Ammonium perchlorate ( NH4ClO4or AP ) is a widely used energetic stuff, which is the most common oxidant in composite solid propellents ( CSPs ) [ 1 ] . The activity of the accelerators during condensed stage thermolysis of AP can be a good index to the catalytic activity of the linear during burning of CSPs [ 2 ] . In recent old ages, many metal and passage metal oxides have been widely used as accelerators to better thermic decomposition of AP [ 3-7 ] . Among others, Fe2Oxygen3is an abundant, low cost, and atoxic stuff, which is an of import accelerator on the thermic decomposition of AP and has been widely studied [ 7-9 ] . To the best of our cognition, in add-on to morphology, the size of accelerators play important functions on their catalytic public presentations. It was found that the catalytic public presentation of nanometer-sized Fe2Oxygen3atoms was superior to that of micrometer-sized Fe2Oxygen3atoms on the thermic decomposition of AP [ 8 ] . However, pure Fe2Oxygen3nanoparticles are disposed to agglomerate so that they are difi¬?cult to blend uniformly with AP and other projectile fuel additives by conventional mechanical commixture engineering, ensuing in a lessening of their catalytic activity. Much attempts have been done to resolvetheproblemofagglomeration, such as, ?-Fe2Oxygen3@ C core–shell nanocomposites [ 9 ] , Fe2Oxygen3/ AP nanocomposites [ 10 ] , Fe2Oxygen3/graphene nanocomposites [ 11 ] and Fe2Oxygen3/CNTs nanocomposites [ 12 ] , and the decomposition temperature of the sample with 2 % add-on of a-Fe2Oxygen3@ C core–shell, Fe2Oxygen3/Ammonium Perchlorate Fe2O3/graphene complexs and with 3 % add-on of Fe2Oxygen3/CNTs is 343 °C, 373 °Ci??367 °C and 329.1 °C, severally. However, the Fe2Oxygen3nanoparticles in these nanocomposites still have agglomeratephenomena to some extent, which lead to comparatively low catalytic activity.
Therefore how to forestall collection is the key to maintain catalytic activity. The accelerator should be dispersed on a high surface country bearer, which is an of import agencies to better the catalytic consequence of the nanocatalyst. Carbonized bacterial cellulose ( CBC ) is a high-purity C fibre with 3-dimensional ( 3D ) web [ 13, 14 ] . The 3D web of CBC provides an ideal platform for the deposition of metal and metal oxide nanoparticles, which may take to beautifully synergistic ei¬ˆects. The growing of nanoparticles onto a CBC-based templet is expected to both heighten the catalytic activity of the nanocatalysts and the homogenous scattering of the nanoparticles. We all know that FeOOH nanoparticles can be transformed into Fe2Oxygen3nanoparticles at low tempreture, whose size become smaller compared with FeOOH nanoparticles [ 15-22 ] . Furthermore, the freshly generated Fe2Oxygen3nanoparticles have a better scattering since they have been loaded on the microfibers of 3D web CBC bearer when they were calcined. Therefore, FeOOH/CBC nanocomposites can be straight used as accelerator alternatively of high temperature calcination. The obtained FeOOH/CBC oi¬ˆers a figure of advantages: ( 1 ) CBC serves as a bearer for in situ growing of FeOOH, it non merely enhances the homogenous scattering of the nanoparticles but besides enhances the catalytic activities of the nanocatalyst ; ( 2 ) it provides a big ei¬ˆective surface country bring forthing more active sites for AP ; ( 3 ) it can cut down energy ingestion to salvage energy.
In the present work, we report for the first clip the readying of a nanocomposite by in situ growing of FeOOH nanoparticles onto CBC. The CBC is decorated indiscriminately by FeOOH with the mean length of 120 nanometers, 30 nm broad. The obtained FeOOH/CBC was used as a new accelerator on thermic decomposition of AP. And their catalytic activity was studied by differential scanning calorimentry ( DSC ) . The as-prepared FeOOH/CBC nanocomposites exhibited a higher catalytic activity toward thermic decomposition of ammonium perchlorate ( AP ) at low temperature.
Pure CBC was obtained by calcining dried BC at high temperture. HCl ( 36 % ~38 % ) and FeCl3·6H2O ( AR ) were provided by Chengdu Kelong Chemical Reagent Company ( Sichuan China ) . AP ( AR ) was provided by Sinopharm Chemical Reagent Co. , Ltd. Aqueous solutions were prepared with deionized H2O ( 18.25 M? centimeter ) from an Ulupure Ultrapure H2O purification system.
2.2.Synthesis ofFeOOH/CBC nanocomposites
FeOOH/CBC nanocomposites were formed by fade outing 10g FeCl3·6H2O in 400ml deionized H2O and dispersed whilst stirring 30 min. Afterwards, 0.1g pure CBC was added into the assorted solution, the ensuing slurry was so heated at 60°C stirring invariably with H2O bath for 4h. The concluding precipitate was filtered, exhaustively washed and dried at 50°C in an oven.
The crystal stage constructions of the FeOOH/CBC nanocomposites were analyzed by PANalytical X’Pert PRO diffractometer ( XRD ) utilizing Cu K? radiation ( ?=1.5406 A ) , operated with 40 kilovolts and 40 ma. Datas were collected in the 2? scope from 3° to 80° utilizing a scan rate of 2°/min. The size and morphology of the merchandises were observed by Zeiss Ultra55 field-emission scanning negatron microscopy ( SEM ) , operated at an acceleration electromotive force of 15 kilovolts and Zeiss Libra200FE transmittal negatron micrographs ( TEM ) , operated at an acceleration electromotive force of 200 kilovolts.
2.4.Catalytic activity measuring
The catalytic activities of the FeOOH/CBC nanocomposites in the thermic decomposition of AP ( 180 ?m ) were besides studied utilizing the Mettler Toledo TGA/DSC 1/1100 LF coincident thermic analyser at a heating rate of 10°C/min in Ar atmosphere ( with i¬‚ow of 50 ml/min ) over the scope of 30-500°C. DSC experiments were performed utilizing air-tight aluminum oxide melting pot. FeOOH/CBC nanocomposites and AP were assorted in 1:49, 1:19 and 1:9 mass ratios, severally, for thermic analysis. A entire sample mass of 2.5 milligram was used in all tallies.
3.Consequences and Discussion
3.1.Crystal construction and morphology of the FeOOH/CBC nanocomposites
The XRD form of the obtained samples is shown in Fig.1. All the extremums in the form are labeled and can be indexed to FeOOH with a Tetragonal stage ( JCPDS i¬?le no. 34-1266 ) . In Fig.1ai??these extremums at 11.84, 16.79, 26.73, 34.00, 35.16, 39.22, 46.43, 52.05, 55.90, 61.01, 64.40 degree correspond to ( 110 ) , ( 200 ) , ( 310 ) , ( 400 ) , ( 211 ) , ( 301 ) , ( 411 ) , ( 600 ) , ( 521 ) , ( 002 ) , ( 541 ) planes of FeOOH, severally. These XRD consequences indicate that FeOOH is synthesized without any noticeable dross. However, as shown in Fig.1b, the broadened extremum runing from 10 to 30 grade can besides be observed, which is ascribed to formless C [ 9 ] . These consequences reveal that the as-synthesized merchandise might be FeOOH/CBC nanocomposites.
Fig.2a shows the SEM images of CBC with three-dimensiona cubic decimeter web, which is twisted with each other. The microfiber of CBC is unvarying with the mean diameter of about 80nm, and the surface of CBC is really smooth and clean. Through the hydrolysis of the FeCl3·6H2O, FeOOH nanoparticles were loaded on microfibers of the 3D web CBC, as shown in Fig.2b. Compared with the pure CBC, the nanocomposites still has a 3-dimensional web, but the fibres become thicker.
Further construction word picture was carried out by TEM. Fig.3a shows the TEM image of FeOOH/CBC nanocomposites, which exhibit homogeneous shuttle-like with mean comprehensivenesss of about 30 nanometers and lengths of 120nm. The contrast class between C fibres and shuttle-like nanopartiles could even be observed, connoting that the nanocomposites have been formed. The deep background is FeOOH, while the shallow background is network-like C fibre with diameter of about 80 nanometers on norm. We can detect that these nanoparticles along the web of CBC are extremely monodisperse instead than agglomerate. In Fig.3b, the corresponding selected country negatron diffraction ( SAED ) form has many diffraction rings made up of many diffraction musca volitanss, which indicate that shuttle-like FeOOH nanoparticles have comparatively high crystalline. All the crystal planes of FeOOH in the SAED are in instead good understanding with those of XRD ( in Fig.1a ) , which besides verify the nanocrystallinity of the sample. A high declaration TEM ( HRTEM ) image of shuttle-like nanoparticles, as shown in figure 3c, the lattice spacing of 0.33 nm corresponds to avitamin Dspacing of ( 310 ) crystal planes. The HRTEM image besides shows that the ( 310 ) way is aligned with the axis of shuttle-like nanopartices.
3.2.Catalytic belongingss of the FeOOH/CBC nanocomposites
The FeOOH/CBC nanocomposites were explored as a accelerator to the thermic decomposition of ammonium perchlorate ( AP ) , which is the cardinal constituent of composite solid propellents. The DSC curves for pure AP and mixtures of AP in the presence of as-obtained FeOOH/CBC nanocomposites with different blending ratio are shown in Fig.4. It can be observed that the DSC curve for thermic decomposition of pure AP shows three events, which is the same to the old consequences [ 23, 24 ] . The temperture of the crystal transmutation for AP is by and large centered at temperatures about 240-250 °C. In the DSC curves ( Fig.4a ) there is an endothermal extremum at a maximal peak temperature of 247.3 °C, which is attributed to the passage of AP crystals from orthorhombic signifier to cubic signifier. The decomposition of pure AP is by and large centered at temperatures range from 300 to 460°C. It is can be seen that there are two obvious exothermal extremums centered at temperatures about 319.7 and 447.6 °C, which are denoted as low-temperature decomposition ( LTD ) and high-temperature decomposition ( HTD ) , severally. The LTD is due to the partial decomposition of AP and formation of some intermediate NH3and HClO4by dissociation and sublimation. Alternatively, the HTD iscloselyrelatedto the complete decomposition of the intermediate merchandises into i¬?nal volatile merchandises, such as, N2O, O2, Cl2, H2O and few NO [ 25 ] .
However, when the FeOOH/CBC nanocomposites were added to the pure AP, the same extremum at 247.3 °C appears in all the curves, bespeaking that there is no catalytic consequence of FeOOH/CBC nanocomposites on the crystal passage procedure of AP. Nevertheless, the difference blending ratio of FeOOH/CBC nanocomposites in AP leads to a signii¬?cant decrease of the stoping decomposition temperature of AP. As seen in Fig.4b-c, in the presence of 2-5 wt. % FeOOH/CBC, temperature of HTD ( 447.6 °C ) decreases lineally from 408.2 to 372.7 °C. Furthermore, the starting temperature for the decomposition of the complexs is evidently lower than that for the decomposition of the pure AP, which indicates FeOOH/CBC nanocomposites exhibit catalytic activity on the thermic decomposition of AP efficaciously. Particularly, when the content of FeOOH/CBC is up to 10 wt. % , the two exothermal extremums of the pure AP are merged into one extremum ( Fig.4d ) , and the high-temperature exothermal extremum of AP displacements to a lower temperature at 290.4 °C. What ‘s more, the evident decomposition heat ( 2838.8 J/g ) is much higher than that of the pure AP ( 667.1 J/g ) ( Table 1 ) . Therefore, it can be concluded that catalytic activity of FeOOH/CBC depends on the saddle horse of the accelerator add-on. The best proportion of the add-on favors the farther decomposition of AP.
For the intent of look intoing the catalytic activity of FeOOH/CBC nanocomposites in the thermic decomposition of AP, a certain blending ratio of the CBC and FeOOH nanoparticles with AP were measured by DSC. The DSC curves for pure AP and mixtures of AP in the presence of as-obtained CBC and FeOOH nanoparticles are shown in Fig.5. Curve for pure AP shows that an endothermal extremum is besides located at 247.3 °C, which exists all the curves ( Fig.5b-c ) . It indicates that the additives have small consequence on this crystallographic passage temperature. For curve B, in the presence of 5 wt. % CBC, temperature of LTD and HTD dropped to 316.2 and 419.7 °C, severally, which indicates that CBC has a certain consequence on the decomposition of AP. However, when 5 % FeOOH nanoparticles are added in AP, the two exothermal extremums of the pure AP are merged into one crisp extremum ( Fig.5c ) , and the exothermal extremum occurs at 346.5 °C. Compared with FeOOH/CBC nanocomposites, the lower effectual catalytic activity of FeOOH nanoparticles may besides be attributed to the serious agglomeration. That is, the better catalytic activity of FeOOH/CBC nanocomposites is ascribed to its larger BET surface country ( 500.2m2/g ) and more active sites. Therefore, the FeOOH/CBC nanocomposites have much higher catalytic activity towards the thermic decomposition of AP than that of FeOOH nanoparticles. From above analysis, the catalytic activity order is: FeOOH/CBC ( 10 wt. % ) › FeOOH ( 5 wt. % ) › FeOOH/CBC ( 2 wt. % ) › CBC ( 5 wt. % ) .
From our experimental consequences, we declare that the accelerator chiefly ini¬‚uences the high temperature decomposition measure. As we all known, FeOOH is an first-class semiconducting material with a set spread of 2.12 eV [ 26 ] . Harmonizing to the traditional electron-transfer theory [ 27, 28 ] , the partly i¬?lled 3d orbit in Fe3+ plays a positive function in an electrotransfer procedure. When AP is assorted with FeOOH/CBC, the positive hole of FeOOH can accept negatrons from AP ion, therefore heightening the thermic decomposition of AP. Furthemore, the heat produced during the thermic decomposition of AP can transform FeOOH into Fe2Oxygen3before 200 °C [ 21 ] and the catalytic coinage is consistent with the dei¬?nition of accelerators. However, without any back uping substrate, pure FeOOH nanoparticles are likely to aggregate and expose fewer active sites, which lead to comparatively low catalytic activity. And yet, CBC non merely is a high-purity C fibre, but besides possesses a 3-dimensional web, which can be helpful to electron transportation and heat conductivity [ 14 ] and besides can speed up the thermic decomposition of AP. From the above treatment, CBC in the as-synthesized FeOOH/CBC nanocomposites could non merely signii¬?cantly cut down the agglomeration of FeOOH nanoparticles but besides offer accelerated negatrons to rush up the high temperture decomposition measure, therefore FeOOH/CBC nanocomposites display higher catalytic activity than pure FeOOH.