Newsgroup: it.scienza.chimica
Titolo: eplosivi a base di clorato

Ne conoscete qualcuno?
Ho provato clorato+zolfo, zucchero o farina [non tutto assieme!] ma nn
mi sembrano granchè
credo che i migliori siano clorato+metallo in polvere, che metallo mi
consigliate? e come fare a polverizzarlo senza farlo ossidare [o
bruciare]?

bruciare]?
io ti consiglio di lasciar perdere.
Tu stai cercando di ucciderti. Renditi conto.
I clorati sono notoriamente imprevedibili, e mescolarli con polveri
metalliche li rende pericolosi: diventano sensibilissimi
all'elettricita statica del corpo umano e possono reagire senza
apparente motivo.
Le miscele di clorati e zucchero sono estremamente pericolose ,
possono reagire a causa del calore di una mano oppure restare stabili
per anni, in modo imprevedibile.
Quelle a base di zolfo, se possibile sono ancora piu' pericolose, a
causa dello zolfo (che reagice lentamente) liberano acido clorico.
Le polveri metalliche pero' sono il peggio, infatti alcune di esse se
contaminate da metalli pesanti causano l'accensione spontanea e
imprevedibile delle miscele.
Tu vuoi morire.
Ma se vuoi suicidarti almeno cerca di non coinvolgere nessun altro
oltre a te stesso.

Esistono NG specifici sugli esplosivi e sulla pirotecnica.
Tutti gli esplosivi e i prodotti pirotecnici a base di clorato possono
essere estremamente instabili, se non si ha sufficiente esperienza sulla
determinazione qualiquantitativa delle impurezze ( di ogni materia prima
commerciale esistono vari gradi di purezza, e a parità di purezza si possono
avere contaminanti piu' o meno importanti per la riduzione della stabilità)
e delle specifiche dei materiali.
A parte l' illegalità insita nel produrre ed usare esplosivi ( e questo non
mi sembra il periodo migliore ), avere anche la certezza di farsi male mi
sembra assurdo.
A titolo di esempio riporto un post, prelevato da un altro NG, dal quale si
evidenziano quali competenze ed esperienza deve avere chi maneggia clorati.
Non è che non vengano usati, semplicemente tutte le condizioni necessarie
devono essere rispettate. Ovviamente il post non è esaustivo, quindi il
contenuto non è sufficiente a non farsi male.
E' come la nitroglicerina: se ne producono migliaia di tonnellate, farla in
casa è facile ma è veramente da grandi bischeri. Personalmente, fossi
costretto con una pistola, preferirei di molto produrre nitroglicerina
piuttosto che le miscele di cui tu parli ( specie con metalli).
MB
.... da un post di D. Harmann
.....Herbert G. Tanner
Instability of Sulfur-Potassium Chlorate Mixture: A chemical view
Journal of Chemical Education  Vol. 36 No. 2, February 1959
Numerous amateur rocket enthusiasts suffered serious casualties from
premature sulfur-chlorate explosions, according to C. Burns (1). This is
most
regrettable. These accidents should challenge elementry, chemistry teachers,
textbook writers, and civic-minded chemists to do their utmost to teach
safety to
tyro chemists. Chemistry without safety is too frequently fatal.
The following exposition of the chemistry of sulfur-mixture is
presented-with the
hope that the information will be conveyed to secondary school chemistry
students as a lesson in safety. Safety is not a series of "'don'ts," but is
a matter
of foresight, with avoidance of hazards. In the discussion of the chemistry
of
sulfur-chlorate mixture, an example of how safety can be designed into an
experiment is included for the benefit of the chemists of tomorrow.
Sulfur, by itself, is not a particularly reactive element at ambient
temperatures.
Even in the finely divided state it is difficult to ignite. Similarly,
chlorate is a
relatively stable compound at ordinary temperature. It decomposes only when
heated (2) almost to its melting point of 368'C. It is much less reactive at
room
temperature than is pure oxygen, for example. These facts would not incline
one
to predict that a simple mixture of sulfur and chlorate might ignite
spontaneously
after being stored in a warehouse many months, or detonate when a fuse is
being stuffed into a rocket charge.
 World accident records for the past, century show that sulfur-chlorate
stability
is erratic and unpredictable. This fact indicates that the mixture might
contain a
concealed chemical trigger. A close look, particularly at sulfur, discloses
this
trigger  and the manner in which it becomes cocked.
There are two basic grades of sulfur-crude and refined. Sulfur produced at
the
mine is called crude sulfur (formerly "roll sulfur"). About half of the
world of sulfur
is extracted from the ground in Texas by the Frasch process. Traditionally,
this
raw product is called crude sulfur, even though it has the amazing purity of
99.8 to 99.9% sulfur. The chief impurities asphalt which is present in the
dissolved
state. This mere trace of asphalt makes raw sulfur difficult to burn on a
large scale.
Air oxidation at ordinary, temperature is detectable only after period of
months.
Moisture in the air assists this slow "rusting" process.
Refined sulfur is produced by distillation. The purist is obtained
conditions that
cause the sulfur to condense directly too the solid state, i.e., the sulfur
is
sublimed. The product , called flowers of sulfur, when freshly prepared has
an
average purity of 100.0% sulfur. Even when both grades of sulfur are
pulverized
to the same degree of fineness, flowers of sulfur oxidize more rapidly
because its
surface is cleaner.
Polythionic Acid, the "Trigger"
Air oxidation probably produces sulfurous acid on the surface of sulfur, but
this
acid has not been detected (3) because, as H. Debus showed, sulfurous acid
reacts quickly with sulfur to form polythionic acids beginning with
trithionic acid,
H2S306. The latter adds sulfur atoms successively to form tetra- and penta-
thionic acids. These acids, particularly pentathionic acid (5), are
responsible for
the fungicidal value of dusting sulfurs. Aqueous polythionic acids
accumulate
until the concentration reaches a limit (6) where evaporation or a
temperature
rise will cause partial decomposition according to the equation:
H2S3O6 = H2SO4 + S02 + (n - 2) S
The reaction is irreversible, but loss of polythionic acids becomes repaired
by air
oxidation of sulfur when the temperature subsides. Reaction (1) is
significant in
that a sudden increase in temperature can, cause a significant amount of
sulfur
dioxide to be formed, not by direct oxidation of sulfur, but by
decomposition of a
concentrated solution of polythionic acids. This event, however, must await
the
formation of a concentrated solution of these acids.
Reaction (1) is responsible also for the accumulation of sulfuric acid on
sulfur.
The sulfuric acid, being hygroscopic, favors additional production of
polythionic
acids. By capillary action, sulfuric acid coats the surface of chlorate and
produces chloric acid. Although dilute chloric acid at ambient temperature
is a
very weak oxidizing agent, its presence has given rise to the theory that
chloric
acid is the primary cause of sulfur chlorate instability.
Sulfur dioxide will react directly with moist chlorate to produce chlorine
dioxide.
S02 + 2KC103 = 2CIO2 + K2SO4  (2)
Chlorine dioxide immediately attacks, sulfur, the chief reaction being,
2CIO2 + 4S = 2SO2. + S2Cl2                       (3)
Expressing reactions (2.) and (3) as one reaction.
S02 + 2KClO3 + 4S = 2SO2 + S2Cl2 + K2S04  (4)
Reaction (4) is a chain reaction because more sulfur dioxide is produced
than is
consumed. Initiation of reaction (4) requires an extraneous source of sulfur
dioxide. This trigger is cocked by the growth of polythionic acids on the
sulfur,
and is "pulled" when the heat from friction, impact, sunshine, the like is
sufficient
to release a threshold amount  of sulfur dioxide from the "reservoir" of
polythionic
acids. Heat from reaction (4) quickly ignites a portion of the mixture, and,
if the
gases produced cannot escape readily, the mixture will explode.
Popular formulas for preparing sulfur-chlorate mixtures generally specify
more
sulfur than can be oxidized by the chlorate to sulfur trioxide. The reasons
for this
are not pertinent to this subject, but it is important to note that the
excess sulfur
increases the instability of the mixture by favoring formation of a greater
amount
of polythionic acids.
This "trigger" theory was capable of explaining some previously baffling
industrial
accident conditions, but it needed experimental confirmation. It predicted
that a
chlorate mixture prepared with an oxidation resistant crude sulfur would be
more
stable than one prepared with flowers of sulfur. Comparative tests were made
using ignition temperature as an index of stability.
Experiment A: 2 g of flowers of sulfur, 4 g of reagent grade chlorate, and 4
g of
cleaned and dried sand were intermingled on unglazed paper with a metal
spatula; 1 ml of water was added dropwise, and the mixing was continued. The
product was pressed lightly into a thin open-ended cardboard tube made from
a
paper match-cover after the striker strip had been cut off. The tube was
laid on
an asbestos board in an empty ventilated hood and was heated at
approximately
1oC temperature rise per minute by a heat lamp suspended above the tube. The
temperature was measured with a thermocouple inserted to the center' of the
mixture. Ignition temperatures on repeat experiments ranged from 82 to 91oC,
and averaged 85oC.
Safety precautions that were designed into the above experiment include
mixing
the powders with a metal spatula and the use of unglazed paper to reduce
accumulation of static charges. The powder was dampened primarily to give it
sufficient cohesion to remain in the cardboard tube, but the dampness no
doubt
helped to suppress static charges. The striker strip was removed from the
match-cover because it contains a sulfide of phosphorus which might ignite
the
mixture prematurely by contact with stray chlorate. Porosity, contributed by
sand,
and the short open-ended tube all owed easy escape of gases, thereby
reducing
the probability of an explosion. Both ends of the tube were left open to
reduce
fire hazard by canceling rocket effects when the mixture ignited. Fire
hazard was
further reduced by the asbestos board and by the emptiness of the hood.
Experiment B: Mixtures similar to those in Experiment A were prepared with
crude sulfur that had been pulverized until the particles had a mass median
diameter of 44 microns, thereby approximating the particle size of flowers
of
sulfur. These mixtures ignited ,sharply at 124oC. This temperature is above
the
melting point sulfur and indicates that ignition may have been initiated by
sulfur
dioxide produced by air oxidation of hot sulfur vapor.
Experiments A and B definitely demonstrated the predicated greater stability
of
the crude sulfur mix. However, the chloric  acid theory could predict that
the
greater sulfuric acid content of the flowers of sulfur, instead of the
polythionic
acids, would cause the lower ignition temperature. As a matter of fact, the
flowers of sulfur contained 0.02%  "acidity" calculated as sulfuric acid.
The
acidity of the crude sulfur was detectable but was too small to titrate.
As a test of the "chloric acid" theory, Experiment A was repeated using
flowers of
sulfur dampened with sufficient 0.2 N H2SO4 to give it an acidity value of
0.50%.
When this highly acidified sulfur was mixed with chlorate, an abnormal
amount of
chloric acid must have been formed. In spite of this excess, the ignition
temperatures averaged only 87oC in close agreement with Experiment A. These
results dismiss the "chloric acid" theory as a primary explanation of
instability.
Final confirmation that sulfur dioxide triggers the ignition was obtained by
repeating Experiment A, but. instead of heating the mixture, a long
capillary
glass tube containing sulfur dioxide flowing at the rate of 0.3 cc per
second was
thrust into the mixture. Ignition occurred almost as quickly as though the
flame of
match had been applied.
Sulfur--chlorate typifies many fuel-chlorate mixtures. Metallic sulfides and
polysufides behave qualitatively like sulfur. Phosphorus cannot yield sulfur
dioxide, but at room temperature it evolves reducing vapors of phosphorus
oxide
and possibly some elemental phosphorus which react so energetically with
chlorate that an explosion usually occurs before mixing can be accomplished.
Carbon disulfide, rosin, turpentine, thiocyanates, aldehydes, sugars,
tannin, and
numerous other materials that form volatile reducing agents on heating,
contribute instability to chlorate mixtures.
 Powdered metals such as oily
aluminum, zinc, and magnesium are sometimes used with or without other fuels
in chlorate mixture. These metals are corroded by chlorate. Their chlorates
are
hygroscopic and decompose at relatively low temperatures. The high heats of
oxidation of these metals could cause local temperatures sufficiently high
to
ignite the mixture. No wonder such concoctions are unpredictable in
stability.
Much of the unsavory reputation assigned to chlorate should be reassigned to
those who have selected the fuels. Apparently availability and cheapness,
instead of chemistry, have dictated the choice of fuels. Any fuel that is
subject to
air oxidation at ordinary temperature, or forms an unstable chlorate, or
produces
an easily oxidizable vapor below 100oC, or reacts with chlorate below 150oC
should be excluded. Starch (7) is a fuel that survives these requirements.
Literature Cited
(1) BURNS, C., J. CHEM. EDUC., 33, 308 (1956).
(2) BROWN, F. E., AND WHITE, W. C. 0., Proc. Iowa .Acad Sci., 31,291(1924).
(3) MELLOR, J. W., "Comprehensive Treatise on Inorganic and Physical
Chemistry," Longmans, Green &, Co., Inc., London, 1947, Vol. 10, pg. S8.
(4) DEBS. H., Ann.. 244, 76 (1888),
(5) YOUNG, H.C. AND WILLIAMS ROBERT, Science, 67, 19 (1928)
(6) MELLOR, J.W. "Modern Inorganic Chemistry," Longmans, Green & Co., Inc.,
London, 1916, p. 458; EPHRAIM, FRITZ, "Inorganic, Chemistry," Gurney  and
Jackson, London, 1926, p, 463.
(7) TANNER, H.G.  U.S Patnet 1,966,652 (1934)