Characterization of elemental boron synthesized by electrolytic method

Abstract

8.1 Synthesis and Characterization of Electrodeposited Elemental Boron Process parameters for large-scale production of elemental boron via molten salt electrolysis were established.

Both “raw boron” and “processed boron” samples were characterized for physical and chemical properties.

High-purity boron conforming to nuclear application specifications was successfully produced.

Sources of residual impurities were identified and controlled by tailoring materials and processes.

Bulk density and surface area of boron powder were found to depend on particle size distribution.

Impurities such as iron and nickel were present as halides, borides, and oxides, confirmed by XPS.

Purging with commercial-grade argon (<10 ppm moisture) minimized halogen gas residence time and prevented corrosion.

8.2 Processing of Electrodeposited Boron Powder Purification and processing steps were optimized to meet specifications for boron carbide synthesis (control rod applications in nuclear reactors).

Water leaching for 5 hours, with fresh water replacement every hour, reduced halide impurities to <50 ppm.

Ball milling produced fine boron powder (10-100 m, with >50% <10 m).

Acid leaching for 24 hours reduced iron and nickel impurities to <1 wt.%.

A complete flow sheet for processing boron powder was developed, yielding boron of >96 wt.% purity.

8.3 Structural Characterization SEM revealed spheroidal boron aggregates (~1 m) deposited on mild steel cathodes.

Controlled voltage increase (~4.5 V over 1 hour) prevented dendritic deposits.

TEM showed nanocrystalline boron (~60 nm) embedded in amorphous mass, with predominant -rhombohedral crystal structure.

Raman spectroscopy confirmed -rhombohedral phase formation after vacuum annealing at 1573 K, though complete conversion of amorphous boron was not achieved.

8.4 Kinetics of Oxidation Oxidation kinetics of electrodeposited boron was studied using thermogravimetry and DTA.

A two-step exothermic oxidation reaction was observed, hindered by the formation of a glassy B2O3 layer.

Activation energy: 122 ± 7 kJ/mol for electrodeposited boron vs. 205 ± 9 kJ/mol for boron from BCl3 reduction.

Oxidation strongly depends on particle size, surface area, and crystalline/amorphous nature.

Rapid oxidation occurs only above 700 K, making boron safe to handle at room temperature.

8.5 Ignition Behaviour Ignition temperature was determined using thermogravimetry and DTA.

Formation of a B2O3 glassy layer during ignition acts as a diffusion barrier for oxygen.

Ignition temperature depends on heating rate and particle size; significant ignition occurs at ~783 K for particles <32 m.

Crystalline boron is more resistant to ignition than amorphous boron.

Safe handling requires inert atmosphere (argon or nitrogen, moisture/oxygen <10 ppm), ideally inside a glove box.

Overall Conclusion This study established the process parameters, purification methods, structural characterization, oxidation kinetics, and ignition behaviour of electrodeposited elemental boron. The optimized methodology enables safe, large-scale production of high-purity boron suitable for nuclear reactor control rod applications.