DR: In this paper, the authors examined Young's modulus, fracture toughness and microstructure of the composites and suggested that the presence of the grain-boundary phases in the composite favors the formation of microcracks at smaller TiN particles.
Abstract: Si3N4/10vol% TiN particulate composites with six TiN particle size distributions (average size: 0.3-13.6μm) were sintered at 1850°C for 4h in 0.9MPa N2 atmosphere, and Young's modulus, fracture toughness and microstructure of the composites were examined. Although all the composites were densified up to >98% theoretical density, Young's modulus of the composites with larger TiN particles decreased due to the pre-existing microcracks. Fracture toughness of the composites showed a maximum value at the particle size of TiN of about 4μm, which is smaller than the predicted critical size. It is suggested that the presence of the grain-boundary phases in the composite favors the formation of microcracks at smaller TiN particles.
33 citations
TL;DR: In this paper, it was found that the sintering behavior of BiT powders strongly depend on the calcination temperature of the precursor, which is high enough to decompose most of the BiT precursor to avoid the cracks in sintered samples, and also low enough to ensure high sinterability.
33 citations
TL;DR: In this article, a boehmite gel 3-D network was formed by the hydration of hydraulic alumina (HA) in CA/CaCO3 mixed slurry.
Abstract: We have developed a new eco-friendly fabrication process for porous ceramics using hydraulic alumina (HA) and water. In the present study, we fabricated porous calcium-hexaaluminate (CaAl12O19, CA6) ceramics using this new process. A boehmite gel 3-D network was formed by the hydration of HA in HA/CaCO3 mixed slurry. The HA/CaCO3 mixed slurry was hardened by the formation of this 3-D network. Even without the addition of an organic binder, green bodies containing the 3-D network demonstrated high compressive strength and retained their original shapes. Furthermore, the water acted as a fugitive material in the green bodies. Consequently, the open porosity of the CA6 ceramics could be controlled over a wide range of 42–62.7% by the addition of water (ratio of water to HA/CaCO3 mixed powder: 0.4 to 1.6 by weight) without the use of organic fugitive materials. The results of evolved gas analysis-mass spectrometry measurements showed that the emissions from the hardened green body consisted mostly of water. Consequently, the new fabrication process for porous calcium-hexaaluminate ceramics was confirmed to be eco-friendly.
31 citations
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TL;DR: This article is focused on nanosized HAp, although recent articles on microsized particles, especially those assembled from nanoparticles and/or nanocrystals, have been reviewed for comparison.
1,036 citations
TL;DR: The nanosized and nanocrystalline forms of calcium orthophosphates have great potential to revolutionize the hard tissue-engineering field, starting from bone repair and augmentation to controlled drug delivery systems.
469 citations
TL;DR: Transparent polycrystalline ceramics have found various applications, such as laser hosts, infrared windows/domes, lamp envelopes and transparent armors, due mainly to their processing flexibility in fabricating items with large sizes and complex shapes and more importantly costeffectiveness as mentioned in this paper.
453 citations
TL;DR: The very fast (within minutes) in situ formation of a tough interlocking microstructure in Si3N4-based ceramics is reported, which is uniform and reproducible in terms of grain size distribution and mechanical properties, and are easily tailored by manipulating the kinetics.
Abstract: Ceramics based on Si3N4 have been comprehensively studied and are widely used in structural applications1, 2. The development of an interlocking microstructure of elongated grains is vital to ensur ...
439 citations
TL;DR: The use of self-reinforcement by larger elongated grains in silicon nitride ceramics requires judicious control of the microstructure to achieve high steady-state toughness and high fracture strength as discussed by the authors.
Abstract: The use of self-reinforcement by larger elongated grains in silicon nitride ceramics requires judicious control of the microstructure to achieve high steady-state toughness and high fracture strength. With a distinct bimodal distribution of grain diameters, such as that achieved by the addition of 2% rodlike seeds, the fracture resistance rapidly rises with crack extension to steady-state values of up to 10 MPa{center_dot}m{sup 1/2} and is accompanied by fracture strengths in excess of 1 GPa. When the generation of elongated reinforcing grains is not regulated, a broad grain diameter distribution is typically generated. While some toughening is achieved, both the plateau (steady-state) toughness and the R-curve response suffer, and the fracture strength undergoes a substantial reduction. Unreinforced equiaxed silicon nitride exhibits the least R-curve response with a steady-state toughness of only 3.5 MPa{center_dot}m{sup 1/2} coupled with a reduced fracture strength.
383 citations