Note: Descriptions are shown in the official language in which they were submitted.
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hY 8T I. NON BIDE l~rUTO OT AIRS G PROS hLANTS
_ _ _ _--.--- Bp~cICGRO~D Og ~ ICON
Field of the Inveatien
The present invention relates to nontoxic gas
generating compositions which upon combustion, rapidly generate
gase~a that are useful for inflating occupant safety restraints
in motor vehicles and specifically, the invention relates to
thermally stable nonazide gas generants having not only
acceptable burn rates, but that also, upon combustion, exhibit
5 - _a. relatively high gas volume to solid particulate ratio at
'acce.ptable flame temperatures_
The evolution from azide-based gas generants to
nona~zide gas generants is well-documented in the prior art.
The advantages of nonazide gas generant compositions in
10' co~aparison with azide gas generants have been extensively
. described in the patent literature, for example, U.S. Patents
No. 4,370,181; 4,909,549; 4,948,439; 5,084,118; 5,139,588 and
. 5, 0:35, 757 ~'. -_ _ . _ ._ _ __ .____.__ __ _
In addition to a fuel constituent, pyrotechnic
non~aaide gas generants contain ingredients such as oxidizers ~to
provide the required oxygen for rapid combustion and reduce the
. quantity of toxic gases generated, a catalyst to promote the
conversion of toxic oxides of carbon and nitrogen to innocuous
2o gases, and a slag forming constituent to cause the solid and
liquid products formed during and immediately after combustion
_,to agglomerate into filterable clinker-like particulates. '~
~otloer optional additives, such as burning rate enhancers yr
ballistic modifiers and ignition aids, -are used. to control the
.ig=~itability and combustion properties of the gas generant.
__
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_ _ _ ..... ..
one of the disadvantages of known nonazide gas
generant compositions is the amount and physical nature of the
solid, residues formed during combustion. The solids produced
as a result of combustion must be filtered and otherwise kept
away from contact with the occupants of the vehicle. It is
therE:fore highly desirable to develop compositions that produce
a ~ainimum of solid particulates while still providing adequate
quantities of a nontoxic gas to inflate the safety device at a
high rate.
The use of phase stabilized ammonium nitrate is
desirable because it generates abundant nontoxic gases and
minimal solids upon combustion. To be useful, however, gas
generants for automotive applications must be thermally stable
when aged for 400 hours or more at 107°C. The compositions
must also retain structural integrity when cycled between -40°C
arid 107°C.
often, gas generant compositions incorporating phase
stabilized or pure ammonium nitrate exhibit poor thermal
stal:~i.lity, and produce unacceptably high levels of toxic gases,
CO sand NOx for example, depending on the composition of the
assc~c3ated additives such as-plasticizers and binders. 2n
addition, ammonium nitxate contributes to poor ignitability,
lower burn rates, and performance variability. Several known
gas generant compositions incorporating ammonium nitrate
uti:Lize weh known ignition aids such as 8xNO3 to solve this
problem. However, the addition of an ignition aid such as
BRN~~ is undesirable because it is a highly sensitive and
energetic compound, and furthermore, contributes to thermal
instability and an increase in the amount of solids produced.
Certain gas generant compositions comprised of
armon~oni.um nitrate are thermally stable, but have burn rates less
tha:n desirable for use .in gas _inflators. To be useful for
passenger restraint inflator applications, gas generant
compositions generally require a burn rate of at least .4
inc:h/second (ips) or store at 1000 psi. Gas generants with burn
rates of less than 0.40 ips at 100o psi.do not ignite reliably
and often result in "no-fires~~ in the inflator.
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Yet another problem that must be addressed is that
the U.S. Department of Transportation (DOT) regulations require
"cap testing" for gas generants _ Because of the sensitivity to
detonation of fuels often used in conjunction with ammonium
nitr~3te, most propellants incorporating ammonium nitrate do not
pass the cap test unless shaped into large disks, which in turn
reduces design flexibility of the inflator.
Accordingly, many nonazide propellants based on
ammonium nitrate cannot meet requirements for automotive
to ~ appl,ications.
nescriptior~of the Related Art
.--,., _ . . ,
U.S. patent No. 5,545,272 to Poole discloses the use
of eras ~ generant compositions cons fisting of nitroguanidine (NQ) .,
at a3 weight percent of 35%-55%, and phase stabilized ammonium
nitrate (PSAN) at a weight percent of 45%-65%. NQ, as a fuel,
is prEferred because it generates abundant gases and yet
consists of very little carbon or oxygen, both of Which
contribute to higher levels of Co and NOx in the combustion
gases. According to Poole, the use of phase stabilized
ammonium nitrate (PSAN) or pure ammonium nitrate is problematic
because many gas generant compositions containing the oxidizer
._ are therutally unstable. Poole has found that combining NQ and
1~PSAN in the percentages given results in thermally stable gas
gen.erant compositions. However, Poole reports burn rates of
Z5 only .32 -,34 inch per second, at 1000 psi. As is we7.1 known;
. burn rates below .4 inch per second at 1000 psi are simply too
lcw for confident use within an inflator.
In U.S. patent No. 5,531,941 to Poole, Poole teaches
the: use of PSAN, and two or more fuels selected from a
3o specified group of nonazide fuels. Poole adds that gas
generants using ammonium nitrate (AN) as the oxidizer are
generally very slow~burning with burning rates at 1000 psi
typically leas than~o.i inch per second. He further teaches
that for air bag applications, burning rates of less than about
35 ' . - . , . . ~~ . .
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0.4 to 0.5 inch per second are difficult to use. The use of
PSAN is taught as desirable.because of its propensity to
produce abundant gases and minimal solids, with minimal noxious
gases.. Nevertheless, Poole recognizes the problem of low burn
rates. and thus combines PsAN with a fuel component containing
a majority of TAGN, and if desired one or more additional
fuel.:. The addition of TAGN increases the burn rate of
ammonium nitrate mixtures. According to Poole, TAGN/PSAN
compositions exhibit acceptable burn rates of .59-.83 inch/per
l0 second. TAGN, however, is a sensitive explosive that poses
safety concerns in processing and handling. In addition, TAGN
is classified as "forbidden" by the Department of
Transportation, therefore complicating raw material
requirexaents .
In U.S. Patent No, 5,500,059 to Lund et al., Lund
states that burn rates in excess of 0.5 inch per second (ips)
at 1, 000 psi, and preferably in the range of from about 1. 0 ips
to about 1.2 ips at 1,000 psi, are generally desired. hand
dxsc:loses gas generant compositions comprised of a 5-
amir.~otetrazole fuel and a metallic oxidizer component. The use
of a. metallic oxidizer reduces the amount of gas liberated per
gram of gas generant, however, and increases the amount 0f_
solids generated upon combustion.
The gas generant compositions described in Foole et
al, U. S. Patents No. 4, 909, 549 and 4, 948, 439, use tetrazole or
triazole compounds in combination with metal oxides and
oxidizer compounds (alkali metal, alkaline earth metal, and
pure annnonium nitrates or perchlorates) resulting in a
relatively unstable generant that decomposes at loGr
3o temperatures. Significant toxic emissions and particulate are
formed upon combustion_ Both patents teach the use of BKN03 as
an .ignition aid.
The gas generant compositions described in Poole,
U.s_ patent No. 5,035,75?, result in more easily filterable
solid products but the gas yie~.d is unsatisfactory..
Chang et al, U. S. Patent No. 3,~ 954, 525., describes the
use of TAGN and a synthetic polymeric binder in combination
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with an oxidizing material. The oxidizing materials include
pure AN although, the use of PsAN is not suggested. The patent
teachea the preparation of propellants for use in guns or other
devices where large amounts of carbon monoxide, nitrogen
oxide.:, and hydrogen are acceptable and desirable. Because of
the practical applications involved, thermal stability is not
considered a critical parameter.
Grubaugh, U.S. Patent No. 3,044,123, describes a
method of preparing solid propellant pellets containing AN as
the major component. The method requires use o~ an oxidizable
organ_~c binder (such as cellulose acetate, PVC, PVA,
acrylonitrile and styrene-acrylonitrile), followed by
comprcassion molding the mixture to produce pellets and by heat
treating the pellets . These pellets would certainly be damaged
by temperature cycling because commercial ammonium nitrate is
used, and the composition claimed would produce. large amounts
of carbon monoxide.
8ecuwe, U.S. Patent No. 5,034,072, is based on the
use oi: 5-oxo-3-vitro-1, 2 , 4-triazole as a replacement for other
explo~5ive materials (Iii, RDX, TATB, etc.) in propellants and
gun powders. This compound is also called 3-vitro-1,2,4-
triaz~~le-5-one ("NTO"). The claims appear to cover a gun
powder composition which includes NTO, AN and an inert binder,
where the composition is less hygroscopic than a propellant
2S containing ammonium nitrate. Although called inert, the binder
would enter into the combustion reaction and produce carbon
monoxide making it unsuitable for air bag inflation.
Land et al, U.S. Patent No. 5,197,758, describes gas
generating compositions comprising a nonazide fuel which is a
transition metal complex of an aminoarazole, and in particular
are copper and zinc complexes of 5-aminotetrazole and 3-amino-
1,2,4 -triazole which are useful for inflating air bags in
automotive restraint systems, but generate excess solids.
wardle Et al, U. s. Patent No. 4, 931,112, describes an
automotive air bag gas generant formulation consisting
essentially of NTO (5-vitro-1,2,4-triazole-3--one) and an
oxidizer wherein said formulation is anhydrous.
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Ramnarace, U.S. Patent No. 4,111,728, describes gas
generators for inflating life rafts and similar devices or that
are useful as rocket propellants comprising ammonium nitrate,
a polyester type binder and a fuel selected from oxamide and
guanidine nitrate. Ramnarace teaches that ammonium nitrate
contr~lbutes to burn rates lower than those of other oxidizers
and further adds that ammonium nitrate compositions are
hygroscopic and difficult to ignite, particularly if small
amounts of moisture have been absorbed.
Bucerius et al, U. S.~ Patent No. 5,198, 046, teaches
the u~~e of diguanidinium-5,5~-azotetrazolate (GZT) with KNO3 as
an ox:~dizer, for use in generating environmentally friendly,
non-toxic gases. Bucerius teaches away from combining GZT with
any chemically unstable and/or hygroscopic oxidizer. The use
of other amine salts of tetrazole such as bis-
(tria~minoguanldirlium) -5, 5 ~-azotetraaolate
(TAGZT) or
amp.noquanidirllum-5,5~-a2otetrazolate are taught as beiTlg much
. less i:henaally stable when compared to GZT.
Boyars, U.S. Patent No. 4,124,368, describes a method
for preventing detonation of ammonium nitrate by using
- potassium nitrate.
Mishra, U.S. Patent No. 4,552,736, and Mehrotra et
~ al, U,.S. Patent No. 5,098,683, describe the use of potassium
fluoride to eliminate expansion and contraction of ammonium
nitrat:e in transition phase.
Chi, U.S. Patent No. 5,074,938, describes the use of
phase stabilized ammona.um nitrate as an oxidizer in propellants
conta~lning boron and as useful in rocket motors.
In U. S. Patent 5, 125, 684 to Cartwright, an extrudable
3o prope7Llant for use in crash bags is described as comprising an
oxidi.:er salt, a cellulose-based binder and a gas generating
component_ Cartwright also teaches the use of ~~at least one
energeaic 'component selected from nitroguanidine (NG),
triaminoguanidine nitrate, ethylene dinitramine,
c y c 7. o t r i m a t h y 1 a n a t r i n i t r a m i n a ~ ( R D X ) ,
cyclot:etramethylenetetranitramine (HMX)_,--trinitrotoluene (TNT) ,
and ps:ntaerythritol tetranitrate (PETN)....~~
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In U.S. Patent 4,925,503 to Canterbury et al, an
explosive composition Xs described as comprising a high energy
material, e.g., ammonium nitrate and a polyurethane polyacetal
elastaiaer binder, the latter component being the focus of the
invention. Canterbury also teaches the use of a "high energy
material useful in the present invention ... preferably one of
the following high energy materials: RDX, NTO, TNT, HI~lX, TAGN,
nitrogruanidine, or ammonium nitrate..."
Hess, U. s. Patent No. 3 , 0~1, 617, describes long known
considerations as to oxygen balance and exhaust gases.
Stinecipher et al, U.S. Patent No. 4,300,962,
describes explosives comprising ammonium nitrate and an
ammonium salt of a nitroazole.
Prior, U.S. Patent No. 3,719,604, describes gas
generating compositions comprising aminoguanidine salts of
azotet.razole or of ditetrazole.
Poole, U.S_ Patent No_ 5,139,588, describes nonazide
gas generants useful in automotive restraint devices comprising
a fuel, an oxidizer and additives.
Hendrickson, U.S. Patent No. 4,798,637, teaches the
use o~~ bitetrazole compounds, such as diammonium salts of
bitetrazole, to lower the burn rate of gas generant
- compositions. Hendrickson describes burn rates below .40 ips,
and an 8% decrease in the burn rate when diammonium bitetrazole
is used.
Chang et al, U.S. Patent No. 3,909,322, teaches the
use of nitroaminotetrazole salts with oxidizers such as pure
ammonium nitrate, I~MX, and 5-ATN. These compositions are used
as gun,'propellants and gas generants for use in gas pressure
actuated mechanical devices such as engines, electric
generators, motors, turbines, pneumatic tools, and rockets. In
contrast to the amine salts disclosed by Hendrickson, Chang
teaches that gas generants comprised of 5-aminotetrazole
nitrate and salts of nitrvaminotetrazole exhibit burn rates in
excess of .40 ips. On the other hand, Chaiig also teaches that
gas generants comprised of I3Mx and salts of nitroaminotetrazole
exhibit burn rates of .243 ips to .360 ips. No data is given
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' 1 4
y: r
' with regard to burn rates associated with pure AN and salts of
nitroaminotetrazole.
Highsmith et al, U.S. Patent No. 5,516,377, teaches
the us,e of a salt of 5-nitraminotetrazole, NQ, a conventional
ignition aid such as BKNO3, and pure ammonium nitrate as an
oxidizer, but does not teach the use of phase stabilized
ammonium nitrate. Highsmith states that a composition
comprised of ammonium nitraminotetrazole and strontium nitrate
exhibits a burn rate of .313 ips. This is to low for
automotive application. As such, Highsmith emphasizes the use
of metallic salts of nitraminotetrazole.
Onishi et al, U.S. Patent No. 5,439,251, teaches the
use off: a tetrazole amine salt as an air bag gas generating
agent comprising a cationic amine and an anionic tetrazvlyl
group having either an a11cy1 With carbon number 1-3, chlorine,
hydroxyl, carboxyl, methoxy, aceto, vitro, or another
tetrazolyl group substituted via diaao or triazo groups at the
5-position of the tetrazole ring. The inventive thrust is tQ
improve the physical, properties of tetrazoles with regard to
2o impact. and friction sensitivity, and therefore does not teach
the combination of an amine or nonmetal tetrazole salt with any
other chemical_
Lund et al, U.S. patent No. 5,501,823, teaches the
use o;E nvnazide anhydrous tetrazoles, derivatives, salts,
complexes, and mixtures thereof, far use in air bag inflators.
The use of bitetrazole-amines, not amine salts of bitetrazoles,
is also taught.
Based on the above, the need remains for a PsAN-based
gas generant which is thermally stable at 107C, ignites readily
and without delay, has a burn rate at 1O00psi of greater than
0.40-0.5oips, and contains no sensitive explosive compounds.
SUMMARY OF THE INVENTION
The afc=ementioned problems are solved by a nonazide
gas generant for a vehicle passenger restraint system
comprising phase stabilized ammonium nitrate, nitroguanidine,
and one or more nonazide fuels_ The nonazide fuels are
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' selected from a group including guanidines; tetrazoles such as
5,5~bi.tetrazole, diammonium bitetrazole, diguanidinium-5,5~-
azotetrazolate (GZT), and nitrotetrazoles such as 5-
riitrot:etraaole; triazoles such as nitroaminotriazole,
nitrot:riazoles, and 3-vitro-1,2,4 triazole-5-one; and salts of
tetraz~~oles and triazolas_
A preferred fuels) is selected from the group
consisting of amine and other nonmetal salts of tetra2oles and
triazoles having a nitrogen containing cationic component and
to a tetrazole and/or triazole anionic component. The anionic
comporuent comprises a tetrazole or triazole ring, and an R
group substituted on the 5-position of the tetrazole ring, or
two R groups substituted on the 3- and 5-positions of the
triasole ring. The R groups) is selected from hydrogen and
any nitrogen-containing compounds such as amino, vitro,
nitramino, tetraaolyl and triazolyl groups. The cationic
component is formed from a member of a group including amines,
aminos~, and amides including ammonia, hydrazine, guanidine
compounds such as guanidine, aminoguanidine, diaminoguanidine,
triami.noguanidi.ne, dicyandiamide, nitroguanidine, nitrogen
subsit,uted carbonyl compounds such as urea, carbohydraaide,
oxamid,e, oxamic hydrazide, bis-(carbonamide) amine,
azodicarbonamide, and hydrazodiearbonamide, and, amine azoles
such as3-amino-1,2,4-triazole,3-amino-5-vitro-1,2,4-triazole,
5-ami~.otetraaole and 5-nitraminotetrazole. Optional inert
additives such as clay, alumina, or silica may be used as a
binder, slag former, coolant or processing aid. Optional
ignition aids comprised of nonazide propellants may also be
utilized in place of conventional ignition aids such as 8KNo3.
3o D~ETA=LSD DDSCRipTION OF T88 BREFSRRSD ~oD~NT(s)
A nonazide gas generant comprises phase stabilized
ammonium nitrate (PSAN), nitroguanidine (NQ), and one or more
nonazide high-nitrogen fuels. One or more high-nitrogen fuels
are selected from a group including tetrazoles such as 5-
nitrotetrazole, 5,5~-bitetrazole, .triazoles such as
nitroaminotriazole, nitrotriazoles, nitrotetrazoles, salts of
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- tetrazoles and triazoles, and 3-nitro-1,2,4 triazole-5-one.
More specifically, salts of tetrazoles include in
particular, amine, amino, and amide salts of tetrazole and
triazole selected from the group including monoguanidinium salt
og 5,5'-Bis-18-tetrazole (BHT~1GAD), diguanidinium salt of
. 5, 5 ~-Ftis-113-tetraaole (BHT ~ 2GAD) , monoaminoguanidinium salt of
5,5'-Bis-1H-tetrazole (BHT~lAGAD), diami~noguanidinium salt of
5,5~-E~is-113-tetrazole (gHT~2AGAD), monohydrazinium salt of
5,5'-Bis-1H-tetrazole (BHT~1H8), dihydrazinium salt of 5,5'-
His-1~1f-tetrazole (BHT~2HH), monoammonium salt of 5,5'-bis-1H
tetraz,ole (HHT ~ 1NH3) , diamalGllium salt of 5, 5' -bis-1H-tetraaole
(BHT~2NH3), mono-3-amino-1,2,4-triazolium salt of 5,5'-bis-1H
tetraz~ole (HHT ~ lATAZ) , di-3-amino--1, 2, 4-triazolium salt of
5,5'-bis-1H-tetrazole (BHT~2ATAZ), and diguanidinium salt of
5,5~-~,2obis~1H-tetraZOle (ABHT~2GAD).
Amine salts of triazoles include monoammonium salt of
3-vitro-1,2,4-triazole (NTA~1NH3), monoguanidinium salt of 3-
nitro-1,2,4-tria2ole (NTA~1GAD), diammonium salt of
dinitrobitriazole (DNBTR~2NH3), diguanidinium salt of
dinitrobitriazole (DNBTR~2GAD), and monoammonium salt of 3,5-
~dinitro-1,2,4-triazole (DNTR-iNH3).
R1
N - N N - C
2 5 ~~ ~~ ~ Z ~~ ~~ ' Z
C N C N
\ / / \ /
R N RZ N
H H
Formula I Formula II
A ~generic nonmetal salt of tetrazole as shown in
Formula I includes a cationic nitrogen containing component, Z,
and an anionic component comprising a tetrazole ring and an R
group substituted on the 5-position of the tetrazole ring. A
generic nonmetal salt of triazole as shown in Formula II
includes a cationic nitrogen containing component, Z, and an
anionic component comprising a triazole ring and two R groups
substituted on the 3- and 5- positions~~of the triazole ring,
wherein R1 may or may not be structurally synonymous with R2.
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- An R c:omponent is selected Pram a group including hydrogen or
any nitrogen-containing compound such as an amino, nitro,
nitramino, or a tetrazvlyl or triazolyl group as shown in
Formu7.a I or II, respectively, substituted directly or via
amine, diazo, or triazv groups. The compound Z is substituted
at the 1-position of either formula, and is formed from a
membex- of the group comprising amines, .aminos, and amides
including ammonia, carbohydrazide, oxamic hydrazide, and
hydra2;ine; guanidine compounds such as guanidine,
amino~~uanidine, diaminoguanidine, triaminoguanidine,
dicyandiamide and n.itroguanidine; nitrogen substituted carbonyl
compdu~nds or amides such as urea, oxamide, bis-(carbonamide)
amine, aaodicarbonamide, and hydrazodicarbonamide; and, amino
azoles; such as 3-amino-1,2,4-triazole, 3-amino-5-vitro-1,2,4-
triazole, 5-aminotetrazole, 3-nitramino-1,2,4-triazole, S-
nitraminotetrazole, and melamine.
In accordance with the present invention, a preferred
gas g~enerant composition results from the mixture of gas
generant constituents including nitroguanidine, comprising s%-
30% by weight of the gas generant composition, one or more
amine salts of t etrazoles and/or triazoles, comprising 4%-40%
by weight of the gas generant composition, and psAN, comprising
" 40%-85$ by weight of the gas generant composition. In the
percentages given, an even more preferred embodiment results
from 'the mixture of gas generant constituents consisting
essentially of NQ, PSAN, and amine salts) of 5,5~-bis-1H-
tetrazvle. In the percentages given, a most preferred
composition results from the mixture of gas generant
constituents consisting essentially of NQ, PSAN, and diammonium
salt of 5,5~-bis-1H-tetrazole (BHT~2Nfi3). When combined, the
fuel component consisting of NQ and one or more high nitrogen
fuels as described herein, comprises 15%-60% by weight of the
gas generant composition.
In accordance with procedures well known in the art,
the foregoing nonazide fuels, and/or nonmetal salts of
tetrazole or triazole, are blended with an oxidizer such as
PSAN, .and NQ. The manner and order in which the components of
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the gas generant compositions of the present invention are
combined and compounded is not critical so long as the proper
particle size of ingredients are selected to ensure the desired
mixture is obtained. The compounding is performed by one
skilled in the art, under proper safety procedures for the
preparation of energetic materials, and under conditions which
will not cause undue hazards in processing nor decomposition of
the components employed. For example, the materials may be wet
blended, or dry blended and attrited in a ball mill or Red
to Devil type paint shaker and then pelletiaed by compression
molding. The materials may also be ground separately or
together in a fluid energy mill, sweco vibroenergy mill or
bantam, micropulveri2er and then blended or further blended in
a v-blender prior to compaction.
Compositions having components more sensitive to
friction, impact, and electrostatic discharge should be wet
ground, separately followed by drying. The resulting fine
powder of each of the components may~then be wet blended by
tumbling with ceramic cylinders in a ball mill jar, for
example, and then dried. Less sensitive components may be dry
,ground. and dry blended at'the same time.
Phase stabilx2ed ammonium nitrate is prepaxed as
taught. in co-owned U. S. Patent No. 5, 531, 941 entitled, "Process
For Preparing Azide-free Gas Generant Composition". Other
nonmetal inorganic oxidizers such as ammonium perchlorate, or
oxidizers that produce minimal solids when combined and
combusted with the fuels listed above, may also be used. The
ratio of oxidizer to fuel is preferably adjusted so that the
amount. of oxygen allowed in the equilibrium exhaust gases is
less than 3% by weight, and more preferably less than or equal
to 2% by weight. The oxidizer comprises 40%-85% by weight of
the gas generant composition.
The gas generant constituents of the present
invention are commercially available. For example, the amine
salts of tetrazoles may be purchased from Toyo Kasei Kogyo
Company Limited, Japan_ rritroguanidine may be purchased from
Nigu Chemie, and, the components used to synthesize PSAN, as
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described herein, may be purchased from Fisher or Aldrich.
Triazole salts may be synthesized by techniques, such as those
described in U.S. Patent No. 4,Z3s,o14 to Lee et al.; in ~~New
Explosives: Nitrotriazoles Synthesis and Explosive properties",
by H.H. Licht, Fi_ Ritter, and H. Wanders, postfach 1260, D-
79574 Weil am Rhein; and in ~~Synthesis of Nitro Derivatives of
Triazoles", by Ou Yuxiang, Chen 8oren, Li Jiarong, Dong Shuan,
Li Jianjun, and Jia Huiping, Heterocvcles, Vol. 38, No. 7, pps.
7.651-'1664, 1994. Other compounds in accordance with the
present invention may be obtained as taught in the above-
mentioned references, or from other sources well known to those
skill~sd in the art, .
Ari optional burn rate modifier, from O-l0% by weight
in tb.e gas generant composition, is selected ~xom a group
including an alkali metal, an alkaline earth or a transition
metal salt of tetrazoles or triazoles; an alkali metal or
alKal:Lne earth nitrate or nitrite; TAGN; dicyandiamide, and
alkali and alkaline earth metal salts of dicyandiamide; alkali
2o and alkaline earth borohydrides; or mixtures~thereof. An
optional combination slag former and coolant, in a range of 0
to 10% by weight, is selected from a group including clay,
. 5111ca, glass, and alumina, or mixtures thereof. When
combining the optional additives described, or others known to
those skilled in the art, care should be taken to tailor the
additions with respect to acceptable thermal stability, burn
rates,, and ballistic properties.
In accordance with the present invention, the
combination of NQ, PSAN, and one or more nonazide high-nitrogen
fuels,, as determined by gravimetric procedures, yields
beneficial gaseous products ,equal to or greater than 90% of the
total product mass, and solid products equal to or lesser than
10% of the total product mass_ Fuels suitable in practicing
the present invention are high in nitrogen content and low in
carbon content thereby providing a high burn rate and a minimal
gener<ition of carbon monoxide.
The synergistic effect of the high-nitrogen fuels, in
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combination with an oxidizer producing minimal solids when
combined with the fuels, results in several long-awaited
benefits. Increased gas production per mass unit of gas
generant results in the use of a smaller chemical charge.
Reduced solids production results in minimized filtration needs
and therefore a smaller filter. Together, the smaller charge
and smaller filter thereby facilitate a smaller gas inflator
system. Furthermore, the gas generant compositions of the
present invention have'burrt rates and ignitability that meet
l0 and surpass performance criteria for use within a passenger
restraint system, thereby reducing performance variability.
As shoran in Example 10, it has also been found that
the use of nitroguanidine functions to retard the volumetric
phase changes nonaally exhibited by pure ammonium nitrate,
thereby further stabiliz~.ng the PsAN.
An unexpected benefit of the present chemical
compositions is thermal stability. The thermal stability of
the ga.s generants is unexpected based an the poor stability of
other fuels and in particular, triazoles and tetrazoles, when
combined with PSAN. In contrast to other thenaally stable
compositions consisting of NQ and PSAN, these compositions
ignite: readily and without delay and have a burn rate greater
than 0.40-0.50 ips at 1000 psi. Furthermore, the amine salts
of tetrazoles and triazoles are neither explosive nor flammable
and ca.n be transported as non-hazardous chemicals.
The present invention is illustrated by the
followung examples. All compositions are given in percent by
weight.
EBASpZE 1 - comparative Example
A mixture of ammonium nitrate (AN) , potassium nitrate
(RN), and guanidine nitrate (GN) was prepared having 45.35%
Nfi4NO3, 8 . 0% KN, and 46 _ 65% GN. The amoononium nitrate was phase
stabilized by coprecipitating with RN.
The mixture was dry-blended and ground in a ball
mill. Thereafter, the dry-blended mixture was compression-
melded into pellets, The burn rate of the composition was
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CA 02260144 2005-05-30
determined by measuring the time required to burn a cylindrical
pellet of known length at constant pressure. The burn rate at
1000 pounds per square inch (psi) was .25~ inches per second
(in/sec); the burn rate at 1500 psi was .342 in/sec. The
corresponding pressure exponent was 0.702.
EYANP~B 2 - Comparative Example
A mixture of 46.13% NI~NO3, 8.14% I~1, 35.73% GN, and
10.0% nitroguanidine (NQ) was prepared and tested as described
in Example 1. The burn rate at 1000 psi was 0.282 in/sec and
20 the burn rate at 1500 psi was 0.368 in/sec. The corresponding
pressure exponent was 0.657.
EZAMP1'~E 3 - Comparative Example
A mixture of 46.91% NI~N03, 8.28% KN, 24.81% GN, and
20 . o% NQ was prepared and tested as described in Example 1.
The bL~trn rate at 1000 psi was 0.282 in/sec and the burn rate at
1500 psi was 0.3'73 in/sec. The corresponding pressure exponent
was 0.,680.
E~Z~E 4 - Comparative Example
A mixture of 52. 20% NIi~N03, 9. Z1% lai, 28. 59% GN, and
~ 10.0$ 5-aminotetrazole (5AT) was prepared and tested as
described in Example 1. The burn rate at 1000 psi was 0.391
in/sec: and the burn rate at 1500 psi was 0.515 in/sec. The
corresponding pressure exponent was 0.677.
AMPLE 5 - Comparative Example
Table 1 illustrates the problem of thermal
instability when typical nonazide fuels are combined with PSAN:
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_ Table 1: Thermal Stability of PSAN - Non-Azide Fuel Mixtures
Non-t~,zide Fuels) Thermal
Stability
Lrombi.ned ovith PSAN
5aaninotetrazole (5AT)Melts with108Conset and 1160 peak.
Decowposedwith6.74% weight loss when
aged
at 107C 336 hours. Poole '2~2 shows
for
melting
with lass
of NHS
when aged
at 1070.
ethylene diamine Poole '272shows
tneltiag
at
less
than
100C
dinitrate,
nitroguaslidine (NQ)
SAT, NQ Melts with103Conset and 110C peak_
SAT,N~Q quaaidine Melts with93C
onset
on
99C
peak_
nitrate (GN)
6N, N~Q Melts withlOOConset and 112C. Decomposed
with 6.49%weight
loss
when
aged
at
1070
for
336 houre-
GN, 3~-vitro-1,2,4- Melts withloseonset and 1100 peak.
triaz~ole (NTA)
NQ, N'rA Melts withlilConset and 113C peak.
aminogusnidine nitrateMelts with1090onset and 110C peak.
1H-teltrazole (18T) Melts with109Conset and 110C peak.
diCyandiamide (DCDA) Melts with114Conset and 114C peak.
.GN, DI:DA Melts with104Conset Gild 105C peak.
NQ, DI~A Melts with1070onset and 115C peak.
Decomposedwith5.66% weight lose when
aged
at 107C hours.
for 336
2 0 SAT, GN Meits with70C
onset
and
99C
peak.
magnelaium salt of Melts with100Conset and 111C peak.
5AT
(MSAT)
In this example, I~decomposed~~ indicates that pellets
of the given formulation were discolored, expanded, fractured,
and/or stuck together (indicating melting), making them
unsuitable for use in an air bag infl-ator. In general, any
pSAN-nonazide fuel mixture with a melting point of less than
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t
1150 will decompose when aged at 1070. As shown, many
compositions that comprise well known nonazide fuels and PSAN
are not fit for use within an inflator due to poor thermal
stability.
N~:LE 6 - Comparative Example
A mixture of 56.30% NI~NO3, 9.94% KN, 17.76% GN, and
16.0% 5AT was prepared and tested as described in Example 1.
The burn rate at 1000 psi was 0 _ 473 in/ sec and the burn rate at
1500 psi was 0.584 in/sec. The corresponding pressure exponent
l0 Was 0.,518. The burn rate is acceptable, however, compositions
containing GN, 5-AT, and PSAN are not thermally stable as shown
in Table l, EXAMPLE 5.
BXANP1~E 7
Table 2: Gas Generating Characteristics of GZT, NQ, and PSAN.
PSAN (Wt%) 78.22 75.83 73.45 71.06 68.68 66.29
GZT (wt%) 21.78 19.17 16.55 13.94 11.32 8.71
NQ (wt%) 0.00 5.00 10.00 15_00 20.00 25.00
Gas
Conversion
(wt%;E 96.36 96.47 69.58 96.69 96.80 96.91
Gas afield
(mol,/100g GG) 4.06 4.05 4.04 4_04 4.03 4.02
Gaseous NZ 37.8 37.7 37.6 37.5 37.5 37.4
Products C02 7.6 7.9 8.1 8.4 8.7 9.0
(vol.,%) HZO 54.7 54.5 54.3 54.0 53.8 53.6
Solid
Products .
K20 (g/lOOg
GG) 3.64 3.53 3.42 3.31 3.20 3.09
3 0 FlamE>_
Temperature
(K) 2254 2275 2296 2317 2337 2358
As shown in table 2, gas generant compositions
consisting essentially of GZT, N~, and PSAN generate mostly gas
and minimal solids when combusted.
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$~~r8 8
Table 3a: Gas generants comprising BHT-2NH3 or GZT, and PsAN.
PSAN 10%
KN (i~i'f%) 74. Z5
PSAN 15%
KN (ZNt%) 76.43 75.40 72.32 75.60
BHT-2 NH3
(wt%) 23.57 24.60 27.68
8HT-2GAD
(wt%) 24.40
GZT (wt%) 25.75
NQ (wt%
Gas Yield 95 95 95 95 9?
Melting
Point (C) 158 159 159 131 125
Aging at No No No No No
107C Deco. Deco. Deco. Deco. Deco.
Ignitability Exc. Exc. Exc. Exc. Exc.
Tailorability
of Ballistic
-
Properties Marq. Marg. Marg. Marg. Mar
Flame
Temperature 21?9 2156 2U74 2052 2166
Rb1000
(ips) 0.48 0.47 0.52 0.57 0.51
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CA 02260144 2005-05-30
table 3b. Gas aenerants com~risina BIiT-2NH~. PSAN. and NO.
PSAN
10% KN
wt% 64.40 7D.28 67.17 65.23 68.08 64.05 71.83
PSAN
% ICN
wt%
. B~-ilNH3
(wt%) 9.60 16.72 19.83 19.77 20.92 22.95 23.17
1D BHT-
2 GAD
wt%
GZT
00t%
15 N wt% 26.00 13.00 13.00 15.00 11.00 13.00 5.00
Gas
Yield 97 97 97 97 97 97 97
wt ~;
Melting
ZO Point: 131 132 131 13Z 131 131 131
C
Aginch No No No No No No No
a 107C Deco. Deco. Deco. Deco. Deco. Deco. Deco.
Ignitx- .
bilit Mar . Exc. Exc. Exc. Exc. Exc. Exc.
Tailos'-
abilit;y
of
sallis~ticF.xc Exc Exc . Exc Exc . Exc . Exc
. . _ .
Pro act.~
' Flame
Tem . 2346 2274 2186 2167 2174 2093 2170
I
~
0C
Rb1000
l s 0.43 0.49 0.52 0.49 0.54 0.52 0.54
Table Reference:
No Deco. - No Decomposition
Exc. - Excellent
Marg. - Marginal
_19- . ,.
CA 02260144 2005-05-30
p~r~t~s 9 ~ ~ 12 5
~1
2 ~ MAY, f~8
Applicants have found that it is difficult to tailor
the ballistic performance of inflators containing gas generants
consisting of PSAN and an amine or amide salts) of tetrazole or
triazole. Applicants have also discovered that in addition to
excellent burn rates and ignitability, the addition of
nitroguanidine to these compositions facilitates simplified
tailorability of ballistic performance, thezeby making inflator
design much simpler. As shown in Tables 3a and 3b, the ballistic
tailorability of compositions comprised of pSAN and amine salts
l0 of tetrazoles is substantially improved by zhe addition of NQ.
Example 9 further illustrates this.
W When foz-mulating these compositions, it was unexpected
wr
that with the addition of nitroguanidine, the mixture would still
be thermally stable at 1070, and experience essentially no
decrease in ignitability or burn rate.
BALE 9
Table 4 illustrates the desirability of maintaining NQ
in percentages below 35%, and more preferably below 26s. Five
curves illustrate the effect of increasing the percentage of NQ
from ~)-26 weight percent. Table 4 lists data corresponding to
each curve, wherein NQ is combined with BI3T-2NFi3. These
compositions were pressed into pellets, loaded into an airbag
inflat:or, and fired in a 6oL tank.' In each of the following
tests, all variables (pellet size, inflator configuration, etc.)
were held constant, except for the formulation. Table 4 reflects
testing that showed no significant change in any of the other
desirable properties such as high gas yield, low solids, thermal
stability, and burn rate.
1~~
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CA 02260144 2005-05-30
:,~~~-L~~ 9 ? / ~ 2 ~ ~ Q
21 MAY 1~$ .
Table 4: Ballistic Tailorability
Curve NQ BHT-ZNH3 Time to Maximum Peak
(wt %) + PSAN 1 kPa Slvpe Tank P
(wt ~) (ms) (JcPa/ms) (kPa)
1 0 100 5.7 20.2 203.5
2 11 89 3.4 15.5 193.0
3 13 87 5.3 13.0 187.5
.4 15 85 4.2 11.3 176.5
5 1 26 ~ 74 ~ ~ 12.2 ~ 6.9 ~ 68.2
The time to a tank pressure of ZkPa (known as time to
first gas in the industry), the maximum slope, and the peak tank
pressure are all used to describe the ballistic performance of
an airbag inflator. It can be seen that as the amount of NQ in
the composition increases, both the maximum slope and the peak
tank pressure decrease. The time to first gas is at an
accept: able level of 3ms to 6ms in curves 1-4. The time to first
gas in curve 5 is at an undesirable high level, and is indicative
of a delay in ignition of the gas generant. This demonstrates
the poor ignitability of gas generant compositions containing
higher- percentages of NQ . The ignition delay seen in curve 5 -can
be corrected by operating at a higher inflator internal
combustion pressure. However, this would result in the need for
a much more robust inflator stnzcture thereby increasing the size
and weight of the inflator.
EB~PL~E 10
Another unexpected result is that nitroguanidine
appears to help stabilize ammonium nitrate against volumetric
phase changes during thermal cycling_ A composition containing
49% AN, 9% KN, and 43o NQ was prepared by grinding and blending
the dry materials together. The AN in this composition was
unstabilized since the AN and ~ were not combined to form a
solution. This composition was tested by DSc and compared to
pure Als_ At room temperature, Arz phase Iv exists. Upon heating
phase IV changes into phase II at about 55°C. This is clearly
seen om the DSc for pure AN. For the composition containing AN
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~9
CA 02260144 2005-05-30
..: r 7US 97i12579
21 MiIY liipg
- and NrQ, the phase change has been eliminated and does not occur
below 110°C. It is believed that lower amounts of NQ will
provide the same benefit of AN phase-stabilization.
EXAadPLE l1
A composition resulting from the mixture of gas
generant constituents consisting of 70.28% PSAN, 16.72% BAT-2NIi~,
and 1:3 . 00% NQ was prepared and pressed into pellets . The pellets
were placed in a covered, but unsealed container in a helium
purged chamber and aged at 107°C_ In this way, any volatiles
formed during decomposition would result in a weight loss in the
sample>. After 408 hours of aging, the volatiles weight loss was
~J
0.30%. After 2257 hours of aging, the volatiles Weight loss was
0.97%.' After aging, the pellets showed no physical signs of
decomposition. In addition, thermal analysis (DSC) showed no
signii'icant differences in the pellets before and after aging.
The pellets which were aged for 2257 hours at 107°C were tested
in an inflator and showed nv significant differences in ballistic
perfox:~mance when Compared to unaged pellets_
EXAMPhE 12
A composition resulting from the mixture of _gas
generant constituents consisting of 6~ _ 17% PSAN, 19 . 83% BHT-2NfI9,
and 13.00% NQ was prepared and pressed into pellets. The PSAN
was a co-crystallized mixture of 90%~AN and 10% KN_ The pellets
were placed in sealed inflators and temperature cycled. One
ZS cycle consisted of holding the inflators at X05°C for two hours,
cooling to -40°C in two hours, holding for two hours, and heating
to 105.°C in two hours. After 50 cycles, the inflators were
tested and showed no significant difference from the baseline
units in ballistic performance. The physical appearance of the
pellets after cycling was unchanged; there were nv expansion or
cracks as is normally seen in unstabilized AN_
Although the components of the present invention have
been described in their anhydrous form, it will be understood
that the teachings herein encompass the hydrated forms as well.
AMEdI~D ~;
-z2-
CA 02260144 2005-05-30
r.
While the foregoing examples illustrate and describe
~~~Ithe use of the present invention, they are not intended to limit
the invention as disclosed in certain preferred embodiments
herein. Therefore, variations and modifications commensurate
- 5 with i~,.he above teachings and the skill and/or knowledge of the
relevant art, are within the scope o~ the present invention.
_23_ - -- ..
