EXTRAPOLATION TO HIGH TEMPERATURE

Barner and Scheuerman (40) Properties of ions and complexes extrapolated to high temperatures by methods of Criss and Cobble, and Helgeson. 

Gohrbandt s data for camphor spheres (40, 97) afford comparison of rates with diffusion controlling and with heat transfer controlling. Extrapolation to low temperatures of the heat transfer portion indicates sufficient heat transfer but inadequate diffusion. Similarly, extrapolation to high temperatures of the diffusion portion indicates sufficient diffusional driving force but inadequate heat transfer to maintain the surface temperature. 

The procedure for heat capacity calculation can be divided into two parts (a) extrapolation to high-temperature region (b) calculation down to T = 0 K. For C60H36 only extrapolation above T = 340 K is required. 

Heat capacity of the C60H2n crystals was extrapolated to high temperatures using Eqs. 4.6 and 4.7 and the following assumptions ... 

Hl(T, P = 0.1 MPa) fP (T, any pressure) since, at low and moderate pressures, the liquid enthalpy is independent of pressure to an excellent approximation. Therefore, Hl(T,P) is taken along the saturation line, and then extrapolated to high temperature, as shown below. 

The first point of interest is that the curves consist of a number of apparently straight lines which change slope abruptly at each phase change. The deviation from actual linearity in most cases is within the experimental errors. The full calculations are not wasted effort, however, because simple extrapolations to high temperatures using low-... 

Because of the doubt expressed above in the data of BaTh03(cr), especially the extrapolation to high temperatures, we have not processed the Gibbs energies data to derive values at 298.15 K. 

There are few substances where it is worth to fit all the coefficients. In most cases, a quadratic polynomial is sufficient. Due to the difficulties described above, data points in the critical area are of ten left out in the regression nevertheless, average deviations of more than 1. .. 2% must often be accepted, which is caused by the experimental uncertainty of caloric measurements. For many components, heat capacity data for temperatures above the normal boiling point do not exist. In these cases, only a linear function is justified for the correlation, and the extrapolation to high temperatures becomes arbitrary. It can help to generate additional artificial data points with an estimation method. High-precision data can be correlated with the following PPDS equation... 

BPA-PC (branched) 425.7 9.61 120.7 425.7 [102] ar,T, from terminal relaxation G (o) data measured over the temperature range from 473 to 573 K. Its T-dependence Is nearly the same as that for Lexan given above and Is much weaker than that of ar,s for linear BPA-PC given above when the latter Is extrapolated to high temperatures and compared at 473 K, the lowest temperature of measurement of... 

Experimental fall-off data and theoretical extrapolations to high temperature are given for pressure-dependent reactions. These extrapolations were done with the aid of a quantum mechanical analog of the simple Kassel formula (Robinson and Holbrook, 1972), which was fitted to low-temperature experimental results by variation of the deactivation collision efficiency. 

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