Various Narpsios consisting of the composition formula of Na3+3x-yR1-xPySi3-yO9(R: rare earth, In and Sc) were synthesized by the crystallization of a glass. The formation of Narpsio-V having high conduction property was influenced by the kind of R element. The specimens with single phase of Narpsio-V were obtained in the use of Sm, Eu, Gd, Y and Er. In particular, the Narpsio-V widely yielded on the composition map of [Y] vs. [P]. The R elements also affected the conduction properties. The activation energy for Na+ conduction in Narpsio-V was improved with increasing the ionic radius of R element. Although the lowest activation energy was confirmed in the case of Sm, the total conductivity of whole specimen with Sm was lower than that with Gd. This was due to the difference in the grain boundary.
Highly dense ceramics of Ba2YCu4O8 (Y-124) superconductor were successfully prepared under ordinary pressure of oxygen by the two-stage sintering, the compacted disks of precedently prepared Y-124 powders were sintered at 930°C for 2h, thereafter annealed at 800°C for 200h. The ceramics thus prepared have relative densities around 95%. It was also confirmed that the Y-124 phase of starting powders was decomposed to Ba2YCu3O7-δ (Y-123) and CuO at 930°C, and then restored in the annealing at 800°C. Liquid-phase sintering may bring about the densification, since partial melt reportedly occurs at 930°C under oxygen pressure of 1013.25 hPa.
Polycrystalline hydroxyapatite (Ca10(PO4)6(OH)2, HAp) coatings were prepared by rf-sputtering combined with hydrothermal annealing, and then their biocompatibility through in vitro biological test was examined. Amorphous calcium phosphate thin films were deposited onto titanium metal plates by an if magnetron sputtering without a substrate heating. The targets for sputtering were three kinds of compressed powder of dicalcium phosphate (DCP), α-tetracalcium phosphate (α-TCP), and hydroxyapatite (HAp). In order, to crystallize the amorphous coatings, hydrothermal annealing was performed using an autoclave at 200°C for 24 h under a saturated water vapor pressure. Biocompatibility of the postannealed specimens was examined by in vitro test using a simulated body fluid (SBF) with pH 7.4 at 36.5°C. Surface morphologies and Ca/P ratios of the films depend on the target composition for sputtering. Since SEM observation shows bonelike crystal growth on the surfaces of the films after soaking in an SBF, all the specimens have good biocompatibility.
Apatite thin films of calcium phosphate were successfully prepared by rf‐magnetron sputtering, followed by postannealing, from calcium phosphate glass targets with Ca/P atomic ratios of 0.6 to 0.75, much lower than the stoichio‐metric value of 1.67 for hydroxyapatite. Using targets with low Ca/P ratios of 0.65 to 0.25, tricalcium and pyrocalcium phosphate thin films were obtained. The formation of these calcium phosphates phases was attributed to the phosphorus oxide losses during sputtering. H 2 O vapor was effective in the formation of the apatite phase at high temperatures; apatite was the exclusive phase in the ambient H 2 O, even when the target with the low Ca/P ratio of 0.4 was used. Based on phase stability at high temperatures, it was assumed that various kinds of apatites, such as stoichiometric and nonstoichiometric hydroxy‐ and Ca‐deficient hydroxy‐apatites were formed, depending on the composition of the glass targets.
The effect of additives such as polyvinylalcohol, polyacrylamide, acrylamide and acrylic acid on the mechanical properties of calcium phosphate cement was investigated, measuring the diametral tensile strength of the hardened cement made by pressing the cement paste. Of the additives tested, the combined use of acrylamide monomer and acrylic acid was effective to improve the mechanical properties of the hardened cement. For the cements made by pressing at various pressures (72.8-291MPa), the addition of acrylamide and acrylic acid resulted in an about 30% increase of the diametral tensile strength and an about 7% increase of the bulk density compared to the control (no additives). The hardened cement with acrylamide and acrylic acid exhibited a diametral tensile strength of 15.4 MPa as the largest values obtained.
Dielectric depression and dispersion were observed in BaTiO 3 ceramic films fabricated by electrophoretic deposition followed by sintering. The dielectric constants were depressed down to 6800‐4600 around the Curie point ( T C ). The dielectric dispersion occurred above T C . These dielectric properties are attributable to a surface layer formed during sintering. XRD analysis indicated that the surface layer was a hexagonal‐like BaTiO 3 phase. A mixed solvent of acetylacetone and alcohol employed in the present work may have been responsible for the formation of the surface layer.
The variation of the Weibull modulus (m) of dielectric strength (Eb) with temperature showed that Eb scatters more widely in the ferroelectric phase than in the paraelectric phase or around the Curie point (Tc). This result was correlated to the fact that the variation of Eb was approximately inverse to that of dielectric constant. It was also found that the modules m varied with sintering conditions; a higher value of m (ca. 10-15) was obtained in a specimen sintered at a lower temperature for a shorter time. This result is probably correlated with the distribution of larger grains.
'/%3e%3cuse xlink:href='%23a' transform='rotate(23.036 .093 25.536)'/%3e%3cuse xlink:href='%23a' transform='rotate(45.87 1.273 16.18)'/%3e%3cuse xlink:href='%23a' transform='rotate(69.945 .996 12.078)'/%3e%3cuse xlink:href='%23a' transform='rotate(20.66 -19.689 31.932)'/%3e%3c/svg%3e)
