Ammonium Perchlorate Particles Research Articles

Research on microscopic structure–activity relationship of AP particle–matrix interface in HTPB propellant

Abstract The matrix and particle interface of hydroxyl-terminated polybutadiene (HTPB) propellant is the weakest part of its mechanical properties, making it prone to dewetting damage and destroying the structural integrity of the propellant. This article uses nano-indentation, gas cluster ion beam etching, and X-ray photoelectron spectroscopy experimental analyses to study the physicochemical properties of the interface and subsequently construct a microscopic model for the HTPB matrix and ammonium perchlorate particle interface. The model fully considers the existing forms of curing agent toluene diisocyanate, bonding agent Tris (2-methyl-aziridine) phosphine oxide (MAPO), and the aging products of the propellant in the interface structure. Meanwhile, the physicochemical properties, mechanical properties, and adhesive properties of the interface under different tensile loading conditions were analyzed. The results indicate that the bonding agent MAPO significantly enhances the mechanical and adhesive properties of the interface. The interface is sensitive to changes in temperature and tensile rate, and the aged interface is more fragile.

Effect of aluminum and ammonium perchlorate particle sizes on the condensed combustion products characteristics of aluminized NEPE propellants

Aluminum (Al) is usually added to solid propellants to improve the combustion performance, however the condensed combustion products (CCPs) especially the large agglomerates generated from aluminum combustion can reduce the specific impulse of the engine, and result in two-phase loss, residue accumulation and throat liner ablation. Al and ammonium perchlorate (AP), as important components of NEPE propellants, can affect the formation process of the CCPs of aluminized NEPE propellants. To clarify the effect of Al and AP particle sizes on the properties of the CCPs of aluminized NEPE propellants, a constant-pressure quench vessel was adopted to collect the combustion products of four different formulations of NEPE propellants. It was found that the condensed combustion products are mainly divided into aluminum agglomerates and oxide particles, the diameter of the aluminum agglomerates of these four different formulations of NEPE propellants at 7 MPa was smaller than that in 3 MPa, and the shells of the aluminum agglomerates were smoother and the spherical shape was more perfect. X-ray diffraction analysis of the CCPs of the four NEPE propellants under 3 MPa revealed the presence of both Al and Al2O3. With the increase of the particle size of Al and AP, the oxidation degree of aluminum particles decreases. The particle size of the CCPs of the four different formulations of NEPE propellants under 1 and 3 MPa was analyzed by using a laser particle size analyzer, it is found that the increase of AP particle size is helpful to reduce the size of condensate combustion products. Based on the classical pocket theory, establishing a new agglomeration size prediction model, which can be used to predict the agglomeration size on the burning surface. Compared with the empirical model, the new agglomeration size prediction model is in good agreement with the experimental results.

Control of burning rate pressure sensitivity for solid propellants by changing the interfacial contact of Al/HMX/AP with precisely located graphene-based energetic catalysts

The control of burning rate pressure sensitivity is essential for stable and reliable combustion of solid propellants. It has been proved that the combustion behavior of propellants can be effectively tuned by interfacial control of Al/oxidizers. In this work, core-shell Al-based composites, using oxidizers such as ammonium perchlorate (AP) and cyclotetramethylene tetranitramine (HMX) as the shell layer, have been prepared with a well-controlled location of graphene-based carbohydrazide complexes (GO-CHZ-M, M = Co2+ or Ni2+) as the catalysts. The catalysts can be located inside HMX or embedded on the surface of AP particles. The decomposition of AP and HMX could be greatly promoted with a trace amount of catalyst. Under the synergistic effects of Al/oxidizer interfacial control and GO-CHZ-M, the ignition delay time is shortened by >48 % with increased in flame radiation. More importantly, the burning rate (r) and pressure exponent (n) of the solid propellants are effectively regulated in a wide range. In particular, the use of Al@HMX/Co results in a lowered n of 0.29 within 1∼20 MPa compared to 0.79 for the blank reference sample. The agglomeration of Al particles during combustion was also inhibited due to the micro-explosion effect of Al@HMX composites. Novelty and Significance statementThe innovative approaches of integrating Al/HMX/AP composites and precise catalysis of graphene-based energetic catalysts in solid propellants have successfully achieved, regarding the modulation of the burning rates and pressure sensitivity. Moreover, the effect of catalyst location on the ignition delay and burning rates has also been studied thoroughly and clarified. This paper provides new insight into the regulation of combustion performance of solid propellants, with improved reaction efficiency and maintained energy density.

SEM/EDX and FTIR/ATR Behavior of Ammonium Perchlorate Under Accelerated Aging in a New Solid Rocket Motor Fuel Composition with Superior Explosive and Mechanical Performance

Abstract The oxidation potential of perchlorates is high, which makes this material suitable for fuels with high specific impulse. Perchlorates are characterized by a ClO4- moiety/anion in their molecular structure and are crystalline materials used in the formation of solid fuels. Ammonium perchlorate (AP) particle size and shape influence the manufacturing process of fuels and their burning rate. The physical and chemical processes that can occur in the natural degradation process of composite fuels are related to molecular reactions and diffusion phenomena governed by kinetic processes and can be accelerated by increasing the temperature. The paper presents studies carried out by scanning electron microscopy and infrared spectrometry on the behavior of ammonium perchlorate in the new composite material of solid rocket motor fuel under the effect of high temperature, in the range of 65-85οC, at regular time intervals. The self-initiation temperature was also determined, with a temperature rise rate controlled at 5ºC/minute. It is very likely that these accelerated aging studies will show the changes that occur in the stability, sensitivity, mechanical and functional properties of fuels during their lifetime.

Effect of pressure, Mg content and AP size on the microscale flame structure of Mg-based propellant

The Mg-based propellant is considered to be a promising fuel for underwater propulsion, but the mechanism of the change of the burning rate is unclear. The Mg-based propellant was divided into two parts on the basis of the BDP multi-flame model: large-size oxidizer particle and pseudo-propellant consisting of fine oxidizer and other components, and the micro steady-state combustion model of Mg-based propellant was established. Quantitatively analysis on the gas-phase multi-flame structure was performed, which focused on the effect of pressure, Mg content, and oxidizer particle size on the burning rate. This model was verified by the results of combustion experiments on ammonium perchlorate (AP) /hydroxyl‑terminated polybutadiene (HTPB) composite propellant and Mg-based propellant, and the mean absolute percentage error between the burning rate obtained from the simulation and the experimental measurements was less than 5%. Results indicated that the flame structure of Mg-based propellant exhibited typical BDP flame characteristic. As pressure increased from 1 MPa to 4 MPa, the premixed AP flame and the preliminary diffusion flame were closer to the burning surface, which enhanced the heat feedback. And accordingly, the burning rate raised from 5.93 mm/s to 9.79 mm/s. Mg content mainly affect the combustion process of the pseudo-propellant. The premixed flame above the pseudo-propellant gradually disappeared as the Mg content increased from 15% to 63%, which led the burning rate to decrease from 17.45 mm/s to 7.83 mm/s. AP particle size affected the effectiveness of the preliminary diffusion flame on the burning surface and resulted in a change in the burning rate. These findings can provide theoretical guidance for the design of Mg-based propellant formulations.

Impacts of metal oxide crystalline structure on the decomposition of solid propellants under combustion heating rates

Ammonium perchlorate (AP) has been the oxidizer of choice for composite solid propellants for decades and has been the object of decomposition studies for safety monitoring. Typically, studies perform differential scanning calorimetry (DSC) or thermogravimetric analysis (TGA) to show how metal oxides (MO) commonly incorporated into propellants alter AP decomposition rates and completeness of reaction. Most past decomposition work studies temperatures below the crystal phase transition (240°C) from orthorhombic phase to cubic, which impose internal stresses within the lattice of AP particles. Phase change induces a partial decomposition, which does not follow a shrinking core behavior; instead, it develops a network of pores up to a few microns in size throughout. During low-temperature decomposition, particles lose approximately 30-40 % of their mass. Simultaneous DSC/TGA (STA) use low heating rates for combustion environments but offer information on MO's catalytic and electron transport modifications. This work demonstrates how the crystalline morphology MO additives mechanistically alter the combustion properties of composite propellants by identifying modes for promoting decomposition in AP and HTPB. MO morphology determines the electron structure of the molecule, which sets the band gap properties of the particles. This study evaluated different morphologies and a range of MOs to identify the most active MO for decomposing A.P. Kissinger analysis was applied using STA data at heating rates of 10-, 20-, and 30-°C/min revealing significant shift in the high-temperature decomposition with a range of metal oxides. Higher heating rates were evaluated using CO2 laser ignition to identify the time to first gas using the MO that offers the best heat absorption, such as the aluminum oxides. This higher heating rate was found do more accurately represent the changes in the combustion rates in the final propellant mixture. Additionally, it was shown that electron transport additives like CuO show the most significant impact on combustion, and thermal absorbers offer the lowest impact on AP/HTPB combustion. This understanding offers a new approach to propellant design not previously presented and suggests future testing for tailoring the use of metal oxides in propellants.

Numerical investigation and experimental validation of aluminized propellant combustion under high pressures: Critical effects of heat feedback

Aluminum is a common metal fuel in propellants, but its effects on the burning rate and the underlying mechanism are still unclear. Numerical calculations and temperature measurement experiments were carried out within the pressure range of 0.1–9 MPa, and the effects of the pressure and the ammonium perchlorate (AP) particle size on the combustion characteristics of aluminized propellants were studied. First, based on a two-dimensional micro-scale combustion model of an AP/hydroxyl‑terminated polybutadiene (HTPB) propellant, by considering the “heat sink” effect of aluminum on the burning surface and the chemical reaction of aluminum in the gas phase, a numerical calculation model of heat flux coupled with the steady-state combustion of an aluminized propellant was established. The flame structure of an aluminized propellant obtained by this model conformed to the multi-flame structure and could correctly reflect the influence of the AP particle size and pressure on the burning rate and other combustion characteristics. Subsequently, the influence of radiation heat feedback was further introduced into the model, which greatly improved its accuracy in predicting the burning rate at low pressures of 1–3 MPa. More importantly, the temperature distributions of the propellants were measured using embedded tungsten–rhenium thermocouples, and the flame temperature was obtained by further processing the temperature measurement data according to the thermocouple response characteristics. The temperature measurement results showed that with the increase in the pressure and the decrease in the size of the AP particles, the temperature gradient increased significantly, the flame temperature increased slightly, and the burning rate of the propellant increased. By analyzing how the temperature gradient and the burning rate changed with pressure, it was found that the conduction heat feedback was important to determine the burning rate.

Preventing Agglomeration and Enhancing the Energetic Performance of Fine Ammonium Perchlorate through Surface Modification with Hydrophobic Reduced Graphene Oxide

AbstractThe combustion rate of energetic composite propellants (ECPs) is adversely affected by the agglomeration of fine ammonium perchlorate (AP), which is the most commonly used oxidizer. To address this issue, this study explores the use of hydrophobic reduced graphene oxide (R‐GO) for surface modification of fine AP particles. An intermittent spray coating technique was used to coat the fine AP particles with graphene oxide (GO) dispersion. Hydrophilic GO was transformed into hydrophobic R‐GO by gentle thermal annealing. Fine AP was then scrutinized for changes in hygroscopicity and thermal decomposition behavior before and after coating with R‐GO. The findings demonstrate that surface modification significantly reduces the hygroscopicity of fine AP, reducing the moisture adsorption rate from 0.28 % to 0.11 % after a 10‐day exposure to ambient humidity. Moreover, this surface modification markedly enhances its energetic performance, doubling the energy release from 717.5 to 1413.5 J ⋅ g−1 when incorporating a 0.3 % mass of R‐GO coating. This study suggests that surface modification of fine AP with R‐GO is a promising strategy for addressing its agglomeration issue and improving its performance in ECPs.

Droplet and solution contact assembled cobalt alginate for enhanced properties of ammonium perchlorate

Ammonium perchlorate (AP) needs to be combined with nano-metal oxides to improve its thermal decomposition performance when applied to propellant, but with reduced safety performance. Herein, inspired by the rapid gelation of sodium alginate (Na-A) in the presence of metal ions to produce well-dispersed metal oxides after calcination, a novel “droplet and solution contact assembly” (DSCA) method is proposed and applied to prepare spherical AP/cobalt alginate (Co-A) composites. In spherical composite, Co-A forms a three-dimensional network structure and AP particles are uniformly and tightly filled in the network structure of Co-A, exhibitng outstanding safety performance. During the thermal decomposition process of it, Co-A thermally decomposes into evenly dispersed nano-Co3O4 and solves the facilely gathering trouble of nano-Co3O4, further results in an enhanced catalytic effect in thermal decomposition. In addition, compared with conventionally used methods for the spherification of composites, such as spray drying and electrospray methods, the method provides simpler, safer preparation conditions without high-temperature or high-voltage, which can be applied for mass production. Moreover, the atomization method is improved by replacing traditional atomization instrument with a hand-held high-velocity air spray gun, reducing the cost of the experiment and improving the convenience of the experiment. This study offers a new perspective for the design and systhesis of spherical composites.

In-situ synthesis of AP@Co/BIM composites with improved thermal performance and anti-hygroscopicity

Reducing the hygroscopicity and thermal decomposition temperature of ammonium perchlorate (AP) is of great significance for its application in solid rocket propellants. The AP@Co/BIM composites was prepared in this work by the coordination reaction of benzimidazole (BIM) and Co2+ on the surface of small-size AP (s-AP) particles, which can significantly reduce the hygroscopicity and improve the thermal performance of s-AP. The prepared AP@Co/BIM composites were characterized by scanning electron microscopy, infrared spectroscopy, x-ray diffraction, differential scanning calorimeter, thermogravimetric analysis and contact angle measurement. The results show that a dense and uniform Co/BIM complex is successfully coated on the surface of s-AP particles. Compared with the s-AP, the decomposition peak temperature of AP@Co/BIM decreases by 75.3 °C when the coating content is 25 wt% and its contact angle with water increases by 69.25°. At the same time, the hygroscopicity test shows that the moisture content of s-AP is only 3.2% of the s-AP after being placed at a relative humidity of 88% for 72 h. In addition, the burning rate of AP@Co/BIM based propellant increases by 5.28 mm s−1 compared with that of the s-AP. This study provides a reference for improving the thermal property and reducing the hygroscopicity of s-AP. It also has a certain application prospect in improving the combustion performance of propellants.

Modern Competing Flames Model for Composite Ammonium Perchlorate/Hydroxyl-Terminated Polybutadiene Propellant Combustion

The competing flames model, also termed the Beckstead–Derr–Price model, for steady-state heterogeneous propellant combustion has been widely used but has not been sufficiently updated in decades or compared to modern propellant combustion databases. In the current study, historical competing flames modeling approaches were thoroughly documented; and an improved framework was outlined and updated to include several improvements, such as variable flame temperatures, specific heat capacities, and latent heat terms. Model parameters were initially taken from previous literature, but the fuel and diffusion flame parameters were optimized based on a compiled database of unimodal propellant burning rates from the literature spanning a wide range of ammonium perchlorate (AP) particle sizes (), AP mass concentrations (70–87.5%), and combustion pressures (0.7–20.7 MPa). The improved model was compared to AP monopropellant, unimodal, and multimodal propellant burning rate databases from the literature. General dependencies of the burning rate-to-oxidizer concentration and size were accurately captured. The predictive capability of the improved model for AP monopropellant burning rates and unimodal propellant formulations was excellent, where the only significant discrepancies were noted for very fine AP particles (). Model predictions for multimodal formulations were moderate and could be improved by alternative pseudopropellant apportionment and statistical accounting schemes.

Enhanced Decomposition of Ammonium Perchlorate-Ethyl Cellulose-Molybdenum Disulfide Nanocomposites.

Ammonium perchlorate (AP) is commonly used in propulsion technology. Recent studies have demonstrated that two-dimensional (2D) nanomaterials such as graphene (Gr) and hexagonal boron nitride (hBN) dispersed with nitrocellulose (NC) can conformally coat the surface of AP particles and enhance the reactivity of AP. In this work, the effectiveness of ethyl cellulose (EC) as an alternative to NC was studied. Using a similar encapsulation procedure as in recent work, Gr and hBN dispersed with EC were used to synthesize the composite materials Gr-EC-AP and hBN-EC-AP. Additionally, EC was used because the polymer can be used to disperse other 2D nanomaterials, specifically molybdenum disulfide (MoS2), which has semiconducting properties. While Gr and hBN dispersed in EC had a minimal effect on the reactivity of AP, MoS2 dispersed in EC significantly enhanced the decomposition behavior of AP compared to the control and other 2D nanomaterials, as evidenced by a pronounced low-temperature decomposition event (LTD) centered at 300 °C and then complete high-temperature decomposition (HTD) below 400 °C. Moreover, thermogravimetric analysis (TGA) showed a 5% mass loss temperature (Td5%) of 291 °C for the MoS2-coated AP, which was 17 °C lower than the AP control. The kinetic parameters for the three encapsulated AP samples were calculated using the Kissinger equation and confirmed a lower activation energy pathway for the MoS2 (86 kJ/mol) composite compared to pure AP (137 kJ/mol). This unique behavior of MoS2 is likely due to enhanced oxidation-reduction of AP during the initial stages of the reaction via a transition metal-catalyzed pathway. Density functional theory (DFT) calculations showed that the interactions between AP and MoS2 were stronger than AP on the Gr or hBN surfaces. Overall, this study complements previous work on NC-wrapped AP composites and demonstrates the unique roles of the disperagent and 2D nanomaterial in tuning the thermal decomposition of AP.

Correction: Copper chromite decorated on nitrogen-doped graphene aerogel as an efficient catalyst for thermal decomposition of ammonium perchlorate particles

Correction: Copper chromite decorated on nitrogen-doped graphene aerogel as an efficient catalyst for thermal decomposition of ammonium perchlorate particles

Investigation on the influence of high rate cooling crystallization process (HRCCP) parameters on the preparation and thermal behavior of ammonium perchlorate particles using Taguchi method

The preparation of fine ammonium perchlorate (AP) particles and its thermal behavior are the most important properties in propellants. In this study, the effects of temperature, pressure, solvent type (water and ethanol), and anticaking agent- sodium dodecyl sulfate (SDS) were investigated on the AP particles using the Taguchi approach in high-rate cooling crystallization process (HRCCP). The average particle size (APS) of AP particles was calculated using laser mass spectrometry (LMS-30). The results showed that the anti-caking agent and solvent type were represented the main effect on the preparation of micronized AP particles, based on analysis of variance. Furthermore, the optimum condition was ethanol solvent, 10 atm pressure, 0.4% SDS, and 60 °C temperature. Also, the thermal behavior of the optimized particles was investigated using TG/DSC analysis.

Numerical simulation of aluminum particle agglomeration near the burning surface of solid propellants

Aluminum is an important additive in solid propellants used to improve energy efficiency, but agglomeration of aluminum particles can reduce the specific impulse of the engine, increase two-phase flow losses and cause ablation of the adiabatic layer. Therefore, it is important to understand the mechanism of formation, mode of movement and particle size characteristics of aluminum agglomerates in solid propellants to study the inhibition of agglomeration. In this paper, a three-dimensional numerical simulation of aluminum particle agglomeration near the burning surface of solid propellants was conducted using the discrete unit method based on direct tracking calculations of the detailed motion of individual particles. The model considered physical processes such as burning surface motion, aluminum particle precipitation, turbulent pulsation and the heating and melting of aluminum particle and used a grid-based contact detection method to accelerate the computational process. The agglomeration process of a solid propellant with specific formulation was experimentally investigated. Aluminum particle aggregates underwent splitting, and the final aluminum particle agglomerates were spherical droplets with typical structure. The agglomeration process of this propellant was investigated by means of a simulation. The accuracy of the agglomeration model was verified by comparing the results of the model for the agglomeration process and the shape and size distribution of agglomerates with available experimental data. Compared with the experimental results, the deviations of the equivalent particle sizes of agglomerates D10, D50, D90, D4,3, and D3,2 obtained by using the simulation results were 6.3%, 6.3%, 9.4%, 7.5% and 6.7%, respectively. The aluminum particle agglomeration model established in this paper can predict the particle size distribution of aluminum agglomerates near the burning surface of solid propellants. The model was also used to further investigate the effects of aluminum particle content, ammonium perchlorate (AP) particle size and environmental pressure on aluminum particle agglomeration. Increasing the aluminum content or AP particle size aggravated aluminum particle agglomeration, whereas increasing pressure weakened it.

Catalytic effect of ferric oxide on burning characteristics of propellants using ammonium perchlorate with varied particle properties

Fe2O3 is an excellent burning catalyst for ammonium perchlorate (AP)-based propellants. There is no sufficient experimental data yet on the burning characteristics of propellants supplemented with Fe2O3. In this study, the burning characteristics of propellants supplemented with less than 4% Fe2O3 were investigated using 69–80% coarse, fine, or fine porous AP. The catalytic effect on the burning rate increased with increasing pressure for the propellant using coarse AP, whereas an opposite effect was observed for the propellant using the fine AP. The catalytic effect for the propellant using porous AP was independent of the pressure. The optimum amount of Fe2O3 for increasing the burning rate was 1%, which was independent of the AP particle properties, AP content, and pressure. The dependence of the catalytic effect on the AP content was affected by the AP particle properties below 72% AP, while it was hardly affected above 74%. The pressure exponent was dependent on the AP particle properties, but the exponents of the propellants with Fe2O3 were not affected by the amount of Fe2O3 added. A qualitative analysis based on the combustion wave structure was conducted to elucidate the catalytic mechanism.

In Situ Cutting of Ammonium Perchlorate Particles by Co-Bipy "scalpel" for High Efficiency Thermal Decomposition.

Burning rate of solid propellants can be effectively improved by adding catalysts and using smaller size ammonium perchlorate (AP). Although few reports, the exploration of changing the size of AP primary particles by catalysts is of great significance for improving combustion performance. Here, taking Co-bipy as an example, the potential advantages of such materials as AP decomposition catalysts are reported. Due to the existence of NO3 - combined with oxygen rich environment provided by AP, the structural self-transformation from micronrods to nanoparticles can be quickly realized during the heating process. More importantly, when Co-bipy decomposes, it can play the role of "scalpel" and in situ cut AP particles. Results show that high-temperature decomposition of Co-bipy/AP occurs at 305.8 °C, which is 137.5 °C lower than that of pure AP. Catalytic mechanism is discussed by in situ IR and TG-IR, CoO can effectively increase the content of reactive oxygen species and weaken the N-H bond, realizing the rapid oxidation of NH3 . Eventually, the behavior of Co-bipy cutting AP particles is tested. This interesting catalyst structure self-transformation behavior can not only realize the influence on AP, but also perform a positive function in the combustion process of solid propellants, such as opening the adhesive AP interface.

High-Pressure Combustion Characteristics of Hydroxyl-Terminated Polybutadiene Propellants

Combustion mechanisms of propellants under high pressures are necessary to solve the problems of a high burning rate pressure exponent in high-pressure solid rocket motors. In this study, the combustion characteristics of hydroxyl-terminated polybutadiene (HTPB) propellants were investigated by analyzing the burning rate, the quenched surface, and the combustion wave up to pressures of 28 MPa. The results showed that the pressure exponent presented an obvious break above 17 MPa, which increased from below 0.4 to approximately one. The characteristic pressure where the exponent break occurred decreased from 19.00 to 17.90 MPa with the increase of coarse ammonium perchlorate (AP) particles and decreased from 18.73 to 16.96 MPa with the addition of octogen. Coarse-AP particles exposed on the burning surface recessed relative to the binder below the characteristic pressure and protruded from the binder above the characteristic pressure. This finding was attributed to the difference in the local mass transfer between the gas phase and the burning surface under high pressures. An important finding of this study was the decline at the AP/HTPB interface above the characteristic pressure, indicating that the local heat transfer might play a crucial role in the pressure exponent break of HTPB propellants under high pressures.

Experimental and simulation research on microscopic damage of HTPB propellant under tension-shear loading

In order to study the influence of loading conditions on propellant mesoscopic failure morphology, scanning electron microscopy was carried out to observe the morphology of the failure section of a hydroxyl-terminated polybutadiene propellant under different temperatures, loading speeds, and loading conditions. Using the finite element method, a mesoscopic model of a composite solid propellant was constructed, and the mechanical parameters of the propellant particle–matrix interface were obtained based on the parameter inversion method. A meso-model of a hydroxyl-terminated polybutadiene propellant under different loading conditions was constructed, and numerical results were compared with experimental results to analyze the meso-damage. With decreasing temperature and increasing loading speed, the level of propellant damage increased, and the particle–matrix interface became more prone to damage under the combined action of tensile and shear loads. In addition, with an increasing loading angle, ammonium perchlorate particles were more prone to dewetting.

Flow improvement of fine oxidizer using nano-additives

Ammonium perchlorate (AP) is an oxidizer and major component for any solid composite propellant. The handling and processing of AP powder plays an important role in the performance of rocket fuel. AP being hygroscopic in nature; especially particle size<50 μm is highly cohesive in nature, which results in extensive agglomeration and poor flowability. This causes inherent handling problems in the propellant processing plant. In this work, the flowability of 8 μm and 50 μm AP particles was improved through the dry coating method using nano-additives such as TiO2 and Fe2O3. In addition, the influence of hydrophobic nano-silica (R972 type) coating on AP particles under high humidity was investigated. The results showed that coating of AP with nano-additive reduced the inter-particle forces hence cohesivity and improves the packing and flowability of fine AP powder. Hydrophobic coating was found to have added advantage at higher humidity. Moreover, coating with these nano-additives also improved the exothermicity of AP.