“…Many investigations, such as those of Holden and Kopelman, 3 Runnalls and Pidgeon, 4 and Shelton, [5][6][7] pointed out that the transport of iodide vapors should determine the process kinetics. On the other hand, the formation of lower iodides [8][9][10] (namely, TiI 3 and TiI 2 in the case of titanium deposition) and the reaction between elemental iodine and the crude metal 11,12 have also been stated to influence the kinetics of the process. Besides, although vapor transport is frequently accepted to control the overall rate of metal deposition, it has not been established whether the slow step is that of the transport of gases between the crude metal and the filament region or just their transfer in the close neighborhood of the filament.…”