An infrared pyrolysis cell has been developed which permits thermal decomposition of microsamples in the beam of an infrared spectrophotometer. Organic and inorganic materials may be degraded at controlled temperatures up to 1100° C in oxidizing, inert, or vacuum atmospheres The system silica-polytetrafluoroethylene (PTFE, Teflon) was studied in the temperature range 500 to 600° C in air and in helium. When heated in air, mixtures containing up to 23 per cent silica were totally volatilized, but in an inert atmosphere only the PTFE is volatilized without loss of significant quantity of silica. The principal species observed following the air pyrolysis of silica-PTFE composite were SiF<sub>4</sub>, COF<sub>2</sub>, and CO<sub>2</sub>; the same material pyrolised in helium resulted in the identical products as unfilled PTFE, namely, C<sub>2</sub>F, C<sub>3</sub>F<sub>6</sub>, and C<sub>4</sub>F<sub>8</sub> The probable equation for the interaction between PTFE and silica in air is (–C<sub>2</sub>F<sub>4</sub>–)<sub>n</sub> + S<sub>1</sub>O<sub>2</sub> + 2O<sub>2</sub> → 2COF<sub>2</sub> + SiF<sub>4</sub> + 2CO<sub>2</sub> + C<sub>2</sub>F<sub>4</sub> + C<sub>2</sub>F<sub>4</sub> recombination products

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