Hirobumi Okabe

Fe-Cr-Al Alloy with an Alumina Layer on the Surface

The biomaterials employed for orthopedic surgery include metals (such as SUS 316L and the Co and Ti alloys), polymeric materials (such as high density polyethylene, ultra high molecular weight polyethylene, silicones, Teflon, and methylmethacrylate), and ceramics (such as alumina, zirconia, hydroxyapatite, tricalcium phosphate, and glass ceramics). Each material has its merits and demerits as a biomaterial. Therefore, in order to utilize only the good points of each, there is an increasing tendency for some kinds of materials to be combined and used as composites. For instance, metal materials have problems such as corrosion and the deposition of metallic elements in the living body, and alumina ceramics, which are quite stable in vivo, have drawbacks such as excessive hardness and brittleness. Thus, to compensate for the respective bad points, studies have been started on the coating of alumina over metallic surfaces. It is very difficult, however, to coat alumina and to prevent exfoliation from the surface. For this reason, we have not only studied the method of coating alumina from the outside, but have, for the last several years, been developing an Fe-Cr-A1 alloy that is a biomaterial having inexfoliatable alumina (a-Al,O,) deposited on the surface layer.

High-Temperature Oxidation of Fe-14Cr-4Al Alloy

High-temperature oxidations have been performed between 1173 and 1573 K on Fe-14Cr-4Al alloy under isothermal conditions, and also under anisothermal conditions at four linear rates of temperature increase from 1×10-3 to 1.5×10-2 K/s. The activation energy obtained in the anisothermal oxidation with low rates of temperature increase was 282 kJ/mol, in agreement with the isothermal activation energy, 284 kJ/mol. The mass gains under linearly-increasing temperature are calculated using the activation energy and the pre-exponential factor obtained in the isothermal oxidation, and are in accordance with the experimental results obtained at low heating rates.

Influence of Giant Pulse Irradiation on a Ruby Laser

In an optical system, consisting of two ruby lasers (one is Q-switching operation, the other normal operation), the following phenomena have been studied on the basis of the experimental results obtained on the fractional metastable state population; 1) quenching of normal laser oscillation, 2) amplification of incident giant pulse by maser mechanism, and 3) changes in giant pulse characteristics by giant pulse irradiation in a Q-switching laser with saturable absorber.