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- Herausgeber: John Wiley & Sons
- Kategorie: Wissenschaft und neue Technologien
- Sprache: Englisch
The recent introduction of the "nano" dimension to pyrotechnics has made it possible to develop a new family of highly reactive substances: nanothermites. These have a chemical composition that is comparable to that of thermites at submillimeter or micrometric granulometry, but with a morphology having a much increased degree of homogeneity. This book discusses the methods of preparation of these energetic nanomaterials, their specific properties, and the different safety aspects inherent in their manipulation.
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Veröffentlichungsjahr: 2016
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Table of Contents
Cover
Title
Copyright
Introduction
1 Elaboration of Nanoparticles
1.1. Solid-phase elaboration
1.2. Liquid-phase elaboration
1.3. Gas-phase elaboration
2 Methods for Preparing Nanothermites
2.1. Introduction
2.2. Physical mixing
2.3. Coating
2.4. Sol-gel method
2.5. Impregnating porous solids
2.6. Assembly
2.7. Structuring at the surface of substrates
2.8. Conclusions and perspectives
3 The Experimental Study of Nanothermites
3.1. Introduction
3.2. Study and properties of main fuels
3.3. Oxidizers of interest for nanothermites
3.4. Methods for the characterization of nanothermites
3.5. Conclusion: performance of nanothermites and their enhancement
4 Nanothermites and Safety
4.1. Introduction
4.2. Pyrotechnic safety
4.3. Neutralization of nanothermites
4.4. Toxicological risk
4.5. Conclusions and perspectives
Conclusion
Bibliography
Index
End User License Agreement
List of Tables
1 Elaboration of Nanoparticles
Table 1.1. Size of nanoparticles obtained by mechanical milling of ductile metals
Table 1.2. Mechanosynthesis of nanosized metal particles
Table 1.3. Mecanosynthesis of nanosized metal oxide particles: D: diameter, E: thickness, L: length
Table 1.4. Sonochemical synthesis of metal oxide nanoparticles acac, acethylacetonate; BS, Schiff base; bis(acethylacetonato) propylene-1,3 diimine or bis (acethylacetonato) butylene-1,4 diimine; SDS, sodium dodecylsulfate; PVP, polyvinylpyrrolidone
Table 1.5. Sonochemical synthesis of metal and carbon nanoparticles
Table 1.6. Common solvents used in the solvothermal synthesis of metal and metal oxide nanoparticles (Tc: critical temperature, Pc: critical pressure)
Table 1.7. Hydrothermal synthesis of metal oxide nanoparticles in closed reactor and in subcritical medium; L, length; l, width; D, diameter; E, thickness; CTAB, cetyltrimethylammonium bromide; PVP, polyvinylpyrrolidone; sc, supercritical
Table 1.8. Hydrothermal synthesis of metal oxide nanoparticles in closed reactor and in supercritical carbon dioxide medium; TTIP, titanium tetraisopropoxide
Table 1.9. Continuous hydrothermal synthesis of metal oxide nanoparticles in subcritical medium: FW, subcritical fluid flow; FS, solute solution flow; DIPBAT, diisopropoxititanium bis (acetylacetonate); TTIP, titanium tetraisopropoxide
Table 1.10. Continuous hydrothermal synthesis of metal oxide nanoparticles in supercritical medium: L, length; D, diameter; FW, flow of supercritical fluid; FS, flow of solute solution
Table 1.11. Discontinuous hydrothermal synthesis of metal nanoparticles in supercritical medium (EDTA(Na)
2
, disodium ethylenediamine tetraacetate dihydrate)
Table 1.12. Continuous hydrothermal synthesis of metal nanoparticles sc, supercritical; FS, flow of solute solution
Table 1.13. Examples of sizes for various metal particles obtained by thermal evaporation techniques as a function of experimental conditions: pressure (P), temperature (T), gas velocity (V)
Table 1.14. Examples of metal nanoparticles synthesized by thermal plasma, according to the literature; APT, ammonium paratungstate
Table 1.15. Metal oxide nanoparticles synthesized by thermal plasma; ATP, ammonium paratungstate
Table 1.16. Examples of metal nanoparticles (NP) synthesized by plasma in liquids; SDS, sodium dodecylsulfate; CTAB, cetyltrimethylammonium bromide; CTAC, cetyltrimethyl ammonium chloride
Table 1.17. Examples of metal oxide nanoparticles (NP) synthesized by plasma in liquids; SDS, sodium dodecylsulfate; CTAB, cetyltrimethylammonium bromide; CTAC, cetyltrimethylammonium chloride
Table 1.18. Metal nanoparticles obtained by laser ablation in gas medium d
0
, mean diameter; F, fluence, E, energy deposited per pulse; T, ablation duration; P, emitted power
Table 1.19. Metal nanoparticles obtained by laser ablation in liquid medium; EG: ethylene glycol, SDS: sodium dodecylsulfate, PVP: polyvinylpyrrolidone, d
0
mean diameter, F: fluence, E: energy deposited per pulse, T: ablation duration, Mw: average molecular weight
Table 1.20. Metal nanoparticles obtained by laser ablation in liquid medium. SDS; sodium dodecylsulfate; CTAB, cetyltrimethylammonium bromide; PVP, polyvinylpyrrolidone; d
0
, mean diameter; F, fluence; E, energy deposited per pulse; T, ablation duration
Table 1.21. Nature of the materials elaborated by detonation and their possible uses for nanothermite formulation
Table 1.22. Comparison of pyrotechnic methods for the preparation of precursors that are part of the composition of nanothermites
2 Methods for Preparing Nanothermites
Table 2.1. Examples of oxidizers structured at submicron scale by aerosolization of aqueous solutions
Table 2.2. Operating conditions used by [QIN 13] for oxide deposit at the surface of aluminum nanoparticles: chemical formulae of precursors, temperature of reactor (T
r
), exposure duration (D
E
), deposit velocity (V
D
), number of cycles (N
C
) and range of thickness of oxide layers (E)
Table 2.3. Precipitation time for nanocomposite materials made up of graphene oxide, bismuth oxide and aluminum as a function of the proportion of graphene oxide [THI 14]
3 The Experimental Study of Nanothermites
Table 3.1. Maximum values of the enthalpy of combustion, taken from the comparative diagram published by Dreizin [DRE 09]
Table 3.2. Evaluation of the ability to react by MDM of certain fuels of interest in the preparation of nanothermites; sources: temperature of phase change Mp, Bp and densities d
Liq.
, d
Sol.
[LID 05]; linear expansion coefficients (α
Sol.
) for the metals [TOU 75] and the oxides [TOU 77]; point values from
a
[KIR 08],
b
[KUR 82],
c
[WAT 04],
d
[KIR 63]
Table 3.3. Maximal pressure (p
max
) and combustion propagation velocity (V
P
) in nanothermites composed of crystallized bismuth oxide (40–50 nm) and aluminum of various granulometries, depending on the diameter (D
Al
) of aluminum particles [WAN 11]
Table 3.4. Maximal pressure (P
max
), rate of pressurization (dP/dt), flame front propagation velocity (V
P
) and specific impulse (I
S
) produced by the reaction of GO/Bi
2
O
3
/Al nanothermites depending on their graphene oxide content. The corresponding data are taken from the diagrams published in [THI 15]
Table 3.5. Evolution of the flame propagation velocity (FPV) and heat of reaction (Q
R
) of the Bi
2
O
3
@nD/Al compositions, depending on the mass proportion of nanodiamond (nD) in the coated oxide [PIC 15]
Table 3.6. Domains of various modes of flame propagation in a CuO/Al nanothermite, depending on the nature and pressure of the gas in which it reacts; the values are taken from Figures 8–10 published in [WEI 09]
Table 3.7. Average values of flame propagation velocity (FPV), intensity of the pressurization peak (P
max
) and the rate of pressurization (T
P
) experimentally determined for NiO/Al and CuO/Al compositions [DEA 10]
Table 3.8. Characteristics of peroxides and superoxides of interest for the formulation of highly reactive nanothermites. Sources: densities, melting temperature T
Fus.
, effects of water [LID 05], except for the values marked by asterisks
Table 3.9. Values of maximum pressure (P
max
), rate of pressurization (dP/dt) and combustion duration (D
c
) measured for various nanothermites, in a 13 cm
3
pressure cell loaded with 25 mg of composition. The @ sign indicates that the compound in the prefix is coated with the compound in the suffix; the / sign indicates a simple mixture
4 Nanothermites and Safety
Table 4.1. Thresholds of sensitivity to friction (S
F
), impact (S
I
) and electrostatic discharge (S
ESD
) of nanothermites based on manganese oxides and aluminum depending on their mass composition; “@” indicates that the oxide MnO
x
is encapsulated in hollow carbon nanofibers, whereas “/” indicates a simple mixture of phases [SIE 10]
Table 4.2. Thresholds of sensitivity to friction (S
F
) and electrostatic discharge (S
ESD
) of Bi
2
O
3
@nD/Al compositions depend on the mass proportion of nanodiamond (nD) in the coated oxide [PIC 15]
Table 4.3. Threshold of sensitivity to electrostatic discharge (S
ESD
) depends on the mass proportion of Viton A
®
in a CuO/Al nanothermite [FOL 07]
Table 4.4. Thickness of the silicone layer (E
S
) and threshold of sensitivity to friction (S
F
) of a membrane of MnO
2
/Al nanothermite depend on its duration of exposure to silicone vapors (D
t
) [YAN 13a]
List of Illustrations
1 Elaboration of Nanoparticles
Figure 1.1. Grain size as a function of melting temperature according to data from [ECK, 92, FEC 90, OLE 96]
Figure 1.2. Principle of blown arc plasma torches: top: axial injection, hollow cathode (A); bottom: perpendicular injection of precursor (A), cooling fluid (B) and plasma gas (C)
Figure 1.3. Principle of transferred arc plasma torches: (A) quench gas, (B) cooling fluid, (C) low pressure and (D) plasma gas
Figure 1.4. Principle of radiofrequency (RF) plasma torches: left: capacitively coupled torch; right: inductively coupled torch. (A) Precursor and carrier gas, (B) central plasma gas, (C) sheath gas, (D) capacitive plate, (E) quench gas and (F) inductive coil
Figure 1.5. Diagram of a microwave system; microwave generator (A), tuners (B), tangential entries for quench gases (C), entries for central plasma gases and precursors (D), discharge tube (E), plasma ((F), waveguide (G) and mobile piston (H)
Figure 1.6. Diagram of a plasma arc system in liquid medium: anode (a), cathode (b), liquid (c) and plasma (d)
Figure 1.7. Tubular charge of hexolite (A) used as container for the nanocomposite material RDX@Cr
2
O
3
(B) used as precursor for the formation of Cr
2
O
3
nanoparticles by detonation [COM 11c]
Figure 1.8. Observation with transmission electron microscope (TEM) of products resulting from the detonation of nanocomposite material RDX@Cr
2
O
3
: raw soots (A) and Cr
2
O
3
nanoparticles extracted from soots after purification (B) [COM 11c]
Figure 1.9. Observation with scanning electron microscope of the morphologies of original Cr
2
O
3
; a) and detonation produced Cr
2
O
3
; b); the specific surface areas of these materials are 44.2 and 20.4 m
2
/g, respectively [COM 11c]
Figure 1.10. Comparison between the size distribution of Cr
2
O
3
of origin and that of Cr
2
O
3
formed by detonation [COM 11c]
2 Methods for Preparing Nanothermites
Figure 2.1. Scanning electron microscopy images of WO
3
nanoparticles before (a) and after aluminum coating (b); transmission electron microscopy images of a WO
3
/Al composite particle (c)
Figure 2.2. a) Hydrated composite gel; b) monolithic xerogel; and c) xerogel powder; d) observation by scanning electron microscopy and transmission electron microscopy (cartridge) of xerogel morphology [COM 06b]
Figure 2.3. Observation with scanning electron microscope of the morphology of Al
x
Mo
y
O
z
phases produced by calcining a composite xerogel depending on their final mass content of aluminum: a) 0%, b) 10.5%, c) 16.8% and d) 24.7% [COM 06b]
Figure 2.4. Observation by electron microscopy of the morphology of porous chromium a) and manganese b) oxides, whose porosity was loaded with hexogen by [COM 08c] in order to produce gas generating nanothermites
3 The Experimental Study of Nanothermites
Figure 3.1. Evolution of the mass content in alumina of spherical aluminum nanoparticles, containing a core/shell morphology, depending on the diameter and thickness of the covering alumina layer
Figure 3.2. Typical curve obtained by thermogravimetric analysis (TGA) of the gradual oxidation of a nanometric aluminum powder, type Alex, formed of particles with an average size of 160 nm
Figure 3.3. Electron micrographs of nanometric aluminum samples whose characteristics a) can; and b) cannot be calculated by Pesiri’s method
Figure 3.4. Evolution of the thermal conductivity measured through experimentation of a nanometric aluminum powder (≈ 100 nm) containing 74 wt% aluminum; the conductivity for a percentage of TMD equal to zero is that of air
Figure 3.5. Analogy of the propagation of combustion in nanothermites with the falling of dominoes
Figure 3.6. Steps governing the reaction kinetics of nanostructured aluminothermic compositions
Figure 3.7. Diagram of the direct or indirect activation of MDM in nanostructured aluminothermic compositions
Figure 3.8. Electron microscope observation of submicron-sized particles of zinc; typical curve obtained by thermogravimetric analysis (TGA) of the progressive oxidation of zinc powder
Figure 3.9. Observation by SEM of a titanium powder containing submicron-sized and nanometric particles; a typical curve obtained by TGA of the progressive oxidation of titanium powder
Figure 3.10. Observation by electron microscope, a) of the morphology of red phosphorus particles; and b) of thermites formed by mixing these particles (15.7 wt%) with a nanometric CuO powder [COM 10b]
Figure 3.11. Image of the products projected during the calcination of a CuO/P thermite containing 30 wt% of red phosphorus
Figure 3.12. Diagram of two forms of hierarchical MnO
2
/SnO
2
heterostructures and a MnO
2
/SnO
2
/Al ternary nanothermite, according to the results published by Yang et al. [YAN 13b]
Figure 3.13. Diagram of the mechanism of reaction of AgIO
3
/Al nanothermites
Figure 3.14. Diagram of a simple system allowing to support a tube used for the nanothermite combustion characterization; the weighty mass that sticks the tube to the backing is not represented
Figure 3.15. Metal splashes produced by the combustion of Bi
2
O
3
/B a) and CuO/B b) nanothermites in a bomb calorimeter
4 Nanothermites and Safety
Figure 4.1. Drop hammer impact device; a) Julius–Peters device; b) and electrostatic discharge test device; c) used for determining the thresholds of sensitivity of nanothermites to impact, friction and ESD
Figure 4.2. Scanning electron microscope images at × 1000 and × 100,000 magnification of aluminum; a) and tungsten trioxide; b) nanoparticles, illustrating the phenomenon of nanoparticle aggregation into micron-sized structures
Figure 4.3. Macro- and microscopic morphology of the residues produced by the reaction in a pressure cell of WO
3
/Al a) and CuO/Al b) nanothermites
Figure 4.4. Scanning electron microscope image of human hair strands exposed to aerosol resulting from combustion of a WO
3
/Al nanothermite
Guide
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Series Editor
Bernard Dubuisson
Nanothermites
Eric Lafontaine
Marc Comet
First published 2016 in Great Britain and the United States by ISTE Ltd and John Wiley & Sons, Inc.
Apart from any fair dealing for the purposes of research or private study, or criticism or review, as permitted under the Copyright, Designs and Patents Act 1988, this publication may only be reproduced, stored or transmitted, in any form or by any means, with the prior permission in writing of the publishers, or in the case of reprographic reproduction in accordance with the terms and licenses issued by the CLA. Enquiries concerning reproduction outside these terms should be sent to the publishers at the undermentioned address:
ISTE Ltd
27-37 St George’s Road
London SW19 4EU
UK
www.iste.co.uk
John Wiley & Sons, Inc.
111 River Street
Hoboken, NJ 07030
USA
www.wiley.com
© ISTE Ltd 2016
The rights of Eric Lafontaine and Marc Comet to be identified as the author of this work have been asserted by them in accordance with the Copyright, Designs and Patents Act 1988.
Library of Congress Control Number: 2016941697
British Library Cataloguing-in-Publication Data
A CIP record for this book is available from the British Library
ISBN 978-1-84821-837-6
Introduction
Thermites are combustible substances, usually little known to the general public, prepared by physically mixing powders of metal oxide and metal. The particular chemical characteristic of thermites lies in the nature of their constituents, which are considered by common sense to be non-combustible.
The displacement of the oxygen contained by metal oxides by aluminum was discovered by the Russian chemist Nikolay Beketov in 1865, but it was only between the late 19th and early 20th Century that the German chemist Johannes Wilhelm Goldschmidt patented the formulation of aluminothermic compounds, which were then intended for welding metal parts [GOL 07]. The mixtures prepared by Goldschmidt consisted of metal oxides or sulfides that were reduced by metals with a marked electropositive character, such as aluminum, calcium or magnesium. It is worth noting that the first thermites were manufactured by the same industrial processes that made use of molten salts electrolysis to obtain the metals used as fuels in these compounds came to maturity. The Hall–Héroult process for producing aluminum by electrochemical reduction of a molten cryolite bath dates back to 1886. Several years later, in 1897, Herbert Henry Dow founded the famous “Dow Chemical Company”, which manufactured magnesium by the electrolysis of molten magnesium chloride. The considerable amount of electrical power required for melting and breaking down the salts employed as reducing metal precursors required a source of abundant and inexpensive electricity. The invention of the dynamo in 1868 by the Belgian physicist Zénobe Théophile Gramme, and then the use by Aristide Bergès, in 1882, of “white coal” to activate it, marked the dawn of the age of industrial production of electricity.
The analysis of the historical context provides an explanation as to why thermites, despite their seeming chemical simplicity and the unsophisticated process used to prepare them by powder mixing, emerged quite late in the history of pyrotechnics.
The term “thermite” was coined by Goldschmidt to denote the reactive compositions he had developed. This term is justified by the very significant amount of heat released during these combustions. The Larousse dictionary defines thermite as “a mixture of metal oxides and fine-particle aluminum powder, whose highly exothermic combustion is used in aluminothermic welding”. This highly restrictive definition should be broadened to allow for taking into account the wide variety of compositions whose reaction modes are similar to aluminothermic reactions. In light of recent scientific advances in this field, thermites may be defined as “energetic compositions formed of reactive constituents that have a high proportion of metal elements, whose self-propagating reaction is accompanied by significant heat release”.
The classical definition of thermites reflects the fact that aluminothermic mixtures were for a long time the main representatives of this particular family of energetic materials. The mixtures of micron-sized powders of aluminum and metal oxides are insensitive to various forms of stress: flame, impact, friction and electrostatic discharge. It is very difficult to ignite micron-sized aluminothermic mixtures by means of a simple flame, and the only way to reliably and rapidly activate the reaction is to use a more sensitive pyrotechnic ignition composition [COM 06a]. The reaction is accompanied by a shower of sparks, but most of the combustion products remain in condensed form, either solid or liquid. Due to the difference in density, the melting metal separates from slags, which consist essentially of alumina. By cooling, the drop of metal forms a nugget that remains encased in its ceramic layer. Rail welding is done by means of a device that uses the effect of gravity to enable flowing of the molten metal resulting from the reaction.
Due to the transfer of the significant amount of heat stored in the liquid metal to the matter it is in contact with, micron-sized thermites can be used as incendiary substances. While flowing, the incandescent metal drops become subdivided into droplets whose oxidation in contact with air provides additional energy. The strong exothermicity of aluminothermic reactions is also taken advantage of in the field of demolition to perform thermal shearing of massive metal structures used as reinforcement. As these examples show, the uses of micron-sized thermites are quite limited and they mainly consist of using the significant amount of heat generated by the aluminothermic reaction in order to melt objects or set them on fire.
Aluminothermic reactions are highly exothermic and propagate slowly and without oxygen inflow. The oxidation–reduction reaction is characterized by the transfer of oxygen contained in the metal oxide toward the aluminum, a highly oxophilic metal. This reaction is difficult to activate, and the ignition of micronsized aluminothermic compositions takes place at a temperature nearing alumina’s melting point (~2,053°C).
Nanothermites are manufactured starting from the same chemical compounds as their ancestors, the thermites. The only difference is the smaller size of the particles that compose them, which is only 5–1,000 nm. The mixtures containing at least one nanostructured reactive species are sometimes called “nanothermites”, but it seems more accurate to assign this designation to mixtures whose constituents are all submicron sized (<1,000 nm). The term “superthermite”, which is sometimes employed in literature, refers rather to reactivity than to structure [PIE 10]. In the English language scientific literature, nanothermites are also frequently referred to as “metastable interstitial (or intermolecular) composites”.
The study of nanothermites began some 20 years ago in the large national laboratories in the United States, and most likely at about the same time in Russia. Approximately one century would therefore elapse between the invention of thermites and their nanosized formulation. In reality, the fabrication of nanothermites was possible only starting with the moment when aluminum was produced in the form of stable nanoparticles and in sufficient quantity. Once again, it is worth noting that the history of thermites is closely linked to the history of the metal fuels that they contain.
Nanothermites ignite at lower temperature than thermites, thus they are more sensitive to ignition than the latter. On the other hand, nanothermites react so rapidly that the behavior of some of them makes them more similar to primary explosives than to combustible substances. The release of a similar amount of heat in a much shorter time confers higher reactive power to nanothermites compared to thermites.
Although research on nanothermites is relatively recent, it has already shown that these new materials have exceptional pyrotechnic properties. What the authors of this work aim at is not only drawing up a state of the art of this fascinating field of pyrotechnics, but also suggesting paths worth exploring by future research.
Chapter 1 refers to methods for the synthesis of metals and metal oxides that are in a highly divided state. The “fundamental bricks” that serve to formulate nanothermites must have the smallest possible size in order to facilitate interfacial contacts in the energetic composition. This chapter will be of particular use to scientists willing to themselves manufacture the nanoparticles they employ for nanothermite formulation.
Chapter 2 describes the main methods for the preparation of nanothermites, which often consist of mixing, in a more or less ordered manner, the nanoparticles of metal fuel and oxidizer.
Chapter 3 details the experimental study of nanothermites and their constituents. The properties of the fuels and oxidants most frequently employed are described here, as well as the methods used to characterize the reactivity and morphology of nanothermites.
Chapter 4 approaches nanothermites from the original perspective of security: pyrotechnic security, neutralization and toxicological risk.
