The authors would like to thank the photographers of ISL, Yves Suma and Yannick Boehrer, for the photos of samples and for the observation by high speed video of the synthesis and the combustion of nanothermite foams. They also would like to express their gratitude to their colleague Dr. Vincent Pichot from NS3E laboratory for the characterization of the materials by X-ray diffraction.

CAUTION: Perform all reactions described in this article in an explosion-proven chamber with an armored window that allows both visual inspection and observation of the foaming/combustion processes by high speed video. Take care regarding the experimental risk arising from the potential ignition of aluminothermic compositions and the hydrogen explosion in the air. For this reason, always work in an explosion-proven chamber equipped with appropriate exhaust ventilation. Remember that experiments on energetic materials must be carried out by experienced scientists, who are fully aware of pyrotechnic hazards, and that all tests must be performed in accordance with local laws and safety regulations. Note that authors decline any responsibility for inappropriate use of these results.
1. Preparation of an Aluminophosphate Matrix
NOTE: Experiments are performed at room temperature (15 - 25 &#176;C).
<ol>
	<li>Weigh 3.00 g of aluminum nanopowder.</li>
	<li>Weigh 4.00 g of a commercial solution (85%) of orthophosphoric acid (H3PO4) in a 150 mL beaker; add the acid dropwise with a 3 mL polyethylene Pasteur pipette.
	<ol>
		<li>Optionally, a volume from 0 - 2 mL of deionized water can be added to the orthophosphoric acid.</li>
		<li>Homogenize the solution by slowing rotating the beaker by hand at approximately 100 rpm.</li>
	</ol>
	</li>
	<li>Place the beaker containing the acid in the explosion chamber.</li>
	<li>Pour the aluminum nanopowder weighed in step 1.1 into the beaker containing the H3PO4 solution.</li>
	<li>Mix quickly with a stainless steel spatula; perform this step in less than one minute.</li>
	<li>Close the explosion chamber immediately.</li>
	<li>Wait until the foaming reaction occurs.</li>
	<li>Afterwards, wait an additional 10 min for the aluminophosphate matrix to cool.</li>
	<li>Remove the beaker from the explosion chamber using a laboratory bow tong.</li>
	<li>Recover the sample, which adheres to the beaker wall, by carefully breaking it. Beware of the presence of acidic residues and do not handle the materials without gloves.</li>
</ol>
2. Synthesis of Nanothermite Foams
NOTE: Experiments are performed at room temperature (15 - 25&#176;C).
<ol>
	<li>Preparation of the nanothermite mixture
	<ol>
		<li>In a 100 mL round-bottom flask, weigh 3.00 g and 3.45 g of Al and WO3 nanopowders, respectively.</li>
		<li>Mix the nanopowders with a vortex mixer operating at 2,500 rpm.</li>
		<li>Gently stir the mixture with a stainless-steel spatula to homogenize it. Avoid any friction between the glass wall of the round-bottom flask and the spatula during this operation. 
		NOTE: In this step, the experimenter must be grounded in order to avoid any electrostatic discharge, which could cause the ignition of the mixture.</li>
		<li>Repeat the operation 2.1.2.</li>
	</ol>
	</li>
	<li>Preparation of H 3 PO 4 solutions
	<ol>
		<li>Weigh 4.00 g of a commercial solution (85%) of orthophosphoric acid (H3PO4) in a 150 mL beaker; add the acid dropwise with a 3 mL polyethylene Pasteur pipette.</li>
		<li>Preparation of diluted H3PO4 solutions:
		<ol>
			<li>Take the sample prepared in step 2.2.1 and add 0 to 2 mL deionised water with a 1-mL polyethylene Pasteur pipette.</li>
			<li>Homogenize the solution by the slow rotation movement of the beaker applied by hand at a speed of about 100 rpm.</li>
		</ol>
		</li>
	</ol>
	</li>
	<li>Preparation of nanothermite foams
	<ol>
		<li>Place the beaker containing the acid prepared in step 2.2 in the explosion chamber.</li>
		<li>Pour the nanothermite prepared in step 2.1 in the beaker containing the H3PO4 solution.</li>
		<li>Mix quickly with a stainless-steel spatula; perform this step in less than one minute.</li>
		<li>Close the explosion chamber immediately.</li>
		<li>Wait until the foaming reaction occurs.</li>
		<li>Afterwards, wait an additional 10 min for the cooling down of the nanothermite foam.</li>
		<li>Remove the beaker from the explosion chamber with a laboratory bow tong.</li>
		<li>Recover the sample, which adheres to the beaker wall, by carefully breaking it. Beware of the presence of acidic residues and avoid handling the materials without gloves.</li>
	</ol>
	</li>
</ol>
3. Combustion of Nanothermite Foams
<ol>
	<li>Place the aluminophosphate matrix prepared in step 1.10 or the nanothermite foam prepared in step 2.3.8 in the explosion chamber.</li>
	<li>Place a pyrotechnic igniter close to the sample from step 3.1.</li>
	<li>Close the explosion chamber.</li>
	<li>Connect the igniter to a secure electronic device.</li>
	<li>Fire the pyrotechnic chain.</li>
	<li>Observe the combustion through the armored window with an ultrafast camera operating at 10,000 to 30,000 frames/s.</li>
</ol>

<ol>
	<li>Comet, M., Martin, C., Schnell, F., Spitzer, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Nanothermite+foams:+From+nanopowder+to+object.">Nanothermite foams: From nanopowder to object.</a> Chem. Eng. J. 316, 807-812 (2017).</li><li>Lafontaine, E., Comet, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Nanothermites. , (2016).</li><li>Comet, M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Preparation+of+Cr2O3+nanoparticles+for+superthermites+by+the+detonation+of+an+explosive+nanocomposite+material.">Preparation of Cr2O3 nanoparticles for superthermites by the detonation of an explosive nanocomposite material.</a> J. Nanopart. Res. 13 (5), 1961-1969 (2011).</li><li>Gibot, P., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Highly+Insensitive/Reactive+Thermite+Prepared+from+Cr2O3+Nanoparticles.">Highly Insensitive/Reactive Thermite Prepared from Cr2O3 Nanoparticles.</a> Propell. Explos. Pyrot. 36 (1), 80-87 (2011).</li><li>Tillotson, T. M., Gash, A. E., Simpson, R. L., Hrubesh, L. W., Satcher, J. H., Poco, J. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Nanostructured+energetic+materials+using+sol-gel+methodologies.">Nanostructured energetic materials using sol-gel methodologies.</a> J. Non-Cryst. Solids. 285 (1-3), 338-345 (2001).</li><li>Yang, Y., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Hierarchical+MnO2/SnO2+Heterostructures+for+a+Novel+Free-Standing+Ternary+Thermite+Membrane.">Hierarchical MnO2/SnO2 Heterostructures for a Novel Free-Standing Ternary Thermite Membrane.</a> Inorg. Chem. 52 (16), 9449-9455 (2013).</li><li>Prentice, D., Pantoya, M. L., Gash, A. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Combustion+Wave+Speeds+of+Sol-Gel-Synthesized+Tungsten+Trioxide+and+Nano-Aluminum:+The+Effect+of+Impurities+on+Flame+Propagation.">Combustion Wave Speeds of Sol-Gel-Synthesized Tungsten Trioxide and Nano-Aluminum: The Effect of Impurities on Flame Propagation.</a> Energ. Fuel. 20 (6), 2370-2376 (2006).</li><li>Bockmon, B. S., Pantoya, M. L., Son, S. F., Asay, B. W., Mang, J. T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Combustion+velocities+and+propagation+mechanisms+of+metastable+interstitial+composites.">Combustion velocities and propagation mechanisms of metastable interstitial composites.</a> Appl. Phys. Lett. 98, 064903 (2005).</li><li>Apperson, S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Generation+of+fast+propagating+combustion+and+shock+waves+with+copper+oxide/aluminum+nanothermite+composites.">Generation of fast propagating combustion and shock waves with copper oxide/aluminum nanothermite composites.</a> Appl. Phys. Lett. 91, 243109 (2007).</li><li>Wang, L., Luss, D., Martirosyan, K. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+behavior+of+nanothermite+reaction+based+on+Bi2O3/Al.">The behavior of nanothermite reaction based on Bi2O3/Al.</a> J. Appl. Phys. 110, 074311 (2011).</li><li>Martirosyan, K. S., Wang, L., Vicent, A., Luss, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Synthesis+and+performances+of+bismuth+trioxide+nanoparticles+for+high+energy+gas+generator+use.">Synthesis and performances of bismuth trioxide nanoparticles for high energy gas generator use.</a> Nanotechnology. 20 (8), 405609 (2009).</li><li>Armstrong, R. W., Baschung, B., Booth, D. W., Samirant, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Enhanced+Propellant+Combustion+with+Nanoparticles.">Enhanced Propellant Combustion with Nanoparticles.</a> Nano Lett. 3 (2), 253-255 (2003).</li><li>Wu, C., Sullivan, K., Chowdhury, S., Jian, G., Zhou, L., Zachariah, M. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Encapsulation+of+Perchlorate+Salts+within+Metal+Oxides+for+Application+as+Nanoenergetic+Oxidizers.">Encapsulation of Perchlorate Salts within Metal Oxides for Application as Nanoenergetic Oxidizers.</a> Adv. Funct. Mater. 22 (1), 78-85 (2012).</li><li>Sullivan, K. T., Piekiel, N. W., Chowdhury, S., Wu, C., Zachariah, M. R., Johnson, C. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Ignition+and+Combustion+Characteristics+of+Nanoscale+Al/AgIO3:+A+Potential+Energetic+Biocidal+System.">Ignition and Combustion Characteristics of Nanoscale Al/AgIO3: A Potential Energetic Biocidal System.</a> Combust. Sci. Technol. 183 (3), 285-302 (2010).</li><li>Wang, H., Jian, G., Zhou, W., Delisio, J. B., Lee, V. T., Zachariah, M. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Metal+iodate-based+energetic+composites+and+their+combustion+and+biocidal+performances.">Metal iodate-based energetic composites and their combustion and biocidal performances.</a> ACS Appl. Mater. Interfaces. 7 (31), 17363-17370 (2015).</li><li>Jian, G., Feng, J., Jacob, R. J., Egan, G. C., Zachariah, M. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Super-reactive+Nanoenergetic+Gas+Generators+Based+on+Periodate+Salts.">Super-reactive Nanoenergetic Gas Generators Based on Periodate Salts.</a> Angew. Chem. Int. Ed. 52 (37), 9743-9746 (2013).</li><li>Comet, M., Vidick, G., Schnell, F., Suma, Y., Baps, B., Spitzer, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Sulfates-Based+Nanothermites:+An+Expanding+Horizon+for+Metastable+Interstitial+Composites.">Sulfates-Based Nanothermites: An Expanding Horizon for Metastable Interstitial Composites.</a> Angew. Chem. Int. Ed. 54 (15), 4458-4462 (2015).</li><li>Zhou, W., Delisio, J. B., Li, X., Liu, L., Zachariah, M. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Persulfate+salt+as+an+oxidizer+for+biocidal+energetic+nano-thermites.">Persulfate salt as an oxidizer for biocidal energetic nano-thermites.</a> J. Mater. Chem. A. 3 (22), 11838-11846 (2015).</li><li>Sun, J., Pantoya, M. L., Simon, S. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Dependence+of+size+and+size+distribution+on+reactivity+of+aluminum+nanoparticles+in+reactions+with+oxygen+and+MoO3.">Dependence of size and size distribution on reactivity of aluminum nanoparticles in reactions with oxygen and MoO3.</a> Thermochim. Acta. 444 (2), 117-127 (2006).</li><li>Levitas, V. I., Asay, B. W., Son, S. F., Pantoya, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Melt+dispersion+mechanism+for+fast+reaction+of+nanothermites.">Melt dispersion mechanism for fast reaction of nanothermites.</a> Appl. Phys. Lett. 89, 071909 (2006).</li><li>Park, E. -. J., Kim, H., Kim, Y., Choi, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Repeated-dose+toxicity+attributed+to+aluminum+nanoparticles+following+28-day+oral+administration,+particularly+on+gene+expression+in+mouse+brain.">Repeated-dose toxicity attributed to aluminum nanoparticles following 28-day oral administration, particularly on gene expression in mouse brain.</a> Toxicol. Environ. Chem. 93 (1), 120-133 (2011).</li><li>Walter, K. C., Aumann, C. E., Carpenter, R. D., O'Neill, E. H., Pesiri, D. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Energetic+materials+development+at+technanogy+materials+development.">Energetic materials development at technanogy materials development.</a> Mater. Res. Soc. Symp. Proc. 800, 27-37 (2004).</li><li>Khasainov, B., Comet, M., Veyssi&#232;re, B., Spiter, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Comparison+of+performance+of+fast–reacting+nanothermites+and+primary+explosives.">Comparison of performance of fast–reacting nanothermites and primary explosives.</a> Propell. Explos. Pyrot. , (2017).</li><li>Siegert, B., Comet, M., Spitzer, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Safer+energetic+materials+by+a+nanotechnological+approach.">Safer energetic materials by a nanotechnological approach.</a> Nanoscale. 3, 3534-3544 (2011).</li><li>Sullivan, K. T., Kuntz, J. D., Gash, A. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Electrophoretic+deposition+and+mechanistic+studies+of+nano-Al/CuO+thermites.">Electrophoretic deposition and mechanistic studies of nano-Al/CuO thermites.</a> J. Appl. Phys. 112, 024316 (2012).</li><li>Blobaum, K. J., Reiss, M. E., Plitzko, J. M., Weihs, T. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Deposition+and+characterization+of+a+self-propagating+CuOx/Al+thermite+reaction+in+a+multilayer+foil+geometry.">Deposition and characterization of a self-propagating CuOx/Al thermite reaction in a multilayer foil geometry.</a> J. Appl. Phys. 94 (5), 2915-2922 (2003).</li><li>Gash, A. E., Tillotson, T. M., Satcher, J. H., Poco, J. F., Hrubesh, L. W., Simpson, R. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Use+of+epoxides+in+the+sol-gel+synthesis+of+porous+iron+(III)+oxide+monoliths+from+Fe(III)+salts.">Use of epoxides in the sol-gel synthesis of porous iron (III) oxide monoliths from Fe(III) salts.</a> Chem. Mater. 13 (3), 999-1007 (2001).</li><li>Yan, S., Jian, G., Zachariah, M. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Electrospun+nanofiber-based+thermite+textiles+and+their+reactive+properties.">Electrospun nanofiber-based thermite textiles and their reactive properties.</a> ACS Appl. Mater. Interfaces. 4, 6432-6435 (2012).</li><li>Puszynski, J. A., Groven, L. J., Altavilla, C., Ciliberto, E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Formation+of+nanosized+aluminum+and+its+applications+in+condensed+phase+reactions.">Formation of nanosized aluminum and its applications in condensed phase reactions.</a> Inorganic nanoparticles. Synthesis, applications and perspectives. , (2011).</li><li>Shimizu, T. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Concept+and+the+use+of+negative+explosives.">Concept and the use of negative explosives.</a> Proceedings of the 11th International Pyrotechnics Seminar, Vail, Colorado, July 7-11. , (1986).</li><li>Molkov, V. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Fundamentals of Hydrogen Safety Engineering. 1, (2012).</li><li>Comet, M., Martin, C., Klaum&#252;nzer, M., Schnell, F., Spitzer, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Energetic+nanocomposites+for+detonation+initiation+in+high+explosives+without+primary+explosives.">Energetic nanocomposites for detonation initiation in high explosives without primary explosives.</a> Appl. Phys. Lett. 107, 243108 (2015).</li></ol>

We have nothing to disclose.

The mixing process of nanopowders with acid and the closing of the explosion chamber must be performed quickly, for safety reasons. The reaction delay may vary to some extent (1 - 10 min), depending on experimental conditions. It is shortened when room temperature is too high or in the presence of external heating sources like a spotlight, which can cause early activation of the foaming reaction. Conversely, it is increased when room temperature is low. In the case of too much foaming delay (&#62; 15 min), the reaction c...

This article reports on a method for transforming nano-sized aluminothermic mixtures (Al/WO3) from a loose powder state to foams1. Nanothermites are fast burning energetic compositions, which are most frequently prepared by the physical mixing of a metallic oxide/salt with a reducing metal, in the form of nanopowders2. The most representative oxides used to prepare nanothermites are Cr2O33,4, Fe2O35, MnO26, WO37, MoO38, CuO9 and Bi2O310,11, while the metallic salts used are perchlorates12,13, iodates14,15, periodates16, sulfates17 or persulfates18. Aluminum nanopowder is the best choice as fuel for nanothermites owing to their numerous desirable properties, such as a high oxidation heat (10 - 25 kJ/g)19, fast reaction kinetics20, low toxicity21, and a fair degree of stability once it has been accurately passivated22.
In Al-based nanothermites, the flame front propagates at high velocities (0.1 - 2.5 km/s), but this cannot, however, be considered as detonation23. The reaction mechanism is actually driven by the convection of hot gases in the porosity of unreacted material. In other words, the porosity is essential to the fast burning of nanothermites. However, loose nanothermite powder is not stable from a physical standpoint. They are compacted by shocks or vibrations, and their densest component (generally the oxide) progressively separates from the composition by the effect of gravity. The stabilization of nanothermite porosity is a crucial challenge for their integration in future pyrotechnic systems.
The main advantage of the preparation process described herein is to give highly porous, solid, nanothermite monoliths, which can be shaped by molding the paste from which they form. Additionally, nanothermite foams are quite insensitive to shock, friction and electrostatic discharge compared to nanothermite loose powders. This insensitivity makes them particularly safe to handle and machine, for instance by sawing or drilling.
When loose nanothermite powders are pressed or pelletized, their porosity decreases and objects are formed. The cohesion of such materials originates from the surface forces, which are responsible for the aggregation of nanoparticles. The mechanical strength of nanothermite pellets can be improved in the presence of carbon nano-fibers, which act as a framework to reinforce these objects24. Unfortunately, pressing strongly decreases the reactivity of nanothermites. According to Prentice et al., the pressing of nano-Al/nano-WO3 compositions induces a collapse of their reaction velocity by two orders of magnitude7. In conclusion, contrary to most explosives, nanothermites cannot be shaped by pressing.
To date, very few methods for structuring nanothermites have been reported in scientific literature dealing with nanothermites. Nanothermites can be deposited on substrates, either from the powders of their components dispersed into a liquid medium by electrophoresis25, or by the sputtering of their components in successive layers26. Both approaches lead to dense deposits, which are less reactive than loose powders and tend to delaminate from the substrate on which they are prepared.
The preparation of &#34;three-dimensional&#34; objects composed of nanothermite was proposed by Tillotson et al.5, who used the sol-gel synthesis developed by Gash et al. that consists of gelling solutions of metallic salts by epoxides27. Nanothermite monoliths are prepared by dispersing Al nanopowder in the sol, before gelling. The gels are subsequently dried either in a heat chamber to produce xerogels or by a complex process involving the use of supercritical CO2 to obtain aerogels. Nanothermite aerogels not only have strong reactivity but can also be machined owing to their excellent mechanical properties. In addition, the sol-gel process allows one to synthesize micro- and mesoporous materials with an unrivalled degree of homogeneity between the fuel (Al) and the oxide in the mix. Despite these interesting features, the use of the sol-gel process is limited by: (i) the complexity of the batch synthesis, which depends on numerous parameters; (ii) the unavoidable presence of synthesis byproducts (impurities) in the final material, and (iii) the very long time needed by the different steps of the process.
Combustible mats of nanothermite were prepared by the electrospinning of nitrocellulose (binder) from solutions charged with Al and CuO nanoparticles28. These nanothermite felts are composed of fibers with sub-micrometer scale diameters, which are a priori non-porous. In these materials, the porosity is defined by the entanglement of fibers. The samples of nanothermite mats burn slowly (0.06 - 1.06 m/s) compared to pure nano-sized Al/CuO mixtures in a loose powder state, in which the flame front propagates at a velocity of several hundred m/s29. Finally, the use of nitrocellulose as a binder for nanothermites is not ideal, because it considerably increases their thermal sensitivity and alters their long-term chemical stability.
Membranes of nanothermites were prepared by Yang et al. from complex hierarchical MnO2/SnO2 heterostructures mixed with Al nanoparticles6. In these materials, the oxide phase has a very specific morphology, in which MnO2 nano-wires are covered by SnO2 branches. Because of its very particular structure, the oxide not only traps Al nanoparticles, but also ensures the mechanical resistance of the membrane. The preparation process of MnO2/SnO2/Al membranes is very simple; it consists of filtering the nanothermite contained in the liquid in which it has been prepared, using the filtration cake as a membrane.
To summarize, the only nanothermite objects mentioned in the scientific literature are deposits on substrates, aerogels, or mats. The idea of preparing nanothermites in the form of solid foams opens new horizons for the integration of these energetic materials into functional pyrotechnics systems. The foaming process reported in this article is simple to perform and can be virtually applied to any nanothermite prepared from aluminum nanopowder. The foaming agent is orthophosphoric acid (H3PO4), a common, inexpensive and non-toxic chemical, which reacts with nano-Al to give the cement (AlPO4) and the gases (H2, H2O vapor) that create the porosity of the material1. Aluminum phosphate is particularly stable at high temperatures, contrary to organic binders such as energetic polymers (nitrocellulose). However, AlPO4 behaves as an oxidizer towards nano-Al at high temperature, according to the concept of &#34;negative explosives&#34; proposed by Shimizu30.

<table>
	<tbody>
		<tr>
			<td>Aluminum nanopowder</td>
			<td>Intrinsiq Materials</td>
			<td>-</td>
			<td>nanopowder, &#8776; 100 nm particle size Al QNA891</td>
		</tr>
		<tr>
			<td>Tungsten(VI) oxide</td>
			<td>Sigma-Aldrich</td>
			<td>550086-25G</td>
			<td>nanopowder, &#60;100 nm particle size (TEM) Lot# MKBR9903V</td>
		</tr>
		<tr>
			<td>Orthophosphoric Acid</td>
			<td>Fisher Scientific</td>
			<td>-</td>
			<td>85% solution</td>
		</tr>
		<tr>
			<td>polyethylene Pasteur pipette 3 mL</td>
			<td>Th. Geyer</td>
			<td>7691062</td>
			<td>LABSOLUTE Pasteur pipettes made of polyethylene (PE) graduation 0,50 ml, Length 145 mm</td>
		</tr>
		<tr>
			<td>polyethylene Pasteur pipette 1 mL</td>
			<td>Th. Geyer</td>
			<td>7691063</td>
			<td>LABSOLUTE Pasteur pipettes made of polyethylene (PE) graduation 0,25 ml, Length 150 mm</td>
		</tr>
		<tr>
			<td>Test tube shaker Reax Control</td>
			<td>Heidolph</td>
			<td>541-11000-00</td>
			<td>Vortex mixer with strong 5 mm vibration orbit yields</td>
		</tr>
	</tbody>
</table>

nanothermite with meringue-like morphology: from loose powder to ultra-porous objects

The goal of the protocol described in this article is to prepare aluminothermic compositions (nanothermites) in the form of porous, monolithic objects. Nanothermites are combustible materials made up of inorganic fuel and an oxidizer. In nanothermite foams, aluminum is the fuel and aluminum phosphate and tungsten trioxide are the oxidizing moieties. The highest flame propagation velocities (FPVs) in nanothermites are observed in loose powders and FPVs are strongly decreased by pelletizing nanothermite powders. From a physical standpoint, nanothermite loose powders are metastable systems. Their properties can be altered by unintentional compaction induced by shocks or vibrations or by the segregation of particles over time by settling phenomena, which originates from the density differences of their components. Moving from a powder to an object is the challenge that must be overcome to integrate nanothermites in pyrotechnic systems. Nanothermite objects must have both a high open porosity and good mechanical strength. Nanothermite foams meet both of these criteria, and they are prepared by dispersing a nano-sized aluminothermic mixture (Al/WO3) in orthophosphoric acid. The reaction of aluminum with the acid solution gives the AlPO4 &#34;cement&#34; in which Al and WO3 nanoparticles are embedded. In nanothermite foams, aluminum phosphate plays the dual role of binder and oxidizer. This method can be used with tungsten trioxide, which is not altered by the preparation process. It could probably be extended to some oxides, which are commonly used for the preparation of high performance nanothermites. The WO3-based nanothermite foams described in this article are particularly insensitive to impact and friction, which makes them far safer to handle than loose Al/WO3 powder. The fast combustion of these materials has interesting applications in pyrotechnic igniters. Their use in detonators as primers would require the incorporation of a secondary explosive in their composition.

The aluminophosphate matrix contains crystallized aluminum (Al) and aluminum phosphate (AlPO4). The presence of these phases was confirmed by X-ray diffraction (Figure 1). Additionally, gravimetric experiments have shown that this material also contains a non-crystalline part, which is amorphous alumina. In these materials, aluminum phosphate behaves both as binder and oxidizer. The oxidizing properties of AlPO4 were evidenced by measuri...

Watch this Scientific Journal Video about Nanothermite with Meringue-like Morphology: From Loose Powder to Ultra-porous Objects at JoVE.com

Nanothermite with Meringue-like Morphology: From Loose Powder to Ultra-porous Objects

This manuscript describes the synthesis of combustible aluminophosphate matrices by the reaction of orthophosphoric acid (H3PO4) with aluminum nanopowder. When this reaction is carried out with excess aluminum in the presence of tungsten trioxide nanopowder, it leads to a solid, porous nanothermite foam.

The goal of the protocol described in this article is to prepare aluminothermic compositions (nanothermites) in the form of porous, monolithic objects. ...

nanothermite-with-meringue-like-morphology-from-loose-powder-to-ultra

Research

JoVE Journal

Chemistry

7.6K Views.  French-German Research Institute of Saint-Louis (ISL). This manuscript describes the synthesis of combustible aluminophosphate matrices by the reaction of orthophosphoric acid (H3PO4) with aluminum nanopowder. When this reaction is carried out with excess aluminum in the presence of tungsten trioxide nanopowder, it leads to a solid, porous nanothermite foam.

Video: Nanothermite with Meringue-like Morphology: From Loose Powder to Ultra-porous Objects

Free Radicals in Chemical Biology: from Chemical Behavior to Biomarker Development

The involvement of free radicals in life sciences has constantly increased with time and has been connected to several physiological and pathological processes. This subject embraces diverse scientific areas, spanning from physical, biological and bioorganic chemistry to biology and medicine, with applications to the amelioration of quality of life, health and aging. Multidisciplinary skills are required for the full investigation of the many facets of radical processes in the biological environment and chemical knowledge plays a crucial role in unveiling basic processes and mechanisms. We developed a chemical biology approach able to connect free radical chemical reactivity with biological processes, providing information on the mechanistic pathways and products. The core of this approach is the design of biomimetic models to study biomolecule behavior (lipids, nucleic acids and proteins) in aqueous systems, obtaining insights of the reaction pathways as well as building up molecular libraries of the free radical reaction products. This context can be successfully used for biomarker discovery and examples are provided with two classes of compounds: mono-trans isomers of cholesteryl esters, which are synthesized and used as references for detection in human plasma, and purine 5',8-cyclo-2'-deoxyribonucleosides, prepared and used as reference in the protocol for detection of such lesions in DNA samples, after ionizing radiations or obtained from different health conditions.

Radical-based biomimetic chemistry has been applied to building-up libraries necessary for biomarker development.

The involvement of free radicals in life sciences has constantly increased with time and has been connected to several physiological and pathological ...

Nucleoside Triphosphates - From Synthesis to Biochemical Characterization

The traditional strategy for the introduction of chemical functionalities is the use of solid-phase synthesis by appending suitably modified phosphoramidite precursors to the nascent chain. However, the conditions used during the synthesis and the restriction to rather short sequences hamper the applicability of this methodology. On the other hand, modified nucleoside triphosphates are activated building blocks that have been employed for the mild introduction of numerous functional groups into nucleic acids, a strategy that paves the way for the use of modified nucleic acids in a wide-ranging palette of practical applications such as functional tagging and generation of ribozymes and DNAzymes. One of the major challenges resides in the intricacy of the methodology leading to the isolation and characterization of these nucleoside analogues.
	
	In this video article, we present a detailed protocol for the synthesis of these modified analogues using phosphorous(III)-based reagents. In addition, the procedure for their biochemical characterization is divulged, with a special emphasis on primer extension reactions and TdT tailing polymerization. This detailed protocol will be of use for the crafting of modified dNTPs and their further use in chemical biology.

The protocol described herein aims to explain and abridge the numerous obstacles in the way of the intricate route leading to modified nucleoside triphosphates. Consequently, this protocol facilitates both the synthesis of these activated building-blocks and their availability for practical applications.

The  traditional strategy for the introduction of chemical functionalities is the  use of solid-phase synthesis by appending suitably modified ...

From Constructs to Crystals &#8211; Towards Structure Determination of &#946;-barrel Outer Membrane Proteins

Membrane proteins serve important functions in cells such as nutrient transport, motility, signaling, survival and virulence, yet constitute only ~1% percent of known structures. There are two types of membrane proteins, &#945;-helical and &#946;-barrel. While &#945;-helical membrane proteins can be found in nearly all cellular membranes, &#946;-barrel membrane proteins can only be found in the outer membranes of mitochondria, chloroplasts, and Gram-negative bacteria. One common bottleneck in structural studies of membrane proteins in general is getting enough pure sample for analysis. In hopes of assisting those interested in solving the structure of their favorite &#946;-barrel outer membrane protein (OMP), general protocols are presented for the production of target &#946;-barrel OMPs at levels useful for structure determination by either X-ray crystallography and/or NMR spectroscopy. Here, we outline construct design for both native expression and for expression into inclusion bodies, purification using an affinity tag, and crystallization using detergent screening, bicelle, and lipidic cubic phase techniques. These protocols have been tested and found to work for most OMPs from Gram-negative bacteria; however, there are some targets, particularly for mitochondria and chloroplasts that may require other methods for expression and purification. As such, the methods here should be applicable for most projects that involve OMPs from Gram-negative bacteria, yet the expression levels and amount of purified sample will vary depending on the target OMP.

&#946;-barrel outer membrane proteins (OMPs) serve many functions within the outer membranes of Gram-negative bacteria, mitochondria, and chloroplasts. Here, we hope to alleviate a known bottleneck in structural studies by presenting protocols for the production of &#946;-barrel OMPs in sufficient quantities for structure determination by X-ray crystallography or NMR spectroscopy.

Membrane proteins serve important functions in cells such as nutrient transport, motility, signaling, survival and virulence, yet constitute only ~1% ...

X-ray Powder Diffraction in Conservation Science: Towards Routine Crystal Structure Determination of Corrosion Products on Heritage Art Objects

The crystal structure determination and refinement process of corrosion products on historic art objects using laboratory high-resolution X-ray powder diffraction (XRPD) is presented in detail via two case studies.
The first material under investigation was sodium copper formate hydroxide oxide hydrate, Cu4Na4O(HCOO)8(OH)2&#8729;4H2O (sample 1) which forms on soda glass/copper alloy composite historic objects (e.g., enamels) in museum collections, exposed to formaldehyde and formic acid emitted from wooden storage cabinets, adhesives, etc. This degradation phenomenon has recently been characterized as &#34;glass induced metal corrosion&#34;.
For the second case study, thecotrichite, Ca3(CH3COO)3Cl(NO3)2&#8729;6H2O (sample 2), was chosen, which is an efflorescent salt forming needlelike crystallites on tiles and limestone objects which are stored in wooden cabinets and display cases. In this case, the wood acts as source for acetic acid which reacts with soluble chloride and nitrate salts from the artifact or its environment.
The knowledge of the geometrical structure helps conservation science to better understand production and decay reactions and to allow for full quantitative analysis in the frequent case of mixtures.

Modern high resolution X-ray powder diffraction (XRPD) in the laboratory is used as an efficient tool to determine crystal structures of long-known corrosion products on historic objects.

The crystal structure determination and refinement process of corrosion products on historic art objects using laboratory high-resolution X-ray powder ...

Using Capillary Electrophoresis to Quantify Organic Acids from Plant Tissue: A Test Case Examining Coffea arabica Seeds

Carboxylic acids are organic acids containing one or more terminal carboxyl (COOH) functional groups. Short chain carboxylic acids (SCCAs; carboxylic acids containing three to six carbons), such as malate and citrate, are critical to the proper functioning of many biological systems, where they function in cellular respiration and can serve as indicators of cell health. In foods, organic acid content can have significant impact on taste, with increased SCCA levels resulting in a sour or &#34;acid&#34; taste. Because of this, methods for the rapid analysis of organic acid levels are of particular interest to the food and beverage industries. Unfortunately, however, most methods used for SCCA quantification are dependent on time-consuming protocols requiring the derivatization of samples with hazardous reagents, followed by costly chromatographic and/or mass spectrometric analyses. This method details an alternate method for the detection and quantification of organic acids from plant material and food samples using free zonal capillary electrophoresis (CZE), sometimes simply referred to as capillary electrophoresis (CE). CZE provides a cost-effective method for measuring SCCAs with a low limit of detection (0.005 mg/ml). This article details the extraction and quantification of SCCAs from plant samples. While the method provided focuses on measurement of SCCAs from coffee beans, the method provided can be applied to multiple plant-based food materials.

Using Capillary Electrophoresis to Quantify Organic Acids from Plant Tissue: A Test Case Examining Coffea arabica Seeds

This article presents a method for the detection and quantification of organic acids from plant material using free zonal capillary electrophoresis. An example of the potential application of this method, determining the effects of a secondary fermentation on organic acid levels in coffee seeds, is provided.

Carboxylic acids are organic acids containing one or more terminal carboxyl (COOH) functional groups. Short chain carboxylic acids (SCCAs; carboxylic ...

Extraction and Purification of Polyphenols from Freeze-dried Berry Powder for the Treatment of Vascular Smooth Muscle Cells In Vitro

Epidemiological studies indicate that increased flavonoid intake correlates with decreased mortality due to cardiovascular diseases (CVD) in the United States (US) and Europe. Berries are widely consumed in the US and have a high polyphenolic content. Polyphenols have been shown to interact with many molecular targets and to exert numerous positive biological functions, including antioxidant, anti-inflammatory, and cardioprotective effects. Polyphenols isolated from blackberry (BL), raspberry (RB), and black raspberry (BRB) reduce oxidative stress and cellular senescence in response to angiotensin II (Ang II). This work provides a detailed description of the protocol used to prepare the polyphenol extracts from freeze-dried berries. Polyphenol extractions from freeze-dried berry powder were performed using 80% aqueous ethanol and an ultrasonic-assisted extraction method. The crude extract was further purified and fractionated using chloroform and ethyl acetate, respectively. The effects of both crude and purified extracts were tested on Vascular Smooth Muscle Cells (VSMCs) in culture.

Extraction and Purification of Polyphenols from Freeze-dried Berry Powder for the Treatment of Vascular Smooth Muscle Cells In Vitro

This work details a step-by-step method to prepare polyphenol-rich extracts from freeze-dried berry powder. In addition, it provides a thorough description of how to use these polyphenol-rich extracts in cell culture in the presence of the peptide hormone angiotensin II (Ang II) using Vascular Smooth Muscle Cells (VSMCs).

Epidemiological studies indicate that increased flavonoid intake correlates with decreased mortality due to cardiovascular diseases (CVD) in the United ...

From Molecules to Materials: Engineering New Ionic Liquid Crystals Through Halogen Bonding

Herein, we demonstrate that a bottom-up approach, based on halogen bonding (XB), can be successfully applied for the design of a new type of ionic liquid crystals (ILCs). Taking advantages of the high specificity of XB for haloperfluorocarbons and the ability of anions to act as XB-acceptors, we obtained supramolecular complexes based on 1-alkyl-3-methylimidazolium iodides and iodoperfluorocarbons, overcoming the well-known immiscibility between hydrocarbons (HCs) and perfluorocarbons (PFCs). The high directionality of the XB combined with the fluorophobic effect, allowed us to obtain enantiotropic liquid crystals where a rigid, non-aromatic, XB supramolecular anion acts as mesogenic core.
X-ray structure analysis of the complex between 1-ethyl-3-methylimidazolium iodide and iodoperfluorooctane showed the presence of a layered structure, which is a manifestation of the well-known tendency to segregation of perfluoroalkyl chains. This is consistent with the observation of smectic mesophases. Moreover, all the reported complexes melt below 100 &#176;C, and most are mesomorphic even at room temperature, despite that the starting materials were non-mesomorphic in nature.
The supramolecular strategy reported here provides new design principles for mesogen design allowing a totally new class of functional materials.

A protocol for the synthesis of a new type of mesogens, based on the halogen-bonded supramolecular anion [CnF2n+1-I&#183;&#183;&#183;I&#183;&#183;&#183;I-CnF2n+1]&#8722;, is reported.

Herein, we demonstrate that a bottom-up approach, based on halogen bonding (XB), can be successfully applied for the design of a new type of ionic liquid ...

Grafting Multiwalled Carbon Nanotubes with Polystyrene to Enable Self-Assembly and Anisotropic Patchiness

We demonstrate a straightforward protocol to graft pristine multiwalled carbon nanotubes (MWCNTs) with polystyrene (PS) chains at the sidewalls through a free-radical polymerization strategy to enable the modulation of the nanotube surface properties and produce supramolecular self-assembly of the nanostructures. First, a selective hydroxylation of the pristine nanotubes through a biphasic catalytically mediated oxidation reaction creates superficially distributed reactive sites at the sidewalls. The latter reactive sites are subsequently modified with methacrylic moieties using a silylated methacrylic precursor to create polymerizable sites. Those polymerizable groups can address further polymerization of styrene to produce a hybrid nanomaterial containing PS chains grafted to the nanotube sidewalls. The polymer-graft content, amount of silylated methacrylic moieties introduced and hydroxylation modification of the nanotubes are identified and quantified by Thermogravimetric Analysis (TGA). The presence of reactive functional groups hydroxyl and silylated methacrylate are confirmed by Fourier Transform Infrared Spectroscopy (FT-IR). Polystyrene-grafted carbon nanotube solutions in tetrahydrofuran (THF) provide wall-to-wall collinearly self-assembled nanotubes when cast samples are analyzed by transmission electron microscopy (TEM). Those self-assemblies are not obtained when suitable blanks are similarly cast from analogous solutions containing non-grafted counterparts. Therefore, this method enables the modification of the nanotube anisotropic patchiness at the sidewalls which results into spontaneous auto-organization at the nanoscale.

A procedure for the synthesis of polystyrene-grafted multiwalled carbon nanotubes using successive chemical modification steps to selectively introduce the polymer chains to the sidewalls and their self-assembly via anisotropic patchiness is presented.

We demonstrate a straightforward protocol to graft pristine multiwalled carbon nanotubes (MWCNTs) with polystyrene (PS) chains at the sidewalls through a ...

Combustion Chemistry of Fuels: Quantitative Speciation Data Obtained from an Atmospheric High-temperature Flow Reactor with Coupled Molecular-beam Mass Spectrometer

This manuscript describes a high-temperature flow reactor experiment coupled to the powerful molecular beam mass spectrometry (MBMS) technique. This flexible tool offers a detailed observation of chemical gas-phase kinetics in reacting flows under well-controlled conditions. The vast range of operating conditions available in a laminar flow reactor enables access to extraordinary combustion applications that are typically not achievable by flame experiments. These include rich conditions at high temperatures relevant for gasification processes, the peroxy chemistry governing the low temperature oxidation regime or investigations of complex technical fuels. The presented setup allows measurements of quantitative speciation data for reaction model validation of combustion, gasification and pyrolysis processes, while enabling a systematic general understanding of the reaction chemistry. Validation of kinetic reaction models is generally performed by investigating combustion processes of pure compounds. The flow reactor has been enhanced to be suitable for technical fuels (e.g. multi-component mixtures like Jet A-1) to allow for phenomenological analysis of occurring combustion intermediates like soot precursors or pollutants. The controlled and comparable boundary conditions provided by the experimental design allow for predictions of pollutant formation tendencies. Cold reactants are fed premixed into the reactor that are highly diluted (in around 99 vol% in Ar) in order to suppress self-sustaining combustion reactions. The laminar flowing reactant mixture passes through a known temperature field, while the gas composition is determined at the reactors exhaust as a function of the oven temperature. The flow reactor is operated at atmospheric pressures with temperatures up to 1,800 K. The measurements themselves are performed by decreasing the temperature monotonically at a rate of -200 K/h. With the sensitive MBMS technique, detailed speciation data is acquired and quantified for almost all chemical species in the reactive process, including radical species.

An investigation of the oxidative combustion chemistry of novel biofuels, fuel components, or jet fuels by comparison of quantitative speciation data is presented. The data can be used for kinetic model validation and enables fuel assessment strategies.This manuscript describes the atmospheric high-temperature flow reactor and demonstrates its capabilities.

This manuscript describes a high-temperature flow reactor experiment coupled to the powerful molecular beam mass spectrometry (MBMS) technique. This ...

Stereolithographic 3D Printing with Renewable Acrylates

The accessibility of cost-competitive renewable materials and their application in additive manufacturing is essential for an efficient biobased economy. We demonstrate the rapid prototyping of sustainable resins using a stereolithographic 3D printer. Resin formulation takes place by straightforward mixing of biobased acrylate monomers and oligomers with a photoinitiatior and optical absorber. Resin viscosity is controlled by the monomer to oligomer ratio and is determined as a function of shear rate by a rheometer with parallel plate geometry. A stereolithographic apparatus charged with the biobased resins is employed to produce complex shaped prototypes with high accuracy. The products require a post-treatment, including alcohol rinsing and UV irradiation, to ensure complete curing. The high feature resolution and excellent surface finishing of the prototypes is revealed by scanning electron microscopy.

A protocol for additive manufacturing with renewable photopolymer resins on a stereolithography apparatus is presented.

The accessibility of cost-competitive renewable materials and their application in additive manufacturing is essential for an efficient biobased economy. ...