NiO Thermite Film by

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Fabrication and Kinetics Study of Nano-Al/NiO Thermite Film by Electrophoretic Deposition Daixiong Zhang† and Xueming Li*,† †

College of Chemistry and Chemical Engineering, Chongqing University, Chongqing 400044, China ABSTRACT: Nano-Al/NiO thermites were successfully prepared as film by electrophoretic deposition (EPD). For the key issue of this EPD, a mixture solvent of ethanol− acetylacetone (1:1 in volume) containing 0.00025 M nitric acid was proved to be a suitable dispersion system for EPD. The kinetics of electrophoretic deposition for both nano-Al and nano-NiO were investigated; the linear relation between deposition weight and deposition time in short time and parabolic relation in prolonged time were observed in both EPDs. The critical transition time between linear deposition kinetics and parabolic deposition kinetics for nano-Al and nano-NiO were 20 and 10 min, respectively. The theoretical calculation of the kinetics of electrophoretic deposition revealed that the equivalence ratio of nano-Al/NiO thermites film would be affected by the behavior of electrophoretic deposition for nano-Al and nano-NiO. The equivalence ratio remained steady when the linear deposition kinetics dominated for both nano-Al and nano-NiO. The equivalence ratio would change with deposition time when deposition kinetics for nanoNiO changed into parabolic kinetics dominated after 10 min. Therefore, the rule was suggested to be suitable for other EPD of bicomposites. We also studied thermodynamic properties of electrophoretic nano-Al/NiO thermites film as well as combustion performance. an energetic film of nanothermite. Compared with other methods of fabrication of nanothermite films, such as sputtering, the electrophoretic thermite film could be prepared more quickly (μm·min−1 for EPD vs nm·min−1 for sputtering) and more inexpensive (only a direct current power required). However, only two kinds of nanothermites (Al/CuO, Al/ Fe2O3) have been successfully fabricated via EPD.10−13 The key issue for fabricating new thermites via EPD was the investigation of a suitable dispersion system as well as the key issue for successful EPD of any other material films.14,15 Al/ NiO thermite was reported to produce less gas.16 Theoretically, gas (vapor and oxygen) generation from the Al/NiO thermite was about 2% of the gas produced from the Al/CuO thermite and was much lower than other comparable thermite systems. Gasless thermite reactions were desired for a microinitiator, which requireed less component vibration and little flow disturbance.1,16 In addition, Al/NiO had a lower onset temperature than Al/CuO.1 For these reasons, this study introduced a suitable dispersion system that was the key for successful EPD of nano-Al/NiO thermite and represented the first attempt at developing EPD for nano-Al/NiO thermite with potential for specific desirable applications. As a kind of bicomposite, the composition of nano-Al/NiO thermite could be significantly affected by the deposition kinetic of nano-Al and nano-NiO, in this work, further investigation on this aspect was deduced theoretically. Finally, the thermodynamic proper-

1. INTRODUCTION Nanothermites, often composed of aluminum nanoparticles and some oxidizer nanoparticles including CuO, Fe2O3, NiO, WO3, MoO3, etc.,1 have attracted great interest for their combustion applications such as higher flame propagation velocities, energy densities, and faster rate of energy release than micron-sized ones due to the nanoscale mixing (in comparison with conventional thermites)2,3 The main focus on these studies was concerned with preparation and evaluation of nanothermites for making further improvement in combustion performance. These results showed that the combustion performance was affected by several factors: the nature of the aluminum and the oxidant, the mixture stoichiometry, particle size, and distribution.4 The excellent nanothermites were prepared with the highest quality interface contact and optimum mass ratio of aluminum and oxidant to pursuing the goal of maximizing the combustion performance.5 For some special applications such as electrothermal bridge in microelectro-mechanical system (MEMS) technologies, fabrication of nanothermites films has been the topic of recent studies;6,7 magnetron sputtering,6,7 cold spray,8 and thermal evaporation9 are the most common methods. Due to several advantages of simplicity, low-cost equipment, easy control of the film thickness, and feasible design of complex shapes, electrophoretic deposition (EPD) as an efficient method for assembling aluminum nanoparticles and oxidizer nanoparticles to form thermite films has recently been reported by Sullivan.10−12 A thermite film of aluminum and copper(II) oxide, Al/CuO, has been first prepared via EPD in their work, and the result showed that EPD was a straightforward and flexible technique for the preparation of © 2015 American Chemical Society

Received: December 26, 2014 Revised: April 11, 2015 Published: May 7, 2015 4688

DOI: 10.1021/jp5129113 J. Phys. Chem. A 2015, 119, 4688−4694

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thermite samples. Both ends of the wire were insulated with a mask and the middle part of the 30 mm length was exposed in suspensions for deposition. The processed resistance wire was dipped into the suspension and used as the cathode during EPD of nano-Al/NiO, while the stainless steel sheet was also used as anode. The resistance wire with a deposited film of nano-Al/NiO thermite was dried after EPD for 1 h. Then, the mask on the end of the wire was removed and connected with direct current power (0−200 V, 0−20 A). Ignition of the prepared samples was studied by using an electrically heated wire ignition test: the nano-Al/NiO thermite was ignited with heating the resistance wire by a constant current of 10 A supplied by direct current power. Movies of the combusting material were taken with a high-speed camera (HG-100 K, Redlake) at an imaging speed of 10 000 frames per second. The data collection was post-triggered digitally after the reaction was observed.

ties and combustion behavior of the novel nano-Al/NiO thermite were investigated.

2. EXPERIMENTAL SECTION Nano-nickel(II) oxide (nano-NiO, 30 nm, 98%, Aladdin Inc., China) and nano-aluminum (nano-Al, 50 nm, 99.9%, Aladdin Inc., China) were used in the study. In energetic reactions, the equivalence ratio was defined as the actual fuel to oxidizer ratio divided by the fuel to oxidizer ratio in a stoichiometric reaction: Φ=

(F/O)actual (F/O)stoich

(2.1)

The stoichiometric fuel:oxidizer ratio was 2:3 from the balanced reaction: 2Al + 3NiO → Al 2O3 + 3Ni

(2.2)

3. RESULTS AND DISCUSSION It was well-known that successful EPD mainly depended on a suitable dispersion system to make a specific kind of particle charged and move directionally under an electric field.17−20 Therefore, a suitable dispersion system was the key issue for successful EPD. Different kinds of dispersion systems were needed for EPD of different kinds of particles, and numerous experimental studies have been conducted to choose a suitable dispersion system for EPD of a specific kind of particle.17−20 For EPD of thermites, another qualification for a desirable dispersion system was that the surface of both aluminum nanoparticles and oxidizer nanoparticles could be charged with the same sign in suspension. In a previous work, we have successfully prepared nano-Al/ Fe2O3 thermite by EPD with a dispersion system of ethanol:acetylacetone (1:1 in volume).13 However, as shown in Figures 1 and 2, the deposition rate for both nano-Al and

To explore the desirable dispersion system, the EPD of nanoAl and EPD of nano-NiO using the same solution were separately performed before codeposition of nano-Al and nanoNiO. Ethanol−acetylacetone (1:1 in volume) was employed as the solvent to prepare the suspension, and nitric acid was an additive. For all EPD processes, the solid loading was 2 g L−1. For the codepositon process, the equivalence ratio of nano-Al to nano-NiO in suspension (Φs) was adjusted in weighting samples. The suspensions were ultrasonicated for 20 min to break up agglomeration. Before coating, stainless steel substrates with dimensions of 0.1 × 40 × 85 mm3 were ultrasonicated and cleaned in ethanol for 10 min and then were used for EPD of nano-Al/NiO thermite. The EPD was performed in a beaker with two electrodes vertically immersed in the suspension of 200 mL with a constant voltage of 100 V. Stainless steel sheets with a deposition area of 45 mm × 40 mm were used as both the anode and cathode. The distance between the anodic and cathodic electrodes was fixed as 10 mm. After deposition, the cathode was removed from the suspension. The as-deposited films were dried in the oven at 60 °C for 1 h, and the deposition weight was measured by an electric balance with accuracy of 0.0001 g. The phase composition of the coatings was measured with Xray diffraction (XRD, 6000, Shimadzu, Japan). The morphology and element distribution of the coating were analyzed using a scanning electronic microscope (SEM, TESCAN VEGA II, Czech) and energy dispersive spectroscopy (EDS). The equivalence ratio in deposited thermite (Φd) was measured by the following method: the weighted nano-Al/NiO thermite was dissolved in nitric acid solution, the Ni mass concentration was measured using atomic absorption spectroscopy (AAS, 180-80, Exter Analytical), and then the equivalence ratio in deposited thermite (Φd) was calculated. The exothermic reactions of nano-Al/NiO thermite films were investigated by DSC (STA449F3, NETZSCH). The DSC experiments were carried out in a temperature range from 100 to 1200 °C at a heating rate of 20 °C·min−1 under a 99.999% Ar flow; the heat release per mass of the composite (J·g−1) was calculated using the DSC software by integrating the area under the exothermic peak. To analyze the combustion behavior, custom-made resistance wires (Cr20Ni80, 5.551 Ω·m−1) with diameters of 0.5 mm and lengths of 40 mm were used for preparing nano-Al/NiO

Figure 1. Deposition weight of Al as a function of deposition time with different concentrations of nitric acid.

nano-NiO was relatively low due to their insufficient surface charging in a dispersion system of ethanol:acetylacetone. Therefore, different amounts of nitric acid were chosen to modify surface charging for both nano-Al and nano-NiO particles and improve their EPD behaviors. The influence of nitric acid on the deposition rate is also shown in Figures 1 and 2; the concentrations of nitric acid in the mixture of ethanol 4689

DOI: 10.1021/jp5129113 J. Phys. Chem. A 2015, 119, 4688−4694

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between the deposition weight and deposition time was observed for prolonged deposition (10−30 min): yb = 0.3900 t + 0.0913

R2 = 0.9918

(3.4)

Therefore, the transition time between linear deposition kinetic and parabolic deposition kinetic for nano-NiO occurred more quickly than that for nano-Al (10 min for nano-NiO vs 20 min for nano-Al). The relation between the deposition weight of nano-Al/NiO and deposition time was also shown in Figure 3, and the

Figure 2. Deposition weight of NiO as a function of deposition time with different concentrations of nitric acid.

and acetylacetone were 0.000025, 0.00025, and 0.0025 M. For both cases, the deposition weight increased with increasing concentrations of nitric acid, which meant that the protons produced by nitric acid could improve the surface charging for both nano-Al and nano-NiO. As a result, their deposition rates were enhanced. Moreover, when the concentration of nitric acid increased from 0.00025 to 0.0025 M, the increases in deposition rate for both nano-Al and nano-NiO were poor, which indicated that 0.0025 M nitric acid was redundant for their sufficient surface charging. The excess nitric acid could reduce the resistance of suspension and increase the current density passing through the EPD circuit, consequently, more energy was consumed during the EPD process. Hence, a mixture of ethanol−acetylacetone (1:1 in volume) containing 0.00025 M nitric acid was suitable for EPD of both nano-Al and nano-NiO and was employed for preparing nano-Al/NiO thermite film in the remainder of the work. To further investigate the kinetics of EPD of Al deposited on substrates in a mixture of ethanol−acetylacetone (1:1 in volume) containing 0.00025 M nitric acid, it was observed that the deposit weight of nano-Al increases linearly with deposition time for a short time period (0−20 min): ya = 0.5554t

R2 = 0.9979

Figure 3. Variation of deposited weight with deposition time during EPD of nano-Al/NiO in a mixture of ethanol−acetylacetone (1:1 in volume) containing 0.00025 M nitric acid.

equivalence ratio of nano-Al to nano-NiO in suspension (Φs) was 1.0. Besides both the linear deposition kinetic for the short period and parabolic deposition kinetic for the prolonged period being observed, the deposition velocity of about 0.2347 mg·cm−2·min−1 for nano-Al/NiO thermite film at the first 10 min, which can be calculated to about 345−869 nm·min−1 (ρNiO = 6.8 g·cm−3 and ρAl = 2.7 g·cm−3), was another exciting feature, which could not be reached by sputtering technology. More interestingly, the deposition velocity of nano-Al/NiO via EPD could be further significantly enhanced when a higher suspension concentration was employed. The prepared films of nano-Al, nano-NiO, and nano-Al/NiO using EPD are shown Figure 4. Regions of large-scale component separations were not observed optically in the smooth films prepared by EPD, which exhibited good film characteristics and uniformity consistent with the result of Sullivan.11 The electrophoretic films could be handled and turned upside-down or vertically, on the substrate, indicating moderate adhesion was obtained. The XRD pattern of co-deposited film was completely indexed to be Al (ICDD #85-1327) and NiO (ICDD #471049) (Figure 5). The results indicated that the presence of both nano-Al and nano-NiO in the deposit obtained through EPD, which meant successful deposition of nano-Al/NiO thermite film, and the mixture of acetylacetone and ethanol bearing 0.00025 M nitric acid was an ideal solvent for EPD of nano-Al/NiO thermite film. In Figure 6 is shown an example of a top view of nanocomposite Al/NiO prepared by EPD along with elemental mapping. From the top view, homogeneously mixed and uniformly thick films were obtained, and the elemental

(3.1) −2

where ya was the deposition weight of nano-Al (mg·cm ) and t was the deposition time (min). A parabolic relation between the deposition weight and deposition time was observed for prolonged deposition (20−30 min), which meant that deposition weight increased linearly with √x, and this parabolic relation was defined by Wang:21 ya = 1.6614 t + 3.5969

R2 = 0.9900

(3.2)

Therefore, the transition time between linear deposition kinetic and parabolic deposition kinetic was 20 min. A similar deposition behavior was also observed for nanoNiO; the deposit weight of nano-NiO increased linearly with deposition time for a shorter time period (0−10 min): yb = 0.1293t

R2 = 0.9993

(3.3)

where yb was the deposition weight of nano-NiO (mg·cm−2) and t was the deposition time (min). A parabolic relation 4690

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In Sullivan’s work, a linear relationship between equivalence ratio in suspension (Φs) and equivalence ratio in deposited film (Φs) was employed to prepare thermite flim with the same composition; even the deposition time ranged in a wide region.11 However, from the investigation of kinetics of EPD for nano-Al and nano-NiO, it was found that the equivalence ratio in the deposited film (Φd) might vary with deposition time even if EPD was performed in suspension with same equivalence ratio (Φs = 1), which is illustrated in Figure 7. This unexpected result will be discussed theoretically in following work.

Figure 4. Image of the films of nano-Al, nano- NiO, and nano-Al/NiO thermite prepared using EPD.

Figure 7. Equivalence ratio of nano-Al/NiO thermite film (Φd) as a function of deposition time.

The linear deposition kinetic and parabolic deposition kinetic for EPD was proposed by Wang.21 For the linear deposition kinetic, the deposition weight increased with deposition time: y(t ) = k′t = kCE′·t =

Figure 5. X-ray diffraction patterns of film of nano-Al/NiO.

Cεξ (E − ΔE) ·t 4πη

(3.5)

where

mapping exemplifies the good mixing that was possible using the EPD technique, and no regions of significant fuel−oxidizer separation were observed, ensuring that compositional homogeneity was in the film. As a result, more opportunities of interfacial contact between nano-Al and nano-NiO were obtained, which could improve the reactivity by decreasing the characteristic mass transport length scale. The improvement in interfacial contact would be of great benefit to contact quality, contact area, dispersion, and homogeneity of nanoreactants, which was crucial for efficient combustion of thermites.

k=

εξ 4πη

(3.6)

(3.7) E′ = E − ΔE where y was the deposition weight, t was the deposition time, k and k′ were constant, C was the solids loading in suspension, ε was the dielectric constant of solvent, ξ was the zeta potential of the particle in the solvent, η was the viscosity of solvent, E was the applied voltage, and ΔE was the voltage drop across the

Figure 6. Scanning electron microscopy top image of an Al/NiO thermite film prepared by EPD. Also shown is an image with elemental maps of Al, Ni, and O. The white dotted region in the top view image corresponds to the elemental mapping region. 4691

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The Journal of Physical Chemistry A deposited layer and was considered a constant. From these equations, it could be concluded that the deposition weight was proportional to deposition time and solid loading under certain voltage in linear deposition kinetic. For the parabolic deposition kinetic, the deposition weight increased linearly with √t and was expressed as the following equation: y(t ) = k′

∫0

t

2 t e−kt d( t )

The equation meant that the composition of electrophoretic composite would change with deposition time in the parabolic deposition kinetic. When the critical transition time for particle B occurred more quickly than that for particle A, which meant tma > tmb, and the effect of deposition time on the composition of electrophoretic film would be more complicated. When t < tmb, the ratio of the deposition weight of particle A to that of particle B could be also expressed as eq 3.17. When tmb < t < tma, which meant the deposition weight of particle A increased linearly with deposition time and that of particle B increased linearly with the ratio of deposition weight of particle A to that of particle B could be expressed as follows:

(3.8)

and this equation can also be expressed as y(t ) = 2k′ tm e−ktm · t + k′b

(3.9)

where b was the intercept and tm was the critical transition time between linear deposition kinetic and parabolic deposition kinetic. From eq 3.9, it could be concluded that the deposition weight increased linearly with and solid loading under certain voltage was in parabolic deposition kinetic: y(t ) = KC t + Cd

Z=

where Cεξ E′ tm e−ktm 2πη

(3.11)

d=

εξ E′b 4πη

(3.12)

and where K and d were constant. For fabricating a composite film via EPD of particle A and particle B, their deposition kinetic equations were shown in the following: C εξ ya (t ) = ka′t = a a Ea′·t 4πη yb (t ) = k b′t =

C bεξb E b′ ·t 4πη

yb (t ) = KbC b t + C bdb

(3.16)

ya (t ) yb (t )

=

CaξaEa′ C bξbE b′

Φd =

ya (t ) yb (t )

=

Ca(K a t + da) C b(Kb t + db)

1.6614 t + 3.5969 0.3900 t + 0.0913

(3.22)

In summary, varying the equivalence ratio in the deposited film (Φs) with deposition time at 10−30 min resulted from the deposition kinetics for nano-Al and nano-NiO. We also suggested that the theoretically deduced and experimentally approved conclusion might be suitable for other bicomposites. It was also worth noting that this theoretical deduction was not suitable for accurately calculating the composition of electrophoretic bicomposites but it could be suitable for proving the existence of the effect of deposition time. Figure 8 shows the DSC data measured from three nano-Al/ NiO thermites with the different equivalence ratios 0.63, 1.23, and 1.90, respectively. For each curve, there was one clearly observed acute exothermic peak corresponding to the thermite reaction; the heat release values of the exothermic reaction for these equivalence ratios of 0.63, 1.23, and 1.90 were 687.7,

(3.17)

Z was the deposition ratio of particle A to particle B. It could be seen that the composition of electrophoretic composite remained steady in the linear deposition kinetic. And the ratio of the deposition weight of particle A to that of particle B in the parabolic deposition kinetic could be deduced as follows: Z=

(3.20)

From this equation, Φd would vary with deposition time during deposition at 10−20 min. And the Φd would also vary with deposition time during deposition at 20−30 min expressed as follows:

Subscripts a and b corresponded to particles A and B. It should be noted that the effect of particle A on the deposition behavior of particle B was negligible in this case, and vice versa. When the critical transition time for particle A and particle B occurred at the same time, which meant tma = tmb, and the ratio of the deposition weight of particle A to that of particle B in the linear deposition kinetic could be deduced as follows: Z=

(3.19)

This equation showed that Φd would remain constant during deposition at 0−10 min. For deposition at 10−20 min, Φd could be expressed as following equation via mathematical transformation: t Φd = (3.21) 0.7022 t + 0.1644

(3.14) (3.15)

CaξaEa′t C b(Kb t + db)

Φd = 4.9254

(3.13)

ya (t ) = K aCa t + Cada

yb (t )

=

The equation meant that the composition of electrophoretic composite would vary with deposition time when tmb < t < tma. And when t > tma, the effect of deposition time on composition of electrophoretic film was shown in eq 3.18 above. Therefore, as a bicomposite of nano-Al and nano-NiO, it is suggested that the unexpected observation for nano-Al/NiO thermite film may result from the effect of deposition time on composition of electrophoretic film, which was discussed above. For the electrophoretic nano-Al/NiO thermite film, the critical transition time between the linear deposition kinetic and parabolic deposition kinetic for nano-NiO (10 min) occurred more quickly than that for nano-Al (20 min). Thus, for the EPD of 0−10 min, the equivalence ratio in the deposited nanoAl/NiO thermite film (Φd) could be expressed as the following equation via some mathematical transformation:

(3.10)

K=

ya (t )

(3.18) 4692

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corresponded to the required current of 10 A. The electrophretic nano-Al/NiO thermite sample was quickly ignited when the circuit was switched on. The flame propagation images of nano-Al/NiO thermite samples prepared by EPD with the different Φd are shown in Figure 9. From this figure, bright flames were observed with loud sounds, which indicated that the thermite reactions were so strong that the energy is released quickly. The combustion behaviors of nano-Al/NiO thermite samples with Φd of 1.23 were obviously more violent than that with Φd of 0.63 and 1.90, which were in accordance with the result of the DSC experiment. In summary, the elecreophoretic nano-Al/NiO thermite film could be successfully ignited, which meant a potential significant enhancement in energy output when these thermites were assembled on an electrothermal bridge for MEMS application, and their combustion performance would be significantly influenced by the equivalence ratio of the film (Φd). EPD is an efficient method for fabricating excellent nanoAl/NiO thermite film, and the electrophoretic thermite film has advantages of good mixing and easy control of equivalence ratios. Combined with other advantages of EPD such as the feasible design of complex shapes, it implied that EPD had great potential interest in fabricating nano-Al/NiO thermite (or other energetic materials) on an electrothermal bridge. Compared with traditional methods for fabricating energetic material films such as magnetron sputtering and thermal evaporation, EPD might provide a novel method that could significant reduce time for fabricating nanothemite (or other energetic materials) bridge films on a microigniter with the same thickness. Therefore, we suggested that future studies could address this attractive field.

Figure 8. DSC curves of nano-Al/NiO thermites with Φd of 0.63, 1.23, and 1.90, and heating rate of 20 K/min.

931.1, and 601 J g−1, respectively. The results indicated that nano-Al/NiO thermite with Φd of 1.23 contained more energy than the others. The value of 931.1 J g−1 was also in a range similar to that (∼1000 J g−1) obtained for nano-Al/NiO thermite prepared through ultrasonic mixing method.16 In the combustion investigations, equivalence ratios in deposited nano-Al/NiO thermite (Φd) of 0.63, 1.23, and 1.90 were chosen; the voltage of 100 V was applied to obtain a series of nano-Al/NiO thermite samples. Because the Al:NiO ratio was changing, the deposition time was not fixed, but instead, we imposed the criterion that the deposited mass was 14.0 ± 0.4 mg/strip so that equal masses could be compared. Compared with the value of 0.16 Ω for the resistance wire before deposition, the measured value of 0.21−0.22 Ω for the resistance wire after deposition meant no significant change in resistance as the result from the electrophretic nano-Al/NiO thermite. The voltage for ignition was about 2 V, which

Figure 9. Still figure and series of snapshots taken during a typical flame propagation study of the nano-Al/NiO thermite prepared by EPD process with different equivalence ratios in deposited thermite (Φd): (a) Φd = 0.63, (b) Φd = 1.23, (c) Φd = 1.90. Time interval between two images was 0.5 ms. 4693

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(11) Sullivan, K. T.; Kuntz, J. D.; Gash, A. E. Electrophoretic Deposition and Mechanistic Studies of Nano-Al/CuO Thermites. J. Appl. Phys. 2012, 112, 024316. (12) Sullivan, K. T.; Zhu, C.; Tanaka, D. J.; Kuntz, J. D.; Duoss, E. B.; Gash, A. E. Electrophoretic Deposition of Thermites onto MicroEngineered Electrodes Prepared by Direct-Ink Writing. J. Phys. Chem. B 2013, 117, 1686−1693. (13) Zhang, D. X.; Li, X. M.; Qin, B.; Lai, C.; Guo, X. G. Electrophoretic Deposition and Characterization of Nano-Al/Fe2O3 Thermites. Mater. Lett. 2014, 120, 224−227. (14) Ohkura, Y.; Liu, S. Y.; Rao, P. M.; Zheng, X. L. Synthesis and Ignition of Energetic CuO/Al Core/Shell Nanowires. Combust. Inst. 2011, 33, 1909−1915. (15) Guo, W.; Liu, B. Liquid-Phase Pulsed Laser Ablation and Electrophoretic Deposition for Chalcopyrite Thin-Film Solar Cell Application. ACS Appl. Mater. Interfaces 2012, 4, 7035−7041. (16) Wen, J. Z.; Ringuette, S.; Nguyen, N. H.; Persic, J.; Petre, C. F.; Zhou, Y. N. Characterization of Thermochemical Properties of Al Nanoparticle and NiO Nanowire Composites. Nanoscale. Res. Lett. 2013, 8, 184. (17) Abdeltawab, A. A.; Shoeib, M. A.; Mohamed, S. G. Electrophoretic Deposition of Hydroxyapatite Coatings on Titanium from Dimethylformamide Suspensions. Surf. Coat. Technol. 2011, 206, 43−50. (18) Mahmoodi, S.; Sorkhi, L.; Farrokhi-Rad, M.; Shahrabi, T. Electrophoretic Deposition of Hydroxyapatite−Chitosan Nanocomposite Coatings in Different Alcohols. Surf. Coat. Technol. 2013, 216, 106−114. (19) Farrokhi-Rad, M.; Shahrabi, T. Electrophoretic Deposition of Titania Nanoparticles: Sticking Parameter Determination by an in Situ Study of the EPD Kinetics. J. Am. Ceram. Soc. 2012, 95, 3434−3440. (20) Bavykin, D. V.; Passoni, L.; Walsh, F. C. Hierarchical Tube-inTube Structures Prepared by Electrophoretic Deposition of Nanostructured Titanates into A TiO2 Nanotube Array. Chem. Commun. 2013, 9, 7007−7009. (21) Wang, Y. C.; Leu, I. C.; Hon, M. H. Kinetics of Electrophoretic Deposition for Nanocrystalline Zinc Oxide Coatings. J. Am. Ceram. Soc. 2004, 87, 84−88.

4. CONCLUSION A smooth and homogeneous film of nano-Al/NiO thermite was prepared by EPD. A mixture of ethanol−acetylacetone (1:1 in volume) bearing 0.00025 M nitric acid was a suitable dispersion system for this EPD. The deposited film exhibited good mixing between nano-Al and nano-NiO particles, which could greatly enhance combustion performance of nano-Al/NiO thermite. The equivalence ratio of nano-Al/NiO thermites film remained stable when the linear deposition kinetics dominated for both nano-Al and nano-NiO. The equivalence ratio would change with deposition time when the deposition kinetics for nanoNiO was changed into parabolic kinetics after 10 min. The phenomenon was explained theoretically through mathematical deduction of the relation between the composition of the bicomposite and deposition time in different deposition periods. This calculated relation could be suitable for other bicomposites. The heat release of electrophoretic nano-Al/NiO thermites film with Φd of 1.23 was 931.1 J g−1. The combustion experiment showed that the obtained nano-Al/NiO thermites film could be successfully ignited.

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AUTHOR INFORMATION

Corresponding Author

*X. M. Li. Tel: +86 23 65105659. Fax: +86 23 65105659. Email address: [email protected]. Notes

The authors declare no competing financial interest.

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REFERENCES

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DOI: 10.1021/jp5129113 J. Phys. Chem. A 2015, 119, 4688−4694