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Abstract
We report the first laser emission from flash ignition of Zr/Al nanoparticles with the addition of strong oxidizer KClO4 using Nd: YAG as a laser medium. The mixture Zr/Al/Kp-45 (mass ratio = 33%Zr: 33%Al: 34%KClO4) has the highest brightness temperature Tb = 4615 K and the adiabatic flame temperature Tf = 4194 K with the duration of 20 ms. At 1064 nm we measured a maximum output energy of 702.5 mJ with the duration of nearly 10 ms by using only 100 mg mixture with an output coupler (transmission T = 10%). Further optimizing the concentration cavity and increasing the mixture content will yield much higher efficiency and output energy.
© 2017 Optical Society of America
1. Introduction
Since the discovery of ignition in single-walled carbon nanotubes by a conventional photographic flash in 2002 [1], the flash ignition of several formulations containing carbons with noble metals [2], silicon nanowires/films [3-4], polymer polyaniline [5], and nano-sized aluminum particles [6–8] have been realized in nano-energetic materials over the past decade. In all these cases, the nanomaterials exhibited a large photoacoustic effect when exposed to a conventional camera flash. The nanostructures show a strong ability to confine heat energy lead to a rapid increase of temperature in milliseconds and subsequent ignition under oxidizing environments.
Aluminum (Al) with high energy density is the most common metal fuel for high-temperature engineering applications as explosives, pyrotechnics, propellants [9–11]. There is a significant interest in nano-sized Al particles as a flash ignition agent due to their high light absorption and relatively low ignition temperature. The flash ignition occurs when the Al nanoparticles (NPs) have suitable diameters and sufficient packing density. Recently, we accidentally found that the metal Zr micro particles (Mps) could be totally ignited with the addition of specific amount of Al Nps by a conventional flash and the reaction is highly exothermic with the addition of a strong oxidizer KClO4 (Kp). Besides, the combustion products are heated and burst with intense lighting accompanied by strong emission in the red region. The flame spectrum contains both the continuous spectrum generated by thermal radiation and the discrete spectrum generated by characteristic radiation of atoms, molecules and ions. The spectral composition of the combusting mixtures matches the absorption bands of Nd-doping laser mediums such as Nd: YAG and Nd: glass which means that the light source from the combustion of the mixtures could be a potential laser pumping source. Actually, the flame of pyrotechnics from fast chemical reactions was first used as laser pumping source in 1967 and mainly used for quasi-cw solid-state laser based on Nd3+ doped glass [12–16]. The pyrotechnically pumped laser has been investigated by a variety of works using combustion of metal/oxidizer (mainly Kp/Zr and Zr/O2). In all cases, the pyrotechnics are ignited by conventional ignition methods. The combustion process is asynchrony and inhomogeneous. Compared with common ignition methods (hotwires, lasers, mechanical fracture, piezoelectric igniters) [17–20], the optical flash ignition method has the following important advantages: (1) the flash signal is immune to varying interference and surrounding environmental conditions of pressure, temperature, space, and time [18]. (2) The flash ignition works without direct physical contact of energetic materials and can easily achieve ignition at a large surface area. More important, the flash pulse energy distributed on the materials almost remains homogeneous during the ignition process.
In this paper, the Zr/Al Nps are simultaneously ignited by a conventional flash to provide an energy fluence suitable for optically pumping an active laser medium Nd: YAG. The pumping time, energy, and flame spectrum could be manipulated by adding certain oxidizer with characteristic radiation. After milliseconds of flash, one single but intense laser pulse is emitted. The laser systems are low cost, miniature, and expendable with high performances.
2. Experiment
2.1 Material fabrication and characterization
15 mg Al NPs (davg = 50 nm, 99.99%, from Aladdin) were mixed with 15 mg Zr Mps (davg = 3 μm, 99.9%, from ST-NANO) in dimethylformamide (DMF) solution and sonicated for 30 min to ensure homogeneous mixing. After sonication, the DMF was evaporated in a vacuum oven at 100 °C for 4 h. To this components was also added various amount of Kp Mps (99.99%, 300 mesh, from Kermel), as listed in Table 1. Flash ignition of the mixtures is achieved by a commercial cameral flash (Cannon Speedlite 600EX II-RT). The maximum energy density of the flash is around 600 mJ/cm2 with the duration of 1 ms. The entire combustion process of Zr/Al Nps with different amount of Kp was recorded by a high-speed camera (Phantom MIRO R310, frame rate 5 kHz). Meanwhile, the flame spectrums of the combusting mixtures within the wavelength range of 400-950 nm are measured by the optical fiber spectrometer (Ocean Avantes2048). The irradiance times are recorded by a digital phosphor oscilloscope (Tektronix, DPO4054B) using a high-speed photodetector (Thorlabs DET36A). The thermodynamic equilibrium calculation HSC Chemistry 6.1 software was used to predict the adiabatic flame temperature Tf. The Gibbs free energy minimization method is applied to study the equilibrium products and combustion temperature. In addition, Scanning electron microscopy (SEM, FEI Quanta 450) at an accelerating voltage of 15 kV and Energy dispersive spectrometry (EDS) were performed on the composite particles to observe surface morphology and detect elements distribution before and after flash ignition.
Table 1. Zr/Al nanoparticles with various amount of Kp
2.2 Laser experiments
A schematic diagram of the Nd: YAG laser system from the flash ignition of Zr/Al Nps is shown in Fig. 1. Specially, certain amount of Zr/Al Nps is pressed into strip shape and placed on the top of a 2 mm thick glass slide which was located 1 cm above the camera flash tube in air. The transversal dimensions of lamellar Zr/Al Nps are controlled below 1 mm. A Nd: YAG laser rod (1.1% doping concentration) was used as laser gain medium with the dimensions of 110 mm in length and 5 mm in diameter. The pumping lights produced by the combustion of lamellar Zr/Al Nps were concentrated by a semi-elliptical Polytetrafluoroethylene (PTFE) cavity. The lengths of the major axis and the minor axis are 14 mm and 9 mm respectively. The lamellar Zr/Al Nps were placed in one focal line and the laser rod in the other focal line which is based on the geometrical theorem that rays originating from one focal line of an elliptical cylinder are reflected to the other focal line [21]. The absorption efficiencies of laser rod with different transversal dimensions of lamellar Zr/Al Nps are calculated by Tracepro7.0. M1 is the resonator mirror with 100% reflectivity at 1064 nm. M2 was employed as the output coupler with 90% reflectivity at 1064 nm. The laser output energy was measured by a calibrated calorimeter using coherent probe. The laser beam quality was measured by a beam profiling camera (OPHIR-SP620U). The stimulated emission (SE) spectrum and time dependence of the Nd: YAG ceramic laser are recorded by an oscilloscope using a photodetector mentioned above.
3. Results and discussion
Figure 2(a) shows the pictures of the mixed Zr/Al-30 powders before and after flash ignition. They change from dark grey powders to greyish white aggregated particles after combustion process. The powders burn in air for hundreds of milliseconds with yellow lights which is shown in Fig. 3(a). In Fig. 2(b) the spherical Al Nps are agglomerated on the surface of Zr Mps after ultrasonic mixing. After flash ignition, they are oxidized into much smaller metal oxides particles with irregular shape which are agglomerated as shown in Fig. 2(c).
Fig. 2 Comparison of Zr/Al-30 NPs and Zr/Al/Kp-45 thermite mixture before and after flash ignition. (a-c) Optical and SEM images of Zr/Al NPs before and after flash ignition. (d–f) Optical and SEM images of Zr/Al-Kp thermite mixture before and after the exposure. (g) EDX images of Zr/Al-Kp thermite mixture after the exposure.
Fig. 3 Photographs of the burning process of a thermite mixture of (a) Zr/Al-30 NPs and (b) Zr/Al/Kp-45 ignited by a flash.
Figure 3(a) shows that the whole reaction process is slow and mild with dim glow which means that the individual Zr/Al mixture was not suitable as a laser pumping source for not enough pumping rate. So to this components was added certain amount of strong oxidizer Kp, the stoichiometric ratio of the mixtures and the degree of mixing were found not critical for the successful ignition. Once the camera flashed, the following reactions happened:
The thermite reactions are highly exothermic and proceed much more violently than the burning of Zr/Al particles. Figure 2(d)–(f) show the optical, SEM images of Zr/Al/Kp-45 thermite mixture before and after the exposure. The reaction process is almost complete and only a small amount of gray powder remains. The whole reaction process lasts less than twenty milliseconds and the reaction products are heated and burst with intense glow which is shown in Fig. 3(b). The large, micron sized Kp oxide particles are broken down into small, nano sized particles which were proven to be KCl Nps by EDS as shown in Fig. 2(g). The reaction products KCl, Al2O3, and ZrO2 are piled together forming white flocculent agglomerates [22].Furthermore, to assess the suitability of the flash ignition mixtures as Nd: YAG solid-state laser pump source, the time-integrated emission spectra and irradiance time of combusting Zr/Al with different amounts of Kp were measured. Figure 4(a) shows that combustion radiation spectrum contains both the continuous spectrum generated by thermal radiation and the discrete spectrum generated by characteristic radiation of atoms (K, O, Cl, etc.), molecules (ZrO, AlO) and ions [23]. The radiation spectrum is the superposition of the two kinds of spectrum, and it matches the strong absorption band (590 ± 10) nm, (750 ± 10) nm and (808 ± 10) nm of laser pump medium Nd ion [24-25]. It is clear seen the emission spectra intensity of Zr/Al mixtures is relatively low and it increased as the addition of Kp. The total emission intensity decreased as the amount of Kp additives increased. On the contrary, the irradiance time increased as the amount of Kp additives increased which is shown in Fig. 4(b).To explain that, the continuous spectrum generated by thermal radiation is simplified as blackbody radiation which could be expressed as [26]:
Where qeq is the spectrum-integral density of the blackbody radiation flux, qweq is Spectral radiant flux of a blackbody, and T is the brightness temperature. As well, the total intensity of spectral lines of atoms excited in flames can be simplified and written as [27]:Where Nm is concentration of atoms in the ground state, At is the Einstein spontaneous transition probability, gm and gn are the statistical weights of the excited (m) and ground (n) states, and T is the adiabatic flame temperature. From the Eqs. (3) and (4), the key to improve the emission spectra intensity is increasing the combustion temperature T and the concentration of atoms in the ground state Nm. Actually the brightness temperature Tb could be calculated by Eq. (3) and the adiabatic flame temperature Tf of each mixture can be estimated by thermodynamic equilibrium calculation, the results are shown in Fig. 5. With the increasing amount of Kp additives, the temperature increases at first and then decreases. The mixture Zr/Al/Kp-45 (33%Zr: 33%Al: 34%Kp) has the highest brightness temperature Tb = 4615 K and the adiabatic flame temperature Tf = 4194 K. Actually, the highest temperature can reached by mixing the fuel Zr and oxidizer powders Kp in stoichiometric ratio (Kp/Zr = 43/57) when Al Nps act as ignition agents. The mass ratio of Zr/Al/Kp-45 (Kp/Zr = 50/50) is closest to the stoichiometric ratio. On the other hand, with the increasing amount of Kp additives, the reduce of mass transport distance between the fuel and oxidizer will lead to higher burning rate. In addition, it’s worth noting that the brightness temperature Tb is higher than the adiabatic flame temperature Tf at the same mass ratio which is related to the thermodynamic parameters obtained during the adiabatic flame temperature calculation.Fig. 4 (a) The time-integrated emission spectra and (b) irradiance time of combusting Zr/Al with different amounts of Kp.
when the total emission spectra intensity and irradiance time of these mixtures are took into account, lasing experiments by flash ignition of different amount Zr/Al/Kp-55 (27%Zr: 27%Al: 46% Kp) were performed. Figure 6(a) plots the output energy versus the input pump energy. The beam intensity distribution at a pump energy of 15 J is shown in the inset of Fig. 6(a). Specially, the pump energy is the emission combusting flame energy of the mixture within the wavelength range of the Nd absorption bands (400 nm-950 nm). For 100 mg mixture, we measured that the pumping energy is around 25 J and assumed that the pumping energy is proportional to the mass of mixture. A lasing threshold with 20 mg mixture (around 5 J pump energy) is obtained by the combusting flame excitation. The maximum laser output energy was 702.5 mJ with the laser pulse duration of 10 ms which is shown in Fig. 6(b). The slope efficiency is estimated as 3.29% by linear fit. The reasons for the low slope efficiency are (1) high mirror reflectivity R = 90% (laser light confinement is too high), (2) low absorption efficiency of emission combusting flame (the PTFE cavity and cavity structure are not efficient, the pump lights are blocked by dust of the burn products), and (3) losses in the laser cavity.
Fig. 6 (a) Laser output energy versus the input pump energy; the inset shows the beam intensity distribution at a pump energy of 15 J; (b) the duration of the pulse laser.
At last, it is necessary to caution the reader that these mixtures are extremely explosive and we only use very small quantities of such mixtures (less than 100 mg) while performing any laser tests. Despite that, thousands of joules output energy can be expected when several grams of mixtures with large surface area are ignited to pump a Nd: YAG laser slab.
4. Conclusions
In conclusion, we have realized the laser emission from the flash ignition of the Zr/Al Nps with the addition of Kp oxidizer for the first time. The mixture Zr/Al/Kp-45 (mass ratio = 33%Zr: 33%Al: 34% KClO4) has the highest brightness temperature Tb = 4615 K and the adiabatic flame temperature Tf = 4194 K with the duration of 20 ms. The mixture Zr/Al/Kp-55 is one of the most efficient laser pump source we found in this paper. The maximum laser output energy was 702.5 mJ with the laser pulse duration of 10 ms by using 100 mg mixture. It provides a new application for the energetic materials which could be flash ignited if the flame spectrum matches the strong absorption band of laser pump medium. Further research will concentrate on optimizing existing formulation and looking for new formulation of pumping sources with higher efficiencies and lower threshold. Moreover, thousands of joules output energy will be easily reached when several grams of mixtures with large surface area are ignited by the camera flash which is driven by a 5 V power supply.
Funding
National Natural Science Foundation of China (No. 51306165, 51606158).
References and links
1. P. M. Ajayan, M. Terrones, A. de la Guardia, V. Huc, N. Grobert, B. Q. Wei, H. Lezec, G. Ramanath, and T. W. Ebbesen, “Nanotubes in a flash--ignition and reconstruction,” Science 296(5568), 705 (2002). [CrossRef] [PubMed]
2. B. Bockrath, J. K. Johnson, D. S. Sholl, B. Howard, C. Matranga, W. Shi, and D. Sorescu, “Igniting nanotubes with a flash,” Science 297(5579), 192–193 (2002). [CrossRef] [PubMed]
3. N. Wang, B. D. Yao, Y. F. Chan, and X. Y. Zhang, “Enhanced photothermal effect in Si nanowires,” Nano Lett. 3(4), 475–477 (2003). [CrossRef]
4. Y. Ohkura, J. M. Weisse, L. Cai, and X. Zheng, “Flash ignition of freestanding porous silicon films: effects of film thickness and porosity,” Nano Lett. 13(11), 5528–5533 (2013). [CrossRef] [PubMed]
5. J. Huang and R. B. Kaner, “Flash welding of conducting polymer nanofibres,” Nat. Mater. 3(11), 783–786 (2004). [CrossRef] [PubMed]
6. L. J. Cote, R. Cruz-Silva, and J. Huang, “Flash reduction and patterning of graphite oxide and its polymer composite,” J. Am. Chem. Soc. 131(31), 11027–11032 (2009). [CrossRef] [PubMed]
7. M. R. Manaa, A. R. Mitchell, R. G. Garza, P. F. Pagoria, and B. E. Watkins, “Flash ignition and initiation of explosives-nanotubes mixture,” J. Am. Chem. Soc. 127(40), 13786–13787 (2005). [CrossRef] [PubMed]
8. A. M. Berkowitz and M. A. Oehlschlaeger, “The photo-induced ignition of quiescent ethylene/air mixtures containing suspended carbon nanotubes,” Proc. Combust. Inst. 33(2), 3359–3366 (2011). [CrossRef]
9. S. H. Fischer and M. C. Grubelich, Proceedings of 24th International Pyrotechnics Seminar, Monterey, California, USA, CA, 27–31 (1998).
10. T. L. Pourpoint, T. D. Wood, M. A. Pfeil, J. Tsohas, and S. F. Son, “Feasibility study and demonstration of an aluminum and ice solid propellant,” Int. J. Aerosp. Eng. 2012, 874076 (2012).
11. L. L. Wang, Z. A. Munir, and Y. M. Maximov, “Thermite reactions: their utilization in the synthesis and processing of materials,” J. Mater. Sci. 28(14), 3693–3708 (1993). [CrossRef]
12. A. A. Kaminskii, A. I. Bodretsova, and S. I. Levikov, “A quasicontinuous laser with pyrotechnical excitation,” J. Appl. Spectrosc. 6(2), 168–169 (1967). [CrossRef]
13. A. A. Kaminskiĭ, A. I. Bodretsova, A. G. Petrosyan, and A. A. Pavlyuk, “New quasi-cw pyrotechnically pumped crystal lasers,” Sov. J. Quantum Electron. 13(7), 975–976 (1983). [CrossRef]
14. M. A. Acharekar and R. LeBeau, “Miniature laser direct-detection radar,” Proc. SPIE 1633(94), 94–110 (1992). [CrossRef]
15. P. Pencikowski and P. Csik, “A long-range synthetic vision system combining a pyrotechnic-pumped laser and range-gated camera,” in IEEE Proceedings of 1996 Aerospace Applications Conference (1996), pp. 97–102.
16. A. A. Kaminskii, S. N. Bagayev, K. Ueda, K. Takaichi, H. Yagi, and T. Yanagitani, “5.5 J pyrotechnically pumped Nd3+:Y3Al5O12 ceramic laser,” Laser Phys. Lett. 3(3), 124–128 (2006). [CrossRef]
17. C. Rossi and D. Esteve, “Micropyrotechnics, a new technology for making energetic microsystems: review and prospective,” Sens. Actuators 120(2), 297–310 (2005). [CrossRef]
18. C. J. Morris, K. E. Laflin, W. A. Churaman, C. R. Becker, L. J. Currano, and D. H. Gracias, “Initiation of nanoporous energetic silicon by optically-triggered, residual stress powered microactuators,” in Proc. 25th IEEE Int. Conf. Micro ElectroMech. Syst. (2012), pp. 1245−1248. [CrossRef]
19. C. Manfletti and G. Kroupa, “Laser ignition of a cryogenic thruster using a miniaturised Nd:YAG laser,” Opt. Express 21(6), A1126–A1139 (2013). [CrossRef] [PubMed]
20. S. Wang, R. Shen, Y. Ye, and Y. Hu, “An investigation into the fabrication and combustion performance of porous silicon nanoenergetic array chips,” Nanotechnology 23(43), 435701 (2012). [CrossRef] [PubMed]
21. D. W. Liang and R. Pereira, “Diode pumping of a solid-state laser rod by a two-dimensional CPC-elliptical cavity with intervening optics,” Opt. Commun. 275(1), 104–115 (2007). [CrossRef]
22. C. L. Yan, R. J. Liu, C. R. Zhang, and Y. B. Chao, “Synthesis and formation mechanism of ZrB2–Al2O3 composite powder starting from ZrO2, Al, and BN,” Adv. Powder Technol. 27(2), 711–716 (2016). [CrossRef]
23. X. L. Kang, Q. Zhang, J. S. Luo, and Y. J. Tang, “Selective emissions during combustion of KClO4/Zr pyrotechnics for laser pump application,” Combust. Sci. Technol. 183(12), 1401–1411 (2011). [CrossRef]
24. D. Liang and J. Almeida, “Solar-pumped TEM00 mode Nd: YAG laser,” Opt. Express 21(21), 25107–25112 (2013). [CrossRef] [PubMed]
25. S. Mizuno, H. Ito, K. Hasegawa, T. Suzuki, and Y. Ohishi, “Laser emission from a solar-pumped fiber,” Opt. Express 20(6), 5891–5895 (2012). [CrossRef] [PubMed]
26. K. Stepanov, L. Stanchits, and Y. Stankevich, “Modeling of explosion thermal radiation,” J. Eng. Phys. Thermophysics 84(1), 179–206 (2011). [CrossRef]
27. J. Winefordner, W. McGee, J. Mansfield, M. Parsons, and K. Zacha, “Intensity of thermal radiation of metal spectra in flame emission spectrometry,” Anal. Chim. Acta 36(66), 25–41 (1966). [CrossRef]
