EP2448885B1 - Method for producing solid composite aluminized propellants, and solid composite aluminized propellants - Google Patents

Description

• un procédé d'obtention d'un propergol solide composite (à liant polyuréthanne chargé en perchlorate d'ammonium et en aluminium),
• un tel propergol solide composite, les chargements de propergol solide et les moteurs de fusée associés.

The main objects of the present invention are:

• a process for obtaining a composite solid propellant (with polyurethane binder loaded with ammonium perchlorate and aluminum),
• such solid composite propellant, solid propellant shipments and associated rocket engines.

The invention is in the field of solid propellant propulsion and more particularly relates to aluminized composite solid propellants.

The applications envisaged mainly concern solid propellant engines for space launchers (accelerators or launchers stages).

The object of the invention is to reduce the alumina deposits at the bottom of the engines with integrated nozzle and tend to reduce aerodynamic thrust oscillations while maintaining the ballistic properties, including the combustion rates, the propellants close to those of industrial propellants for space applications known to date.

The solid propellant engines for space launchers are of the type of the Ariane 5 rocket or the American Space Shuttle, large (h ~ 20 m, D ~ 5 m), with integrated nozzle. The solid propellant loads contained in this type of engine have a mass ranging from a few hundred kilograms to several hundred tons. Their operating time is of the order of a few tens of seconds to a few minutes. The present invention is in this context large solid propellant engines.

Solid propellants for these applications are composite propellants with an inert binder of the polyurethane type. They contain a charge of ammonium perchlorate (oxidizing charge) and an aluminum charge (reducing charge). The oxidizing charge of ammonium perchlorate contained in said propellants is generally composed of several charges of ammonium perchlorate of different monomodal particle size distributions. which have been added during the preparation of said propellants. It may be the same for the reducing load of aluminum. This family of propellants is that concerned by the present invention. The mass ratios of these ingredients are generally about 68% for ammonium perchlorate, 20% for aluminum and 12% for binder.

Ladite vitesse de combustion Vc et l'exposant de pression n du propergol sont des paramètres fondamentaux pour le réglage balistique d'un moteur à propergol solide (durée de combustion, poussée, stabilité de combustion...).The burning rate of the solid propellant depends on the pressure P prevailing in the combustion chamber and conventionally follows a law (called the law of old) expressed in the form: $$\mathrm{Vc}={\mathrm{aP}}^{\mathrm{not}}.$$

Said combustion rate Vc and the pressure exponent n of the propellant are fundamental parameters for the ballistic adjustment of a solid propellant engine (combustion time, thrust, combustion stability, etc.).

The standard values of the ballistic parameters for the propulsion applications concerned by the present invention, using polyurethane-bonded aluminized composite propellants, are a combustion rate Vc of a few mm / s to 10 mm / s and a pressure exponent n = 0, 2 to 0.4, in an operating pressure range of 3 to 10 MPa.

The person skilled in the art knows how to choose the particle sizes of the constituent raw materials of the solid propellant for controlling the combustion speed levels of said solid propellant.

MM Iqbal and W. Liang were interested in the Journal of Propulsion and Power, vol. 23, N ° 5, September 2007 , the effect of the particle size of ammonium perchlorate on the burning rate of solid propellants. Their objective was to validate a mathematical model of surface combustion, making it possible to predict the combustion rates of this type of propellant.

L. Massa and TL Jackson were interested in the Journal of Propulsion and Power, vol. 24, N ° 2, March-April 2008 , the effect of the particle size of aluminum on the burning rate of solid propellants. Their objective was also to validate a mathematical model of surface combustion allowing to predict the combustion rates of this type of propellant.

These two publications give no information on the granulometry of the alumina generated following the combustion of the propellants. and the technical problems associated with this particle size (see below). Moreover, the various charges of ammonium perchlorate, referred to in these publications, are characterized only by one parameter, namely the particle diameter at the peak of their particle size distribution.

The aluminized composite propellants produce, during their combustion, gases and solid particles consisting mostly of alumina (about 30% of the mass ejected by the propellant).

The combustion of alumina aluminum in composite propellants has been extensively studied. However, those skilled in the art do not know how to control the particle size of the alumina produced by said propellant combustion.

The aluminum introduced into the aluminized composite solid propellants is in the form of grains, more or less spherical, with a median diameter generally between 1 and 50 microns. The combustion of a drop of aluminum, expelled from the burning surface, is schematized on the figure 1 attached. A flame surrounds the drop of aluminum and a cap of alumina is formed at the bottom of the drop. The combustion generates alumina fumes (drops of small size, of the order of 1 μm) and larger alumina drops from the cap, which explains the bimodal particle size distributions of alumina finally produced by solid propellants. Studies on the combustion of these aluminized propellants (the figure 2 graphically, the phenomena involved) show that the aluminum particles escaping from the surface of the propellant are likely to agglomerate to form drops much larger than those of aluminum introduced. The rest leaves the surface without agglomerating. Laboratory observations show that the particle size distribution of the combustion residues generated by an aluminized composite propellant generally has two peaks, one centered around a diameter of 60 μm and a second centered around 0.5 μm to 3 μm, independently the particle size of the aluminum introduced. The percentage of the total volume represented by particles of diameters greater than 10 μm is typically about 30%.

The alumina generated by the combustion of the aluminized propellant represents, as indicated above, approximately 30% of the mass ejected by the propellant.

In the foreground, the production of large-diameter (> 10 μm) alumina particles leads to an accumulation in the backplane in space thrusters equipped with an integrated nozzle, resulting in a reduction of the impulse. It is estimated that more than 0.5% of the mass of the propellant is thus in the form of alumina trapped in the rear bottom, and therefore not ejected from the engine. Indeed, the larger particles have a high aerodynamic drag, do not follow the flow lines and are trapped in the rear engine bottom (bowl-shaped formed by the integrated structure of the nozzle). This non-expelled mass penalizes, on the one hand, the performance of the engine and can, on the other hand, generate, after the extinction of the engine and by a vacuum emptying phenomenon, orbital debris of non-dimensional alumina. negligible (ie> to a few millimeters).

The person skilled in the art therefore wishes to have a solid propellant generating alumina of fine particle size, since smaller particles will better follow the current lines to be ejected by the nozzle, thus avoiding their accumulation in the back of the container. engine.

On a second level, problems of aerodynamic instability inherent to the internal geometry of large solid propellant engines may appear (lateral injection of combustion products, jet confluence, geometric accidents or beats of elements exceeding ...) . These aerodynamic instabilities can interact with propellant combustion and / or combustion chamber acoustics and induce resonance phenomena. Such phenomena cause mechanical vibrations on the launcher payload. So we always try to reduce these phenomena to preserve the payload.

Those skilled in the art have sought by various means, all penalizing, to reduce these aerodynamic instabilities. One method is to introduce into the flow obstacles such as baffles, inserts or rods of resonances, cavities (we can see in this regard the lessons of the documents FR 2,844,557 , US 3,795,106 and FR 2,764,645 ). The implementation of these methods requires tests of development and is always at the expense of engine performance, due to an increase in the embedded mass on board.

More recently, according to complex theoretical considerations, it has been demonstrated that, in the case of large engines, it is necessary to favor the production of alumina small particle size (diameter ~ 1 micron), to reduce these aerodynamic instabilities.

Those skilled in the art therefore wish to have aluminized solid propellants which, by combustion, produce small diameter alumina (thus promoting the reduction of thrust oscillations in solid propellant propellants and having the combined positive effect of reducing the deposit in the rear bottom of the nozzle) while maintaining ballistic properties, including combustion rates, similar to those of industrial propellants for space application known to date.

In the remainder of the document, all the particle size data are obtained from measurements carried out using a photon correlation optical particle size analyzer (PCS-DLS: Photons Correlation Spectroscopy-Diffusion Light Scattering), according to a procedure defined by the standard NF 11-666.

The results of granulometric measurements of a particle size class are expressed in the form of curves, giving: on the one hand, the histogram of the volume percentages of particles (also called percentages of passing volume) as a function of the diameter (equivalent spherical) of particles and, on the other hand, the cumulation of the volume percentages of particles as a function of the diameter (equivalent spherical) of the particles, cumulated carried out according to the increasing diameters.

• D₁₀ : diamètre pour lequel le pourcentage volumique cumulé est égal à 10 % ;
• D₅₀ : diamètre pour lequel le pourcentage volumique cumulé est égal à 50 % ;
• D₉₀ : diamètre pour lequel le pourcentage volumique cumulé est égal à 90 %.

Three characteristic values of the analyzed sample are recorded on the cumulative curve of the volume percentages:

• D ₁₀ : diameter for which the cumulative volume percentage is equal to 10%;
• D ₅₀ : diameter for which the cumulative volume percentage is equal to 50%;
• D ₉₀ : diameter for which the cumulative volume percentage is equal to 90%.

A particle size class of a particulate material is defined by its particle size envelope defined by minimum and maximum values of D ₁₀ , D ₅₀ , D ₉₀ .

• à liant polyuréthanne renfermant une charge de perchlorate d'ammonium et une charge d'aluminium,
• présentant des propriétés balistiques (Vc, n) adéquates pour des applications de propulsion, et
• générant, lors de leur combustion, des particules d'alumine de faible granulométrie.

The present invention relates to solid propellants:

• with a polyurethane binder containing an ammonium perchlorate charge and an aluminum charge,
• having ballistic properties (Vc, n) suitable for propulsion applications, and
• generating, during their combustion, particles of alumina of small particle size.

The Applicant has been able to select and associate different granulometries (monomodal) of ammonium perchlorate, so that, during the combustion of the propellant, the agglomeration of the aluminum in combustion is limited, in order to reduce, or almost to remove, the production of particles larger than 10 microns diameter, while maintaining the standard values of the ballistic parameters for a propulsive space application.

Thanks to the fine particle size of alumina produced by the solid propellants (in combustion) of the present invention, deposits in the rear engine bottoms are reduced and the pressure oscillations are attenuated.

• l'obtention d'une pâte par malaxage, dans un mélangeur, d'un mélange renfermant un polymère polyol (polybutadiène hydroxytéléchélique) liquide (présent, dans le mélange, à raison de 5 à 15 % en masse, plus généralement à raison de 7 à 14 % en masse), une charge oxydante de perchlorate d'ammonium (présente, dans le mélange, à raison de 60 à 75 % en masse), une charge réductrice d'aluminium (présente, dans le mélange, à raison de 15 à 20 % en masse, plus généralement à raison de 16 à 19 % en masse), au moins un agent de réticulation dudit polymère polyol liquide en une quantité telle que le rapport de pontage NCO/OH soit compris entre 0,8 et 1,1, soit avantageusement de 1, au moins un plastifiant et au moins un additif (lesdits agent(s) de réticulation, plastifiant(s) et additif(s) étant présents, dans le mélange, à raison de moins de 5 % en masse, plus généralement à raison de 1 à 3 % en masse) ;
• la coulée de la pâte obtenue dans un moule ;
• la réticulation thermique de ladite pâte dans ledit moule.

The present invention firstly relates to a process for obtaining a composite solid propellant, said process comprising:

• obtaining a paste by kneading, in a mixer, a mixture containing a liquid polyol polymer (polybutadiene hydroxytelechelic) (present in the mixture at a rate of 5 to 15% by weight, more generally at a rate of 7 at 14% by weight), an oxidizing charge of ammonium perchlorate (present in the mixture at a rate of 60 to 75% by weight), a reducing charge of aluminum (present in the mixture at a rate of at 20% by weight, more generally at a rate of 16 to 19% by weight), at least one agent for crosslinking said liquid polyol polymer in an amount such that the NCO / OH bridging ratio is between 0.8 and 1, 1, advantageously 1, at least one plasticizer and at least one additive (said agent (s) of crosslinking, plasticizer (s) and additive (s) being present in the mixture, at the rate of less than 5% by weight, more generally at a rate of 1 to 3% by weight);
• casting the paste obtained in a mold;
• thermal cross-linking of said paste in said mold.

• + une première charge dont la distribution granulométrique monomodale (dite de classe A) présente une valeur de D₁₀ comprise entre 100 µm et 110 µm, une valeur de D₅₀ comprise entre 170 µm et 220 µm et une valeur de D₉₀ comprise entre 315 µm et 340 µm, et
• + une seconde charge dont la distribution granulométrique monomodale (dite de classe B) présente une valeur de D₁₀ comprise entre 15 µm et 20 µm, une valeur de D₅₀ comprise entre 60 µm et 120 µm et une valeur de D₉₀ comprise entre 185 µm et 220 µm ; et, éventuellement,
• + une troisième charge dont la distribution granulométrique monomodale (dite de classe C) présente une valeur de D₁₀ comprise entre 1,7 µm et 3,6 µm, une valeur de D₅₀ comprise entre 6 µm et 12 µm et une valeur de D₉₀ comprise entre 20 µm et 32 µm.

Said oxidizing charge of ammonium perchlorate in said paste results from the introduction into said mixer, separately or as a mixture, of at least:

• + a first charge whose monomodal particle size distribution (called class A) has a value of D ₁₀ of between 100 μm and 110 μm, a value of D ₅₀ of between 170 μm and 220 μm and a value of D ₉₀ of between 315 and μm and 340 μm, and
• + a second charge whose monomodal particle size distribution (called class B) has a D ₁₀ value between 15 μm and 20 μm, a D ₅₀ value between 60 μm and 120 μm and a D ₉₀ value between 185 μm and 220 μm; and eventually,
• + a third charge whose monomodal particle size distribution (called class C) has a D ₁₀ value between 1.7 μm and 3.6 μm, a D ₅₀ value of between 6 μm and 12 μm and a D value of ₉₀ between 20 microns and 32 microns.

• un polymère polyol liquide : ledit polymère polyol est un polybutadiène hydroxytéléchélique ;
• une charge oxydante de perchlorate d'ammonium (PA) ;
• une charge réductrice d'aluminium (Al). Les particules d'aluminium ont un diamètre médian inférieur ou égal à 40 µm ;
• au moins un agent de réticulation (généralement liquide) dudit polymère polyol : ledit au moins un agent de réticulation (au moins bifonctionnel) est généralement choisi parmi les polyisocyanates, il consiste de préférence en un polyisocyanate alicyclique. Il consiste avantageusement en le dicyclohexylméthylène diisocyanate (MCDI) ;
• au moins un plastifiant : ledit au moins un plastifiant est choisi préférentiellement parmi l'azélate de dioctyle (DOZ), le sébaçate de diisooctyle, le pélargonate d'isodécyle, le polyisobutylène, le phtalate de dioctyle (DOP) ;
• au moins un additif : ledit au moins un additif peut notamment consister en un ou plusieurs agents d'adhésion entre le liant et la charge oxydante, comme par exemple l'oxyde de bis(2-méthylaziridinyl)-méthylaminophosphine (méthyl BAPO) ou le triéthylène pentamine acrylonitrile (TEPAN), en un ou plusieurs agents antioxydants issus de ceux de l'industrie du caoutchouc, comme par exemple le ditertiobutylparacrésol (DBC) ou le 2,2'-méthylène-bis(4-méthyl-6-tertio-butylphénol) (MBP5), en un ou plusieurs catalyseurs de réticulation, comme par exemple l'acétylacétonate de fer ou de cuivre, le dibutyldilaurate d'étain (DBTL), en un ou plusieurs catalyseurs de combustion, comme l'oxyde de fer, ...

The method of the invention is a method by analogy which comprises, in a conventional manner, obtaining a paste from the constituent ingredients of the propellant referred to, casting said paste in a mold and its crosslinking by heat treatment (baking ). The ingredients involved are the classic ingredients for this type of propellant. They understand :

• a liquid polyol polymer: said polyol polymer is a hydroxytelechelic polybutadiene;
• an oxidizing charge of ammonium perchlorate (AP);
• a reducing charge of aluminum (Al). The aluminum particles have a median diameter less than or equal to 40 μm;
• at least one crosslinking agent (generally liquid) of said polyol polymer: said at least one crosslinking agent (at least bifunctional) is generally chosen from polyisocyanates, it preferably consists of an alicyclic polyisocyanate. It consists advantageously of dicyclohexylmethylene diisocyanate (MCDI);
• at least one plasticizer: said at least one plasticizer is preferably selected from dioctyl azelate (DOZ), diisooctyl sebacate, isodecyl pelargonate, polyisobutylene, dioctyl phthalate (DOP);
• at least one additive: said at least one additive may in particular consist of one or more adhesion agents between the binder and the oxidizing filler, such as, for example, bis (2-methylaziridinyl) -methylaminophosphine oxide (methyl BAPO), or triethylene pentamine acrylonitrile (TEPAN), one or more antioxidant agents derived from those of the rubber industry, such as, for example, ditertiobutyl paracresol (DBC) or 2,2'-methylenebis (4-methyl-6-tertiary) butylphenol) (MBP5), in one or more crosslinking catalysts, such as, for example, iron or copper acetylacetonate, tin dibutyldilaurate (DBTL), in one or more combustion catalysts, such as iron oxide, ...

Said ingredients are involved in the amounts (percentages by mass) conventional indicated above.

Incidentally, the list of ingredients given above is not exhaustive. Thus, it is not excluded that another energy charge is introduced into the mixer.

The composite solid propellant, obtained according to the process of the invention, has, over an operating pressure range of 3 to 10 MPa, a combustion rate of between 6 and 12 mm / s and a pressure exponent of between 0, 15 and 0.4, advantageously between 0.2 and 0.4. The combustion of said solid propellant obtained generates less than 15%, generally between 2 and 10% by volume of alumina particles whose diameter is greater than 10 microns.

With reference to the technical problems mentioned above, the charge of ammonium perchlorate is, in the context of the process of the invention, optimized: it is obtained from at least a first and second (or even third) charges having , each, a monomodal particle size distribution as specified above. It results, typically, from the introduction into the mixer, separately or in mixture, of at least two charges of different monomodal particle size: the first of class A (see above) and the second of class B ( see above). The introduction of a third class C load (see above) is expressly provided for. The introduction of at least one other load (in addition to those of class A, B and C) is not excluded from the scope of the invention. It is a priori hardly advisable.

Typically, the charge of ammonium perchlorate of the mixture, in the mixer, is at least partly advantageously in its entirety, constituted from a first and second charges (each) of specific monomodal particle size, or even first, second and third charges (each) of specific monomodal particle size.

The mixture (binary or ternary) of the first and second or first, second and third oxidizing charges of different specific monomodal granulometry can be performed upstream. According to this variant, the oxidizing charge of the propellant is carried out upstream and is then added, pre-constituted, in the mixer.

The mixture (binary or ternary) of the first and second or first, second and third oxidizing charges of different specific monomodal granulometry may be carried out only in the mixer within the dough. According to this variant, it is not pre-constituted. The first, second or even third charges can thus be introduced separately. In the context of this variant, when three types of oxidizing charges are introduced, it is however possible to pre-constitute a mixture (binary), first and second, first and third, or second and third, oxidizing charges of specific monomodal granulometry. The said mixture is then added to the mixer, followed by the third, the second or the first oxidizing charge (the complementary oxidizing charge), so that the said first, second and third charges constitute the oxidizing charge of the propellant.

It will be understood that the above notions of separate introduction or introduction in a mixture (binary or ternary mixtures) cover all these variants.

It is the merit of the inventors to have identified monomodal particle size classes A, B and C of ammonium perchlorate and demonstrated their interest in the constitution of the oxidizing charge of an aluminized composite solid propellant.

According to an advantageous variant, the oxidizing charge of ammonium perchlorate in the dough results only from the introduction into the mixer (separately or in mixture) of the first and the second charge, the monomodal particle size of which has been specified above. (using the value ranges of D ₁₀ , D ₅₀ and D ₉₀ ).

With regard to the respective amounts of intervention of said first, second or even third, oxidizing charges, it is possible, in no way limiting, to specify the following.

• 12 à 70 % en masse de ladite première charge (classe A),
• 10 à 81 % en masse de ladite seconde charge (classe B),
• 0 à 23 % en masse de ladite troisième charge (classe C).

The oxidizing charge of ammonium perchlorate (100%) in the paste results, generally, from the introduction into the mixer, separately or as a mixture, of:

• 12 to 70% by weight of said first charge (class A),
• 10 to 81% by weight of said second charge (class B),
• 0 to 23% by weight of said third charge (class C).

• 20 à 65 % (voire 20 à 60 %) en masse de ladite première charge (classe A),
• 35 à 80 % (voire, respectivement, 40 à 80 %) en masse de ladite seconde charge (classe B),
• 0 à 22 % en masse de ladite troisième charge (classe C).

It may in particular result from the introduction into the mixer, separately or as a mixture, of:

• 20 to 65% (or even 20 to 60%) by mass of said first charge (class A),
• 35 to 80% (or, respectively, 40 to 80%) by mass of said second charge (class B),
• 0 to 22% by weight of said third charge (class C).

• 12 à 61% en masse de ladite première charge (classe A),
• 36 à 81 % en masse de ladite seconde charge (classe B),
• 0 à 23 % en masse de ladite troisième charge (classe C).

The oxidizing charge of ammonium perchlorate (100%) in the paste results, very generally, from the introduction into the mixer, separately or as a mixture, of:

• 12 to 61% by weight of said first charge (class A),
• 36 to 81% by weight of said second charge (class B),
• 0 to 23% by weight of said third charge (class C).

• 20 à 65% en masse de ladite première charge (classe A),
• 35 à 80 % en masse de ladite seconde charge (classe B) ;

de façon encore plus préférée, de :

• 42 à 61 % en masse de ladite première charge (classe A),
• 39 à 58 % en masse de ladite seconde charge (classe B).

In the context of the advantageous variant specified above (intervention of the first and second oxidizing charges only), the oxidizing charge of ammonium perchlorate (100%) in the paste results, preferably, from the introduction into the mixer , separately or in combination, from:

• 20 to 65% by weight of said first charge (class A),
• 35 to 80% by weight of said second charge (Class B);

even more preferably, of:

• 42 to 61% by weight of said first charge (class A),
• 39 to 58% by weight of said second charge (class B).

The particle size of the aluminum load (recall here that different unimodal particle size distribution of aluminum fillers may also occur (see examples below)) is a parameter of the second order, with reference to technical problems cited above . The aluminum particles therefore have a median diameter less than or equal to 40 microns. The best results, up to the production of alumina monomodal particle size centered at 1 to 3 microns, are obtained with aluminum particles with a median diameter of between 1 and 10 microns and certain combinations of ammonium perchlorate class A and B (see examples below) introduced into the mixer to form the ammonium perchlorate feedstock.

Said aluminum filler therefore generally has a median diameter (D ₅₀ ) less than or equal to 40 μm, advantageously between 1 and 10 μm. The values of D ₁₀ and D ₉₀ of said aluminum charge advantageously correspond, respectively, to at least 1/4 and at most 4 times said median diameter.

According to its second object, the present invention relates to aluminized solid propellants that can be obtained by the above process, which process involves oxidizing ammonium perchlorate charges of different specific monomodal particle sizes.

The process of the invention, as described above, leads indeed to new composite solid propellants. Such composite solid propellants - with polyurethane binder loaded with ammonium perchlorate and aluminum - whose combustion generates less than 15%, generally between 2 and 10% by volume of alumina particles whose diameter is greater than 10 μm , are claimed per se. Their diameter (spherical equivalent) is measured by means of an optical photon correlation particle size analyzer (see above and below).

The solid propellants of the invention generally have combustion rates of between 6 and 12 mm / s and pressure exponents of between 0.15 and 0.4, advantageously between 0.2 and 0.4, over a range of operating pressure of 3 to 10 MPa, which corresponds to the standard values of the ballistic parameters. The great advantage of the method of the invention is thus to make it possible to obtain solid propellants which have such ballistic properties and whose combustion generates particles of alumina of small particle size.

The particle size of the alumina produced by the combustion of the propellants of the invention was determined by means of measuring equipment, recognized by the international community, named "rotary trap" or "Quench Particle Combustion Bomb". It was developed by the Morton Thiokol company (see PC BRAITHWAITE, WN CHRISTENSEN, V. DAUGHERTY (Morton Thiokol), Quench Bomb Investigation of Aluminum Oxide Formation from Solid Rocket Propellants (Part I): Experimental Methodology, 25th JANNAF Combination Meeting, CPIA Publication 498, vol.1, p. 175, October 1988 ). The principle is to burn a small sample of propellant at the end of a fixed rod in a chamber at room temperature pressurized, in general, with nitrogen. A bowl containing alcohol rotates around the sample. The distance between the sample and the alcohol film formed in the wall of the bowl is adjustable. Most drops ejected from the burning surface impacted the rotating liquid. After the test, the liquid is recovered and the particles analyzed.

The particle size distribution, by volume, of the recovered particles is then measured by means of a photon correlation optical particle size analyzer (PCS-DLS: Photons Correlation Spectroscopy-Diffusion Light Scattering).

The solid propellants of the invention produce, during their combustion, particles of smaller dimensions than those produced by the propellant combustion of the same type of the prior art. The percentage of the total volume (passing) corresponding to particles of diameter (spherical equivalent) greater than 10 μm is thus less than 15%, generally between 2% and 10%, for the propellants of the invention, much lower than that reference propellants of the prior art (~ 30%).

The particle size curves of the particles produced by the combustion of the propellants of the invention always show, like those of the propellants of the prior art, a particle size peak centered on approximately 0.1 to 3 μm. For certain propellants of the invention, there is also observed, as for the propellants of the prior art, a second particle size peak corresponding to particles of diameter greater than 10 μm. This second peak is centered at 10 to 50 μm for the propellants of the invention, values lower than those (60 to 100 μm) observed for the propellants of the prior art. The preferred propellants of the invention do not exhibit said second particle size peak and therefore only produce a residual percentage of particles with a diameter greater than 10 μm.

According to another of its objects, the invention relates to a solid propellant charge containing a solid propellant of the invention.

According to yet another of its objects, the invention relates to a rocket engine comprising at least one load containing a propellant of the invention.

The invention finally relates to an oxidizing charge of ammonium perchlorate, in particular useful for carrying out the process for obtaining a composite solid propellant of the invention as described above, in particular useful for obtaining a composite solid propellant of the invention as described above. Said filler is capable of being obtained by mixing at least a first filler and at least a second filler (binary mixtures) and optionally at least a third filler (ternary mixtures) as defined above, very advantageously obtainable by mixing at least a first filler and at least a second filler (binary mixtures) as defined above. It advantageously contains said feeds in the weight proportions specified above.

• La figure 1 montre un schéma de la combustion d'une goutte d'aluminium.
• La figure 2 illustre les phénomènes produisant les différentes granulométries d'alumine générées lors de la combustion d'un propergol solide.
• La figure 3 présente les courbes granulométriques en volume, mesurées au moyen d'un granulomètre optique à corrélation de photons (PCS-DLS : Photons Correlation Spectroscopy-Diffusion Light Scattering), des particules produites par le propergol préféré selon l'invention (voir l'exemple 9 ci-après) en comparaison à celles produites avec un propergol de référence de l'art antérieur (voir ci-après).

The invention is now described, in no way limiting, with reference to the accompanying figures and examples below.

• The figure 1 shows a diagram of the combustion of a drop of aluminum.
• The figure 2 illustrates the phenomena producing the different granulometries of alumina generated during the combustion of a solid propellant.
• The figure 3 presents the particle size distribution curves, measured by means of a photon correlation optical particle size analyzer (PCS-DLS: Photons Correlation Spectroscopy-Diffusion Light Scattering), particles produced by the preferred propellant according to the invention (see Example 9 below) in comparison with those produced with a reference propellant of the prior art (see below).

On the figure 1 the solid propellant, at 2, the combustion surface of said solid propellant, at 3, a drop of aluminum in combustion, at 4, the alumina cap at the bottom of said droplet 3, in 5, the flame and in 6, the plume of smoke.

On the figure 2 in 1 the solid propellant, in 2 its combustion surface, in 3 drops of aluminum, in 4 the alumina cap at the bottom of drops 3 in combustion. On said figure 2 3 'was a drop of agglomerated aluminum, 7 was charged with fumes in small particles (about 1 μm diameter) and 8 and 8' of residual oxide particles (about 0.5 diameter). - 4 μm and 40-100 μm, respectively).

It is now proposed to illustrate the invention by the examples (examples of formulation of propellants of the invention) below.

Table 1 below gives the mass percentages of the constituents (PA, AI) of solid propellants according to the invention, the ballistic properties of said propellants as well as the particle sizes of the alumina produced during the combustion of said propellants. These same data are given for three reference propellants. The solid propellants of Table 1 are solid polyurethane-bonded composite propellants and contain an oxidizing charge of ammonium perchlorate and an aluminum charge.

Reference propellants 1 and 2 have a conventional composition. They are of the type used for space applications. The reference propellant 3 shows the influence of the strong presence (42%) of small particles of ammonium perchlorate on the rate of combustion (logically small alumina particles are then obtained).

The solid propellants of the invention according to Examples 1 to 12 have combustion rates and pressure exponents measured at 5 MPa in the expected speed and exponent ranges for the targeted application area, close to those of the reference propellants. 1 and 2.

The last row of Table 1 relates to propellant M12 in Table 3 of Massa et al. (Journal of Propulsion and Power, Vol 24, No. 2, March-April 2008 ). It contains ammonium perchlorate particles of 200 μm (26.92% = 27%) and 82.5 μm (40.38% = 40%) as well as aluminum particles of 3 μm (20%) .

The size envelopes of the aluminum fillers referenced in Table 1 are shown in Table 2.

• l'échantillon de propergol testé a la forme d'un cube (d'un centimètre d'arête) sans face inhibée ;
• le porte échantillon sur lequel est collé l'échantillon à tester est placé à l'intérieur du piège rotatif ;
• pendant l'essai, l'alcool contenu dans le piège rotatif se retrouve plaqué, sous la forme d'un film (d'une épaisseur d'environ 2 mm), sur les parois latérales du bol, grâce à la mise en rotation de ce dernier ;
• la pression à l'intérieur de l'enceinte est réglée à 5 MPa relatifs. La pressurisation est effectuée par de l'azote et la distance entre l'échantillon de propergol et le film d'alcool est de 20 mm au départ de la combustion. Les particules émises sont prélevées horizontalement ;
• la face libre du cube de propergol faisant face au film d'alcool est allumée (la durée très brève de la combustion permet de maintenir une surface de combustion quasi-constante).

The alumina particles produced by the solid propellants of Table 1 were recovered using a pressurized vessel equipped with trapping means ("rotary trap" test means previously described). The procedure for capturing the particles is as follows:

• the propellant sample tested has the shape of a cube (one centimeter of edge) without an inhibited face;
• the sample holder on which is glued the sample to be tested is placed inside the rotary trap;
• during the test, the alcohol contained in the rotary trap is plated, in the form of a film (about 2 mm thick), on the side walls of the bowl, thanks to the rotation of this last ;
• the pressure inside the chamber is set to 5 MPa relative. Pressurization is carried out by nitrogen and the distance between the propellant sample and the alcohol film is 20 mm from the combustion. The emitted particles are taken horizontally;
• the free face of the propellant cube facing the alcohol film is lit (the very short duration of the combustion makes it possible to maintain an almost constant combustion surface).

The principle of recovery consists in recovering in the alcohol the condensed phase particles emitted in the combustion gases of the propellant sample.

The particle size distribution, by volume, of the recovered particles is then measured by means of a photon correlation optical particle size analyzer (PCS-DLS: Photons Correlation Spectroscopy-Diffusion Light Scattering).

Before being introduced into the granulometer, the residues recovered in suspension in ethanol are subjected to ultrasound.

With reference to the figure 3 the distribution or particle size distribution of the particles collected in ethanol during the combustion of the propellant is expressed in the form of two curves: on the one hand, the histogram giving the volume fraction of the particles as a function of the class of equivalent spherical diameter of the particles analyzed, and, on the other hand, the curve giving the cumulated volume fraction as a function of the class of equivalent spherical diameter particles analyzed.

The figure 3 shows the curves obtained for the reference propellant 1 and that of Example 9 according to the invention.

Table 1 shows the characteristic values recorded on the particle size curves of the recovered particles produced by the combustion of the reference solid propellants and examples according to the invention (see the last three columns of Table 1).

The compositions of the solid propellants of Table 1 are given by the mass percentage of the ammonium perchlorate charge and the constitution of this charge (class A / B / C), the mass percentage of aluminum and its particle size class (specified in Table 2), the complement to 100% of the mass consisting of the polymer polyol polybutadiene hydroxytelechelic PBHT R45HTLO sold by the company Sartomer, the crosslinking agent MDCI, the plasticizer DOZ and additives.

The particle size histograms always have at least one granulometric peak for diameters of less than 10 μm. The values given in the "Dpic <10 μm" column of Table 1 correspond to the value or the range of values (when there are several peaks, or when a dispersion of the values is measured over several tests) of the maximum of said at least one granulometric peak for diameters less than 10 microns measured. When the granulometric curve furthermore has a particle size peak for particles with a diameter of greater than 10 μm, the value or the range of values recorded (for example taken from several tests) of the diameter of the maximum of said particle size peak for particles with a diameter larger than 10 μm. 10 μm is indicated in the "Dpic> 10 μm" column of Table 1.

The values recorded for "Dpic <10 μm" for the propellants of the invention are close to those of the references. On the other hand, the "Dpic> 10 μm" values for the propellants of the invention are all lower than to those of references 1 and 2. For examples 7, 8, 9, 11 and 12 according to the invention, no peak particle size greater than 10 microns is observed.

The solid propellants of the invention produce a reduced amount of alumina particles larger than 10 μm in diameter, relative to the reference propellants 1 and 2. This is expressed in Table 1 by the value of the volume percentage ( volume passing on the curve giving the cumulative volume fraction as a function of the class of equivalent spherical diameter of the particles analyzed) corresponding to the classes of particles of diameter greater than 10 microns. All the propellants of the invention lead to a passing volume percentage corresponding to particles of diameter greater than 10 microns much lower than that of the reference propellant.

Among the solid propellants listed in Table 1, we can note the interest of those of Examples 8 and 9, which have a combustion rate close to that of the reference propellants (1 and 2) and produce a very low percentage of particles. of diameter greater than 10 μm.

The propellant M12 of Table 3 of Massa et al. (Journal of Propulsion and Power, Volume 24, No. 2, March-April 2008 ) contains two ammonium perchlorate ammonium perchlorate feeds of particle size distribution centered respectively on 200 μm and 82.5 μm (thus centered in the range of D ₅₀ class A and B charges according to the invention ).

Said propellant M12 has a combustion rate of 14 mm / s at 4 MPa (Figure 12c). As the burning speed of the solid propellants increases with the pressure, the burning rate of the M12 propellant at a pressure of 5 MPa (reference pressure for the examples of the invention) can only be greater than this value of 14 mm / s. It is therefore much higher than those of the reference propellants 1 and 2.

This shows that the selection of ammonium perchlorate feedstocks on the sole criterion of their median diameter (D ₅₀ ) is insufficient to ensure both a very close combustion rate of those of the reference propellants 1 and 2 and a very low percentage of alumina particles produced with a diameter greater than 10 μm (incidentally, it is recalled here that Massa et al. on the particle size of the alumina produced). It is therefore by selecting charges of ammonium perchlorate with D ₁₀ , D ₅₀ and D ₉₀ spectra adapted that the applicant has achieved the desired objective. <u> Table 1 </ u> Mass rate of ammonium perchlorate and mass distribution of size classes A / B / C Mass ratio and size class of aluminum Vc not D peak <10μm D peak> 10μm % passing volume> 10 μm 5 MPa mm / s microns microns Réf.1 68% 85/0/15 18% (D) 7.9 0.35 0.8-1.5 60-80 29 Réf.2 60% 85/0/15 18% (E) 8.3 0.35 0.8-1.5 20-80 22 ref.3 69% 58/0/42 19% (I) 11.8 0.34 1.68 - 6 Ex.1 68% 41/37/22 18% (E) 11.1 0.24 1.2-2.0 20-40 6 Ex.2 68% 25/60/15 18% (F) 10.3 0.27 1.5-2.0 10-40 4 Ex.3 68% 30/50/20 18% (E) 11 0.28 1.5-2.0 20-40 5 Ex.4 68% 13/80/7 18% (F) 10.8 0.26 1.5-2.5 10-40 2 ex.5 68% 50/50/0 18% (F) 7.4 0.16 1.3 45 10 Ex.6 68% 43/57/0 18% (F) 7.8 0.22 1.5 35 4 Ex.7 68% 13/80/7 18% (E) 10.8 0.29 1.45 - 5 Ex.8 69% 60/40/0 19% (F) 8.4 0.25 0.3 - 3 Ex.9 70% 60/40/0 16% (F) 7.8 0.26 0.3-2.0 - 3 Ex.10 68% 50/50/0 18% (50% F / 50% G blend) 7.1 0.33 0.4 55 7 Ex.11 69% 69.6 / 11.6 / 18.8 19% (50% H / 50% I mixture) 9.6 0.3 1.44 - 5.5 Ex.12 69% 69.6 / 11.6 / 18.8 19% (50% H / 50% J mix) 9.9 0.27 1.24 - 10.8 M12 67% 27% 200 μm 40% 82.5 μm) 20% 3 μm 14 (at 4 MPa) Granulometric classes of aluminum fillers used for reference and Examples 1 to 10 of Table 1 D 13.9 <D ₁₀ <17.7 33.7 <D ₅₀ <42.9 72.5 <D ₉₀ <86.4 E 2.5 <D ₁₀ <3.7 4.5 <D ₅₀ <7.3 9.0 <D ₉₀ <16.0 F 3.0 <D ₁₀ <4.5 7.5 <D ₅₀ <10.0 11.0 <D ₉₀ <19.0 BOY WUT 13.0 <D ₁₀ <15.0 38 <D ₅₀ <50 85.0 <D ₉₀ <100.0 H 0.3 <D ₁₀ <0.6 3.5 <D ₅₀ <7 84 <D ₉₀ <100 I 9 <D ₁₀ <11 14.5 <D ₅₀ <16.5 23 <D ₉₀ <26 J 7.5 <D ₁₀ <9 30 <D ₅₀ <32 81 <D ₉₀ <85

Claims (15)

1. A process for obtaining a solid composite propellant, comprising:

   - the production of a paste by blending, in a mixer, a mixture containing from 5 to 15 wt.% of a liquid hydroxytelechelic polybutadiene,
   from 60 to 75 wt.% of an oxidizing charge of ammonium perchlorate,
   from 15 to 20 wt.% of a reducing charge of aluminum, and
   less than 5 wt.%, of at least one agent for crosslinking said liquid hydroxytelechelic polybutadiene in an amount such that the NCO/OH bridging ratio is between 0.8 and 1.1, is advantageously 1, at least one plasticizer and at least one additive;

   - pouring of the paste obtained into a mold;

   - thermal crosslinking of said paste in said mold;

   said oxidizing charge of ammonium perchlorate in said paste resulting from the introduction, into said mixer, separately or as a mixture, of at least:

   + a first charge whose monomodal particle size distribution has a D₁₀ value of between 100 µm and 110 µm, a D₅₀ value of between 170 µm and 220 µm and a D₉₀ value of between 315 µm and 340 µm, and

   + a second charge whose monomodal particle size distribution has a D₁₀ value of between 15 µm and 20 µm, a D₅₀ value of between 60 µm and 120 µm and a D₉₀ value of between 185 µm and 220 µm; and, optionally,

   + a third charge whose monomodal particle size distribution has a D₁₀ value of between 1.7 µm and 3.6 µm, a D₅₀ value of between 6 µm and 12 µm and a D₉₀ value of between 20 µm and 32 µm;

   said reducing charge of aluminum having a median diameter of less than or equal to 40 µm;
   the solid composite propellant obtained having, over an operating pressure range from 3 to 10 MPa, a rate of combustion between 6 and 12 mm/s and a pressure exponent between 0.15 and 0.4 and advantageously between 0.2 and 0.4 and the combustion of said solid propellant generating less than 15% and generally between 2% and 10% by volume of alumina particles greater than 10 µm in diameter.
2. The process according to claim 1, characterized in that said oxidizing charge of ammonium perchlorate in said paste results from the introduction into said mixer, separately or as a mixture, of said first charge and of said second charge.
3. The process according toclaim 1 or 2, characterized in that said oxidizing charge of ammonium perchlorate in said paste results from the introduction into said mixer, separately or as a mixture, of:

   + 12 to 70 wt.% of said first charge,

   + 10 to 81 wt.% of said second charge,

   + 0 to 23 wt.% of said third charge.
4. The process according to any one of claims 1 to 3, characterized in that said oxidizing charge of ammonium perchlorate in said paste results from the introduction into said mixer, separately or as a mixture, of:

   + 12 to 61 wt.% of said first charge,

   + 36% to 81 wt.% of said second charge,

   + 0 to 23 wt.% of said third charge.
5. The process according to any one of claims 1 to 3, characterized in that said oxidizing charge of ammonium perchlorate in said paste results from the introduction into said mixer, separately or as a mixture, of:

   + 20 to 65 wt.% of said first charge, and

   + 35 to 80 wt.% by weight of said second charge.
6. The process according to claim 5, characterized in that said oxidizing charge of ammonium perchlorate in said paste results from the introduction into said mixer, separately or as a mixture, of:

   + 42 to 61 wt.% of said first charge,

   + 39 to 58 wt.% of said second charge.
7. The process according to any one of claims 1 to 6, characterized in that said reducing charge of aluminum has a median diameter between 1 and 10 µm.
8. The process according to any one of claims 1 to 7, characterized in that the D₁₀ and D₉₀ values of the particle size distribution of said reducing charge of aluminum correspond, respectively, to at least a quarter of the value of said median diameter and to not more than 4 times the value of said median diameter.
9. A solid composite propellant with a polyurethane binder filled with ammonium perchlorate and aluminum, able to be obtained via the process according to any one of claims 1 to 8; said solid composite propellant having, over an operating pressure range from 3 to 10 MPa, a rate of combustion between 6 and 12 mm/s and a pressure exponent between 0.15 and 0.4 and the combustion of said propellant generating less than 15% by volume of alumina particles greater than 10 µm in diameter.
10. The solid propellant according to claim 9, whose combustion generates between 2% and 10% by volume of alumina particles greater than 10 µm in diameter.
11. The solid propellant according toclaim 9 or 10, characterized in that, over an operating pressure range from 3 to 10 MPa, its rate of combustion is between 0.2 and 0.4.
12. A solid propellant charge, characterized in that it contains a solid propellant according to any one of claims 9 to 11.
13. A rocket engine, characterized in that it comprises at least one charge according to claim 12.
14. An oxidizing charge of ammonium perchlorate, which is especially useful in the process for obtaining a solid composite propellant according to any one of claims 1 to 8, able to be obtained by mixing at least a first charge and at least a second and optionally a third charge as defined in claim 1, able to be very advantageously obtained by mixing at least a first charge and at least a second charge as defined in claim 1.
15. The oxidizing charge according to claim 14, containing said first, second and optionally third charges in the weight percentages indicated in any one of claims 3 to 6.

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