The utility of infrared Fourier transform photothermal beam deflection spectroscopy (PBDS) for the examination of intumescent systems was explored. Infrared spectra were recorded of a model system consisting of a mixture of pentaerythritol and (NH<sub>4</sub>)<sub>2</sub>HPO<sub>4</sub>, and of a film of a commercial fire-retardant paint painted on sheet metal, at various stages before, at, and after intumescence. Although the morphology of the materials changes greatly during the thermal decompositions, infrared spectra can be recorded which can provide useful information about the systems and intumescent chars.
P. G. Varlashkin and M. J. D. Low, "Infrared Spectra of Intumescent Chars," Appl. Spectrosc. 40, 393-397 (1986)