Melting point estimation

The estimated melting point of CBr4 is about 90°C. The actual value is 90.1°C according to the Handbook of Chemistry and Physics. 

Alloy crystal and thermal data symbols. A number of tables show, for selected alloys, the highest melting points observed in the systems considered, as well as the mechanism of formation (p = peritectic melting, syn = synthetic reaction, s.s.r. = solid-state reaction, est. = estimated melting point, etc.), the value of the Raynor Index (<1, =1 or>l). The question mark means that no reliable data are available. 

The van Laar technique for estimating melting points. Tf can be obtained by extrapolation from the liquidus of alloy systems which contain a phase of structure by a technique originally suggested by van Laar (1908) but not considered seriously until resuscitated by Hume-Rothery and Raynor (1940). It is described succinctly in the following extract from their paper ... 

The agreement between heats of fusion of the same polymer is excellent in some cases, but very poor in others. Obviously, in the case of polypropylene more work needs to be done before the heat of fusion of this substance will be known with any certainty. Heats of fusion calculated from the copolymer equation, Eq. (6), are uniformly low, except in the case of Rybnikar s data. As pointed out by Dole and Wunderlich (1957) this is probably due to the failure to measure the maximum melting of carefully annealed samples. Thus, Dole and Wunderlich (1959) found that the calorimetrically estimated melting point in the case of the carefully annealed copolyester, the 80/20 polyethylene terephthalate and sebacate, was 240° C, whereas the value calculated from Eq. (6) using the heat of fusion estimated from the calorimetric data of Smith and Dole (1956) was 245° C. The unannealed sample had a melting point of ca. 210°. 

The melting-point-depression method can also be used to estimate melting points of polymers that degrade before they melt. The depressed melting points are simply plotted against the volume fraction vl of solvent in the solution, and extrapolated to the point where Vi equals zero. The method, illustrated in Figure 2.45, has been used for a variety of polymers, particularly for cellulosic materials. 

This chapter deals primarily with practical applications of theoretical principles to the estimation of melting enthalpy and entropy in order to estimate melting point. As necessitated by the situations described above, the methods are based entirely upon molecular structure. 

Examples of Parameters Used to Estimate Melting Point. 

The melting point is assumed to be 2400 K as estimated by Douglas and Victor (1 ) and Schick et al. (5). Prom the estimated melting point, 2400 K, and an estimated 2.5 cal g-atom for the entropy of melting, the heat of melting was calculated. 

The heat capacity is assumed constant and equal to the heat capacity of solid BOgC at the estimated melting point. 

For estimating melting points by interpolation the normal melting point versus atomic number plot serves just as well and saves one the step of calculating the reduced melting temperatures and plotting them. 

The hot-spot linear power was determined in accordance with the criterion that no fuel should be higher than the melting temperature, even at 10% overpower. The fuel at the peak linear power of 24.2 kW/ft has a center temperature of 4928°F (the estimated melting point of the mixed oxide fuel). The ability of the fuel to operate under these conditions is dependent upon the formation of a central void in the hot-spot... 

Problem 7.3. Solid silver has a density of 9.3 g/cm, a liquid-solid surface energy of 1.8 X 10 " J/cm, and an enthalpy of melting of -11.3 kJ/mol. Given that silver has a bulk melting point of 962 °C, calculate the estimated melting point of a silver nanoparticle with a radius of 7.0 nm. 

Poly(para-phenylene), with its rodlike structure composed of highly delocalized n-electron orbitals, satisfies most of the requirements for high thermal stability. Possessing Ti/2 > 400°C and an estimated melting point of 1400°C, PPP constitutes a reference for heat-resistant polymer. Poly(para-phenylene) can be synthesized by a number of routes, with the best heat-resistant material obtained by polymerization of 1,3-cyclohexadiene, followed by dehydrogenation of the polymer formed according to Eq. (35) [16]. 

In summary, designing low melting, low viscosity ionic liquids is a challenging task because several molecular features contribute. Additionally some molecular features, like ion pairing, enhance the mobility of the ions only over a selected range before their influence show a reversed effect. Therefore, semiemperical and quantitative structure-property relationship (QSPR) approaches seem to be a good choice to estimate melting points or... 

The estimated melting point of the infmite poIy(ethylene) crystal is in dispute (see Refs. 30,95). Values in parentiieses indicate temperature in kelvin. 

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