報告書番号

W00025

タイトル（和文）

セラミックス粉注入時の移行形交流プラズマの安定性とその機構

タイトル（英文）

Stability and mechanism of transferred type AC arc plasma injected ceramic powder

概要 （図表や脚注は「報告書全文」に掲載しております）

交流プラズマを用いて，導電性を持たないセラミックス粉体の溶融処理が試行されており，電流零点における交流プラズマの安定性が重要な課題である。今回，代表的なセラミックスであるアルミナ（Al2O3）の粉体が注入された場合の，電流零点における交流プラズマの安定性を検討した。(1) Al2O3粉を注入することにより再発弧電圧が低くなり，電源電圧を８割程度に低くしてもプラズマは安定化した。(2) 電流零点直前の分光観測結果から，粉の注入により，プラズマの温度は12,000K程度から10,000K程度に低下し，プラズマ中のAl2O3混入率が10％程度であった。Al2O3が混入したArプラズマの電流零点直前のエネルギー密度はAl2O3の解離に伴い高くなるため，プラズマのコンダクタンスの時間上昇率が高くなり短時間で熱的再発弧が起こると考えられる。(3) プラズマ中のAl2O3粉の蒸発・混入により，Arより電離電圧の低いAlが存在し電極間の電子密度が高くなった。このため，電流零点後の電極間の絶縁回復が遅くなり，低い電圧で短時間に電圧的再発弧が起こると考えられる。以上の(2)(3)の両現象が起こるために，Al2O3粉を注入した場合，電流零点において交流プラズマは安定化傾向を示したと考えられる。

概要 （英文）

AC arc plasma heating technology has recently been utilized to melt ceramics powder. Injection of the powder into AC arc plasma would change the stability of arc plasma at current zero point. Stability of AC arc plasma depends on two physical parameters of an energy density of arc plasma just before current zero point and a dielectric recovery characteristics between electrodes after current zero point. This paper describes the effect of injection of alumina powder on stability of transferred type AC argon arc plasma. The alumina is typical ceramics. The experimental conditions are as follows; AC current 70Arms, plasma length 25-100mm, flow rate of argon 20l/min, mean diameter of alumina powder 15μm and injection speed of the powder 11-84g/min (1kg/kWh). Main results are as follows;(1) Injection of the powder caused the re-ignition voltage after current zero point to decrease by around 30% and arc plasma to be stabilized at 20% lower power supply voltage.(2) Owing to injection of the powder, the temperature of arc plasma before current zero point decreased from 12,000K to 10,000K and the alumina concentration (molar rate) in arc plasma increased to 10%. The energy density of arc plasma just before current zero point was calculated by means of the thermodynamic properties of high temperature argon mixed with alumina and the measured temperature and alumina concentration. The injection of alumina powder into arc plasma caused the energy density to increase. The increase of the energy density was due to dissociation of alumina in arc plasma.(3) In order to grasp the dielectric recovery characteristics between electrodes after current zero point, the electrical conductivity was calculated by means of the transport properties of high temperature argon mixed with alumina and the measured temperature and alumina concentration. The injection of alumina powder caused the electrical conductivity to keep a high level. The result indicates that the aluminum of lower ionization potential than argon will exist between electrodes.Due to the phenomena mentioned in (2)&(3), AC arc plasma injected alumina powder had a tendency to be stabilized at current zero point.

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