Discussion of particle size effects

1 Particle size effect on thermodynamic data for Th02(s) 

M is the molecular weight and p the density of the solid, d describes the particle size and a is a geometrical factor which depends on the shape of the particles. For approximately spherical particles with diameter d the geometry factor is a 6. According to Schindler [1967SCH] the mean free surface energy of the solid-liquid interface can be estimated by Eq. (VI1.44)  

With the known data for crystalline Th02(cr) (logi W° 0) = 

708 kJ-mol at 25°C, the interfacial tension y is calculated to be 1.22 J m [2000BUN/KNO]. The relations between AjG° and log,oW° of small Th02 particles (particle size d) and large crystals of Th02(cr) are thus given by  

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Thus, the beneficial effect seen in oxygen index has been shown, in this system at least, to be mirrored in a range of other tests. Furthermore, the particle size effect is also observed in all of the tests, although it appears more marked in some than in others. In an attempt to explain the particle size effect, the fillers were all examined by differential scanning calorimetry (DSC) but only minor differences, insufficient to account for tbe observed variation in performance, were found (see the section on ATH in Chapter 2 for a detailed discussion of particle size effect on kinetics of decomposition). 

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