Isothermal weight gain

Figure 2,14 Isothermal weight gain in air at 950 C for BN specimens with d 002) from 3.33 A to 3.67 A.

While the rate of decomposition in air was more rapid than in nitrogen, the kinetics of oxidative decomposition cannot be estimated reliably by isothermal weight loss because ofthe possibility of competing oxidative weight gain process. For this reason the kinetics were not estimated from the available data... 

The polymer sample is suspended from a balance under a uniform concentration of vapour at a known temperature and pressure. By studying the equilibrium weight gain or loss at different vapour concentrations, a sorption isotherm may be determined. A typical isotherm observed for Fickian diffusion is shown in Figure 2. 

Table 1 Isothermal thermogravimetric data including time until onset of weight gain, time until maximum weight gain and percent weight gain at maximum as a...

The amount of water adsorbed after the samples were outgassed was controlled by adjustment of the pressure in one of three ways use of a sensitive Cartesian diver manostat, use of a water source at a controlled temperature, or use of the mixed magnesium perchlorate hydrates mentioned above. The amount of water adsorbed by the sample was measured either by the gain in weight of a companion sample or by interpolation from the isotherm at 23.5° C. The heat of immersion of samples with no water adsorbed was determined with samples sealed off from the vacuum line while they were still in the furnace at 500° C. 

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