U.S. patent application number 15/518701 was filed with the patent office on 2017-08-17 for an explosive composition.
This patent application is currently assigned to Richard John Goodridge. The applicant listed for this patent is Ivana Alilovic, Richard John Goodridge, Marilyn Emily Karaman, ORICA INTERNATIONAL PTE LTD, Johann Zank. Invention is credited to Ivana Alilovic, Richard John Goodridge, Marilyn Emily Karaman, Johann Zank.
Application Number | 20170233305 15/518701 |
Document ID | / |
Family ID | 55745882 |
Filed Date | 2017-08-17 |
United States Patent
Application |
20170233305 |
Kind Code |
A1 |
Goodridge; Richard John ; et
al. |
August 17, 2017 |
AN EXPLOSIVE COMPOSITION
Abstract
An explosive composition comprising a reagent that inhibits
corrosion of a metal or metal alloy when the explosive composition
comes into contact with the metal or metal alloy.
Inventors: |
Goodridge; Richard John;
(Melbourne, AU) ; Karaman; Marilyn Emily;
(Melbourne, AU) ; Alilovic; Ivana; (Melbourne,
AU) ; Zank; Johann; (Melbourne, AU) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Goodridge; Richard John
Karaman; Marilyn Emily
Alilovic; Ivana
Zank; Johann
ORICA INTERNATIONAL PTE LTD |
Melbourne
Melbourne
Melbourne
Melbourne
Singapore |
|
AU
AU
AU
AU
SG |
|
|
Assignee: |
Goodridge; Richard John
Melbourne
AU
Zank; Johann Emily
Melbourne
AU
Karaman; Marilyn Emily
Melbourne
AU
Alilovic; Ivana Emily
Melbourne
AU
Zank; Johann Emily
Melbourne
AU
|
Family ID: |
55745882 |
Appl. No.: |
15/518701 |
Filed: |
October 14, 2015 |
PCT Filed: |
October 14, 2015 |
PCT NO: |
PCT/AU2015/050631 |
371 Date: |
April 12, 2017 |
Current U.S.
Class: |
102/332 |
Current CPC
Class: |
C06B 23/006 20130101;
C06B 47/145 20130101; C06B 23/002 20130101; F42D 1/04 20130101 |
International
Class: |
C06B 23/00 20060101
C06B023/00; F42D 1/04 20060101 F42D001/04; C06B 47/14 20060101
C06B047/14 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 14, 2014 |
SG |
10201406593W |
Claims
1. An explosive composition comprising a reagent that inhibits
corrosion of a metal or metal alloy when the explosive composition
comes into contact with the metal or metal alloy.
2. An explosive composition according to claim 1, wherein the
reagent inhibits corrosion of copper and copper alloys when the
explosive composition comes into contact with copper or the copper
alloy.
3. An explosive composition according to claim 1, wherein the
explosive composition comprises an explosive precursor and
sensitising species.
4. An explosive composition according to claim 3, wherein the
explosive precursor comprises the reagent.
5. An explosive composition according to claim 4, wherein the
emulsion precursor is an emulsion produced by mixing an aqueous
oxidizer salt solution with a fuel and emulsifier, and wherein the
reagent is water soluble and provided in the aqueous oxidizer salt
solution.
6. An explosive composition according to claim 3, wherein the
reagent is introduced into the explosive composition or explosive
precursor via an aqueous lubricant that is used to lubricate
delivery of the explosive composition or explosive precursor
through a loading hose.
7. An explosive composition according to claim 3, wherein the
reagent is included in a gassing solution that is mixed with the
explosive precursor in order to generate gas bubbles as the
sensitising species.
8. An explosive composition according to claim 1, wherein the
reagent inhibits corrosion by a direct mechanism.
9. An explosive composition according to claim 1, wherein the
reagent inhibits corrosion by an indirect mechanism.
10. An explosive composition according to claim 1, wherein one or
more reagents are used to provide corrosion inhibition by a
combination of direct and indirect mechanisms.
11. A blasting system comprising a detonator having a shell formed
of a metal or a metal alloy and an explosive composition as claimed
in claim 1.
12. A blasting system according to claim 11, wherein the detonator
shell is formed of copper or a copper alloy.
13. A blasting system according to claim 12, wherein outer surfaces
of the shell of the detonator comprises a coating that inhibits
corrosion of copper or copper alloy when in contact with the
explosive composition.
14. A blasting system according to claim 13, wherein the explosive
composition is sensitised with gas bubbles produced by mixing a
gasser solution with an explosive precursor, and wherein the gasser
solution comprises a reagent that inhibits corrosion of the
detonator shell by reducing the affinity of the gas bubbles for the
coating.
15. A blasting system according to claim 14, wherein outer surfaces
of the shell of the detonator comprise a multi-layer coating
comprising a first hydrophobic layer that is provided on outer
surfaces of the detonator shell and that passivates the outer
surface with respect to corrosive species present in the explosive
composition and a second hydrophilic layer provided over the
hydrophobic layer.
16. A method of blasting in which an explosive composition as
claimed in claim 1 is provided in a blasthole and initiated using a
detonator.
17. A method of producing an explosive composition as claimed in
claim 1, wherein the reagent is introduced into an explosive
precursor or explosive composition in a component that is used to
produce the explosive precursor or explosive composition.
18. A method of producing an explosive composition according to
claim 1, wherein the reagent is included in a gassing solution that
is mixed with an explosive precursor in order to generate
sensitising gas bubbles and yield an explosive composition.
19. A method of producing an explosive composition according to
claim 1, which comprises introducing the reagent into the explosive
composition or an explosive precursor via an aqueous solution that
is used to lubricate delivery of the explosive composition or
explosive precursor through a loading hose.
Description
SUMMARY OF THE INVENTION
[0001] In general terms the present invention relates to inhibiting
corrosion caused by certain types of explosive composition with
respect to metals and metal alloys, in particular copper and copper
alloys. The invention has applicability in the context of
commercial operations where explosive compositions are used, such
as mining and blasting operations.
BACKGROUND TO THE INVENTION
[0002] Commercial mining and blasting operations frequently use
explosive compositions that contain ammonium nitrate. The explosive
composition is conveniently used in the form of a watergel or
emulsion. These are well known and commonly used forms of explosive
composition. The detonation sensitivity of the explosive can be
increased by addition of sensitising species, such as gas bubbles
or solid agents such as microballoons and microspheres. Gas bubbles
may be introduced into the explosive composition using a chemical
gassing solution. A gasser solution is an aqueous solution
comprising species that will react with one or more components of
the explosive composition (usually ammonium nitrate) to generate
gas bubbles. Various gasser solution technologies are known in this
regard. By way of example, the gasser solution may be an aqueous
solution of sodium nitrite. The gasser solution may include other
additives that control the rate at which the gassing reaction
proceeds as might be required depending on such things as
prevailing conditions, e.g. temperature.
[0003] The sensitised explosive composition is commonly initiated
using one or more initiation devices. The initiation device will
typically comprise a detonator, possibly used in conjunction with a
booster charge (commonly referred to simply as a booster) in which
the detonator is inserted.
[0004] Detonators typically take the form of an elongate cylinder
(shell) that houses a small explosive charge and componentry
required to initiate that charge. The cylinder is manufactured from
a metal or a metal alloy, and aluminium, copper, brass (an alloy of
copper and zinc) and steel are commonly used. Copper and brass tend
to be preferred because of ease of manufacture and because they can
provide a detonator shell that has suitably high physical strength
to withstand shock and pressure encountered in extreme blasting
conditions.
[0005] It has been observed however that blasthole conditions such
as water, reactive ground, leachants, and physical contact with
explosive compositions may cause corrosion of copper and brass
detonator shells. Various mechanisms may be responsible for this
depending upon the characteristics of the explosive composition,
the conditions under which it is being used and the manner in which
the explosive composition has been sensitised to render it
detonable.
[0006] If corrosion of a detonator shell is extensive, the physical
strength of the shell can be impaired and this may impact on
detonator efficacy. Corrosion may also compromise the integrity of
the shell, thereby allowing ingress of external species such as
water. In turn, this may cause the detonator to malfunction and
misfire. This may have significant time and cost implications.
Detonator misfire may also have associated safety issues since an
undetonated explosive charge remains in the blasthole.
[0007] There is on-going demand for higher mine productivity and
the desire to undertake blasting operations in more challenging
environments. This might involve such things as longer sleep times
and/or blasting in hot and reactive ground. In such situations, the
potential for corrosion of detonator shells may actually be
increased.
[0008] Efforts to address corrosion in this context have included
the use of physical barriers that are intended to isolate the outer
surfaces of the detonator shell from the environment in which it is
used. Such efforts have included providing a lacquer, coating or
polymeric sleeve on the exterior of the shell. However, these
approaches had limited success on copper and brass shells, the cost
may be prohibitive and/or there may be manufacturing
difficulties.
[0009] It has also been suggested to form the detonator shell of a
material that has suitable mechanical properties but that is more
corrosion resistant than copper and brass. However, material
selection is not straightforward. For example, plastics and
aluminium are too soft a material and will result in failure due to
shock compression. Steel and other alloys may have suitable
physical properties but shell manufacture may be more difficult and
the cost may be prohibitive. The use of copper and brass as the
material for the detonator shell is therefore still preferred.
[0010] Against this background there remains the need to provide an
alternative and effective way of addressing corrosion of detonator
shells in this context.
SUMMARY OF THE INVENTION
[0011] The present invention seeks to address the corrosion
problems discussed by providing modified explosive compositions
that are less corrosive with respect to metal/metal alloys. The
present invention may be applied to inhibit corrosion of copper and
copper alloys and this is of particular interest. The invention
will therefore be described with particular reference to this.
However, the principles of the invention may be more broadly
applicable and may be applied to inhibit corrosion of other
metals/metal alloys.
[0012] Accordingly, in one embodiment the invention provides an
explosive composition comprising a reagent that inhibits corrosion
of a metal or metal alloy when the explosive composition comes into
contact with the metal or metal alloy. Related to this the
invention provides components used to produce such explosive
compositions, to blasting systems including the explosive
compositions in combination with an initiating device and to a
method of blasting using the explosive compositions. These various
embodiments will be better understood with reference to the
following more detailed discussion of the invention in the context
of inhibiting corrosion of copper and copper alloys.
[0013] Noting the emphasis explained above, embodiments of the
present invention are based on identifying reagents that inhibit
corrosion of copper and copper alloys (such as brass) when
contacted with certain types of explosive composition. Accordingly,
the invention provides an explosive composition comprising a
reagent that inhibits corrosion of copper and copper alloys when
the explosive composition comes into contact with copper or the
copper alloy.
[0014] Embodiments of the invention relate to the production of
such explosive compositions and to components used in the
production of such explosive compositions. The invention also
relates to blasting systems comprising an explosive composition in
accordance with the invention in combination with an initiating
device having a copper or copper alloy surface that in use will
contact the explosive composition. The initiating device will
generally be a detonator. In embodiments of the invention the shell
of the detonator may be coated with a functional coating to provide
further enhanced corrosion resistance.
[0015] In another embodiment the present invention provides a
method of blasting in which an explosive composition in accordance
with the invention is provided in a blasthole and initiated using
an initiation device. In the embodiments of particular interest
this will be a detonator with a copper or copper alloy (usually
brass) shell.
[0016] The invention may also be implemented using a combination of
embodiments as disclosed herein.
[0017] In describing the invention the expression "explosive
composition" refers to an explosive that may be initiated using a
conventional initiating system, for example using one or more
detonators, possibly in combination with one or more boosters. The
explosive composition will invariably include sensitising species.
In the present specification such species will be introduced into
what is referred to herein as an "explosive precursor". The term
"explosive precursor" is intended to mean a composition that
contains stored chemical energy that can be released when the
composition is suitably sensitized and detonated. The explosive
precursor will usually be ammonium nitrate containing. It may be a
conventional emulsion explosive or a watergel explosive
formulation. The formulated explosive composition may also contain
ammonium nitrate (AN) prill or ammonium nitrate/fuel oil (ANFO)
prill. Such formulations are well known in the art.
[0018] Reagents useful in the present invention may be referred to
simply as a "corrosion inhibitor" since that is the effect achieved
in the context of the invention. However, as will be explained,
additives that are known to inhibit corrosion of copper and copper
alloys in other fields of use may not be useful in the context of
the present invention since the chemical make-up of (sensitised)
explosive compositions and the corrosion causing species/reactions
associated with such compositions and their use can be complex.
There are also various factors that influence selection of a
suitable reagent. The invention may be implemented using one or
more reagents that impart corrosion resistance by the same or
different mechanisms.
[0019] Throughout this specification and the claims which follow,
unless the context requires otherwise, the word "comprise", and
variations such as "comprises" and "comprising", will be understood
to imply the inclusion of a stated integer or step or group of
integers or steps but not the exclusion of any other integer or
step or group of integers or steps.
[0020] The reference in this specification to any prior publication
(or information derived from it), or to any matter which is known,
is not, and should not be taken as an acknowledgment or admission
or any form of suggestion that prior publication (or information
derived from it) or known matter forms part of the common general
knowledge in the field of endeavour to which this specification
relates.
DETAILED DISCUSSION OF THE INVENTION
[0021] In accordance with the present invention enhanced corrosion
resistance as between an explosive composition and an initiating
device including a copper or copper alloy that in use will come
into contact with the explosive composition may be achieved by
modification of the explosive composition to include a functionally
active reagent. This is believed to represent a significant
departure from previous approaches where the focus has been to
provide a protective or passivating coating on the copper or copper
alloy itself. In accordance with the invention the manner in which
the reagent is provided in the explosive composition may vary
depending upon various factors, including how the explosive
composition has been sensitised, the type of composition and how it
is made, and how the explosive composition is delivered into a
blasthole during use.
[0022] As foreshadowed, the mechanism by which corrosion takes
place may vary depending upon various factors. For example,
conventional explosive compositions may contain a number of species
that are corrosive to copper and copper alloys. These species may
include, but are not limited to, nitrate ions, nitrite ions,
ammonia and various amines. Blasthole conditions and the presence
of species such as chlorides, sulphates, or leachants may also
encourage corrosion.
[0023] Ammonium and nitrate ions are present because the explosive
compositions to which the invention may be applied invariably
contain ammonium nitrate in aqueous form, and possibly as a solid
additive in the form prills. The latter may be ammonium nitrate
prill or ammonium nitrate in fuel oil (ANFO) prill. When the
explosive composition is sensitised with gas bubbles, nitrite ions
may be present due to the chemistry of the gasser solution being
used. Typically, the gasser solution contains sodium nitrite. In
emulsion explosive, emulsifiers are a source of amines.
[0024] Ammonia is released from ammonium nitrate containing
explosive compositions under alkaline conditions. This may take
place when gasser solution is added to the composition since the
gasser solution may be basic (a gasser solution based on sodium
nitrite typically has a pH of 8-9). Addition of the gasser solution
may therefore result in an increase in the overall pH of the system
thereby causing release of ammonia. A gas-sensitised explosive
composition may therefore exhibit a relatively fast rate of
corrosion. Glass microspheres used for sensitisation can also react
with ammonium nitrate in an explosive composition to yield ammonia
thereby inducing corrosion.
[0025] The temperature at which the explosive composition is being
used, the presence of other species found in blasthole or mine
water and leachants causing pH changes can also influence the rate
at which corrosion will take place.
[0026] During the corrosion process copper forms copper complexes
thereby stripping copper from a surface. In a copper and/or copper
alloy structure this may also lead to crack formation due to stress
corrosion cracking. One possible reaction involving ammonium
nitrate and ammonia with copper is to form tetra-amino copper
nitrate (TACN). This is a base catalysed reaction that proceeds as
follows:
Cu+NH.sub.4NO.sub.3+NH.sub.3.fwdarw.(TACN)
[0027] In accordance with the invention it has been found that it
is possible to modify the otherwise corrosive nature of an
explosive composition with respect to copper and copper alloys by
inclusion in the composition of a suitable reagent.
[0028] The reagent used in accordance with the present disclosure
may inhibit corrosion of a copper or copper alloy by a direct
and/or indirect mechanism. Direct inhibition occurs when the
reagent interacts with the metal/metal alloy itself to inhibit
corrosion. For example, this may occur by the reagent
protecting/passivating the metal/metal alloy thereby reducing the
availability of metal/metal alloy for reaction with corrosive
species. Indirect inhibition occurs when the reagent influences the
properties of the corrosive environment to which the metal/metal
alloy is exposed in order to render the environment less corrosive.
Thus, the reagent may interact with corrosion causing species in an
explosive composition to render them less corrosive. By way of
example here reference may be made to gas sensitised explosive
compositions in which potentially corrosive gas bubbles are
hydrophobic in nature. If the surface of the metal/metal alloy has
hydrophobic character, the gas bubbles will be attracted to the
metal/metal alloy thereby causing corrosion. In this case it may be
desirable to use a reagent that has the effect of changing the
surface properties of the gas bubbles in order to reduce their
surface hydrophobicity. This will reduce the affinity of the gas
bubbles for the metal/metal alloy and in doing so inhibit
corrosion. Additionally, or alternatively, the reagent may modify
the surface charge of the gas bubbles in order to reduce their
affinity for the surface of the metal/metal alloy. In an embodiment
one or more reagents are used to provide corrosion inhibition by a
combination of direct and indirect mechanisms.
[0029] It has been found that benzotriazole (BTA) may be suitable
for use as the reagent in the various embodiments of the invention.
In embodiments BTA may inhibit corrosion by direct and/or indirect
mechanisms. Structurally, BTA consists of benzene and triazole
fused ring. BTA is believed to prevent undesirable surface
reactions by forming a protective layer on copper and brass. It is
surprising that BTA acts as a corrosion inhibitor for copper in AN
solutions.
[0030] The mechanism by which the complex forms is proposed and
illustrated by the following reactions:
Cu(s)+BTA(aq).fwdarw.Cu:BTA(ads)
where Cu:BTA(ads) stands for BTA adsorbed onto a copper surface. In
the presence of oxidants or by anodic polarization it can be
oxidised to a protective complex:
Cu:BTA(ads).fwdarw.Cu(I)BTA(s)+H.sup.+(aq)+e.sup.-
[0031] From this reaction it can be seen that increase of BTA
concentration shifts the reaction towards formation of larger
amount of the complex Cu(I)BTA. An increase in pH has also been
observed to favour formation of the complex.
[0032] The copper complex forms a film on the copper surface that
prevents corrosive reactions at the surface due to species present
in the explosive composition. Adsorption of the inhibitor on the
metal surface and film formation are believed to be important steps
in the mechanism of corrosion inhibition.
[0033] It may also be possible to use derivatives of BTA as the
reagent. For example it has been observed that the introduction of
the substituent groups (imidazole and its derivatives) has no
effect on the mechanism of the inhibitive action while it does have
an influence on inhibition efficiency. Useful derivatives may
include substituted BTA derivatives in which substituents are
present on the benzene ring but not on the triazole ring.
[0034] Examples of other compounds that may be useful as reagent in
the context of the present invention include imidazoles, triazoles,
mercaptotriazoles, napthotriazoles, mercaptobenzimidazoles, azoles,
triazines and tolyltriazines.
[0035] The present invention may be implemented using one or more
suitable reagents and/or embodiments of the invention, thereby
reducing/inhibiting corrosion of a number of different metals or
metal alloys that may be in contact with an explosive composition.
It may also be possible that a single reagent may be effective with
respect to more than one metal or metal alloy. It is possible that
the efficacy of the reagent with respect to inhibition of corrosion
may be increased by use of it in combination with other
compounds.
[0036] BTA, useful BTA derivatives and other compounds that
potentiate the effect of these are commercially available. BTA may
act as both a direct and indirect inhibitor of corrosion. While
acting directly on the metal or metal alloy as described above, BTA
may also modify the surface properties of gas bubbles thereby
indirectly inhibiting corrosion. Without wishing to be bound by
theory, this may involve a reduction in the hydrophobicity of the
gas bubbles and/or varying the charge of the gas bubbles. The
intention is to reduce the affinity of the gas bubbles for the
surface to be protected against corrosion. Other reagents that may
indirectly inhibit corrosion by the same mechanism include block
copolymers, hydrophilic polymers and surfactants.
[0037] The amount of reagent to achieve effective results may vary
depending upon various factors including the mechanism by which
corrosion inhibition is to be achieved, the propensity of the
explosive composition to cause corrosion and the prevailing
environmental conditions in which the explosive composition is
being used. The amount of reagent used may also be influenced by
the solubility in the chosen solvent (carrier) and the molecular
weight of the reagent. Broadly speaking the amount of reagent may
be from 0.0001 to 1 wt % based on the weight of explosive
composition.
[0038] In embodiments of the invention the reagent is required to
be soluble in aqueous solution and the solubility of the reagent
may also be a relevant consideration. The chosen reagent should not
react with or otherwise interfere with the gassing reaction or the
stability or intended function of the explosive composition being
gassed. The reagent should not interfere with formation or
stability of the explosive composition and it should remain
functionally active in the composition once formed. It is possible
that the reagent may be included in a non-aqueous carrier depending
upon its solubility and the manner in which the reagent is to be
incorporated into an explosive composition.
[0039] In an embodiment, the reagent may be introduced into an
explosive precursor or explosive composition in a component that is
used to produce the explosive precursor or explosive composition.
It is also possible that the reagent may be introduced by use of a
separate component the sole function of which is to introduce the
reagent. The explosive composition will comprise an explosive
precursor and sensitising species. The reagent may be introduced
into the explosive precursor before sensitising species are added
to it, for example when the explosive precursor is being made.
Alternatively, or additionally, the reagent may be introduced when
sensitising species are being included in the explosive precursor.
Additionally, or alternatively, the reagent may be introduced into
an explosive composition after sensitisation of an explosive
precursor has taken place. These possibilities are discussed in
more detail below.
[0040] In an embodiment the reagent may be provided in the
explosive precursor when the latter is being produced. In this
case, if the reagent is water soluble, it may be incorporated into
the explosive precursor in an aqueous component from which the
explosive precursor is made. For example, in the case of an
emulsion explosive the reagent may be included in the oxidiser salt
solution from which the emulsion is made. To make the emulsion the
salt solution and a fuel are mixed in the presence of an
emulsifier. A functionally effective amount of the reagent will be
used. This approach may be useful for, but is not limited to,
explosive compositions that are not gas-sensitised. Such explosive
compositions can be sensitized with solid density reducing agents,
such as glass microspheres.
[0041] In an embodiment the reagent may be included in an explosive
precursor or explosive composition during loading of the explosive
precursor or explosive composition into a blasthole. In the case of
an explosive precursor sensitisation, for example by using a gasser
solution, may occur during the loading process. When the explosive
composition is an emulsion explosive individual, streams of
explosive composition and reagent (typically provided in a suitable
carrier) may be delivered using one or more loading hoses for
mixing in the hose or as the streams exit the end of the hose. A
mixing device may be required if mixing is to take place as the
streams exit the loading hose.
[0042] In an embodiment the reagent may be introduced into an
explosive precursor or explosive composition via an aqueous
solution that is used to lubricate delivery of the explosive
precursor or explosive composition through a blasthole loading
hose. In this case the aqueous solution will be provided as an
annular stream around a stream of explosive precursor or explosive
composition as it is being pumped through a loading hose. The
annular stream acts as a lubricant thereby improving flow of the
stream within the loading hose. The use of this type of
"water-ring" is known but not the inclusion in the aqueous solution
of a reagent to impart corrosion resistance. In this embodiment it
is important that the aqueous solution used for lubrication is
mixed with and into the stream being pumped. This ensures suitable
distribution of the reagent. Mixing may be achieved using a mixing
head provided at the end of the loading hose from which the stream
emerges. At that point the aqueous annular stream has served its
role as a lubricant.
[0043] In another embodiment the reagent may be included when an
explosive precursor is being sensitised with gas bubbles. In this
case the reagent may be included in the gassing solution that is
mixed with an explosive precursor in order to generate sensitising
gas bubbles and yield an explosive composition. The gasser solution
may be mixed with explosive precursor before or during delivery
into a blasthole. In the latter case this may be achieved by
providing the gasser solution as an annular stream around a stream
of explosive precursor as it is being pumped through a loading hose
and into a blasthole. The annular stream acts as a lubricant and
should be mixed with and into the explosive precursor to ensure an
even distribution of gas bubbles when the gassing reaction has
taken place.
[0044] Related to this there is provided a method of producing a
gas-sensitised explosive composition with reduced propensity to
cause corrosion of copper and copper alloys, the method comprising
adding a gasser solution to an explosive precursor in order to
generate gas bubbles in the explosive precursor, wherein the gasser
solution comprises a reagent that inhibits corrosion of copper and
copper alloys when in contact with the gas-sensitised explosive
composition. Also provided is a gas-sensitised explosive
composition that has been produced by the method.
[0045] An effective concentration of the reagent in the gasser
solution may be determined taking into account the concentration of
gasser solution that is to be added to the explosive composition.
The solubility of the reagent in the gasser solution may also
determine the amount of reagent that can be used. The gasser
solution may itself be added to the explosive composition in
conventional amounts, for example from 0.25 to 2.0 wt. % based on
the total weight of the explosive precursor.
[0046] Further details are provided below with respect to one
embodiment of the disclosure related to the use of a reagent in the
gasser solution: [0047] 1. A gasser solution for generating gas
bubbles in an explosive precursor to provide a gas-sensitised
explosive composition, the gasser solution comprising (a) one or
more species that will react with one or more species in the
explosive precursor to generate gas and (b) a reagent for a metal
or metal alloy, preferably for a copper or copper alloy. The
corrosion inhibitor should be soluble in the gasser solution.
[0048] 2. The use of such a gasser solution for generating gas
bubbles in an explosive precursor and providing a gas-sensitised
explosive composition that exhibits reduced propensity to cause
corrosion of a metal or metal alloy preferably of a copper or
copper alloy. [0049] 3. A method of blasting in which this type of
gas-sensitised explosive composition is provided in a blasthole and
initiated using an initiation device.
[0050] Embodiments of the invention also involve using detonator
shells that have been pre-treated to provide a functional coating
to assist with corrosion resistance.
[0051] In an embodiment, when the reagent acts indirectly by
reducing the surface hydrophobicity of gas bubbles, the invention
also contemplates pre-treating of a detonator shell to provide
functionally active layer(s) in order to achieve corrosion
resistance.
[0052] With respect to pre-treating the detonator shell, it has
been observed that the affinity that the corrosive species have for
water may have a significant impact on the corrosion resistance
that can be achieved. Thus, it has been found that when
conventional gassing solution chemistry is used in an explosive
composition, coating the detonator shell with a coating that should
provide corrosion resistance but that is hydrophobic in nature can
actually increase the rate of corrosion. This is believed to be
because the conventional gassing process produces gas bubbles that
are themselves hydrophobic in nature and that are therefore
attracted to the hydrophobic surface. A high concentration of gas
bubbles at the shell surface may accelerate the rate of corrosion
notwithstanding the presence of the corrosion inhibitor. However,
in this case it may be desirable to provide in the explosive
composition (be that via the gassing solution or otherwise) a
reagent that has the effect of changing the surface properties of
the gas bubbles in order to reduce surface hydrophobicity. In turn
this will lower the affinity of the gas bubbles for the hydrophobic
coating of corrosion inhibitor provided on surface of the detonator
shell.
[0053] Thus, in an embodiment of the invention beneficial results
may be achieved by the combined effect of providing a hydrophobic
coating on the detonator shell and by incorporating a suitable
reagent in the explosive composition to reduce the hydrophobic
character of the gas bubbles produced during the gassing reaction.
In an embodiment the reagent will be present as a component of the
gasser solution that is used. An example of a suitable corrosion
inhibitor for coating the detonator shell and reagent for inclusion
in the bulk of the explosive composition is BTA. In this case the
reagent may also passivate any areas of the detonator shell that
have not been covered with corrosion inhibitor.
[0054] In another embodiment it has been observed that coating the
shell of a detonator with a hydrophilic coating can reduce the rate
of corrosion when conventional gassing solutions are used. This is
believed to be because the gas bubbles produced are hydrophobic in
nature and as such will be repelled from the surface of the
detonator shell. However, it has also been observed that
hydrophilic coatings provided on the detonator shell tend to swell
over time in the presence of water. This is likely to occur with
long sleep times of detonators loaded in blastholes prior to
firing. Swelling of the coating can lead to the presence of pores
in the coating. Even though the walls of the coating surrounding
the pores may be hydrophilic and water molecules may actually plug
the pores, pitting corrosion may still be problematic. This
embodiment may therefore only be useful in dry environments or in
wet environments where short sleep times are employed to minimise
swelling of the hydrophilic coating.
[0055] In accordance with another embodiment of the invention in an
attempt to mitigate this issue, it may be desirable to provide a
multi-layer coating on the detonator shell. Specifically, it may be
desirable to provide a first layer of a corrosion inhibitor on the
detonator shell, for example a coating comprising BTA. This coating
is preferably chemisorbed by the material of the detonator shell. A
hydrophilic coating is then applied over the top of that coating.
In use the hydrophilic coating will repel hydrophobic gas bubbles.
However, if the hydrophilic coating swells and pores develop, the
corrosion inhibitor should then prevent corrosive reactions at the
surface of the shell. As explained above complex formation is
believed to be responsible for preventing corrosive reactions at
the shell surface due to species present in the explosive
composition.
[0056] In this embodiment the layer of corrosion inhibitor provided
on the detonator shell may have hydrophobic character and thus
attract gas bubbles. It may be desirable therefore to include in
the explosive composition a reagent that will reduce the
hydrophobicity of the gas bubbles that will be present, as
described above.
[0057] In an embodiment a lacquer or varnish may be used to provide
a coating on the detonator shell to impart corrosion resistance.
Preferably, the surface of the shell should be clean before
application of the lacquer/varnish. The lacquer/varnish may be
applied to the shell by dipping the shell in the lacquer/varnish or
by spraying. Various suitable lacquers/varnishes are commercially
available and generally include a polymeric resin dissolved in a
suitable solvent and dosed with a suitable reagent to impart
corrosion resistance. For example, products are available
comprising an acrylic ester resin dissolved in toluene with BTA
added to impart corrosion resistance.
[0058] In an embodiment a lacquer or varnish may be used to provide
a hydrophilic coating to the shell of the detonator. Preferably,
the surface of the shell should be clean before application of the
lacquer/varnish. The lacquer/varnish may be applied to the shell by
dipping the shell in the lacquer/varnish or by spraying. Various
suitable lacquers/varnishes are commercially available and
generally include a hydrophilic polymer provided in a suitable
solvent or carrier. Epoxy and acrylic systems may be useful.
[0059] The suitability of a particular lacquer/varnish, the
preferred method of application and the optimum thickness may be
varied to optimise results.
[0060] An additional embodiment of the invention is a blasting
system comprising a detonator having a shell formed of copper or a
copper alloy and an explosive composition in accordance with the
invention, i.e. an explosive composition modified to include a
reagent that is functionally effective in reducing corrosion as
described. In this embodiment outer surfaces of the shell of the
detonator may comprises a coating that inhibits corrosion of copper
or copper alloy when in contact with the explosive composition.
When the explosive composition is sensitised with gas bubbles
produced by mixing a gasser solution with an explosive precursor,
the gasser solution may comprise a reagent that inhibits corrosion
of the detonator shell by reducing the affinity of the gas bubbles
for the coating.
[0061] In a further embodiment outer surfaces of the shell of the
detonator may comprise a multi-layer coating. In this embodiment
outer surfaces of the shell of the detonator comprise a multi-layer
coating comprising a first hydrophobic layer that is provided on
outer surfaces of the detonator shell and that passivates the outer
surface with respect to corrosive species present in the explosive
composition and a second hydrophilic layer provided over the
hydrophobic layer. In this embodiment, no addition of a reagent to
the explosive composition is necessary to provide inhibition of
corrosion.
[0062] Usually, in a blasting operation, one or more detonators are
positioned in a blasthole (possibly in conjunction with a booster
charge) with explosive composition then being delivered into the
blasthole and around the detonator(s). Strictly speaking, to
inhibit corrosion of a (copper or brass) detonator shell it is
necessary for the corrosion inhibitor to be present in that portion
of the explosive composition that is in direct contact with the
detonator shell. The invention could be implemented to achieve that
by varying the composition of the gasser solution (to include or
omit corrosion inhibitor) that is injected into an explosive
composition as the explosive composition is being delivered into
the blasthole. However, this adds a degree of complexity to the
loading operation. Instead, it may be more practical to simply use
gasser solution including corrosion inhibitor for the entirety of
explosive composition being delivered into a blasthole.
[0063] Additional steps may be taken in an attempt to minimise
corrosion of the detonator shell. Thus, the detonator shell may be
pre-treated with a suitable reagent to provide a protective layer
on the shell. The reagent will usually be provided in a suitable
carrier. When the detonator is positioned in a detonator well in a
booster charge, the solution may surround the detonator in the gap
that exists between the outer surface of the shell and the internal
surface of the detonator well.
[0064] The invention also provides a method of blasting in which an
explosive composition in accordance with the invention is provided
in a blasthole and initiated using a detonator comprising a shell
formed of copper or a copper alloy. The method may utilise blasting
systems in accordance with the invention.
[0065] In relation to this embodiment it will be noted that in
practice there may be some considerable time (sometimes weeks)
between loading blastholes (with initiation devices and sensitised
explosive composition) and firing of a blast. This may be the case
for example when the area being blasted and thus the number of
blast holes is large. The present invention may allow detonators to
be left in the potentially corrosive environment of a loaded
blasthole for extended periods of time without corrosion that would
otherwise effect detonator functionality.
[0066] The present invention may also find use in extreme
ground/blasting conditions that are particularly aggressive with
respect to detonator corrosion. The present invention may therefore
allow blasting to be implemented in situations that have otherwise
proved difficult or impossible.
[0067] Embodiments of the invention are now illustrated with
reference to the following non-limiting examples.
[0068] A standardised accelerated corrosion test was developed to
assess the rate of detonator shell corrosion, allowing a comparison
of various treatments and reagents.
[0069] This accelerated test used was designed to corrode a brass
detonator shell within 18-24 hours, using a test solution
containing 66 g ANS (50% ammonium nitrate solution) or emulsion, 33
g sodium nitrite solution (30% sodium nitrite) to mimic a
commercial gasser formulation, and additional corrosive salts 1 g
sodium chloride and 0.150 g sodium sulphate to mimic mine water
leachants normally seen in a blasthole. The test conditions are far
more aggressive than is normally seen in a typical blasthole.
[0070] Dummy detonators (operational printed circuit board, no
explosive secondary base charge and non-functional fusehead) were
exposed to the aggressive test solution both at room temperature
and at 40.degree. C. for several weeks or until the integrity of
the detonator was seen to fail. Detonators were continuously
monitored both electronically (detonator circuitry functionality)
and by visual and microscopic examination of the detonator shell.
For the electronic functionality testing of the detonators a logger
is used.
Example 1
BTA in Gasser
[0071] Detonators were tested using the extremely aggressive test
solution described above, both in the presence and absence of BTA
(benzotriazole) in the gasser solution.
[0072] The non-BTA gasser was prepared by dissolving 30% w/w sodium
nitrite in water
[0073] For the BTA containing gasser 0.25% w/w of the BTA was
dissolved in water (Composition for a 100 g BTA gassing precursor
solution: 0.25 g BTA; 99.75 g water). Once the BTA is completely
dissolved (slow process due to limited solubility of the compound)
sodium nitrite is added to achieve a 30% w/w solution. (Composition
for a 100 g gassing solution: 30 g sodium nitrite; 70 g of
BTA/water gassing precursor solution above)
[0074] The additional corrosive reagents, i.e. chloride and
sulphate salts, were added to the gassing solution prior to
addition of emulsion. The mixture was then stirred to prepare the
suspension.
[0075] Three brass shell dummy detonators were placed into the
suspension of gasser/emulsion starting the corrosion reaction. The
dummy detonators were monitored for performance as described above.
In the absence of BTA severe stress corrosion cracking was evident
within one day leading to failure of electronic functionality and
structural failure of the dummy detonators, whereas the three dummy
detonators placed into the BTA containing test solution showed
structural integrity and full electronic functionality after 30
days.
Example 2
Coated/Lacquered Detonators
[0076] To protect the brass shell dummy detonators against general,
pitting and stress corrosion cracking the detonators were coated
with hydrophilic and hydrophobic lacquers and combinations thereof.
The hydrophobic lacquer contains BTA as a corrosion inhibitor.
Coatings were applied using a dipping process allowing the lacquer
to cure for a period of 24 hours before applying a second coating.
The following lacquer combinations were exposed to the accelerated
ANS/gasser test solution, described previously. The lacquered
detonator corrosion experiments were carried out at room
temperature. [0077] a) Dual hydrophilic lacquer combination [0078]
b) Hydrophilic/hydrophobic (BTA containing) lacquer combination
[0079] c) Hydrophobic (BTA containing)/hydrophilic lacquer
combination
[0080] Detonators were continuously monitored both electronically
(detonator circuitry functionality) and by visual and microscopic
examination of the detonator shell.
[0081] Results obtained were as follows: [0082] a) Extremely
significant pitting and general corrosion, electronic functionality
compromised after 4 days. [0083] b) Significant pitting and general
corrosion, electronic functionality compromised after 7 days.
[0084] c) No Stress cracking or pitting corrosion and full
electronic functionality observed after 30 days. (Detonators fully
operational after 40 days. Experiment was stopped.)
Comparative Example
[0085] In a separate experiment dummy detonators were washed with a
BTA/water solution (Composition for a 100 g solution: 0.25 g BTA;
99.75 g water) and allowed to completely air dry. Three detonators
were then subjected to the accelerated corrosion test described
earlier (no BTA in gasser). The hydrophobic modified shell appeared
to increase corrosion. This is believed to be due to drawing of
hydrophobic, corrosive species containing gas bubbles to the metal
alloy interface, accelerating the rate of corrosion. Within one day
extreme pitting corrosion was observed and the dummy detonators
failed electronically. These results shows that BTA physically
bonding to a brass metal surface, specifically the copper
component, is not sufficient in providing corrosion protection.
However when BTA is present in the gasser solution protection
against corrosion can be achieved. Without wishing to be bound by
theory, it is believed that the BTA in the gassing solution is
believed to modify the corrosive gas bubbles by changing surface
hydrophobicity and/or charge.
* * * * *