Papers by Author: Katsuhiko Asami

Abstract: Characterization of heat-treated CaTiO3 thin films of 10, 20, 30 and 50 nm in thickness and their change after immersion in a simulated body fluid were investigated by grazing incident angle X-ray diffractometry and Auger electron spectroscopy (AES). The CaTiO3 films were prepared on titanium substrate by sputter-deposition of CaTiO3 target followed by heating in an electric furnace at 873 K in air for 7.2 ks. The CaTiO3 films were immersed in 0.8% NaCl solution for 14 d. All the films before heat treatment were non-crystallized films and after heat treatment, only the 50-nm film was crystallized to perovskite-type CaTiO3. In AES in-depth profiles after heating, Ca diffusion was not observed in the 50-nm film, whereas Ca diffusion toward the Ti substrate was observed in the 10-, 20- and 30-nm films. After immersion for 14 d, the vicinity of surface of the 10, 20 and 30 nm thick CaTiO3 films were dissolved into the NaCl solution, while the 50-nm thick CaTiO3 film was scarcely dissolved. Since dissolution from biomaterials in a human body has possibility to harm, the CaTiO3 film should be deposited more than 50 nm in thickness and heat-treated at 873 K.

Abstract: Rusts formed on several types of weathering steels and a plain carbon steel exposed to environments for a long term were investigated by EPMA, XRD and TEM/ED. Information about distribution of elements, type of rusts, depth distribution of rusts, and their relation with type of steels and environments are made clear.

Abstract: In order to examine the critical content of AlN for phase change from B1 type to B4 type, Zr-Al-N and Nb-Al-N pseudobinary films were synthesized with an inductively combined rf-plasma assisted magnetron sputtering method. From phase identification of these films by XRD and Raman scattering methods, it is found that phase change from B1 structure to B4 one occurs in the range from 30mol%AlN to 35mol%AlN for Zr-Al-N pseudobinary films and from 62mol%AlN to 70mol%AlN for Nb-Al-N pseudobinary films. The critical AlN content for Zr-Al-N pseudobinary films shows excellent agreement with the value (33mol%AlN) predicted by band parameters. The critical content for Nb-Al-N pseudobinary films is larger than the predicted value (53mol%AlN). It is suggested that the disagreement is attributed to a highly defective structure in Nb-Al-N pseudobinary films.

Abstract: Recent development of corrosion resistant bulk glassy alloys such as Zr-, Fe-, Ni- and Cu-base alloys were presented. It was clarified that the enrichment of cations in the passive film, which is responsible to corrosion resistance, depends on both alloy composition and environment. TEM observation also made it clear that alloys lose their advantageous properties such as corrosion resistance when they are devoid of or lose amorphous structure even in part due to low glass forming ability or heating. These findings were essentially similar to those of conventional amorphous alloys.