Through careful experimentation, this paper establishes that moisture trapped inside the pores of activated charcoal was the reason for the burn-rate enhancement of composite solid propellant observed in literature. This paper demonstrates that, even with the presence of moisture in activated charcoal, the propellants can not only be cured to be free from blow holes and voids but also have good mechanical properties. Experiments were also carried out to examine the possible mechanism for high burn rates and burn-rate pressure index observed in composite propellants when moisture was present in activated charcoal. Scanning-electron-microscope images show that moisture in activated charcoal reduces the binder melt flow. It is noticed that formation of the bubbly layer is more when moisture is present in the binder. This bubbly layer might be exploding near the surface of the propellant and taking away the binder melt layer. This could be the cause for the observed increase in the burn rate and burn-rate pressure index of aluminized composite propellants.

Periyapatna A. Ramakrishna

Department of Aerospace Engineering

Sumit Verma

ALUMINIZED COMPOSITE PROPELLANTS

BUBBLY LAYERS

Burn rates

Composite solid propellant

MELT FLOW

MELT LAYER

Possible mechanisms

PRESSURE INDEX

Binders

Experiments

Mechanical properties

Moisture

Propellants

Composite propellants

IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

Investigations on Activated Charcoal, a Burn-Rate Enhancer in Composite Solid Propellant

Journal of Propulsion and Power

This studymakes an attempt to demonstrate a technique to embed the catalyst on ammoniumperchlorate surface. In the present study, various techniques like differential scanning calorimeter, thermogravimetric analysis, scanning electron microscope, and x-ray computed tomography scan analysis as well as others were used to establish the effectiveness of this technique.Micron-sized iron oxide was used in this study for embedding the catalyst on ammonium perchlorate. Burn rates of pellets containing different fractions of iron oxide from various sources were measured to establish an optimumfraction for highest burn rate of ammoniumperchlorate pellets achievable with iron oxide. These burn ratesweremeasured using aCrawford bomb, and a fraction of1%iron oxide (Sigma-Aldrich)was highestamong them for pellets. The burn rate of the ammoniumperchlorate pellet with 1%iron oxide at 70 bar pressure recordedwas 13.33 mm/s. This fraction of iron oxide was also used to study the effect of embedding the catalyst on ammonium perchlorate surface when used in nonaluminized composite solid propellants. It is observed that catalyst-embedded ammonium perchlorate yields a higher burn rate as compared to the mechanically mixed catalyst. ©2017 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.

Effects on burn rates of pellets and propellants with catalyst-embedded AP

Iron oxide and copper chromite have been used as burn-rate modifiers of composite solid propellants. In recent times, studies have been reported on potassium-doped ammonium perchlorate and on dry activated charcoal. These have shown an increase in composite solid propellant burning rates. The studies on composite solid propellants using dry activated charcoal have also shown a reduction in the burn-rate pressure index for a composite solid propellant. With this knowledge, experiments are conducted to develop compositions that result in both high burning rates and low burn-rate pressure index of the propellant.In additiontothese, the study also reports propellants with dual burnrate pressure index. The change in the burn-rate pressure index is from 0.2 to 0.65 in one of the propellants. These could be very useful in that the same grain can act as boost and sustain grain depending on the combustion chamber pressure. With the addition of different burn-rate modifiers, the pressure at which the change in burn-rate pressure index is observed shifts. This could be a very useful tool for propellant designers. It was observed that, with the use of activated charcoal along with potassium-doped ammonium perchlorate, the burn-rate pressure index was brought down from around 0.65 to 0.38, whereas the burn rates were still higher (60%) than the base propellant. Copyright © 2015 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.

Burning rate studies: Potassium-doped ammonium perchlorate with other burn-rate modifiers

This study deals with the mechanical activation of pyral with PTFE. Pyral is a flake-like aluminium particle with a large specific surface area (~22.5m2/g). This paper, through a variety of tests like the TGA, DSC, particle size analysis, SEM analysis and other tests tries to establish that this mechanically activated aluminium is a good replacement for conventional aluminium used in a solid propellant. Burn rates were also measured at pressures ranging from 10 to 70bar using a modified Crawford bomb. The burn rates of solid propellants prepared with this mechanically activated pyral powder were found to be higher than that of non-activated pyral powder and much higher than that of those reported in literature with similar mechanically activated aluminium. This has been explained to be due the large specific surface area of aluminium used in these experiments which undergo exothermic fluorination reactions with PTFE. Two phase losses and slag accumulation are the two problems encountered when aluminium is used in composite solid propellants. Slag accumulation has shown a significant reduction with the use of this activated powder over non-activated pyral. © 2016 The Combustion Institute.

Combustion and Flame

Effect of mechanical activation of high specific surface area aluminium with PTFE on composite solid propellant

Ammonium perchlorate is the most widely employed oxidizer for composite solid propellants. When exposed to atmosphere, it absorbs moisture and agglomerates. It is usually vacuum dried in order to avoid this agglomeration. When ammonium perchlorate that has been exposed to atmosphere for a certain period of time, is used in making a composite solid propellant, the burning rate is different because of the change in particle size distribution due to its agglomeration. This change in burning rate will change the thrust-time profile from that of what it is designed for. As one goes to a finer ammonium perchlorate particle size this problem becomes more evident. Experimental studies aimed at reducing the agglomeration of ammonium perchlorate by coating it with activated charcoal. Ammonium perchlorate coated with 1 % activated charcoal showed almost no agglomeration, even when the particle size of ammonium perchlorate is approx. 1 μm. The burning rates also remained unchanged when ammonium perchlorate coated with 1 % activated charcoal was employed in propellant composition, after it has been exposed to the atmosphere for a period of 1 h. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Propellants, Explosives, Pyrotechnics

Reducing Agglomeration of Ammonium Perchlorate Using Activated Charcoal

This paper examines the effect of mixer size on the density of the propellant and it also explores the role of the propellant density with regards to burning rate and burn rate pressure index. Propellant samples were prepared in the four different size (15, 70, 200 and 1000 g) mixers with identical input of ingredients to examine the effect of mixer size on density and burning rate of the composite solid propellant. It was noticed that density and burning rate of the propellant changes significantly with change in the mixer size from 15 g to 1000 g. This is because for the smaller mixers the surface area to volume ratio is large and the actual percentage of aluminum and ammonium perchlorate (especially coarse) that goes into the propellant reduces. High burning rate with decrease in mixer size is also accompanied with increase in burn rate pressure index. The composition analysis was also carried out and it is noticed that the actual percentage of the ingredients is different from the intended percentage of the ingredients and percentage change is more when the mixer size decreases. © 2013 IAA.

Acta Astronautica

Dependence of density and burning rate of composite solid propellant on mixer size

This paper reports the discovery of activated charcoal as an effective burn rate enhancer of aluminized composite solid propellant. Experiments were carried out using a strand burner at pressures ranging from 10 to 70. bar with varying fractions of activated charcoal. The results show that with the addition of activated charcoal in an aluminized composite propellant higher burn rates (in excess of 25. mm/s at 70. bar) were obtained. This paper also explores the possibility of further enhancing the burn rates of aluminized composite propellant by using iron oxide along with activated charcoal. Burn rates recorded with iron oxide and activated charcoal both present in the propellant were in excess of 50. mm/s at 70. bar. It was noticed that these high burn rates were accompanied by a higher (0.65) pressure index of combustion. A series of experiments were designed to understand the burn rate enhancement with activated charcoal in aluminized composite propellant. TGA and DSC tests were carried out on AP pellets with and without activated charcoal to detect any condensed phase activity of activated charcoal. These tests did not show any significant difference between the AP pellets with and without activated charcoal. The AP pellets with and without activated charcoal were also burnt in a strand burner to understand if any gas phase reaction was being catalyzed by activated charcoal. AC does not enhance any gas phase activity while addition of AC in AP increased the LPDL of AP and reduced the burn rate. Lastly, sandwich propellant with activated charcoal at the interface was prepared to determine if interface reactions were being affected with the addition of activated charcoal. It has been observed that with the addition of activated charcoal at the AP-binder interface the burn rates are higher than those recorded without activated charcoal at the AP-binder interface. © 2009 The Combustion Institute.

Activated charcoal - A novel burn rate enhancer of aluminized composite propellants

Nano-aluminium particles of ∼50 nm size, produced at this laboratory, are added to composite solid propellants based on ammonium perchlorate and hydroxyl-terminated poly-butadiene binder that exhibit plateau burning rate trends and those including burning rate catalysts. The nano-aluminized propellant burning rates are compared with corresponding micro-aluminized and non-aluminized ones in the 1-12 MPa pressure range. The mid-pressure extinction of the matrixes containing the fine-sized ammonium perchlorate particles in the propellant along with the binder is investigated in all the cases to understand the mechanism of plateau-burning. Further, the variations in aluminium content, the aluminium size (within nano- and micro-ranges), bimodal combination of nano- and micro-aluminium are considered. Ferric oxide and titanium dioxide are the burning rate catalysts considered. Large scale accumulation of aluminium is observed not only in micro-aluminized matrixes, but also in nano-aluminized ones as clusters of 1-5 μm size. Since aluminium is added at the expense of the coarse ammonium perchlorate particles to preserve the total-solids loading in the present formulations, addition of micro-aluminium decreases the burning rate; whereas, nano-aluminized propellants exhibit ∼80-100% increase in the burning rate under most conditions. The near-complete combustion of nano-aluminium close to the burning surface of the propellant provides heat feedback that controls the burning rate. Mid-pressure extinctions of matrixes and plateau burning rates of propellants are washed out when nano-aluminium is progressively added beyond 50% in bimodal aluminium blends, but low pressure-exponents are observed in the nano-aluminized propellant burning rates at elevated pressures. Adjusting the plasticizer content in the binder alters the pressure range of plateau burning rates in non-aluminized propellants. Catalysts increase the burning rate by ∼50-100% in non-aluminized and micro-aluminized propellants, but in nano-aluminized propellants, the μm-sized catalyst does not affect the burning rate significantly; whereas, the nanometre size catalysts increases the burning rate merely by ∼5-15%. © 2009 The Combustion Institute.

Effect of nano-aluminium in plateau-burning and catalyzed composite solid propellant combustion

47th AIAA/ASME/SAE/ASEE Joint Propulsion Conference &amp; Exhibit

Role of moisture in activated charcoal in composite solid propellant

Effect of mixer size on density and burn rate of composite solid propellant

Journal of Hazardous Materials

Studies on the effect of plasticiser and addition of toluene diisocyanate at different temperatures in composite propellant formulations

Investigations on activated charcoal, a burn-rate enhancer in composite solid propellant

Journal	Journal of Propulsion and Power
ISSN	07484658
Open Access	No