Akaki Peikrishvili

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Liquid-phase Shock-assisted consolidation of
superconducting MgB2 composites

• Akaki Peikrishvili
• EPNM14
• May 25-30, 2014 Krakow, Poland

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OutlineOutline

• Introduction
• Purpose
• Technique
• Precursors
• Results
• Summary of Previous Work
• Current Work
• Prognosis

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Background

• The superconductive properties of MgB2 was
  discovered on 2001 with structure C32 and
  critical temperature of transformation Tc39K.
  Since that time the intensive investigation
  toward of development different type of MgB2
  superconductive materials in the forms of films,
  sheets or bulk rods and increasing their critical
  temperature of transformation Tc above 39K takes
  place at different laboratories worldwide.
• The technology of development superconductive
  materials belongs to traditional powder
  metallurgy preparing and densification Mg B
  powder blends in static conditions with their
  further sintering processes.
• Existing data of the application of shock wave
  consolidation technology to fabricate high dense
  MgB2 billets with higher Tc temperature
  practically gave same results and limit of Tc40K
  still is maximal.
• Additionally as shows published data additionally
  sintering processes after shock wave compression
  highly recommended providing full transformation
  of consolidating blend phases into the MgB2
  composites.

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Goals of Investigation

• To develop technology of Hot shock wave
  fabrication of high dense billets from MgB2
  without any further sintering processes.
• To investigate the role of temperature on the
  process of consolidation and sintering MgB2.
• To consolidate MgB2 billets above the melting
  point Mg up to 1000C in partially liquid
  condition of Mg-B blend powders.
• To evaluate advantages/disadvantages of LPh HEC
  processes.

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• Experimental Set-up

• Set-up of HEC device.
• 1. consolidating powder material 2. Cylindrical
  Steel container, 3. Plugs of steel container, 4.
  Heating wires of furnace, 5. Opening and closing
  movement of furnace, 6. Opening sheet of furnace,
  7. Closing sheet of furnace, 8. Basic
  construction of HEC device, 9. Feeding steel tube
  for samples. 10. Movement tube for heated
  container, 11. Connecting tube from rub, 12.
  Accessory for fixing explosive charge, 13. Circle
  fixing passing of steel container. 14. El.
  Detonator, 15. Detonating cord, 16. Flying tube
  for HEC, 17. Explosive charge, 18. Lowest level
  of steel container, 19.Bottom fixing and stopping
  steel container, 20. Send,

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Experiment Results
The view of billets after predensification and
after HEC. Left- predensification at room
temperatures Right- billet after HEC at 100C
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HEC of MgB2 composites at 1000C with Intensity
of loading 10GPa.
Traces of oxidation are observed on the
microstructures (light places).
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HEC of MgB2 composites at 1000C with Intensity
of loading 10GPa.
The application of pure Mg and B powder blend
prevents the formation of MgO in HEC billets and
increases of Tc of obtained MgB2 composites up to
38.5K
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The Microstructures of HEC MgB2 composites HEC at
1000C.
The application of pure Mg and B powder blend
prevents the formation of MgO in HEC billets and
increases of Tc of obtained MgB2 composites up to
38.5K. The traces of formed oxides not observed.
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Changed of Stekheometry of Mg-B composites
Changed stekheometry between the Mg and B and HEC
of MgB1.8 composites at same 1000C temperature
leads to reducing Tc up to 35K
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Discussion

• The HEC of Mg-B precursors were performed under
  and above of melting point Mg phase. The
  consolidation were carried out at 500, 700, 950
  and 1000C temperatures with intensity of loading
  10GPa.
• As it was established based on
  investigation the low temperature consolidation
  at 500 C and 700 C gives no results and
  obtained compacts has no superconductive
  properties.
• The application of too high temperatures
  and consolidation at 1000 C provides formation
  of MgB2 composition in whole volume of HEC
  billets with maximal value of Tc38.5K without
  any post sintering processes of samples. The
  mentioned confirms the important role of
  temperature in formation of superconductive MgB2
  phase in whole volume of sample and corresponds
  with literature data where only after sintering
  processes above 900C the formation of MgB2 phase
  with Tc40K there took place. The difference
  of Tc between the HEC and sintered MgB2
  composites may be explained with rest unreacted
  Mg and B phases or existing some oxides in
  precursors. The mentioned could be checked by
  increasing HEC temperature or application of
  further sintering processes. The careful
  selection of initial Mg and B phases is
  important too and in case of consolidation Mg-B
  precursors with mentioned above corrections the
  chance to increase Tc of HEC samples
  essentially increases. The next stage
  experiments to fabricate MgB2 superconductive
  materials will be implemented in this direction.
  

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Concluding Remarks

• The liquid phase HEC of Mg-B precursors above the
  900 C provides formation MgB2 phase in whole
  volume of billets with maximal Tc38.5K
• The type of applied B powder has influence on
  final result of superconductive characteristics
  MgB2 and in case of amorphous B precursors
  better results is fixed (38.5K against 37.5).
• The purity of precursors is important factor and
  existing of oxygen in the form oxidized phases in
  precursors leads to reducing Tc and uniformity
  of HEC billets.