From: glhurst@onr.com (Gerald L. Hurst)
Newsgroups: alt.engr.explosives,rec.pyrotechnics
Subject: Re: AN Mfg. (Was: Homemade bomb recipes for prisoners?)
Date: 21 Dec 1996 02:38:09 GMT

In article <59ehqg$bic@hptemp1.cc.umr.edu>, brandonb@umr.edu (Seymour) says:

>Most AN plants get their ammonia from natural gas.  Yea, you can make
>it by the Haber process (requires lots of heat and catalysts) but it's
>not economical.

They get their HYDROGEN from natural gas then react it with nitrogen 
from the air in the very economical HABER process to form ammonia.  The
ammonia is then oxidized catalytically to form nitric acid, which is 
neutralized with additional ammonia to form a AN.

>There are two basic ways of making prill, commercial grade
>(fertilizer) and explosives grade.
>
>The fertilizer grade is sprayed in a big spinning drum on its side.
>When the prill becomes too heavy it falls to a conveyer supported in
>the middle of the drum.

This sounds more like the Stengel process for making dense flake AN.

>Explosives grade is sprayed into a tower.  The best way to describe
>its process is how hail forms.  The ammonia and nitric acid is sprayed
>in at the top.  The stuff condenses and starts falling.  The size and
>weight is controled by a flow of air from the bottom.  When the weight
>is heavy enough to overcome the flow of air, it falls to a conveyer at
>the bottom.  If it is not heavy enough, it gets lifted back to the top
>where it is able to obtain more AN.

Most fertilizer and explosive grade AN is converted to its final form
in prilling towers. Ammonia and nitric acid are NOT reacted in these 
towers.  Instead, concentrated AN solution is sprayed and allowed to 
fall like raindrops. The water evaporates on the way down leaving 
porous solid prills. The prills do not grow as they fall. The porosity 
of the prills depends on the amount of water in the starting solution.

Jerry (Ico)

From: glhurst@onr.com (Gerald L. Hurst)
Newsgroups: rec.pyrotechnics
Subject: Re: Amonnium Nitrate
Date: 15 Jan 1996 00:30:55 GMT

In article <4da0ch$j5d@dub-news-svc-4.compuserve.com>,
<103362.343@compuserve.com> says:

>You didn't spell oxidizer correctly

In my previous post on the same subject, I neglected to point
out that you also spelled "ammonium" wrong in the title. I
can certainly understand your need for anonymity. BTW, we have
no way of knowing who it was that misspelled "oxidizer," not
that anyone really cares, because you apparently originated 
this thread. The following is added to give this post some 
redeeming virtue:

It is often said that ammonium nitrate swells during storage
as a result of cyclic phase changes at just over 30 degC. This
swelling prevents the use of an otherwise excellent source
of explosive energy in military ordnance except in times of
great shortages when such materials as amatol or ammonal 
may be used to stretch supplies of TNT.

Many additives have been suggested to inhibit the phase changes,
such as acid fuchsin and potassium chloride. I believe that
there is a treated AN on the market which is described as
phase stabilized, but I have personal doubts about the 
viability of such a product.

The results of experiments in the early 70's suggested that 
the major problem was not phase transitions per se, but
moisture. It is true that one phase has a lower density than
the other, but this fact per se does not explain why the
AN doesn't shrink back to its original size during the next 
half of the cycle. It has been suggested that wratchet-like
swelling is the result of new voids or cracks which do not heal. 
Whether these cracks are real or not is probably less important
than the fact that as the temperature increases, modest amounts
of moisture dissolve increasing amounts of AN which are
redeposited preferentially in the tiny spaces between adjacent
crystals or prills on cooling. These spaces are probable loci
for the solution because of capillary forces. The deposits 
subsequently support any separation, already existing or caused 
by the most recent thermal expansion half cycle. This swelling 
and subsequent support will occur in a simple simple heating and 
cooling cycle whether a phase change is involved or not.

Jerry (Ico)


 

From: glhurst@onr.com (Gerald L. Hurst)
Newsgroups: rec.pyrotechnics
Subject: Re: Amonnium Nitrate
Date: 16 Jan 1996 09:17:53 GMT

In article <4dea69$kge@cloner2.ix.netcom.com>, silent1@ix.netcom.com (The
Silent Observer) says:

>In article <4dc77v$8to@geraldo.cc.utexas.edu>, posted on 15 Jan 1996 
>00:30:55 GMT, Gerald L. Hurst (glhurst@onr.com) writes...
>>
>>
>>The results of experiments in the early 70's suggested that 
>>the major problem was not phase transitions per se, but
>>moisture. It is true that one phase has a lower density than
>>the other, but this fact per se does not explain why the
>>AN doesn't shrink back to its original size during the next 
>>half of the cycle. It has been suggested that wratchet-like
>>swelling is the result of new voids or cracks which do not heal. 
>>Whether these cracks are real or not is probably less important
>>than the fact that as the temperature increases, modest amounts
>>of moisture dissolve increasing amounts of AN which are
>>redeposited preferentially in the tiny spaces between adjacent
>>crystals or prills on cooling. These spaces are probable loci
>>for the solution because of capillary forces. The deposits 
>>subsequently support any separation, already existing or caused 
>>by the most recent thermal expansion half cycle. This swelling 
>>and subsequent support will occur in a simple simple heating and 
>>cooling cycle whether a phase change is involved or not.
>
>
>That's an interesting hypothesis, and one that was not presented at 
>college-level (College of Mines) courses in explosives as last as 1981. 
> What we were told at that time was that the increasing temperature 
>phase transition was nearly immediate, but that the decreasing 
>temperature transition involved substantial undercooling and a 
>significant delay in the phase change -- of up to several months.  The 
>main problems with the phase change weren't so much with straight AN in 
>any case, but with compositions incorporating AN in cast or pressed 
>grains (like the huge grains of BP that were used in large naval rifles 
>before conversion of those guns to nitrocellulose-based powders), where 
>the volume change with a single phase transition would lead to grain 
>cracking that would increase burn area, and hence pressure, and lead to 
>burst gun events.

Cast grains and such mixtures as TNT/AN are a different kettle
of fish for the simple reason that the other component doesn't
expand in concert during a phase change so you get an additional
wratchet effect just as you do when dissimilar metals are 
mechanically bonded, i.e creep. There's the rub with schools.
The military  problems are completely different from the simple
industrial problem of storing and handling 8 billion pounds
of nearly straight AN per annum.  The reason your mining school 
is unaware of the study is that it was not published in a journal 
but in a patent (which they surely never read) which discloses a 
method for reducing the bulk density of AN prills by thermal 
cycling of the very slightly moistened prills. The inventor showed 
that the material swells irreversibly regardless of whether it 
passes through a phase change or not.

You mention substantial undercooling. Such conditions make the 
idea of slow transition a self-fufilling prophecy. If you want AN 
to cycle to the lower temperature phase, you must cool the 
material to just under the phase change temperature, else the 
transition speed drops at the usually expected exponential rate. 
That is to say that chilling can impart the same sort of kinetic 
stability you always hear about in diamonds. Simple thermodynamics 
will tell you that a phase transition either does or does not occur 
at a given temperature. Kinetic theory then tells you that the 
highest rate is likely to occur at the highest temperature of 
thermodynamic stability. 

Despite the obviousness of this idea, it is easy to imagine 
professor X thinking that the driving "force" would be greater
far below the transition temperature. There are situations where
this is true, but they are subjects for unrelated discussions.

Water (traces) plays a catalytic role in the phase transitions
both ways. Dissolved AN has no way of really knowing which
solid phase it was formed from and therefore is prepared  to
precipitate either phase depending on temperature. The solubility 
versus temperature curve has a very high slope so again higher 
temperatures favor faster phase changes as A dissolves and
precipitates as B.

Here is an example of the role humidity plays. I had occasion
once to run some quality control checks on some packaged
ground and particle sized AN which had been in storage in
the Reno, Nevada area for two years. One of the most important 
properties of the material was tap density. In most parts of
the country after prolonged storage and thermal cycling, the
very well packaged material would tend to sinter and often
swell. Not only was the packaged product in perfect  condition,
but floor sweepings of the spilled nitrate which had lain for 
two years in an open manufacturing shed were pourable as sand 
and had the ideal tamping and tap densities. Although the 
original material was manufactured in a controlled low humidity 
plant the Reno ambient dried material was more stable.

>Since the phase transition temperature is within the range of human 
>comfort, it is likely that it will occur in normal storage, and the 
>undercooling properties of AN will mean that, once the transition has 
>occurred, the AN is likely to remain in the lower-density phase more or 
>less permanently.

If it's dry enough it may stay in either phase for a long time.

>I'd suspect there may be some factors from the phenomena you mentioned 
>involved as well -- but grain cracking due to volume changes is quite 
>sufficient to make AN useless for any application where a finished 
>composition will be stored without temperature control and where 
>reaction area (as in propellants) is a factor.

Again, if you have dissimilar materials in a cast or pressed form
you can often expect problems if the coefficients of expansion are
different or if a phase change occurs in one or the other, unless
the bond strengths between the components are very strong. Of
course you can get away with a lot with smaller aglommerations.
Prills of very dry AN are remarkably stable. Obviously, some
blends are more forgiving than others.

>I might also mention another factor that can affect "ratchet-like" 
>expansion -- similar to the phenomenon that caused several houses to be 
>destroyed by fire when aluminum house wiring was introduced, some 
>materials will expand and contract normally, and still seem to 
>"ratchet."  With aluminum wiring, the aluminum would expand in all 
>directions, but be constrained by the attachments until stress exceed 
>the yield value; it would then take a permanent "set."  When the 
>material cooled and contracted, it again contracted equally in all 
>directions.  The net result, after several cycles, was that connections 
>would "work loose" and sparks, local resistance heating, and similar 
>phenomena then conspired to start a fire.

Right, but the wire was not of the same composition as the attachments,
and the hard aluminum oxide coat played the role of a third phase.
As you know, contrary to common opinion, that coat is not always
limited to a few atoms thickness. (I have noted in this forum that
some do not realize Al powder can contain substantial percentages of 
Al2O3 depending on its history).

>With AN, if a loose or semi-loose mix expands in a package, it will 
>swell the package to some extent.  In addition, the moisture phenomenon 
>you mention may cause partial welding of grains at various points in the 
>cycle.  Now, when the AN shrinks (assuming it stays cool long enough to 
>do so), it will settle in the swelled package, to fill the space to a 
>lower level.  Next time it expands, with partially welded grains, it 
>will swell the package again, like ice breaking a jar even though 
>there's a substantial air space at the top.  Next shrink cycle, it will 
>settle more.  Several cycles of this can develop considerable pressure 
>and stress and, like frost flaking spalls off a boulder, can eventually 
>lead to burst packaging, completely crumbled "solid" compositions, and 
>so forth.

This behaviour sounds more like that of a composition. In simple
packaged AN the basic problem is simple swelling and sintering.
It can help a lot if the stuff does (re)pulverize itself. Typically
it tries to climb right out of the lightweight packages, which
are permeable to moisture. I've watched the production, sale and 
storage of hundreds of thousands of heavy plastic containers of 
the salt, produced in a dry plant, and never seen a case crack.
One reason is that the thicker plastic inhibits the passage of
moisture vapor in and out through the walls.

You can observe packages in which the AN has turned largely to
powder. This occurs when the prill density drops very low because
of excess wet cycling and then the AN drys out in a long hot spell.
The result is swollen prills which have such high porosity that
their crush strength is gone. You can demonstrate this in a single
cycle in the lab if you run the water up to the low whole percentage
range. One cycle and you have prills like fuzzy little snow balls.

Think about the origins of salt peter. You probably learned long
ago that it appears as an efflorescence on the walls of caves.
There in the cycle free atmosphere the mass of crystals swells
as a result of water transport and evaporation to give a porous 
mass. AN can do the same thing under the same conditions, but
it can do it in spades if you throw the additional pumping forces 
of thermally driven cycling solubility.

Silent, I am not trying to tell you that AN crystals don't crack
as a result of phase changes. They do. What I was stressing in
my original article is that water and cycling solubility are
responsible for most of the observed deleterious effects of 
thermal cycling. Because researchers were always aware of the
phase transition at 32 degC, which lies in the typical summer
storage range, there has always been tendency to ascribe cause
and effect status to the phase transitions and the adverse 
changes and to thereby grossly underestimate the role played
by simple solubility cycling.

The reasoning usually goes like this: "water catalyzes the
phase transition which causes the swelling and powdering."
In my opinion it would be better to say "Water catalyzes
the phase transitions, back and forth, and it also causes
swelling, sintering and powdering. The latter effects also
occur in the absence of phase transitions, although the 
transitions may contribute to the effect."  At any rate, in 
the absence of water, there is little problem with ammonium 
nitrate per se as far as industrial explosive and agricultural 
uses are concerned. Composites, as always are a problem, 
moreso with materials that change phases, but also with many 
that do not.

Or so it seems to me at first glance :)

Jerry (Ico) 

From: glhurst@onr.com (Gerald L. Hurst)
Newsgroups: rec.pyrotechnics
Subject: Re: Amonnium Nitrate
Date: 16 Jan 1996 09:43:59 GMT

In article <4dea69$kge@cloner2.ix.netcom.com>, silent1@ix.netcom.com (The
Silent Observer) says:

>That's an interesting hypothesis, and one that was not presented at 
>college-level (College of Mines) courses in explosives as last as 1981. 

Why am I not surprised?

I wrote a treatise of several hundred additional lines on this
subject, but the computer ate it. It was probably an omen 
warning me not to bore people with a lot of AN technology, so 
I'll let Silent have the last word :) If anybody is interested
in the subject of thermal cycling, phase changes and moisture
effects in AN, more information can probably be found in one of 
my old patents on the subject, circa 1973. I think the title
was "Method of Manufacturing Porous Prills." Yawn. Probably
not as interesting to most as the  Teenybomber Anthology
of Amputation Technology, but still good reading for people
who enjoy the telephone book.  

Jerry (Ico)

From: glhurst@onr.com (Gerald L. Hurst)
Newsgroups: rec.pyrotechnics,sci.chem
Subject: Re: Amonnium Nitrate (& other people's problems)
Date: 19 Jan 1996 20:46:27 GMT

In article <spiegl.822037845@lobster>, spiegl@lobster.cig.mot.com (Mark
Spiegl) says:

>So why does the addition of certain phase stabilizers - KN, ZnO, NiO, 
>dinitramides, etc - make AN less susceptible to swelling, sintering and 
>powdering. My laymans (and possibly incorrect) understanding is that the 
>addition of of these phase stabilizers raises the temperature of the 
>phase3-phase4 transition into a range which is unlikely to occur during 
>normal handling and storage. Is this correct? How do the catalytic effects 
>of water which you described play into this? 

Obviously, I can't speak for every proposed mechanism, but many of 
them have been held to be ineffective invalid in later literature
or in the unpublished reports of industrial chemistry labs.

Many of the claims concerning "phase stabilization" simply do not
work as advertized. However, it is true that certain additives
retard the end effect, swelling. My GUESS is that additives
change the behaviour of the surface by competing for water or
aqueous solution with the AN. Most additives are put on the
surface of the AN so that their concentration is very high where
the competition is needed. Clay is frequently added as a 2%
coating to improve flow and inhibit sticking. Clays can also
act as pourous agents to help wick moisture away from prill
contact points. Remember that clays (bentonite, China clay) are
often used to crosslink aqueous gels and are among the most water
adsorptive materials. Other additives may act as surfactants, 
lowering the surface tension of water and therby again reducing 
capillary bridging contact.

I've studied a few additives on my own. It was once indicated
to me that guar gum might inhibit swelling, but was a bit 
expensive. Thinking by analogy, I tried a series of multiweek
tests using ordinary wheat flour as a dusted coating. Sure
enough, the samples swelled much less than the controls. It 
seems likely that those tiny, heterogeneous particles of
insoluble carbohydrate worked by the mechanism of binding
surface moisture.

It is rather easy to see how early researchers might happen
to try some relatively esoteric compound like acid magenta
and discover "unique" properties of stabilization. People,
including my researcher friends with the guar, often do not
try the obvious because we are sort of programmed to expect 
more if the method involves the rare or the expensive.

An example: Many years ago there was a major explosives
company which manufactured a water-base ammonium nitrate
gel explosive which incorporated a very small quantity of
ammonium perchlorate (sensitizer), a relatively expensive 
ingredient as commercial explosive ingredients go.

When the formulation was called to my attention because of
a material availability problem, I got a big grin by 
sending the client a memo which said:

	You are putting AN, sodium nitrate and ammonium
	perchlorate in your formulation. Ammonium
	perchlorate is much more expensive than sodium
	perchlorate. If you use sodium perchlorate in
	place of ammonium perchlorate, you can get exactly
	the same final composition (mix of ions) at a lower 
	price and with fewer supply problems. In particular,
	you can use raw sodium perchlorate liquor, which is
	even cheaper, because the manufacturer doesn't have
	to dry it.

The research group at that company had over 50 scientists and
technicians working on a daily basis on explosives formulation 
and manufacturing problems. The tip I gave them might have come
off of an early page in a freshman chemistry text. The people I
was helping were nothing less than well educated and competent,
but in the press of solving difficult problems they had  all
overlooked the cheap, easy and obvious solution to an ongoing
problem in a major tonnage mainline product.

Second example: Also many years ago, a large explosives company
had designed a delay primer which was initiated by a line of
detonating cord through a tube along the cylindrical side of
the charge. A delay cap was located in the body of the charge
and required the conduction of the shockwave from the cord via
a low-energy shock tube such as Nonel. The problem was that
Nonel and its patent belonged to someone else.

I suggested to the research group: "why don't you just use a
hollow tube?"  It worked. As it turned out, for distances of
several inches, a hollow tube with no explosive on its surface
(a la Nonel) will happily transmit a more than adequate amount
of shock energy around a couple of right angle bends and still 
reliably initiate a delay element. Had there been no anticipated 
trouble getting and using Nonel, that's what would have been 
used at greater cost. Had this happened, it would be taken for
granted still today that an explosive coating was necessary.

Why did these simple solutions come from a consultant and not
from within the groups working daily on the problem? The answer
to that question is simply that any consultant has the advantage
of fresh perspective on OTHER PEOPLES PROBLEMS. Where consultants
need help is in the swamp of their own personal jungles.

It helps also to remember that simple information is more highly 
valued when you have to pay an expensive consultant for it. I have
also earned my wages by simply advising management to listen to 
the advice of one of their own employees who had been trying 
unsuccessfully to get their attention for a long time.

I suppose it is human nature to undervalue or ignore that which
isn't expensive, difficult or rare and to try to apply quantum
mechanics where Popular Mechanix will suffice. I know that I
have been guilty all my life of overlooking the obvious.

Jerry (Ico) 

Newsgroups: sci.chem
From: ahahma@polaris.utu.fi (Arno Hahma)
Subject: Re: Let's have a laugh
Message-ID: <1992Aug13.131329.25746@polaris.utu.fi>
Keywords: N2O nitrous oxide dinitrogen monoxide
Date: Thu, 13 Aug 92 13:13:29 GMT

In article <1992Aug4.121705.14284@morgan.ucs.mun.ca> fsmith@morgan.ucs.mun.ca (Frank Smith) writes:

>Back when I was a student I learned that nitrous oxide can be made by gentle
>heating of ammonium nitrate. You also get water vapour produced as well, so
>this would have to be removed by cold trapping before you would get fairly
>pure N2O. There should not be any other oxides of nitrogen present but if
>there is any ammonium nitrite this will decompose to nitrogen gas.

That is true. However, heating pure ammonium nitrate will lead to
several kinds of decomposition and other oxides of nitrogen are
formed, although in small amounts. Others have already pointed out
that the other oxides of nitrogen are poisonous.

A better alternative is to add some water (a couple of per cent of the
weight of the ammonium nitrate) and a phosphate, say calcium
phosphate. Any phosphates will catalyze the decomposition greatly and
it will take place a few ten centigrades lower than without the
phosphate. The water is required to make the reacting mixture liquid
at a lower temperature at the start thus getting the catalyst and the
ammonium nitrate into a better contact.

They also make N2O industrially by heating ammonium nitrate with a
phosphate catalyst. The resulting N2O will be considerably purer than
that obtained from pure AN.

>Beware that ammonium nitrate is an explosive so small quantities and gentle
>heating are imperative.

Ammonium nitrate requires a strong detonator to be detonated as such.
As a mixture with organic fuels, it requires less strong a detonator,
a few grams of a high explosive may be enough.

Alternatively, extremely large amounts of ammonium nitrate
contaminated with organic impurities may explode, if set to fire.
Extremely large amounts here means tens of tons or more. So, ammonium
nitrate is pretty safe to handle and heat in a laboratory scale.

ArNO
    2