Freeze drying technique to prepare doped nanosized B powder

ABSTRACT

In this study, we propose a new approach for the large-scale production of doped nanosized boron powder, which is also useful for manufacturing a wide choice of compounds. This work deals with synthesis of B with cryogenic freezing and lyophilization-based technique, evaluation of its structural properties, and study of superconducting properties of MgB₂ wires manufactured with two types of B powder. This new process begins with dissolution of B₂O₃ precursor in hot water together with doping agents, which can be organic macromolecule or nanosized inorganic compound. This hot solution was then cryogenically frozen in liquid N₂ and finally lyophilized. Nanostructured and doped boron powders were produced by magnesiothermic reaction of the lyophilized precursor (B₂O₃). After the structural and morphological characterization, these boron powders were used for preparation of MgB₂ phase and MgB₂-based conductors. Boron and MgB₂ powders were morphologically analyzed by SEM technique to determine grain size distribution. Phase formation was studied and confirmed by XRD analysis. Short pieces (10 m long) of MgB₂ superconducting wires were manufactured by ex situ PIT technique and characterized by magnetic and transport measurements. Results reported in this study confirm the suitability of the proposed method to produce nanostructured and doped boron powder. This nanosized boron can be used also in different fields where doping and nanosizing are fundamental and required characteristics.

KEYWORDS:

• Boron microstructure
• ceramics
• freeze drying
• powder technology

Additional information

Funding

The authors wish to thank Compagnia San Paolo and Fondazione Carige for their financial support, reserved for the upgrade of instrumentation, EDS analysis, and MPMS Quantum Design SQUID magnetometer, respectively.