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Pulsed electric current sintering of MoO$$_{3}$$ and the neutron irradiation tests

パルス通電焼結によるMoO$$_{3}$$の焼結および中性子照射試験

末松 久幸*; 関 美沙紀 ; 中山 忠親*; 西方 香緒里 ; 南口 誠*; 鈴木 達也*; 土谷 邦彦 

Suematsu, Hisayuki*; Seki, Misaki; Nakayama, Tadachika*; Nishikata, Kaori; Nanko, Makoto*; Suzuki, Tatsuya*; Tsuchiya, Kunihiko

研究用原子炉での$$^{99m}$$Tc製造開発の一環として、照射ターゲットである高密度MoO$$_{3}$$ペレットの製作をパルス通電焼結法にて行った。焼結は、昇温速度100$$^{circ}$$C/min、焼結温度450$$sim$$550$$^{circ}$$C、印加荷重0$$sim$$40MPaの条件で行った。焼結温度550$$^{circ}$$Cにて二段階加圧焼結を行った結果、相対密度94%の焼結体が得られ、一段階加圧焼結よりも高密度の焼結体を得た。焼結中の温度を測定した結果、試料内部の温度が一段階加圧焼結より二段階加圧焼結の方が高いことが分かった。これは低圧状態の際に、試料内部に気孔が多く存在するためにMoO$$_{3}$$が還元されMoO$$_{3-x}$$となり、電気抵抗がより小さくなったためと考えられる。

Pulsed electric current sintering (PECS) of MoO$$_{3}$$ was carried out for a high density target to produce $$^{99m}$$Tc from $$^{98}$$Mo in a nuclear reactor. The green compacts of MoO$$_{3}$$ were heated in a PECS apparatus with a heating rate of 100 $$^{circ}$$C/min to 450 - 550 $$^{circ}$$C in vacuum and changing the pressurization profile from 0 to 40 MPa. After two step pressurization for sintering at 550 $$^{circ}$$C, the sintered MoO$$_{3}$$ bulk had a relative density of 94%, which was higher than that of one step pressurization. Direct temperature measurements near the sample were carried out. The results indicated that the sample temperature was higher for the two step than for the one step pressurization even in the same die temperature experiments. By the low pressure in two step pressurization, it was thought that open pores remained in the sintered body to reduce MoO$$_{3}$$ in vacuum. This oxygen depleted MoO$$_{3-x}$$ grains showed low electrical resistivity and formed a current path in the sintered body to increase the temperature to increase the relative density.

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