Synthesis of boron nitride from ferroboron Part 2 – Leaching

Fully nitrided ferroboron powder is leached in simple mineral acids (including hydrochloric acid and sulphuric acid) in order to separate iron/iron nitrides from boron nitride. Weight loss is used to indicate the extent of leaching. Leaching begins with violent chemical reaction and this is followed by a slower, parabolic-like kinetics lasting from 24 to 48 h. In 1 M to 5 M hydrochloric acid leaching can be effectively carried out within 24 h. Amorphous boron nitride produced in mixed NH₃–N₂ at low temperature (400°C) leaches more readily than partially hexagonal boron nitride produced at higher temperatures in pure N₂. The possibility of recycling the leaching acid is also demonstrated using an electrochemical cell.