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Effect of AlN addition on the reaction sintering of Al2TiO5 composites fabricated by spark plasma sintering
(2023-01-01)
Kitiwan, Mettaya
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Atong, Duangduen
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Endo, Fumio
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Goto, Takashi
Fully dense Al<inf>2</inf>TiO<inf>5</inf>–Al<inf>2</inf>O<inf>3</inf>–TiN (ATN) composites were fabricated by reactive sintering using spark plasma sintering at 1400°C for 5 min under 100 MPa in vacuum. An equimolar ratio of Al<inf>2</inf>O<inf>3</inf>:TiO<inf>2</inf> was used as the starting powder, while the addition of 0–36 mol% AlN was investigated. The thermodynamic calculation indicates that the initial reaction was that of TiO<inf>2</inf> and AlN, forming TiN and Al<inf>2</inf>O<inf>3</inf>, and then the remaining TiO<inf>2</inf> reacted with Al<inf>2</inf>O<inf>3</inf> to produce Al<inf>2</inf>TiO<inf>5</inf>. With the increase in AlN precursor, Al<inf>2</inf>TiO<inf>5</inf> gradually decreased, while Al<inf>2</inf>O<inf>3</inf> and TiN increased. The lattice parameters of Al<inf>2</inf>TiO<inf>5</inf> were enlarged with AlN addition, implying the incorporation of N atoms in the Al<inf>2</inf>TiO<inf>5</inf> unit cell. The addition of AlN effectively produced fully densified bodies with small grain size, and microcrack-free, which therefore enhanced the mechanical properties of ATN composites. At 36 mol% AlN addition, the composite shows Vickers hardness and fracture toughness of 16.26 ± 1.61 GPa and 5.20 ± 0.46 MPa.m1/2, respectively.
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Preparation of SiO2-diamond composites by spark plasma sintering
(2021-01-01)
Kitiwan, Mettaya
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Katsui, Hirokazu
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Goto, Takashi
SiO<inf>2</inf>-diamond composites with 65–85 mass% diamond were fabricated by spark plasma sintering at 1873 K under 130 MPa for 300 s using bimodal diamond particle size of 2 and 25 µm in diameter. The diamond particles were coated with a SiC layer by chemical vapor deposition. The effects of diamond content on relative density, microstructure, and Vickers hardness of the SiO<inf>2</inf>-diamond composites were investigated. The SiO<inf>2</inf>-diamond composites exhibited relative density of 96%, and Vickers hardness of 36.2 ± 3.6 GPa at 75 mass% diamond content.
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Positive ionic conduction of mayenite cement Ca12Al14O33/nano-carbon black composites on dielectric and thermoelectric properties
(2020-03-01)
Rudradawong, Chalermpol
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Kitiwan, Mettaya
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Goto, Takashi
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Ruttanapun, Chesta
Mayenite Ca<inf>12</inf>Al<inf>14</inf>O<inf>33</inf>/nano-carbon black composites (C12A7/nCB) were investigated regarding the mechanism of oxygen ion vacancy in the extra cage framework of positive ionic transport in thermoelectric and dielectric properties. The oxygen ion vacancy in C12A7/nCB composites was produced from C12A7 composited with nano-carbon back (nCB) for 0, 1, 3, 5 and 10 wt% by the rapid spark plasma sintering. The C12A7/nCB samples were characterised by X-ray diffraction (XRD), UV–vis spectroscopy, Raman spectroscopy, Scanning electron microscopy (SEM), Transmission electron microscopy (TEM) and UV–vis spectroscopy. The O− <inf>2</inf> ions vacancy was confirmed by Raman spectrum. The positive ionic conduction was verified by the positive sign of Seebeck coefficient. The ionic conductivity was in order 5 S/cm of C12A7/nCB of 10 wt% content. The thermal conductivity was reduced by the effects of the O− <inf>2</inf> ions vacancy as point defect. The ZT for thermoelectric materials of C12A7/nCB of 10 wt% content were in a range from 0.01 × 10−3 to 0.16 × 10−3, respectively. Positive ion conduction of C12A7/nCB composites resulting from oxygen ion vacancy occupying in extra framework affected to enhance dielectric constant, Seebeck coefficient, electrical conductivity and reduce thermal conductivity.
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Fabrication of tungsten carbide–diamond composites using SiC-coated diamond
(2019-12-01)
Kitiwan, Mettaya
;
Goto, Takashi
Tungsten carbide (WC) and SiC-coated diamond composites were prepared by spark plasma sintering at 1473–1873 K for 300 s under 130 MPa under vacuum. The diamond particle surface was coated with silicon carbide (SiC) via rotary chemical vapor deposition to improve the interfacial bonding of the WC–diamond composites. The relative density of the WC–20 vol% diamond (SiC) composite increased from 61% to 94% with increasing sintering temperature. Raman spectroscopic analysis showed that the diamond-to-graphite transition did not occur at any of the investigated sintering temperatures. The WC–20 vol% diamond composite sintered at 1773–1873 K exhibited high hardness (30.5 GPa) and fracture toughness (12.3 MPa m1/2). The high hardness resulted from the SiC coating functioning as an interlayer to improve the bonding between the diamond and WC body. The improvement in fracture toughness was attributed to the presence of diamond, which effectively blocks crack propagation and promotes crack deflection.
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Effect of B doping on electrical and thermal properties of SiC bodies fabricated by spark plasma sintering
(2019-01-01)
Taki, Yukina
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Kitiwan, Mettaya
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Katsui, Hirokazu
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Goto, Takashi
B-doped SiC bodies were fabricated by spark plasma sintering at 2373 K, 50 MPa, 300 s in a vacuum and N<inf>2</inf> atmosphere. The relative density of 1 mol% B doped-SiC body sintered in a vacuum and 5 mol% B doped-SiC body sintered in N<inf>2</inf> atmosphere were 97 and 98%, respectively. The electrical conductivity of B-doped SiC bodies sintered in a vacuum with 0.5 mol% B and that with 1 mol% B sintered in N<inf>2</inf> atmosphere showed semi-insulative conduction in the range of 3-510-3 S m-1 at room temperature. The thermal conductivity of B-doped SiC body at 0.5 at% B sintered in a vacuum were 185 W m-1 K-1 while that at 1 at% B sintered in N<inf>2</inf> atmosphere were 177 W m-1 K-1 at room temperature.

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