Post by Tim WilliamsPost by LeoThose pages are just a portion of chapter 5 "Ignition and Propagation"
(pages 97-124) and it goes into much more detail than I can relate here. >
Basically he's saying though that the melted sulfur can penetrate into > the
lattice of the KClO3 before the chlorate has itself melted. In fact > he
states that the ignition of chlorate/sulfur occurs 200C degrees below > the
melting point of the chlorate.
But what of nitrate? KNO3 and KClO3 melt at nearly the same temperature as
I recall, yet BP is notoriously difficult to ignite by impact.
Tim
--
Deep Fryer: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms
Hmmm, I just realized that I've been spelling the name incorrectly. I
see now in the book that Conkling spells it Tammann with two n's. I
can't believe I looked at that word so many times today and missed that!
I guess I just assumed that it was spelled correctly in the original
post. My temperature nomenclature was also a little funky since I
couldn't seem to get a proper degree symbol entered. I think I have
that problem licked now anyway.
You have a good question there Tim. You're going to make me read the
whole chapter yet aren't you? The table shows potassium nitrate with
both a lower melting point and lower Tammann temperature than potassium
chlorate. However nitrate/sulfur ignites way up at 334°C (it's melting
point) and chlorate/sulfur ignites at only 150°C, despite the fact that
the melting point of the chlorate is over 200°C higher at 356°C. So why
does the nitrate/sulfur have a higher ignition temperature than
chlorate/sulfur?
I sorta made up my own word in the earlier post and mentioned the
decompositive nature of the reactants being a factor in their ignition
temperature. What I meant was that some oxidizers are exothermic and
some are endothermic. Well here is some of what conkling says about
potassium nitrate:
"Several examples will be given to illustrate these principles. In the
potassium nitrate/sulfur system, the liquid state initially appears
during heating with the melting of the sulfur at 119°C. Sulfur appears
in nature as an 8-member ring, the S8 molecule. This ring begins to
fragment into species such as S3 at temperatures above 140°C. However,
even with these fragments present, reaction between the sulfur and the
solid KNO3 does not occur at a rate sufficient to produce ignition until
the KNO3 melts at 334°C. Intimate mixing can occur when both species
are in the liquid state, and ignition is observed just above the KNO3
melting point. Although some reaction presumably occurs between sulfur
and solid KNO3 below the melting point, the low heat output obtained
from the oxidation of the sulfur combined with the endothermic
decomposition of KNO3 prevent ignition from taking place until the
entire system is liquid. Only then is the reaction rate great enough to
produce a self-propagating reaction."
(From Conkling's COP, page 101)
BTW... It's a good book. It may not be for everyone of course, but good
for those who want to know what's really happening with published
formulas or maybe want to do some experimenting with creating their own
formulas. I still have one extra copy (mint inside, a little shelf-worn
outside) for $41.95 plus the actual shipping cost. That's less than
half of what AFN sells it for. It will be going up on Ebay soon unless
someone speaks up first.
Leo