U.S. patent application number 14/002740 was filed with the patent office on 2014-01-16 for thermite ignition and rusty iron regeneration by localized microwaves.
This patent application is currently assigned to Yehuda MEIR. The applicant listed for this patent is Eli Jerby, Yehuda Meir. Invention is credited to Eli Jerby, Yehuda Meir.
Application Number | 20140013982 14/002740 |
Document ID | / |
Family ID | 45888441 |
Filed Date | 2014-01-16 |
United States Patent
Application |
20140013982 |
Kind Code |
A1 |
Meir; Yehuda ; et
al. |
January 16, 2014 |
THERMITE IGNITION AND RUSTY IRON REGENERATION BY LOCALIZED
MICROWAVES
Abstract
A method and corresponding devices employ a mixture of at least
a metal oxide and a metal which undergoes an exothermic chemical
reaction. Microwave radiation is applied to the mixture so as to
generate a localized hot spot in the mixture, thereby initiating
the exothermic chemical reaction. The use of localized microwave
radiation facilitates low power and portable implementations.
Devices and techniques for cutting, drilling, welding, material
synthesis, generating thrust, and mechanical power and motion are
also disclosed.
Inventors: |
Meir; Yehuda; (Bat Yam,
IL) ; Jerby; Eli; (Rishon Letzion, IL) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Meir; Yehuda
Jerby; Eli |
Bat Yam
Rishon Letzion |
|
IL
IL |
|
|
Assignee: |
MEIR; Yehuda
Bat Yam
IL
|
Family ID: |
45888441 |
Appl. No.: |
14/002740 |
Filed: |
March 1, 2012 |
PCT Filed: |
March 1, 2012 |
PCT NO: |
PCT/IB2012/050964 |
371 Date: |
September 3, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61449674 |
Mar 6, 2011 |
|
|
|
Current U.S.
Class: |
102/205 |
Current CPC
Class: |
B01J 19/126 20130101;
B01J 2219/1293 20130101; C06B 33/00 20130101; B01J 2219/0879
20130101; B01J 2219/1296 20130101; B01J 2219/1269 20130101; C22B
5/04 20130101 |
Class at
Publication: |
102/205 |
International
Class: |
C06B 33/00 20060101
C06B033/00 |
Claims
1. A method comprising the steps of (a) providing a mixture of at
least a metal oxide and a metal which undergoes an exothermic
chemical reaction; and (b) applying microwave radiation to the
mixture so as to generate a localized hot spot in the mixture, said
localized hot spot having at least one dimension smaller than the
wavelength of the microwave radiation, thereby initiating the
exothermic chemical reaction.
2. The method of claim 1, wherein said exothermic chemical reaction
has an ignition temperature in excess of 900 degrees Celsius.
3. The method of claim 1, wherein said exothermic chemical reaction
has an ignition temperature in excess of 1400 degrees Celsius.
4. The method of claim 1, wherein said exothermic chemical reaction
is a thermite reaction.
5. The method of claim 1, wherein the microwave radiation is
generated by a microwave source of power less than 2 kW.
6. The method of claim 1, wherein the microwave radiation is
generated by a microwave source of power less than 200 W.
7. The method of claim 1, wherein the microwave radiation is
generated by a solid-state microwave source.
8. The method of claim 1, wherein the microwave radiation is
generated at one or more frequency in the range of 300 MHz to 300
GHz.
9. The method of claim 1, wherein a total mass of said mixture is
less than 10 g.
10. The method of claim 1, wherein a total mass of said mixture is
less than 1 g.
11. The method of claim 1, wherein said applying is performed by
coupling an evanescent field with the mixture.
12. The method of claim 1, wherein said applying is performed using
an open ended waveguide as an applicator.
13. The method of claim 1, wherein said applying is performed using
a waveguide terminating at one or more slot as an antenna.
14. The method of claim 1, wherein the mixture is deployed so as to
achieve cutting, drilling, or welding of adjacent materials when
initiated.
15. The method of claim 1, wherein said applying is performed
underwater or in another oxygen free environment.
16. The method of claim 1, wherein the mixture includes rust formed
on the surface of an iron-based metal object and a reactive metal
such that the chemical reaction is effective to convert said rust
to iron.
17. The method of claim 1, wherein the mixture is dynamically added
to a reaction region within which the microwave radiation is
applied to the mixture during application of the microwave
radiation to the mixture.
18. The method of claim 1, wherein the mixture includes at least
one gas-generating reagent.
19. The method of claim 18, wherein said applying microwave
radiation is performed within a rocket motor arrangement to
generate thrust.
20. The method of claim 18, further comprising converting gas
pressure to mechanical motion so as to serve as an engine powering
a mechanical device.
21. The method of claim 1, wherein said mixture is chosen so that
said exothermic reaction performs a self-propagating
high-temperature synthesis (SHS) of a porous material.
22. The method of claim 1, wherein the microwave radiation is
provided to the mixture via a plurality of applicators.
23. A method comprising the steps of: (a) providing a mixture of at
least a metal oxide and a metal which undergoes an exothermic
chemical reaction; and (b) applying microwave radiation to the
mixture so as to generate heat within the mixture, thereby
initiating the exothermic chemical reaction, wherein said microwave
radiation is applied in a manner so as to satisfy at least one of
the conditions: (i) a hot spot is generated in the mixture, said
hot spot having at least one dimension smaller than the wavelength
of the microwave radiation; (ii) heat is generated in a region
having at least one dimension smaller than the wavelength of the
microwave radiation; (iii) a hot spot is generated in a region
smaller than a volume of the mixture.
24. A method comprising the steps of: (a) providing a mixture of at
least a metal oxide and a metal which undergoes an exothermic
chemical reaction; and (b) applying electromagnetic radiation at
one or more frequency in the range of 1 MHz to 1 THz to the mixture
so as to generate heat within the mixture, thereby initiating the
exothermic chemical reaction, said electromagnetic radiation is
applied in a manner so as to satisfy at least one of the
conditions; (i) a hot spot is generated in the mixture, said hot
spot having at least one dimension smaller than the wavelength of
the electromagnetic radiation; (ii) heat is generated in a region
having at least one dimension smaller than the wavelength of the
electromagnetic radiation; (iii) a hot spot is generated in a
region smaller than a volume of the mixture.
Description
FIELD AND BACKGROUND OF THE INVENTION
[0001] Thermite is a general term for exothermic reactions between
metals and oxidizers. The latter is typically a metal oxide, which
utilizes the reduction of the metallic oxide with the metallic
element to exhaust a significant amount of heat. One of the most
common mixtures of thermite powder contains hematite and aluminum,
which function as the metal-oxidizer and the metallic element,
respectively. The final products generated are pure iron, alumina,
and heat energy. The corresponding chemical formula that describes
this reaction is
Fe.sub.2O.sub.3+2Al.fwdarw.2Fe+Al.sub.2O.sub.3+Q.sub.heat, (1)
where the heat energy released Q.sub.heat is 3.947 kJ/g in this
reaction (for the sake of comparison, the heat released in
trinitrotoluene (TNT) explosion is 4.247 kJ/g theoretically).
Furthermore, the thermite adiabatic flame temperature in the
example above may reach 4,382 K (reduced though to 3,135 K if
including the losses due to the phase change during the process).
This combustion temperature is found to be much hotter than
hydrocarbon-based fuel flame such as Benzene, which has a flame
temperature of 2,342 K. Moreover, the thermite combustion
temperature is higher than the melting temperatures of its two
initial components in separate (1,838 K for iron rust and 933 K for
aluminum). Consequently, the combustion of a thermite mixture can
be a self propagating process. Due to the intense blackbody
radiation emitted by the high-temperature thermite combustion, the
thermite reaction can be detected by a radiation detector even at
microwave frequencies.
[0002] The bi-molecular thermite reaction rate is limited by
diffusion due to the mass transfer mechanism between the metal and
the oxidizer particles. Hence this reaction is significantly slow
compared to the monomolecular based explosives such as TNT.
Thermite combustion rate was studied and simulated, and was found
to be in the range of .about.0.02-0.05 m/s. This speed is extremely
slow compared to the TNT detonation velocity of 6,850 m/s. The
thermite combustion rate is highly dependent on the contact surface
area of the metal and the oxidizer, as determined by the powder
particle size (smaller particles cause faster combustion rates).
Thus, nano-composite thermite powders benefit a significant
increase in the combustion rate value. In a thermite mixture of
Al--MoO.sub.3 for instance the combustion speed may reach 600-1,000
m/s. In addition, the ignition time delay can be shortened by two
orders of magnitude compared to the micron-sized thermite
composites. Except that the inhalation of any thin powder should be
avoided, the ferro-thermite components are relatively non toxic,
which is not the case for TNT explosives or nitroglycerin.
[0003] The gas phase is absent in the thermite reaction, as can be
seen by its chemical formula in Eq. (1), hence the direct blast
pressure formed is significantly reduced compared to common
explosives. TNT for example, releases large amount of gas during a
complete balanced decomposition, even though additional oxygen is
required as inferred from the following formula
2C.sub.2H.sub.5N.sub.3O.sub.6.fwdarw.14CO.sub.2+5H.sub.2O+3N.sub.2-21O
(2)
[0004] The pressure fowled can be calculated by the ideal gas
formula modified for high pressure values with the co-volume factor
.alpha.
P e = nRT e V ( 1 - .alpha. ) ( 3 ) ##EQU00001##
where V is the volume of the closed test cell, n is the produced
number of gas moles, T.sub.e is the explosion temperature, and R is
the molar gas constant. When oxygen is lack and the TNT
decomposition is not balanced, the generated gas is reduced and it
contains different kinds of molecules such as carbon monoxide and
hydrogen according to Kistiakowsky-Wilson rules. While the oxygen
has to come from an external source in TNT and in other
conventional hydrocarbon based fuels, it is an inherent component
in the thermite mixture, and it is sufficient for a balanced
combustion. As a result, the thermite fuel can be incinerated at
oxygen-free environments, such as underwater operations. In
addition, thermite as a fuel can be used as a "clean" energy
source; due to the lack of carbon molecules it never emits carbon
monoxide contamination.
[0005] The thermite ignition temperature is higher than
1500.degree. C. for the Fe.sub.2O.sub.3--Al thermite mixture.
However, for the nanometer-size thermite mixtures, the ignition
temperature, as one of their superior properties, can reach as low
as 410.degree. C. as super-thermite. This temperature is derived
from the high melting temperature of the ingredients which is
extremely high as opposed to TNT which requires a temperature of
only 300.degree. C. to be ignited. This fact makes the thermite
mixture more stable, but also harder to ignite, thus a suitable
igniter is required for this kind of metal fuel. The ignition of
the thermite mixture above can be achieved by a laser beam for
MoO.sub.3--Al and Fe.sub.2O.sub.3--Al thermite mixture. Microwave
ignition has been reported in the literature, but it involved a
microwave pulse of high power (>50 kW) and high frequency (75
GHz) from a gyrotron. Other microwave schemes were proposed for
heating energetic materials.
[0006] Thermite ignition by a conventional flame requires a
significant reduction of the ignition temperature, typically by
adding oxidizer and binder to the thermite powder. For example the
`Thermate-TH3` mixture, which is used in AN-M14 incendiary hand
grenade of the US army, is composed of 29% barium nitrate (BaN2O6),
sulfur, and a binder, added to 68.7% of thermite. Furthermore,
thermite-based grenades contains a starter mixture composed of 66%
potassium nitrate (KNO3) and other materials (for the ignition as
enriched oxide source) added to the oxide enriched thermite powder.
The starter mixture may contain ultra fine thermite powder which is
easier to ignite with a hotwire energized by DC current.
[0007] In the absence of an oxidizer in the intermediate starting
mixture, it is almost impossible to initiate the thermite
combustion in a closed can, even with a Nichrome hotwire energized
by electric current (melted at 1,400.degree. C.). Hence, calcium
peroxide (CaO2) is added in order to lower the ignition temperature
and enable the mixture ignition. Another method to ignite a
thermite mixture is by adding barium peroxide (BaO2) to the
thermite and lighten it by a magnesium ribbon. Yet, it is a
dangerous process since it is hard to control the magnesium
combustion. Alternatively the magnesium can be replaced by
potassium permanganate (KMnO4) with glycerin. This kind of salt is
used as an oxidizing agent that generates enough heat as required
to ignite the thermite when it burns. Due to their unique features,
thermite powders are used in explosive charges, in devices used for
cutting or penetrating metals, and in air-bag system inflators.
[0008] Except for its explosive features, the thermite reaction is
used in material processing including metals, ceramics, and
composite materials. Due to the thermite high combustion
temperature, it is utilized also for welding techniques. Thermite
based reactions can be utilized for covering iron alloys by an
intermediate pure metal and alumina coating, as the ceramic
material created by the thermite combustion (note that a
centrifugal thermite process uses this feature for making composite
steel pipes by filling them with thermite and ignites it while the
pipe is rolling around its symmetrical axis).
[0009] There is also a special need to ignite small quantities of
pure thermite, which is usually less efficient by conventional
ignition techniques because of the relatively large igniter needed
(possibly even larger the thermite mixture itself). Small-quantity
thermite applications could be useful for example in thermite
welding of small parts, or for small-scale material synthesis by
the thermite combustion (e.g. for production of alumina and iron as
in Eq. (1)).
[0010] There are therefore various needs for methods and
corresponding devices for employing thermite reactions actuated by
localized application of microwaves.
SUMMARY OF THE INVENTION
[0011] The present invention is a method and corresponding devices
for employing thermite reactions actuated by localized application
of microwaves.
[0012] According to the teachings of the present invention there is
provided, a method comprising the steps of: (a) providing a mixture
of at least a metal oxide and a metal which undergoes an exothermic
chemical reaction; and (b) applying microwave radiation to the
mixture so as to generate a localized hot spot in the mixture, the
localized hot spot having at least one dimension smaller than the
wavelength of the microwave radiation, thereby initiating the
exothermic chemical reaction.
[0013] According to an embodiment of the present invention, the
exothermic chemical reaction has an ignition temperature in excess
of 900 degrees Celsius.
[0014] According to an embodiment of the present invention, the
exothermic chemical reaction has an ignition temperature in excess
of 1400 degrees Celsius.
[0015] According to an embodiment of the present invention, the
exothermic chemical, reaction is a thermite reaction.
[0016] According to an embodiment of the present invention, the
microwave radiation is generated by a microwave source of power
less than 2 kW.
[0017] According to an embodiment of the present invention, the
microwave radiation is generated by a microwave source of power
less than 200 W.
[0018] According to an embodiment of the present invention, the
microwave radiation is generated by a solid-state microwave
source.
[0019] According to an embodiment of the present invention, the
applying is performed by coupling an evanescent field with the
mixture.
[0020] According to an embodiment of the present invention, the
applying is performed using an open ended waveguide as an
applicator.
[0021] According to an embodiment of the present invention, the
applying is performed using a waveguide terminating at one or more
slot as an antenna.
[0022] According to an embodiment of the present invention, the
mixture is deployed so as to achieve cutting, drilling, or welding
of adjacent materials when initiated.
[0023] According to an embodiment of the present invention, the
applying is performed in an oxygen free environment such as
underwater.
[0024] According to an embodiment of the present invention, the
mixture includes rust formed on the surface of an iron-based metal
object and a reactive metal such that the chemical reaction is
effective to convert the rust to iron.
[0025] According to an embodiment of the present invention, the
mixture is dynamically added to a reaction region within which the
microwave radiation is applied to the mixture during application of
the microwave radiation to the mixture.
[0026] According to an embodiment of the present invention, the
mixture includes at least one gas-generating reagent.
[0027] According to an embodiment of the present invention, the
applying microwave radiation is performed within a rocket motor
arrangement to generate thrust.
[0028] According to an embodiment of the present invention, gas
pressure is converted to mechanical motion so as to serve as an
engine powering a mechanical device.
[0029] According to an embodiment of the present invention, the
mixture is chosen so that the exothermic reaction performs a
self-propagating high-temperature synthesis (SHS) of a porous
material.
[0030] There is also provided according to the teachings of an
embodiment of the present invention, a method comprising the steps
of: (a) providing a mixture of at least a metal oxide and a metal
which undergoes an exothermic chemical reaction; and (b) applying
microwave radiation to the mixture so as to generate heat within
the mixture, thereby initiating the exothermic chemical reaction,
wherein said microwave radiation is applied in a manner so as to
satisfy at least one of the conditions: (i) a hot spot is generated
in the mixture, said hot spot having at least one dimension smaller
than the wavelength of the microwave radiation; (ii) heat is
generated in a region having at least one dimension smaller than
the wavelength of the microwave radiation; (iii) a hot spot is
generated in a region smaller than a volume of the mixture.
[0031] There is also provided according to the teachings of an
embodiment of the present invention, a method comprising the steps
of: (a) providing a mixture of at least a metal oxide and a metal
which undergoes an exothermic chemical reaction; and (b) applying
electromagnetic radiation having a at one or more frequency in the
range of 1 MHz to 1 THz to the mixture so as to generate heat
within generate a localized hot spot in the mixture, said localized
hot spot having at least one dimension smaller than the wavelength
of the electromagnetic radiation, thereby initiating the exothermic
chemical reaction, said electromagnetic radiation is applied in a
manner so as to satisfy at least one of the conditions: (i) a hot
spot is generated in the mixture, said hot spot having at least one
dimension smaller than the wavelength of the electromagnetic
radiation; (ii) heat is generated in a region having at least one
dimension smaller than the wavelength of the electromagnetic
radiation; (iii) a hot spot is generated in a region smaller than a
volume of the mixture.
BRIEF DESCRIPTION OF THE DRAWINGS
[0032] The invention is herein described, by way of example only,
with reference to the accompanying drawings, wherein:
[0033] FIG. 1 is an optional block diagram of an embodiment of the
present invention for initiating thermite reactions by localized
application of microwave radiation;
[0034] FIG. 2 is a schematic representation of a suggested but
non-limiting principle of operation of thermite ignition by
localized application of microwave radiation according to an aspect
of the present invention, illustrated with a coaxial microwave
applicator;
[0035] FIGS. 3A and 3B are a schematic isometric and side view,
respectively, of a tapered near-field microwave applicator for use
in an embodiment of the present invention;
[0036] FIG. 4 is a schematic illustration of a slot-type near-field
microwave applicator for use in an embodiment of the present
invention;
[0037] FIG. 5 is a schematic illustration of a strip-line-type
near-field microwave applicator for use in an embodiment of the
present invention;
[0038] FIG. 6A is a schematic isometric view of a device for
employing a thermite reaction actuated by localized application of
microwaves according to an embodiment of the present invention;
[0039] FIG. 6B is a schematic cross-sectional view of the device of
FIG. 6A while in use;
[0040] FIG. 7A is a schematic isometric view of a device for
employing a thermite reaction actuated by localized application of
microwaves according to an embodiment of the present invention
serving as a torch;
[0041] FIG. 7B is a schematic isometric view of a device for
employing a thermite reaction actuated by localized application of
microwaves according to an embodiment of the present invention
serving as a torch;
[0042] FIG. 8 is a schematic isometric view of a device for
employing a thermite reaction actuated by localized application of
microwaves according to an embodiment of the present invention
serving as a cutting tool;
[0043] FIG. 9 is a schematic isometric view of a device for
employing a thermite reaction actuated by localized application of
microwaves according to an embodiment of the present invention
serving as a cutting tool;
[0044] FIG. 10 is a schematic isometric view of a device for
employing a thermite reaction actuated by localized application of
microwaves according to an embodiment of the present invention
serving as a cutting tool;
[0045] FIG. 11 is a schematic isometric view of a device for
employing a thermite reaction actuated by localized application of
microwaves according to an embodiment of the present invention
performing rust conversion;
[0046] FIG. 12 is a schematic isometric view of a device for
employing a thermite reaction actuated by localized application of
microwaves according to an embodiment of the present invention
performing rust conversion;
[0047] FIG. 13 is a schematic isometric view of a device for
employing a thermite reaction actuated by localized application of
microwaves according to an embodiment of the present invention
performing material synthesis in batch processing;
[0048] FIG. 14 is a schematic isometric view of a device for
employing a thermite reaction actuated by localized application of
microwaves according to an embodiment of the present invention
performing material synthesis in continuous processing;
[0049] FIG. 15 is a schematic isometric view of a device for
employing a thermite reaction actuated by localized application of
microwaves according to an embodiment of the present invention
operating as a rocket engine; and
[0050] FIG. 16 is a schematic representation showing the ignition
of a larger volume of thermite by an arrangement of several
microwave applicators in an array radiating simultaneously, or
sequentially, into the volume to ignite it in several places or in
a joint focal point.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0051] The present invention is a method and corresponding devices
for employing thermite reactions actuated by localized application
of microwaves.
[0052] The principles and operation of methods and devices
according to the present invention may be better understood with
reference to the drawings and the accompanying description.
[0053] Referring now to the drawings, FIG. 1 illustrates
schematically a system, generally designated 10, according to
certain embodiments of the present invention, and suitable for
implementing certain methods according to the present invention.
Generally speaking, system 10 includes a microwave source 12 that
supplies microwave radiation to a waveguide 16 which terminates at
an applicator 18, referred to as a "concentrator", configured for
coupling of near-field microwave radiation into a mixture 20
containing at least a metal oxide and a metal which undergo an
exothermic chemical reaction. As illustrated schematically in FIG.
2, applicator 18 is configured to localize delivery of the
microwave radiation so as to generate a localized hot spot 23 in
mixture 20, the localized hot spot having at least one dimension
smaller than a wavelength of the microwave radiation and/or being
smaller than the volume of the mixture, thereby initiating the
exothermic chemical reaction.
[0054] Thus, the present invention provides a novel ignition method
and corresponding igniter for thermite mixtures without requiring
intermediate chemical additives. Localized microwave energy has
been shown to generate sufficient heat to ignite thermite. Instead
of lowering the ignition temperature of the thermite, the hotspot
induced intentionally by a relatively low power microwave
applicator with a concentrator generates enough heat-per-volume for
thermite ignition.
[0055] Since no starter mixture is required in order to achieve
ignition of a thermite mixture according to the present invention,
the invention provides a viable solution for situations where small
quantities of mixture (particularly pure thermite) are to be
ignited. Thus, in certain preferred applications, the method of the
present invention is used to ignite a quantity of thermite mixture
of less than 10 g, and in certain cases, less than 1 g.
[0056] On the other hand, the present invention is also scalable
for igniting large quantities of thermite mixture. Larger
quantities may range from 10 g up to 1000 g, and in certain
preferred cases, more than 1 kg. In certain cases, it may be
advantageous to employ a penetrating applicator for delivering the
microwave radiation to a location within the volume of the mixture.
In other cases, it may be advantageous to employ simultaneous
delivery of microwave radiation at several locations, such as will
be described below with reference to FIG. 16.
[0057] According to another aspect of the invention, the microwave
igniter is used for the removal of rust by iron regeneration. This
reaction is achieved by local thermite combustion of rust and
aluminum powder ignited by the microwave igniter. The regenerated
iron and alumina obtained as the final products can be used to coat
the originally rusted object. These and other aspects of the
present invention will be better understood by reference to the
following detailed description and accompanying drawings.
[0058] At this stage, it will be helpful to define certain
terminology as used herein in the description and claims. The
invention is described as relating to ignition of a mixture of a
metal oxide and a metal which undergoes an exothermic chemical
reaction, and particularly, reactions of this type which have a
high ignition temperature. Preferably, the invention is implemented
with mixtures that undergo exothermic chemical reactions with
ignition temperature in excess of 900 degrees Celsius, and more
preferably in excess of 1400 degrees Celsius. In certain
particularly preferred but non-limiting implementations, the
exothermic chemical reaction is a thermite reaction, namely, a
two-component mixture of a metal oxide and a metal, and in certain
particularly preferred options, a pure thermite mixture without any
additives.
[0059] The use of pure thermite mixture which is facilitated by the
present invention makes available a range of additional
applications which would either otherwise not be feasible due to
the need for expensive and bulky high-energy equipment to initiate
the reaction according to conventional techniques.
[0060] The general term "microwave" is used herein in the
description and claims, except where otherwise qualified, to refer
broadly to the broadest range of electromagnetic radiation normally
referred to as "microwave", and its bordering regions of the
spectrum which, for the purpose of the present invention, may be
used to achieve similar effects. In quantitative terms, the present
invention is applicable for electromagnetic waves in frequencies
between .about.1 MHz to .about.1 THz, which overlaps frequencies
typically referred to as radio frequencies (RF) and millimeter
waves, respectively. Certain particularly preferred implementations
employ microwave radiation at frequencies in the range of 300 MHz
to 300 GHz (wavelengths of 1 meter to 1 millimeter). In some cases,
where the wavelength is longer than the dimensions of the volume of
the mixture to be ignited, the entire volume of mixture may be
considered the "hot spot" according to the present invention, still
being a "spot" in the sense that the radiation is localized into a
volume having at least one dimension less than the wavelength. In
cases of very small wavelengths, the hot spot may not always remain
localized within less than a wavelength, but in such cases will be
small compared to the volume of the mixture. Thus, preferred
applications of the present invention typically satisfy at least
one of the conditions:
[0061] (i) a hot spot is generated in the mixture, the hot spot
having at least one dimension smaller than the wavelength of the
radiation;
[0062] (ii) heat is generated in a region having at least one
dimension smaller than the wavelength of the radiation;
[0063] (iii) a hot spot is generated in a region smaller than a
volume of the mixture.
[0064] In this context, the term "hot spot" is used to refer to a
localized region or volume within a larger volume within which
material is heated significantly above the temperature of the
surrounding material. The size of the hot spot may conveniently be
defined by the full width at half maximum (FWHM), i.e., the
dimensions of the region for which the temperature is above 50% of
the temperature difference between the peak temperature and the
surrounding mixture.
[0065] According to certain preferred implementations of the
present invention, the microwave source is a relatively low power
source, typically generating no more than 2 kW, and in certain
particularly preferred implementations, no more than 200 W. Also
according to certain preferred embodiments, the frequency used is
also preferably a relatively low frequency in the microwave range
(typically 2.45 GHz). Despite this low power and low frequency, as
a result of the concentration of the radiation into a small volume,
sufficient localized heating is achieved to generate a localized
hot spot at high enough temperature to ignite the reaction. The low
power requirements enable the use of a solid-state microwave
source, thereby making it feasible to implement the system as a
compact and light-weight portable device.
[0066] It should be appreciated, however, that the present
invention is not limited to the aforementioned low-power
implementations. Other implementations may, for example, apply
power above .about.1 kW, either by a vacuum tube or by employing an
array of lower power radiating elements. Furthermore, the operating
frequency may be any frequency in the microwave range as defined
above.
[0067] As shown in FIG. 1, microwave source 12 is preferably
protected by an isolator 14 (optional), which is a standard
off-the-shelf component preventing reflected radiation from
damaging the microwave source. Adjustable matching components 22
(optional) may be used to optimize energy delivery to the mixture
20 via applicator 18.
[0068] A wide range of structures may be used to implement
applicator 18 of the present invention. Applicator 18 may be
implemented either as an antenna located adjacent to, or immersed
in, mixture 20, or may be implemented employing coupling of an
evanescent field at the termination of a non-radiating waveguide
with the mixture.
[0069] By way of a first non-limiting example, FIG. 2 illustrates
an implementation of applicator 18 as a coaxial structure including
a central conductor 24 extending within an outer conductive sheath
26. Central conductor 24 extends beyond the end of conductive
sheath 26 and is in close proximity to, or more preferably immersed
in, mixture 20. Optionally, as illustrated below in FIG. 6A, part
or all of the extending portion of central conductor 24 may be
protected by a ceramic layer, provided for example as ceramic beads
36. It should be note that, in some cases, the open end of a
coaxial waveguide without projection of the central conductor, or
the end of a circular waveguide above cutoff may also be effective
as an applicator when brought into close proximity or contact with
mixture 20.
[0070] A further non-limiting example of applicator 18 is
illustrated in FIGS. 3A and 3B which show an implementation with a
tapered waveguide 30.
[0071] A further non-limiting example of applicator 18 is
illustrated in FIG. 4 which shows an implementation using a
waveguide terminating at one or more slot 32 as an antenna.
[0072] A further non-limiting example of applicator 18 is
illustrated in FIG. 5 which shows an implementation using an open
ended waveguide, in this case with a protruding central stripline
conductor 34, as an applicator.
[0073] Embodiments of the present invention may be implemented in a
range of different configurations to provide a range of different
types of functionality, as will now be illustrated with reference
to a number of non-limiting examples portrayed in FIGS. 6A-15.
[0074] Referring to FIGS. 6A and 6B, these show a simple
arrangement in which mixture 20 is included within a reaction
chamber 40 with an opening 42 formed in its base through which
applicator 18 is inserted. The mixture is ignited locally at
hot-spot 23 adjacent to the end of the applicator, resulting in
self-ignition of the entire contents of the reaction chamber and
ejecting a flame in region 44.
[0075] FIGS. 7A and 7B illustrate two non-limiting examples of a
thermite-based blow-torch implementation according to the present
invention in which mixture 20 is dynamically added to a reaction
region within which the microwave radiation is applied to the
mixture, thereby providing an ongoing source of intense heat for a
variety of applications. In the example of FIG. 7A, a microwave
input port 46 (typically present in all embodiments of the
invention, but not separately labeled) feeds the microwave signal
into coaxial waveguide 48. An external thermite source 50 is fed by
a flow of air pressure 52 or by some other feed arrangement (not
shown) through a metal pipe 54 into coaxial waveguide 48. Pipe 54
is configured to be in microwave cutoff, so the microwave energy
cannot propagate through it. A thin ceramic disc 56 blocks thermite
mixture from moving up the waveguide, but allows the microwave
radiation to pass through it. The thermite powder 20 passes through
the hollow coaxial waveguide 48 towards a nozzle 58. The high
microwave power density in this vicinity of the tip 60 of the
central conductor ignites the mixture, and consequently a flame 62
is ejected from nozzle 58.
[0076] FIG. 7B is conceptually similar to FIG. 7A, with equivalent
elements labeled similarly. In this case, pipe 54 connects directly
to the inner channel of a hollow section of the central conductor
64 of the coaxial waveguide 48. Hot-spot ignition occurs at region
60, just beyond the end of hollow central conductor 64, as
described above.
[0077] Depending upon the density of the thermite mixture flow, the
reaction may or may not be self-propagating. In both torch
implementations, switching off of the torch is typically achieved
by interrupting both the flow of mixture and the microwave
delivery.
[0078] Turning now to FIGS. 8-10, these illustrate a number of
non-limiting but preferred examples of implementations of the
present invention useful as cutting tools for cutting material.
[0079] The example of FIG. 8 is based on a thermite torch 68, which
may be implemented according to any of FIGS. 6A, 7A or 7B. Torch 68
has a microwave input port 46, a source of thermite 50 (unless
pre-loaded according to FIG. 6A), and generates an output flame 62
towards the body 70 to be cut or otherwise processed, for example,
forming a cut 72.
[0080] According to preferred but non-limiting option, flame 62 can
be collimated by use of a suitable nozzle shape (not shown).
Additionally, or alternatively, for magnetic thermite powder, such
as Fe3O4--Al, the collimation can be done by externally induced
magnetic fields. For example, by attaching a permanent magnet to
the metallic substrate it can be magnetized. Consequently the flame
made of hot magnetic particles can be collimated to the metal
substrate by the induced magnetic field. Alternately, the
collimation can be done by a coil that surrounds the flame so it
induces an axial magnetic field.
[0081] Turning now to FIG. 9, this shows an alternative cutting
technique in which thermite mixture 20 is applied to the surface of
the body to be cut or otherwise processed, and is then ignited by
the system 10 of FIG. 1 using any suitable applicator, such as
those discussed above. Thus, microwave radiation delivered to input
port 46 along waveguide 16 via applicator 18 ignites mixture 20 at
a hotspot generated in the interaction region 60, and results in
cutting or melting of body 70 at region 72.
[0082] FIG. 10 shows an arrangement essentially similar to FIG. 9,
and similarly labeled, but in which the thermite mixture is
initially at least partially located within a preformed notch 74
formed in the body.
[0083] These devices and techniques described here may also be used
for drilling holes, or for welding together two initially separate
bodies.
[0084] Turning now to FIGS. 11 and 12, the ability to ignite a pure
thermite mixture conveniently in situ facilitates another
particularly preferred aspect of the present invention, namely, a
rust conversion technique in which iron can be regenerated from a
layer of rust through a thermite reaction which preferably
simultaneously generates a protective layer. As illustrated in FIG.
11, a layer of thermite mixture including the oxide of the
substrate metal and an additional metal is applied to the substrate
metal which has an oxide (rust) outer layer 76. The mixture is
ignited using a device such as was described in FIG. 9. After the
thermite is ignited, the oxide layer is converted to the final
products of the thermite reaction. For example, thermite made of
rust (Fe.sub.2O.sub.3) and aluminum (Al) that covers an iron or
steel body with a rusty layer, converts the outer layer to iron and
alumina.
[0085] FIG. 12 illustrates a system and technique similar to that
of FIG. 11, but in which an entire surface is treated by covering
in a layer of the thermite mixture 20 and then moving the igniter
device progressively across the region (represented by arrow 78) to
ensure ignition of the thermite layer across the entire surface.
The resulted layer of regenerated iron and alumina is designated
80.
[0086] Turning now to FIGS. 13 and 14, these illustrate processes
for production of materials with particular mechanical or chemical
properties by self-propagating high-temperature synthesis (SHS)
methods. One particularly preferred example is synthesis of porous
ferrite. The production process may be either a batch process (FIG.
13) or a continuous process (FIG. 14).
[0087] According to the option of FIG. 13, a microwave igniter such
as that of FIG. 9 ignites the mixture 20 located in a mold 82. The
mixture may be either pure thermite powder or may contain other
materials that interact with the byproducts of the thermite
reaction. For example,
3TiO.sub.2+3C+4Al.fwdarw.3TiC+2Al.sub.2O.sub.3. The reaction
between titania (TiO2) and aluminum (Al) is a thermite reaction.
The titanium (Ti) reacts with the carbon (C) to produce titanium
carbide (TiC). The ignition temperature of this synthesis reaction
is 900 C.
[0088] FIG. 14 illustrates a continuous flow process in which the
microwave igniter ignites the mixture 20 in interaction region 60.
The mixture is placed on a moving conveyer 84 which feeds it under
igniter 10, continuously generating the desired product 86.
[0089] Turning now to FIG. 15, according to a further option,
certain embodiments of devices and methods according to the present
invention employ mixtures 20 which include at least one
gas-generating reagent. The device then becomes a thermite-fueled
thrust-generating device, which may be used directly in a rocket
engine, or may be employed with a piston arrangement or other
device for converting gas pressure to mechanical motion, as a
combustion engine, in order to power a mechanical device.
[0090] Structurally, FIG. 15 shows schematically a non-limiting
example of a thermite-fueled thrust-generating device according to
this aspect of the present invention in which a mixer 90 mixes
thermite powder mixture 20 with carbon 92. This mixture is fed into
a microwave igniter 94 that utilizes a near-field applicator to
ignite the thermite in the mixture by microwave energy. The added
carbon is incinerated with the oxygen in the air, or with
additional metal oxide that produces extra oxygen, for a balanced
chemical reaction. The generated byproducts are emitted outside
through a dedicated exhaust 96. The high pressure gas produced
generate the thrust 98. An external rocket engine or a piston
utilizes the emitted thrust to generate mechanical power and
motion.
[0091] Turning finally to FIG. 16, this illustrates schematically a
further set of implementations of the present invention according
to which a plurality of microwave applicators 100, constructed
according to any of the above examples, are used as an array 101 or
otherwise coordinated to generate one or more ignition hot-spot 102
within a mixture 99. This approach may be valuable in a wide range
of applications including, but not limited to: coordinated heating
of a single hot-spot by a plurality of applicators in order to
achieve higher overall power, or to reach a greater depth, than
would be achieved by a single applicator; simultaneous multi-point
ignition of a large quantity, or geometrical extent, of mixture at
spaced-apart locations; and sequential ignition of mixture at
spaced-apart locations in order to achieve a particular ignition
sequence or sequential processing of different regions.
Appendix
[0092] The following is an incomplete list of thermite mixtures to
which the teachings of the present invention are believed to be
applicable:
2Al+3AgO, 2AL+3Ag.sub.2O, 2Al+B.sub.2O.sub.3, 2Al+Bi.sub.2O.sub.3,
2Al+3CoO, 8Al+3Co.sub.3O.sub.4, 2Al+Cr.sub.2O.sub.3, 2Al+3CuO,
2Al+3Cu.sub.2O, 2Al+Fe.sub.2O, 8Al+3Fe.sub.3O.sub.4, 2Al+3HgO,
10Al+3I.sub.2O.sub.5, 4Al+3MnO.sub.2, 2Al+MoO.sub.3,
10Al+3Nb.sub.2O.sub.5, 2Al+3NiO, 2Al+Ni.sub.2O.sub.3, 2Al+3PbO,
4Al+3PbO.sub.2, 8Al+3Pb.sub.3O.sub.4, 2Al+3PdO, 4Al+3SiO.sub.2,
2Al+3SnO, 4Al+3SnO.sub.2, 10Al+3Ta.sub.2O.sub.5, 4Al+3TiO.sub.2,
16Al+3U.sub.3O.sub.8, 10Al+3V.sub.2O.sub.5, 4Al+3WO.sub.2,
2Al+WO.sub.3, 2B+Cr.sub.2O.sub.3, 2B+3CuO, 2B+Fe.sub.2O.sub.3,
8B+3Fe.sub.3O.sub.4, 4B+3MnO.sub.2, 8B+3Pb.sub.3O.sub.4,
3Be+B.sub.2O.sub.3, 3Be+Cr.sub.2O.sub.3, Be+CuO,
3Be+Fe.sub.2O.sub.3, 4Be+Fe.sub.3O.sub.4, 2Be+MnO.sub.2,
2Be+PbO.sub.2, 4Be+Pb.sub.3O.sub.4, 2Be+SiO.sub.2,
3Hf+2B.sub.2O.sub.3, 3Hf+2Cr.sub.2O.sub.3, Hf+2CuO,
3Hf+2Fe.sub.2O.sub.3, 2Hf+Fe.sub.3O.sub.4, Hf+MnO.sub.2,
2Hf+Pb.sub.3O.sub.4, Hf+SiO.sub.2, 2La+3AgO, 2La+3CuO,
2La+Fe.sub.2O.sub.3, 2La+3HgO, 10La+2I.sub.2O.sub.5,
4La+3MnO.sub.2, 2La+3PbO, 4La+3PbO.sub.2, 8La+3Pb.sub.3O.sub.4,
2La+3PdO, 4La+3WO.sub.2, 2La+WO.sub.3, 6Li+B.sub.2O.sub.3,
6Li+Cr.sub.2O.sub.3, 2Li+CuO, 6Li+Fe.sub.2O.sub.3,
8Li+Fe.sub.3O.sub.4, 4Li+MnO.sub.2,
6Li+MoO.sub.38Li+Pb.sub.3O.sub.4, 4Li+SiO.sub.2, 6Li+WO.sub.3,
3Mg+B.sub.2O.sub.3, 3Mg+Cr.sub.2O.sub.3, Mg+CuO,
3Mg+Fe.sub.2O.sub.3, 4Mg+Fe.sub.3O.sub.4, 2Mg+MnO.sub.2,
4Mg+Pb.sub.3O.sub.4, 2Mg+SiO.sub.2, 2Nd+3AgO, 2Nd+3CuO, 2Nd+3HgO,
10Nd+3I.sub.2O.sub.5, 4Nd+3MnO.sub.2, 4Nd+3PbO.sub.2,
8Nd+3Pb.sub.3O.sub.4, 2Nd+3PdO, 4Nd+3WO.sub.2, 2Nd+WO.sub.3,
2Ta+5AgO, 2Ta+5CuO, 6Ta+5Fe.sub.2O.sub.3, 2Ta+5HgO,
2Ta+I.sub.2O.sub.5, 2Ta+5PbO, 4Ta+5PbO.sub.2, 8Ta+5Pb.sub.3O.sub.4,
2Ta+5PdO, 4Ta+5WO.sub.2, 6Ta+5WO.sub.3, 3Th+2B.sub.2O.sub.3,
3Th+2Cr.sub.2O.sub.3, Th+2CuO, 3Th+2Fe.sub.2O.sub.3,
2Th+Fe.sub.3O.sub.4, Th+MnO.sub.2, Th+PbO.sub.2,
2Th+Pb.sub.3O.sub.4, Th+SiO.sub.2, 3Ti+2B.sub.2O.sub.3,
3Ti+2Cr.sub.2O.sub.3, Ti+2CuO, 3Ti+2Fe.sub.2O.sub.3,
Ti+Fe.sub.3O.sub.4, Ti+MnO.sub.2, 2Ti+Pb.sub.3O.sub.4,
Ti+SiO.sub.2, 2Y+3CuO, 8Y+3Fe.sub.3O.sub.4, 10Y+3I.sub.2O.sub.5,
4Y+3MnO.sub.2, 2Y+MoO.sub.3, 2Y+Ni.sub.2O.sub.3, 4Y+3PbO.sub.2,
2Y+3PdO, 4Y+3SnO.sub.2, 10Y+3Ta.sub.2O.sub.5, 10Y+3V.sub.2O.sub.5,
2Y+WO.sub.3, 3Zr+2B.sub.2O.sub.3, 3Zr+2Cr.sub.2O.sub.3, Zr+2CuO,
3Zr+2Fe.sub.2O.sub.3, 2Zr+Fe.sub.3O.sub.4, Zr+MnO.sub.2,
2Zr+Pb.sub.3O.sub.4, Zr+SiO.sub.2,
[0093] It will be appreciated that the above descriptions are
intended only to serve as examples, and that many other embodiments
are possible within the scope of the present invention as defined
in the appended claims.
* * * * *