The thermal decomposition of poly(α,α,α′,α′-tetrafluoro-p-xylylene) (parylene AF-4) films with thicknesses of ca. 7.5 and 10 μm has been studied by both dynamic (10°C min−1) and isothermal TG in either nitrogen or oxygen atmospheres.
In dynamic studies with nitrogen, gross decomposition occurs between 546.7±1.4 and 589.0±2.6°C, with 26.8±4.4% of the initial
mass remaining at 700°C. With oxygen as the purge gas, the onset of decomposition shifts slightly to 530.8±4.2°C. The end
of the transition at 587.4±2.6°C is within experimental error of the nitrogen value, but no polymer remains above 600°C.
Isothermal data were obtained at 10°C intervals from 420 to 490°C in nitrogen, and from 390 to 450°C in oxygen. Plots of log(Δ%wt/Δt)vs. T−1 are linear throughout the specified range for oxygen and from 420 to 470°C for nitrogen. The calculated activation energies
of (147±16) kJ mol−1 and (150±12) kJ mol−1 in N2 and O2, respectively, are equal within experimental error.
A new method for the determination of aluminum and silicon has been developed for zeolite catalysts. In contrast to previous methods, thermal neutrons are used for the analysis of both elements, and cadmium absorbers are not needed. The silicon determination utilizes a one-hour irradiation to observe the31Si produced by the (n, ) reaction of30Si. A 15-second irradiation is used for the27Al(n, )28Al reaction. The28Al activity is corrected for the contribution from the28Si(n,p)28Al reaction by using the analyzed weight of silicon in the sample and the data for a silicon standard irradiated simultaneously with the zeolite and the aluminum standard. The quantitation limits are 0.012 g for silicon and 3.3×10–5 g for aluminum. Sodium presents a significant interference, but this element can be removed by taking advantage of the ion exchange properties of these materials.