The role of the porous structure and its effect on reactivity was stud
ied from changes of macroscopic properties. We present a review of our
experimental-modeling effort that concerns porosity and reactivity. S
hrinkage gave an understanding into the structure, and occurs because
of the reduction of microcrystal dimensions. Detailed modeling for the
porous structure was developed and reproduced the shrinkage. Fragment
ation increased the understanding into the behavior of the porous stru
cture; it depends on the structure geometry and threshold porosity, an
d has been shown to occur when macroporosity reaches a threshold. Tiny
details of the structure were gained from thermal conductivity (TC).
A five-time decrease was measured from 0 to 30% burnout, then TC remai
ned constant up to 80% burnout and increased twofold to 100% burnout.
Heat transfer calculations using the same model showed an excellent fi
t to experimental data, indicating that the extent of connectivity bet
ween microcrystals is the single most important parameter for TC. The
behavior of TC at low conversions is consistent with the reactivity da
ta, since steep changes in TC are accompanied by generating defects wh
ich are attributed to active sites. (C) 1998 Elsevier Science Ltd. All
rights reserved.