Refining of Liquid Metal by Hydrogen Cold Plasma

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Refining of Liquid Metal by Hydrogen Cold Plasma
Shanghai University
Weizhong Ding

School of Material Science and Engineering
Shanghai University
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Plasmas play important roles in several
scientific and industrial applications, which
include Manufacture of semiconductor devices
Modification of the surface of polymers
Chemical processes Metallurgical refining
Environmental pollution
Plasma applications

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Two types of plasma

• Electron temperature Te and ion temperature Ti
• When TeTi,it is called as thermal plasma or
  equilibrium plasma, such as plasma torch?arc.
  Thermal plasma usually serves as a high-enthalpy
  source in metallurgical process.
• When TegtgtTi,it is defined as cold plasma or
  non-equilibrium plasma, like glow discharge
  ?corona, etc.

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DC pulsed glow discharge plasma

• The advantage of DC pulsed glow discharge plasma
  are
• simple equipment
• easy to control
• less thermal energy input
• suitable for industrial applications in large
  scale

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An interesting phenomenon

• The refining effect of cold plasma on liquid
  metal.
• The purification of metal can be enhanced by
  cold plasma.
• Under hydrogen cold plasma atmosphere, nitrogen,
  sulfur and phosphorus in the melts are converted
  into volatile compounds and then distilled off.

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1-DC power2-Pulse generator3-Reaction
chamber4-Electrode5-Support rods of
electrode6-Vacuum pump7-Sealing
plug8-Thermocouple9-Pressure gauge10-Vacuum
meter11-Flow meter12-H2 container13-N2
container14-Furnace
Experimental apparatus
plasma
crucible
melt
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Experimental results
System Sn-S Temp. 650C Distance between two
electrodes 3 cm Voltage 350-600V Plus frequency
1600Hz Crucible size ? 25x30 cm
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Experimental results
Influence of gas type and polarity on refining

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Experimental results

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Experimental results

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Experimental results
Nitrogen removal from liquid steel
System low carbon steel Temp. 1550C Distance
between two electrodes 3 cm Voltage 250 -
350V Plus frequency 1250Hz Crucible size ?
2.5x30 cm

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Experimental results

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Mechanism of refining with hydrogen cold plasma
H
H
H hydrogen ions H hydrogen atoms
H2S
H2S
2HSH2S? 2HSH2S?
If melt serves as a cathode, both hydrogen ions
and atoms impact on the surface of melt and react
with dissolved sulfur to form volatile compounds.

Melt as an anode
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Mechanism of refining with argon cold plasma
Inert gas as a refining agent
Argon ions will be accelerated by electrical
field and impact on the surface of the melt.,Thus
sulfur or nitrogen escape from the melts.

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Conclusion
The molecules of hydrogen in the gas are ionized
when applied a DC pulsed electric power. Thus the
different radicals are produced. The refining
ability of hydrogen is enhanced in such process.
While the radicals reach the surface of the melt,
they react with the impurities to form some
volatile compounds, such as NH3, H2S and PH3.
Because the compounds are insoluble into the
melts, they will be carried off by fluent gas.
Finally the impurity elements are removed from
metal.

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Thanks