DEViCE

The present invention relates to a method of production of electricity &om explosive compositions, to devices embodying the method of the invention and to & method of conductin a commercial blasdog operation relying on the method of the invention.

Background to the invention

The use of eleetrieal eicc ronic devices is growing rapidly in commercial hiasiing operations. For example, some detonators now rely on integrated circuits io provide fiaictionaiit . Providing electrical power io such devices is therefore necessary. This could be achieved ia, far example wireless initiation devices, using a built-in battery or charged capacitor but providing the devices "live" presents significant safety concerns since the device may itself contain an explosive (detonators include a small charge of explosive) or be positioned within or in proximity to an explosive during use. Addressing these concerns by specifically designed safety systems, such as multiple layers of control at the level of circuit design, is possible. However, this adds to design complexity and operation and, m turn, Shis has implications with respect to cost, efficiency and application. Furthermore, safe operation is compromised if the safety system itself fails.

The possible problems of providing an expiosiye-containing initiation device with a busU-tn power supply csn be overcome by supplying the device- in msilti-comportent form, with she power supply containing component being distinct ftoro any component containing explosive material However, ia such cases, the use of a built-in power supply, such as a battery or other charge storage device, can limit She shelf life of thai component due to unintended (bleeding of) electrical discharge. This may occur by a number of mechanisms, including chemical and physical mechanisms. An embodiment of this invention seeks to avoid the problem of shelf life limitation that may be associated with power supplies such as batteries. Further, in & blasting operation ii is sometimes desirable to leave electrical devices in a borehole for a long time, in such cases the v.se of sr. on-board battery may limit the sleep time of such devices, i.e. the period for which the device can be left in the bor hole be fore len ed use. In an embodiment, the invention seeks to provide a ower source that can easily be scaled to provide very long sleep mes in the borehole.

Against this background it would be desirable to provide as alternative approach to providing electrical energy for ekctrieai-'eieetrodc devices used is commercial blasting operations,

Accordingly, the present invention provides a method of generating electricity which comprises forming a galvanic ceil comprising two electrodes in contact with an ionic conductor, wherein the ionic conductor comprises an explosive composition or is derived from an explosive composition.

In accordance with the present invention electricity is generated eiecttocltetnkally by redox reactions involving a selected anode/cathode electrode pair and an ionic conductor. Broadly speaking this is a well-known methodology. However, unique to the present invention is the natuce of the ionic conductor that is used. Thus, in accordance with the present invention the ionic conductor is an explosive composition or derived from an explosive composition.

The present invention also provides aa electrical device for use in a (comjnerciai) blasting operation, wherein electricity for powering the device is generated in accordance with the method of the invention. Herein, unless context dictates otherwise, the term "device" embraces a stand atone/discrete device, such as a detonator and a component or subs stem of a stand alone/discrete device. The component or sub-system is intended to provide some desired functionality, such as firing ot communications functionality. The present invention lso provides a method of conducting a (commercial) Mastdsg operation in which electricity required for o eration of a device employed hi the operation is generated its accordance with the method of the invention.

s

Throughout this specification and the claims which follow, unless the context requires otherwise, the word "comprise", end variations such as "comprises" arid "comprising", will be understood to artely the inclusion of a stated integer or step or group of ia egers or steps but not she exclusion of any other integer or step or group of integers or steps. to

1 he reference in this specification to any prior publication (or information derived from it), or so any matter which is known, is not, and should not he taken as as acknow½dgrne?)t or admission or any form of suggestion thai prior publication (or information derived from it) or known matter forms part oftije common general knowledge is the field of endeavour to • 5 which this specification relates.

Embodiments of the present invention are illustrated with reference to the accompanying 0 non-limiting drawings in which:

Figure 1 is s schematic showing various battery cell designs;

Figure 2 is a plot of recorded potential of a "dummy" mmonium nitrsteyammorijura 25 saaiphauj emulsion, as referred to in the examples;

Figure 3 is a plot of recorded potential of three ammonium nhrate emulsions; as referred to hi the exam l s;

30 Figure 4 shows an experimental set-up used to assess emulsion electricity generation by a

Galvanic cell; Figure 5 is & plot oi ^' VoKags--time data fecotded for six different conductor pairs, as r ferred to in the examples; Fi ure 6 is a plot of Voltsige--4ime data recorded for six different galvanic couples, as referred to in she examples;

Figure 7 is a plot illustrating power output increase by ixicrensrag electrode surface area; as referred to ia the example:;;

Figure 8 is a series of ^' usa e:; from a ttme-!apse scries, lakes showing she breakdown of an emulsion aft r the addition of deimiisiiier, as referred to in s e examples;

Figures 9 and JO are photographs; illustrating experimental arrangements employed in Example 4(a) and 4(b).

The method of the present invention relies on formation of a galvanic (electrochemical) cell for electsssity generation. One skilled in the art will appreciate that suitable selection of electrode fnateriais and ionic conductor is relevant to the galvanic reactions required to generate an electrical current The ionic conductor that is used &y be an explosive composition that .¾'f .«? has; tfee necessary characteristics to function in this context. Alternatively, some dopji^mod fscatioru'transformation of the explosive com osition may be required in order fot it to junction as a suitable ionic conductor. In the latter cases, herein .reference is made to the ionic conductor being derived from an explosive composition. All of these possibilities will be discussed in more detail below. It is necessary in accordance with the invention to provide an ionic conductor only between the electrodes. The present invention uses a galvanic ceil to gene ate electricity. In the cell two materials wife different electron affinities are used as electrodes. Electrons flow from one electrode to fee other when the cell is shorted through sat external circuit. ithin the ceil the circuit is closed by movement ©Hons through the ionic conductor, in this way electrode reactions s convert chemical energy to electrical energy. The ionic conductor includes an electrolyte dissolved its <t suitable ionizing solvent such as yvaier. Explosive compositions typically include ionic salts, such as a niKORium nitrate, and these salts may he suitable electrolytes.

In an emb dime t of fee invention explosive composition b ing employed in a blasting SO operation is used to provide the ionic conductor for power generation in accordance wife fee present invention. For example, the explosive composition may be contained in a booster or it may be a bulk explosive that has been loaded in a blast hole. As will become apparent, only a small amount of explosive composition is required to function as, or be used to form, the ionic conductor. The remainder of fee explosive composition retains its 55 intended fm∞tiona!ky. in this regard, the present invention relies on in xltu electricity generation.

Generating in situ electricity means that the use of "live" devices (e.g., charged with sufficient electricity to achieve all functions of a firiiig sequence) may be avoided during

:¾ transport and deployment operations. Thus devices embodying the present invention will be "inherently safe" until they have come into contact wish fee ionic conductor. The present invention will also overcome the relatively short sheif-Hfe and potential hazard posed by fee use of batteries, which are known to, on occasion, explode due to internal reactions. The present invention will enable the development of intrmsically-sat ^' e electric

25 and/or electronic devices for use within or near explosive materials.

Its an embodiment of the invention the explosive composition is an tonic conductor and is per se electrically conducting, typically having a conductivity of at least 0.1 Sat ^" * and preferably 10 tn" ^' . By way of example, fee explosive composition may be a waiergel, for .10 example a wa ergel based on ammonium nitrate. In this case, once the galvanie electrode pair contact the watergel (and an electrical circuit closed by hard wiring the electrodes to each other), electricity generating reactions commence. in another esabodiment of the invention the explosive comp sition has low electrical conductivity 0.G00 i Saf'. This means thai ¾he. explosive composition is essentially nonconducting. In this case the explosive conjpedticm may be doped modifiedA¾ansformed is order to increase its electrical cotiductivity so a practically useful level so thai is may function as as ionic conductor in electricity generation. This could involve introducing art additive (an ionic conductor) into the explosive composition that per se provides ionic conductivity without otherwise altering the explosive composition. In this case the additive is responsible for ionic conduction between electrodes. For example, it ma be possible to increase the electrical conductivity of an explosive composition by incorporating into the composition a suitable ionic salt, such as chloride salt, that does not otherwise, or unduly, interfere with the ft.mctiorudi.ty of the composition as an explosive. Thus, the explosive composition ma be doped with a suitable, additive in order to provide or increase electrical conductivity.

In another embodiment the explosive composition is caused to undergo some physical or chemical transformation in order to provide art ionic conductor having the required electrical condtKuVify. This will be discussed farther in relation to emulsion explosives as these are of particular interest in the context of the present invention.

Braulsion explosives are made by mixing rut aqueous oxidizer salt phase with an immiscible organic, fuel phase in the presence of a surfactant (emuisifier). Water-in-oil emulsions include droplets of the salt in a matrix of the fuel phase. A commonly used salt is ammonium nitrate, typically in combination with ne or m s other satis. By v ay ol example, the emulsion is typically a 93:7 w/w water-tn-oil emulsion, in which the salt phase is a supersaturated solution of ammonium nitrate. In such emulsions micton-sszed droplets of the s&ll phase are completely isolated from each other by a thin film of the oil phase (and surfactant used in formation of the emulsion). This makes the emulsion electrically resistive. In this state, it is unlikely that any galvanic couple wilt generate ower because ionic conduction through the emulsion will be very low, if occurring at ail. However, t e salt phase may per se suitably electrically conducting and in accordance with the present invention a demulsifkr (an emulsion-breaking agent) is contacted with the emuisson thereby releasing She sail phase from the emulsion, at least in fee immediate vicinity of {at least between) the electrodes. The salt phase is then able to function as an ionic conductor in ¾ galvanic cell with the electrodes and thus e!sctricity-geaeratiag reactions can commence. The commercially available surface active agent Petro®AG {AfcKf Nobe!, IL) may be osed as a demulst er in this regard. The demukifkr typcially contains vaster and this will lead to dissolution and dilution of the salt phase. This also contributes to formation of the ionic conductor, ia addition to breaking the emulsion, the detnulsifier may itself also ad as an ionic conductor to assist ionic conductivity within the galvanic ceil. This function may be independent of the tonic conductor generated by breaking of the enialsioo, although there may be some form of combi ed ( ^' additive or possibly synergistic) effect in terms of ionic conductivity as between the two ionic conductors. In general terms in this embodiment the explosive composition is an emulsion explosive comprising droplets comprising an oxidizer sals in a matrix of a fuel phase, and wherein a demulsifier is contacted with emulsion explosive between the electrodes in order to produce an ionic conductor between the electrodes. When using an emulsion explosive composition, one possible complication may he that electrodes may be fouled by the oil-phase, or other component of the emulsion. This phenomenon may vary between de u!sifiers and/or electrode materials. Wish this problem in mind it may be desirable to coat or modify at least a portion of the electrode surface m order to repel oil, or in some other way reduce resultant passivation, either by oil or other substance. in another embodiment the explosive composition comprises an electrolyte such as ammonium nitrate and the some condxsctor is formed by dissolution of the electrolyte in a suitable solvent The solvent may be arty suitable polar solvent, typically water. For example, the explosive composition Kiay be made up of ammonium nitrate prill distributed in a fuel oil matrix (so-called ANFO). In this case the explosive per se does not exhibit stsitabie electrical conductivity to be useful in the present invention. Some aiodificatton iiansfonnatioe is therefore required is order to provide an ionic conductor having ekctricai conductivity at a practically useful level. One way that this may be done is to form an aqueous solution of the salt using water as solvent. Tims, in this case, formation of the ionic conductor involves dissolution in water of some ammonium nitrate prill The ioriic conductor should be formed at least in the vicinity (ai least between) the electrodes, it may be possible to form a suitably conducting ionic, conductor b dissolving prill in aaothet solvent _* but water is believed to be the most convenient solvent to use, Selecting the best electrode materials for use based on their eiecirochemicaJ activities with respect to a particular ionic conductor is necessary, it is believed thai one skilled in the art would be able to do this based on knowledge- of ekclrochetnisir and by routine experimentation. However, predicting the- electrocbenskal behaviour of any galvanic couple in ihe contest of She present invention may be complicated by at least three possible ..nterierences.

Firstly, local ceils may form leading to corrosion of electrodes. Corrosion of the electrodes by the formation of local cells can occur when both half-reactions (reduction and oxidation) take place on the same electrode and no current flows in the external circuit. In this case of a nitrate-containing ionic conductor fot example, the -concurrent reduction of nitrate ions and oxidation of the electrode material on the same electrode will lead to corrosion. For example, spot tests of various metals in 33% ammonium nitrate solutions have shown that local cells can form, particularly on mote reactive metals such as zinc and pure- iron. However, an emulsion contains a number of additional compounds and the ttnpaci these compounds have on the rates of the two reactions which comprise a local ceil may be hard to determine. Consequently, it is not wise to select electrode materials on die basis of tests conducted in pure solutions alone. Control of this process relies on. identifying materials that either catalyse or inhibit the reduction of nitrate, and using one of each in She galvanic couple. Given this knowledge, one skilled in the art would be able to optimise selection of electrode materials tor a given ionic conductor system. Secondly, the eieetroc½raistry of the ionic conductor may be coinpiex. Commonly the ionic conductor wiil comprise ammonium nitrate as Shis is commonly used in explosive formulations. In this case, mo likely ekcirt hemic.ai reactions that would lead to energy generation from this type of emulsion are reduction of nitrate ions at die positive electrode, and oxidation of electrode material (preferably s metal) at the negative electrode. The reduction of nitrate is a complex reaction, ft involves from one to eight electrons, depending on H, nitrate concentration, catalytic processes and other species present, including she reduction products of nitrate itself. These latter products can catalyse or inhibit further nitrate reduction. Moreover, the derrmfsifier itself may also contain electroa tivc species thai could contribute to, or dominate the electrochemistry. Ibe only realistic way io handle ihss complexity is by directly observing the activities of various electrode combinations and carefully considering not just instantaneous energy geueratson, but also how energy generation varies with lime. Thirdly, conductivity issues may arise due to passivation of the electrodes by species present in the explosive composition. For example, when the explosive composition is an emulsion, the fad phase, surfactant and/or other additives in the emulsion may coat one or both electrode thereby impeding conductivity. it has also beers observed that electrocheToical reactions are particularly sensitive to certain compounds, such as adsorbates. A complex system, such as an emulsion explosive composition, may exhibit profoundly different electrochemical behaviour than would an aqueous solution containing the same electrolyte species. Experimentation may therefore be required in order to fully assess die operability useMtjess of a particular combination of electrodes and ionic conductor.

Noting these considerations it is believed thai one skilled in the art would nevertheless be able to determine suitable electrode materials for use with a given ionic conductor. By way of example, whe the ionic conductor comprises atrsmonium nitrate, possible combinations of electrodes include steel, alloy and graphite, titanium and graphite, aluminium and graphite, iron and graphite- and iron and titanium, nickel and titanium, nickel and graphite, steel alloy and activated carbon, zinc and activated carbon and zinc - 50 - and graphite. Here reference is made to vising carbon as electrode material wish the carbon being in the form of graphite or activated carbon. It may be possible also to tasks- use of graphene, or other carbon structural fort!! as electrode material. 5; should be noted thst in the case of generating electricity fern explosive emulsions (eves when de ulsiSed), some combinations will be incompatible due to potential reactivity resulting in nndesired events. It is thus preferable that ail components of this electrical generation system are inherently utmacuve, or have been rendered mweactive by methods known to one skilled in the art, with components of the explosive emulsion and/or. its entirety. The positive electrode should have a large elec rocheraicafly accessible surface area {i.e., surface area for contacting the ionic conductor), for example up to, or exceeding 20O0n Vg and retain acceptable activity throughout she discharge. Equally, the negative electrode must also have sufficient surface area and retain high activity throughoat the discharge. A variety of different cell configuraiions may be employed, for example including planar arrangements, spiral ound cells and bobbin cells, as illustrated in Figure 1. Typically, the volume of ionic conductor in contact with the electrodes will be between 5tnl and lOOOmJ, however, cars be any volume sufficient to provide me desired electrochen cal energy.

The electrodes may be mounted on a suitable housing that is adapted to allow the electrodes to be immersed in an explosive composition during use. The present invention extends: so a device comprising such an arrangement. The housing may include means that allow ii to be connected or fitted to a contained explosive charge as might be required, such as to a booster shell. The housing y also include means that allow electrical ajKisectton to the electrodes. Lead wires may therefore be provided.

The invention rosy be used to provide electrical power to a device used for initiating an explosive. The device may be an electric or electronic detonator or a wireless electronic booster or other device intended to initiate a explosive, for example, the device may achieve initiation of an explosive by irradiation of explosive with a suitable wavelength of light light source, such as a laser. - ! 1 - its the device the electrodes may be electrically coupled or not depending upon the Intended activation mechanism for electricity generation. The device may aiso include one or more additional components such s charge storage devices, aad components feat provide specific functionality. The present invention may be used as a source of electrical s energy to provide power to an electric or electronic- detonator to control operation thereof, it; the ease of an electric detonator this may simply be to iite the detonator. i» electronic blasting systems the present invention may be used to provide electrical power to support 3 variety of other fetctsonslities. For example, its electronic blasting systems, the invention may be applied to provide power to a component or sub-system for {two-way} so communication. Here it is envisaged that the vention may be used so provide power to allow electronic detonators within a blast-hole to communicate with control equipment. In the same wa the invention may be employed to power a communications component or sub-system of a wireless electronic booster so that the booster cat! communicate with control equipment. Thus, thi aspect of the invention may h particularly useful in the

(5 contest of a wireless initiation system. For a wireless network she cell voltage requited to run most commercially available microcontrollers is between 3.1 and 4V. This may determine a number of design elements, such as wherher it is better to connect several cells in series, or design arid build an electronic booster circuit, or a combination of both.

20 The invention stay be used to supply all of the electrical energy necessary to power a device, component or sub-system in order to achieve desired functionality. However, the invention m also be applied to supply only a pari of the electrical energy so required with further energy coming from another source,

25 in an embodiment of the invention an explosive device may be provided with a built-in power source (e.g. a battery) that can supply sufficient electrical energy to power required functionality mat is not directly related to, or sufficient for, initiation of the devsce. in this case electrical power for initiation may be generated in accordance with the present invention whets the device is used in the field. Desirably, the built-in power source is

38 incapable of supplying sufficient electrical power to cause initiation of the device. TMs has safety advantages because until the device is bei tg used is the field if is inherently s fe, even if there is some malfunction in she device whereby an itatlation firiRg circuit receives power from the built-in power source. By way of ex mple, a wireless booster may be provided with a low-power battery to drive comimjnjcatiotis and/or sensor iwsciionality, wiih the battery output being inadequate to ike the booster. The booster is therefore inherently safe, for example when transported and stored. The power for firing the booster may be generated Srt accordance with th present invention when the booster is used in she field. Prior to such use inadvertent initiation is not possible.

In genera! the expression "wireless electronic booster" encompasses a device comprising an explosive charge to be actuated by actuation of an associated detonator. The booster xna be associated with or comprise a detonator, mm preferably as electronic detonator {typically comprising at least a detonator shell and a base charge). Further examples of wireless electronic boosters are described in international patent publication WO 2007/124539 published November 8, 2007. winch is incorporated herein by reference.

The present invention may also be at: enabling technology for a whole series of ancillary (function specific; devices. This includes, for example, telemetry sensors to indicate, blast-hole conditions (e.g. to detect elevated temperatures in reactive ground applications or to detect water ingress in holes for detonation fume control) or in fact any devices, including potentially those whose power usage is higher than that delivered by batteries.

It is also desirable to control when electricity generation begins and that rate at which power Is delivered for storage. Ibis in tern will depend upon the context of use. associated operating parameters and safety considerations. For example, it may be desired for a device to become active/live only after a predetermined period of time, after which the device or devices has/have been located at a desired position. The reaction kinetics of the electricity-generating reactions will be relevant here, although other control mechanisms are possible, including stimulus-response mechanisms. When the ionic conductor is the explosive composition per seMs control may be achieved by controlling when electrically pre-coonected electrodes are contacted with ionic con itio; and/or when electrically unconnected electrodes i contact with ionic conductor are connected, hi this case one or boils electrodes may be co ted with a passivating material that is gradually consumed when She eiectrode(s) contact ihe ionic conductor thereby causing the electrodes) to contact she ionic conductor directly with a galvanic eeis thes being treated. Burst-disc technology may also be used to release/expose the electrodes as required under blast-hole pressures. Ihe idea ©fusing a burst disk is to limit exposure of ihe electrodes until the device is under some hydrostatic pressure, for exam le wh n placed its an explosive er&ulskm filled shot-bole. Pressure alone may trigger ingress of the- emulsion iato the cell, so the device is totally inactive until the disk lias burst Another example that may provide a means to allow generation of decides! power following deployment of the ower source includes designing die system for suitable capillary action movement of ionic conductor o er the electrodes.

When some form of mmMpuladon tt xsfortnation of the explosive composition is required in order to produce the ionic conductor, the rate at which this is done may be used for control purposes. When it is necessary to break an emulsion explosive composition to yield a discrete aqueous salt phase that will function as ionic conductor, control may be achieved based on when s dernulsifxer is contacted with the emulsion and/or the reaction kinetics associated that contact, in this case it may he appropriate to introduce the demulsxfser in a controlled fashion at the electrodes so that & galvanic cell is activated at the correct time to enable electricity generation to begin. This should be done without compromising the remainder of the emulsion explosive.

By way of example, ihe dernu &sr m be provided ss a costing on one or (usually) both electrodes with the dernnlsiSer acting on emulsion between the electrodes when the electrodes and emulsion come into contact. Such things as the reaction kinetics (based on the intended operating environment) and electrode spacing/volume of eraulsion between the electrodes will influence when thai portion of emulsion between the electrodes is sransfonned into ionic conductor and feus when electricity generation begins. In another embodiment burst-disc technology ma be used to release deroulsifier or expose the electrodes as required under b!ast-bole pressures. Equally by example, the deroulsifier can be microencapsulated within particles des gned to release the agent under blast-hole conditions,

S

Similarly, when formation of ionic conductor involves dissolution of prill, control may be achieved based on when solvent is contacted with the emulsion and/or the dissolution kinetics. Burst-disc technology may be used to release solvent or expose the electrodes as required under blast-hole pressures. A m riad oi ^' other mechanisms, preferably for 50 aqueous, solvent containment, exist that could be applied to this purpose.

I: will be appreciated that in these various embodiments rates of reaction and dissolution may vary depending upon prevailing conditions of isse, such as temperature, pressure and concentration of reagents. These variables may be takes into account when implementing : s the present invention.

In the cases whe e the explosive composition must be modi&ed¾aasfonned in some way in order for it to function as an ionic conductor, when the electrodes are electrically coupled may also be a control option.

30

Typically, it is desired that the methodology of the present invention generates s steady {and relatively low) level of electricity, which is expected to provide safety advantages whilst maximizing the electricity-generating life-time or practically useful she!f-tirae. For example, typical electricity generation will range from 0.1 mA to 10mA, operating at IV to

25 5V. This steady electrical generation may be used to power an energy-storage device {for example a capacitor or super-capacitor), or less preferably directly power a coupled device. Discharge of the energy storage device can then be used as required, for example to control a firing circuit or other specific electronics. In this regard she charging efficiency (and cost) of the energy storage device will need to be taken into account. Super-capacitors are-

30 known to offer high energy density and rapid discharge rates required to enable driving a tiring circuit. However, their ass m&y be limited by thek background discharge rates as this might reduce system sleep-times. if the -methodology of the present invention is being employed to generate electricity for j firing an initiating system, the main reason f r requiring low-level electrical power generation for storage is to ensure that at no time is sufficient electricity generated directly from the galvanic reactions to fire the system. This will also allow the seamless overlay of existing control citcuiiry to ensure safe and effective operation of associated electronics. so The design and construction of the eiectrichy-generating cell may also be optimised for energy production. Parameters to be optimised include cell materials and geometry, electrode materials, electrode surface areas, electrode geometry and arrangement of the electrodes within the cell. It may be necessary to employ several galvanic ceils in series to ensure adequate voltages are generated, in this case the overall series resistance will need

Ϊ5 to be takess iisto account.

This design and construction may also involve measuring the maximum power point and the optimum impedance of the cell based on voltage-current curves. Matching the cell impedance is a design goal for achieving die most cost-effective final design. The power

20 generated by the eel! will usually be measured across different resistances a number of times to determine ihe maximum power point, reliability and the reproducibility of the ceil discharge. These measurements will also determine some fundamental characteristics of the cell, including hours to full discharge, total capacity, power-time profile and possible modes of failure. Changes to ce. design and electrode geometry may be necessary to

25 optimise power output. During the design phase the temperature of the electrodes may also be measured periodically to check whether the current flowing leads to any heat generation in the cell

The design and choice of materials of construction may also be influenced by the 30 robustness required taking into account intended contest of use. Cost may also have at! impact on design and materials selection. Another design variable is inter-electrode spacing and it! tuns this will tenpac! on the ovetafi size of the ceil and ihe amount of Ionic conductor ased. Hers the equivalent series resistance of ihe galvanic ceil will go up as the intet-eiectrode spacing goes op. Hits will also enable she number of electrodes in series to be altered to boost the overall voltage available if desired. If the negative electrode does passivate during reaction, different electrode materials may be used to test their effectiveness. Surface treatment of the electrode will be kept to a minimum initially to avoid the need for a costiy pre-trastrneftt step.

Embodiments of the present .invention are illustrated with reference to ihe following non-limiting examples.

Assuming a galvanic couple behaves ideally (that IK. thai ail electrochemical reactions generate currents that flow its ihe external circuit), Faraday's laws predict that the amount of charge la Coulombs, Q, which will be generated because of an electrochemical reaction, is: ) ·· ^■ n ^■' ■ ^■ } where » is the number of electrons involved in ihe electrochemical reaction, m is the mass of eactara consumed in grams, A is the atomic (or molecular) mass of the rcaoant and F is Faraday's constant.

For example, if 10 grams of iron is consumed by oxidation to , then the number of Coulombs generated by this reaction is: Q = 2 x 10/55.85 x 96485 - 34,551 Coulombs. The energy getisrated, J. {in joules) is simply Q multiplied by the vehage of the galvanic couple, E:

Or, by combining (i) aad (2>:

Using the example above and assuming the galvanic couple generates a voltage of 200 afV fa conservative figure- for this work), then the energy generated by the electrochemical reaction is:

0.2 x 34,55! ~ 6,9)0 J

For atmparison. art alkaline ioagUfe AA battery stores approximately 9.400 J. Ihe power is simply the instantaneous rate at which energy is generated:

P ^< * dQ/ds E (4) which is more recognisable as::

!' ·- iE (5)

The power output cannot be determined unless the rate at which the iron was consumed is kflovwt. However, this rate is one of She fundamental experimental variables that is routinely measured: the ekctroche nkaf current. /.

Exaasaie

Mmertais and. methods Ammonium nitrate emulsion formulations

A range of ausmonium nitrate emulsions were used so deiertnine the effect that varying Ibrrsttlations raay have on the generation of potential in a graphite/iron galvanic ceil ANB Coal V2P is a standard arjuno um nitrate emulsion used for the manufacture of a number of eofsmerda! bulk explosives, lis composition is set out in Table i below.

Table 1

Raw Materia! % In Fennafsrtsoa

Ammonium

Nitrate 69.45

ater 22.92

Acetic Acid (?5%) 0.17

Thiourea 0,05

Soda Ash 0.02

E25 66T J .04

Paraffin Oil 4.66

Csnoia Oil 1.70

E2S/66T is a surface active agent, used an etnulsi&er. Urea is used a an inhibiting agent to eas re compatibility of emulsion explosives in reactive ground conditions.

To investigate the effect that u ea may have on the generation of potential in the iron/graphite galvanic ceil, the inhibited emulsion fonnulaSon - ANE 230 was investigated, see ^' fable 2. Zonyl is a ftuorosurfactant used in some products, predominately underground, as a babbie stabtiiser lo optimise babbie retention and distribution dusii.g seasitizatioa of she emulsion wife gas bubbles.

Table 2

Raw Material % ia Formulation

Ammonium

Nisr ie 71.15

W&tet 20.38

Urea 1.64

Acetic Acid (75%) 0.17

Thiourea 0.14

Soda Ash 0,0.2

K7.S/6ST 2.:H

Paraffin Oil LSI

Canoia Oi! 2.34

Zcmyi 0.01

A high araraonium nitrate fornmiaiion, ANE Extra, was mvesttgaieci to determine the eifeet thai as iticreased ssBnion urn nitrate content emulsion -will have oa the generatioss of potential in the graphite/iron galvanic ceil, see Table 3.

Table 3

Raw Material

Ammonium

Nisme 76.78

Water 15.49

Acetic Acid (75%) 0.17

Thiourea 0.05

Soda Ash 0.02 W

- 20 -

E25/66T Ϊ.80

Distillate 5.70

A dummy emulsion was formnkted for ease of transport and use in the laboratory, complying wit the various codes f transport and security surrounding ammonium nitrate; see Table 4.

Table 4

Raw Material

Ammonium Nitrate 32.55

Ammoni m

15.8!

Sulphate

Urea 1.63 :

Sodium Ace-ate 0,09

Acetic Acid (75%) 0J 7

Thioruea 0.09

Water 42.66

E25/66T 2.52

Canola Oil 2.52

YK-DBO 1.93

1 L dyne S300 0.0 s

YK-DBO and Lodyne 300 are not expected to participate in the electrical generation ΐδ reaction. ΥΚ-.013Ο is a hydrocarbon thai will act as fuel during co»t ustioii/di»o«ation.

ILcdyne S300 is a surface active agent with desired wetting properties.

Galvanic celt Experiments! set up

Immediately prior to use, she iron and graphite electrodes of 3tnm diameter and lOOram Song were abraded witii fine silicon carbide paper, washed with distilled water and then dried.

A DATAQ data logger, software aad hardware was used to snessare and record the potential generated by the galvanic cell To mitigate possible compatibility issues, the copper ailigstor clips which connected the electrodes to the data logger were replaced with nickel plated sUigaior clips.

The emulsion being tested was syringed into a 40ml, capacity glass phial {see Table S). Use clean dry electrodes were then placed in the emulsion and connected ro the DATAQ data logger and the recording of potential initiated. Petxot'AG special liquid was then added to the emulsion at a dose rale of -3% w/w (see Tab!e 5). A control of 100% Petra®AG special liquid (demuisifier) was added to the glass phial. Pot consistency, the circuit of the Petro®AG control phia; was connected at the same time Petn&AG was added to the emaision samples. 'FatJte 5

D¾is C. ^' nset Em hkm Emalsktfs Mass (g) Petro®AO Mass (g)

1 Dummy ANE 30.02 1.03

2 Dummy AN 30.72 L06

3 Dummy ANE 29.59 5.00

1 ANE Extra ^~ " 29.92 1 .10

ANE Coal V2.P 30.90 3.07

3 ANE 230 30.43 1.03

LZZ ^" - - 29.90 Experiments were set up between 3pm a d 4pm on two consecutive days of similar ambient environmental cosdiiions; temperature, etc. Measurements were made over a -24 hour period with an effective sampling rate oi~9.3/romine.

5 For all samples, the negative terminal was attached to the graphite electrode and the positive terminal ¾¾s attached to the iron electrode.

Resuiia and discussion

'. ^β The potential generated by the galvanic cell containing the iron/graphite electrode couple with she dummy emulsion and 3% Petro€AG special liquid is shown in Figure 2. No current is generated until the addition of Petro®AG special liquid, at which point the maximum potential is generated almost instantly. Following this initial potential generated, a decrease in the absolute potential is observed to an approximate steady state is for each sample, after -4-7 hours. Some slight variation follows, at the -18 hour mark.

This can be attributed to fluctuations in ambient temperatures affecting the rate of reaction, similar fluctuations are observed at similar times in the second trial, see Figure 3.

The potential generated using three ammonium nitrate emulsions; ANE Extra. ANE Coal 20 V2P, and ANE 230, under similar conditions to the dummy emulsion, and {100%) Pet ^j roSAG special liquid are shown ia Figure 3. Similar to the dummy emulsions, addition of PelxottAG resulted in an immediate response and generation of potential. However, the initial resp nse is not as drastic for the ANE 230 and ANE Extra samples. The maximum absolute potential is generated after the initial activity when a steady state is achieved after 25 -4 hours.

The Coal V2P sample more closely resembles the dummy emulsions with a peak absolute potential occurring at -45 minutes after Petro®AG addition. The recurring theme of ail emulsion samples investigated suggests a bimodal mechanism whereby the addition of 30 PetrofsAG solution results in an immediate ptstesrttiat generation, which slowly equilibrates to a "steady state" reaction after -4-7 hoars. The mechanism for the initial potential generate seems to differ with the lower arnrnoaium nitrate containing samples generating a peak absolute potential in the initial rrwdianism; when compared to she higher arettnoni tn nitrate containing samples, where a gradual increase in absolute potential generation until steady state is observed. Although the slight variation between A E Coal 5 V2P and ANE 230, 69.45% ammonium nitrate to 71. ί 5% arnmonsurn nitrate, respectively, may not be significant enough to explain the observed difference.

The i 00% Petro®AG special liquid sample generated a peak absolute potential at a slower rate than the 'low" ammonium ntSrale emulsions, Dummy and Coal V2P. It is evident that if) the generation of potential with the iron/graphite electrode couple is not reliant on the presence of nitrates from the emulsion, but can be generated by the presence of Petro®AG- liquid only. Unsurprisingly, the mode of potential generation in the Petra€>AG liquid sample is simpler than fee cmuision Petro®AO samples, with only a single mechanism of potential generation, suggested by the uniform increase in absolute potential up to the

^■ 5 steady state. Similar to the emulsion/PetrotiAG samples, the neat ΡβΰοΦΑΟ sample displayed ftuciuations in potential generated, consistent with the warning of lab conditions due to the time of day.

A small quantity of bubbles were observed forming around the surface of the graph e 20 electrode, this is likely the formation of nitrous oxides as nitrates are reduced. The production of gaseous by-products should be considered when applying the technology, as hydrostatic pressure at the bottom of a column may result in equilibrium conditions which reduce the observed rate and magnitude of redox reactions at S ^' FP.

25 The data generated in these experiments is a {unction of the distances of the electrodes from one another and the diffusion of charged species through the solution, as is relevant for the generation of potential. As the electrodes are further removed from one another, the rate of reaction will become more dependent on the transfer of charged species through ionic conductor. The experimental set up did not strictly control the proximity of the

30 electrodes, particularly towards the bottom of the glass phial. Given the small size of the cell and the highly conductive solutions used, it is possible that slight variations in elecirode distances did n t play a large role is the quantitative data generated. Although the si nificant variation in the data generated across the three identical cells in Figure 2 is possibly the result of th s phenomenon.

5 Conclusions

The ass of a graphite/ires electrode couple in a dummy amsnoniam nitrate emuis.on/Petro¾iAG liquid mixture generated a reliable potential, and this effect was validated on several ammonium nitrate emulsions.

The mechanism of potential generation is likely binjodal, with observed variations in the initial potential generation mechanism in different fonsrusauons. prior to an ap arent steady state about 4-7 hoars after Petro^AO liquid addition.

IS The magnitude of potential generation is ismpe arare dependant, coinciding with iie temperature dependence on the rase of reaction, it is aiso li.keiy that the generation of gas a: the graphite electrode adds a pressure dependence on the rate of reaction and magnitude of potential generation.

20 Example 3 in this essrepie a simple method for testing a number of galvanic couples in an emulsion is described. Two experiments were run using this method, .in which the voltages generated by ten cortpies across a megaohm (JO ⁶ CI) resistor were recorded. These experiments ran ?.S for between 530 and 160 h and aimed to test two main variables:

I . whether any of the couples would be capable of generating power from within the an (unaltered) emulsion

30 2. whether certain surfactants for 'breaking" the emulsion would assist in power generation. The nature of she em sian

The emulsion employed is & 90:10 w/w aier-in- i] trrici¾emuisioc, in whic the aqueous phase is a super-saturated solution of ammonium mwe, importeBily for this works the micron-shsed droplets of the waier phase are completely isolated from each other by thin films of oii, surfactant ars other additives. This makes the emulsion electrically resistive, in this state, it is unlikely thai any galvanic couple will generate power, because ionic conduction through the emulsion will be vsaishing!y small. A s rtkeiam that was known to be particularly effective for breaking this emulsion was also employed.

In this experiment for safety purposes a ηοα-detorsating Mammy ^* emulsion of ammonium sulphate was used. This 'd mm ' emulsion contains 44% w w ammonium nitrate in the aqueous phase, the amount that mast b;; exceeded for detonation to occur within a confined vessel. The formulation of this Mummy' emulsion was approximately 44% ammo-m m nitrate and 16% ammonium sulphate in the aqueous phase. For the purposes of this work, it was that considered this emulsion would behave similarly to a 'real' emulsion explosive. This is because the dilution of the nitrate concentration, due to the addition of sulphate is not significant for the electrochemistry. In addition, the presence of the sulphate ton is believed to be irrelevant, because is is not involved in the anticipated electrochemical reactions.

Also for safety reasons the experimental apparatus was operated inside a fume hood to minimise the possibility of reaction products, such as oxides of nitrogen, contaminating the laboratory.

The cells used - glass phials with 40 ml capacity ~ were mounted in a custom-built polyethylene base for stability. Loose-fitting caps machined from Deirin. into which two 3-niffl holes had been bored fot locating she electrodes, were used to minimise contamination from dust and debris (see Figure 4 for the experimental arrangement). The electrodes were made from 3-tnns diameter rods of nickel alloy type 20! (Ni), stainless steel iype 316 L <SS), aluminium alloy type 4043 A (A¾ sJt&ni m (Ti), tool steel type A2 (IS), iron <Fe) and graphite {(¾). Typical coxnpositioas of i s alloys are given below. s Aluminium alloy iype 4043 A

Ekrsem Si F« Ca Mn Mg Xf! Ti

Weight % 4.5-6.0 0.80 0.30 0.05 0.05 0.10 0 70

Nickel alloy type 201

Element Ni Cu Fe Mn e Si S

Weight % 9 ^f i.O min 0.25 tnax 0.40 max 0.35 max 0.02 max 0.35 max 0,01 max

^■ 0

Stainless steel type 316 L

Tool Stael type A2

i s

Element C Cr Kit Mo V" j

Weight % ⁵ \ 5 0.3 1 o.is-osj

A Ssed amount of emulsion (30 * i g) was placed into each cell at the start of the experiment. The selected electrode pairs were abraded on clean silicon carbide- paper, washed assd dried before being placed into the cells through holes drilled into the Beirin 20 lids. Pairs of leads tertninated with alligator clips provided electrical connection so the data tagger. The surfactant used for 'breaking' the emulsion was PeiroCI- AG: a commercially available liquid comaicsaig predominantly sodium alkyI«aplifl¾¾ienes«Ifonat«. fc was added directly to Use surface of the emulsion at a concentration of 3% w/w (approximately I g per celi). Voltages generated by the electrode paiis were recorded by a data logger from DATAQ (Ohio, US) controlled using DATAQ's proprietary software kDAQ. The data logger allowed up to eight difemtia!-input channels to be recorded simultaneously. The input impedance of the data logger was ί Ω. Text isles recovered from the logger were reduced in size using a method that did not bias she data and the results were plotted using Microsoft Excel

In a separate experiment, the 'breaking' of the emulsion by the surfactant is a single ceil was recorded by time-lapse photography. The experimental conditions were identical to those used in the energy generation experiments. A Logitech HD Pro C i0 webcam controlled b F!k software from N mtsis ( ¾t^://mw.niraisjs.corn projectssi'flsx.plip>) was used to sake images of the emulsion in the cell every 10 ram for ?2 h. The surfactant was added alter the first how. The resulting images were converted into a single animated gif image using Gimp software (<http://www.ghnp.org >).

Reitslls

Plots of the data recovered from all twelve galvanic couples are- shown in Figures 5 aad 6. In these figures TS - Tool Steel, type A2, SS - Stainless Steel; Gr ^« Graphite, AN sol 33% ~ aqueous solution of ammonium nitrate 33% w w. In each experijnenl. five couples were immersed in the emulsion, and one couple was immersed ia a 33% w w aqueous solution of armnoniurn nitrate for comparison. In all cases, the conductor listed first in the pair was connected to the positive terminal of she data logger.

Experiment Q!

Experiment OJ used i-l i, Al-Ni, Al-Ti, Ai-TS and Fe- ^' Π immersed in the emulsion, and Al-TS immersed in the 33% ammonium nitrate solution. -The experiment was allowed to run for approximately 47 h before the surfactant was added, to test whether any of the couples would begin to generate a voltage from the unaltered emulsion. None did to any significant degree. However, upon adding the surfactant, the effect was immediate. All couples shoved a strong response. The Al-Ti couple recorded a voltage of almost -0.6 V initially, bat then begat! to passivate and continued to do so througboai the next SO h. A similar, but smaller, response was measured for the Ai-Ni couple, Is contrast, Pe-Ti and Ni-Ti showed a slower initial increase i voit&ge, ut their responses persisted or increased with time, with the Fe-Ts couple reaching -G. V after 80 h. The Ai-TS pair was unusual, in that is increased isnraediaiely to about ÷03 V and stayed close this potential thereafter, !n contrast, the couple immersed in the ama-ostium nhrate solution behaved erranc&Uy: a common tespoose when electrochemical reaction rates are low. The reason this couple behaved differently con-spared with the identical coapie immersed is?, the emulsion is not dear. iixperh m 02 The main reason for running a second experiment tss to test the effectiveness of Gr as an electrode material. The electrode pairs used were SS-Gr, T -Gr, Ah-Gr, Fe-Gr and SS-Ti its the emulsion, and SS-Gr in the 33% ammonium nilraie solution. Again, none of she electrode pairs generated significant voltages until the surfactant was added. Only Ai-Gr and Fe-Gr generated voltage whose absolute value was greater than 0.2 V 24 h after the addition. Furthermore, the Αϊ-Gr couple showed a slow passivation of its response, reaching -0.2? V after 1 7 h. In contrast, ihe Fe-Gr couple maintained -0.6 V or greater throughout ihe entire experiment, a most pleasing result and the best of any of the couples in either experiment, in this, experiment, the couple immersed in the ammonium nitrate solution behaved mote predictably and pve a similar response to the same couple immersed in ihe emulsion: a sharp initial rise followed by a slow decay.

Data from this study has identified that the low-surface area of the graphite electrode limits the power available. Preliminary trials to replace the graphite- with high surface-area activated carbon has significantly increased power ou¾>ut to levels relevant to foreshadowed applications. Figure 7 below demonstrates this effect, in relation to this figure She top panel shows the power-response curves of rod-shaped iron-Graphite electrode airs, in the lower panel the graphite- is replaced with high surface-area activated carbon. The circles are drawn at the equivalent resistor levels and demonstrate a very significant increase in power output. Time-lapse photography of emulsion breakdown

The addition of surfactant0% sodium alky aphthyiwiesuiibnste (Petro®AG) had an immediate impact on (he voltage recorded on nil of the galvanic couples tested. However, (he visible changes produced to the emulsion wete far slower, so time-lapse photography was used to measure the speed at which ihe emulsion broke down. The ssrrte ex erimen s., conditions as tor the voltage measurements were used for this experiment and the images recorded show the emulsion takes between 3 and 4 days to completely break down. Four selected images from entire sequence of images captured are reproduced i n Figure 8. Discussion

The voltage responses recorded on four galvanic couples Fc-Gr, Al-Or, Fe-Ti and Al- TS - indicate these couples may offer ihe possibility of generating energy from ammonium nitrate emulsions, as iong as the emulsion is broken.

While these results are encouraging, they do not indicate how much energy these galvanic couples might provide. Kinetics factors, such as diffusion of reactants and/or products, precipitation of insoiubie materials and adsorption of passive compounds, could all play a role in limiting energy production in aa emulsion. The measurement of energy production from cells designed to optimise their electrochemical activities would be desirable. it -was noted that the rate at which the emulsion broke down in the experimental arrangement uaed for the voltage measurements has a similar time constant to the decay rates exhibited by some of the voitage~thae curves. On this basis, it is tempting to equate the two processes, but such an interpretation may be overly simplistic. If fresh electrode surface is constantly being exposed during emulsion breakdown, then a more constant voltage-time curve would be expected. However, if passivation processes do sake place within the emulsion, then slow breakdown could also be desirable for sustaining «oetgy generation. The srnali periodic variation in all traces roost likely results &om daily temperature fuactuatiotis in the Laboratory. The large spike at 120 h in the Fe-Gr couple was a de iser&ie <fiseomec«iott.

Conch&iam

A method for generating electrical energy from a proprietary nitrate sulphste-corstainisg water-La-eil emulsion using galvanic couples has been identified. The initial tests show that three couples - iiotwitaniura, aluminium-tool steel and iron-graphite - can generate a significant voltage at close to open circuit concisions, but only otioe the emulsion has been ^ roken' by the addition of a suitable surfactant. The imact emulsion effectively blocks ionic transport between the galvanic couples and hence, inhibits all electrochemical activity. This could be & positive asset, as it may provide en effective chemical switch for the energy generation process. The responses of the galvanic couples to the addition of surfactant were immediate, although time-lapse photography showed the emulsion takes three to four days to completely break down. This slow rate of degradation may help provide sustained power generation.

The results of the rests described in ibis report are considered sufficient to plan the next stage of the project

Example 4

In another exemplification the positive electrode is constructed from activated carbon and the negative electrode from zlne. Individual cells can be stacked together to boost the overall voltage and many different forms of the cell stack can be envisaged. Two examples demonstrate the utility of this exemplification.

Electrodes are constructed from piste m& activated carbon with dimensions of lOOntii- x I item. A cell stack is formed by arranging two unipolar electrodes at each end of the slack and the desired number of bipolar electrodes within the stack. The electrode arrangement is thus:

(positive) AC! Za-ACj Zn-AC'l Zo-AC....i¾s-AC i¾j (negative) where Zn-AC denotes a bipolar electrode and the vertical line indicates a cell space to be filled by solution. The dashed line represents an electrical connection.

The unipolar electrodes are a zinc sheet and 3 rectangle of activated carbon doth attached to a rigid PVC sheet. The bipolar electrodes ate an cti at d carbon cloth attached to the insulated back of a zinc sheet. Electrical contact is made between the activated carbon cloth and the xinc sheet using electrically-conductive, adhesive copper tape. These electtodes form the body of the stack and the ceil void is de fitted by a 3mm thick nitrite rubber gasket, cut so as to seal the sides and base of cell. The stack is clamped together firmly to seal the individual cells which are Sited with emulsion during assembly (Figure 9 below), in relation to Figure 9 this illustrates a three-ceil stack showing the individual components (left) and when fully assembled (right).

£m ?kJ

Individual cells are made from glass vials of the desired sfee. Electrodes ate made from 2i»c spray wire (2.5mm diameter x 90mm) and activated carbon cloth (40ram x SOrnrn) wrapped around an inert current collector (titanium or stainless steel rod. 3mtn diameter x 90mm). This electrode assembly is clamped firmly in position and individual cells are connected electrically thus: (positive) ACjZu-AC!Zt5-AC|Zn...ACiZn (negative) where the vertical line indicates a call space to be fsllesi by solution and ths das represents an electrical connection. Any msraber of these ceils may be connected as required (see Figure 10). In relation to Figure 10 this illustrates individual components (left) ami when Iwily assembled (right).