Akaki Peikrishvili EPNM’14 May 25-30, 2014 Krakow, Poland Liquid-phase Shock-assisted consolidation of superconducting MgB2 composites

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

Background The superconductive properties of MgB2 was discovered on 2001 with structure C32 and critical temperature of transformation Tc=39K. 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 Tc=40K 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.

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.

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,

Experiment Results The view of billets after predensification and after HEC. Left- predensification at room temperatures; Right- billet after HEC at 100˚C

HEC of MgB2 composites at 1000˚C with Intensity of loading 10GPa. Traces of oxidation are observed on the microstructures (light places).

HEC of MgB2 composites at 1000˚C 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

The Microstructures of HEC MgB2 composites HEC at 1000˚C. 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.

Changed of Stekheometry of Mg-B composites Changed stekheometry between the Mg and B and HEC of MgB1.8 composites at same 1000˚C temperature leads to reducing Tc up to 35K

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 1000˚C 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 Tc=38.5K 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 900˚C the formation of MgB2 phase with Tc=40K 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.

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 Tc=38.5K 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.