Mutsuo Sando

PZT nanocomposites reinforced by small amount of oxides

Pb(Zr,Ti)O 3 (PZT) nanocomposites were prepared from high purity PZT powder and small amount (0.1-1.0 vol%) of oxides, i.e. Al 2 O 3 , MgO and ZrO 2 . Effects of the additives on mechanical and piezoelectric properties of the nanocomposites were investigated. The fracture strength and hardness of PZT nanocomposites with 0.5 vol% Al 2 O 3 or 0.1 vol% MgO additives were significantly improved. The reduced grain size of the nanocomposites is considered to be responsible for the excellent mechanical properties. Though the dielectric constants of the composites were decreased with an addition of Al 2 O 3 or MgO, the planar electromechanical coupling factor, K p , of MgO-added composites was higher than that of Al 2 O 3 -added. As a consequence, the PZT/0.1 vol% MgO nanocomposite showed good mechanical and suitable piezoelectric properties. Addition of ZrO 2 had little effect on mechanical and electrical properties of the composites.

Mechanical and magnetic properties of Ni-Co dispersed Al2O3 nanocomposites

Effects of the fabrication processing on the microstructure and properties of composites were investigated. High-density Ni-Co dispersed-Al2O3 (Al2O3/Ni-Co) composites were obtained by hydrogen reduction and consolidated using hot pressing and pulse electric current sintering (PECS) of Al2O3, Ni(NO3)2·6H2O and Co(NO3)2·6H2O powder mixtures. Microstructural investigations of the hot-pressed composite fabricated using again wet/dry ball-milled powder mixture after calcination revealed that fine Ni-Co particles, about 145 nm in diameter, dispersed homogeneously at the matrix grain boundaries. In particular, fine microstructure of dispersion with the average size of 90 nm was realized for the specimen consolidated by PECS method. High strength of over 1 GPa and hardness of 19 GPa were measured for the nanocomposites prepared from the again ball-milled powder mixture. The ferromagnetism of nano-sized Ni-Co contributes to the magnetic properties of the composites. A change in the coercive force with dispersion size was observed. Also, the extent of magnetic response by an applied stress was strongly influenced by the size of Ni-Co particles. The relations between microstructure and mechanical as well as magnetic properties are discussed.

Processing and properties of Ni-Co alloy dispersed Al2o3 nanocomposites

Ceramic matrix nanocomposites, i.e., ceramic matrices reinforced with nano-sized particles up to several hundred nanometers in size, are currently the subject of intensive work to improve the mechanical properties of ceramics. In this regard, new types of ceramic/metal nanocomposites such as Al{sub 2}O{sub 3}/Ni, Al{sub 2}O{sub 3}/Cu and BaTiO{sub 3}/Ni have been successfully developed. In this field, reinforcement models underline the interest of a homogeneous dispersion of submicron metal particles in a ceramic matrix. In addition, the study of the ceramic/metal interface and the electrical, magnetic, and optical properties, represent other interesting subjects to consider. With the recent progress in chemical processing, it is now possible to obtain desirable microstructures with homogeneous dispersions of metal phases whose dimensions are nano-sized and which show unique physical properties. However, in order to develop such a material, optimization of the powder preparation process, control over the properties, and an understanding of the roles of the nano-sized dispersions are required. In this paper, differences in the preparation process and in the resulting microstructural and mechanical characteristics will be described for the Al{sub 2}O{sub 3}/Ni-Co alloy system. Moreover, the authors discuss the effects of the dispersion of Ni-Co on the mechanical and magnetic properties.

Simultaneous determination of common mono- and divalent cations by ion chromatography with an unmodified silica gel column

In order to characterize the cation-exchange properties of a silica gel column in the acidic region, the retention behavior of common mono- and divalent cations (Na+, NH4+, K+, Mg2+ and Ca2+) was investigated. When using 5 mM nitric acid (pH 2.3) as an eluent, these cations were retained on a silica gel column (150×4.6 mm I.D.) packed with Develosil 30-5 unmodified silica gel that has a very large surface area (ca. 770 m2/g), showing that such a stationary phase could be used as a cation-exchanger for ion chromatography with acidic eluents. When using 1.5 mM 2,6-pyridinedicarboxylic acid as an eluent, a good separation of these cations was obtained in 12 min using conductimetric detection. This separation was applied successfully to the simultaneous determination of the five cations in various environmental water samples.

Crystallization and microstructural characterization of ZrO2 (3 mol% Y2O3) nano-sized powders with various Al2O3 contents

3Y–ZrO2 gels containing 0–40 mol% Al2O3 were obtained by a sol–gel process with isopropoxide precursors. Crystallization behavior and microstructural characterization of the dried gels and calcined powders were studied by DSC, in situ XRD and TEM. The peak temperature of the exotherm corresponded to crystallization of gels in DSC and the activation energy for the crystallization increased with an increase of Al2O3 content. From the XRD analysis including the estimation of lattice parameter, the crystallized phase was confirmed as a solid solution of the tetragonal ZrO2 with Al2O3. Examination by TEM and EDX showed that the powder mixtures after calcination consisted of the homogeneous and very fine grains with the size less than 10 nm.

Synthesis of nanograined ZrO2-based composites by chemical processing and pulse electric current sintering

Abstract Nanograined yttrium-stabilized ZrO 2 /Al 2 O 3 composites were fabricated by a pulse electric current sintering (PECS) method. The starting powders with sizes less than 10 nm were successfully synthesized by the chemical process. The composites sintered at temperatures above 1300°C showed the relative density above 98%. Examination by transmission electron microscopy (TEM) showed that the yttrium-stabilized ZrO 2 /10 mol% Al 2 O 3 composite consisted of the homogeneous and very fine matrix grains with sizes less than 100 nm.

Processing and properties of copper dispersed alumina matrix nanocomposites

Abstract An optimum route to fabricate Al2O3/Cu composites with sound microstructure and desired mechanical properties was investigated. The Al2O3 matrix composites with Cu content of 2.5 to 10 vol.% were prepared by reduction and hot-pressing of Al2O3/CuO powder mixtures. Homogeneous microstructures with nanosized Cu dispersoids and improved fracture strength of 820 MPa could be achieved in the composites with Cu content of 2.5 and 5 vol.%. The influence of the Cu content upon the mechanical properties is discussed based on the observed microstructural characteristics. The toughness increase is explained by crack bridging. The strengthening is mainly attributed to the refinement of Al2O3 matrix grains by the nano-sized Cu dispersion.

Seeding effects on crystallization and microstructure of sol-gel derived PZT fibers

Dense and fine micro-structured lead zirconate titanate (PZT) fibers were successfully fabricated by sol-gel process from lead acetate dehydrate, zirconium normal butoxide, and titanium isopropoxide. An addition of perovskite seed particles (2 wt%) can lower the formation temperature of the perovskite phase and a single-phase perovskite PZT fiber can be obtained by heat-treating the precursor fiber at 500°C. Crystallization of perovskite phase was improved with the seed content. The diffraction peaks of (200) and (002) in the PZT fiber with 6 wt% seed was better split than in the PZT fiber without seed, which indicates that the tetragonality of PZT fiber was increased by adding seed particles. Seed particles also affected microstructure development of the PZT fibers.

Ion-chromatographic behavior of alkali metal cations and ammonium ion on zirconium-adsorbing silica gel.

The preparation and evaluation of zirconium-adsorbing silica gel (Zr-Silica) as an ion-exchange stationary phase in ion chromatography for inorganic anions and cations was carried out. The Zr-Silica was prepared by the reaction of silanol groups on the surface of the silica gel with zirconium butoxide (Zr(OCH2CH2CH2CH3)4) in ethanol. The ion-exchange characteristics of the Zr-Silica were evaluated using 10 mM tartaric acid at pH 2.5 as eluent. The Zr-Silica was found to act as a cation-exchanger under the eluent conditions. The retention behavior of alkali and alkaline earth metal cations was then investigated. The Zr-Silica column was proved to be suitable for the simultaneous separation of alkali metal cations and ammonium ion. Excellent separation of the cations on a 15 cm Zr-Silica column was achieved in 25 min using 10 mM tartaric acid as eluent.

Simultaneous separation of common mono- and divalent cations on a zirconium-modified silica gel column by ion chromatography with non-suppressed conductimetric detection and tartaric acid–15-crown-5 as eluent

The application of laboratory-made zirconium-modified silica gels (Zr-silicas) as cation-exchange stationary phases to ion chromatography with conductimetric detection (IC-CD) for common mono- and divalent cations (Li+, Na+, NH4+, K+, Mg2+ and Ca2+) was carried out. Zr-silicas were prepared by the reaction of the silanol group on the surface of silica gel with zirconium tetrabutoxide (Zr(OCH2CH2CH2CH3)4) in ethanol. Zr-silica adsorbed on 10 mg zirconium g(-1) silica gel was a suitable cation-exchange stationary phase in IC-CD for the separation of these mono- and divalent cations. Excellent simultaneous separation and highly sensitive detection for these cations were achieved in 10 min by IC-CD using a Zr-silica column (150x4.6 mm I.D.) and 10 mM tartaric acid containing 10 mM 15-crown-5 (1,4,7,10,13-pentaoxacyclopentadecane) as the eluent. The proposed IC-CD method was successfully applied to the determination of major mono- and divalent cations in natural water samples.