Burning Rate Catalysts Research Articles

Thermal stability of the burning of the base subsystem of components of a composite propellant

The problem of the thermal stability of the base subsystem of components of a composite solid propellant with respect to the introduction of heat-absorbing agents, inhibitors, and burning rate catalysts was considered. It was demonstrated that the response of the base subsystem to the introduction in it of additives is equivalent to a change in the initial temperature of the propellant, i.e., is determined by its burning rate temperature sensitivity. The competition of the fuel components for oxidative species and the role of this phenomenon in the formation of the structure of the combustion wave were examined. Extensive experimental data on the effect of heterogeneous fillers of various natures on the burning rate of the composite system were obtained.

Characterization studies on aging properties of acetyl ferrocene containing HTPB‐based elastomers

AbstractIn composite solid propellants, low‐molecular‐weight species such as burning rate catalysts, plasticizer, etc. which migrate into liner and thermal insulation layers during curing and storage invariably result in poor mechanical and ballistic properties of the propellants. In the present study, the migration of the burning rate catalyst, acetyl ferrocene, was investigated spectrophotometrically (UV–visible) by evaluating the extent of hindrance to such migration after applying a barrier (liner) of various crosslink densities between the additive (HTPB‐TDI‐plasticizer–acetyl ferrocene) and nonadditive (HTPB‐TDI) gumstocks replicating the propellant and insulating layer, respectively. Enhancing the crosslink densities of liner via a trifunctional aziridine crosslinking agent inhibited migration. The aging of additive gumstock was done at 60°C and its mechanical properties and extent of acetyl ferrocene migration were also evaluated and analyzed. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 2538–2545, 2006

The Effect of Ammonium Nitrate, Coarse/Fine Ammonium Nitrate Ratio, Plasticizer, Bonding Agent, and Fe2O3 Content on Ballistic and Mechanical Properties of Hydroxyl Terminated Polybutadiene Based Composite Propellants Containing 20 % AP

Abstract It was aimed to develop the HTPB (hydroxyl terminated polybutadiene) based composite solid propellant with reduced smoke in acceptable mechanical and ballistic properties by using AN (ammonium nitrate) and AP (ammonium perchlorate) as oxidizing agents. For this reason, five different combinations, employed by increasing the AN content as 33, 43, 53, 63, and 73 % and decreasing the AP content as 40, 30, 20, 10, and 0 % were used. The propellant containing 20 % AP and 53 % AN was selected to have good processability and lower smoke content among five compositions. The content of DOA (dioctyl adipate) used as a plasticizer was varied between 35 % and 25 % of HTPB binder to improve the mechanical properties with taking the above composition as a reference. In decreasing the DOA content, mechanical properties could not be improved to the desired level, and the amount of the bonding agent TEPANOL (tetraethylene pentamineacrylonitrileglycidol) was increased from 0.2 % to 0.35 mass percent with keeping DOA content at the level of 25 % of HTPB binder. 0.495 N/mm2 maximum tensile stress and 25.5 % elongation at maximum tensile stress and 3.635 N/mm2 elastic modulus values were then obtained with 0.35 % TEPANOL value. The effect of coarse/fine AN ratio on buring rate of the propellant was also tested for three different ratios, i.e., 80/20, 70/30, and 60/40. The 70/30 ratio gave the highest burning rate. Then, the content of burning rate catalyst Fe2O3 (iron oxide) was varied between 2 % and 1.0 % with keeping the coarse/fine AN ratio at 70/30, and it was found that 2 % Fe2O3 gave the highest burning rate. Values of densities and heat of explosion were also determined for all compositions tested.

Novel Segmented Thermoplastic Polyurethanes Elastomers Based on Tetrahydrofuran Ethylene Oxide Copolyethers as High Energetic Propellant Binders

AbstractNovel thermoplastic polyurethane (TPU) elastomers based on copolyether (tetrahydrofuran ethylene oxide) as soft segments, isophorone diisocyanate and 1,4‐butanediol as hard segments were synthesized for the purpose of using as propellant binders. In order to increase the miscibility of thermoplastic polyurethane elastomers with nitrate ester, polyethylene glycol (PEG) is incorporated in the co‐polyether (tetrahydrofuran ethylene oxide) as soft segment. When the molecular weight and content of polyethylene glycol are controlled to 4000 and 6% of soft segments, respectively, the properties of thermoplastic polyurethane elastomers are most perfect. If plasticizing ratio of nitrate ester to thermoplastic polyurethane elastomers exceeds 4 no crystallinities are determined at room temperature. The propellant samples were prepared by a conventional absorption‐rolling extrusion process and the mechanical and combustion properties evaluated afterwards. The maximum impulse reaches up to 265∼270 s which is a little bit higher than that of a HTPB propellant. The measured results reveal a promising TPE propellant candidate which shows good processing temperature (<393 K) and excellent mechanical properties. An attracting feature which can be pointed out is that the burning rate pressure exponent reaches as low as 0.36 without the addition of burning rate catalysts. This enables an easy control of propellant combustion.

Plateau Burning Behavior of Ammonium Perchlorate Sandwiches and Propellants at Elevated Pressures

Further results on combustion of sandwiches made of alternating layers of ammonium perchlorate (AP) and a matrix of AP particles in polymeric binder in an expanded pressure range of 0.345-13.78 MPa (50-2000 psig), over a wide range of matrix lamina thicknesses, are reported. Inclusion of a nanoparticle-size burning rate catalyst in the matrix is also considered. The sandwich burning rates indicate plateaus over the 6.89-13.78 MPa (1000-2000 psig) pressure range for select ranges of matrix lamina thickness. These are correlated with similar plateau trends in the burning rates of composite propellant formulations with bimodal particle size distribution of the oxidizer and appropriate choice of coarse AP size, wherein the fine AP/binder matrices are of identical composition to those tested in the sandwiches. The dependence of the sandwich burning rates on the matrix lamina thickness and the quenched surface features are examined to explain the plateau burning rate trends. The results indicate that the two-dimensional coupling of heat feedback from the hot, near-surface parts of the oxidizer/fuel diffusion flamelets is diminished at elevated pressures due to their greater proximity to the burning surface and the corresponding shrinking of their lateral extent.

Universal behaviour in erosive burning of solid propellants

This paper considers the extensive data and correlations on the erosive burning of solid propellants. A relatively simple nondimensional relationship between the ratio of the actual to nonerosive burn rate (η) and a quantity g, which is the product of g 0—the ratio of free stream mass flux to the mass flux from the surface for nonerosive condition- and Re 0 m , where Re 0 is the Reynolds number based on the nonerosive mass flux of the propellant and port diameter, is shown to correlate most data within the accuracies of the experiments with m = −0.125. This shows the above relationship to account for the effects of pressure, aluminum, even up to a proportion of 17%, burn rate catalysts, and motor size. It is concluded that the suggested correlation between η and g may be adopted universally for most practical propellants.

Thermal decomposition of phase-stabilised ammonium nitrate (PSAN), hydroxyl-terminated polybutadiene (HTPB) based propellants. The effect of iron(III) oxide burning-rate catalyst

Phase-stabilised ammonium nitrate (PSAN) and hydroxyl-terminated polybutadiene (HTPB) are the main ingredients of propellants used with success in some pyrotechnic igniter components of the VULCAIN liquid rocket engine for the ARIANE 5. Small amounts of selected additives play an important role in solving some of the problems presented by composite propellants that include ammonium nitrate (AN). Iron(III) oxide (Fe 2O 3), for example, can be used as a burning-rate modifier in PSAN/HTPB propellants and although its effect on the burning rate is well known, its mechanism of action is not well understood. Thermogravimetry (TG), differential thermogravimetry (DTG) and differential thermal analysis (DTA) have been applied to study the slow thermal decomposition of selected compositions to investigate the mechanism of action of Fe 2O 3 as a burning-rate modifier of PSAN/HTPB propellants. The compositions evaluated include PSAN, Fe 2O 3 and HTPB cross-linked with isophorone diisocyanate (IPDI) as ingredients. No effect of Fe 2O 3 on PSAN decomposition is found. Fe 2O 3 shows an effect on the kinetics of the first stage of HTPBIPDI decomposition and increases the exothermicity of HTPBIPDI decomposition. In the decomposition of PSAN HTPBIPDI Fe 2O 3 propellants, the effect of Fe 2O 3 is also observed and a synergetic interaction between PSAN and HTPBIPDI is found, for which a physical-chemical explanation is given.

Effect of iron-containing catalysts on thermal decomposition of cured GAP-AP propellants

The effects of various burning rate catalysts on thermal decomposition of cured glycidyl azide polymer (GAP)-ammonium perchlorate (AP) propellants have been studied by means of thermal analysis and a modified vacuum stability test (MVST). Four types of iron-containing catalysts examined in this paper are catocene, ferrocenecarboxaldehyde (FCA), ferrocene, and ferric oxide. Results of differential thermal analysis (DTA) and thermogravimetric analysis (TG) revealed that the catalysts play an important role in the decomposition of both AP and GAP. The peak decomposition temperature (Tm) of DTA curves and onset decomposition temperature (To) of TG patterns considerably shifted to a lower temperature as the concentration of catalysts increased in the propellants. The endothermic temperature of AP, however, is unaffected by the presence of burning rate catalysts in all cases. The activation energy of decomposition of the propellants in range of 80 to 120°C is determined, based on the MVST results.

Prediction of performance of burning-rate catalysts: a group contribution approach

Prediction of performance of burning-rate catalysts: a group contribution approach

Effect of certain lead and copper compounds as ballistic modifier for double base rocket propellants

Abstract During our search for better burn rate catalysts and platonizers the effect of lead oxide with lead copper salts of organic acids was studied. Basic lead and copper salts of aliphatic acids have been found to produce more or less similar catalytic and plateau effects, whereas basic copper salts of aromatic acids were comparatively more effective in producing higher burn rates than basic lead salts, although reduction of pressure index values was more pronounced with basic lead salts. The results have been explained in the light of existing theories on catalysis and platonization.

Energetic Solid Fuels for Ducted Rockets (II)

AbstractThe combustion characteristics of variable‐flow ducted rockets were evaluated in order to obtain optimum design parameters of the gas generators. The energetic solid fuels used for the gas generators were glycidyl azide polymer (GAP) with burning rate catalysts. The burning rate of GAP based energetic fuels was much higher than that of composite and double‐base based fuel‐rich propellants. The pressure exponent of the burning rate was high enough to obtain a wide range of variable‐flow rat. Two types of combustion test were conducted: a semi‐free jet and a direct connect flow. The pressure‐time response in the primary combustor obtained by the use of a throttable nozzle was evaluated.

Effects of liquid burn rate catalysts on Rheological Properties of High‐Energy Composite Propellants

AbstractEffects of several liquid burning rate catalysts on rheological properties of composite rocket propellants on the basis of hydroxy‐terminated polybutadiene as a binder and ammonium perchlorate as an oxidizer have been examined. Theoretical explanation of the observed effects of liquid catalysts on certain rheological properties of the mentioned propellants are given. Laboratory procedures for synthesis of used catalysts are described. The results of physico‐chemical characterization of synthesized catalyst are also presented.

Ballistic Modification of RDX‐Based CMDB Propellants

AbstractThe effect of lead and copper salts and certain metallic oxides was studied on the burning rates of RDX‐based CMDB propellants in the pressure region 35–105 [kg/cm2]. Lead methylene disalicylate (LMDS), basic copper salicylate (BCS). cobaltic oxide and lead stannate produced higher burning rates by 10%–16%. However, these additives were comparatively more effective with nitramine‐based CMDB propellants than AP‐based CMDB propellants. Fluorides of iron, lead and chromium were ineffective as burning rate catalysts. Inclusion of carbon black along with lead salts or metallic oxide gave only marginally higher burning rates. None of the ballistic modifiers studied produced plateau/mesa effect.

Temperature sensitivity of Burning Rate of Ammonium Perchlorate Propellants

AbstractThe temperature sensitivity of burning rate of ammonium perchlorate (AP) composite propellants was studied as a function of AP particle size and a burning rate catalyst. A simplified temperature sensitivity model was presented in order to discriminate the effect of the gas phase and solid phase reactions on the initial propellant temperature (T0). The temperature sensitivity was decreased by the addition of small sized AP particles and/or 2,2‐bis(ethylferrocenyl)propane (BEFP). This is caused by the insensitive burning surface temperature to T0. Thus, the gas phase reaction rate becomes little dependent on T0, and the temperature sensitivity decreases.

Combustion Mechanism of Double‐Base Propellants with lead burning rate catalysts

AbstractOn the basis of relevant experimental phenomena and results, which also include the results on the domain of non‐propellant combustion, this paper has determined basic reactions caused by lead burning rate catalysts in the combustion process and their approximate reaction temperature. In the presence of carbonaceous matter on the burning surface the partial NO is reduced to N2 through six reactions occurred on the carbonaceous matter instead of the reaction between NO and CO. As a result of changing the reducing path of a part of NO the burning rate rises through increasing the temperature gradient in the fizz zone at the burning surface. The reactions between PbO and C and between PbO and CO check the burning rate to rise through expending carbonaceous matter on the burning surface and causing char particles to “fly off” the burning surface. The super‐rate, plateau and mesa effects are perfectly explained with these reactions and the fundamentals of heat transference. The production of the effects arises from the competing of two actions to increase burning rate and to check the burning rate enhancement of lead burning rate catalysts and the effect of the pressure on the burning rate. Because of the fact that the chance to form carbon nuclei and the time of the carbon deposit, the covering ratio of the carbonaceous matter on PbO particles, and the temperature increasing rate and the lagging temperature difference in C‐PbO interfaces depend on the pressure, the ability by the reaction between PbO and C and between PbO and CO checking the burning rate to rise makes a great difference in different ranges of the pressure. In addition, according to the combustion mechanism advanced in the paper the effects of the physical and chemical properties of lead burning rate catalysts, especially their ability to absorb the ultraviolet light, on the rate‐increased values and the pressure ranges of the plateau and the mesa regions have been expounded.

Selective Radiative Preheating of Aluminum in Composite Solid Propellant Combustion

A two-phase model has been developed to study aluminum (Al) particle preheating through selective radiation absorption in composite solid propellants. The two phases considered are one strongly absorbing particle (Al) phase and another weakly absorbing matrix (ammonium perchlorate (AP), binder and catalyst particle) phase surrounding the Al phase. Separate energy balance equations for the Al and matrix phases are developed. Both the matrix and the Al phase are assumed to be nonemitting, anisotropically scattering, absorbing media. The parameters identified which strongly influence Al preheating and melting are Al size, mass fraction, burn rate, and level of incident radiant flux. It was found that large Al mass fractions and small Al particle sizes promote lower Al temperatures. The effect of adding submicron iron oxide burn rate catalyst particles on aluminum preheating was also investigated. It was found that the addition of small amounts of catalyst can theoretically reduce Al temperatures significantly by dominating the optical properties. These results should prove useful to propellant formulators in trying to reduce the problem of unwanted Al agglomeration.

Ballistic anomalies in solid rocket motors due to migration effects

Double base and composite propellants are generally used for rocket motors, whereby double base propellants basically consist of nitrocellulose plasticized with an explosive plasticizer, mostly nitroglycerine, and in some cases with an additional inert plasticizer and ballistic additives. Composite propellants consist of an oxidizer like ammonium perchlorate and of aluminum, binder and plasticizer and often contain liquid or solid burning rate catalysts. A common feature of both propellants is that they contain smaller or larger amounts of chemically unbonded liquid species which tend to migrate. If these propellants loose part of the plasticizer by migration into the insulation layer, not only will there be a change in mechanical propellant properties but also the bond between propellant and insulation may degrade. However, depending on the severity of these effects, the change in the ballistic properties of the propellant grain caused by plasticizer migration may be of even more importance. In the past, most emphasis was placed on the behaviour of end-burning configurations. However, more recent theoretical and experimental studies revealed that not only for end-burning grain configurations but also for internal burning configurations there is a common effect which is responsible for ballistic anomalies: migration of liquid species from the propellant into the insulation. By using a plasticizer equilibrated insulation in an internal burning configuration the liquid species migration and thus the previously observed ballistic anomalies are avoided. Using this approach for end-burning configurations provides similar positive results. The various factors affecting plasticizer migration are studied and discussed, and several methods to prevent liquid species migration are described as well as methods to obtain plasticizer resistant insulations.

Mixtures of oxides of copper and chromium as potential burning-rate catalysts for composite solid propellants

Mixtures of oxides of copper and chromium as potential burning-rate catalysts for composite solid propellants

Role of Binders in Solid Propellant Combustion

Abstract : The objective of this program was to investigate and define the effects of inert binder properties on composite solid propellant burning rate. Experimental pyrolysis data were obtained for many binders of practical interest over a wide range of heating rates and pressures, in several environmental gases, with and without 10-percent ammonium perchlorate (AP) contained in the sample, and in some cases with catalysts. These data were used to extract kinetics constants from Arrhenius plots, and heat of decomposition. In addition, motion pictures were taken of the pyrolyzing surface and gas samples were extracted for analysis. Pyrolysis kinetics varied between binders, but were found to be independent of pressure, the presence of AP, and the presence of burn rate catalysts; however, a chlorine gas environment had a material effect upon the results. All of the binders exhibited molten, boiling surfaces mingled with char, to varying degrees; the amount of char increased with AP present, and in chlorine. Relevant data were input to the Derr-Beckstead-Price combustion model in order to associate binder properties with known binder effects on burning rate. Although the effects were predictable, they stemmed from properties other than pyrolysis kinetics; however, the binder data as applied to the model revealed possible deficiencies in the model, which are discussed. It appears that the approach of combustion tailoring by binder modification would have to involve the gas phase combustion processes rather than surface pyrolysis. Therefore, future work concerning the role of binder should be directed toward the gas phase.

An Experimental Investigation of Rapid Depressurization Extinguishment

Results are presented from an experimental study of solid propellant extinguishment by rapid depressurization. Systematic variations in propellant binder, oxidizer loading level, burning rate catalyst, metal loading, and exhaust pressure level were studied. The effects of motor configuration on extinguishment and reignition are discussed. Results indicate that combustion extinguishment requirements are determined by the binder type, percentage of ammonium perchlorate oxidizer, motor geometry, and exhaust pressure level as well as the pressure and depressurization rate. The von Elbe model with a coefficient of one provides a rough correlation of extinguishment requirements.