[0001] This invention relates to materials for prowinding an efficient propulsion of vehicles
such as rockets. The invention further relates to materials having a high density
and stable properties at ambient temperatures and providing considerable energy at
elevated temperatures for producing an efficient propulsion of vehicles such as rockets.
The invention is particularly concerned with propellants which combust to provide
end products which are not deleterious to the propulsion chamber.
[0002] For many rocket applications, the amount of propulsion energy capable of being stored
in a limited volume of propulsion material is of prime importance. By increasing the
amount of energy in each cubic inch of volume of such propulsion material, the volume
of propulsion material required to store a particular amount of energy can be accordingly
reduced. This in turn allows the rocket to be reduced in size and in weight, thereby
causing the drag imposed on the rocket during the flight of the rocket through a fluid
such as air or water to be correspondingly reduced. Since the drag imposed on the
rocket is reduced, the amount of energy required to propel the rocket through a particular
distance is reduced so that the amount of propulsion material required becomes correspondingly
reduced. This in turn allows a further reduction in the size of the vehicle, with
a corresponding reduction in drag. For the above reasons, a rocket required to push
a heavy payload or move through a dense or viscous medium may have an increased efficiency
if its propulsion material can be stored in a relatively small volume and can be provided
with a high energy level.
[0003] The propulsion energy of a material is commonly measured in pound-seconds of force
per pound of propellant (lb.sec./lb.). For example, if a propellant has a "specific
impulse" of two hundred (200) lb.sec./lb., it can produce in a rocket motor two hundred
(200) pounds of thrust (or force), per pound of weight of the propellant, for a duration
of one (1) second. It can also produce any combination of thrust and time which, when
multiplied, equals two hundred (200) lb.sec.per pound of propellant.
[0004] Various attempts have been made to increase the efficiency of propellants. For example,
attempts have been made to increase the temperature of combustion of the different
materials in the propellant. One broad line of effort has been to use, in the propellant,
materials which have a low heat of formation or a low bond energy so that an increased
amount of energy is available to be converted into heat. However, in order to have
a low heat of formation, the materials generally must have a low margin of stability
so that they are more dangerous to process, to store and to use than conventional
materials.
[0005] Another approach toward increasing the specific impulse of the propulsion material
has been to de.crease the average molecular weight of the exhaust products. For example,
attempts have been made to combust highly energetic materials such as beryllium. However,
these metals are quite toxic when vaporized and greatly increase the health hazards
of anyone using such metals. Furthermore.any use of such metals in a combustible material
would tend to add to contaminants in the atmosphere, if the metals should become adopted
on a widespread basis.
[0006] When materials such as magnesium, beryllium and titanium are used in the propulsion
material, the density of the propulsion material tends to be reduced since magnesium,
titanium and beryllium are relatively light. This has tended to be disadvantageous
since the amount of energy obtained in combustion per cubic inch of volume becomes
reduced. In other words, even though such metals as beryllium, titanium and magnesium
have a high energy, the available energy per cubic inch of the propulsion material
has not tended to be increased in view of the decreased density of the material.
[0007] When metals such as beryllium have been used in the propulsion material, gases such
as hydrogen have been added to the material, generally as a hydride of the metals.
These hydrides tend to be somewhat unstable, requiring considerable care and special
equipment for safe handling of them.
[0008] An extensive list of metallized solid propellants was published in 1966 by Reinhold
Publishing Corp. in a book entitled, "Propellant Chemistry". This book was written
by Stanley F. Sarner, Senior Research Chemist and Theoretical Analyst of Thiokol Chemical
Corporation of Elkton, Maryland. This book lists values of specific impulse and density
for approximately twenty (20) formulations of solid propellants which allegedly provide
a high energy. The values of specific impulse for these formulations range upwardly
to approximately 313.8 lb.sec.per pound of propellant formulation. The value density
are -as high as approximately 0.0737 lb./inch
3. However, the maximum value of density impulse capable of being provided by any of
these formulations is less than approximately 17.9 lb.sec./in
3. Furthermore, these formulations involve the use of toxic materials. Actually, practical
and operable formulations heretofore available provide maximum values of density impulse
of approximately fifteen (15) lb.sec./in
3. As will be appreciated, values of density-impulse are important since they indicate
the amount of energy available for propulsion per cubic inch of propulsion material.
[0009] United States Patent No. 3,945,20.2 issued to me and Hugh J. McSpadden discloses
a propellant which overcomes the disadvantages described above. The propulsion materials
disclosed and claimed in patent 3,945,202 have a high density and provide a high value
of specific impulse. They can be safely and easily formulated and are stable 'at ambient
and elevated temperatures. They are not toxic in their formulation, storage or use.
Furthermore, density-impulses as high as approximately twenty-four (24) lb.sec. per
pound of formulation have been obtained from the propulsion materials disclosed and
claimed in this patent.
[0010] The propulsion materials disclosed and claimed in patent 3,945,202 include a binder,
an oxidizer..and a fuel additive. The binder preferably constitutes a hydrocarbon;
the oxidizer preferably constitutes an inorganic lead oxidizer; and the fuel additive
preferably constitutes particles of a metal such as aluminum. The propellants combust
in the combustion chamber to produce end products, one of which may be vaporized lead.
[0011] The production of vaporized lead in the combustion chamber is not advantageous. This
results from the fact that lead vapor is an effective solvent for steel and for other
me.tals. Lead vapor condenses at a temperature of approximately 1751°C, whereas iron
melts at a temperature of approximately 1530°C. Since the combustion chamber will
tend to be made from a material such as iron, the walls of the combustion chamber
tend to become melted as the lead is vaporized during combustion. Furthermore, the
heat of fusion of iron is approximately 3.67 kilocalories per mole and the heat of
vaporization of lead is approximately 46.34 kilocalories per mole. As a result, for
each mole of lead vapor condensate produced, 12.6 moles of iron can be melted.
[0012] Although lead vapor acts as a solvent on steel and other metals, lead oxide does
not have such an effect. This results from the fact that lead oxide condenses at a
temperature of approximately 1472°C, which is below the melting temperature of iron.
Since lead oxide does not have any adverse effects on the. walls of the combustion
chamber, it is desirable that the end products of the combustion of inorganic lead
oxidizer salts should be lead oxide rather than lead.
[0013] This invention provides a propellant which preferably includes a binder having hydrocarbon
linkages, an inorganic lead oxidizer salt and a fuel made from a fuel additive such
as aluminum. The propellant of this invention combusts to produce as an end product
lead oxide rather than lead. The propellant of this invention has a density-impulse
which approximates, if not exceeds, the density-impulses of the propellants of patent
3,945,202 while providing significantly reduced temperatures during the combustion
of the propellant.
[0014] The propellant of this invention preferably includes a binder having hydrocarbon
linkages and a lead compound oxidizer formed from an inorganic lead oxidizer salt.
This oxidizer has dense characteristics and stable properties at ambient temperatures
and through a particular range of temperatures above ambient. The propellant also
includes in one embodiment, a fuel additive, preferably a metal such as aluminum,
having properties of being oxidized by the oxidizer and of reducing the lead. The
fuel additive has a percentage by weight relative to the lead compound oxidizer to
reduce the lead to the lead oxide. The fuel additive is preferably included in such
embodiment of the propellant in the range to approximately twenty precent (20%) by
weight and is preferably in a fragmentary form. The binder preferably is included
in the range of approximately eight percent (8%) to ten percent (10%) by weight. A
second oxidizer such as potassium perchlorate may also be included in the propellant..
The oxidizers are preferably included in the propellant in the range of approximately
seventy-two percent (72%) to ninety-two percent (92%) by weight. An additional binder
such as carbon can also be included in the propellant.
[0015] A second embodiment of the propellant preferably includes a binder also acting as
a reducing agent and a lead compound oxidizer formed from an inorganic lead oxidizer
salt.
[0016] This oxidizer has dense characteristics and stable properties at ambient temperatures
and through a range of temperatures above ambient. A second oxidizer made from a metallic
salt such as potassium perchlorate may also be included in the propellant. Carbon,
preferably in particulate form, may also be included in the mixture. The second embodiment
dies not include a fuel additive such as aluminum.
[0017] The different materials are included in the second embodiment in relative amounts
by weight to reduce the lead salt in the oxidizer to lead oxide. The oxidizing materials
including the lead compound oxidizer may be included in the propellant in the range
of approximately eighty-four percent (84%) to ninety-one percent (91%) by weight,
the hydrocarbon in the range of approximately eight percent (8%) to ten percent (10%)
by weight and the carbon in the range of approximately zero percent (0%) to eight
percent (8%) by weight.
[0018] The propellant of this invention has certain distinct advantages over the propellants
of the prior art. It provides high density-impulses and, when combusted, produces
end products which do not have any deleterious effects. This results at least partly
from the fact that the propellant produces lead oxide rather than lead when it combusts.
The propellant is also advantageous in that it generates relatively low temperatures
during combustion. For example, temperatures less than 1000°F can be generated by
at least some of the propellants of this invention. The invention accomplishes this
by eliminating the fuel such as aluminum from the propellant. This is further advantageous
in that it tends to simplify the formulation of the
0
[0019] By forming lead oxide and the other exhaust gases at relatively low temperatures
during the combustion of the propellant, the formation of the propulsion chamber can
be simplified. For example, the walls of the chamber can be made from a relatively
standard material such as steel or copper and the heat insulation in the walls of
the chamber can be minimized.
[0020] In the drawings:
Figure I illustrates the configuration of a combustion chamber suitable for combusting
the propellants of this invention;
Figure 2 constitutes curves showing the relationship between the pressure of the exhaust
gases from the propellant burning in the chamber of Figure 1 and the rate at which
the propellant burns;
Figure 3 is a curve illustrating the relationship between time and pressure of the
exhaust gases from the burning propellant;
Figure 4 is a curve in triangular coordination of the relative percentages of different
chemical components in one embodiment of the propellant of this invention for different
formulations of such propellant.
Figure 5 is a curve in triangular coordination of the relative percentages of different
chemical components in another embodiment of the propellant of this invention for
different formulations of such propellant.
[0021] Figure 1 schematically illustrates a chamber, generally shown at 10, for combusting
the propellants of this invention. The walls of the chamber 10 may be made from a
suitable material such as iron or steel. The components of the propellant combust
in a burning area 12 and escape through a throat area 14. As will be seen, the propellant
is isolated ; from the atmosphere so that the combustion occurs entirely from the
components in the propellant.
[0022] Figure 2 illustrates the relationship between the pressure of the gases escaping
from the burning area 12 into the throat area 14 and the rate at which the propellant
is combusted in the burning area 12. As will be seen, the relationship between rate
and pressure is essentially linear with changes in pressure. Figure 2 also indicates
the relationship between pressure of the gases escaping from the burning area 12 into
the throat area 14 and the area ratio. As will be seen, this relationship is also
essentially linear with changes in pressure.
[0023] Figure 3 illustrates the pressure of the gases at progressive instants of.time in
the chamber illustrated in Figure 1. As will be appreciated, the term t
a represents the time between an initial pressure of ten percent (10%) of maximum pressure
during the period of pressure build up and ten percent (10%) of maximum pressure during
the period of pressure reduction.
[0024] The propellants of this invention include a binder preferably having hydrogen and
carbon linkages. Preferably the binder includes a material having a formula such as
CH
2. The binder preferably has properties of being cured at a particular temperature.
The binder may also be selected from a group including polysulfides, carboxy-terminated
polybutadiene polymers, tetrafluorethylene, polyfluorethylene propylene and acetal
homopolymers (which do not cure but remain thermoplastic). These binders are advantageous
since they retain good physical properties even in environments at high temperatures.
For example, acetal homopolymers designated by the trademark or tradename "Delrin"
melt at approximately 354°F and tetrafluorethylenes designated by the trademark or
tradename "Teflon" melt at temperatures above 600°F. Certain of these binders such
as the polysulfides and the carboxy-terminated polybutadiene polymers are castable
and can be cured at ambient temperatures and also at oven temperatures with other
materials to form the propellant formulations constituting the invention.
[0025] A number of propulsion materials have been formulated successfully with a mixture
of a binder such as polybutadiene with carboxy-terminated linkages and a curing agent
such as 1, 2, 4 Tris [2-(1-Aziridinyl)Ethyl] Trimellitate. The polybutadiene has been
designated as "Butarez CTL Type
II". Such a binder constitutes a liquid rubber polybutadiene with carboxy-terminated
linkages. It has carboxy end-groups on both ends of the polymer chain, as illustrated
as follows:

The binder has a relatively narrow molecular weight distribution and is not easily
crystallized. This allows the cured composition of the polymer to remain rubbery to
very low temperatures.
[0026] A lead compound oxidizer, such as an oxidizer formed from an inorganic lead oxidizer
salts, is also included in the propellant. The oxidizer preferably constitutes lead
nitrate. However, other lead oxidizers such as lead dioxide or lead iodate or any
combination of the lead compounds specified above may also be used.
[0027] Lead nitrate has approximately 0.041 moles of oxygen per cubic centimeter. It has
a specific gravity of approximately 4.53 grams per cubic centimeter. It has a decomposition
temperature of approximately 470°C and has a heat of formation of only approximately
107.35 Kilocalories per mole of oxygen. It can be reacted chemically to produce reasonably
good enthalpy.
[0028] Lead vaporizes at a temperature of approximately 1751°C. Since this temperature is
considerably higher than the melting temperature of iron or steel,, the lead melts
the. iron or steel when it vaporizes and contacts the iron or steel. Since the chamber
10 is generally made from iron or steel, the vapors from the propellant attack the
iron or steel when the lead compound oxidizer becomes reduced to lead vapor. It is
accordingly desirable to have the lead compound oxidizer become reduced to an end
product other than lead. For example, lead oxide condenses at a temperature of approximately
1472°C, which is below the melting temperature of iron. As a result, lead oxide vapor
does not act as a solvent on iron or steel.
[0029] A fuel additive is also included in one embodiment of the propellant of this invention.
The fuel additive is preferably a metal such as aluminum, which becomes oxidized to
aluminum oxide by the oxidizer. Preferably the. aluminum is in a fragmented form such
as in a particulate form. Although such metal is commonly added as a powder, it can
be added as filaments of fine wire or as sheets or strips of thin foil. When used
in a fragmentary form such as in filaments or sheets or strips, the aluminum provides
substantial physical reinforcement to the propellant. In these forms, the aluminum
can provide composites or laminates of high strength. This is desirable since considerable
forces must be withstood by a propellant in various applications such as anti-missile
rocket applications.
[0030] Other metals than aluminum are also theoretically useful as the fuel additive in
some propulsion formulations. These include beryllium, magnesium, lithium and titanium.
All of these metals are advantageous since they have high melting temperatures. For
example, aluminum has a melting temperature of approximately 1220°F and strontium
has a melting temperature of approximately 1202°F. In this way, the propulsion materials
can be formulated with reasonable safety when these additives are included. Furthermore,
although the melting temperatures of these metals are relatively high, they are still
below the melting temperature of steel or iron.
[0031] Other materials may be used as secondary oxidizers in association with the inorganic
lead compounds. These include strontium nitrate, barium nitrate, cesium nitrate, rubidium
nitrate, ammonium perchlorate, potassium permanganate, potassium chlorate, potassium
periodate, potassium nitrate, urea nitrate and guanidine nitrate. In addition to serving
as oxidizers, these materials have the properties of altering the ballistic and physical
properties of the rocket as desired. This secondary oxidizer preferably constitutes
potassium perchlorate.
[0032] Various additives have been used to control the rate of propellant burning or to
change the sensitivity of the burning rate to pressure. These additives have included
copper manganite, cupric oxide, iron oxide and a liquid iron containing a burning
rate catalyst designated by the trademark or tradename "HYCAT 6". The amount of additive
used has varied between zero percent (0%) and five percent (5%) by weight of the propulsion
formulation, but in certain formulations the amount of additive has been as high as
approximately fifteen percent (15%). Other additives tested have included chromium
oxide, manganese dioxide, cuprous oxide, n-butyl ferrocene, cupric acetylacetonate,
molybdenal-bis-acetylacetonate, titanium acetylacetonate, calcium oxalate and lead
oxalate.
[0033] The different materials have been included as follows in the propellant of the prior
art:

[0034] The inclusion of the different materials in the relative amounts of equation (1)
offers a number of important advantages. For example, the formation of carbon monoxide
is desirable because it constitutes approximately -105.6 Kilocalories (-25.4 Kilocalories
per mole) of combustion enthalpy. This tends to provide a cooling effect on the combustion
gases. Since the carbon is oxidized to carbon monoxide, the carbon cannot absorb heat.
This is particularly important since carbon has a high heat capacity.
[0035] The propulsion formulation specified above also has other important advantages. For
example, although the values of specific impulse for the propellants using the oxidizers
specified above range from approximately 190 lb. sec/lb. to approximately 260 lb.
sec/lb. and are accordingly within the range of previous propellants, the high density
of the propellants using these oxidizers produces theoretical values of density-impulse
from approximately 22 lb. sec./in
3 to approximately 27.6 lb. sec./in
3. Comparing such values with previously available values of approximately 15 lb. sec./in
3, this represents an increase of approximately sixty percent (60%) over the density-impulses
of previously available propellants.
[0036] In spite of the advantages described above, there is one serious disadvantage from
the reaction specified in equatior (1). This results from the formation of vaporized
lead. As previously described, the vaporized lead tends to melt the steel or iron
walls of the combustion chamber, thereby limiting the effectiveness of the combustion
chamber. The lead vapor iv produced by the thermal decomposition of the lead nitrate
in the material specified in equation (1).
[0037] The materials specified above can be varied in relative amounts to overcome the disadvantage
specified in the previbus paragraph without losing any of the advantages specified
above. For_example, the different materials can be included in the relative percentages
specified below for one embodiment of the invention to provide a combustion which
produces lead oxide, rather than lead, in the combustion gases:

[0038] The inclusion of the different materials in the percentages specified above in equation
(2) offers certain distinct advantages. For example, the formation of lead oxide in
the combustion gases inhibits any tendency for the walls of the combustion chamber
to melt. This results from the fact that lead oxide vaporizes at a temperature below
the melting temperature of steel. or iron.
[0039] The improved formulation of equation (2) also offers other important advantages.
For example, the formulation of equation (2) provides an increased enthalpy over the
formulation of equation (1) even though the amount of fuel in the formulation of equation
(2) is significantly reduced relative to the amount in the formulation of equation
(1). Specifically, the formulation of equation (2) produces ah estimated combustion
enthalpy of approximately -988 gram-calories/gram versus approximately -931 gram-calories/gram
estimated for the formulation of equation (1).
[0040] The increased enthalpy for the formulation of equation (2)' results in part from
the formation of lead oxide. The heat of formation of lead oxide is approximately
-52.1 Kilocalories per mole. This is in contrast to an endothermic heat of absorption
of approximately 46.34 Kilocalories per mole for the formation of lead. This produces
a resultant increase in combustion enthalpy of 52.1 + 46.34
= 98.44 Kilocalories per mole for the formulation of equation (2) relative to the formulation
of equation (1).
[0041] As will be seen, there is a reduction of one third (1/3) of a mol of aluminum oxide
in the propellant of equation (2) relative to the propellant of equation (1). This
represents a reduction in enthalpy, particularly since the reduction of one third
(1/3) of a mole in the amount of aluminum oxide formed represents a loss in enthalpy
such as approximately -133 Kilocalories. However, the net enthalpy per gram is increased
by the relative increase in the amount of oxidizer and binder in the propellant of
equation (2) relative to the propellant of equation (1). This relative increase results
from the reduction of the weight and volume of aluminum in the propellant of equation
(2) relative to the propellant of equation (1).
[0042] The propellant of equation (2) produces an increase of approximately three percent
(3%) in density-impulse relative to the propellant of equation (1). The propellant
of equation (2) maintains burning rates and other performance characteristics comparable
to the propellant of equation (1). As a result, the propellant of equation (2) can
provide a simple replacement for the propellant of equation (1). However, the elimination
of lead vapor from the exhaust products of the propellant of equation (2) offers significant
improvements in the design of the combustion chamber. This can be accomplished by
reductions in the required insulating weight and volume of the combustion chamber,
by reduction in the size of special seals and heat sinks and reduction in the heat
transfer of vapor condensates at -temperatures above the melting point of the material
of the chamber walls. As a result, the propellant of equation (2) provides an aggregate
improvement in product performance and reliability relative to the propellant of equation
(1).
[0043] An additional improvement has resulted from a further reduction in the level of aluminum
from that of equation (2). This further reduction in aluminum produces a reduction
in combustion enthalpy and gas temperatures. This in turn enables the design of members
such as rockets with increased burning time without encountering any serious material
problems in the construction of rocket chambers and nozzles. The further reduction
in the level of aluminum has caused a chemical reaction to be produced as follows:

As will be seen, the propellant of equation (3) has the advantage of the propellant
of equation (2) because lead oxide, rather than lead, is obtained as one of the combustion
products. The decreased amount of the fuel such as aluminum causes the estimated enthalpy
to be reduced to an estimated value such as approximately -826 gram-calories/gram
from an estimated value of approximately -931 gram-calories/gram for the propellant
of equation (1). This constitutes a reduction of approximately eleven and three tenths
percent (11.3%) in enthalpy. However, the propellant of equation (3) has an increase
of approximately ten percent (10%) in density relative to the propellant of equation
(1). This increase is from a value of approximately 0.10 lb/cubic inch to a value
of approximately 0.11 lb/cubic- inch. This results in an estimated decrease of approximately
only one percent (1%) in the density-impulse of the propellant of equation (3) relative
to the propellant of equation (1).
[0044] The slight reduction in density-impulse in the formulation of equation (3) relative
to the formulation of equation (1) is in contrast to the significant reduction in
the temperatures of the combustion gases from the propellant of equation (3) relative
to the propellant of equation (1). Corresponding reductions occur in the average molecular
weight of the exhaust gases. This can in fact increase the specific impulse to produce
an over-all improvement in the density-impulse performance of the propellant formulation
of equation (3) relative to the propellant formulation of equation (1).
[0045] As the level of aluminum is deduces from the formulation of equation (1) toward the
formulation of equation (3), the volume displaced by the reduction in the amount of
aluminum can be replaced by an equal volume of high density oxidizer or hydrocarbon
binder or by a combination of the two (2). Aluminum has a lower density than the high
density oxidizer such as lead nitrate (2.70 vs. 4.53). This causes an increased volume
of lead nitrate equal to that in the reduction in the amount of aluminum to produce
a sixty-eight percent (68%) increase in specific gravity of lead nitrate relative
to aluminum. In other words, replacing aluminum with lead nitrate causes the propellant
density to be increased.
[0046] Aluminum reduces the burning rate of the propellant of equations (1), (2) and (3).
Therefore, as the amount of aluminum in the propellant is reduced, the burning of
the propellant is accelerated. This allows some of the potassium perchlorate to be
removed from the propellant to maintain a particular burning rate. The potassium perchlorate
removed from the propellant can be replaced in volume with a corresponding amount
of lead nitrate. Potassium perchlorate has a specific
( gravity of approximately 2.5298 grams/cubic centimeter whereas lead nitrate has a
specific gravity of approximately 4.53 grams/cubic centimeter. The replacement of
the potassium perchlorate by lead nitrate accordingly produces an increase in specific
gravity of approximately seventy-nine percenc (79
%) in a given volume.
[0047] As the aluminum content of the propellant is reduced below a critical ratio, the
combustion enthalpy decreases more rapidly than the increase in density. This causes
some reduction in density-impulse to occur. However, the reduction in the temperature
of the exhaust gases from the combustion may facilitate design economy and simplicity
within an acceptable level of density-impulse performance to warrant the use of such
propellants with reduced amounts of aluminum.
[0048] Formulations having reduced levels of aluminum are plotted in Figure 4 in triangular
coordinates. In the plots of Figure 4, the amount of the oxidizer is plotted in the
vertical direction, with the apex of the triangle indicating an amount of one hundred
percent (100%) and the base of the triangle indicating an amount of zero percent (0%).
Similarly, the amount of the hydrocarbon binder is plotted from the left leg of the
triangle representing zero percent (0%) as a base and the lower right corner representing
one hundred percent (100%). The amount of aluminum is also plotted from the right
leg of the triangle representing zero percent (0%) as a base and the lower left corner
representing one hundred percent (100%).
[0049] As will be seen from Figure 4, the levels of aluminum can be varied between approximately
zero percent (0%) and twenty percent (20%) by weight. The minimal amount of aluminum
is preferably at least two percent (2%) by weight for beneficial effects and less
than approximately eighteen percent (18%) by weight. This preferred range provides
for ease of mixing, processing and casting. The percentage of the hydrocarbon by weight
is preferably between approximately eight percent (8%) and ten percent (10%) to provide
optimal density-impulse performance for the propellants. This range of weights for
the hydrocarbon carbon also facilitates mixing and processing since the binder is
a liquid polymer during the mixing and casting processes.
[0050] Specific percentages are specified in the table below for the different components
in the propellant:

These different formulations are plotted in the curve illustrated at 20 in Figure
4.
[0051] Specific formulas can be developed at any point selected along the curve illustrated
in Figure 4. Specific performance criteria such as burning rate, specific impulse
and density-impulse can be formulated by extrapolating from established data points
or by interpolating between established data points. It will be appreciated, however,
that the invention is not to be limited to the formulations along the curve of Figure
4 or the extrapolations or interpolations along the points of such curve.
[0052] Carbon can be added to the formulations having reduced levels of aluminum. The carbon
acts as a heat transfer mechanism to increase the burning rate of the propellant.
Carbon also acts as a physical reinforcing agent in the synthetic rubber matrix. Adding
carbon also alters the interior ballistics of the propellant by increasing the mols
of gas. This results from an increase in the production of carbon monoxide in the
combustion gases. The relatively low heat of formation (approximately -26.4 kilocalories
per mol) of carbon monoxide provides an additional cooling effect on the combustion
gases.
[0053] Combinations of aluminum and carbon as fuel additives expand the spectrum of useful
propellant formulations. Specific performance parameters can be modified or tailored
to fit. an exacting application by ranging the levels of the two (2) additives and
by changing their weight ratio.
[0054] The formulations constituting this invention provide certain important advantages.
One distinct advantage is the production of lead oxide, rather than lead, in the combustion
gases. This has resulted from the reduction in the amount of aluminum oxide produced
in the combustion gases. This is an unexpected result since aluminum oxide is the
highest enthalpy species produced in the combustion gases.
[0055] The reduction in the amount of aluminum in the propellant and the production of lead
oxide, rather than lead, in the combustion gases has caused some serious thermodynamic,
thermochemical and metallurgical problems to be eliminated. It has also enhanced the
density-impulse performance of the propellant over a wide range of formulas. The range
of formulas is even extended through an additional range of some significance where
the density-impulse formulation is not degraded from that obtained from the formulation
of'equation (1).
[0056] Propellant formulations having high density-impulses and containing less than the
stoichiometric ratio of aluminum fuel have demonstrated improvements in ballistic
performance in rocket motors. The chemically improved exhaust gases of these propellants
have caused substantial improvements in their containment to be obtained and have
significantly reduced problems of heat transfer and insulation. These problems have
been associated with previous propellants and have been based upon stoichiometric
levels of aluminum in the formulations.
[0057] As will be seen, all of the above propellants include a fuel such as aluminum. The
propellants of the second embodiment of this invention do not include the fuel such
as aluminum. For example, one formulation of this invention may be as follows:

[0058] This formulation represents a reduction in specific impulse of approximately twenty-two
percent (22%) from the propellants which include aluminum. However, since aluminum
has been eliminated, the relative amount of the lead nitrate in the formulation is
proportionately increased. This causes the formulation of equation (4) to be increased
in density by approximately eleven percent (11%). This at least partially compensates
for the decrease in the specific impulse of the formulation.
[0059] The formulation of equation (4) has a number of the advantages discussed above. For
example, it produces lead oxide, rather than lead, as an end product during combustion.
The formulation of equation (4) also has other advantages in addition to those discussed
above. For example, it produces, during combustion, temperatures considerably lower
than the conventional propellants of the prior art and the propellants of equations
(1), (2) and (3). This enables the throat of the propulsion chamber to be made of
a conventional material such as steel or copper. It also enables significant reductions
to be provided in the volume and weight of the propulsion chamber. It also provides
for significant reductions in the volume and weight of the insulation materials in
the propulsion chamber, and particularly at the nozzle exit from the chamber.
[0060] The temperatures of the propellant exhaust gases can be further reduced by including
carbon as a fuel to obtain a propellant such as set forth below:

[0061] This propellant has a high density and burns at a relatively low temperature. It
can be considered as a high density "cool" gas generator. It provides an estimated
heat of combustion of approximately -360 gram-calories/gram with an average density
or specific gravity of approximately 0.099 pounds (lb)/(in
3).
[0062] All of the above equations have included an inorganic salt oxidizer such as potassium
perchlorate. The combustion enthalpy can be further reduced by eliminating the potassium
perchlorate from the propellant. This is also advantageous in increasing the specific
gravity of the propellant since the relative amount of the lead nitrate in the propellant
is increased. This causes the propellant to have a formulation such as specified below:

[0063] As will be seen, carbon monoxide is produced during the combustion of the propellant
of equation (6). Partly because of the generation of carbon monoxide, the heat of
combustion for the formulation of equation (6) is reduced to approximately -106 gram-calories/gram
from the heat of combustion for the formulation of equation (5). As will be seen,
this constitutes a significant reduction in the heat of combustion. Even with this
considerable reduction in the heat of combustion, the density of the propellant of
equation (6) is increased to a value of approximately 0.116 pound (lb)/inch
3 (in3). Furthermore, the temperatures of the exhaust gases produced by the propellant
of equation (6) tend to be below 1000°F. This is particularly pertinent since the
formulation of equation (6) has a density almost twice as great as that of conventional
gas generator propellants. The propellant also has a low burning rate. This is desirable
for many designs of gas generators.
[0064] As the amount of carbon is reduced below that shown in equation (6), increased amounts
of carbon dioxide, and reduced amount of carbon monoxide, are produced in the exhaust
gases. The amount of combustion enthalpy tends to become increased at a relatively
rapid rate as the amount of carbon is reduced. When the amount of carbon has been
reduced to zero, the propellant may be as specified below:

[0065] The combination enthalpy for the propellant of equation (7) may be expressed as H
f = -94.05 kilocalories/mol. As will be seen from equation (7), all of the oxygen in
the propellant is used to generate carbon dioxide in the combustion, except for the
one half (1/2) mole of oxygen used to generate lead oxide (Pb0). This produces the
maximum heat of combustion from the available oxygen.
[0066] A comparison of equations (6) and (7) indicates that two (2) moles of carbon monoxide
are produced in the propellant of equation (6) in comparison to each mole of carbon
dioxide produced by the propellant of equation (7). Thus, the addition of carbon to
the propellant tends to be advantageous since it facilitates the use of oxygen in
the formation of carbon monoxide. This produces an increase in the moles of exhaust
gases produced in the combustion, a decrease in the average molecular weight of such
exhaust gases and a reduction in the combustion enthalpy. It also tends to cool the
exhaust gases.
[0067] The production of carbon monoxide in the exhaust gases also has other important advantages
in the production of gas generators in addition to those discussed above. For example,
carbon monoxide is chemically stable and is not chemically reactive. It also has a
low oxidizing potential and a low heat of formation of approximately -26.4 kilocalories/mol.
Because of this low heat formation, it would appear that oxygen can be easily removed
from the carbon monoxide. However, the heat of formation of carbon vapor is approximately
17.17 kilocalories/ mol. Because of the considerable difference between the heat of
formation of carbon monoxide and the heat of formation of carbon vapor, carbon monoxide
is quite resistant to thermal disassociation.
[0068] The range of practical formulations of propellants including a hydrocarbon binder,
oxidizers and carbon is shown in Figure 5. As will be seen, the hydrocarbon binder
has a range of approximately eight percent (8%) to ten percent (10%) by weight; the
oxidizers have a range of approximately eighty-four percent (84%) to ninety-one percent
(91%) by weight; and the carbon has a range of approximately zero percent (0%) to
eight percent (8%) by weight.
[0069] Typical formulations of the propellant in the embodiment of the invention are specified
below:
Example 1:
[0071] The different formulations specified above in Examples 1 through 5 are plotted in
the curve illustrated at 20 in Figure 5. Specific formulas can be developed at any
point selected along the curve illustrated in Figure 5. Specific performance criteria
such as burning rate, specific impulse and density-impulse can be formulated by extrapolating
from established data points or by interpolating between established data points.
It will be appreciated, however, that the invention is not to be limited to the formulations
along the curve of Figure 5 or the extrapolations or.interpolations along the points
of such curve.
[0072] The propellants disclosed above as being included in this inventon have certain important
advantages. They produce lead oxide, rather than lead, in the exhaust gases. This
allows the walls of the combustion chamber to be made from conventional materials
such as iron or steel without damaging such walls during the combustion. The propellants
produce the exhaust gases at relatively low temperatures during the combustion. For
example, some of the propellants of this invention even produce exhaust gases with
temperatures below 1000° F during the combustion. This allows the walls of the chamber
to be made from such materials as copper and it further allows the amount of insulation
in the chamber to be minimized. The propellants of this invention also produce, during
the combustion, a relatively high energy per cubic inch of the propellant.
[0073] Although this application has been discclosed and illustrated with reference to particular
applications, the principles involved are susceptible of numerous other applications
which will be apparent to persons skilled in the art. The invention is, therefore,
to be limited only as indicated by the scope of the appended claims.
1. In combination tor use as a propellant,
a binder also acting as a reducing agent,
a first oxidizing material containing lead and oxygen, and
a second oxidizing material containing oxygen and a metal,
the first and second oxidizing materials and the binder being provided in relative
percentages by weight to obtain a reduction of the first oxidizing material to lead
oxide, rather than lead, during the combustion of the propellant.
2. The combination set forth in claim 1 wherein carbon is also included in the combination.
3. The combination set forth in claim 1 wherein
the first and second oxidizing materials are included in the combination in a relative
percentage of approximately eighty-four percent (84%) to ninety-one percent (91%)
by weight.
4. The combination set forth in claim 1 wherein
the binder has a relative percentage by weight of approximately eight percent (8%)
to ten percent (10%) and has hydrogen and carbon linkages.
5. The combination set forth in claim 2 wherein
the first and second oxidizing materials are included in the combination in a relative
percentage of approximately seventy-four percent (74%) to ninety-one percent (91%) by weight Claim 5 continued and the binder is included
in the combination in a relative percentage of approximately eight percent (8%) to
ten percent (10%) by weight.
6. The combination set forth in claim 2 wherein
the first oxidizing material is included in the combination in a relative percentage
of approximately fifty-two percent (52%) to seventy-two percent (72%) by weight.
7. The combination set forth in claim 6 wherein
the binder is included in the combination in a relative percentage of approximately
eight percent (8%) to ten percent (10%) by weight and is provided with hydrogen carbon
linkages.
8. The combination set forth in claim 1 wherein
carbon is included in the propellant as an additional reducing agent.
9. In combination for use as a propellant,
lead nitrate as an oxidizer,
potassium perchlorate as an oxidizer,
a binder also acting as a reducing agent, and
an amount of aluminum sufficient to obtain the reduction of the lead nitrate to lead
oxide, rather than lead, during the combustion of the propellant.
10. The combination set forth in claim 9 wherein
the aluminum has a percentage by weight in the combination to approximately twenty
percent (20%) by weight.
11. The combination set forth in claim 9 wherein
the alumimum has a percentage by weight in the combination of approximately two percent
(2%) to eighteen percent (18%).
12. The combination set forth in claim 9 wherein
the potassium perchlorate has a percentage by weight in the mixture of approximately
twenty percent (20%) to twenty-four percent (24%) and the lead nitrate has a percentage
by weight in the mixture of approximately fifty-two percent (52%) to seventy-two percent
(72%).
13. The combination set forth in claim 12 wherein
the binder has a percentage by weight in the mixture of approximately eight percent
(8%) to ten percent (10%).
14. The combination set forth in claim 13 wherein
carbon is included as an additional reducing agent.
15. In combination for use as a propellant,
a binder also acting as a reducing agent,
a lead compound oxidizer formed from lead oxidizer salts and having dense characteristics
and stable properties at ambient temperatures and through a particular range of temperatures
above ambient temperatures, and
a fuel additive disposed in a combustible form and having properties of being oxidized
by the oxidizer and of reducing the lead, the fuel additive having a percentage by
weight relative to the lead compound oxidizer to reduce the lead Claim 15 continued
compound oxidizer to the lead oxide, rather than lead, during the combustion of the
propellant.
16. The combination set forth in claim 15 wherein
the fuel additive is included in the combination in the range to approximately twenty
percent (20%) by weight.
17. The combination set forth in claim 16 wherein
the binder included in the combination in the range of approximately eight percent
(8%) to ten percent (10%) by weight and is provided with hydrogen and carbon linkages.
18. The combination set forth in claim 16 wherein
the lead compound oxidizer is selected from the group consisting of lead nitrate,
lead peroxide amd lead iodate.
19. The combination set forth in claim 16 wherein
carbon is included as an additonal reducing agent.
20. In combination for use as a propellant,
a binder also acting as a reducing agent,
a lead compound oxidizer formed: from inorganic lead oxidizer salts and having dense
characteristics and stable properties at ambient temperatures and through a particular
range of temperatures above ambient temperatures, and
a metal fuel additive disposed in a fragmented form for combustion and having properties
of being oxidized by the oxidizer and of reducing the lead,
the metal fuel additive having a percentage by weight in the combination relative
to the lead compound oxidizer to Claim 20 continued
reduce the lead compound oxidizer to lead oxide, rather than lead, during the combustion
of the propellant.
21. The combination set forth in claim 20, including;
a second inorganic oxidizer containing a metal other than lead.
22. The combination set forth in claim 20, including,
carbon serving as an additional reducing agent.
23. The combination set forth in claim 20 wherein
the inorganic lead compound oxidizer is selected from the group consisting of lead
nitrate, lead peroxide and lead iodate.
24. The combination set forth in claim 20 wherein
the metal fuel additive is included in the combination in the range to approximately
twenty percent (20%) by weight.
25. The combination set forth in claim 24 wherein
the binder is included in the combination in the range of approximately eight percent
(8%) to ten percent (10%) by weight and is provided with hydrogen and carbon linkages.
26. The combination set forth in claim 18 wherein
the lead compound oxidizer is included in the combination in the range of approximately
fifty-two percent (52%) to seventy-two percent (72%) by weight.
27. The combination set forth in claim 1 wherein
the fuel additive is aluminum.
28. The combination set forth in claim 9 wherein
the aluminum is fragmented.
29. The combination set forth in claim 11 wherein
the aluminum is in particulate form.
30. The combination set forth in claim 16 wherein
the fuel additive is in particulate form.
31. The combination set forth in claim 15 wherein
the fuel additive is in particulate form and consists of a metal selected from a group
consisting of aluminum, beryllium, magnesium, titanium and lithium.
32. The combination set forth in claim 25 wherein
the lead compound oxidizer is included in the combination in the range of approximately
fifty-two percent (52%) to seventy-two percent (72%) by weight.
33. The combination set forth in claim 1 wherein
the binder, the first and second oxidizing agents and the additive are provided in
relative percentages by weight to obtain the production of carbon monoxide during
the combustion of the propellant.
34. The combination set forth in claim 9 wherein Claim 34 continued
the lead nitrate, the potassium perchlorate, the binder and the aluminum have relative
percentages by weight to obtain the formation of carbon monoxide during the combustion
of the propellant.
35. The combination set forth in claim 15 wherein
the binder, the lead compound oxidizer and the fuel additive are provided in relative
percentages by weight to obtain the production of carbon monoxide during the combustion
of the propellant.
36. In combination for use as a propellant,
a hydrocarbon constituting as a reducing agent and a binder,
a first oxidizing material containing lead and oxygen,
a second oxidizing material containing oxygen and a metal,
aluminum as a reducing agent,
the first and second oxidizing materials and the aluminum being provided in relative
percentages by weight to obtain a reduction of the first oxidizing material to lead.
oxide during the combustion of the propellant.
37. The combination set forth in claim 36 wherein
the aluminum is included in the combination in a relative percentage to approximately
twenty percent (20%) by weight.
38. The combination set forth in claim 36 wherein Claim 38 continued'
the first and second oxidizing materials are included in the combination in a relative
percentage of approximately seventy-four percent (74%) to ninety-one percent (91%)
by weight.
39. The combination set forth in claim 36 wherein
the hydrocarbon has a relative percentage by weight of approximately eight percent
(8%) to ten percent (10%).
40. The combination set forth in claim 27 wherein
the first and second oxidizing materials are included in the combination in a relative
percentage of approximately eighty-four percent (84%) to ninety-one percent (91%)
by weight and the binder is included in the combination in a relative percentage of
approximately eight percent (8%) to ten percent (10%) by weight and the carbon is
included in the combination in the range of approximately zero percent (0%) to eight
percent (8%) by weight.
41. The combination set forth in claim 36 wherein
the first oxidizing material is selected from a group consisting of lead nitrate,
lead peroxide and lead iodate.
42. The combination set forth in claim 41 wherein
the second oxidizing agent"is selected from a group consisting of strontium nitrate,
barium nitrate, cerium nitrate, rubidium nitrate, ammonium perchlorate, potassium
periodate, potassium nitrate, area nitrate and guanidine nitrate,
the binder has hydrogen and carbon linkages, and
Claim 42 continued
the oxidizing agent and the binder are provided in relative percentages to obtain
the production of carbon monoxide during the combination of the propellant.
43. The combination set forth in claim 36 wherein
the first oxidizing material is lead nitrate and the second oxidizing material is
potassium perchlorate.
44. In combination for use as a propellant,
lead mitrate as an oxidizer,
potassium perchlorate as an oxidizer, and
a binder also acting as a reducing agent, and
the relative amounts of the lead nitrate, the potassium perchlorate and the binder
being selected to obtain the reduction of the lead nitrate to lead oxide during the
combustion of the propellant.
45. The combination set forth in claim 44 wherein
the lead nitrate, the potassium perchlorate and the binder are provided with relative
proportions to produce combustion temperatures less than approxiamtely 1000°F.
46. The combination set forth in claim 44 wherein
the lead nitrate and the potassium perchlorate have a relative percentage by weight
of approximately eighty-four percent (84%) to ninety-one percent (91%).
47. The combination set forth in claim 44 wherein
the hinder has a range by weight in the combination of approximately eight percent
(8%) to ten percent (10%).
48. The combination set forth in claim 47 wherein
carbon is included as an additional reducing agent.
49. The combination set forth in claim 48 wherein
the carbon has a range by weight in the combination to approximately eight percent
(8%) and the binder has hydrogen and carbon linkages.
50. In combination for use as a propellant,
a binder also acting as a reducing agent,
a lead compound oxidizer formed from lead oxidizer salts and having dense characteristics
and stable properties at ambient temperatures and through a particular range of temperatures
above ambient temperatures, and
a second oxidizer,
the binder, the lead compound oxidizer and the second oxidizer being provided with
relative percentages by weight to reduce the lead compound oxidizer to the lead oxide
during the combustion of the propellant.
51. The combination set forth in claim 50 wherein
the second oxidizer is an inorganic salt and the binder has hydrogen and carbon linkages.
52. The combination set forth in claim 51 wherein
the binder is included in the combination in the rang< of approximately eight percent
(8%) to ten percent (10%) by weight.
53. The combination set forth in claim 51 wherein Claim 53 continued
the lead compound oxidizer is selected from the group consisting of lead nitrate,
lead peroxide and lead iodate.
54. The combination set forth in claim 51 wherein
carbon is included in the binder.
55. In combination for use as a propellant,
a binder also acting as a reducing agent,
a lead compound oxidizer formed from an inorganic lea oxidizer salt and having dense
characteristics and stable properties at ambient temperatures and through a particular
range of temperatures above ambient temperatures,
the binder and the lead compound oxidizer having relative percentages by weight in
the combination to reduce the lead compound oxidizer to lead oxide during the combustion
of the propellant.
56. The combination set forth in claim 55, including,
the lead compound oxidizer being included in the combination in the range of approximately
eighty-three percent (83%) .to ninety-one percent (91%) by weight.
57. The combination set forth in claim 55, including,
carbon serving as an additional binder.
58. The combination set forth in claim 55 wherein Claim 58 continue]
the inorganic lead compound oxidizer is selected from the group consisting of lead
nitrate, lead peroxide and lead iodate.
59. The combination set forth in claim 57 wherein
the carbon has a range in the combination to approximately ten percent (10%) by weight.
60. The combination set forth in claim 59 wherein
the binder is included in the combination in the ran of approximately eight percent
(8%) to ten percent (10%) by weight.
61..The combination set forth in claim 59 wherein
the lead compound oxidizer is lead nitrate.
62. In combination for use as a propellant,
a binder also acting as a reducing agent, and lead nitrate,
the binder and the lead nitrate having relative proportions by weight to reduce the
lead nitrate to lead oxid during the combustion of the propellant.
63. The combination set forth in claim 62, including,
carbon as a reducing agent.
64. The combination set forth in claim 63 wherein
the lead nitrate has a range of approximately eighty-three percent (83%) to ninety-one
percent (91%) by weight, the binder has a range of approximately eight percen Claim
64 continued (8%) to ten percent (10%) by weight and the carbon has a range to approximately
ten percent (10%) by weight.
65. The combination set forth in claim 62 wherein
the binder has carbon and hydrogen linkages and the binder and the lead nitrate have
relative proportions by weight to produce carbon monoxide during the combustion of
the propellant.
66. The combination set forth in claim 36 wherein
the binder has carbon and hydrogen linkages and the oxidizing agent and the binder
are provided in relative percentages by weight, to obtain the production of carbon
monoxide during the combustion of the propellant.
67. The combination set forth in claim 44 wherein
the binder has carbon and hydrogen linkages and the lead nitrate, the potassium perchlorate
and the binder are provided in relative percentages by weight to obtain the production
of carbon monoxide during the combustion of the propellant.
68. The combination set forth in claim 50 wherein
the binder has carbon and hydrogen linkages and the binder, the lead compound oxidizer
and the second oxidizer are provided in relative percentages by weight to obtain the
production of carbon monoxide during the combustion of the propellant..
69. The combination set forth in claim 55 wherein Claim 69 continued
the binder and the lead compound oxidizer are provided in relative percentages by
weight to obtain the production of carbon monoxide during the combustion of the propellant.