Synthesis of boron nitride from ferroboron Part 2 - Leaching

Fully nitrided ferroboron powder is leached in simple mineral acids (includ ing hydrochloric acid and sulphuric acid) in order to separate iron/iron ni trides from boron nitride. Weight loss is used to indicate the extent of le aching. 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. Am orphous boron nitride produced in mixed NH3-N-2 at low temperature (400 deg reesC) leaches more readily than partially hexagonal boron nitride produced at higher temperatures in pure N-2. The possibility of recycling the leach ing acid is also demonstrated using an electrochemical cell.