INDEX versus temperature curves

Addition of alkali oxides to germania initially reduces the thermal expansion coefficient, which passes through a minimum at 2 to 5 mol% alkali oxide. Further additions of alkali oxides result in a continuous increase in the thermal expansion coefficient out to the limit of glass formation. The position of the minimum in thermal expansion coefficient is near the low alkali germanate anomaly in viscosity and glass transformation temperature, which occurs at 2 mol% alkali oxide. No unusual behavior in the thermal expansion coefficient is found in the 15 to 20 mol% alkali oxide region where the traditional germanate anomaly in density and refractive index occurs. Replacement of alkali oxides by alumina reduces the thermal expansion coefficient, but has little effect on the shape of the thermal expansion coefficient versus composition curve, which still displays a minimum at 2 to 5 mol% alkali oxide. 

As mentioned in the introduction, hydroperoxides can be measured by recording the area under the CL curve in an inert atmosphere i.e. the total luminous intensity (TLI). Kron et al. found that when measuring CL in inert atmosphere together with peroxide concentration, as measured by iodome-try, for oxidised polypropylene, proportional relationships were obtained when the TLI was plotted versus peroxide concentration (see Fig. 3) [60]. In addition, changes in melting temperature and polydispersity index with aging time have also been found to correlate with changes in the TLI [59]. 

Figure 4.19 Memory effect in B2 O3. The Active temperature (here calculated from the refractive index) is plotted versus time t—12 after a second temperature step. The first temperature step was from equilibrium at 583.2 K to Ti = 498.7 K, and the second step at time t2 was from T to T2 = 543.4 K. The solid curve is calculated from Eqs. (4-22), (4-27), and (4-28) using C = 5.6 x 10 sec, AH 92 kcal/mol, fi — 0.82, and x = 0.50. In Kovacs original experiments, the memory effect was monitored by careful measurement of an increase, followed by a decrease, in the sample s volume after the second temperature step. (From Moynihan et al. 1976, with permission from the New York Academy of Sciences.)...

Fig. 3 compares the NOx and C2H4 conversions over the two Ga-based catalysts. The results have been plotted as the conversion of NOx to N2 as a function of the extent of the C2H4 conversion, considered to be an index of the extent of the reaction. C2H4 is indeed the common species simultaneously able to reduce NOx to N2 while it can also be oxidized by O2 in the parallel side reaction. In this representation, the curve of Ga-Al (sg) lies above that of Ga-Al (i). Fig. 4 shows the NO and NO2 concentrations versus reaction temperature for the two catalysts. Starting from 673 K, the NO concentration decreased in a marked way as well as that of NO2, leading to N2 formation. The curve of NO concentration is steeper for Ga-Al (sg) than for Ga-Al (i), indicating the superior activity of Ga-Al (sg). N2 production over the two catalysts is also reported in Fig. 4. 

Fig. 10.31 Illustration of the Ozawa method to treat (a) several DSC curves with various cooling rates a. (b) A group of crystallinity data Xc are read at a constant temperature, then (c) the Ozawa index can be obtained from the slope of lg[—ln(l — X )] versus lg(a)...

Here, q is called the Ozawa index. Corresponding to one-dimensional growth, q = 2 two-dimensional growth, q = 3 and three-dimensional growth, = 4. In practical measurements, one may determine the values of crystallinity XJa) at a constant temperature from a series of DSC crystallization curve with various cooling rates a, and then plot lg[—ln(l—X )] versus lg(a), to obtain the Ozawa index directly from the slope, as illustrated in Fig. 10.31a-c. 

Since common processing techniques for polymers involve shear rates of about 100-100 000 s there is no substitute for the comprehensive study of shear-stress versus shear rate over the typical processing windows of shear rate and temperature. Clearly, one-point tests such as melt flow index cannot be used as a guide to processability since the shapes of pseudoplastic curves are not identical (Figure 9.9). 

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