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Volume 47, Issue 11
Displaying 1-21 of 21 articles from this issue
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Akihisa Kajiyama, Takayuki Yoshida, Tatsuya Nakamura2000 Volume 47 Issue 11 Pages 1139-1143
Published: November 15, 2000
Released on J-STAGE: May 22, 2009
JOURNAL OPEN ACCESSLi4Mn5O12 particles were prepared by calcination of Li-hydroxide monohydrate and γ-Mn2O3, which was synthesized by the thermal decomposition of Mn-oxalate, at temperature from 400 to 750°C in static air or oxygen atmosphere. The lattice constant varied with the preparation conditions: in the same atmosphere, the lattice constant increased with the calcination temperature, and in the fixed preparation temperature, the calcination in oxygen atmosphere brought smaller lattice constant than that in static air. Additionally, the specimen prepared at lower calcination temperature exhibited higher electrochemical capacity in 3 V region with better cycle performance. These variations are related to the average Mn valence state, and higher valence state of Mn is required for high perfromance of Li4Mn5O12 as 3 V cathode material. The low-temperature synthesis is thought to be suitable for them.View full abstractDownload PDF (407K) -
Ritsuko Tsuzuki, Eiji Yuasa2000 Volume 47 Issue 11 Pages 1144-1149
Published: November 15, 2000
Released on J-STAGE: May 22, 2009
JOURNAL OPEN ACCESSAs its excellent mechanical and chemical properties, the formation processes of Al-Ni-Zr amorphous alloys, which was formed by mechanical alloying (MA) method, were investigated in this study. Planetary ball mill was used to carry out MA. Double mechanical alloying (DMA) method was also taken, where the binary amorphous alloys are first synthesized by MA from a elemental powder mixture and are further milled with the third elemental powder to form ternary amorphous alloys. On the first step, Ni-35-40mol%Zr amorphous phases were formed at the rotation frequency of 250 rpm. Aluminum powder was added to the amorphous Ni-Zr powder after that, and Al-40mol% (Ni40mol%Zr) could be obtained when the DMA was carried out at 200 rpm. In this case, however, the recovery ratio of milled powder would be under 20% of initial weight. Then 1 mass% stearic acid was added and it was found to be effective to improve the yield of milled powders as well as the formation range of amorphous phase. Furthermore, the synthesized alloys by two types of ball mill were compared, and it was confirmed that when oscillatory ball mill was used for MA, Al-Ni-Zr amorphous alloys were formed over a wider range than that in the case of using planetary ball mill.View full abstractDownload PDF (3518K) -
Manabu Matsubara, Hitoshi Hashimoto, Yong-Ho Park2000 Volume 47 Issue 11 Pages 1150-1155
Published: November 15, 2000
Released on J-STAGE: May 22, 2009
JOURNAL OPEN ACCESSIn order to improve the mechanical properties of MoSi2 alloys, the alloys with Al, B or Nb addition were prepared by an advanced consolidation process which combined mechanical alloying with pulse discharge sintering (MA-PDS). Their microstructure and mechanical properties were investigated. The MoSi2 alloys fabricated by MA-PDS process showed very fine microstructure when compared with the sample sintered from commercial MoSi2 powder. The sintered alloys made from powder milled in Ar atmosphere had dense microstructure compared with that milled in air because of suppression of oxide formation during milling, except for Al added alloy. On the effect of added elements in densification of the alloys, addition of B was more effective than Al or Nb. Both in the Vickers hardness test and in the tensile test at ambient temperature, the alloys fabricated by MA-PDS process showed good performance compared with the sample sintered from commercial MoSi2 powder due to the fine grain.View full abstractDownload PDF (7240K) -
[in Japanese]2000 Volume 47 Issue 11 Pages 1158
Published: November 15, 2000
Released on J-STAGE: May 22, 2009
JOURNAL OPEN ACCESSDownload PDF (55K) -
Michitaka Ohtaki, Eishi Maeda2000 Volume 47 Issue 11 Pages 1159-1164
Published: November 15, 2000
Released on J-STAGE: May 22, 2009
JOURNAL OPEN ACCESSThe thermoelectric properties of sintered bodies of NaCo2O4, which is so far the most promising p-type candidate for oxide thermoelectric material, are investigated in terms of their sintering conditions. Double-step sintering, for which single-phase NaCo2O4 obtained by calcination and sintering with addition of 10% excess of Na each time is re-ground and sintered again, is revealed to attain a marked improvement in the thermoelectric performance of the oxide. The improvement is due to increase in both Seebeck coefficient and electrical conductivity, and is attributed to a distinct enhancement of the two-dimensionality in the crystallites constituting the sintered body. The oxide sintered body consequently attains the figure-of-merit of 0.88×10-3K-1 at 600°C, and the maximum ZT of 0.78 at 800°C.View full abstractDownload PDF (2104K) -
Xinfeng Tang, Lidong Chen, Takashi Goto, Toshio Hirai2000 Volume 47 Issue 11 Pages 1165-1169
Published: November 15, 2000
Released on J-STAGE: May 22, 2009
JOURNAL OPEN ACCESSFilled skutterudite compounds, BayFexCo4-xSb12 (x=0-3.0, y=0-0.7), were synthesized by a two step solid state reaction method. Electrical transport properties of BayFexCo4-xSb12 were investigated. The lattice constants of BayFexCo4-xSb12 increased with increasing Ba filling fraction and Fe content. The maximum filling fraction of Ba (ymax) in BayFexCo4-xSb12 increased with increasing Fe content, and was found to be rather greater than that of CeyFex Co4-xSb12. The ymax, varied from 0.35 to near 1.0 when Fe content (x) changed from 0 to 4.0. Carrier concentration and electrical conductivity increased with increasing Fe content, and decreased with increasing Ba filling fraction for BayFexCo4-xSb12. At the same x and y, carrier concentration and electrical conductivity of BayFexCo4-xSb12 were larger than that of CeyFexCo4-xSb12.View full abstractDownload PDF (360K) -
Hirotsugu Takizawa, Masayuki Ito, Kyota Uheda, Tadashi Endo2000 Volume 47 Issue 11 Pages 1170-1174
Published: November 15, 2000
Released on J-STAGE: May 22, 2009
JOURNAL OPEN ACCESSThermoelectric properties of tin-filled skutterudites, SnxCo4Sb12, are evaluated. The tin-filled compounds were synthesized under high pressure and temperature condition from powder mixture of CoSb3 and elemental tin. The tin-filled compounds exhibit n-type semiconducting behavior indicating that the incorporation of tin atoms causes the formation of a donor level. A remarkable reduction in the thermal conductivity was achieved by tin insertion. Thermal conductivity of the tin-filled sample is two orders of magnitude lower than that of the unfilled CoSb3. Effect of void filling on the thermoelectric properties of SnxCo4Sb12 is compared to that of other filled skutterudites. It is concluded that tin atom is a better "rattler" in the CoSb3 host lattice.View full abstractDownload PDF (1776K) -
Kazuo Ueno, Shuhei Nakahama, Hideki Kondo, Kazutoshi Nagai, Rei Kiumi, ...2000 Volume 47 Issue 11 Pages 1175-1178
Published: November 15, 2000
Released on J-STAGE: December 04, 2009
JOURNAL OPEN ACCESSLarge sized n-and p-type FeSi2 thermoelectric devices were spray-formed by high-velocity oxy-fuel thermal spraying (HVOF) method. One is a plate 100mm square with the thickness of 6mm and another is a tube-type device which was formed on a stainless tube (25 mm in diameter, 500 mm long) with the thickness of 5 mm. Their microstructure and physical properties were compared to those of hot-pressed material. The bulk density of HVOF-formed FeSi2 was lower than that of hot-pressed materials due to higher amount of pore. For n-type FeSi2, Seebeck coefficient and thermal conductivity of HVOF-formed material were comparable to those of hot-pressed material. While electrical conductivities of both n-and p-type HVOF-FeSi2 were quite lower than that of hot-pressed n-type material, resulted in low performance as thermo electric device.View full abstractDownload PDF (2296K) -
Mitsuya Hashii, Masashi Wada, Mutsumi Atarashi, Naoyuki Kanetake2000 Volume 47 Issue 11 Pages 1179-1183
Published: November 15, 2000
Released on J-STAGE: December 04, 2009
JOURNAL OPEN ACCESSThe powder which has a FeSi2 stoichiometric composition was obtained by a water-atomization. A phase change of the powder by annealing was characterized by XRD. The atomized powder has a fine microstructure composed with (α-Fe2Si5+ε-FeSi) phases. The phase of the atomized powder changed to β-FeSi2 phase by annealing in the temperature range from 870K to 1000K for the short time. The change to β-FeSi2 phase can be realized by only heating without holding at temperatures above 1000K. It means that the atomizing process has the same effect on shortening the annealing time to obtain β-FeSi2 phase as a mechanical alloying process. It would be expected that the thermoelectric compact with β-FeSi2 phase could be obtained by only sintering the atomized powder at a temperature lower than peritectoid point.View full abstractDownload PDF (2213K) -
Itaru Gunjishima, Takaya Akashi, Takashi Goto2000 Volume 47 Issue 11 Pages 1184-1188
Published: November 15, 2000
Released on J-STAGE: December 04, 2009
JOURNAL OPEN ACCESSThermoelectric properties of directionally solidified B4C-TiB2 composites by a Floating Zone method were studied at temperatures from RT to 1023 K. The composition of TiB2 was changed between 0 and 25 mol% (eutectic composition). The difference of electrical conductivity (σ) and Seebeck coefficient (α) between parallel (//) and perpendicular (⊥) to the growth direction were measured. At the eutectic composition, σ// was greater than σ⊥, and α⊥ was greater than α//. Both α⊥ and α//, showed the maximum around 2 mol%. The greatest power factor of 0.48×10-3 WK-2m-1 was obtained at 2 mol% in the perpendicular to the growth direction.View full abstractDownload PDF (2310K) -
Yasushi Iwaisako, Tatsuhiko Aizawa, Atsushi Yamamoto, Toshitaka Ohta2000 Volume 47 Issue 11 Pages 1189-1193
Published: November 15, 2000
Released on J-STAGE: May 22, 2009
JOURNAL OPEN ACCESSFor improvement of the figure of merit in Bi-Te system, anisotropic microstructure control becomes very important with grain size refinement. The conventional powder compaction processes are mostly ineffective or inefficient in texture control. New alternative processing is strongly awaited to make anisotropic microstructure control for enhancement of thermoelectric properties. In this study, the shear extrusion processing was proposed to make texture control in Bi0.4Sb1.6Te3 alloyment from green compact. In this method, strong shear strain is applied to the sample, resulting in selective shear deformation along the cleavage crystal surface and rearrangement of crystalline orientations through the extrusion passage.
As the result, the electrical resistivity of sheared sample was improved from 2.11×10-5(Ωm) to 1.17×10-5 (Ωm) without decrease of Seebeck coefficient. Then, higher power factor of 4.09×10-3 (W/mK2) can be achieved.View full abstractDownload PDF (2176K) -
Junyou Yang, Tatsuhiko Aizawa, Atsushi Yamamoto, Toshitaka Ohta2000 Volume 47 Issue 11 Pages 1194-1197
Published: November 15, 2000
Released on J-STAGE: May 22, 2009
JOURNAL OPEN ACCESSp and n-type bismuth telluride based materials prealloyed by bulk mechanical alloying are directly hot pressed with one-step to yield thermoelectric pn junction. Variation of constitutional element concentrations across the pn interface is characterized by EPMA to determine the interface thickness of pn junction. Electrical resistivity of the interface layer is greater than that of both p and n semiconductor materials. Analytic expressions for Seebeck coefficient and figure of merit versus interface layer size are deduced. Seebeck coefficient of the pn junction is inversely proportional to the ratio of interface layer length to pn junction height (hi/h). It agrees well with experimental result. As for a pn junction with a certain thickness of interface layer, there is a maximum figure of merit at the optimal hi/h; and with a decrease of the thickness of the interface, the maximum increases, correspondingly the optimal hi/h decreases. In other words, pn composite billet with a thinner interface layer can attain larger figure of merit at the same hi/h than the one with a thicker interface. Adjusting process parameter, with proper cutting, thermoelectric properties can be improved greatly, this method for pn junction is feasible.View full abstractDownload PDF (3044K) -
[in Japanese]2000 Volume 47 Issue 11 Pages 1200
Published: November 15, 2000
Released on J-STAGE: May 22, 2009
JOURNAL OPEN ACCESSDownload PDF (78K) -
Masamichi Nishihara, Takashi Sagawa, Hirotaka Ihara, Rika Nishimura, S ...2000 Volume 47 Issue 11 Pages 1201-1204
Published: November 15, 2000
Released on J-STAGE: May 22, 2009
JOURNAL OPEN ACCESSA method to prepare the multi-component oxide glass with graded structure was proposed. This method is based on the facts that colloid particles can sediment during a sol-gel transition process under comparatively low gravity field, and the resultant gel can be converted into glass at lower temperature treatment than a conventional method. The graded structure was formed by centrifuging (10, 000g level) the Si and Ti mixed colloids, and immobilized by removal of solvent at 90°C. This graded precursor gel was heated to 900°C to convert into a glass state. The proper condition to prepare the graded glass was examined especially focusing on the growth time of colloids before the centrifugation. A transparent SiO2-TiO2 glass with molecular-scale graded structure was obtained in many trials.View full abstractDownload PDF (2088K) -
Youping Ren, Junshan Lin, Yoshinari Miyamoto, Guanjun Qiao, Zhihao Jin2000 Volume 47 Issue 11 Pages 1205-1209
Published: November 15, 2000
Released on J-STAGE: May 22, 2009
JOURNAL OPEN ACCESSDense Functionally Graded Materials (FGMs) in the systems of Al2O3/TiC/Ni and (Al2O3-WC/Co)/TiC/Ni were fabricated at 1300°C and 10 minutes by pulsed-electric current sintering method. The grain growth was effectively prevented and fine microstructure could be obtained by this rapid sintering. The residual stress produced in the outer Al2O3 and Al2O3-WC/Co layers of FGMs, which was induced by the thermal expansion mismatch between the inner TiC/Ni layer and the outer layers, was in the range of-180 MPa to-300 MPa. The compressive stress and the dispersion of WC/Co particles enhanced the toughness of the outer ceramic layers, and developed steep R-Curve behavior.View full abstractDownload PDF (3643K) -
Takashi Fujii, Ryousuke Nakamura, Shigeru Ito2000 Volume 47 Issue 11 Pages 1210-1215
Published: November 15, 2000
Released on J-STAGE: December 04, 2009
JOURNAL OPEN ACCESSFunctional gradient Ba(ZrxTi1-x)O3 ferroelectrics ceramics with flat temperature dependence of dielectric constant were fabricated by Hot Isostatic Pressing. Functional gradient Ba(ZrxTi1-x)O3 ceramics compacts were prepared by piling each green compact with different composition. The piling compact sintered under atmospheric pressure cracked at an interface of each component. On the other hand, the piling compacts hipped at 1200°C were densified without separating to each component. Dielectric constant of hipped sample has a flat temperature dependence in a particular temperature range. The piling compact hipped at 200 MPa and 1200°C after pressurized to 200 MPa at 900°C suppressed grain growth and provided flat temperature dependence of dielectric constant over wide temperature range. It was suggested that application of high hipping pressure at lower temperature remarkably suppressed diffusion in the interface of the components.View full abstractDownload PDF (4602K) -
Noriaki Terakubo, Jing-Feng Li, Masaru Ono, Ryuzo Watanabe2000 Volume 47 Issue 11 Pages 1216-1220
Published: November 15, 2000
Released on J-STAGE: May 22, 2009
JOURNAL OPEN ACCESSPiezoelectric materials have received increasing attention in the field of electromechanical system because they can readily transfer an electrical signal to a mechanical movement. Unimorph and bimorph actuators that contain a piezoelectric plate and a metal plate are widely used to generate a larger bending displacement than an extensionalmode transducer. However, degradation may occur at the organic bonding interfaces after long time service. In this work, to develop a functionally graded PZT/Pt piezoelectric actuator, PZT/Pt composites with various composition ratios were prepared and characterized. (1) Dense PZT/Pt composite samples without any chemical reaction between the PZT and Pt phases were obtained by sintering in air at 1200°C for 1 h. (2) The PZT/Pt composites that contained 20vol% Pt or less exhibited dielectric and piezoelectric properties, with piezoelectric constant decreasing with increasing Pt content. (3) FGM PZT/Pt bimorph actuators were designed using Taya's model and successfully fabricated via powder metallurgical routes.View full abstractDownload PDF (4312K) -
Masayasu Hashimoto, Osamu Ohashi, Hiromasa T. Kaibe, Isao Nishida2000 Volume 47 Issue 11 Pages 1221-1225
Published: November 15, 2000
Released on J-STAGE: May 22, 2009
JOURNAL OPEN ACCESSIt is important to control dopant concentration with different amount for n-type PbTe thermoelement with graded structure. It was clarified that the starting materials by a gas transport method have quite homogeneous thermoelectric properties. PbTe sintered compacts were prepared by means of hot pressing technique. Hall mobility μH of the sintered compacts with the dopant amount of 0.20 mass% exceeded 0.1 m2Ns at room temperature. This value is comparative to those of single crystals. The high value of μH led to the high thermoelectric performance.
It is found that gas transport method is a promising method to prepare the starting materials for fabricating PbTe thermoelement with grade structure.View full abstractDownload PDF (2114K) -
Fumio Watari, Mamoru Omori, Toshio Hirai, Atsuro Yokoyama, Hironobu Ma ...2000 Volume 47 Issue 11 Pages 1226-1233
Published: November 15, 2000
Released on J-STAGE: May 22, 2009
JOURNAL OPEN ACCESSFunctionally graded implants composed of titanium (Ti) and hydroxyapatite (HAP) were fabricated by powder metallurgy to satisfy both mechanical properties and biocompatibilities. Concentration gradience was formed either by sedimentation in solvent liquid or by packing dry powders into mould, followed by compressing and sintering. Electric furnace heating, high frequency induction heating and spark plasma sintering (SPS) methods were used for sintering. SPS could make the stable functionally graded materials (FGM) with the gradual change of concentration in the longitudinal direction from pure Ti to 100%HAP (Ti/100HAP). Animal implantation tests were done to evaluate biocompatibility in soft tissue and osteogenesis in hard tissue. Histological observation by optical microscopy using the thinly sectioned, stained specimens and elemental mapping by EPMA and XSAM (X-ray scanning analytical microscope) using the unstained block specimens showed that the tissue reacted gradiently in response to the graded composition of FGM implant. This implies the possibility to control the tissue response through the gradient function of FGM.View full abstractDownload PDF (9637K) -
Mamoru Omori, Akira Okubo, Rika Miyao, Fumio Watari, Toshio Hirai2000 Volume 47 Issue 11 Pages 1234-1238
Published: November 15, 2000
Released on J-STAGE: May 22, 2009
JOURNAL OPEN ACCESSComposites of hydroxyaptite (HA) and titanium (Ti) decompose for few days. The composite prepared from titanium hydride (TiH) and HA is stable for more than a year, but its toughness is very low. Functionally graded materials (FGMs) fabricated from TiH and HA by SPS cracked in the HA layer by the residual stress due to thermal expansion mismatch between Ti and HA and due to the higher relative density of the HA layer. A nitrided titanium (Ti(N)) was synthesized in N2 gas at 800°C for 180min, which formed a stable composite with HA. The Ti(N)/HA FGM free from crack was fabricated at 900°C, which includes pores in the layer of Ti(N). The sintering temperature of 900°C was low for the densification of the Ti(N) layer. A dense Ti/HA FGM was fabricated with layers of Ti, Ti(N), 80vol%Ti(N)-20vo1%HA, 60vo1%Ti(N)-40vo1%HA and 40vol%Ti(N)-60vol%HA.View full abstractDownload PDF (2208K) -
Rika Miyao, Mamoru Omori, Fumio Watari, Atsuro Yokoyama, Hironobu Mats ...2000 Volume 47 Issue 11 Pages 1239-1242
Published: November 15, 2000
Released on J-STAGE: May 22, 2009
JOURNAL OPEN ACCESSThe titanium (Ti)/hydroxyapatite (HAP) functionally graded materials (FGM) for implant were fabricated by Spark Plasma Sintering (SPS) method. The specimens were sintered at 950°C under 40 MPa. After sintering, the square rods of 1×1×10mm were cut for implant. The various FGM specimens were observed by SEM and evaluated by X-ray scanning analytical microscope. The FGMs with the gradient composition ranging from pure Ti to 100% HAP were implanted into the bone marrow of femora of rats for 2 and 4 weeks. The bone formation around the FGM specimens was histologically observed by optical microscopy. The present study showed that the sintering temperature could be lowered considerably by use of SPS from 1300°C compared to less than 1050°C by conventional electric furnace heating. The Ti/HAP FGM implant showed the biocompatibility and affinity for osteogenesis.View full abstractDownload PDF (6378K)
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