Chemical speciation analysis for amorphous boron and precipitated boron carbide in sintered boron-added carbon nanotubes

The separation method and the determination of amorphous boron and boron carbide in carbon nanotubes (CNTs) were investigated. The boron carbide was precipitated in the CNTs when they were sintered after adding amorphous boron. The carbon nanotubes and boron carbide were not dissolved, whereas the amorphous boron could be dissolved with 7 N nitric acid. After dissolving amorphous boron in CNTs with 7 N nitric acid, residual boron carbide and CNTs were separated by filtration with a membrane filter. The separated insoluble boron carbide and CNTs on the filter were fused with molten sodium carbonate in a platinum crucible. The concentrations of boron in the filtrate and the insoluble residue were determined by inductively coupled plasma-optical emission spectrometry. It was found that the amount of the precipitated boron carbide increased along with an increase in the addition amount of boron and the rise of the temperature. The amount of unreacted amorphous boron in the CNTs was only a little.