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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.