Halide-activated pack cementation typically involves the generation of vapor species that move through porous "filler" material to arrive at the surface of the substrate material. Typically the filler material is thought to play a minimal role in controlling the mass transfer of the vapor species and also in the generation of a depletion zone adjacent to the substrate surface.

In this talk, we will review relevant kinetic models, and present our current thoughts on the importance of the filler in controlling the arrival of the halide vapor species at the substrate surface. The focus will be on the effects of particle size, distribution and possibly shape on the rate of transport of the vapor species. Attention will be paid to the definition of dimensionless numbers to help delineate reaction kinetics from mass transfer rate. Schematics will be presented to illustrate the model.