COMPARISON OF PHOTOACOUSTIC, DIFFUSE-REFLECTANCE AND TRANSMISSION INFRARED-SPECTROSCOPY FOR THE STUDY OF CARBON-FIBERS

Three infrared spectroscopic methods-photoacoustic, diffuse reflectanc e and transmission-were evaluated for the qualitative analysis of carb on fibres. Transmission spectra of a potassium bromide (KBr) pellet de tect the bulk of a carbon fibre, and are subject to interference by wa ter in the KBr pellet. Extensive dehydration of a KBr pellet at elevat ed temperatures may cause chemical changes. In contrast, photoacoustic and diffuse reflectance methods are free of water interference. Both methods differentiate the near-surface region of a carbon fibre from i ts bulk, thus providing information about chemical structures in the n ear-surface. The photoacoustic, diffuse reflectance and transmission i nfrared spectra of a carbon fibre have similar band frequencies. There fore diffuse reflectance and photoacoustic methods can be used for rel iable qualitative analysis of carbon fibres.