Chemical durability of BaK122 superconducting cores under different environmental conditions

The chemical durability and reaction mechanism of the BaK122 superconducting cores of PIT (powder-in-tube) tapes were investigated in de-ionized water, dry air, anhydrous ethanol, and anhydrous hexane at room temperature. It is found that H ₂ O is the most toxic to superconductivity. It corrodes the core from the surface and drastically suppresses J _c by 95%. It reacts with the Ba _0.6 K _0.4 Fe ₂ As ₂ compound and transforms it into iron arsenate, potassium carbonate and barium carbonate. The critical current density is therefore suppressed considerably. The air with 10% moisture causes a 20% decrease of J _c after 7 days, implying that pure O ₂ may have a trivial influence on the BaK122 compounds at room temperature. We also find that the anhydrous ethanol and the anhydrous hexane are friendly solvents. We suggest that water and moist air must be carefully avoided in processing BaK122 compounds under any circumstances. After that, the chemical stability of this superconductor would be greatly improved.