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Applied Surface Science 288 (2014) 349– 355

Contents lists available at ScienceDirect

Applied Surface Science

j ourna l ho me page: www.elsev ier .com/ locate /apsusc

reparation and characterization of energetic materials coateduperfine aluminum particles

ongsong Liu, Mingquan Ye ∗, Aijun Han, Xin Chenchool of Chemical Engineering, Nanjing University of Science and Technology, Nanjing 210094, Jiangsu Province, China

r t i c l e i n f o

rticle history:eceived 31 July 2013eceived in revised form0 September 2013ccepted 4 October 2013vailable online 12 October 2013

eywords:uperfine Aluminumoatingolvent/non-solventropellanthermal characterization

a b s t r a c t

This work is devoted to protect the activity of aluminum in solid rocket propellants by means ofsolvent/non-solvent method in which nitrocellulose (NC) and Double-11 (shortened form of double-base gun propellant, model 11) have been used as coating materials. Scanning electron microscopy(SEM) and transmission electron microscopy (TEM) were employed to characterize the morphology ofcoated Al particles. Other characterization data of coated and uncoated Al particles, such as infraredabsorption spectrum, laser particle size analysis and the active aluminum content were also studied.The thermal behavior of pure and coated aluminum samples have also been studied by simultaneousthermogravimetry–differential thermal analysis (TG–DTA) and differential scanning calorimetry (DSC).The results indicated that: superfine aluminum particles could be effectively coated with nitrocelluloseand Double-11 through a solvent/non-solvent method. The energetic composite particles have core-shellstructures and the thickness of the coating film is about 20–50 nm. The active aluminum content of differ-ent coated samples was measured by means of oxidation–reduction titration method. The results showedthat after being stored in room temperature and under 50% humidity condition for about 4months the

active aluminum content of coated Al particles decreased from 99.8 to 95.8% (NC coating) and 99.2%(Double-11 coating) respectively. Double-11 coating layer had a much better protective effect. TheTG–DTA and DSC results showed that the energy amount and energy release rate of NC coated andDouble-11 coated Al particles were larger than those of the raw Al particles. Double-11 coated Al parti-cles have more significant catalytic effect on the thermal decomposition characters of AP than that of NCcoated Al particles. These features accorded with the energy release characteristics of solid propellant.

. Introduction

Great attentions have been focused today on ultra-fine Al par-icles, because of its outstanding characters and wide applicationn propellants, explosives and pyrotechnics. As a metal incendiarygent, it can contribute energy to the energy system [1,2]. Superfineluminum powders (1–10 �m) which was used to replace theicronized aluminum powders (10–100 �m) in propellants, can

ncrease the combustion efficiency of aluminum, decrease thegglomeration of combustion products, and reduce the two-phaseosses [3]. However, there are significant drawbacks associated

ith the use of ultra-fine Al particles for energetic applications,arge specific surface area and high activity of superfine aluminum,

ake it easy to react with steam and oxygen during storage and

anding, leading to the decrease of active aluminum content [4–6].

To keep the high active aluminum content and improve the dis-ersibility of ultra-fine Al particles, microencapsulation technique

∗ Corresponding author. Tel.: +86 025 84315957; fax: +86 025 84315957.E-mail address: liusong8366@gmail.com (M. Ye).

169-4332/$ – see front matter © 2013 Elsevier B.V. All rights reserved.ttp://dx.doi.org/10.1016/j.apsusc.2013.10.031

© 2013 Elsevier B.V. All rights reserved.

has been used to alter the physic-chemical properties of superfineAl particles [7]. Microcapsules provide a protection shell for alu-minum powders from oxygen, moisture and carbon dioxide. Whatis more, the microcapsule shell can be burnt quickly at high tem-perature and then the fresh ultra-fine Al particles were releasedquickly. Various materials-coated ultra-fine Al particles have beenstudied by many researchers, such as perfluoroalkyl (C13F27COOH)[8], polyethylene [9], transition metals [10], aluminum diboride(Al B2) [3], Teflon [11], carbon [12], stearic acid (C17H35COOH)[13], palmitic acid [14], polymethyl methacrylate (PMMA) [15],hydroxyl-terminated polybutadiene (HTPB) [16,17], dioctyl seba-cate (DOS) [6], nitrocellulose (NC) [11], etc. However, except forNC, HTPB and DOS which are components of rocket propellants,other coating materials are not energetic materials or componentsof rocket propellants, which may have a defect on compatibilityof the different coating materials with the other compositions ofpropellants or decreasing of system energy. It should be pointed

out that HTPB is often used as binders in rocket propellants; DOSis used as a kind of plasticizer in propellants and NC also is used asone of the compositions of modified double base propellant. Gro-mov [11] and Kwon [13] have used NC as coating agent to modify

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he active aluminum nanopowders by means of solvent evapora-ion methods. Stored the NC-coated aluminum powders in roomemperature and under 70% humidity conditions for 12 months,he active aluminum content reduced to 58% from 68%, measuredy gas-volumetric method. However, the solvent evaporation may

eads to the agglomeration of composite particles.In this paper, fast and controllable solvent/non-solvent method

as used in the coating experiments, NC and Double-11 were useds coating materials. Nitrocellulose is a versatile polymer used asain component of propellant and high explosive formulations

18] and it has also been used as coating agent for sensitive mate-ials and energetic materials, which has an outstanding chemicaltability. Double-11 is known as one kind of double-base gun pro-ellant, which is composed of nitrocellulose (58.5%), nitroglycerine40.5%), centralite II (0.8%), vaseline (0.2%). The main componentsf Double-11 are nitrocellulose and nitroglycerine. Solvent/non-olvent method is widely used in refinement, modification of thenergetic materials and preparation of composite energetic mate-ials. The coating quality and thermal characteristics of coating Alarticles have been investigated by means of scanning electronicroscopy (SEM), transmission electron microscopy (TEM), grain

ize analysis, simultaneous thermogravimetry–differential thermalnalysis (TG–DTA) and differential scanning calorimeter (DSC).

. Experimental

.1. Materials

Superfine aluminum powder with average particle size of.0 �m and the active aluminum content of 99.75%, which made byuan Yang Aluminum Industry Co., Ltd., China. Nitrocellulose (NC)nd Double-11 used as coating materials made by lab of Nanjingniversity of Science and Technology, China. Amino silane couplinggents KH-550, NH4ClO4, NaOH, butyl phthalate (DBP) and all sol-ents (acetic ether, cyclohexane and ethyl alcohol absolute) werell analytical grade, purchased from Sinopharm Chemical Reagento., Ltd., China.

.2. Equipment and characterization

The morphology of superfine aluminum powder and coatedl particles were observed by JSM-6300 scanning electronicicroscope (SEM) made by JOEL Ltd., Japan. The micrographs of

oating film were characterized by Tecnai 12 transmission elec-ron microscope (TEM) made by Philips, the Netherlands. Theourier transform infrared (FTIR) absorption spectrums of coatedluminum particles and pure NC and Double-11 were measured byicolet IS-10 instrument and the IR data were collected in the rangef 500–4000 cm−1. Particle size and size distribution of coated andncoated samples were measured by Mastersizer Microplus Instru-ent, by Malvern Ltd., England. The thermochemical behavior of

aw Al particles and coated samples was characterized by TG–DTAnd DSC methods. Thermogravimetry (TG) and differential thermalnalysis (DTA) were carried out by HCT-2 Instrument, by Beijingenven Scientific Ltd., China. The conditions of TG–DTA are as fol-

ows: with an Al2O3 crucible, from 30 ◦C to1000 ◦C with a heatingate of 20 ◦C/min, under air atmosphere. The TG–DSC curves werebtained by Netzsch differential scanning calorimeter model STA49C, in the temperature range of 30–1000 ◦C, at a heating rate of0 ◦C/min, under air atmosphere with the flow rate of 20 ml/min.

he DSC curves of pure AP and mixture of coated Al particles andP were obtained by Mettler Toledo differential scanning calorime-

er model 823e, in the temperature range of 40–500 ◦C using anluminum crucible, at a heating rate of 20 ◦C/min, under nitrogen

nce 288 (2014) 349– 355

atmosphere with the flow rate of 20 ml/min. The average sampleweight was about 5.0 mg.

2.3. Coating procedures

2.3.1. Pretreatment of raw aluminum powdersA proper amount of superfine aluminum powder was added

to 0.01 mol/l NaOH solution to remove the oxide layer. The con-sumption amount of NaOH solution is decided by the content ofactive Al of raw material, which was determined by means ofoxidation–reduction titration according to the national militarystandard GJB 1738–1993 of China. The reaction equation as follow:Al2O3 + 2NaOH = 2NaAlO2 + H2O. The treated ultra-fine Al particleswith high activity were stored in ethyl alcohol absolutely. Theethanol solution of amino silane KH-550 (KH-550 weight basedon aluminum powder weight is 5%) was added to the pretreatedfresh Al powder immediately, the powder suspension was mechan-ically stirred at 60 ◦C for 2 h under nitrogen atmosphere, in order toavoid oxidation of the Al powder. Finally, the modified aluminumpowders were filtered and vacuum dried at 45 ◦C for 12 h.

2.3.2. Solvent/non-solvent methodSolvent/non-solvent was one alternative microencapsulation

procedure which works based on the coacervation principle [19].In representative experiments, 0.15 g NC and DBP (10% weight ofNC) dissolved in 50 ml acetic ether with the help of ultrasonic dis-persion. The concentration of NC in acetic ether solution is 4 g/l.Then, the solution was added to the container involving 2 g of thealuminum powder modified by KH-550, the solution was heatedin water bath to 40 ◦C under nitrogen atmosphere. After 30 min ofmixing under 200 rpm stirring with a magnetic stirrer, the mixturewas added to 250 ml cyclohexane slowly with vigorous stirring andultrasonic dispersion. In which cyclohexane acted as non-solventfor NC. The temperature of cyclohexane was room temperature(20 ◦C) and the addition speed of the mixture was 2 ml/min. Theaddition of mixture results in the precipitation of NC out of ethylacetate solution. The precipitated NC stuck to the surface of alu-minum powder and formed the desired coating layer. Reaction timewas 50 min at room temperature under nitrogen atmosphere afterthe addition of mixture was over. Then, the coated aluminum par-ticles were filtered and washed with cyclohexane two times anddried at 50 ◦C under vacuum conditions.

The coating technology of Double-11 is similar to that of NC,except that the acetic ether solution of Double-11 was preparedwithout adding DBP.

2.3.3. The composition of AP and the coated samplesIn solid rocket propellants, ultra-fine Al particles were often

used as metal incendiary agent and AP used as oxidant. The mixingof Al and AP can simulate the combustion performance of rocketpropellants. In a representative experiment, 1 g of AP was slurredin 50 ml alcohol–water solution (volume ratio is 1:2), 0.2632 g of5% NC-coated (NC by weight with respect to Al powder) Al powderor Double-11-coated Al powder was added to the alcohol–watersolution. The mixture was turbulently mixed at a stirring rate of120 rpm with a magnetic stirrer. The solvent phase was removedby distillation under reduced pressure, the mixed solid phase wasvacuum dried at ambient temperature and the mixture of AP andcoated Al particles was achieved.

3. Results and discussion

3.1. Results of SEM and TEM analysis

Morphological investigation of microencapsulated particles,through SEM and TEM analysis, proper information about coating

S. Liu et al. / Applied Surface Science 288 (2014) 349– 355 351

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the main component of Double-11 is nitrocellulose (NC). FromFig. 4b, it can be seen that the infrared absorption band of the twocoated samples were almost the same. The appearance of absorp-tion peaks at 2975 cm−1, 2886 cm−1 are CH stretching vibration.

Table 1Particle size and distribution of coated and uncoated Al particles.

No. Samples D10 (�m) D50 (�m) D90 (�m) SPANa

a Al 0.8374 2.0161 6.7199 5.62b Al/NC (2%) 0.8066 2.0648 5.3298 4.05

Fig. 1. SEM images of coated and uncoated Al particles (a) uncoated raw

uality and effectiveness can be given [20]. Fig. 1 shows SEM imagesf different samples including raw Al particles (Fig. 1a), NC coatedl particles (Fig. 1b) and Double-11 coated Al particles (Fig. 1c). Inig. 1a, the surface of uncoated Al particles was smooth and clean,articles dispersed well. Fig. 1b and c showed that after coating withured NC and Double-11, the surface of Al particles was coated with

layer of film. Meanwhile it can be seen that the coated compos-te particles have regular shape and homogeneous size. Fig. 1a and

disclose the phenomenon that the surface of NC-coated Al par-icles appeared folds which due to the adhesion of coating agentC. Fig. 1c showed that the surface of Double-11-coated Al parti-les was more smooth and uniform than that of the NC coated Alarticles.

For further studying of the cured NC layer and Double-11 layeroated on Al particles, TEM was employed to characterize thencoated and coated samples. Fig. 2 shows TEM images of raw Alarticles (Fig. 2a), NC coated Al particle (Fig. 2b) and Double-11oated Al particles (Fig. 2c). From the TEM images in Fig. 2b and, we can see that NC-coated Al particles and Double-11-coated Alarticles have a core–shell structure and the thickness of the outerhell is ranging from 2 to 50 nm. Because the size of the compositearticles was big and the thickness of the outer shell was very thin,he effect of TEM pictures was not very perfect.

.2. Particle size analysis

The particle size and size distribution of raw Al particles andoated samples were shown in Fig. 3. From Fig. 3, it can be seenhat the particle size and distribution of these composite particlesre nearly Gaussian distribution. The SPAN can be used to describehe relative width or the inhomogeneity of the particle size and

he particle size distributional, it can be calculated by the formulaf SPAN = (d90 − d50)/d10. According to data in Table 1, the SPANf raw Al particles, NC-coated Al composite particles with 2% NCnd Double-11-coated Al composite particles with 3% Double-11 is

rticles, (b) NC coated Al particles and (c) Double-11 coated Al particles.

respectively 5.62, 4.05, and 3.58 respectively. The calculated resultsshowed that the composite particles have a more uniform disper-sion than that of the uncoated Al particles. At the same time, themedian size (D50) of 2% NC-coated Al particles is 2.0648 �m largerthan that of raw aluminum particles. Moreover, the cumulativedistribution curves of the coated samples (Fig. 3b and d) and theraw Al particles (Fig. 3a) were similar. The thickness of the coat-ing film increased with the increasing of covering content. Theseresults also proved that each Al particle was evenly coated by afilm and the coated particles were well dispersed. The thickness ofcover layer can be estimated by the median size (D50). The shell of2% NC-coated Al particles and 3% Double-11-coated Al particles is24.35 nm, 45.25 nm in thickness respectively.

3.3. Fourier transforms infrared absorption spectrums (FTIR)analysis

In order to determine the materials coated on the particles sur-face, the Fourier transform infrared absorption spectrums of pureNC, Double-11 and coated samples were measured and shown inFig. 4. The FTIR spectrum of Double-11 is similar to pure NC, because

c Al/NC (5%) 0.9479 2.7845 12.6409 10.40d Al/Double-11 (3%) 0.8891 2.1066 5.2930 3.58e Al/Double-11 (5%) 1.0485 3.0321 9.6957 6.36

a SPAN = (d90 − d50)/d10.

352 S. Liu et al. / Applied Surface Science 288 (2014) 349– 355

Fig. 2. TEM images of coated and uncoated Al particles (a) uncoated raw Al pa

Fig. 3. Particle size distribution of coated and uncoated Al particles (a) raw Al pow-der, (b) Al/NC composite particles with 2% NC, (c) Al/NC composite particles with 5%Nc

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C, (d) Al/Double-11 composite particles with 3% Double-11 and (e) Al/Double-11omposite particles with 5% Double-11.

he Strong absorption peak at 1700 cm−1 is NO2 antisymmet-ic stretching vibration. The peak near 1300 cm−1 is attributable

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o the bending stretching of CH. The FTIR band at 1100 cm ishe stretch vibration absorption spectra of CO. The peaks near50 cm−1, 700 cm−1 are attributable to the bending vibration of

NO2. From Fig. 4b, it can be seen that the FTIR spectrums of NC or

rticles, (b) NC coated Al particles and (c) Double-11 coated Al particles.

Double-11 coated Al particles not only embodied the characteristicabsorption peaks of pure NC or Double-11, but also appeared somecharacteristic peaks of ultrafine aluminum respectively. This phe-nomenon showed that the coexistence of raw Al particles and thecoating agent in NC or Double-11 coated Al particles. New absorp-tion peaks appeared in the FTIR spectrums of coated Al particles andthe spike, the height and the position of some characteristic absorp-tion peaks of the coated Al particles are different from those of pureNC and Double-11. The results showed that the coated Al particlesare not of the simple mixture of solid samples. Some characteristicabsorption peaks of NC and Double-11 Shifted to the higher wavenumber after the surface coating of Al particles as a result of the rawAl particles have an effect on the characteristic absorption peaks ofpure NC or Double-11. In conclusion, the results of SEM (Fig. 1),TEM (Fig. 2) and FTIR (Fig. 4) showed that the organic substancescoated on Al particles surface was NC or Double-11.

3.4. The active aluminum content analysis

The active aluminum content is defined as the mass percent-age of pure aluminum in per unit weight of raw Al particles. Fig. 5showed the relationship between the active aluminum content andthe storage time of the coated samples. The coated samples werestored in room temperature under 50% relative humidity conditions

for about 4 months. The measuring method in this experiment isoxidation–reduction titration [21] according to the national mil-itary standard GJB 1738–1993 of China. From Fig. 5, we can seethat after about 120 days storage, the active aluminum content

S. Liu et al. / Applied Surface Science 288 (2014) 349– 355 353

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f uncoated raw Al particles decreased from 96.1 to 93.8%, andhe data of NC coated sample is 99.8 to 95.8%, while the data ofouble-11 coated sample is from 99.8 to 99.2%, the active alu-inum content of coated samples was high than that of uncoated

ample, the active aluminum content of all samples decreased withhe storage time, which indicated that coating has some effect onhe protection of active aluminum content. The active aluminumontent of the first data of coated samples was higher than that ofaw Al particles as a result of the preliminary activation of the sur-ace. From the data above, we can also see that the active aluminumontent of NC-coated Al particles changed greatly than that of rawl particles and that of Double-11 coated sample, the active alu-inum content of Double-11-coated Al particles was steadier and

hanged little and the coating effect of Double-11 coated sampleas much better than that of NC coated sample.

.5. Thermal properties of samples

Fig. 6 shows simultaneous TG–DTA curves for the 2% NC-coatedl particles and the raw Al particles. The TG/DTA data were carried

ut by HCT-2 Instrument (Beijing Henven Scientific Ltd., China). Inig. 6a, the TG curves showed that the particles weight increasedith the temperature after 250 ◦C, the obvious weight gain temper-

ture range of the raw Al particles before 800 ◦C is about 577.3 ◦C to

ig. 5. The effects of storage time on active aluminum content of coated andncoated Al particles raw Al particles (a), 5% NC-coated samples (b) and 5% Double-1-coated samples (c).

-11 (a) and coated Al particles (b).

681.8 ◦C, and that of the NC-coated Al composite particles is about618–672.7 ◦C. The oxidation weight gain of the raw Al particles andNC-coated samples increased constantly when the temperatureincreased over 800 ◦C. The particle weight gain is due to the oxida-tion of Al particles, but in the temperature range of 500–800 ◦C, onlypart of the Al particles were oxidized. Comparing the TG curves ofthe two aluminum particles, the slope of thermogravimetric curveof NC-coated samples is larger than that of raw Al particles from577 to 680 ◦C, which indicated that the oxidation rate of NC-coatedAl particles in high temperature was larger than that of raw Alparticles.

In Fig. 6b, the DTA curve of 2% NC-coated samples showed a weakexothermic peak at 220 ◦C, which was probably due to the oxida-tion of NC decomposition products. The DTA curves (Fig. 6b) of rawAl particles and coated samples show an obvious exothermic peakat the temperature range of 620–650 ◦C before the melting point(670 ◦C) of aluminum powder, which could be due to the oxidationof Al particles. The main weight gain appeared in TG curves cor-responded to these exothermic peaks. Comparing DTA results (inFig. 6b) of the two different aluminum particles, it can be seen thatthe oxidation temperature (644 ◦C) and oxidation heat of NC-coatedAl particles were higher than those of raw Al particles. The main rea-son was that the coating layer NC was also an energetic materialand its oxidation was also exothermic. The endothermic peaks atabout 670 ◦C in DTA curves were due to the melting endothermicof aluminum powders.

TG/DSC curves of raw Al particles and 5% Double-11-coated Alcomposite particles in air atmosphere are shown in Fig. 7. TheTG/DSC curves were obtained by differential scanning calorimeter(model STA 449C, Netzsch). From Fig. 7a, it can be seen that the par-ticles weight increased with the temperature after about 220 ◦C, thelittle loss of raw Al particles before 200 ◦C was caused mainly by thedesorption of gaseous species and water vapor. There was no sig-nificant variation in raw Al particles weight before 500 ◦C, becauseof the existence of the surface oxide film of aluminum powder,which can prevent the further oxidation of aluminum powder. Themass loss of Double-11 coated aluminum powders before 250 ◦Cwas caused mainly by the combustion and thermal decompositionof Double-11. Both the raw Al particles and the Double-11 coatedsamples had a big mass gain of 4.40%and 6.04% at the temperature of566–644 ◦C and 575–657 ◦C respectively. The particles weight gain

was due to the oxidation of Al particles. Comparing TG curves of thetwo different Al particles, the mass gain amount and mass increas-ing rate of Double-11-coated Al particles were higher than thoseof raw Al particles, which indicated that the Double-11-coated Al

354 S. Liu et al. / Applied Surface Science 288 (2014) 349– 355

Fig. 6. TG (a)–DTA (b) curves of 2% NC-coated Al particles and raw Al particles.

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particles and coated samples did not affect the endothermic peakof AP. However, the low-temperature exothermic peak of samplesa and c are almost the same, and that of samples b and d was

Fig. 7. TG (a)–DSC (b) curves of raw Al particl

articles had a higher oxidation rate in high temperature than theaw Al particles.

In Fig. 7b, the DSC curves exhibited exothermic peaks at 632.9nd 604.4 ◦C respectively, which are corresponding to the oxida-ion of Al particles in both Double-11-coated and uncoated rawl samples. The significant exothermic peaks in DSC curves areorresponded with the main weight gain appeared in TG curvesFig. 7a). Comparing DSC results (in Fig. 7b) of the two different alu-

inum particles, it can be seen that the oxidation peak temperature632.9 ◦C) of Double-11-coated Al particles was higher than that ofhe raw Al particles (604.4 ◦C), and the oxidation heat of Double-1-coated Al particles was 720.8 J/g, higher than that of the rawluminum powders (424.5 J/g). The results may be due to the coat-ng layer of Double-11, which was also an energetic material andts oxidation was also exothermic. The endothermic peaks at about60.5 and 661.7 ◦C in DSC curves were due to the melting endother-ic peak of aluminum particles. The above results indicated that

he energy amount and energy release rate of Double-11-coatedamples were larger than those of the raw Al samples and thisharacteristic agrees with the combustion requirements of solidropellants.

.6. Catalytic effect on AP decomposition

The catalytic effects of different coated samples on the decom-osition of AP were studied by the DSC method. The DSC curves

f pure AP and the mixtures of coated samples and AP are shownn Fig. 8. From Fig. 8a, we noticed that the thermal decomposi-ion of pure AP consists of three stages. On the first stage, thendothermic peak exhibits at 245.7 ◦C, which dues to the transition

5% Double-11-coated Al composite particles.

from orthorhombic form to cubic form. In the subsequent twostages, there are two exothermic peaks on DSC curve, which are at350.1 and 420.6 ◦C respectively. The first exothermic peak is low-temperature exothermic process of AP decomposition. The secondexothermic peak is high-temperature exothermic process, corre-sponding to the complete decomposition of AP [22,23].

It is noted that all the Al contained samples have the sameendothermic peak as pure AP at 245.7 ◦C, indicating that the raw Al

Fig. 8. DSC curves of pure AP and mixtures of coated samples and AP. (a) pure AP; (b)AP/Al (25 wt%); (c) AP/NC-coated Al (25 wt%); (d) AP/Double-11-coated Al (25 wt%).

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ifferent from sample a (AP), indicating that the raw Al and Double-1-coated Al particles can affect the low-temperature exothermicharacter of AP, while NC coated Al have little effect on that of AP.or the positions of high-temperature exothermic peaks of Al con-ained samples b, c and d, they are different from that of sample aAP), Al contained additives can lower the decomposition tempera-ure of AP more or less and promote the thermal decomposition ofP at high-temperature. NC-coated Al composite particles shifted

he high-temperature exothermic peak of AP a little (0.5 ◦C only).owever, raw Al and the Double-11-coated Al particles shifted theigh-temperature exothermic peaks from 420.6 to 410.9 ◦C and06.4 ◦C (curve b and d in Fig. 8). The results showed that NC coatedl particle has little catalytic effect on the thermal decompositionf AP, while, raw Al particles and the Double-11 coated Al parti-les have significant catalytic effect on the thermal decompositionharacters of AP.

. Conclusions

Micron NC-coated and Double-11 coated Al composite particlesere prepared by means of solvent/non-solvent method. The mor-hology and structure of the coated samples were characterizedy SEM, TEM, FTIR and particle size analysis. The results indicatedhat NC and Double-11 have been successfully coated on the sur-ace of Al particles, and the average thickness of coating layerss 20–50 nm. The energetic composite particles are spherical withore–shell structures and with a uniform size distribution. The coat-ng layers can protect the active aluminum in the coated samplesrom being oxidized effectively. The experimental results showedhat after being stored in room temperature and under 50% rela-ive humidity condition for about 4 months, the active aluminumontent of NC coated and Double-11 coated Al particles changed aittle, from 99.8 to 95.8% (NC coating) and 99.2% (Double-11 coat-ng) respectively, showed that Double-11 coating layer had a betterrotective effect for active Al particles. The TG–DTA and TG–DSCesults showed that the energy amount and energy release raten high temperature of NC coated and Double-11-coated Al parti-les were larger than those of the uncoated raw Al particles. Theseharacters of coated Al particles have a good agreement with theequirement of combustion characteristics of the solid propellants.eanwhile, the coated Al particles have a higher oxidation heat

han the raw aluminum particles at about 640 ◦C. The DSC resultsf the mixture of AP and coated Al particles showed that Double-1 coated Al particles have a more significant catalytic effect on thehermal decomposition of AP than that of NC coated Al particles.

cknowledgements

This work was supported by grants National Ministries Researchrojects of China (40406010201). Thanks are due to Y. Wei for assis-ance with the experiments and to T. Wu for valuable discussion.

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nce 288 (2014) 349– 355 355

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