The Experts below are selected from a list of 2412 Experts worldwide ranked by ideXlab platform

Takashi Nakamura - One of the best experts on this subject based on the ideXlab platform.

  • enhanced osteoinductivity of porous titanium implant by Sodium removal
    Key Engineering Materials, 2006
    Co-Authors: Mitsuru Takemoto, Tomiharu Matsushita, Shunsuke Fujibayashi, J. Suzuki, Takashi Nakamura
    Abstract:

    The aim of this study was to optimize the surface treatment and to accelerate the osteoinductivity of porous bioactive titanium implant. Previous studies have reported that Sodium removal with hot water treatment converts Sodium Titanate on the surface of an alkali-treated titanium plate into titania with a specific structure, which has better bioactivity than Sodium Titanate. We developed a dilute hydrochloric acid (HCl) treatment for porous titanium, which removed Sodium from the complexly shaped porous structure more effectively than conventional hot water treatment. Three types of surface treatments were applied: (a) alkali and heat treatment, (b) alkali, hot water, and heat treatment (conventional treatment), and (c) alkali, dilute HCl, hot water, and heat treatment (Na-free treatment). The osteoinductivity of the materials implanted in the back muscles of adult beagle dogs was examined at three, six, and twelve months. Na-free porous bioactive titanium exhibited the highest osteoinductivity, and bone formation was observed within three months. This study showed that Sodium removal has a significant positive effect on the osteoinductivity of the porous bioactive titanium implant.

  • bioactive metals preparation and properties
    Journal of Materials Science: Materials in Medicine, 2004
    Co-Authors: Tadashi Kokubo, Masakazu Kawashita, Takashi Nakamura
    Abstract:

    Some ceramics, such as Bioglass®, sintered hydroxyapatite, and glass-ceramic A-W, spontaneously form a bone-like apatite layer on their surface in the living body, and bond to bone through the apatite layer. These materials are called bioactive ceramics, and are clinically important for use as bone-repairing materials. However, they cannot be used at high-load sites, such as is found in femoral and tibial bones, because their fracture toughness values are not as high as that of human cortical bone. Titanium metal and its alloys have high fracture toughness, and form a Sodium Titanate layer on its surface when soaked in a 5 M-NaOH solution at 60 °C for 24 h, followed by a heat treatment at 600 °C for 1 h. On moving toward the metal interior, the Sodium Titanate layer gradually changes into the pure metal within a distance of 1 μm from the surface. The mechanical strength of the titanium metal or a titanium alloy is not adversely affected by these chemical and thermal treatments. The titanium metal and its alloys resulting from the above treatment can release Na+ ions from its surface into a surrounding body fluid via an ion exchange reaction with H3O+ ions, resulting in many Ti–OH groups forming on its surface. These Ti–OH groups initially combine with Ca2+ ions to form amorphous calcium Titanate in the body environment, and later the calcium Titanate combines with phosphate ions to form amorphous calcium phosphate. The amorphous calcium phosphate eventually transforms into bone-like apatite, and by this process the titanium metals are soon tightly bonded to the surrounding living bone through the bone-like apatite layer. The treated metals have already been subjected to clinical trials for applications in artificial total hip joints. Metallic tantalum has also been found to bond to living bone after it has been subjected to the NaOH and heat treatment to form a Sodium tantalate layer on its surface.

  • surface potential change in bioactive titanium metal during the process of apatite formation in simulated body fluid
    Journal of Biomedical Materials Research Part A, 2003
    Co-Authors: Teruyuki Himeno, Tadashi Kokubo, Masakazu Kawashita, Takashi Nakamura
    Abstract:

    Bioactive titanium metal can be prepared by NaOH and heat treatments that present the metal with a graded bioactive surface layer of amorphous Sodium Titanate. This study used laser electrophoresis together with transmission electron microscopy (TEM) and energy-dispersive X-ray microanalysis (EDX) to relate the surface potential change of the bioactive titanium metal with its surface structural change in simulated body fluid (SBF). The surface potential of the metal was highly negative immediately after immersion in SBF. With increasing soaking time, the surface potential increased, revealing a maximum positive value, and then decreased to a constant negative value. TEM-EDX showed that immediately after immersion in SBF, the metal surface formed Ti-OH groups by exchanging Na+ ions in the surface Sodium Titanate with H3O+ ions in the fluid. Thereafter, with increasing soaking time the metal surface formed an amorphous calcium Titanate, then an amorphous calcium phosphate, and, finally, apatite with bone-like composition and structure. These results indicate that the process of apatite formation on bioactive titanium metal is initiated by the formation of Ti-OH groups with negative charges that interact with calcium ions with positive charges to form calcium Titanate. The calcium Titanate gains a positive charge and later interacts with phosphate ions with negative charges, forming amorphous calcium phosphate. The amorphous calcium phosphate eventually transforms and stabilizes into bone-like crystalline apatite with a negative charge. © 2003 Wiley Periodicals, Inc. J Biomed Mater Res 67A: 1305–1309, 2003

  • tem edx study of mechanism of bonelike apatite formation on bioactive titanium metal in simulated body fluid
    Journal of Biomedical Materials Research, 2001
    Co-Authors: Hiroaki Takadama, Tadashi Kokubo, Hyun Min Kim, Takashi Nakamura
    Abstract:

    Bioactive titanium metal, which forms a bonelike apatite layer on its surface in the body and bonds to the bone through the apatite layer, can be prepared by NaOH and heat treatments to form an amorphous Sodium Titanate layer on the metal. In the present study, the mechanism of apatite formation on the bioactive titanium metal has been investigated in vitro. The metal surface was examined using transmission electron microscopy and energy dispersive X-ray spectrometry as a function of the soaking time in a simulated body fluid (SBF) and complemented with atomic emission spectroscopy analysis of the fluid. It was found that, immediately after immersion in the SBF, the metal exchanged Na+ ions from the surface Sodium Titanate with H3O+ ions in the fluid to form Ti-OH groups on its surface. The Ti-OH groups, immediately after they were formed, incorporated the calcium ions in the fluid to form an amorphous calcium Titanate. After a long soaking time, the amorphous calcium Titanate incorporated the phosphate ions in the fluid to form an amorphous calcium phosphate with a low Ca/P atomic ratio of 1.40. The amorphous calcium phosphate thereafter converted into bonelike crystalline apatite with a Ca/P ratio of 1.65, which is equal to the value of bone mineral. The initial formation of the amorphous calcium Titanate is proposed to be a consequence of the electrostatic interaction of negatively charged units of titania, which are dissociated from the Ti-OH groups, with the positively charged calcium ions in the fluid. The amorphous calcium Titanate is speculated to gain a positive charge and to interact with the negatively charged phosphate ions in the fluid to form the amorphous calcium phosphate, which eventually stabilizes into bonelike crystalline apatite. © 2001 John Wiley & Sons, Inc. J Biomed Mater Res 57: 441–448, 2001

  • xps study of the process of apatite formation on bioactive ti 6al 4v alloy in simulated body fluid
    Science and Technology of Advanced Materials, 2001
    Co-Authors: Hiroaki Takadama, Tadashi Kokubo, Hyun Min Kim, Takashi Nakamura
    Abstract:

    Bioactive Ti–6Al–4V alloy, which spontaneously forms a bonelike apatite layer on its surface in the body and bonds to living bone through this apatite layer, can be prepared by producing an amorphous Sodium Titanate on its surface by NaOH and heat treatments. In this study, the process of apatite formation on the bioactive Ti–6Al–4V alloy was investigated in vitro, by analyzing its surface with X-ray photoelectron spectroscopy as a function of soaking time in a simulated body fluid (SBF). Thin-film X-ray diffractometry of the alloy surface and atomic emission spectroscopy of the fluid were also performed complementarily. It was found that immediately after immersion in the SBF, the alloy exchanged Na+ ions from the surface Sodium Titanate with H3O+ ions in the fluid to form Ti-OH groups on its surface. The Ti-OH groups, immediately after their formation, incorporated the calcium ions in the fluid to form calcium Titanate. The calcium Titanate thereafter incorporated the phosphate ions in the fluid to form an amorphous calcium phosphate, which was later crystallized into bonelike apatite. This process of apatite formation on the alloy was the same as on the pure titanium metal, because the alloy formed the Sodium Titanate free of Al and V by the NaOH and heat treatments. The initial formation of the calcium Titanate is proposed to be a consequence of the electrostatic interaction of negatively charged units of titania dissociated from the Ti-OH groups with the positively charged calcium ions in the fluid. The calcium Titanate is postulated to gain a positive charge and interact with the negatively charged phosphate ions in the fluid to form amorphous calcium phosphate, which eventually stabilizes into crystalline apatite.

Tadashi Kokubo - One of the best experts on this subject based on the ideXlab platform.

  • design of bioactive bone substitutes based on biomineralization process
    Materials Science and Engineering: C, 2005
    Co-Authors: Tadashi Kokubo
    Abstract:

    Abstract A material able to form bone-like apatite on its surface in the living body bonds to living bone through the apatite layer. Functional groups such as Si-OH, Ti-OH, Zr-OH, Nb-OH and Ta-OH induce apatite formation in the living body. On the basis of these findings, various kinds of bioactive materials with different mechanical properties can be designed. For example, bioactive titanium metal, its alloys and tantalum metal can be obtained by forming a thin Sodium Titanate or tantalate layer on their surfaces by NaOH solution and heat treatments. Bioactive organic polymers can be obtained by forming a thin CaO–SiO 2 or TiO 2 layer on their surfaces by a sol–gel method. These bioactive materials are believed to be useful as unique bone substitutes.

  • bioactive metals preparation and properties
    Journal of Materials Science: Materials in Medicine, 2004
    Co-Authors: Tadashi Kokubo, Masakazu Kawashita, Takashi Nakamura
    Abstract:

    Some ceramics, such as Bioglass®, sintered hydroxyapatite, and glass-ceramic A-W, spontaneously form a bone-like apatite layer on their surface in the living body, and bond to bone through the apatite layer. These materials are called bioactive ceramics, and are clinically important for use as bone-repairing materials. However, they cannot be used at high-load sites, such as is found in femoral and tibial bones, because their fracture toughness values are not as high as that of human cortical bone. Titanium metal and its alloys have high fracture toughness, and form a Sodium Titanate layer on its surface when soaked in a 5 M-NaOH solution at 60 °C for 24 h, followed by a heat treatment at 600 °C for 1 h. On moving toward the metal interior, the Sodium Titanate layer gradually changes into the pure metal within a distance of 1 μm from the surface. The mechanical strength of the titanium metal or a titanium alloy is not adversely affected by these chemical and thermal treatments. The titanium metal and its alloys resulting from the above treatment can release Na+ ions from its surface into a surrounding body fluid via an ion exchange reaction with H3O+ ions, resulting in many Ti–OH groups forming on its surface. These Ti–OH groups initially combine with Ca2+ ions to form amorphous calcium Titanate in the body environment, and later the calcium Titanate combines with phosphate ions to form amorphous calcium phosphate. The amorphous calcium phosphate eventually transforms into bone-like apatite, and by this process the titanium metals are soon tightly bonded to the surrounding living bone through the bone-like apatite layer. The treated metals have already been subjected to clinical trials for applications in artificial total hip joints. Metallic tantalum has also been found to bond to living bone after it has been subjected to the NaOH and heat treatment to form a Sodium tantalate layer on its surface.

  • surface potential change in bioactive titanium metal during the process of apatite formation in simulated body fluid
    Journal of Biomedical Materials Research Part A, 2003
    Co-Authors: Teruyuki Himeno, Tadashi Kokubo, Masakazu Kawashita, Takashi Nakamura
    Abstract:

    Bioactive titanium metal can be prepared by NaOH and heat treatments that present the metal with a graded bioactive surface layer of amorphous Sodium Titanate. This study used laser electrophoresis together with transmission electron microscopy (TEM) and energy-dispersive X-ray microanalysis (EDX) to relate the surface potential change of the bioactive titanium metal with its surface structural change in simulated body fluid (SBF). The surface potential of the metal was highly negative immediately after immersion in SBF. With increasing soaking time, the surface potential increased, revealing a maximum positive value, and then decreased to a constant negative value. TEM-EDX showed that immediately after immersion in SBF, the metal surface formed Ti-OH groups by exchanging Na+ ions in the surface Sodium Titanate with H3O+ ions in the fluid. Thereafter, with increasing soaking time the metal surface formed an amorphous calcium Titanate, then an amorphous calcium phosphate, and, finally, apatite with bone-like composition and structure. These results indicate that the process of apatite formation on bioactive titanium metal is initiated by the formation of Ti-OH groups with negative charges that interact with calcium ions with positive charges to form calcium Titanate. The calcium Titanate gains a positive charge and later interacts with phosphate ions with negative charges, forming amorphous calcium phosphate. The amorphous calcium phosphate eventually transforms and stabilizes into bone-like crystalline apatite with a negative charge. © 2003 Wiley Periodicals, Inc. J Biomed Mater Res 67A: 1305–1309, 2003

  • tem edx study of mechanism of bonelike apatite formation on bioactive titanium metal in simulated body fluid
    Journal of Biomedical Materials Research, 2001
    Co-Authors: Hiroaki Takadama, Tadashi Kokubo, Hyun Min Kim, Takashi Nakamura
    Abstract:

    Bioactive titanium metal, which forms a bonelike apatite layer on its surface in the body and bonds to the bone through the apatite layer, can be prepared by NaOH and heat treatments to form an amorphous Sodium Titanate layer on the metal. In the present study, the mechanism of apatite formation on the bioactive titanium metal has been investigated in vitro. The metal surface was examined using transmission electron microscopy and energy dispersive X-ray spectrometry as a function of the soaking time in a simulated body fluid (SBF) and complemented with atomic emission spectroscopy analysis of the fluid. It was found that, immediately after immersion in the SBF, the metal exchanged Na+ ions from the surface Sodium Titanate with H3O+ ions in the fluid to form Ti-OH groups on its surface. The Ti-OH groups, immediately after they were formed, incorporated the calcium ions in the fluid to form an amorphous calcium Titanate. After a long soaking time, the amorphous calcium Titanate incorporated the phosphate ions in the fluid to form an amorphous calcium phosphate with a low Ca/P atomic ratio of 1.40. The amorphous calcium phosphate thereafter converted into bonelike crystalline apatite with a Ca/P ratio of 1.65, which is equal to the value of bone mineral. The initial formation of the amorphous calcium Titanate is proposed to be a consequence of the electrostatic interaction of negatively charged units of titania, which are dissociated from the Ti-OH groups, with the positively charged calcium ions in the fluid. The amorphous calcium Titanate is speculated to gain a positive charge and to interact with the negatively charged phosphate ions in the fluid to form the amorphous calcium phosphate, which eventually stabilizes into bonelike crystalline apatite. © 2001 John Wiley & Sons, Inc. J Biomed Mater Res 57: 441–448, 2001

  • xps study of the process of apatite formation on bioactive ti 6al 4v alloy in simulated body fluid
    Science and Technology of Advanced Materials, 2001
    Co-Authors: Hiroaki Takadama, Tadashi Kokubo, Hyun Min Kim, Takashi Nakamura
    Abstract:

    Bioactive Ti–6Al–4V alloy, which spontaneously forms a bonelike apatite layer on its surface in the body and bonds to living bone through this apatite layer, can be prepared by producing an amorphous Sodium Titanate on its surface by NaOH and heat treatments. In this study, the process of apatite formation on the bioactive Ti–6Al–4V alloy was investigated in vitro, by analyzing its surface with X-ray photoelectron spectroscopy as a function of soaking time in a simulated body fluid (SBF). Thin-film X-ray diffractometry of the alloy surface and atomic emission spectroscopy of the fluid were also performed complementarily. It was found that immediately after immersion in the SBF, the alloy exchanged Na+ ions from the surface Sodium Titanate with H3O+ ions in the fluid to form Ti-OH groups on its surface. The Ti-OH groups, immediately after their formation, incorporated the calcium ions in the fluid to form calcium Titanate. The calcium Titanate thereafter incorporated the phosphate ions in the fluid to form an amorphous calcium phosphate, which was later crystallized into bonelike apatite. This process of apatite formation on the alloy was the same as on the pure titanium metal, because the alloy formed the Sodium Titanate free of Al and V by the NaOH and heat treatments. The initial formation of the calcium Titanate is proposed to be a consequence of the electrostatic interaction of negatively charged units of titania dissociated from the Ti-OH groups with the positively charged calcium ions in the fluid. The calcium Titanate is postulated to gain a positive charge and interact with the negatively charged phosphate ions in the fluid to form amorphous calcium phosphate, which eventually stabilizes into crystalline apatite.

Tadashi Takenaka - One of the best experts on this subject based on the ideXlab platform.

  • thermal depoling process and piezoelectric properties of bismuth Sodium Titanate ceramics
    Journal of Applied Physics, 2009
    Co-Authors: Yuji Hiruma, Hajime Nagata, Tadashi Takenaka
    Abstract:

    Stoichiometric and nonstoichiometric (Bi0.5Na0.5)TiO3 (BNT) ceramics were prepared by a conventional ceramic fabrication process. This study revealed that the high conductivity of BNT ceramics is associated with Bi vaporization during sintering. An x-ray study revealed that a tetragonal phase exists in the temperature range between 330 and 480 °C in BNT ceramic as well as BNT single crystals. In addition, the depolarization temperature Td, rhombohedral-tetragonal phase transition temperature TR-T, and the temperature Tm of the maximum dielectric constant were determined to be 187, approximately 300, and 325 °C, respectively, from the temperature dependences of dielectric properties using unpoled and poled specimens. The piezoelectric properties of all vibration modes and the temperature dependences of the piezoelectric properties were measured using fully poled BNT ceramics. It was also revealed that BNT ceramics exhibit three thermal depoling processes at Td, between Td and TR-T, and between TR-T and Tm ...

  • large piezoelectric constant and high curie temperature of lead free piezoelectric ceramic ternary system based on bismuth Sodium Titanate bismuth potassium Titanate barium Titanate near the morphotropic phase boundary
    Japanese Journal of Applied Physics, 2003
    Co-Authors: Hajime Nagata, Masaki Yoshida, Yoichi Makiuchi, Tadashi Takenaka
    Abstract:

    A lead-free piezoelectric ceramic ternary system based on bismuth Sodium Titanate, (Bi1/2Na1/2)TiO3 (BNT) - bismuth potassium Titanate (Bi1/2K1/2)TiO3 (BKT) - barium Titanate BaTiO3 (BT) near the morphotropic phase boundary (MPB) between the tetragonal and rhombohedral phases has been investigated. In the case of a(Bi1/2Na1/2)TiO3–bBaTiO3–c(Bi1/2K1/2)TiO3 [BNBK(100a/100b/100c)] solid solution ceramics, the highest piezoelectric constant d33=191 pC/N, Curie temperature, Tc=301°C, electromechanical coupling factor, k33=0.56 and dielectric constant, e33T/e0=1141 are observed for the BNBK(85.2/2.8/12) composition which has a tetragonal phase near the MPB. The d33 value is the highest so far reported for all lead-free piezoelectric ceramics with Tc>300°C. The BNT-BKT-BT ternary ceramics system sintered at 1200°C for 2 h in air has a pure perovskite structure and a high density more than 95% of the theoretical density.

  • morphotropic phase boundary and electrical properties of bisumuth Sodium Titanate potassium niobate solid solution ceramics
    Japanese Journal of Applied Physics, 2001
    Co-Authors: Hideki Ishii, Hajime Nagata, Tadashi Takenaka
    Abstract:

    A morphotropic phase boundary (MPB) between (Bi1/2Na1/2)TiO3 (rhombohedral system) and KNbO3 (orthorhombic system) was determined by using X-ray diffraction and dielectric measurements. A solid solution, (1-x)(Bi1/2Na1/2)TiO3–xKNbO3 [BNTK-100x], shows a rhombohedral symmetry and orthorhombic symmetry at a composition of around 0x0.95 and 0.96x1.00, respectively. The dielectric constant, es, at Curie temperature, Tc, was the largest value in the BNTK-96 system. From these results, the MPB of the BNTK system seems to exist in BNTK-96. The BNTK ceramics were confirmed to be ferroelectric by observing their hysteresis loops. Resistivities, ρ, of BNTK-100x (0.94x0.98) are 109–1012 Ωcm. An electromechanical coupling factor, k33, of BNTK-96 is 0.16 which is an unsaturated value.

  • additive effects on electrical properties of bi1 2na1 2 tio3 ferroelectric ceramics
    Journal of The European Ceramic Society, 2001
    Co-Authors: Hajime Nagata, Tadashi Takenaka
    Abstract:

    Microstructure, dielectric, ferroelectric and piezoelectric properties of bismuth Sodium Titanate (Bi1/2Na1/2)TiO3 (BNT) were studied for a candidate as lead-free piezoelectric ceramics. In the case of Mn addition, the Curie temperature, Tc, decreases rapidly with increasing amount of doped MnCO3. The resistivity, ρ, is enhanced to 3×1014 (Ωcm) (at 40°C) for BNT+MnCO3 0.2 (wt.%) and electromechanical coupling factor, k33, was obtained the relatively high value under the condition of the low poling field, Ep for the Mn-doped BNT ceramics. It seems that Mn ions exist in the grain, and substitute for the A- or B-site of the perovskite structure, and eject Bi ions to the air.

  • piezoelectric properties of some lead free ferroelectric ceramics
    Ferroelectrics, 1999
    Co-Authors: Tadashi Takenaka
    Abstract:

    Abstract The use of lead-free materials in piezoelectric ceramics has recently become a very important issue in environmental protection of the earth. Some lead-free piezoelectric materials, namely bismuth Sodium Titanate, (Bi1/2Na1/2)TiO3 (BNT) – based solid solution ceramics, such as (1-a)BNT-a·BaTiO3 [BNBT], (1-b)BNT-b·NaNbO3 [BNTN] and a(Bi1/2Na1/2)TiO3-b KNbO3-c 1/2(Bi2O3·Sc2O3) [KTNS] (a+b+c=1) systems, were studied for their dielectric, ferroelectric and piezoelectric properties as candidates for a new family of lead-free piezoelectric ceramics. The electromechanical coupling factor, k 33 in the longitudinal mode was found to be 0.55, 0.43 and 0.47 for BNBT-6. BNTN-3 and KTNS, respectively. On particular, the amount of modified Bi3+ ions has an effect on k 33. Consequently these ceramics are potential candidates as lead-free piezoelectric ceramics.

Hajime Nagata - One of the best experts on this subject based on the ideXlab platform.

  • thermal depoling process and piezoelectric properties of bismuth Sodium Titanate ceramics
    Journal of Applied Physics, 2009
    Co-Authors: Yuji Hiruma, Hajime Nagata, Tadashi Takenaka
    Abstract:

    Stoichiometric and nonstoichiometric (Bi0.5Na0.5)TiO3 (BNT) ceramics were prepared by a conventional ceramic fabrication process. This study revealed that the high conductivity of BNT ceramics is associated with Bi vaporization during sintering. An x-ray study revealed that a tetragonal phase exists in the temperature range between 330 and 480 °C in BNT ceramic as well as BNT single crystals. In addition, the depolarization temperature Td, rhombohedral-tetragonal phase transition temperature TR-T, and the temperature Tm of the maximum dielectric constant were determined to be 187, approximately 300, and 325 °C, respectively, from the temperature dependences of dielectric properties using unpoled and poled specimens. The piezoelectric properties of all vibration modes and the temperature dependences of the piezoelectric properties were measured using fully poled BNT ceramics. It was also revealed that BNT ceramics exhibit three thermal depoling processes at Td, between Td and TR-T, and between TR-T and Tm ...

  • large piezoelectric constant and high curie temperature of lead free piezoelectric ceramic ternary system based on bismuth Sodium Titanate bismuth potassium Titanate barium Titanate near the morphotropic phase boundary
    Japanese Journal of Applied Physics, 2003
    Co-Authors: Hajime Nagata, Masaki Yoshida, Yoichi Makiuchi, Tadashi Takenaka
    Abstract:

    A lead-free piezoelectric ceramic ternary system based on bismuth Sodium Titanate, (Bi1/2Na1/2)TiO3 (BNT) - bismuth potassium Titanate (Bi1/2K1/2)TiO3 (BKT) - barium Titanate BaTiO3 (BT) near the morphotropic phase boundary (MPB) between the tetragonal and rhombohedral phases has been investigated. In the case of a(Bi1/2Na1/2)TiO3–bBaTiO3–c(Bi1/2K1/2)TiO3 [BNBK(100a/100b/100c)] solid solution ceramics, the highest piezoelectric constant d33=191 pC/N, Curie temperature, Tc=301°C, electromechanical coupling factor, k33=0.56 and dielectric constant, e33T/e0=1141 are observed for the BNBK(85.2/2.8/12) composition which has a tetragonal phase near the MPB. The d33 value is the highest so far reported for all lead-free piezoelectric ceramics with Tc>300°C. The BNT-BKT-BT ternary ceramics system sintered at 1200°C for 2 h in air has a pure perovskite structure and a high density more than 95% of the theoretical density.

  • morphotropic phase boundary and electrical properties of bisumuth Sodium Titanate potassium niobate solid solution ceramics
    Japanese Journal of Applied Physics, 2001
    Co-Authors: Hideki Ishii, Hajime Nagata, Tadashi Takenaka
    Abstract:

    A morphotropic phase boundary (MPB) between (Bi1/2Na1/2)TiO3 (rhombohedral system) and KNbO3 (orthorhombic system) was determined by using X-ray diffraction and dielectric measurements. A solid solution, (1-x)(Bi1/2Na1/2)TiO3–xKNbO3 [BNTK-100x], shows a rhombohedral symmetry and orthorhombic symmetry at a composition of around 0x0.95 and 0.96x1.00, respectively. The dielectric constant, es, at Curie temperature, Tc, was the largest value in the BNTK-96 system. From these results, the MPB of the BNTK system seems to exist in BNTK-96. The BNTK ceramics were confirmed to be ferroelectric by observing their hysteresis loops. Resistivities, ρ, of BNTK-100x (0.94x0.98) are 109–1012 Ωcm. An electromechanical coupling factor, k33, of BNTK-96 is 0.16 which is an unsaturated value.

  • additive effects on electrical properties of bi1 2na1 2 tio3 ferroelectric ceramics
    Journal of The European Ceramic Society, 2001
    Co-Authors: Hajime Nagata, Tadashi Takenaka
    Abstract:

    Microstructure, dielectric, ferroelectric and piezoelectric properties of bismuth Sodium Titanate (Bi1/2Na1/2)TiO3 (BNT) were studied for a candidate as lead-free piezoelectric ceramics. In the case of Mn addition, the Curie temperature, Tc, decreases rapidly with increasing amount of doped MnCO3. The resistivity, ρ, is enhanced to 3×1014 (Ωcm) (at 40°C) for BNT+MnCO3 0.2 (wt.%) and electromechanical coupling factor, k33, was obtained the relatively high value under the condition of the low poling field, Ep for the Mn-doped BNT ceramics. It seems that Mn ions exist in the grain, and substitute for the A- or B-site of the perovskite structure, and eject Bi ions to the air.

  • lead free piezoelectric ceramics of bi1 2na1 2 tio3 knbo3 1 2 bi2o3 sc2o3 system
    Japanese Journal of Applied Physics, 1997
    Co-Authors: Hajime Nagata, Tadashi Takenaka
    Abstract:

    Bismuth Sodium Titanate, (Bi1/2Na1/2)TiO3 (BNT)-based solid solution, (1- x)(Bi1/2Na1/2)TiO3– x1/2(Bi2O3Sc2O3) [BNST-100 x], was studied in order to determine its dielectric, ferroelectric and piezoelectric properties as a new group of lead-free piezoelectric ceramics. Measurements of dielectric and piezoelectric properties show that the BNST-100 x ceramics of composition near BNT composition have relatively low free permittivity, e33 T/e0 (=431) and high electromechanical coupling factor, k33 (=0.42). These ceramics are good candidates for use as lead-free piezoelectric ceramics.

Hiroaki Takadama - One of the best experts on this subject based on the ideXlab platform.

  • tem edx study of mechanism of bonelike apatite formation on bioactive titanium metal in simulated body fluid
    Journal of Biomedical Materials Research, 2001
    Co-Authors: Hiroaki Takadama, Tadashi Kokubo, Hyun Min Kim, Takashi Nakamura
    Abstract:

    Bioactive titanium metal, which forms a bonelike apatite layer on its surface in the body and bonds to the bone through the apatite layer, can be prepared by NaOH and heat treatments to form an amorphous Sodium Titanate layer on the metal. In the present study, the mechanism of apatite formation on the bioactive titanium metal has been investigated in vitro. The metal surface was examined using transmission electron microscopy and energy dispersive X-ray spectrometry as a function of the soaking time in a simulated body fluid (SBF) and complemented with atomic emission spectroscopy analysis of the fluid. It was found that, immediately after immersion in the SBF, the metal exchanged Na+ ions from the surface Sodium Titanate with H3O+ ions in the fluid to form Ti-OH groups on its surface. The Ti-OH groups, immediately after they were formed, incorporated the calcium ions in the fluid to form an amorphous calcium Titanate. After a long soaking time, the amorphous calcium Titanate incorporated the phosphate ions in the fluid to form an amorphous calcium phosphate with a low Ca/P atomic ratio of 1.40. The amorphous calcium phosphate thereafter converted into bonelike crystalline apatite with a Ca/P ratio of 1.65, which is equal to the value of bone mineral. The initial formation of the amorphous calcium Titanate is proposed to be a consequence of the electrostatic interaction of negatively charged units of titania, which are dissociated from the Ti-OH groups, with the positively charged calcium ions in the fluid. The amorphous calcium Titanate is speculated to gain a positive charge and to interact with the negatively charged phosphate ions in the fluid to form the amorphous calcium phosphate, which eventually stabilizes into bonelike crystalline apatite. © 2001 John Wiley & Sons, Inc. J Biomed Mater Res 57: 441–448, 2001

  • xps study of the process of apatite formation on bioactive ti 6al 4v alloy in simulated body fluid
    Science and Technology of Advanced Materials, 2001
    Co-Authors: Hiroaki Takadama, Tadashi Kokubo, Hyun Min Kim, Takashi Nakamura
    Abstract:

    Bioactive Ti–6Al–4V alloy, which spontaneously forms a bonelike apatite layer on its surface in the body and bonds to living bone through this apatite layer, can be prepared by producing an amorphous Sodium Titanate on its surface by NaOH and heat treatments. In this study, the process of apatite formation on the bioactive Ti–6Al–4V alloy was investigated in vitro, by analyzing its surface with X-ray photoelectron spectroscopy as a function of soaking time in a simulated body fluid (SBF). Thin-film X-ray diffractometry of the alloy surface and atomic emission spectroscopy of the fluid were also performed complementarily. It was found that immediately after immersion in the SBF, the alloy exchanged Na+ ions from the surface Sodium Titanate with H3O+ ions in the fluid to form Ti-OH groups on its surface. The Ti-OH groups, immediately after their formation, incorporated the calcium ions in the fluid to form calcium Titanate. The calcium Titanate thereafter incorporated the phosphate ions in the fluid to form an amorphous calcium phosphate, which was later crystallized into bonelike apatite. This process of apatite formation on the alloy was the same as on the pure titanium metal, because the alloy formed the Sodium Titanate free of Al and V by the NaOH and heat treatments. The initial formation of the calcium Titanate is proposed to be a consequence of the electrostatic interaction of negatively charged units of titania dissociated from the Ti-OH groups with the positively charged calcium ions in the fluid. The calcium Titanate is postulated to gain a positive charge and interact with the negatively charged phosphate ions in the fluid to form amorphous calcium phosphate, which eventually stabilizes into crystalline apatite.

  • an x ray photoelectron spectroscopy study of the process of apatite formation on bioactive titanium metal
    Journal of Biomedical Materials Research, 2001
    Co-Authors: Hiroaki Takadama, Tadashi Kokubo, Hyun Min Kim, Takashi Nakamura
    Abstract:

    Bioactive titanium metal, prepared by treatment with NaOH followed by an annealing stage to form a Sodium Titanate layer with a graded structure on its surface, forms a biologically active bone-like apatite layer on its surface in the body, and bonds to bone through this apatite layer. In this study, process of apatite formation on the bioactive titanium metal in a simulated body fluid was investigated using X-ray photoelectron spectroscopy. The bioactive titanium metal formed Ti-OH groups soon after soaking in the simulated body fluid, via the exchange of the Na(+) ions in the Sodium Titanate on its surface with H(3)O(+) ions in the fluid. The Ti-OH groups on the metal combined with the calcium ions in the fluid immediately to form a calcium Titanate. After a long period, the calcium Titanate on the metal took the phosphate ions as well as the calcium ions in the fluid to form the apatite nuclei. The apatite nuclei then proceeded to grow by consuming the calcium and phosphate ions in the fluid. These results indicate that the Ti-OH groups formed on the metal induce the apatite nucleation indirectly, by forming a calcium Titanate. The initial formation mechanism of the calcium Titanate may be attributable to the electrostatic interaction of the negatively charged Ti-OH groups with the positively charged calcium ions.