EP0705809A1 - Propelland based on phase-stabilized ammonium nitrate - Google Patents

Abstract

A solid propellant (I) for rocket motors or gas generators contains 35-80 wt. % ammonium nitrate (AN) with a mean particle size of 5-200 microns, in pure form or phase-stabilised with NiO, KNO3 or CsNO3 (i.e. PSAN), 15-50 wt.% of a binder system contg. a binder polymer and an energy-rich plasticiser, and 0.2-5.0 wt. % of a combustion moderator (II) consisting of V/Mo oxides as an oxide mixt. or mixed oxide.

Description

The invention relates to a solid fuel for rocket engines or gas generators, which contains ammonium nitrate (AN) in pure or phase-stabilized form (PSAN) as an oxidizer.

Solid fuels of the type mentioned generally have a low burning rate and a high pressure exponent. The burning rate can be increased by adding solid energetic substances, such as octogen (HMX) or hexogen (RDX), or metals with high heat of combustion, such as aluminum or boron. Combinations with high-energy binders serve the same goal. These include isocyanate-bound glycidyl azidopolymer (GAP), polymers containing nitrate esters, such as polyglycidyl nitrate and polynitratomethylethyloxetane, or nitroamino-substituted polymers. Even if this can increase the rate of combustion, the pressure exponent and the temperature coefficient are not or only slightly reduced.

Additions of ammonium perchlorate, which lead to an increase in the rate of combustion, lower the pressure exponent at higher doses, but lead to the formation of hydrochloric acid in the exhaust gas and thus to strong smoke formation in high air humidity.

In doublebase and composite doublebase solid fuels, the combustion behavior can be influenced favorably by adding lead and copper salts or oxides in combination with soot, but these additives can only be used to a limited extent with fuels containing ammonium nitrate. The salts and oxides mentioned in turn act primarily to increase the rate of combustion, but cannot reduce the pressure exponent sufficiently.

The object of the invention is to improve the combustion behavior of solid fuels on the basis of pure and phase-stabilized ammonium nitrate.

According to the invention, such a solid fuel consists of 35 to 80% by mass ammonium nitrate (AN) in pure form or phase-stabilized form (PSAN) with nickel oxide, potassium or cesium nitrate with an average grain size of 5 to 200 µm, 15 to 50% by mass of a binder system from one Binder polymer and a high-energy plasticizer as well as 0.2 to 5.0 mass% of a combustion moderator made of vanadium / molybdenum oxide as an oxide mixture or mixed oxide.

Solid fuels of this formulation show a very favorable burning behavior. Depending on the composition, burning rates of over 8mm / s at normal temperature and a combustion chamber pressure of 10 MPa are achieved. The pressure exponent in the range from 4 to 25 MPa, possibly 7 to 25 MPa, reaches values of n ¾ 0.6, in the favorable case n ¾ 0.5. This combustion behavior makes the solid fuel composed according to the invention particularly suitable for use in missiles for tactical or strategic missile defense.

The solid propellants according to the invention are initially distinguished by the fact that they contain pure AN as the oxidizer or phase-stabilized ammonium nitrate reacted with nickel oxide, potassium or cesium nitrate as the oxidizer, the nickel oxides preferably containing 1 to 7% by mass, potassium or cesium nitrate containing 3 to 15 % By mass are used. They stabilize the crystal phases of the AN and suppress larger volume changes in the grain in the temperature range from -40 ° to + 70 ° C. The incorporation into the crystal matrix of the AN takes place via a chemical reaction of the additives with the melt of the pure ammonium nitrate with elimination of water. The most favorable particle shape for the production of the fuel can be obtained by spraying the melt and rapid cooling in a cold, cyclone-like air flow. For low-smoke fuels, AN is preferably used in pure form with a water content below 0.2% by mass or NiO-stabilized PSAN, while PSAN stabilized with potassium or cesium nitrate brings with it somewhat higher smoke proportions.

The combustion behavior is significantly influenced by the grain size of the AN or PSAN. A finely crystalline form with an average grain size of 5 to 200 μm with a proportion of 35 to 80 mass% in the fuel is preferred. Particularly favorable burn-up values result when the AN or PSAN fraction predominantly in smaller ones Grain size from 10 to 80 µm and less in average grain size from 100 to 160 µm is available.

The solid propellant according to the invention can also contain high-energy substances, in particular nitramines, such as hexogen (RDX) or octogen (HMX) with an average particle size of 2 to 200 μm with a proportion of 1 to 4% by mass.

Furthermore, metals such as aluminum, magnesium or boron can be part of the fuel with 0.5 to 20% by mass. A grain size of 0.1 to 50 µm is recommended.

In order to give the fuel sufficient chemical stability, it is advantageous to add stabilizers which act as nitrogen oxide and acid scavengers. These are preferably diphenylamine, 2-nitrodiphenylamine, N-methylnitroaniline, which are used alone or in combination with one another in concentrations of 0.4 to 2% by mass. These can be combined, in particular in the case of fuels containing nitric acid ester, with small amounts in the range of 0.5% by mass of the magnesium oxide acting in the same sense.

The combustion moderators made from vanadium / molybdenum oxide as oxide mixture or mixed oxide used according to the invention with 0.2 to 5.0 mass% are advantageously added with carbon black or graphite in a fraction of 5 to 20 mass% of the fraction of the combustion moderator.

Another essential component in concentrations of 15 to 50 mass% is a binder system consisting of a binder polymer and a high-energy plasticizer. The binder polymer itself can be inert, it preferably being an isocyanate-curing, bifunctional or trifunctional hydroxyl-substituted polyester or polyether prepolymer. Instead, high-energy polymers, preferably isocyanate-curing, di- or trifunctional hydroxy-substituted glycidyl azidopolymer, can also be used.

The high-energy plasticizers are preferably selected from the group of chemically stable nitrate esters, nitro, nitroamino or azido plasticizers.

Trimethylolethane trinitrate (TMETN), butanetriol trinitrate (BTTN) or diethylene glycol dinitrate (DEGDN) are particularly suitable as nitrate esters.

An example of a nitro plasticizer is a 1: 1 mixture of bisdinitropropyl formal / acetal (BDNPF / A), while a nitro amino plasticizer is a 1: 1 mixture of N-ethyl and N-methylnitratoethylnitroamine (EtNENA, MeNENA) or Nn-butyl-N -nitratoethylnitroamine (BuNENA) or N, N'-dinitratoethylnitroamine (DINA) is suitable.

In particular, short-chain, bisazido-terminated GAP oligomers (GAP-A) or 1, 5-diazido-3-nitroaminopentane (DANPE) come into consideration as azide softeners.

Depending on the content, compatibility and energy content of the binder components, the ratio polymer / plasticizer is 1: 3 to 20: 1 mass%. The binder polymers can of course also be used in pure form.

The purer or phase stabilized ammonium nitrate is preferably 0.1 to 1% by mass of its anti-caking agent fraction, e.g. ultra-fine (grain size about 0.02 µm) silica gel, sodium lauryl sulfonate, tricalcium phosphate or other surfactants are added.

According to the invention, the vanadium / molybdenum oxide combustion moderators can be ideally combined with nickel and copper salts, oxides or complexes, which leads to a further increase in the combustion rate.

The combustion moderators preferably consist of mixed oxides in which molybdenum is present in the + VI and + V oxidation states and vanadium in the + IV and + V oxidation states. Exemplary compositions of the mixed oxides are V₆Mo₄O₂₅ and V₆Mo₁₅ O₂₅O₆₀.
The mixed oxides can furthermore contain chromium (III) and titanium (IV) oxides as the inactive carrier material or one which also participates in the reaction.

In a preferred embodiment, the combustion moderators have a grain size in the range from 1 to 60 μm, preferably 1 to 10 μm and a high internal surface area of 5 to 100 m 2 / g, preferably 20 to 60 m 2 / g.

With an average grain size of less than 10 µm and a constant, high inner surface, the burning rate in the low pressure range can be increased further compared to coarser grain and the pressure exponent can be further reduced.

The solid propellants according to the invention experience an advantageous further development in that high-melting Metal carbides or nitrides, preferably silicon and zirconium carbide in the concentration range from 0.1 to 1 mass% are added. Above all, this suppresses an unstable, oscillating combustion behavior when used in rocket engines. This is particularly important for low-smoke burning fuels without the addition of metal.

Solid fuels of the type described, in particular with oxidizers in the form of pure AN or Ni-PSAN, are suitable due to their energy content, their low-smoke, hydrochloric acid-free combustion and their comparatively low, mechanical and detonative sensitivity for use in rocket engines, while lower-energy formulations with a higher binder content are suitable for use as gas generator propellants.

Examples

The upper part of Table 1 shows nine different formulations with pure ammonium nitrate and a PSAN phase-stabilized with 3% nickel oxide. The burning rate r (mm / s) at 20 ° C and at three different combustion chamber pressures is given in the lower part of the table for the individual formulations. Below this is the pressure exponent n for various pressure ranges given in brackets.

In addition to the dependency on the type of combustion moderator added, a dependency on the coarse / fine fraction of the ammonium nitrate used and on the content of the azidopolymer in relation to the plasticizer part can also be observed. With a predominant share of AN The average grain size 160 µm can be achieved with V / Mo oxide combustion moderators with AN1 only a mere 8 mm / s at 10 MPa combustion chamber pressure. Without or with conventional combustion moderators based on lead salts and soot, the same formulation only results in 6.6 mm / s. In contrast, with AN2 with a predominantly fine fraction of the ammonium nitrate, there is a significant increase in the burning rate with a further reduction in the pressure exponent.

Due to the high plasticizer content, AN3 to AN8 have high specific impulses of 234s for AN6 and AN8 and 237s for AN3, AN4 and AN5 with a relaxation ratio of 70: 1. In this case, the synergistic effect of copper compounds and V / Mo oxide combustion moderators has proven to be particularly favorable. Copper phthalocyanate has proven to be the most favorable in the combination of increase in the rate of combustion, reduction in the pressure exponent and acceptable stability properties.

The burning behavior of the formulation AN9 shows that the nickel diaminodinitrate as phase stabilizer in the AN also has a favorable effect on the burning behavior. This is also observed with the addition of nickel phthalocyanate in the AN8 formulation. The addition of RDX also increases the burning rate without, however, positively influencing the pressure exponent.

Table 2 shows with the examples AN10, AN11 and AN12 AN / GAP fuel formulations in which the combustion moderator is contained in different grain sizes and grain distributions with otherwise the same composition. in the The lower part of the table clearly shows the increase in the burn-off rate achieved with the grain becoming smaller, while at the same time lowering the pressure exponent. AN13 shows the burning behavior when formulated with an azido softener, while AN14 is a formulation with the addition of zirconium carbide, with the help of which combustion oscillations are suppressed when the fuel is used in rocket engines.

, wobei $\text{A=Konstante}$

(Vieilles Gesetz: ${\text{r=A x p}}^{\text{n}}$

) aufgezeigt, und zwar in Abbildung 1 für die Formulierungen AN1, AN2 und AN9, in Abbildung 2 für AN3, AN4 und AN5, in Abbildung 3 für AN7, AN8 und AN9 und in den Abbildungen 4 und 5 für die Formulierungen AN10, AN11, AN12 bzw. AN 13 und AN14.The combustion behavior is a function in the diagrams $\text{lg r [mm / s] = f (lg p) [MPa] = n lg p + A}$

, in which $\text{A = constant}$

(Vieille's law: ${\text{r = A xp}}^{\text{n}}$

), namely in Figure 1 for the formulations AN1, AN2 and AN9, in Figure 2 for AN3, AN4 and AN5, in Figure 3 for AN7, AN8 and AN9 and in Figures 4 and 5 for the formulations AN10, AN11, AN12 or AN 13 and AN14.

). Abbildung 3 zeigt eine wirkungsvolle Abbrandregelung auch bei hohem Nitratesteranteil im Treibstoff ohne RDX-Zusatz. Hierfür verantwortlich ist die synergistische Wirkung von Cu- und Ni-Komplexen mit den V-/Mo-Oxid Abbrandmoderatoren.

Tabelle 2 Treibstofformulierungen und Abbrandeigenschaften AN 10 AN 11 AN 12 AN 13 AN 14 AN 160 µm 25,6 25,6 25,6 25,6 18 AN 55 µm 38,4 38,4 38,4 38,4 42 RDX 5 µm - - - - 5 GAP/N 100 11 11 11 11 15 TMETN 11 11 11 17,6 8 BTTN 11 11 11 - 8 GAP-A - - - 4,4 - DPA 0,6 0,6 0,6 0,6 0,5 V/Mo-oxid 53 µm - 2,0 - - - V/Mo-oxid 11 µm 2,0 - - 2,0 - V/Mo-oxid 3,7 µm - - 2,0 - 2,4 Ruß 0,4 0,4 0,4 0,4 0,6 Zirkoncarbid - - - - 0,5 Abbrandgeschwindigkeit bei 20°C (mm/s) r₂MPa 3,8 3,2 5,1 4,4 5,3 r₇MPa 6,5 6,1 7,5 7,6 8,7 r₁₀MPa 8,3 7,3 9,4 9,2 10,5 Druckexponenten n 0,59 0,51 (2-10) 0,55 (4-25) 0,49 (2-18) 0,50 (4-25) (Bereich MPa) (4-25) 0,69 (10-25) The comparison of Figures 1 and 2 shows that with the same RDX content of 10%, the effect of the burn moderator is less pronounced with a high plasticizer content than with a high GAP content ( $\text{Pl = platicizer}$

). Figure 3 shows effective combustion control even with a high nitrate ester content in the fuel without RDX addition. This is due to the synergistic effect of Cu and Ni complexes with the V / Mo oxide combustion moderators.

Table 2 Fuel formulations and burning properties AN 10 ON 11 ON 12 AN 13 AN 14 AN 160 µm 25.6 25.6 25.6 25.6 18th AN 55 µm 38.4 38.4 38.4 38.4 42 RDX 5 µm - - - - 5 GAP / N 100 11 11 11 11 15 TMETN 11 11 11 17.6 8th BTTN 11 11 11 - 8th GAP-A - - - 4.4 - DPA 0.6 0.6 0.6 0.6 0.5 V / Mo oxide 53 µm - 2.0 - - - V / Mo oxide 11 µm 2.0 - - 2.0 - V / Mo oxide 3.7 µm - - 2.0 - 2.4 soot 0.4 0.4 0.4 0.4 0.6 Zirconium carbide - - - - 0.5 Burning rate at 20 ° C (mm / s) r₂MPa 3.8 3.2 5.1 4.4 5.3 r₇MPa 6.5 6.1 7.5 7.6 8.7 r₁₀MPa 8.3 7.3 9.4 9.2 10.5 Pressure exponent n 0.59 0.51 (2-10) 0.55 (4-25) 0.49 (2-18) 0.50 (4-25) (Range MPa) (4-25) 0.69 (10-25)

Claims (25)

Solid fuel for rocket engines or gas generators, consisting of 35 to 80% by mass ammonium nitrate (AN) in pure form or phase-stabilized form (PSAN) with nickel oxide, potassium or cesium nitrate with an average grain size of 5 to 200 µm, 15 to 50% by mass of a binder system from a binder polymer and a high-energy plasticizer, and 0.2 to 5% by mass of a combustion moderator made of vanadium oxide / molybdenum oxide as an oxide mixture or mixed oxide. Solid fuel according to claim 1 with a further proportion of 1 to 40% by mass of high-energy nitramines selected from hexogen or octogen, with an average grain size of 2 to 200 µm. Solid fuel according to claim 1 or 2 with a further proportion of 0.5 to 20% by mass of metals, selected from aluminum, magnesium and boron with a grain size of 0.1 to 50 µm. Solid fuel according to one of claims 1 to 3 with a further proportion of 0.4 to 2 mass% of a stabilizer acting as a nitrogen oxide and acid scavenger from diphenylamine, 2-nitrodiphenylamine or N-methylnitroaniline or a combination thereof. Solid fuel according to one of claims 1 to 4 with the addition of carbon black or graphite with 5 to 50% by mass of the fraction of the combustion moderator. Solid propellant according to one of Claims 1 to 5, in which the binder polymer is an isocyanate-curing bi- or trifunctional hydroxy-substituted polyester or polyether prepolymer. Solid propellant according to one of claims 1 to 5, wherein the binder polymer is a high-energy polymer. Solid propellant according to claim 7, wherein the high-energy polymer is an isocyanate-curing, bi- or trifunctional hydroxy-substituted glycidyl azidopolymer (GAP). Solid propellant according to one of Claims 1 to 8, in which the high-energy plasticizer is selected from the group of chemically stable nitrate esters, nitro, nitroamino or azido plasticizers. Solid fuel according to claim 9, wherein the nitrate ester is a trimethylolethane trinitrate (TMETN), butanetriol trinitrate (BTTN) or diethylene glycol dinitrate (DEGDN) is. Solid fuel according to claim 9, wherein the nitro plasticizer is a 1: 1 mixture of bisdinitropropyl formal / bisdinitropropylacetal (BDNPF / BDNPA). Solid propellant according to claim 9, wherein the nitroamino plasticizer is a 1: 1 mixture of N-ethyl- and N-methylnitratoethylnitroamine (EtNENA and MeNENA) or Nn-butyl-N-nitratoethylnitramine (BuNENA) or N, N'-dinitratoethylnitramine (DINA) . Solid propellant according to Claim 9, in which the azido plasticizer consists of short-chain GAP oligomers (GAP-A) with terminal bisazido groups or of 1,5 diazido-3-nitroaminopentane (DANPE). Solid fuel according to one of Claims 1 to 13, characterized in that the binder polymers and the plasticizers are present in the binder system in a ratio of 1: 3 to 20: 1% by mass, depending on the type, compatibility and energy content. Solid fuel according to one of Claims 1 to 14, in which the pure ammonium nitrate has a water content of less than 0.2% by mass. Solid fuel according to one of claims 1 to 14, in which ammonium nitrate is used, which is phase-stabilized by reaction with 1 to 7% by mass of nickel oxide or 3 to 15% by mass of potassium or cesium nitrate. Solid propellant according to claim 16, wherein the phase stabilized Ammonium nitrate (PSAN) can be obtained by mixing the additives into the melt of pure ammonium nitrate (AN) and spraying the melt with simultaneous cooling. Solid propellant according to any one of claims 15 to 17, wherein 0.1 to 1 mass% of its fraction of ultrafine silica gel (grain size about 0.02 µm), sodium lauryl sulfonate, tricalcium phosphate or other surface-active surfactants are added as anti-caking agents to the ammonium nitrate. Solid fuel according to one of claims 1 to 18, wherein the ammonium nitrate is present with an average grain size of 10 to 80 µm. Solid fuel according to one of Claims 1 to 19, in which the vanadium oxide / molybdenum oxide combustion moderators are used in conjunction with Cu and Ni salts, oxides or complexes. Solid fuel according to one of claims 1 to 20, wherein the combustion moderators contain mixed oxides of molybdenum of the oxidation levels + VI and vanadium of the oxidation levels + V and + IV. Solid fuel according to one of claims 1 to 21, wherein the combustion moderators have chromium (III) or titanium (IV) oxides as carrier material. Solid fuel according to one of claims 1 to 22, characterized in that the combustion moderators have a grain size in the range from 1 to 60 µm, preferably 1 to 10 µm, and a large inner surface from 5 to 100 m² / g, preferably 20 to 60 m² / g. Solid fuel according to one of claims 1 to 23, characterized in that it contains 0.1 to 1% by mass of high-melting metal carbides or nitrides as additives for suppressing an unstable, oscillating combustion behavior when used in rocket motors. Solid fuel according to claim 22, characterized in that the additives are silicon and / or zirconium carbide.

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