Study on the Formation of Ultrafine Iron Particles with Paramagnetism (Gamma-Fe)

采用微波等离子体加热法制备γ-Fe超微粒子。采用气相蒸发法制备了α-Fe超微粒子。α-Fe超微粒子通过微波等离子体区域漂移到下游气体中。α-Fe超细颗粒被加热，然后快速淬火。在此之后，γ-Fe超微粒子被获得。(1)γ-Fe超微粒子的丰度γ-Fe超微粒子的丰度取决于Ar气压、微波功率和等离子体区气体流速。当气压为15 Torr、微波功率为500 W、气速为40 m/s时，富集度最高可达40%。当微波功率大于500 W时，γ-Fe的丰度逐渐降低。当微波功率为1 KW时，产率可达30%。当气速为10 m/s时，γ-Fe的丰度比气速为40 m/s时有所降低。(2)在无油真空系统中，在Ar气中加入少量CH_4气体，进行了类似的实验。当CH_4含量为90 ppm时，在Ar气压为15 Torr，气体流速为40 m/s，微波功率为500 W的条件下，γ-Fe的丰度为55%。当CH_4含量为450 ppm时，除α和γ外，还存在Fe-C系（Fe-C，Fe_3C），在CH_4气中加入He气的实验中，γ-Fe的丰度小于Ar气中的γ-Fe。在这种情况下没有观察到Fe-C系统。

Production of gamma-Fe ultrafine particles was done with the use of microwave plasma heating. Alpha-Fe ultrafine particles were prepared by the gas evaporation method. The alpha-Fe ultrafine particles were drifted through a microwave plasma region to the gas downstream. Alpha-Fe ultra-fine particles were heated and then quenched rapidly. After that, gamma-Fe ultrafine particles were obtained.(1) Abundance of gamma-Fe ultrafine particlesThe abundance of gamma-Fe ultrafine particles depends on Ar gas pressure, microwave power and gas velocity in the plasma region. A maximum abundance of 40% was achieved with the gas pressure of 15Torr, the microwave power of 500W and gas velocity of 40m/s. As the microwave power increases above 500W, the abundance of gamma-Fe decreases gradually. The abundance of 30% was obtained at microwave power of 1KW. When the gas velocity was changed to 10m/s, the abundance of gamma-Fe decreased in comparison with the case of 40m/s.(2) Effect of carbon (CH_4) on the production of gamma-Fe ultrafine particlesIn an oil-free vacuum systems, a similar experiment was done with a small amount of CH_4 gas added to Ar gas. When the CH_4 content was 90ppm, the abundance of gamma-Fe was 55% at the following conditions as 15Torr in Ar pressure, 40m/s in the gas velocity and 500W in the microwave power. When the CH_4 content was 450ppm, Fe-C system (Fe-C,Fe_3C) was found in addition to alpha and gamma.In an experiment carried out in the CH_4 gas added to He gas, the abundance of gamma-Fe was less than in that of Ar. No Fe-C system was observed in this case.