U.S. patent application number 13/637552 was filed with the patent office on 2013-03-21 for gas generant manufacturing method.
The applicant listed for this patent is Slaven Domazet, Sudhakar R. Ganta, Deborah L. Hordos, Graylon K. Williams. Invention is credited to Slaven Domazet, Sudhakar R. Ganta, Deborah L. Hordos, Graylon K. Williams.
Application Number | 20130068354 13/637552 |
Document ID | / |
Family ID | 44673522 |
Filed Date | 2013-03-21 |
United States Patent
Application |
20130068354 |
Kind Code |
A1 |
Domazet; Slaven ; et
al. |
March 21, 2013 |
Gas Generant Manufacturing Method
Abstract
A method of forming a gas generating composition containing a
salt of dinitrosalicylic acid and ammonium nitrate or phase
stabilized ammonium nitrate. The method involves the
co-precipitation of a salt of 3,5-dinitrosalicylic acid with phase
stabilized ammonium nitrate. A gas generating composition 12 is
also presented along with a gas generator 10 containing the gas
generating composition 12. The gas generator 10 may be contained
within a gas generating system 200 such as an airbag inflator 10 or
seat belt assembly 150, or more broadly within a vehicle occupant
protection system 180.
Inventors: |
Domazet; Slaven; (Troy,
MI) ; Hordos; Deborah L.; (Troy, MI) ; Ganta;
Sudhakar R.; (Troy, MI) ; Williams; Graylon K.;
(Warren, MI) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Domazet; Slaven
Hordos; Deborah L.
Ganta; Sudhakar R.
Williams; Graylon K. |
Troy
Troy
Troy
Warren |
MI
MI
MI
MI |
US
US
US
US |
|
|
Family ID: |
44673522 |
Appl. No.: |
13/637552 |
Filed: |
March 28, 2011 |
PCT Filed: |
March 28, 2011 |
PCT NO: |
PCT/US11/00562 |
371 Date: |
September 26, 2012 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
61318161 |
Mar 26, 2010 |
|
|
|
Current U.S.
Class: |
149/105 |
Current CPC
Class: |
C06B 21/00 20130101;
C06B 21/0066 20130101; C06B 31/38 20130101; C06B 25/04 20130101;
C06B 31/00 20130101; C06D 5/06 20130101 |
Class at
Publication: |
149/105 |
International
Class: |
C06B 25/04 20060101
C06B025/04 |
Claims
1. A method of forming a gas generating composition comprising the
following steps: providing a solvent within a jacketed mixing
vessel; adding a stoichiometric amount of dinitrosalicylic acid to
the solvent and stirring; adding at least one oxidizer in a
stoichiometric amount to the solution and stifling, the oxidizer
selected from ammonium nitrate and phase stabilized ammonium
nitrate; and adding a precipitating agent to the composition and
continuing to stir, thereby forming solids.
2. The method of claim 1 wherein the solvent is selected from
water, ethanol, methanol, propanol, and any other solvent miscible
with water.
3. The method of claim 1 wherein the precipitating agent is a
potassium source and is added when ammonium nitrate is added to the
vessel.
4. The method of claim 3 wherein the precipitating agent is
selected from potassium nitrate, potassium hydroxide, and
dipotassium carbonate.
5. The method of claim 1 wherein the precipitating agent is an
ammonium source and is added when phase stabilized ammonium nitrate
is added to the vessel.
6. The method of claim 5 wherein the precipitating agent is
selected from ammonium hydroxide and ammonium carbonate.
7. The method of claim 1 further comprising the step of adding a
secondary fuel to the vessel and continuing to stir.
8. The method of claim 7 wherein diammonium salt of
5,5'-bis-1H-tetrazole is added as a secondary fuel.
9. The method of claim 7 wherein the secondary fuel that is added
to the vessel is selected from tetrazoles and salts thereof;
triazoles and salts thereof; azoles and salts thereof; guanidine
salts and derivatives; imides; amides; aliphatic carboxylic acids
and salts thereof; aromatic carboxylic acids and salts thereof;
nitro-aromatic carboxylic acids and salts thereof; nitrosalicylic
acids and salts thereof; amines; nitrophenols; pyrazoles;
imidazoles; azines; and mixtures thereof.
10. The method of claim 1 further comprising the step of adding
additional solvent after adding the oxidizer to enhance the
solubility of the constituents that are added to the vessel, while
continuing to heat and stir the solution.
11. The method of claim 1 further comprising the step of forming
the solid precipitate into a desired form.
12. The method of claim 11 wherein the method is selected from
compression and extrusion methods.
13. A composition formed from the method of claim 1.
14. A composition formed from the method of claim 7.
15. A composition formed from the method of claim 8.
16. A composition formed from the method of claim 9.
17. A gas generator containing a composition formed from the method
of claim 1.
18. A vehicle occupant protection system containing a composition
formed from the method of claim 1.
19. The method of claim 1 further comprising the step of heating
and maintain the temperature of the solution to about 100 C-110
C.
20. The method of claim 1 further comprising the step of stirring
and heating the solids until the desired dryness within the
resultant solids is attained.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. Provisional
Application Ser. No. 61/318,161 filed on Mar. 26, 2010 and PCT
Application Serial No. PCT/US11/00562 filed Mar. 28, 2011.
TECHNICAL FIELD
[0002] The present invention relates generally to gas generating
systems, and to gas generating compositions employed in gas
generator devices for automotive restraint systems, for
example.
BACKGROUND OF THE INVENTION
[0003] The present invention relates to gas generating compositions
that upon combustion produce a relatively smaller amount of solids
and a relatively abundant amount of gas. It is an ongoing challenge
to reduce the amount of solids and increase the amount of gas
thereby decreasing the filtration requirements for an inflator. As
a result, the filter may be either reduced in size or eliminated
altogether thereby reducing the weight and/or size of the inflator.
Additionally, reduction of combustion solids provides relatively
greater amounts of gaseous products per gram or unit of gas
generating composition. Accordingly, less gas generant is required
when greater mols of gas are produced per gram of gas generant. The
result is typically a smaller and less expensive inflator due to
reduced manufacturing complexity.
[0004] In a related challenge, when increasing the amount of gas,
the effluent must be tailored to ensure that carbon monoxide or
other less-than-desirable gases are attenuated. For example, when
increasing the relative amounts of carbon in the gas generant, one
concern is whether the gas generant might produce more carbon
monoxide as a combustion product. As such, the effort to reduce
solids and increase gas production upon combustion, must be
balanced with combustion products that meet current effluent
standards.
[0005] Another challenge is providing gas generating compositions
that meet current USCAR requirements for chemical and thermal
stability. Chemical stability is indicative of a propellant
retaining its structural integrity over time. Dimensional stability
is indicative of chemical stability, the retention of density over
time for example. Components of the composition must be compatible
with each other with a minimum of interaction. Therefore, chemical
stability involves the mitigation of interaction of the various
constituents that are included in the gas generating
composition.
[0006] Thermal stability is the ability to retain structural
integrity when cycled between -40 C and 107-110 C, for example. For
example, the composition may be held at a temperature of -40 C for
a period of time and then quickly brought to a temperature of about
107 to 110 C and held there for a period of time. Accordingly,
retaining gas generant structural integrity while undergoing
periodic cycling between the two temperature regimes over time is
yet another challenge. Furthermore, USCAR requirements include
thermal testing by holding compositions at about 107 C for about
400 hours without thermal decomposition of the compositions.
Certain compositions containing phase stabilized ammonium nitrate,
for example, oftentimes present concerns with regard to thermal
stability.
[0007] Yet another concern is that the compositions must exhibit
burn rates that are satisfactory with regard to use in vehicle
occupant protection systems. In particular, compositions containing
phase stabilized ammonium nitrate may exhibit relatively lower burn
rates requiring various measures to improve the burn rate.
Accordingly, the development of energetic fuels is one ongoing
research emphasis whereby the less aggressive burn characteristics
of preferred oxidizers such as phase stabilized ammonium nitrate
are accommodated and compensated for by careful blending or
combining of new and useful constituents.
[0008] Furthermore, it has been found that oftentimes nitrated
aromatic compounds combined with ammonium nitrate or phase
stabilized ammonium nitrate are not clean burning and may form
large amounts of soot-like residues when combusted. Acidic
nitro-aromatic compounds provide some measure of catalytic impetus
to ammonium nitrate or phase stabilized ammonium nitrate
compositions, particularly in view of the ignitability and
sustained combustion concerns with some compositions containing
ammonium nitrate (stabilized or not).
[0009] With regard to gas generant formulation or processing,
pyrotechnic constituents may oftentimes be blended as dry powders
consisting of fuels, oxidizers, and other known additives. When
using acidic fuels or constituents, however, handling and
processing concerns due to sensitivity of the acidic compound
requires careful handling to prevent any unintended reactions.
Oftentimes, when an acidic fuel is employed in a gas generating
composition, it may be advisable to form a salt with the acid prior
to combining it with the composition. The time constraints, and the
additional steps in the processing add cost to the formulation
process, and detract from the benefit of the acidic fuel, less
combustion solids for example. Yet another challenge is that the
composition formed from the acidic fuel must also exhibit favorable
impact sensitivity and comply with Department of Transportation
regulatory requirements, and exhibit favorable chemical and thermal
stability.
[0010] In view of these concerns, it would be an improvement in the
art to provide a "smokeless" gas generant, or one that upon
combustion provides more than 90% of gas as a combustion product
without the aforementioned concerns. For example, an ammonium
nitrate or phase stabilized ammonium nitrate based composition that
meets or exceeds the relative gas output of typical high-nitrogen
fuels combined with an ammonium nitrate or phase stabilized
ammonium nitrate oxidizer while yet retaining the performance of or
improving upon the considerations provided above would be an
improvement in the art. It would also be an improvement to simplify
the formulation or processing of gas generating compositions that
incorporate acidic fuels without the hazards that might be
attendant due to the acidity of the fuel.
SUMMARY OF THE INVENTION
[0011] The above-referenced concerns are resolved by gas generators
or gas generating systems containing a novel fuel constituent,
3,5-dinitrosalicylic acid (DNSA), a metallic salt of DNSA, a
non-metallic salt of DNSA, or an adduct of DNSA with another
compound that forms a hydrogen bonded complex. When combined with
phase stabilized ammonium nitrate (PSAN) (stabilized, for example
only, with potassium nitrate provided at 10-15% by weight of the
PSAN), one or more of the present fuels result in a gas generant
composition that exhibits optimum burn rates at relatively lower
operating combustion pressures, and optimum thermal and chemical
stability, notwithstanding the use of PSAN. Furthermore, one or
more of the present compositions combust readily at relatively
lower combustion pressures thereby resulting in relaxed
manufacturing and structural requirements for an associated gas
generator or airbag inflator. Yet further, one or more of the
present compositions when combusted result in relatively greater
amounts of gas and lower amounts of solids, and therefore improved
effluent quality.
[0012] An optional second fuel may be selected from tetrazoles and
salts thereof, triazoles and salts thereof, azoles and salts
thereof, guanidines and salts thereof, guanidine derivatives,
imides, amides, aliphatic carboxylic acids and salts thereof,
aromatic carboxylic acids and salts thereof, nitro-aromatic
carboxylic acids and salts thereof, nitrosalicylic acids and salts
thereof, amines, nitrophenols, pyrazoles, imidazoles, azines, and
mixtures thereof.
[0013] A primary oxidizer may be selected from metal and nonmetal
nitrates, nitrites, chlorates, perchlorates, oxides, other known
oxidizers, and mixtures thereof.
[0014] If desired, other known constituents may also be utilized in
known effective amounts.
[0015] In further accordance with the present invention, a wet
method of formulating ammonium nitrate and phase stabilized
ammonium nitrate (PSAN) based compositions, containing a salt of
DNSA, is provided. It is believed that the co-precipitation of PSAN
and a salt of DNSA results in an intimate mixture that provides
substantial effluent improvements and substantial improvement in
ballistic performance, as well.
[0016] In further accordance with the present invention, a gas
generator or gas generating system, and a vehicle occupant
protection system incorporating the gas generant composition are
also included.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] FIG. 1 is a cross-sectional side view showing the general
structure of an inflator in accordance with the present
invention.
[0018] FIG. 2 is a schematic representation of an exemplary vehicle
occupant restraint system containing a gas generant composition in
accordance with the present invention.
[0019] FIG. 3 is a first microstructure of a co-precipitation of
ammonium dinitrosalicylic acid and phase stabilized ammonium
nitrate.
DETAILED DESCRIPTION OF THE INVENTION
[0020] The above-referenced concerns are resolved by gas generators
or gas generating systems containing an acidic nitrated aromatic
compound as a primary fuel, the primary fuel including a member
selected from the group of 3,5-dinitrosalicylic acid (DNSA), a
metallic salt of DNSA, a non-metallic salt of DNSA, or an adduct of
DNSA with another compound that forms a hydrogen bonded complex.
Examples of adducts include an adduct of DNSA and 3-amino-triazole;
DNSA and melamine; and DNSA and alkyl amines. When combined with
phase stabilized ammonium nitrate (PSAN) (stabilized for example
only, with 10-15% by weight of the PSAN with an alkali metal salt
such as potassium nitrate), one or more of the present fuels result
in a gas generant composition that exhibits optimum burn rates at
relatively lower operating combustion pressures, and optimum
thermal and chemical stability, notwithstanding the use of PSAN.
Furthermore, one or more of the present compositions combust
readily at relatively lower combustion pressures thereby resulting
in relaxed manufacturing and structural requirements for an
associated gas generator or airbag inflator. Yet further, one or
more of the present compositions when combusted result in
relatively greater amounts of gas and lower amounts of solids, and
therefore improved effluent quality. When used without other fuels,
the primary fuel may be provided at 20 wt % to 80 wt %, 25 wt % to
75 wt %, or at 40 wt % to 60 wt % of the total composition. All
other percentages hereinafter make reference to weight percents of
the total composition.
[0021] Optional secondary fuels may be selected from tetrazoles
such as 5-aminotetrazole; metal salts of azoles such as potassium
5-aminotetrazole; nonmetal salts of azoles such as diammonium salt
of 5,5'-bis-1H-tetrazole: nitrate salts of azoles such as
5-aminotetrazole; nitramine derivatives of azoles such as
5-aminotetrazole; metal salts of nitramine derivatives of azoles
such as potassium 5-aminotetrazole; nonmetal salts of nitramine
derivatives of azoles such as monoammonium 5-aminotetrazole; salts
of guanidines such as guanidine nitrate; nitro derivatives of
guanidines such as nitroguanidine; azoamides such as
azodicarbonamide; nitrate salts of azoamides such as
azodicarbonamidine dinitrate; aliphatic carboxylic acids such as
fumaric acid, tartaric acid, and succinic acid, and metal and
nonmetal salts thereof; aromatic carboxylic acids such as benzoic
acid, phtalic acid, and isophthalic acid, and metal and nonmetal
salts thereof; nitro-aromatic carboxylic acids such as nitrobenzoic
acid, dinitrobenzoic acid, nitroisophthalic acid, and
4-hydroxydinitobenzoic acid, and metal and nonmetal salts thereof;
mono-nitrosalicylic acids such as 3-nitrosalicylic acid and
5-nitrosalicylic acid and metal and nonmetal salts thereof; amines
such as melamine; amides such as oxamide; imides; nitrophenols such
as nitrophenol, 2,4-dinitrophenol, and picric acid, and metal and
nonmetal salts thereof; triazoles such as 3-nitrotriazole and
nitrotriazolone (NTO); pyrazoles imidazoles; azines; and mixtures
thereof. The secondary fuel can be used within this system as
co-fuels to the primary fuel. U.S. Pat. Nos. 5,872,329 and
6,210,505 describes the use of these and provision of these fuels
and are both herein incorporated by reference in their entirety.
When used, the secondary fuel in combination with the primary fuel
may constitute about 10-90 wt % of the gas generant composition.
Also, when the secondary fuel is employed, the primary fuel may be
provided from 5 wt % to 80 wt % of the total composition. By
itself, the optional secondary fuel may constitute 0.1-45 wt % when
used, and more preferably about 3-30 wt % when used.
[0022] An oxidizer is selected from metal and nonmetal nitrates,
nitrites, chlorates, perchlorates, oxides, hydroxides, other known
oxidizers, and mixtures thereof. The preferred primary oxidizer is
selected from ammonium nitrate and phase stabilized ammonium
nitrate, and most preferably phase stabilized ammonium nitrate. The
primary oxidizer may be provided at 20 wt % to 80 wt %, and more
preferably at 50 wt % to 80 wt % of the total composition. All
other percentages hereinafter make reference to weight percents of
the total composition.
[0023] A secondary oxidizer component is optionally selected from
at least one exemplary oxidizer selected from basic metal nitrates,
and, metal and nonmetal nitrates, chlorates, perchlorates,
nitrites, and oxides, including such oxidizers as basic copper (II)
nitrate, strontium nitrate, potassium nitrate, potassium nitrite,
iron oxide, and copper oxide. Metal-containing oxidizers include
those formed from alkali, alkaline earth, and transitional metal
oxidizers. Other oxidizers as recognized by one of ordinary skill
in the art may also be employed. The secondary oxidizer is
generally provided at about 0-50 wt % of the gas generant
composition.
[0024] If desired, other known constituents may also be utilized in
known effective amounts.
[0025] Metal and non-metal carbonates such as potassium carbonate
and ammonium carbonate may also be employed with an oxidizer such
as ammonium nitrate.
[0026] Processing aids such as fumed silica, boron nitride, and
graphite may also be employed. Accordingly, the gas generant may be
safely compressed into tablets, or slugged and then granulated. The
processing aid is generally provided at about 0-15 wt %, and more
preferably at about 0-5 wt %.
[0027] Slag formers may also be provided and are selected from
silicon compounds such as elemental silicon; silicon dioxide;
silicones such as polydimethylsiloxane; silicates such as potassium
silicates; natural minerals such as talc and clay, and other known
slag formers. The slag former is typically provided at about 0-10
wt %, and more preferably at about 0-5 wt %.
[0028] The compositions of the present invention may be formed from
constituents as provided by known suppliers such as Aldrich or
Fisher Chemical companies. The compositions may be provided in
granulated form and dry-mixed and compacted in a known manner, or,
wet-mixed and formulated as described in the examples, or otherwise
mixed as known in the art. The compositions may be employed in gas
generators typically found in airbag devices or occupant protection
systems, or in safety belt devices, or in gas generating systems
such as a vehicle occupant protection system, all manufactured as
known in the art, or as appreciated by one of ordinary skill.
EXAMPLES
Example 1
Wet Mix Method Including a Secondary Fuel
[0029] A composition was made by providing a jacketed mixing vessel
containing about two liters of ethanol. To this solution, about 753
grams of dinitrosalicylic acid (DNSA) was added while continuously
stirring. The solution was then heated slowly to about 105 C over
about thirty minutes and maintained throughout the remaining
process. Once the DNSA was completely dissolved, about 4352 grams
of ammonium nitrate, about 122 grams of potassium nitrate, about
227 grams of potassium carbonate (whereby potassium nitrate and
potassium carbonate taken together provide a potassium source for
phase stabilization of the ammonium nitrate), about 595 grams of
diammonium bitetrazole, and one liter of water are added together
into the vessel, while continuously and mechanically stilling. A
bright yellow precipitate forms immediately in a viscous,
paint-like consistency. After about one hour, the mix forms crumbly
solids. The mixing and heating is continued until the desired
dryness is obtained. If desired, the mix may be formed into desired
shapes such as pellets or tablets and then dried to a desired
moisture content, in an oven for example.
Example 2
Wet Mix Method
[0030] A composition was made by providing a jacketed mixing vessel
containing about two liters of water or ethanol, or any other
suitable solvent such as ethers or alcohols. To this solution, an
approximate stoichiometric amount of dinitrosalicylic acid (DNSA)
or a metal or nonmetal salt of DNSA was added while continuously
stirring. The solution was then heated slowly to about 105 C over
about thirty minutes and maintained throughout the remaining
process.
[0031] Once the DNSA was completely dissolved, an approximate
stoichiometric amount of ammonium nitrate was added and stirred
into the solution. A potassium source such as potassium nitrate was
then added in about 10-15% by weight with regard to the total
amount of ammonium nitrate added. The mixture was continually
stirred and the heat maintained as a solid formed. The mixing and
heating is continued until the desired dryness is obtained. If
desired, the mix may be formed into desired shapes such as pellets
or tablets and then dried to a desired moisture content, in an oven
for example. The resultant solid included stoichiometric amounts of
phase stabilized ammonium nitrate (PSAN) and ammonium
dinitrosalicylic acid (ADNSA). The resultant ADNSA crystals are
comparatively small and therefore form an intimate co-precipitation
with the ammonium nitrate.
Example 3
Wet Mix Method Including a Secondary Fuel
[0032] A composition was made by providing a stainless steel
jacketed mixing vessel containing about two liters of water. To
this solution, about 753 grams of dinitrosalicylic acid (DNSA) was
added while continuously stirring. The solution was then heated
slowly to about 105 C over about thirty minutes and maintained
throughout the remaining process. Once the DNSA was completely
dissolved, about 4352 grams of ammonium nitrate, about 122 grains
of potassium nitrate, about 227 grams of potassium carbonate
(whereby potassium nitrate and potassium carbonate taken together
provide a potassium source for phase stabilization of the ammonium
nitrate), about 595 grams of diammonium bitetrazole, and one liter
of water are added together into the vessel, while continuously and
mechanically stirring. A bright yellow precipitate forms
immediately in a viscous, paint-like consistency. After about one
hour, the mix forms crumbly solids. The mixing and heating is
continued until the desired dryness is obtained. If desired, the
mix may be formed or extruded into desired shapes such as pellets
or tablets and then dried to a desired moisture content, in an oven
for example.
Example 4
[0033] A composition containing about 73 wt % ammonium nitrate and
about 27 wt % monopotassium dinitrosalicylic acid was wet mixed and
formed into a homogeneous composition in accordance with the
present invention. The resultant composition included phase
stabilized ammonium nitrate at about 75.20 wt % (the PSAN
containing 64.95 wt % of ammonium nitrate and 10.25 wt % potassium
nitrate) and ammonium dinitrosalicylic acid at about 24.80 wt
%.
Example 5
[0034] A composition containing about 76.39 wt % phase stabilized
ammonium nitrate (containing about 7.64 wt % potassium nitrate as a
phase stabilizer); about 10 wt % di-ammonium salt of
5,5'-bis-1H-tetrazole; and about 13.61 wt % ammonium
dinitrosalicylic acid was dry mixed and formed into a homogeneous
composition in accordance with the present invention.
Example 6
[0035] A composition containing about 68.75 wt % ammonium nitrate;
about 7.64 wt % potassium nitrate; about 10 wt % diammonium salt of
5,5'-bis-1H-tetrazole; and about 13.61 wt % ammonium
dinitrosalicylic acid was dry mixed and formed into a homogeneous
composition in accordance with the present invention.
Example 7
[0036] A composition containing about 67.58 wt % ammonium nitrate;
about 7.51 wt % potassium nitrate; about 7.0 wt % diammonium salt
of 5,5'-his-1H-tetrazole; about 3.0 of dipotassium tartaric acid;
and about 1491 wt % ammonium dinitrosalicylic acid was dry mixed
and formed into a homogeneous composition in accordance with the
present invention.
Example 8
[0037] A composition containing about 68.4 wt % ammonium nitrate;
about 7.6 wt % potassium nitrate; about 3.5 wt % diammonium salt of
5,5'-bis-1H-tetrazole; and about 20.5 wt % ammonium
dinitrosalicylic acid was dry mixed and formed into a homogeneous
composition in accordance with the present invention.
Example 9--Comparative Example (PSAN-Tetrazole)
[0038] A composition containing about 73.5 wt % phase stabilized
ammonium nitrate and about 26.5 wt % ammonium salt of
5,5'-bis-tetrazole amine was dry mixed and formed into a
homogeneous composition in accordance with methods known in the
art.
Example 10--Comparative Example (PSAN-Tetrazole)
[0039] A composition/gas generant formed as provided in Example 9
was evaluated based on gaseous effluent. A given mass of the
composition contained about 3.9% carbon and when combusted in a
single-stage one mole inflator (that is containing one mole of gas
generant and operating at about 33-35 MPa), the parts per million
of the following gaseous products were measured from a 100 cubic
foot tank: 126 ppm carbon monoxide; 41 ppm ammonia; 13 ppm nitrogen
oxide; and 0 ppm nitrogen dioxide. The same mass of the same fuel
was also combusted in a double stage one mole inflator (that is
containing one mole of gas generant and operating at about 40 MPa),
and resulted in the following gaseous products as also measured
from a 100 cubic foot tank: 129 ppm carbon monoxide; 35 ppm
ammonia; 11 ppm nitrogen oxide; and 0 ppm nitrogen dioxide.
Example 11
[0040] A composition/gas generant formed as provided in Example 4
was evaluated based on gaseous effluent. A given mass of the
composition contained about 8.5% carbon and when combusted in a
single-stage one mole inflator (the same model inflator as used in
Example 10, and one that contained one mole of gas generant and
operated at about 33-35 MPa), the parts per million of the
following gaseous products were measured from a 100 cubic foot
tank: 173 ppm carbon monoxide; 14 ppm ammonia; 12 ppm nitrogen
oxide; and 0 ppm nitrogen dioxide. In accordance with the present
invention, the results illustrate that although this example had
more than twice the amount of carbon content in the gas generant
composition as compared to Example 10, there was only about a 37%
increase in the amount of carbon monoxide produced upon combustion.
Furthermore, the ammonia content was about one third or about 33%
of the amount of ammonia produced in the composition of Example 10.
The results were unexpected and counterintuitive in that the
expectation had been to see a linear and increased amount of carbon
monoxide produced upon combustion. Instead, useful amounts of
acceptable gas such as carbon dioxide were produced while
attenuating the production of carbon monoxide as analyzed from the
pre-combustion content of carbon in the gas generant. Accordingly,
the present invention supplants less desirable gases such as
ammonia with acceptable gases such as carbon dioxide, while
surprisingly mitigating the production of carbon monoxide.
Example 12
[0041] A composition/gas generant formed as provided in Example 4
was evaluated based on gaseous effluent. A given mass of the
composition contained about 6.0% carbon and when combusted in a
single-stage one mole inflator (the same model inflator as used in
Example 10, and one that contained one mole of gas generant and
operated at about 33-35 MPa), the parts per million of the
following gaseous products were measured from a 100 cubic foot
tank: 122 ppm carbon monoxide; 11 ppm ammonia; 20 ppm nitrogen
oxide; and 0 ppm nitrogen dioxide. In accordance with the present
invention, the results illustrate that although this example had
more than 150% if the amount of carbon content in the gas generant
composition as compared to Example 10, there was less carbon
monoxide (96.8% as compared to Example 10) produced upon
combustion. Furthermore, the ammonia content was about 26.8% of the
amount of ammonia produced in the composition of Example 10. The
results were unexpected and counterintuitive in that the
expectation had been to see a linear amount of carbon monoxide
produced upon combustion. Instead, useful amounts of acceptable gas
such as carbon dioxide were produced while attenuating the
production of carbon monoxide as analyzed from the pre-combustion
content of carbon in the gas generant. Accordingly, the present
invention supplants less desirable gases such as ammonia with
acceptable gases such as carbon dioxide, while surprisingly
mitigating the production of carbon monoxide.
[0042] The same mass of the same fuel was also combusted in a
double stage one mole inflator (the same model inflator as used in
Example 10, and one that contained one mole of gas generant and
operated at about 40 MPa), and resulted in the following gaseous
products as also measured from a 100 cubic foot tank: 135 ppm
carbon monoxide; 14 ppm ammonia; 12 ppm nitrogen oxide; and 0 ppm
nitrogen dioxide. Again, the present invention supplants less
desirable gases such as ammonia with acceptable gases such as
carbon dioxide, while surprisingly mitigating the production of
carbon monoxide.
Example 13--Comparative Example (PSAN-Tetrazole)
[0043] A composition/gas generant formed as in Example 10 was
combusted within a single stage one mole inflator as employed in
Example 10. The peak inflator chamber pressure attained in
sustained combustion was about 37 MPa at about 0.015 seconds after
combustion began. Gas outputs within a 60-liter ballistic tank were
measured from the beginning of combustion at T.sub.0 through 0.1
seconds after combustion. The ballistic tank pressure steadily
increased up through 0.05 seconds after combustion began, and then
leveled off at a sustained pressure of about 31-32 MPa through 0.1
seconds after combustion began. Sustained pressure indicates
suitable gas generating properties that accommodate the sustained
pressure utilized in vehicle occupant protection systems.
Example 14
[0044] A composition/gas generant formed in accordance with the
present invention and as described in Example 4, was combusted
within a single stage one mole inflator as employed in Example 10.
The peak inflator chamber pressure attained in sustained combustion
was about 32 MPa at about 0.013 seconds after combustion began. Gas
outputs within a 60-liter ballistic tank were measured from the
beginning of combustion at T.sub.0 through 0.1 seconds after
combustion. The ballistic tank pressure steadily increased up
through 0.05 seconds after combustion began, and then leveled off
at a sustained pressure of about 28-31 MPa through 0.1 seconds
after combustion began. Sustained pressure indicates suitable gas
generating properties that accommodate the sustained pressure
utilized in vehicle occupant protection systems. Quite
unexpectedly, it has been discovered that compositions provided in
accordance with the present invention operate at a peak inflator
pressure that is 5 MPa lower than the inflator of Example 13, and
yet provide substantially equivalent amounts of sustained pressure
in the ballistic tank. Accordingly, it can be seen that the present
compositions can sustainably combust at a lower inflator pressure
thereby relaxing the structural requirements of the inflator while
yet providing similar performance from the standpoint of gas
generation over time.
Example 15
[0045] A composition/gas generant formed in accordance with the
present invention and as described in Example 4, was combusted
within a single stage one mole inflator similar or equivalent to
the one employed in Example 10. The peak inflator chamber pressure
attained in sustained combustion was about 26 MPa at about 0.015
seconds after combustion began. Gas outputs within a 60-liter
ballistic tank were measured from the beginning of combustion at
T.sub.0 through 0.1 seconds after combustion. The ballistic tank
pressure steadily increased up through 0.05 seconds after
combustion began, and then leveled off at a sustained pressure of
about 30-28 MPa through 0.1 seconds after combustion began.
Sustained pressure indicates suitable gas generating properties
that accommodate the sustained pressure utilized in vehicle
occupant protection systems. Quite unexpectedly, it has been
discovered that compositions provided in accordance with the
present invention operate at a peak inflator pressure that is about
11 MPa lower than the inflator of Example 13, and yet provide
substantially equivalent amounts of sustained pressure in the
ballistic tank. Accordingly, it can be seen that the present
compositions can sustainably combust at a lower inflator pressure
thereby relaxing the structural requirements of the inflator while
yet providing similar performance from the standpoint of gas
generation over time.
Example 16
[0046] A composition/gas generant formed in accordance with the
present invention and as described in Example 4, was combusted
within a single stage one mole inflator similar or equivalent to
the one employed in Example 10. The peak inflator chamber pressure
attained in sustained combustion was about 22.5 MPa at about 0.013
seconds after combustion began. Gas outputs within a 60-liter
ballistic tank were measured from the beginning of combustion at
T.sub.0 through 0.1 seconds after combustion. The ballistic tank
pressure steadily increased up through 0.05 seconds after
combustion began, and then leveled off at a sustained pressure of
about 30-28 MPa through 0.1 seconds after combustion began.
Sustained pressure indicates suitable gas generating properties
that accommodate the sustained pressure utilized in vehicle
occupant protection systems. Quite unexpectedly, it has been
discovered that compositions provided in accordance with the
present invention operate at a peak inflator pressure that is about
14.5 MPa lower than the inflator of Example 13, and yet provide
substantially equivalent amounts of sustained pressure in the
ballistic tank. Accordingly, it can be seen that the present
compositions can sustainably combust at a lower inflator pressure
thereby relaxing the structural requirements of the inflator while
yet providing similar performance from the standpoint of gas
generation over time.
Example 17
[0047] A composition/gas generant formed in accordance with the
present invention and as described in Example 4, was combusted
within a single stage one mole inflator similar or equivalent to
the one employed in Example 10. The peak inflator chamber pressure
attained in sustained combustion was about 20 MPa at about 0.015
seconds after combustion began. Gas outputs within a 60-liter
ballistic tank were measured from the beginning of combustion at
T.sub.0 through 0.1 seconds after combustion. The ballistic tank
pressure steadily increased up through 0.05 seconds after
combustion began, and then leveled off at a sustained pressure of
about 28-30 MPa through 0.1 seconds after combustion began.
Sustained pressure indicates suitable gas generating properties
that accommodate the sustained pressure utilized in vehicle
occupant protection systems. Quite unexpectedly, it has been
discovered that compositions provided in accordance with the
present invention operate at a peak inflator pressure that is about
17 MPa lower than the inflator of Example 13, and yet provide
substantially equivalent amounts of sustained pressure in the
ballistic tank. Accordingly, it can be seen that the present
compositions can sustainably combust at a lower inflator pressure
thereby relaxing the structural requirements of the inflator while
yet providing similar performance from the standpoint of gas
generation over time.
Example 18
[0048] A composition/gas generant formed in accordance with the
present invention and as described in Example 4, was combusted
within a single stage one mole inflator similar or equivalent to
the one employed in Example 10. The peak inflator chamber pressure
attained in sustained combustion was about 17.5 MPa at about 0.015
seconds after combustion began. Gas outputs within a 60-liter
ballistic tank were measured from the beginning of combustion at
T.sub.0 through 0.1 seconds after combustion. The ballistic tank
pressure steadily increased up through 0.05 seconds after
combustion began, and then leveled off at a sustained pressure of
about 28-27 MPa through 0.1 seconds after combustion began.
Sustained pressure indicates suitable gas generating properties
that accommodate the sustained pressure utilized in vehicle
occupant protection systems. Quite unexpectedly, it has been
discovered that compositions provided in accordance with the
present invention operate at a peak inflator pressure that is about
19.5 MPa lower than the inflator of Example 13, and yet provide
substantially equivalent amounts of sustained pressure in the
ballistic tank. Accordingly, it can be seen that the present
compositions can sustainably combust at a lower inflator pressure
thereby relaxing the structural requirements of the inflator while
yet providing similar performance from the standpoint of gas
generation over time.
Example 19
[0049] A composition formed as described in Example 4 exhibited
burn rates in inches per second (ips) of about: 0.64 at 1000 pounds
per square inch gauge (psig); 0.82 at 2000 psig; 0.98 at 2500 psig;
1.02 at 3500 psig; 1.12 at 4500 psig; and 1.22 at 5500 psig.
Example 20--Comparative Example (PSAN-Tetrazole)
[0050] A composition formed as described in Example 10 exhibited
burn rates in inches per second (ips) of about: 0.48 at 1000 pounds
per square inch gauge (psig); 0.82 at 2000 psig; 0.92 at 2500 psig;
1.02 at 3500 psig; 1.08 at 4500 psig; and 1.12 at 5500 psig.
Example 21
[0051] A composition is formed to contain a primary fuel of
ammonium dinitrosalicylic acid at about 10-20 weight percent, a
secondary fuel of diammonium salt of 5,5'-bis-1H-tetrazole at about
3-15 weight percent, and phase stabilized ammonium nitrate
(containing ammonium nitrate and potassium nitrate) as an oxidizer
with the ammonium nitrate at about 60-75 weight percent and
potassium nitrate at about 5-10 weight percent.
[0052] When compared to Example 19, it can be seen that
compositions of the present invention exhibit suitable burn rates
substantially equivalent to another state-of-the-art gas generant
composition as described in Example 10.
[0053] As illustrated above, gas generating compositions of the
present invention including salts of dinitrosalicylic acid combined
with phase stabilized ammonium nitrate result in low combustion
solids, with reduced levels of less desirable combustion gases
compared to other state-of-the-art gas generants while operating at
reduced combustion pressures. Other benefits may include reduced
manufacturing costs, improved thermal stability, improved chemical
stability, and/or reduced processing costs.
[0054] As shown in FIG. 1, an exemplary inflator or gas generating
system 10 incorporates a dual chamber design containing a primary
gas generating composition 12 formed as described herein, that may
be manufactured as known in the art. U.S. Pat. Nos. 6,422,601,
6,805,377, 6,659,500, 6,749,219, and 6,752,421 exemplify typical
airbag inflator designs and are each incorporated herein by
reference in their entirety.
[0055] Referring now to FIG. 2, the exemplary inflator or gas
generating system 10 described above may also be incorporated into
an airbag system 200. Airbag system 200 includes at least one
airbag 202 and an inflator 10 containing a gas generant composition
12 in accordance with the present invention, coupled to airbag 202
so as to enable fluid communication with an interior of the airbag.
Airbag system 200 may also include (or be in communication with) a
crash event sensor 210. Crash event sensor 210 includes a known
crash sensor algorithm that signals actuation of airbag system 200
via, for example, activation of airbag inflator 10 in the event of
a collision.
[0056] Referring again to FIG. 2, airbag system 200 may also be
incorporated into a broader, more comprehensive vehicle occupant
restraint system 180 including additional elements such as a safety
belt assembly 150. FIG. 2 shows a schematic diagram of one
exemplary embodiment of such a restraint system. Safety belt
assembly 150 includes a safety belt housing 152 and a safety belt
100 extending from housing 152. A safety belt retractor mechanism
154 (for example, a spring-loaded mechanism) may be coupled to an
end portion of the belt. In addition, a safety belt pretensioner
156 containing gas generating composition 12 may be coupled to belt
retractor mechanism 154 to actuate the retractor mechanism in the
event of a collision. Typical seat belt retractor mechanisms which
may be used in conjunction with the safety belt embodiments of the
present invention are described in U.S. Pat. Nos. 5,743,480,
5,553,803, 5,667,161, 5,451,008, 4,558,832 and 4,597,546,
incorporated herein by reference. Illustrative examples of typical
pretensioners with which the safety belt embodiments of the present
invention may be combined are described in U.S. Pat. Nos. 6,505,790
and 6,419,177, incorporated herein by reference.
[0057] Safety belt assembly 150 may also include (or be in
communication with) a crash event sensor 158 (for example, an
inertia sensor or an accelerometer) including a known crash sensor
algorithm that signals actuation of belt pretensioner 156 via, for
example, activation of a pyrotechnic igniter (not shown)
incorporated into the pretensioner. U.S. Pat. Nos. 6,505,790 and
6,419,177, previously incorporated herein by reference, provide
illustrative examples of pretensioners actuated in such a
manner.
[0058] It should be appreciated that safety belt assembly 150,
airbag system 200, and more broadly, vehicle occupant protection
system 180 exemplify but do not limit gas generating systems
contemplated in accordance with the present invention.
[0059] In yet another aspect of the invention, a method of making
gas generating compositions containing DNSA and PSAN is provided.
Because of the acidic nature of DNSA, dry mixing may not be
desired. Furthermore, using a salt of DNSA or an adduct of DNSA and
another compound may be desirable if dry mixing, however, forming
and isolating the respective DNSA derivative may be time consuming
and costly. Accordingly, forming a DNSA salt or adduct in situ
obviates the need to form the salts or adducts independently.
Furthermore, co-crystallization of PSAN can occur at the same time.
To begin with, an aqueous slurry of stoichiometric amounts of
reactants is prepared including stoichiometrically appropriate,
amounts of DNSA, ammonium nitrate, and a potassium source such as
potassium nitrate, potassium hydroxide, or potassium carbonate. The
resultant formulation as co-precipitated is ammonium DNSA and PSAN.
Alternatively, a wet mix of DNSA, an ammonium source such as
ammonium hydroxide or di-ammonium carbonate, and PSAN will provide
the same results. Even further, a wet mix of DNSA, an ammonium
source, a potassium source, and ammonium nitrate would also produce
ammonium DNSA and PSAN. All of the aforementioned aqueous mixes
provide a base to form a salt of DNSA as a fuel, phase stabilized
ammonium nitrate as an oxidizer, wherein sufficient potassium ion
is present to stabilize the ammonium nitrate. The aqueous mixture
may be blended at room temperature and then gently heated to drive
off excess moisture and co-precipitate a blend of DNSA salt and
PSAN.
Exemplary Salt-Forming Reactions of DNSA:
[0060] DNSA+potassium carbonate=potassium DNSA+water+carbon
dioxide
DNSA+potassium hydroxide=potassium DNSA+water
[0061] One advantage of the wet mix method is the formation of
relatively small DNSA salt crystals. As shown in the microstructure
of FIG. 3, PSAN is represented as a plurality of large smooth
portions having smaller DNSA salt crystals interspersed within the
PSAN. As shown, PSAN grains are relatively large, and because of
the relatively smaller size of the DNSA salt crystals, the DNSA
salt crystals embed between the relatively larger PSAN grains,
thereby providing an intimate mixture or blend of the fuel and the
oxidizer. As a result, the resultant free-flowing co-precipitated
blend may be pressed or compacted into tablets wafers, or other
shapes very readily without having to grind or mill ingredients
together as dry ingredients. This eliminates an additional
processing step. It is also believed that the small DNSA crystals
may contribute to improved or enhanced ballistic and effluent
performance of an associated inflator, as described in the
examples, particularly because of favorable combustion kinetics due
to the intimate mixture of DNSA within PSAN.
[0062] Accordingly, a method of processing gas generating
compositions of the present invention is provided. Liquid or
granulated constituents are preferred in the following steps. The
following steps may be followed in all wet method formulations. It
should be appreciated that initially, the DNSA must be solvated
within the solvent before any other step is conducted. The order of
steps 4-8 is not critical, and these steps may be done in any
desired order. [0063] 1. Provide a solvent within a jacketed mixing
vessel. The solvent may, for example, be selected from water,
ethanol, propanol, methanol, or some other solvent miscible with
water. [0064] 2. Place a stoichiometric or predetermined amount of
dinitrosalicylic acid in the solvent. [0065] 3. Stir the solution.
[0066] 4. If desired, the solution may be heated and the
temperature of the solution may be maintained at temperatures about
100-110 C throughout the process. [0067] 5. Add at least one
oxidizer selected from ammonium nitrate and phase stabilized
ammonium nitrate to the solution and continue to stir. [0068] 6.
Add a precipitating agent to the composition and continue to stir.
The precipitating agent may be a potassium source such as potassium
nitrate, potassium hydroxide, or potassium carbonate if ammonium
nitrate is added in step five. Alternatively, the precipitating
agent may be an ammonium source such as ammonium hydroxide,
ammonium bicarbonate, or ammonium carbonate when adding phase
stabilized ammonium nitrate in Step 5. [0069] 7. If desired, a
secondary fuel as described herein, diammonium salt of
5,5'-bis-1H-tetrazole for example, may be added to the slurry while
continually stirring. [0070] 8. If desired, additional solvent such
as distilled water may be added to enhance the solubility of the
constituents that are added to the vessel, while continuing to heat
and stir the solution. A solid then forms. [0071] 9. If desired,
the solids and slurry may be continually stirred while heating the
solids and slurry, until the desired dryness within the resultant
solid is attained. [0072] 10. If desired, the solid precipitate may
be formed into desired shapes by compression and other known
methods of forming tablets or pellets, for example.
[0073] Compositions 12 formed by the method provided above are also
provided as are gas generators 10 that contain the compositions 12.
Further, gas generating systems such as a seat belt assembly 200 or
vehicle occupant protection system 180 are also provided,
containing a composition 12 formed by the method provided
above.
[0074] The formation of small particles of DNSA salt crystals is
advantageous in that the relatively small particles, equal to or
less than 10 microns in length or width or depth, are readily
entrained or precipitated or embedded within the much larger
ammonium nitrate crystals as shown in FIG. 3. Unlike other
precipitates, the microstructure is therefore readily amenable to
pressing into tablets, wafers, or other shapes, without having to
grind or mill ingredients together as dry ingredients. The wet mix
process forms rounded granules that flow well in-bulk in press
feeders to make tablets, for example. In essence, the
aforementioned process results in reduced processing of raw
materials, and fewer number of ingredients compared to dry
blending. It is also results in free flowing granules from the
wet-mix process and obviating the need to mill the constituents or
the composition.
[0075] It should further be understood that the preceding is merely
a detailed description of various embodiments of this invention and
that numerous changes to the disclosed embodiments can be made in
accordance with the disclosure herein without departing from the
scope of the invention. The preceding description, therefore, is
not meant to limit the scope of the invention. Rather, the scope of
the invention is to be determined only by the appended claims and
their equivalents.
* * * * *