Note: Descriptions are shown in the official language in which they were submitted.
~L~gL8Z72
LOW TEMP RAruRE GAS GENER~TOR PROPELLANT
BACXGROUND OF THE INVENTION
_
This invention relates to a pyrotechnic composition
adapted, upon combustion, for gene.rati.ng gas. In particular,
this invention relates to a pyrotechnic composition which, upon
combustion, generates a low temperature, non-toxic gas. Among
the uses for such a gas is to inflate a safety bag in a vehicle
to restrain movement of an occupant in ~he vehicle in the event
of collision, or in the case of slower burning mixtures, to be
defined in one embodiment latex, producing gas with a relatively
low temperature, the substantially non-toxic gas produced may be
used to inflate life rafts, emergency airline slides, buoys, tires
or other inflatable devices. ~ ;
; It is necessary that pyrotechnic compositions be able to
meet certain criteria in order to be adapted for use with a
vehicle safety air bag restraint or other such inflatable devices.
Ths pyrotechnic composition must be able to withstand storage
in an environment from approximately -40F. to approximately
+220F. For the vehicle safety air bag applications, it is ~:~
also necessary that the composition be capable of being ignited
rapidly, for exampl~, within a matter of milliseconds, and that
it be capable of being totally ignited to produce gas. In some
other applications, a slow burn is not a disadvantage and a
relatively cool gas is highly advantageous, as will be discussed.
It is necessary that the gas produced have only a negligible
amount of toxic gases, such as nitrogen oxides or carbon monoxide.
Previously used pyrotechnic compositions normally include
the use of an organic binder. The organic binder also acts as a
fuel and tends to raise the ~lame temperature of the gas to an -
unacceptable level. As a resul.t, the temperature of the outer
surface of the vehicle safety bag or other inflatable device,
using such prior art compositions, would be so high that it might
burn the user. ....................................................... ~.
~"~ r ~
~8~72
This is understandable because the compositions using
such binders were incended for applications such as high-energy
propellants for rockets, where low temperature was not an ob-
jective. See: U. S. Patents 2,929,697 to Perry and 2,994,598
to Dickey. In addition, many of the compositions disclosed in
the prior art produce a toxic gas, such as some of the compo-
sitions in U. S. Patents 3,020,180 to Morello and 3,047~524 to
Bowman.
SUMMARY OF THE INVENTION
In accordance with this invention, there is provided
a pyrotechnic composition adapted, upon combustion, for generating
a low temperature, substantially non-toxic gas, th-e- composition
comprising: a fuel selected ~rom the group consisting of a
carbonaceous material, aluminum and magnesium; an inorganic
oxidizer selected ~rom the group consisting of a metal chlorate,
a metal perchlorate, a metal nitrate, ammonium nitrate, ammonium
chlorate, and ammonium perchlorate; and a coolant selected from
the group consisting of magnesium hydroxide and a mixture of
magnesium carbonate and magnesium hydroxide. This gas is useful
for inflating various devices, such as a safety bag in a vehicle.
A safety bag is inflated to restrain the movement of an occupant ~;;
of the vehicle in the event of collision. Where a composition
producing a low temperature gas from a relatively slow burn is
utilized, as will be discussed later, application to other already
mentioned inflatable de~ices is advantageous. In general, the
pyrotechnic composition comprises a fuel; an inorganic oxidizer;
and a coolant or combined binder and coolant (which also is re
ferred to as just a coolant in the following description), which
is selected from the group consisting of magnesium hydroxide,
magnesium carbonate, and a mixture of magnesium carbonate and
magnesium hydroxide It has been found that one may use as much
of t-he binder-coolant as i-s necessary in the pyrotechn}c compo-
sition to obtain the desired binder properties for the composition
~ - 2 -
- . . - . . :
: . . .- :
~48~7;~
without raising the flame temperature of the gas, generated upon
combustion, -to an unacceptable level.
DETAILED DESCRIPTION
-
This pyrotechnic composition is adapted for generating
a low temperature, non-toxic gas upon combustion for inflating
a vehicle safety bag or other inflatable device. In general,
the composition comprises: a fuel selected from the group con-
sisting of a carbonaceous material (such as carbon, carbon black
or lamp black), aluminum and magnesium; an inorganic oxidizer
selected from ~e group consisting of an alkali metal chlorate,
such as potassium chlorate or sodium chlorate, an alkali metal
perchlorate, such as potassium perchlorate or sodium perchlorate,
an alkali metal nitrate, such as potassium nitrate or sodium
nitra~e, ammonium chlorate, ammonium perchlorate, and ammonium
nitrate; and a coolant or combined binder and coolant selected
from the group consisting of: magnesium carbonate, magnesium
hydroxide, and a mixture of magnesium carbonate and magnesium
hydroxide. A typical formulation of this pyrotechnic composition
comprises: carbon which acts as a fuel; potassium chlorate (KC10
or potassium perchlorate (KC104) which acts as an oxidizer; and a
magnesium carbonate (MgCO3) and magnesium hydroxide (MgOH2) mix-
ture which acts as a coolant and binder.
In the case of the composition of carbonaceous fuel,
inorganic oxidi2er and magnesium carbonate coolant, a low
temperature gas (about 800F in one embodiment) is generated
relatively slowly (in, for example, about l~:;to 3 seconds) ~hich
may be cooled, as by contact with a metal chip bed, to a
!.
, . ,- . . ~ ,, ~ ~ '
~. :: . . .. .
8~
temperature o f rrom 2û0F. to 600Fl., for inflal;ing an
in~latable dev:lce such as a life raft, inflatable bwoy, tire,
emergency slide, etc., which may then be in contact with the user.
The pyrotechnic composition of this invention comprises
by weight: ~rom less than 1% to about 10% of one of the
foregoing fue]s, such as carbon; from about 30% to about 70%
of one of the foregoing inorganic oxldizers, such as potassium
chlorate; and from abouk 10% to about 60% of one Or the foregoing
coolants or combined binders and coolants, such as magnesiurn
carbonate or a mixture of magnesium carbonate and magnesium
hydroxide.
Preferably, in one embodiment, the pyrotechnic composikion
comprises by weight: about 3% to about 7% of one of the foregoing
fuels~ such as carbon; about 40% to about 60% of one o~ the
foregoing inorganic oxidizers, such as potassium chlorate; and
about 35% to about 55% o~ one of the foregoing combined binders
and coolants, such as a mixture of magnesium hydroxide and
magnesium carbonate. Whem such compositions are burned in the
presence of air, the magnesium hydroxide reacts with carbon
dioxide (CO2) in the air to form magnesium carbonate (MgCO3).
Magnesium carbonate is a highly oxygenated, cement-like material
and, by itself, provides no binding properties. The conversion
of magnesium hydroxide to magnesium carbonate provides the binding
effect. Neither the magnesium hydroxide nor the magnesium carbonate
acts as a fuel. Since magnesium hydroxide and magnesium carbonate
are both coolants, not fuels, one can use as much as necessary.
As a result, one has enough binder for the composition without
raising the flame temperature of the gas to unacceptable levels.
The free oxygen formed from the inorganic oxidizer, such as
potassium perchlorate, is consumed by the fuel, such as carbon,
forming carbon dioxide and evolving heat which is cooled by the
--4--
~4~
magne~lum hy(lroxicle.
I~ thls last mentloned embodiment (in the precedin~
paragraph) lt ls preferable, in most instarlces 5 to start with
a mixture of magnesium hydroxide and magnesium carbonate, rather
than magnesium hydroxide without magnesium carbonate. One should
use enough magnesium hydroxide in the mixture to obtain the
desired bind:ing e~ect caused by the carbonation of the
magnesium hydroxide. But~ one should use only enough magnesium
hydroxide to obtain the necessary physical properties as a
binder because in compositions using a mixture o~ ~agnesium
; hydroxide and magnesium carbonate~ lt has been ~ound that the
higher the proportion of magnesium hydroxide to magnesium ~ -
carbonate that is used in the composition, the longer the reaction
` time will take.
More specificalIy, in this last discussed embodiment,
; the magnesium hydroxide in the pyrotechnic composition should
comprlse by weight not less than about 10% o~ the entire
composition and pre~erably ~rom about 10% to about 30% o~ the
entire composition. In instances where a mixture o~ magnesium
hydroxide and magnesium carbonate is used as the combined
binder and coolant, the compositlon ma~y comprise: ~rom about
10% to about 30% magnesium hydroxide as compared to the entire
composition and from about 20% to about 40% magnesium carbonate
as compared to the entire compoæition. In many compositions it
has been found advantageous ~or the mixture o~ magnesium hydroxide
and magnesium carbonate to comprise about 1/2 magnesium hydroxide
and about 1/2 magnesium carbonate.
In the pre~erred embodiment previously mentioned (carbon
~uel, potassium chlorate or perchlorate oxidizer, and -
magnesium carbonate coolant) where a relatively low burning
composition produces a rela~ively low temperature gas (which may
optionally be ~urther cooled as already discussed), it has been
~:
.: ., ,. .. ~ ,,, .. . . , -
sur7prislngly found that the magneslurn carbonate burns ln the
presence Or the oxldizer and the carbon fuel to support the
combustlon at a very high temperatllre, but relatlvely slowly,
wlth the magnesium carbonate decomposing to absorb the heat
and produce the relatively low temperature gas product made up
of, substantiallya carbon dioxide (C02) and oxygen, with trace
amounts of carbon monoxlde (C0).
The following examples, ln whlch percent is by weight~
are provided for purposes of illustration.
~XAMPLE 1
The composltion used comprises: 5% carbon as the fuel,
50% potasslum chlorate as the inorganic oxidizer, and 45% of a
mixture of magneslum hydroxide and magneslum carbonate as the
binder-coolant. The proportlon of this mixture was approximately
1/2 magnesium hydroxide and 1/2 magnesium carbonate so that the
magnesium hydroxide and magnesium carbonate each formed
22 1/2% of the total composition.
EXAMPLE 2
The composition comprised: 5% carbon~ 50% potassium
chlorate; and lJ5% magnesium hydroxide.
EXAMPLE 3
:
The composition comprised 5% carbon, 51% potassium
chlorate;;and 44% magnesium hydroxide.
EXAMPLE 4
The composition comprised: 6% carbon; 50% potassium
chlorate; and 44% magnesium hydroxide.
The compositions in the foregoing examples each produce
a gas having a flame temperature from about 1500F. to less
than 2000F.
3o
.. .. . .. . . . . .
The pyIotec~lnlc composltlons above o~ this l~entlon
achieve ~lexibillty in reference to the amount of binder which
may be used, consistent with the ob~ect o~ producing a gas having
a low-flame temperature and a negligible amount Or toxic gases,
such as nitrogen oxides or carbon monoxide. ;~
XAMPL~ 5
The compositlon comprised: 3~ carbon as the fuel; 45%
potassium chlorate as the inorganic oxidizer; and 52% magnesium
carbonate as the coolant.
It has been found useful in one embodiment to pelletize
the pyrotechnic composition of this invention in order to achibve
a predictable combustion performance of the compo-sition, ~ath~r
than to use the composition in powder form. Pelletizing can be
achieved by severely mixing the powdered ingredients and then
using a pill press to produce pellets, or by granulating the
powdered mixture, extruding it through a screen and forming
noodles. Pelletizing has been found advantageous because of the
following undesirable characteristics of a mixed powder. The
powder bends to separate, with the oxidizer at the bottom and
the fuel at the top. When the powder burns, it burns with
different characteristics depending upon the degree to which the
powder mixture is homogeneous. In addition, the powder may be
loosely packed or it may become tightly packed which also affects
its burning or combustion characteristics. The result is that
inconsistent results are sometimes obtained when using the
composition in powder form. Whem using the composition in pellet -~
form, more consistent results are generally produced. Optionally,
an organic lubricant, such as stearic ac~d or Carbowax (a trade
name of Union Carbide Corporation for polyethylene glycols)~ may
be added to pelletizing.
