Kazutoshi Kiyokawa

Surface treatment of steel using non-equilibrium plasma at atmospheric pressure

A mixed gas plasma of argon and hydrogen could be generated by irradiation of a microwave to perovskite-type oxide powders at atmospheric pressure. The results of electron and gas temperature measurements showed that this atmospheric pressure plasma is in a non-equilibrium. By using this plasma, we tried to remove surface scales, such as a metal oxide layer, on steel products. Consequently, the scales were removed with little damage in a short period of time, while it is difficult for the ordinary hydrogen reduction process to remove them. The plasma-treatment effect was advanced with increases in the microwave power and treatment time. Optical emission spectroscopy indicated that a large amount of hydrogen radicals existed in the plasma. It is considered that the existence of hydrogen radicals was effective in removing the scales rapidly.

Generation of non-equilibrium plasma at atmospheric pressure and application for chemical process

Abstract When various oxide powders were prepared by microwave heating under an argon gas flow, we found that an atmospheric pressure non-equilibrium plasma generates around some powders. This phenomenon was peculiar to electrically conductive and heat-resisting materials. These plasmas could also be generated easily using gas mixtures consisting of argon and additive gases. With an eye towards industrial applications, we tried to modify the surface of substrates as application examples. The water contact angles of substrates were varied by plasma surface modification. CF4/Ar plasma treatment of polypropylene film increased the contact angle of water from 101 degrees to 124 degrees. The results indicated that the polymer surfaces became highly hydrophobic. On the other hand, the contact angle of water decreased when O2/Ar gas was used.

Role of perovskite-type metal oxides on atmospheric pressure non-equilibrium plasma generation

Abstract A non-equilibrium plasma can be generated by applying microwave power to an La 0.8 Sr 0.2 CoO 3 sample under an argon gas flow. However, since the plasma generation mechanism has not yet been fully understood, we investigated the effect of La 1− x Sr x CoO 3 on plasma generation by varying x in La 1− x Sr x CoO 3 from 0.0 to 1.0. As a result, we found out that the plasma could be generated by using samples whose x in La 1− x Sr x CoO 3 was between 0.0 and 0.6. The temperature rise of these samples (0.0≤ x ≤0.6) during microwave irradiation was much higher than that of other samples (0.8≤ x ≤1.0) which had no ability to produce a plasma. The low work function of the sample also affected the ability to produce a plasma. In conclusion, we considered that the prime requirement for the ability to produce a plasma would be a large increase in temperature of the sample during microwave irradiation, and that the sample would play roles of both triggering and maintaining the plasma.