From: glhurst@onr.com (Gerald L. Hurst)
Newsgroups: rec.pyrotechnics
Subject: Re: KNO3+S+C/Saltpeter(even more;-)
Date: 8 Nov 1995 07:48:01 GMT
Organization: Consulting Chemist
Lines: 32

In article <270532606.14830757@deepthnk.kiwi.gen.nz>,
jamie@deepthnk.kiwi.gen.nz (Jamie Connor) says:

>A while ago under the thread "C4 home manufacture" there was info about Salt
>Peter Sulfer and Charcol. I was going to production of this after many times
>of using this but when I went to the gaurden Center to buy KNO3 they were not
>selling it anymore.
>I tried about 20 different other gaurden stores and none were selling it.
>But I did see some Calcium Nitrate and some Sodium Nitrate. I am assuming
>that this would be the same sought of thing because Potassium and Sodium
>similer in a way. So wouldn't Sodium Nitrate work? 

Jamie, your post suggests that you probably have no
experience in handling these materials. If you've
got to play with them, do a little more reading up
on the subject first.

Sodium nitrate tends to absorb water more easily
than the potassium salt and it contains a tad more
oxidizer per gram than KNO3. The calcium nitrate is
undoubtedly a hydrate and is not suited for energetic
formulations in unmodified form.


Jerry

From: glhurst@onr.com (Gerald L. Hurst)
Newsgroups: rec.pyrotechnics
Subject: Re: KNO3+S+C/Saltpeter(even more;-)
Date: 15 Nov 1995 09:57:54 GMT
Organization: Consulting Chemist
Lines: 31

In article <48c983$3k3@nntp.hut.fi>, esuni@snakemail.hut.fi (Erik D Suni) says:

>It should work with Sodium Nitrate, provided you live in a low humidity
>area. Sodium Nitrate is quite hygroscopic and will start to collect
>moisture at relative humidity levels of about 70% (73% ?).

There's a nice exercise for you budding chemists out there.  Erik
has opined that NaNO3 becomes hygroscopic at about 73% (?)
relative humidity. How about checking this figure using only
solubility data and comparing the result with similar calculations
for KNO3. In other words, see if you can figure out the highest
relative humidity at which you would expect black powder made from
the two materials to remain stable at say 0 deg and 30 deg C.

Calculations like this are naturally subject to errors arising 
from the nonideality of strong solutions, so how would you
check the results experimentally using only materials you can
buy over the counter, not including a hygrometer?

OK, I'll furnish the solubility data:

Soly in g of KNO3 in 100 g H2O is 13.9 (0 deg), 21.2 (10 deg), 
31.6 (20 deg) and 45.3 (30 deg).

The corresponding values for the sodium salt in g are:

73.0 (0 deg), 80.8 (10 deg) , 87.6 (20 deg) and 94.9 (30 deg)

Jerry

From: glhurst@onr.com (Gerald L. Hurst)
Newsgroups: rec.pyrotechnics
Subject: Re: KNO3+S+C/Saltpeter(even more;-)
Date: 16 Nov 1995 07:05:18 GMT
Organization: Consulting Chemist
Lines: 63

In article <48ef6s$i4i@tiber.uoknor.edu>, major@rodent.ecn.uoknor.edu
(Dan Major) says:

>>There's a nice exercise for you budding chemists out there.  Erik
>>has opined that NaNO3 becomes hygroscopic at about 73% (?)
>>relative humidity. How about checking this figure using only
>>solubility data and comparing the result with similar calculations
>>for KNO3. In other words, see if you can figure out the highest
>>relative humidity at which you would expect black powder made from
>>the two materials to remain stable at say 0 deg and 30 deg C.
>>
>>Calculations like this are naturally subject to errors arising 
>>from the nonideality of strong solutions, so how would you
>>check the results experimentally using only materials you can
>>buy over the counter, not including a hygrometer?
>>
>
>Does "buy over the counter" include two thermometers I can use to make
>a wet bulb/dry bulb pair for a sling psychrometer?
>
>>OK, I'll furnish the solubility data:
>>
>>Soly in g of KNO3 in 100 g H2O is 13.9 (0 deg), 21.2 (10 deg), 
>>31.6 (20 deg) and 45.3 (30 deg).
>>
>>The corresponding values for the sodium salt in g are:
>>
>>73.0 (0 deg), 80.8 (10 deg) , 87.6 (20 deg) and 94.9 (30 deg)
>>
>>Jerry
>
>
>And what's the vapor pressure of water at 0 and 30 ? We *are* assuming
>760torr pressure aren't we? Awww - this sounds too much like *homework*!

You're not supposed to buy one so you're going to build one, heh?
Your apparatus must be pretty large if you're going to sling one
of those gadgets around in it.

It is not necessary to know the vapor pressure of water for the 
calculations, but I can see where you MIGHT want to devise an
experiment based on these data. The values are 4.579 mm @ 0 deg
and 31.824 mm @ 30 deg. The ambient atmospheric pressure really 
is irrevelant, but 760 Torr is fine.

Don't be silly. Homework is only work when you HAVE to do it. 
Besides, once this exercise is over everybody will have a
better perspective on the relative merits of KNO3 and NaNO3
formulations.

Jerry

From: glhurst@onr.com (Gerald L. Hurst)
Newsgroups: rec.pyrotechnics
Subject: Re: KNO3+S+C/Saltpeter(even more;-)
Date: 16 Nov 1995 21:14:25 GMT
Organization: Consulting Chemist
Lines: 110

In article <1995Nov16.152055.17452@cs.rochester.edu>,
nelson@cs.rochester.edu (Randal Nelson) says:

>>>>There's a nice exercise for you budding chemists out there.  Erik
>>>>has opined that NaNO3 becomes hygroscopic at about 73% (?)
>>>>relative humidity. How about checking this figure using only
>>>>solubility data and comparing the result with similar calculations
>>>>for KNO3. In other words, see if you can figure out the highest
>>>>relative humidity at which you would expect black powder made from
>>>>the two materials to remain stable at say 0 deg and 30 deg C.
>
>>>>OK, I'll furnish the solubility data:
>>>>
>>>>Soly in g of KNO3 in 100 g H2O is 13.9 (0 deg), 21.2 (10 deg), 
>>>>31.6 (20 deg) and 45.3 (30 deg).
>>>>
>>>>The corresponding values for the sodium salt in g are:
>>>>
>>>>73.0 (0 deg), 80.8 (10 deg) , 87.6 (20 deg) and 94.9 (30 deg)
>>>>
>>>>Jerry
>
>OK, since I havn't seen anyone take a shot at this.
>
>You can make a first approximation based on the molar fractions
>of the ionic solutions. For example, take NaNO3 at 20 degrees.
>100 gm of water is 100/18 = 5.56 moles. 87.6 gm of NaNO3 is
>87.6/85 = 1.03 moles, which in solution is twice that number, or
>2.06 moles of ions. The molar percentage of water is then
>5.56 / (5.56 + 2.06) = 72.9%, which, to a first approximation is
>the vapor pressure as a fraction of the 100% relative humidity pressure,
>and hence the humidity at which a saturated solution will pull moisture
>from the atmosphere. This agrees with Erik's figure.
>
>For KNO3, 31.6 gm is 31.6/101 = .313 moles = .626 moles of ions,
>giving a molar fraction for water of 5.56/(5.56+.616) = 90.0%.
>Pretty sticky conditions.

YES! Very nicely done, and probably not too far from reality.
Sodium nitrite has a slightly higher molal solubility than 
the nitrate and is known to maintain RH at 66 percent 
@ your 20 deg, versus 69.5 percent calculated by the method 
you used. We might expect the value for KNO3 to be even more
accurate because of the lesser solubility.

Your answer explains why NaNO3 is not as well suited for 
commercial black powder. Although the relative humidity
occasionally climbs over 90 percent in some parts of the
country, it spends a lot more time under this figure. If 
BP is anything like AN then it probably dries out at least
as fast as it gets wet from atmospheric moisture and
that means your powder is probably going to be dry when you
go to use it unless your timing sucks.

70 percent humidity is another scene entirely. In the Dallas
area, the humidity tends to rise every summer evening to well
over 60 percent so that if you have spilled AN around, it
will be in liquid pools every morning when you come to work,
but dry out by mid morning and then reliquify as you're heading
home.  SN is just about 10 RH units better, so it also spends
a fair portion of its time absorbing moisture, if not in 
Dallas, then in Houston :)  If you happen to live in Reno,
then you could probably get away with an AN-based powder,
at least most of the time.

As a matter of mainly academic interest, it might be noted
that the solubility of KNO3 increases more rapidly with
temperature than does that of NaNO3. The steeper slope
of the curve means that difference in the hygroscopicity
of the two salts grows narrower at high temperatures and
both salts become increasingly deliquesent, i.e absorb
moisture at lower RH.

If you want to determine the exact RH at which KNO3 and
NaNO3 become deliquescent, the easiest method would be to
put an excess of the well wetted solid salt in a jar
with much a much smaller weighed quantity of either
carefully dried CaCl2 or a strong aqueous solution 
of known concentration of CaCl2.  THe CaCl2 will slowly
absorb moisture from the wet nitrate, forming a solution
which becomes more dilute with time until equlilbrium
is reached. If the nitrate is still wet at this point,
the solution above it must must have the same vapor
pressure (i.e. the same RH) as the now diluted CaCl2
solution, and that value can be obtained by calculating
the CaCl2 concentration from the weight gained by H2O
absorption and looking up the corresponding RH in the
convenient tables of such values in the CRC or Lange's
handbook.

There are also tables for H2SO4 and NaOH, but I originally
suggested that the materials could be purchased "over-
the-counter" and I now  suggest that CaCl2 may be a bit easier
and safer to purchase and handle. There are any number of 
other common substances with known solution vapor pressures,
but you might have to look farther than he CRC to find them.

Lest you accuse me of being too academic (or as Beavis might put
it: "Fancy Schmantzy"), allow me to mention that I have used the
method outlined above to determine the parameters for building
an explosives manufacturing facility (using H2SO4) and to
gather data on emulsion explosives for a patent battle between 
a couple of major corporations.  In both cases, I employed Mason
jars for the experiments. The plant (Kinepak) worked fine, and
we won our case :)

Jerry