Abstract: Pre-oxidized polyacrylonitrile fibers were carbonized in BCl₃. Effect of processing temperature and time on B element content in the PAN-based carbon fibers was studied. A series of techniques including XPS, FTIR and SEM, were employed to characterize the composition and structure of the sample. The microwave absorbing properties of the resultant PAN-based carbon fibers were studied by voten network analyzer. The results indicate that the pre-oxidized polyacrylonitrile fibers are converted to carbon fibers by carbonization in BCl₃ and BCN attachments are formed. The resultant fiber forms B–N bonds at the same time. The permittivity of carbon fibers/paraffin is lower in comparison of that of fibers carbonized in N₂, especially the imaginary part of the permittivity of carbon fibers paraffin reduces fastly. The carbonization in BCl₃ is beneficial to improve the microwave absorbing property.

Key words: polyacrylonitrile, BCl₃, carbonization, microwave absorbing property