Search

The process of preparing porous metal foam titanium powder has been developed In this process, polystyrene foam powder is used as a space holder, and a water solution of polymer is used as a binder. The slurry of the titanium powder, space holder and binder is added to the gelatinizing agent to increase its viscosity. It can then be formed by hand like clay. The slurry is dried, sintered and porous titanium is obtained. The binder and space holder are decomposed in a heating process before sintering. Using this process, porous titanium with porosity in the range of 17-77% is produced, and the mechanical properties are evaluated. From these results, porous titanium that has a porosity of 50 to 60% has a strength of about 30-100 MPa and Young's modulus about 10-30GPa. These mechanical properties arc appropriate for use as implant bone.

This paper reports some experimental results on a concave piezoelectric element, conical backing and first amplifier for high-sensitivity and wide-band AE transducer. The piezoelectric element, conceived according to a “resonance dispersion” design, was fabricated based on piezoelectric ceramics/polymer 1-3 connectivity composites by Newnham. To control ringing characteristics, the backing was conical in shape. The first amplifier was inserted in a FET zero-bias amplifier in a cable connecter. The AE transducer had half sensitivity and a wider resonance frequency (100kHz-1.9MHz) than a conventional type AE transducer (resonance frequency; 180kHz). The residual noise was 20μVp-p (10kHz-50MHz) at first stage amplifier, the measurement of hold level was able to reduce the noise to 10μV with a wide frequency. Using this AE transducer, AE measurement with a high-sensitivity and wide-band was realized in material testings.

The sintering of fibrous BaTiO3 powder particles was investigated. Special emphasis was given to the role of particle orientation in the compact on densification and microstructure development. Compacts were made by dry-pressing. During the initial stage of sintering, the fibrous particles rearranged and bundles of particles were formed. The volume of pores between bundles of particles decreased on further heating. Grain growth started when the sintered density reached ca. 56% of the theoretical density. Higher temperatures of sintering increased the degree of the crystal axis orientation. Thus, highly orientated sintered bodies with high densities were prepared by heating at 1500 °C.

A fibrous lead titanate (PbTiO3) powder with light-yellow color has been prepared by hydrothermal synthesis. The influence of Pb/Ti (0.3 to 1.0) ratio in the mixture and reaction time on the formation of fibrous PbTiO3 under hydrothermal conditions have been investigated. The preferable conditions for preparing fibrous perovskite-type PbTiO3 from fibrous potassium titanate are that Pb/Ti ratio is 1.0, reaction temperature is 150°C, and time is 72h. The fibrous powder of perovskite-type is usually less than 2μm in diameter and more than 50μm in length. The morphology on the face of fibers is essentially unchanged up to 800°C, but it changed after heating at 900°C. But the fibrous morphology is unchanged at 1000°C.

Continuous Pb(Zr 1−x Ti x )O 3 ceramic fibers have been prepared by the alginate method, which is based on a gelation of sodium alginate aqueous solution by sodium ion-exchange with protons or multivalent metal ions. In this work, a new process by use of a 5 % sodium alginate aqueous solution mixed with ZrO 2 -sol and TiO 2 -sol has been studied. The Pb-Zr-Ti-alginate precursor fibers were converted to Pb (Zr 1−x Ti x )O 3 ceramic fibers by firing at 1200°C for 3h. The Pb(Zr 1−x Ti x )O 3 ceramic fibers were examined by the powder X-ray diffraction technique and scanning electron microscopy.

BaTiO3 ceramics were fabricated by sintering a mixture of fibrous and commercial powders, and the effects of crystal-axis orientation on the resonance characteristics of the poled specimens was investigated. Resonance in the radial direction was observed only for the fibrous BaTiO3 ceramic disk. The degree of c-axis orientation of the sintered compact decreased with an increase in the initial amount of the commercial powder, and the decrease in the degree of orientation caused the appearance of the resonance in the thickness direction.

Long-fibrous barium titanate (BaTiO3) particles were prepared by a hydrothermal reaction of potassium titanate hydrate (2K2O·11TiO2·3H2O) and barium hydroxide (Ba(OH)2). Effects of preparation conditions on crystal structure and powder morphology were examined. Fur-fibres of K2O·4TiO2, 1–10 mm long and 1–100 Μm in diameter, were obtained by heating a mixture of K2CO3 and TiO2 powders at 1000 ‡C for 100 h. Keeping the fur-fibres in ion-exchanged water for 4 days gave fur-fibres of 2K2O·11TiO2·3H2O). Long-fibrous BaTiO3, with fibres 100Μm–1mm long and 1–10 Μm in diameter, was obtained by a hydrothermal reaction of the hydrate and Ba(OH)2 (Ba/Ti ratio of 1) at 150 ‡C for 24 h. As-prepared long-fibrous BaTiO3 was composed of fine crystallites (average size about 270 nm) of cubic phase. The cubic phase and morphology of fur-fibres were maintained up to 1250 ‡C, but heat treatment at 1300 ‡C brought about a growth of crystallites to a few micrometers and a phase transformation to tetragonal phase. It was found that the hydrothermal reaction was effective in producing crystalline BaTiO3 powder at a low temperature of 150 ‡C.

An acoustic-emission sensor includes a composite synthetic resin-ceramic piezoelectric element which has a plurality of substantially mutually parallel columnar ceramic piezoelectric bodies. The columnar ceramic piezoelectric bodies are polarized in a longitudinal direction and are disposed in a synthetic-resin matrix. Since only longitudinal waves can be detected from among acoustic-emission waves, an intensity and variation in intensity can be detected accurately.

Barium titanate ceramics with high degrees of c-axis orientation were fabricated from fibrous particles. The maximum piezoelectric constant, d33, obtained was ≅270 pC/N, which is much higher than values reported previously.