Structural changes with temperature

A(Cp) contribution from the structural change with temperature B(Cp) contribution from thermal expansion of the system as a whole C(Cp) contribution from external work Hereafter the contribution from kinetic energy is discarded in Cp and H. 

P. E. Eberly, Jr. 1 share your concern about structural changes with temperature. Consequently, we have consistently given consideration to what conditions would be most desirable for measuring acidity. We have effected a compromise. At reaction temperatures much above 260 °C, pyridine can undergo some decomposition, and this clouds the experimental results. We selected 260°C for pyridine adsorption. This is higher than that used by other investigators and hence should yield acidities which more nearly represent those at the cracking temperature of 274°C used in this study. 

The Raman spectrum of Na2Si20s at temperatures up to 1773 K was used to characterise structural changes with temperature. IR data have been reported for cyclosilicates containing (Si03) , where n = 3,4 or 6, units. The position of the... 

Within the phase, various structural changes with temperature and an electric field occur [32], [79], [80]. 

The neutron diffraction studies confirmed earlier X-ray results about other important structural changes with temperature [2.5] the mean Si-0 and Al-0 tetrahedral distances were found to decrease continuously with temperature, whereas the Li-0 distances increased see Table 2.2. The decrease in the Si-O and Al-0 distances is comparable to the decrease in the Si-0 distance measured in quartz, also listed in Table 2.2. In fact, zero expansion or slight apparent contraction of T-O bond lengths with temperature has been found in high-temperature structural analyses of many silicates. Hazen and Finger compiled data for silicates and other compounds and evaluated them statistically [2.33]. The large positive thermal expansion of the Li-0 bonds in /3-eucryptite is also in line with their findings for electrostatically weak M-0 bonds. 

The neutron diffraction studies confirmed earlier X-ray results about other important structural changes with temperature [2.5] the mean Si and Al-O tetrahedral distances were found to decrease continuously with temperature, whereas the Li distances increased see Table 2.2. The decrease... 

The lattice constants change with temperature, as will be discussed in Section 1.6.1, and with pressure as already mentioned in Section 1.2. Consequently, the electronic band structure changes with temperature and pressure. The bandgap (at F point) shrinks with increasing temperature and the dependence is given by the empirical relationship [62]... 

Figure 6. Sequence of structural changes with temperature for plagioclases of various compositions.

This potential-energy surface will change when the electrode potential is varied consequently the energy of activation will change, too. These changes will depend on the structure of the double layer, so we cannot predict the value of the transfer coefficient a unless we have a detailed model for the distribution of the potential in the double layer. There is, however, no particular reason why a should be close to 1/2. Also, a temperature dependence of the transfer coefficient is not surprising since the structure of the double layer changes with temperature. 

In derivatives structurally related to pirenzepine (144), a muscarine antagonist, biological activity is likely to differ (84MI7) as a function of conformer composition. In pirenzepine (144), NMR reveals two conformers (84M17) at 10°C, with the relative amount changing with temperature. 

The sweetness of fmctose is 1.3—1.8 times that of sucrose (10). This property makes fmctose attractive as an alternative for sucrose and other commercially available sweeteners. Fmctose is probably sweetest in comparison with sucrose when cold and freshly made up in low concentrations at a slighdy acidic pH (5). This relative sweetness difference is commonly attributed to changes in fmctose structure when cold ( p-D-fmctopyranose(l), sweet) as compared to the structure when the sweetener is warm ( p-D-fmctofuranose (2), less sweet). Based on nmr spectroscopy and sensory panel evaluation of sweetness, however, it has been observed that the absolute sweetness of fmctose is the same at 5°C as at 50°C, and is not dependent on anomeric distribution (11). Rather, it maybe the sweetness of sucrose, which changes with temperature, that gives fmctose sweetness the appearance of becoming sweeter at low temperatures. 

Phase contrast photomicrographs for a 50% polyblend are shown in Figure 7. The granular structure and the changes with temperature in the relative content of light vs. dark regions are noticeable. Also, note that the specimen heated above 120°C. retained its appearance when cooled to room temperature (Figure 8). 

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