WO2007070934A1

WO2007070934A1 - Explosive composition

Info

Publication number: WO2007070934A1
Application number: PCT/AU2006/001923
Authority: WO
Inventors: Vladamir Sujansky
Original assignee: Orica Explosives Technology Pty Ltd
Priority date: 2005-12-22
Filing date: 2006-12-18
Publication date: 2007-06-28

Abstract

An explosive composition comprising: a liquid oxidant; a fuel comprising particles of energetic material homogeneously distributed throughout the liquid oxidant, wherein the energetic material is capable of reacting with the liquid oxidant at elevated temperature to release energy, and wherein the particles of energetic material comprise shock-sensitive particles for which reaction between the energetic material and liquid oxidant can be shock initiated and secondary-initiation particles for which reaction between the energetic material and the liquid oxidant can be initiated by energy released as a result of reaction of the shock-sensitive particles and the liquid oxidant.

Description

EXPLOSIVE COMPOSITION

The present invention relates to explosive compositions and to the manufacture thereof. The invention also relates to the use of explosive compositions in accordance with the invention in blasting operations.

Explosives used in commercial blasting operations typically include ammonium nitrate as principal oxidiser component. Bulk explosives, for example, will generally include as much as 70 to 85% by weight ammonium nitrate. Whilst widespread and generally effective, the use of ammonium nitrate is not without drawbacks.

One problem with the use of ammonium nitrate-based explosives is that under certain conditions they can produce large amounts of yellow/orange fumes in the gases produced on detonation. These fumes contain nitrogen oxides as a result of incomplete reactions during the detonation process. Such "after blast" fumes are very undesirable from an environmental perspective and it would be useful to provide explosive compositions that are more environmentally friendly with respect to the detonation fumes that are produced.

The heavy reliance on ammonium nitrate for blasting operations also has the attendant problem that a shortage of supply of this compound has potential to cause significant disruption to blasting operations. It would therefore be desirable to provide alternative explosive technologies that are not reliant on ammonium nitrate. For an alternative technology to be acceptable to the industry it must be capable of providing at least equivalent blast energy on detonation when compared with conventional (ammonium nitrate-based) explosives. It is also important that any alternative technology is easy to formulate using conventional equipment and methodology, and that it is not prohibitively expensive.

From a safety perspective it would also be useful to provide an explosive composition that is stable under normal conditions of storage and transportation etc. and that may only be detonated by significant energetic input. Such compositions would be safe to formulate and handle. The present invention seeks to meet these needs by providing an explosive composition comprising: a liquid oxidant; a fuel comprising particles of energetic material homogeneously distributed throughout the liquid oxidant, wherein the energetic material is capable of reacting with the liquid oxidant at elevated temperature to release energy, and wherein the particles of energetic material comprise shock-sensitive particles for which reaction between the energetic material and liquid oxidant can be shock initiated and secondary-initiation particles for which reaction between the energetic material and the liquid oxidant can be initiated by energy released as a result of reaction of the shock- sensitive particles and the liquid oxidant.

The present invention relies for explosive output on the release of energy due to the reaction between the energetic material and liquid oxidant present in the explosive composition of the invention. Thus, the energetic material and liquid oxidant are selected to be exothermally reactive with one another. The energetic material will not be reactive with the liquid oxidant under ambient conditions since the energetic material will include on its surface a passivating oxide layer. This oxide layer prevents further oxidation of the energetic material. This means that the explosive compositions of the invention are stable and non-hazardous prior to initiation. Reaction between the energetic material and the liquid oxidant is however activated at elevated temperature and by this is typically meant above 500°C, preferably above 750°C. This is believed to be due to the fact that at elevated temperature the passivating oxide layer is disrupted, possibly by cracking and/or melting, thereby allowing the energetic material and liquid oxidant to come into contact with each other. Preferably, the energetic material and liquid oxidant are highly reactive towards each other so that large amounts of energy are released when the reaction proceeds/has been activated. Having said this, by selection of suitable combinations of energetic material and liquid oxidant, the energy released by an explosive composition of the invention can be manipulated and tailored, as might be useful in practice. The kind of exothermic oxidation reactions referred to above are well known. For instance, there are a number of references that describe initiating water-metal type reactions. Common to these references is the appreciation that a significant energetic input is required in order to activate the reaction. For example, some researchers describe initiating the water-metal reaction by high power electrical discharge into a water-metal (aluminium) mixture. It is reported that the reaction proceeds explosively but it has not been found to be self-sustainable under ambient conditions. The ability for an explosive composition to sustain detonation is an important property since the composition will typically be provided as a column/continuous length in a blasthole. It is also relevant to note that initiation using electrical energy is unlikely to be practical in the field due to the need to employ a cumbersome power supply, high voltage electrodes etc.

Other researchers have reported that the water-metal reaction may be im^'tiated using conventional explosive detonators or primers. This is a preferred initiation method from a practical perspective but, again, it has not been possible to provide compositions that are able to sustain detonation after initiation.

The explosive compositions of the present invention may be shock-initiated using conventional detonators or primers, and are able to sustain detonation once initiated. This is due to the form in which the energetic material is incorporated in the explosive compositions. On the one hand, the energetic material is provided in a form such that reaction with the liquid oxidant can be initiated/activated by subjecting the composition to a high-pressure shock wave, as may be generated using conventional detonators and primers. Herein these are referred to as "shock-sensitive particles". These particles are believed to comprise gas bubbles associated with particles of the energetic material that have a relatively high surface area. In this context the term "associated" is intended to mean that gas bubbles are present at the surface of, or in close proximity to, the (high surface area) particles.

On the other hand, the energetic material is provided in explosive compositions of the invention in a form such that reaction between the energetic material and the liquid oxidant is unlikely to be shock-initiated. Rather, reaction of the energetic material making up these particles can be initiated/activated by thermal energy released as a result of the shock- initiated reactions described above. Herein these particles are referred to as secondary- initiation particles. These latter particles have a relatively small surface area when compared with the shock-sensitive particles.

It is believed that the shock-sensitive and secondary-initiation particles perform different but equally important roles in the explosive compositions of the present invention. Without wishing to be bound by theory, it is believed that when an explosive composition in accordance with the present invention is initiated using a conventional detonator or primer, the resultant high pressure shock wave propagating through the composition causes gas bubbles present in the composition to be compressed. This compression results in the creation of localised "hot spots" and at least some of these will be located at the surface of, or adjacent to the surface of, shock-sensitive particles of energetic material. These "hot spots" are believed to cause rapid and significant localised heating. This may cause disruption (by cracking and/or melting) of the oxide layer normally present at the surface of the shock-sensitive particles and/or melting/vapourisation of the energetic material making up those particles. The result is that the otherwise passivated energetic material will come into contact with liquid oxidant in the composition. An exothermic oxidation reaction then proceeds with release of energy.

This shock-initiated reaction of particles of the energetic material is thought to be related to the surface area of the particles, and it is believed to apply for particles having a relatively large surface area, for example from 3 to 50 m²/g, such as from 5 to 40 m²/g, energetic material.

As noted, the shock-sensitive particles are distributed homogeneously throughout the explosive composition. Propagation of a high-pressure shock wave through the composition will therefore have the effect of initiating reaction between the shock- sensitive particles and liquid oxidant as a result of the creation of "hot spots" throughout the composition. The shock-initiated reactions will have the effect of rapidly raising the temperature behind the shock wave as it propagates through composition and the effect of this will be to disrupt the passivating oxide layer on the surface of any unreacted particles of energetic material and/or vapourise the energetic material, thereby activating the reaction between the energetic material of these particles and the liquid oxidant, thereby releasing further energy. These (latent) reactions are contingent upon the thermal energy released by the shock-initiated reactions and as such will occur behind the propagating shock wave (the C-J plane). These secondary-initiated reactions are believed to be responsible for the explosive composition being able to sustain detonation once initiated by suitable shock.

The secondary-initiated particles will have a relatively low surface area compared with the shock-sensitive particles, for example from 0.3 to 1.5 m²/g, such as from 0.8 to 1.2 m²/g, energetic material.

Thus, the explosive composition of the invention comprises particles of energetic material that serve different functions based on surface area.

The shock-sensitive and secondary-initiated particles may comprise the same or different energetic material. Herein the expression "energetic material" denotes any chemical element that may be oxidised by contact with liquid oxidant included in the explosive compositions of the invention, thereby releasing energy. Typically, the energetic material is selected from so-called high energetic metals and alloys of metals. By way of example, the energetic material may be selected aluminium, boron, magnesium, silicon, titanium, zirconium, iron, zinc, copper, nickel and beryllium and mixtures thereof. The energetic material may also be selected from alloys, such as ferrosilicon, aluminium-magnesium, and the like. Preferably, the energetic material is selected from aluminium, silicon, iron and zirconium. The use of aluminium is particularly preferred since oxidation of it releases significant quantities of energy.

When the shock-sensitive and secondary-initiated particles comprise the same readily energetic material, these particles can nevertheless be distinguished on the basis of the physical form in which the energetic material is present in the explosive compositions of the invention. What this means will become clear but by way of illustration, the shock- sensitive particles will have a smaller average particle size, and thus a higher surface area, than the particles of secondary-initiated particles.

The compositions of the present invention include a liquid oxidant for reaction with the particles of energetic material. Typically, the liquid oxidant will consist of or comprise predominantly (at least 50 wt%, preferably at least 75wt%) water. A variety of sources of water may be used, such as distilled water, tap water and possibly even seawater. The explosive compositions may include other oxidants, subject to their compatibility in the context of the present invention. If one or more additional oxidants are used they may be selected from hydrogen peroxide, nitric acid, perchloric acid, sulphuric acid, and the like.

The explosive compositions of the present invention may include other oxidant components and these are preferably soluble in the liquid oxidant that is being used. Additional oxidants include metal salts, such as metal nitrates, perchlorates and sulphates). Typically, the metal is selected from sodium, potassium, calcium, magnesium, zinc, strontium, aluminium, barium, iron, manganese, and copper. The amount of such additional oxidant components is usually less than 10% by weight of the total composition.

The explosive compositions of the present invention may also include metal oxides that are capable of reacting with the energetic material by a so-called thermite reaction. By way of example, when the energetic material is aluminium the metal oxide may be any metal oxide that can easily be reduced by aluminium, such as Fe₂O₃, Fe₃O₄, Co₃O₄, NiO, MnO₂, Mn₃O₄, CrO₃, MoO₃, MoO₂, V₂O₅, SnO₂, CuO and Cu₂O. One skilled in the art will be familiar with this kind of reaction and with the kind of ratios of reactants that will be required. In this embodiment the amount of energetic material will also be selected based on the amount required for reaction with the liquid oxidant.

When compared with ammonium nitrate-based explosive formulations, the compositions of the present invention are intended to produce at least reduced amounts of noxious detonation fumes. This is likely to influence the choice of additional oxidants to be used in the compositions of the present invention. It may be acceptable for the compositions of the invention to include a small amount (less than 10% by weight of the total composition) of ammonium nitrate whilst still providing benefits in terms of relatively low after blast fumes. Preferably, however, the compositions of the invention produce harmless after blast fumes, i.e. fumes devoid of NO_x, when used. Thus, preferably the compositions are free of ammonium nitrate and other oxidants that are likely to yield after blast fumes that are not environmentally friendly. In other words, if the compositions of the present invention do include one or more additional oxidants, these oxidants are not nitrogen- containing and chlorine-containing compounds.

As will be appreciated, for an explosive composition in accordance with the invention to be functional, it is important that gas bubbles and the particles of energetic material are homogeneously distributed throughout the composition. It is also important that once so- distributed, and before detonation, the gas bubbles and particles maintain this distribution, i.e. there is no settling or segregation. In accordance with the present invention this is achieved by formulating the explosive composition as a stable dispersion/suspension, gel, slurry or paste. Formation of such forms of explosive is conventional in the art and one skilled in the art will be familiar with the various forms may be produced. Typically, this will involve the use of a thickener that acts on the liquid oxidant component of the compositions of the present invention. Herein the term "thickener" is also intended to embrace gelling agents, cross-linking agents, and the like.

The viscosity of the explosive composition required to achieve the desired effect may vary depending upon such things as the specific gravity of the particles of energetic material and the proportion and/or size of gas bubbles present in the formulated composition. The appropriate viscosity can be determined experimentally based on the intended outcome of providing a homogeneous distribution of components. Generally, the viscosity of an explosive composition in accordance with the present invention will be from 3000 cP at 20°C (Brookfield viscometer RVT #4 spindle at 20 rpm) to 80,000 cP at 20°C (Brookfield viscometer RVT #6 spindle at 10 rpm).

As thickener, any conventional agent may be used. The thickener may be selected from natural gums, such guar gum, xanthan gum and tragacanth gum, carboxymethyl cellulose, and the like. Synthetic thickeners, such as polyacrylamide, may also be used. Inorganic thickeners, such as fumed silica, clays and carbosil, may also be used and these may provide advantages in terms of reduced fumes on detonation. The amount of thickener used is typically up to 5%, more usually from 0.2 to 2% by weight based on the total weight of the composition.

Typically the total amount of oxidant(s) present in the explosive compositions of the present invention will range from 20-90 % by weight. Preferably, however, the oxidant(s) and (the sum of) the particles of energetic material will be present in approximately equi molar ratios. Thus, normally the oxidant(s) will be present in an amount of 45-55 % by weight based on the total weight of the composition. In this case, the total amount of particles of energetic material will be from 55-45 % by weight based on the total weight of the composition.

In an embodiment of the invention it may be advantageous for the shock-sensitive particles, and possibly the secondary-initiated particles, to include a surface coating that will have the effect of holding or absorbing gas bubbles onto the surface of the particles. This may be beneficial in terms of forming the kind of particle-gas associations that are believed to be significant to the explosive compositions of the invention.

The surface coating that may be used in this embodiment is typically hydrophobic in character. By way of example, the coating may comprise a normally liquid oil component

(with a viscosity of, for example, 30 to 400 Saybolt Universal seconds at 100⁰F) and an aliphatic monocarboxylic acid. The amount of oil is usually from 10 to 90%, for example from 70 to 85%, and the amount of acid component is usually from 10 to 90%, for example

15 to 30%, by weight of the coating. The coating typically makes up from 1 to 10% by weight of the particle weight.

The oil used in the coating may be paraffinic, naphthenic or aromatic in character. The oil should not contain any species that will cause corrosion of the particles of energetic material being used or otherwise be detrimental to the explosive composition. The viscosity of the oil is such that the coating should adhere to the particles. The oil is generally a commercially available hydrocarbon oil of suitable viscosity grade. The aliphatic monocarboxylic acid is preferably a C_8-22 fatty acid, more preferably a C_16-22 fatty acid. Examples of fatty acids that may be used include straight-chain saturated acids, such as caprylic acid, pelargonic acid, capric acid, undecylic acid, lauric acid, tridecanoic acid, myristic acid, pentadecanoic acid, palmitic acid, margaric acid, stearic acid, nondecanoic acid, arachidic acid, heneicosanoic acid, behenic acid, branched-chain fatty acids, such as 2-ethylhexanoic acid, an unsaturated fatty acids, such as 10-undecylenic acid, petroselenic acid, oleic acid, elaidic acid, vaccenic acid, erucic acid, brassedic acid, linoleic acid, linolelaidic acid, linolenic acid, elaidolinolenic acid, pseudoeliostearic acid, elestearic acid, arachidonic acid. Mixtures of two or more fatty acids may be used.

When used the surface coating is provided on the particles of energetic material before formulation of the explosive composition. The coating can be applied to the particles by simple mixing of the particles and the coating components. Thorough coating of the particles is preferred.

In order to minimise or even eliminate dust formation during mixing and preparation of explosive compositions in accordance with the invention, de-dusted grades of coated particles (e.g. aluminium) may be employed. In addition to the kind of coating described, these grades comprise of a small amount of Teflon to impart non-dusting properties.

The kind of surface coating described may also be useful where additional inorganic oxidant components are included in the explosive compositions of the invention. Such components can react with particles of the energetic material and this should be avoided. The coating can be used to protect the particles against any reactive effect of inorganic oxidants, and other possibly reactive components, that may be present in the explosive compositions of the invention.

In the case of nano-metallic particles, such as nano-aluminium, it may be beneficial to employ grades in which the particles are coated with an organic polymer, for example selected from polysiloxanes and derivatives thereof, high density polyethylene, polypropylene or polymers of fiuorinated derivatives. The polymer is provided to inhibit reaction of the nano-metallic particles with oxygen and water at the kind of temperatures at which the explosive compositions would be formulated, stored and transported. Thus, the polymer contributes to the stability of explosive compositions of the invention.

The coating may also assist in the formation of stable thickened/gelled explosive compositions that require less thickener when compared with compositions that use uncoated particles. This may be particularly beneficial when the explosive composition includes an (additional) inorganic oxidant component.

The present invention also provides a method of making an explosive composition as described herein. The method involves mixing the various components of the composition in the requisite proportions and in a manner that will introduce gas bubbles into the composition. Gas bubbles may be entrained during mixing of the various components, for example by suitable agitation during mixing. Conventional mixing equipment and methodology may be used in this regard. Usually, the thickener is added to the liquid oxidant and a thickened product formed before introduction and distribution of the particles of energetic material, and possibly additional components.

It may be beneficial to mix the various types of particles of energetic material thoroughly prior to mixing with the other components of the composition as this may lead to the formation of aggregates in which air is trapped. These aggregates may assist in introducing air into the composition.

Gas bubbles may also be formed in the composition by reaction of the with the liquid oxidant. For example, and without any intended limitation, metals can react with water to yield hydrogen and the metal oxide. Normally, a layer of oxide on the metal surface will prevent this reaction. However, mixing of the various particles of energetic material may lead to some limited disruption of the oxide layer as a result of frictional effects, thereby allowing the reaction to proceed. Gas-generating reactions may be more prevalent with particles of energetic material having high surface area.

If necessary, undesired reaction between the energetic material and oxidant can be avoided by manipulation of pH. For example, it may be beneficial to adjust the pH of the liquid oxidant to about 6.0 or below, preferably in the range of 4.5-5.5. By making the liquid oxidant slightly acidic the energetic material, e.g. metallic aluminium, remains passive to water attack under normal conditions of use. Moreover, the compositions remain stable over long periods of time.

Generation and/or entrainment of gas in the explosive compositions of the present invention will lead to a slight reduction in density. Typically, the compositions are formulated to be of the highest functional density. The extent to which gas must be present in a composition of the invention may be determined experimentally based on the ability of the composition to be detonated and sustain detonation.

In carrying this invention there are various ways to prepare the explosive compositions. The actual mixing method will depend on the quantity to be mixed and the availability of the relevant equipment. It is possible to use batch mixing or continuous mixing procedures. The actual equipment can vary from a simple paddle type mixer to more sophisticated rotary mixers. Standard laboratory mixing equipment consisting of a mixing bowl and stirrer may be employed, as well as more sophisticated laboratory mixers like Kenwood or Hobart mixers. In the field it may be advantageous to use a small hand operated concrete mixer or a large concrete bowl truck.

The preferred method for preparation of the compositions of the invention involves a two- step process as follows. For the purposes of illustration the energetic material is referred to as metal.

Preparation of an aqueous sol or metal dispersion

In order to obtain a homogeneous aqueous sol, a polymeric thickening agent is predispersed in a small amount of polyhydric alcohol, for instance ethylene glycol to ensure a lump free, viscous aqueous sol. While continuously stirring the required amount of water or water solution, the syrup like polymer-glycol dispersion is slowly poured into the volume of water or water solution. After about 10 minutes standing to allow sufficient hydration of the polymeric thickening agent a homogeneous aqueous sol is obtained. There are possible variations to this first step. For example, if desired, the polyhydric alcohol may be omitted as dispersing agent for the polymeric thickener. In this case, powder materials of organic or inorganic thickeners may be premixed with particulate metal. The resulting dry blend powder is then dispersed in water or water solution, while utilising a suitable stirrer. In this instance, high shear rate design stirrer and high-speed mixers are preferred. However, a slow speed, concrete type mixer may be satisfactory.

The aqueous sol or aqueous metal fuel dispersions that are prepared by the methodology described above can be designated as Part 1— liquid oxidiser or liquid oxidiser/fuel dispersion

Preparation of aqueous explosive dispersion

The aqueous explosive dispersion is prepared by a gentle mixing of the Part 1- liquid oxidiser or liquid oxidiser/fuel dispersion and Part 2 - metal fuel powders or their blends that are characterised by very high surface area (as defined previously). Low shear mixing devices and commensurate mixing processes are preferable in order to maintain the associations between metal, water and air (gas) bubbles. Hence, it will be necessary to provide sufficient micro-bubbles in the Part 1 -oxidiser or fuel dispersion and this can be done by methods that are well known in the art, for example using various void materials, gassing and air entrainment to regulate explosive density of the aqueous explosive dispersion (usually between 0.10 to 1.50 g/cc).

It is an advantage of this methodology to provide two components (binary) that are each presented in a non-explosive state and that can be stored and transported separately to locations where the explosive is going to be used. A significant advantage is that it is possible to transport a single bag of premix of dry (fuel) materials. The simplest and most economical mixing procedure is to prepare a premix of dry powders comprising thickeners, metallic fuel powders (micro) and reactive large surface area metallic powders. When required, these dry materials are dispersed in water at the site where they are going to be used. A simple hand mixing or electrically powered concrete mixer may be employed. In one embodiment of the present invention, the secondary-initiated particles having an average particle size of from 5 to 50 microns. This corresponds to a surface area of 0.3- 1.5 m²/g. The shock-sensitive particles have an average particle size much less than the secondary-initiated particles and this corresponds to a relatively high surface area. Thus, the shock-sensitive particles typically having an average particle size of 20 to 500 run (corresponding to a surface area of 3-50 m²/g), preferably less than 200 nm, for example 20 to 150 nm. From this it will be appreciated that the secondary-initiated particles are used in the form of microparticles whereas the shock-sensitive particles are provided in the form of nanoparticles. Both forms of particles are commercially available for a range of materials suitable for use in the present invention.

In this particular embodiment the ratio by weight of the secondary-initiated particles to the shock-sensitive particles is typically from 20:1 to 5:1, preferably from 20:1 to 8:1.

In this embodiment the particles of energetic material are usually formed of the same metal. Preferably, the metal is aluminium or iron and the oxidant consists of water.

Again, without wishing to be bound by theory, it is believed that in this embodiment the gas bubbles associated with the shock-sensitive particles are derived from two sources. Firstly, gas bubbles may be present as a result of reaction between the liquid oxidant and the energetic material of the shock-sensitive particles. Secondly, gas (air) may become entrained in the composition as a result of the mixing process by which it is made.

In another embodiment of the invention the composition comprises secondary-initiated particles having an average particle size of 5 to 50 microns, and the shock-sensitive particles comprises particles in the form of flakes. Metals such as aluminium are commercially available in this form. The flake typically has an average particle size range (longest dimension) of from 20 to 70 microns. Such flakes also have a relatively high surface area and this is of the same order of magnitude as described above for the shock- sensitive nanoparticles. In this particular embodiment the ratio by weight of the secondary-initiated particles to the shock-sensitive particles (flake) is typically from 20:1 to 5:1, preferably from 20:1 to 8:1.

In this embodiment, and again without wishing to be bound by theory, it is believed that gas (air) introduced into the explosive composition when it is made becomes located at the surface of the particles flake. This sensitises the composition in the same general way as has already been described. The physical form of the flake particles may also contribute to entrainment of gas during the manufacturing process. For the reasons explained above, it may be useful to mix the microparticles and flake prior to mixing with the remaining components that make up the explosive composition of the invention.

In a preferred embodiment the shock-sensitive flake particles are coated with a hydrophobic material, such as stearic acid, and this provides a hydrophobic surface that will hold or absorb air onto the surface of the flake, thereby forming the kind of association that is believed to be important to implementation of the present invention.

In view of the embodiments described, in one aspect the present invention provides an explosive composition comprising: a liquid oxidant; a fuel comprising particles of energetic material homogeneously distributed throughout the liquid oxidant, the energetic material being capable of reaction with the liquid oxidant at elevated temperature to release energy, wherein the particles of energetic material comprise particles having a surface area of from 3 to 50 m²/g energetic material and particles having a surface area of 0.3 to 1.5 m²/g energetic material, and wherein the composition comprises gas bubbles associated with at least the particles having a surface area of from 3 to 50 m²/g energetic material. The relative particle sizes of the particles of energetic material may be as described more generally above.

As will be appreciated, the compositions of the invention may consist of components that are innocuous even when mixed. The compositions of the invention may therefore be formulated, stored and transported in an inherently safe manner. As significant energetic- input is required to detonate the compositions and this may also contribute to safety since unintentional detonation will not occur, as might be the case for sensitive or unstable explosive compositions. As the compositions of the invention may be formulated from innocuous components, disposal of undetonated or misfired explosive does not present a problem.

This safety benefit and the fact that explosive compositions of the invention may be detonated with clean/environmentally after-blast fumes means that the compositions will have utility over a wide range of fields. Thus, the explosive compositions may be used in blasting/mining operations, in construction, metal forming, oil exploration and seismic work and in underwater blasting. The explosive compositions may also have utility in military applications. For example in heat stable and energetic shaped charges.

The present invention also provides a method of blasting which comprises loading an explosive composition in accordance with the present invention in a blasthole and detonating the explosive composition. The explosive composition of the present invention may be used in a conventional manner in blasting operations. The explosive composition may be initiated using conventional initiation means, such as detonating cord or a detonator.

Embodiments of the present invention will now be illustrated in the following non-limiting examples.

Examples 1, 2 &3

Compositions 1, 2 & 3 were prepared in a 1000 ml volume plastic beaker by mixing an oxidiser liquid with aluminium powder using a hand held electric stirrer -homogeniser. In order to obtain homogeneous oxidiser liquid, the guar gum thickening agent was pre- dispersed in a small amount of ethylene glycol to ensure formation of a lump free, viscous aqueous sol. While continuously stirring, the guar gum-ethylene glycol dispersion was slowly poured into pre-weighed amount of the water. The process of dispersion lasted about 2 minutes. After about 10 minutes standing to allow for sufficient hydration of the polymeric thickening agent a homogeneous aqueous sol was obtained. This was the part 1- oxidiser liquid.

Prior to detonation testing, the part 2 that represented the pre determined amount of aluminium powder was added slowly into part 1-oxidiser liquid. The mixing time on addition of the aluminium powder was 2 minutes. The resulting aqueous dispersion was poured into a steel pipe of internal diameter of 36 mm and length of 250 mm.

The composition was primed with 1O g Pentolite primer and initiated by a standard industrial strength No 8 detonator. Depending on the sound report and the damage to the steel pipe the failure or detonation pass was assigned to experiment as shown in table above.

The experimental results show that only the sample containing nanoaluminium powder was able to be initiated and subsequently a propagate detonation wave.

Table 1

Examples 4-8

Compositions 4, 5, 6, 7 & 8 were prepared in a 1000 ml volume plastic beaker by mixing an oxidiser liquid with aluminium powder using a hand held electric stirrer — homogeniser. In order to obtain homogeneous oxidiser liquid, the guar gum thickening agent was pre-dispersed in a small amount of ethylene glycol to ensure formation of a lump free, viscous aqueous sol.

While continuously stirring, the guar gum-ethylene glycol dispersion was slowly poured into pre-weighed amount of water. The process of dispersion lasted about 2 minutes. After about 10 minutes standing to allow for sufficient hydration of the polymeric thickening agent a homogeneous aqueous sol was obtained. This was the part 1 -oxidiser liquid.

Prior to detonation testing, the part 2 that represented the pre determined amount of aluminium powder was added slowly into part 1- oxidiser liquid. The nanoaluminium was added last. The mixing time on addition of the aluminium powder was 2 minutes. In the case of examples 4, 5, & 6, a density reducing agent Expancel 551 DE was added and mixed in over period of 1 minute.

The resulting aqueous dispersion was poured into a steel pipe of internal diameter of 36 mm and 50mm with the length of 250 mm. The composition was primed with 50 g Pentolite primer and initiated by a standard industrial strength No8 detonator. Depending on the sound report and the damage to the steel pipe the failure or detonation pass was assigned to experiment as shown in Table 2.

Experiments 4 & 5 are control experiments that demonstrate failure to detonat when only a fuel type aluminium powder is used in the aqueous dispersion. The surface area of the aluminium powders ECKA- 45 micron and ECKA- 5 micron is well below 1.5 sq m/g. Addition of the sensitiser bubbles in the form of Expancel 551 DE made no difference in detonation capability.

Experiment 6 has shown that addition of l%w/w of nanoaluminium is not sufficient to ensure the complete detonation of the aqueous dispersion. Experiments 7 & 8 show that presence of about 4% w/w nanoaluminium ensured the complete detonation of the samples as judged by the sound and complete destruction of 6-7 mm thick steel pipes. Table 2

Examples 9-13

Compositions 9, 10, 11, 12 & 13 were prepared in a 2000 ml volume plastic beaker by mixing an oxidiser liquid with aluminium powder using a hand held electric stirrer — homogeniser. In order to obtain homogeneous oxidiser liquid, the guar gum thickening agent was pre-dispersed in a small amount of ethylene glycol to ensure formation of a lump free, viscous aqueous sol. While continuously stirring, the Guar gum-ethylene glycol dispersion was slowly poured into pre-weighed amount of the water. The process of dispersion lasted about 2 minutes. After about 10 minutes standing to allow for sufficient hydration of the polymeric thickening agent a homogeneous aqueous sol was obtained.

This was the part 1 -oxidiser liquid.

Prior to detonation testing, the part 2 that represented the pre determined amount of aluminium powder was added slowly into part 1 -oxidiser liquid. The mixing time on addition of the aluminium powder was 2 minutes. The nanoaluminium powder was added last. The mixing time on addition of the aluminium powder was 2 minutes.

Experiments 9 and 10 indicate that at 2%w/w level of nanoaluminium, the sample with the finer fuel grade aluminium (5 micron) detonates more readily than the 45-micron grade fuel aluminium.

Experiments 11, 12, and 13 demonstrate excellent detonability even at 0.5% level of nanoalumium, when the finer, larger surface area flake aluminium is present.

Table 3

** Oxidiser liquid- 49% water, 1% Glycol, 1% Guargum • * Expancel 551 DE

Examples 14-19

Compositions 14, 15, 16, 17,18 and 19 were prepared in a 2000 ml volume plastic beaker by mixing an oxidiser liquid with aluminium powder using a hand held electric stirrer - homogeniser. In order to obtain homogeneous oxidiser liquid, the guar gum thickening agent was pre-dispersed in a small amount of ethylene glycol to ensure formation of a lump free, viscous aqueous sol. While continuously stirring, the guar gum-ethylene glycol dispersion was slowly poured into pre-weighed amount of water. The process of dispersion lasted about 2 minutes. After about 10 minutes standing to allow for sufficient hydration of the polymeric thickening agent a homogeneous aqueous sol was obtained. This was the part 1 -oxidiser liquid.

The series of experiments in Table 4 show that detonable dispersions are produced (15,16,18) when the required quantity of large surface area aluminium powder is used in aqueous dispersions. In order to produce detonable aqueous dispersion of metallic powders it is possible to exchange large surface area pigment/flake aluminium for nanoaluminium powder. In doing so the detonation performance of aqueous dispersions is maintained.

Table 4

Oxidiser liquid- 49% water, 1% Glycol, 1% Guar gum

Examples 20-24

Compositions 20, 21, 22, 23 & 24 were prepared in a 2000 ml volume plastic beaker by mixing an oxidiser liquid with aluminium powder using a hand held electric stirrer - homogeniser. In order to obtain homogeneous oxidiser liquid, the guar gum thickening agent was pre-dispersed in a small amount of ethylene glycol to ensure formation of a lump free, viscous aqueous sol. While continuously stirring, the guar gum-ethylene glycol dispersion was slowly poured into pre-weighed amount of water. The process of dispersion lasted about 2 minutes. After about 10 minutes standing to allow for sufficient hydration of the polymeric thickening agent a homogeneous aqueous sol was obtained. This was the part 1 -oxidiser liquid.

Prior to detonation testing, the part 2 that represented the pre determined amount of aluminium powder was added slowly into part 1 -oxidiser liquid. The mixing time on addition of the aluminium powder was 2 minutes. The pigment/flake aluminium powder was added last. The mixing time on addition of the aluminium powder was 2 minutes.

These series of experiments have shown that there is a minimum quantity of large surface area pigment/flake aluminium required in order to obtain stable detonation in a long length pipes. It appears that at least 10 %/w/w Blitz Aluminium 2019D is needed to produce a detonable system.

Table 5

K) Ul

' Oxidiser liquid- 49% water, 1% Glycol, 1% Guargum

Examples 25-27

Compositions 25, 26 and 27 were prepared in a 2000 ml volume plastic beaker by mixing an oxidiser liquid with aluminium powder using a hand held electric stirrer -homogeniser. In order to obtain homogeneous oxidiser liquid, the guar gum thickening agent was pre- dispersed in a small amount of ethylene glycol to ensure formation of a lump free, viscous aqueous sol. While continuously stirring, the guar gum-ethylene glycol dispersion was slowly poured into pre-weighed amount of water. The process of dispersion lasted about 2 minutes. After about 10 minutes standing to allow for sufficient hydration of the polymeric thickening agent a homogeneous aqueous sol was obtained. This was the part 1 -oxidiser liquid.

Prior to detonation testing, the part 2 that represented the pre determined amount of aluminium powder was added slowly into part 1 -oxidiser liquid. The mixing time on addition of the aluminium powder was 2 minutes. The pigment/flake powder was added last. The mixing time on addition of the aluminium powder was 2 minutes.

Experiments 25, 26 and 27unequivocally demonstrate a stable detonation propagation of metallic powders dispersed in aqueous liquids. The measured Velocities of detonation (VOD) clearly show that aqueous explosive suspensions that are prepared with fuel type aluminium powder and moderate amounts of Carlfors Bruk flake aluminium are readily detonable.

The hydrodynamic calculations that employ Orica "IDEX" explosive code have confirmed values of detonation velocities obtained in our experiments. Table 6

K) -4

* 98% water, 1% Ethylene Glycol, 1% Guar Gum

Example 28

Example 24 was repeated using two different types of the pigment/flake aluminium at level of 5% w/w to assess their effectiveness to provide detonable compositions.

* Blitz Aluminium grade 2019D ** Carlfors Bruk CB 180 VTS Approx surface area 6.7 m²/g Approx surface area 12.2 m²/g

The results indicate stable detonation for 5% w/w Carlfors Bruk CB 180 VTS aluminium, while detonation failure occurred with Blitz Aluminium grade 2019D. The results clearly demonstrate greater effectiveness of the larger surface area of the particles in terms of an exothermic oxidation reaction and faster energy release. Due to the lower bulk density of the Carlfors Bruk CB VTS grade, it is believed that more air is entrained into the composition in Experiment 28 B. Examples 29 and 30

The purpose of these experiments was to assess the propagation of detonation in a relatively weak confinement. Two representative compositions were mixed by using standard methodology and packaged into 65 x 400 mm and 95 x 400 mm thin PVC pipes.

The results above show that compositions are able to support propagation of detonation in a relatively weak confinement when initiated by 50 gr Pentolite primer. Examples 31 and 32

The compositions used in Examples 29 and 30 were loaded into plastic shells in length of 365 mm with diameter of 55 mm at the top of the charge and 30 mm at the bottom (charges tapered down). The charges were initiated with a No 8 det + 50 gr of Pentolite and detonated. The charges detonated with the exception of the last 50 mm of the 30 mm diameter charge. This indicates that charges exhibit unconfined critical diameter, somewhere around 30-40 mm.

Aluminium characteristics and supplier's detail

1. QinetiQ Nanomaterials Ltd

Cody Technology Park, Farnborough Hampshire, UK

Nanoaluminium powder

Aluminium min: 63% Nominal particle size: 90 nm Morphology: Spherical

Approx. surface area: 20-28 m²/g

2. Ecka granules

Mepura Metallpurverges. m.b.H A-5282 Ranshofen, Austria

Atomised aluminium MEP103

Average particle size: 4.0 - 5.5 micron Aluminium min: 99.5% Bulk density 0.65 g/cc 3. Ecka Granules Australia

Metal Powder Technologies Bell Bay 7253, Tasmania, Australia

Fine aluminium powder 75 Average particle size: 45 microns (65-75%) Aluminium min: 99.7% Bulk density 1.30 g/cc

4. Benda-Lutz Werke Franzhausen 31, Traismauer, Austria A-3133

Blitz Aluminium flakes 2019 D

Aluminium min: 99.7%

Approx surface area 6.7 m²/g

Average particle size 23 micron

Bulk density 0.25 g/cc

Depuval non-dusting aluminium powder 3083 D

Aluminium min: 99.7%

Approx surface area 16.1 m²/g

Average particle size 23 micron Bulk density 0.25 g/cc

5. Carlfors Bruk

Huskvarna, 561 21 Sweden AIuminium powder CB 180 VTS

Aluminium min: 86% Approx surface area 12.2 m²/g Average particle size 17 micron

Bulk density 0.18 g/cc

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.

Claims

THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS:

1. An explosive composition comprising: a liquid oxidant; a fuel comprising particles of energetic material homogeneously distributed throughout the liquid oxidant, wherein the energetic material is capable of reacting with the liquid oxidant at elevated temperature to release energy, and wherein the particles of energetic material comprise shock-sensitive particles for which reaction between the energetic material and liquid oxidant can be shock initiated and secondary-initiation particles for which reaction between the energetic material and the liquid oxidant can be initiated by energy released as a result of reaction of the shock- sensitive particles and the liquid oxidant.

2. The composition of claim 1, wherein the shock-sensitive particles have a surface area of from 3 to 50 m²/g.

3. The composition of claim 2, wherein the shock-sensitive particles have a surface area of from 5 to 50 m²/g.

4. The composition of claim 1, wherein the secondary-initiated particles have a surface area of from 0.3 to 1.5 m²/g.

5. The composition of claim 4, wherein the secondary-initiated particles have a surface area of from 0.8 to 1.2 m²/g.

6. The composition of claim 1, wherein the shock-sensitive energetic particles and the secondary-initiated particles are independently selected from aluminium, boron, magnesium, silicon, titanium, zirconium, iron, zinc, copper, nickel, beryllium and mixtures thereof, ferrosilicon and aluminium-magnesium.

7. The composition of claim 6, wherein the shock-sensitive energetic particles and the secondary-initiated particles are independently selected from aluminium, silicon, iron and zirconium.

8. The composition of claim 7, wherein the shock-sensitive energetic particles and the secondary-initiated particles are formed of aluminium.

9. The composition of claim 1, wherein the liquid oxidant comprises at least 50 wt% water.

10. The composition of claim 9, wherein the liquid oxidant comprises at least 75 wt% water.

11. The composition of claim 1 , wherein the total amount of oxidant(s) present is from 20-90 % by weight.

12. The composition of claim 11₅ wherein the oxidant(s) and (the sum of) the particles of energetic material are present in approximately equi-molar ratios.

13. The composition of claim 1, wherein the shock-sensitive particles, and optionally the secondary-initiated particles, include a surface coating that will have the effect of holding or absorbing gas bubbles onto the surface of the particles.

14. A method of making an explosive composition as claimed in claim 1, which method comprises mixing the liquid oxidant and the fuel in a manner that will introduce gas bubbles into the composition.

15. An explosive composition comprising: a liquid oxidant; a fuel comprising particles of energetic material homogeneously distributed throughout the liquid oxidant, the energetic material being capable of reaction with the liquid oxidant at elevated temperature to release energy, wherein the particles of energetic material comprise particles having a surface area of from 3 to 50 m²/g energetic material and particles having a surface area of 0.3 to 1.5 m /g energetic material, and wherein the composition comprises gas bubbles associated with at least the particles having a surface area of from 3 to 50 m²/g energetic material.

16. Use of an explosive composition as claimed in claim 1 or claim 15 in a blasting operation.