I wrote: > > - The general area of the reaction is somewhat localized, and the > normal thermal gradient that would lead heat to dissipate from that > location must be countered from outside of it by the resistance heaters, so > that sufficient heat is retained in that area. > > There is a third possibility as well. The reaction is localized, and it depends upon an elevated temperature to kick off. But the local region is destroyed by the reaction, so you have apply heat once more to initiate the reaction in other parts of the charge. You don't want to do this too fast, however, since if you do the process will become self-sustaining for a brief period and result in runaway and the destruction of the charge. So you have to turn up the heat, then turn it down and then turn it up again, etc., using little temperature excursions.
Eric
