Abstract:
A pumpable watergel explosive composition comprises 10 to 40 wt %, based on the total weight of the pumpable explosive composition, of a continuous liquid phase comprising a solvent, a solubilized chemical sensitizer and a gelling agent and 60 to 90 wt %, based on the total weight of the pumpable explosive composition, of a discontinuous solid phase comprising particulate oxidizer salt particles having interstitial spaces between the salt particles. The watergel explosive composition has a density of 1.05-1.4 g/cc and, a shear thinning rheology such that, when subjected to an external force, the explosive composition has a viscosity sufficiently low to render the watergel explosive composition pumpable. The combination of density and low water content provides energy numbers normally associated with more expensive aluminized formulations.

Description:
FIELD OF THE INVENTION  
       [0001]     This invention relates to explosive compositions utilizing a continuous liquid phase and a discontinuous solid phase. In particular, the invention relates to ammonium nitrate fuel oil (ANFO) or ammonium nitrate (AN)/watergel blend explosive compositions. In another aspect, this invention also relates to different methods to manufacture the explosive composition.  
       BACKGROUND OF THE INVENTION  
       [0002]     Various different forms of explosive compositions are known including ANFO explosive compositions, watergel, explosive compositions, slurry-type explosive compositions and emulsion explosive compositions. Each type of explosive compositions has its own advantages and disadvantages. For example, ANFO explosive compositions are useful in applications not requiring a water resistant explosive formulation, due to its low cost.  
         [0003]     Watergel blasting explosives may be selected when a combination of water resistance and superior heave is required.  
         [0004]     Slurry-type blasting explosives may be selected when water resistance is required and superior sensitivity is not required.  
         [0005]     Emulsion explosive compositions might be selected when water resistance is required and superior heave is not required.  
         [0006]     In all cases, the explosive composition must have characteristics which will allow it to be readily loadable into a bore hole while, at the same time, ensuring that the explosive composition will not degrade if the explosive composition remains in the bore hole for an extended period of time while a site is prepared for initiation. For example, the explosive composition might be loaded into a plurality of boreholes (typically from about 50-100 holes to more than about 200 holes) over a period of hours to days. Accordingly, the explosive composition could be kept in a borehole for from several days to several months prior to being detonated. The explosive composition must be sufficiently stable to not segregate into its component parts thereby permitting the explosive composition to detonate after being stored in a borehole for an extended period of time.  
         [0007]     In addition, water may accumulate in a borehole, such as from the inflow of ground water. Particulate ammonium nitrate will readily dissolve in water. Accordingly, if the explosive composition contains ammonium nitrate, such as in the case on an ANFO explosive composition or a blended explosive composition that contains particulate ammonium nitrate, the explosive composition must be sufficiently water resistant so as to permit the explosive composition to detonate, even after being stored for an extended period of time in a wet borehole.  
         [0008]     Many different approaches have been suggested in the prior art for producing explosive compositions that can be formulated from readily available materials and which will have the required stability and water resistance characteristics. For example, Sandell (U.S. Pat. No. 4,380,482) discloses water-bearing explosive compositions comprising oxidizer, fuel and sensitizer components in a thickened or gelled continuous aqueous phase wherein the aqueous phase is stabilized against degradation of its thickened or gelled structure by the incorporation therein of iodide and/or iodate ions.  
         [0009]     Honeyman et al (U.S. Pat. No. 4,585,495) discloses an explosive composition comprising a sensitized blend of ANFO and an aqueous slurry composition. In the blends of Honeyman et al, storage-stability is achieved because of the water-retentive character of the slurry per se, in contrast to the film barriers and waterproof prill coatings previously required (column 3, lines 4-8).  
         [0010]     Machacek et al (U.S. Pat. No. 4,718,954) discloses an explosive composition comprising 5 to 60 parts by weight of a gel concentrate and 95 to 40 parts by weight of a particulate oxidizer. In the composition, the gel concentrate partially, but not completely, fills the interstitial voids between the particles of the oxidizer (column 2, lines 39-47). One disadvantage of some of the explosive compositions is limited sensitivity. For example, as shown in tables 2 and 3 of this patent, the explosive composition failed in some three inch and four inch diameter tests.  
         [0011]     Another approach is set out in Cranney et al (U.S. Pat. No. 5,490,887) which discloses a watergel explosive composition having a density of 0.8 g/cc. The explosive composition is described as being advantageous for use in soft blasting operations and is water resistant (column 1, line 61-67).  
         [0012]     Richard et al (U.S. Pat. No. 5,925,846) discloses an ANFO blasting composition having improved water resistance.  
       SUMMARY OF THE INVENTION  
       [0013]     In accordance with this invention, a watergel type explosive composition is prepared which has a high prill content, a high energy level yet is still pumpable. Accordingly, in accordance with one embodiment of the instant invention, there is provided a pumpable explosive composition comprising:  
         [0014]     a) 10 to 40 wt %, based on the total weight of the pumpable explosive composition, of a continuous liquid phase comprising a solvent, a solubilized chemical sensitizer and a gelling agent: and,  
         [0015]     b) 90 to 60 wt %, based on the total weight of the pumpable explosive composition, of a discontinuous solid phase comprising particulate oxidizer salt particles having interstitial spaces between the salt particles  
         [0016]     wherein the liquid phase fills the interstitial spaces, the watergel explosive composition has a density of 1.05-1.4 g/cc and, when subjected to an external force, has a viscosity sufficiently low to render the watergel explosive composition pumpable.  
         [0017]     In accordance with another embodiment of the instant invention there is provided a pumpable explosive composition comprising:  
         [0018]     a) 10 to 40 wt %, based on the total weight of the pumpable explosive composition, of a continuous liquid phase comprising a solvent, a solubilized chemical sensitizer, and a gelling agent: and,  
         [0019]     b) 90 to 60 wt %, based on the total weight of the pumpable explosive composition, of a discontinuous solid phase comprising particulate oxidizer salt particles  
         [0020]     wherein, the gelling agent comprises a guar gum which, 60 minutes after 9.00±0.01 g of the guar gum is added to a solution of 702 g of AN, 240 g of sodium nitrate and 258 g of distilled water at 43° C. and stirred for 2 minutes, has a viscosity of 9000-12,000 cps at 25° C., the watergel explosive composition has a density of 1.05-1.4 g/cc and, when subjected to an external force, has a viscosity sufficiently low to render the watergel explosive composition pumpable.  
         [0021]     The solid phase preferably comprises a substantial portion of ammonium nitrate and, may consist essentially of ammonium nitrate particles. Ammonium nitrate is generally one of the lower cost ingredients used in explosive compositions. Accordingly, the use of substantial quantities of ammonium nitrate in the explosive composition permits a reduction in the cost of the explosive composition while still providing an explosive composition that has good explosive characteristics (e.g. velocity of detonation) as well as good pumpability.  
         [0022]     In practice, aluminum is commonly added to increase the energy in explosive compositions, such as ANFO, emulsions and watergels. While aluminum is one of the most expensive ingredients which is included in explosive compositions, the energy provided by the aluminum is generally required to offset the amount of water which is required in prior art watergel explosive compositions to render the explosive composition pumpable. In accordance with the instant invention, the explosive composition has a relatively low water content, preferably from 5 to 13 wt. % water, and, more preferably, from 7 to 10 wt. % water. At such water levels, the explosive composition of the instant invention remains pumpable. Due to this lower water content, the explosive composition may utilize a reduced amount of aluminum and, preferably, no aluminum depending on the energy required for a particular application. In particular, the explosive composition preferably comprises less than 15%, more preferably less than 5% and, most preferably no aluminum.  
         [0023]     Accordingly, the explosive compositions of the instant invention have a higher energy, which increases heave and fragmentation compared to previous non-aluminized bulk water gels of the same density.  
         [0024]     A further advantage of the instant invention is that the increased energy of the explosive composition permits an alteration in the drill pattern required at a blasting site. For example, essentially the same performance can be obtained at a reduced powder factor (i.e. in the amount of rock which is broken by an explosion using fewer holes) than would be required if a prior art watergels having the same density was used. Further, the pattern of the blasting may be expanded with no loss of fragmentation of heave.  
         [0025]     The explosive composition of the instant invention also exhibits a shear-thinning rheology. Pursuant to this rheology, when the explosive composition is subjected to shear forces (e.g. the explosive composition is passed through a pump so as to load the explosive composition into a bore hole), the shear forces result in the viscosity of the explosive composition being reduced thereby facilitating the pumping of the explosive composition. When the shear force is removed, the viscosity increases. This results in reduced slumping (i.e. the explosive composition is less likely to flow into imperfections in a borehole). This reduced slumping can result in the explosive being less environmentally hazardous. For example, if less of the explosive composition seeps into cracks in the walls of the borehole, this will result in less low-order detonation or deflagration. The lower order detonation can result in toxic fumes being produced during detonation. Further, it is less likely that undetonated product will be left in the broken rock thereby reducing the environmental impact of utilizing the explosive composition.  
         [0026]     In order to be pumpable, it is preferred that the explosive composition has a viscosity of less than 35,000 cps at 20 rpm, more preferably less than 20,000 cps, and, most preferably less than 15,000 cps at 21° C. The shear thinning rheology is evidenced by the viscosity of the explosive composition at rest. In order to simulate the viscosity of the explosive composition at rest, the viscosity of the explosive composition at 21° C. and 2 rpm was measured. Preferably, at these conditions, the explosive composition has a viscosity from 50,000 to 300,000 cps, more preferably from 75,000 to 200,000 cps and, most preferably, from 100,000 to 150,000 cps.  
         [0027]     In one embodiment, the solubilized chemical sensitizer comprises an organic nitrogen based salt of an inorganic oxidizing acid. Preferably, the nitrogen based salt comprises an amine salt. Optionally, the solubilized chemical sensitizer further comprises ammonium nitrate.  
         [0028]     In another embodiment, the solvent is selected from the group consisting of water, an alcohol, a glycol and mixtures thereof. Preferably, the solvent comprises water.  
         [0029]     In another embodiment, the particulate oxidizer salt is selected from the group consisting of alkali metal nitrates and perchlorates, alkaline-earth metal nitrates and perchlorates and mixtures thereof.  
         [0030]     In another embodiment, the particulate oxidizer salt comprises, and preferably consists essentially of, ammonium nitrate particles having a tapped bulk density of 0.9-1.05 g/cc. The particulate oxidizer salt may further comprise at least one additional alkali metal nitrates and perchlorates, alkaline-earth metal nitrates and perchlorates and mixtures thereof.  
         [0031]     In another embodiment, the liquid phase comprises from 30 to 85 wt% solubilized chemical sensitizer, from 15-40 wt % solvent and up to 30 wt % solubilized oxidizer salt, based on the total weight of the liquid phase.  
         [0032]     In another embodiment, the liquid phase comprises from 50 to 80 wt % solubilized chemical sensitizer, from 18 to 27 wt % solvent and up to 30 wt % solubilized oxidizer salt, based on the total weight of the liquid phase.  
         [0033]     In another embodiment, the liquid phase comprises an aqueous MMAN solution and the oxidizer salt comprises ammonium nitrate.  
         [0034]     In another embodiment, the explosive composition comprises 12 to 21 wt % of the solubilized chemical sensitizer and from 7-10 wt % solvent, based on the total weight of the liquid phase.  
         [0035]     In another embodiment, the solubilized chemical sensitizer consists essentially of nitric or perchloric acid salts derived from organic amines.  
         [0036]     In another embodiment, the pumpable watergel explosive composition comprises from 5 to 15 wt %, and preferably 7 to 10 wt % solvent, based on the total weight of the pumpable explosive composition.  
         [0037]     In another embodiment, the pumpable watergel explosive composition further comprises an insoluble sensitizer. Preferably, the insoluble sensitizer comprises perlite, microspheres, a gassing agent and mixtures thereof.  
         [0038]     In another embodiment, the gelling agent comprises guar gum, xanthan gum, locust bean gum, polyvinyl acetate, polyethylene oxides, polyacrylamide, starch and mixtures thereof.  
         [0039]     In another embodiment, the pumpable watergel explosive composition further comprises a cross linking agent.  
         [0040]     In another embodiment, the gelling agent comprises a guar gum which, 60 minutes after 9.00±0.01 g of the guar gum is added to a solution of 702 g of AN, 240 g of sodium nitrate and 258 g of distilled water at 43° C. and stirred for 2 minutes, has a viscosity of 7000-17,000 cps at 25° C.  
         [0041]     In another embodiment, the pumpable watergel explosive composition comprises from 0.3 to. 1 wt %, and preferably 0.3 to 0.6 wt %, of the gelling agent, based on the total weight of the pumpable explosive composition.  
         [0042]     In another embodiment, the watergel explosive composition has a viscosity of 10,000-35,000 cps at 20 rpm and 21° C.  
         [0043]     In another embodiment, the watergel explosive composition has a viscosity of from 50,000 to 300,000 cps at 2 rpm and 21° C.  
         [0044]     In another embodiment, the particulate oxidizer salt is associated with an organic combustible fuel.  
         [0045]     In another embodiment, the particulate oxidizer salt is combined with the organic combustible fuel to form a mixture prior to mixing the liquid phase with the mixture.  
         [0046]     In another embodiment, the particulate oxidizer salt comprises an ANFO blend.  
         [0047]     In another embodiment, the watergel explosive composition comprises less than 15% aluminum.  
         [0048]     In another embodiment, the watergel explosive composition comprises essentially no aluminum.  
         [0049]     In another embodiment, the watergel explosive composition comprises 15 to 35 wt % of the continuous liquid phase and 85 to 65 wt %, of the discontinuous solid phase, based on the total weight of the pumpable explosive composition.  
         [0050]     In another embodiment, the watergel explosive composition comprises 20 to 30 wt % of the continuous liquid phase and 80 to 70 wt %, of the discontinuous solid phase, based on the total weight of the pumpable explosive composition.  
         [0051]     In accordance with another embodiment of the instant invention, there is provided a method of manufacturing a pumpable watergel explosive composition comprising:  
         [0052]     a) preparing a liquid chemical sensitizer solution comprising a solvent a solubilized chemical sensitizer and a gelling agent at a first location;  
         [0053]     b) transporting the liquid chemical sensitizer solution to a second location;  
         [0054]     c) combining 10 to 40 wt % of the liquid chemical sensitizer solution, based on the total weight of the pumpable explosive composition, with 90 to 60 wt % of a solid phase comprising particulate oxidizer salt having interstitial spaces between the salt particles, based on the total weight of the pumpable explosive composition, to form the pumpable explosive composition  
         [0055]     wherein a gelling agent is added either to the liquid chemical sensitizer prior to combining the liquid chemical sensitizer with the solid phase, or during step (c), the liquid chemical sensitizer solution fills the interstitial spaces, the watergel explosive composition has a density of 1.05-1.4 g/cc and, when subjected to an external force, has a viscosity sufficiently low to render the watergel explosive composition pumpable.  
         [0056]     An advantage of this embodiment of the invention is that the liquid chemical sensitizer solution (preferably an aqueous MMAN solution) may be made at one central location and then shipped to a site at which the watergel explosive composition will be prepared. Aqueous MMAN solutions are classified as explosives. Accordingly, as explosives, special handling is required for storing and transporting MMAN solutions. However, the liquid chemical sensitizer comprises only a small proportion of the explosive composition. A substantial portion of the explosive composition comprises a solid phase (e.g. AN) that may be shipped and stored as non-explosives thereby reducing transportation and storage costs. In some cases, blasting sites are accessible only on winter roads. In such cases, either a year&#39;s worth of the explosive composition must be stored at site or, alternately, the explosive composition must be manufactured at site. For example, if the explosive composition is a 70/30 blend of an emulsion explosive and ANFO, then 70% of the formula by weight would be classified as an explosive and must be transported and stored as an explosive. In such cases, it may be cheaper to build a production plant to produce the emulsion explosive at site as opposed to transporting and storing the explosive composition at the site.  
         [0057]     In a preferred embodiment of the instant invention, the explosive composition comprises only 20 to 30 wt. % of a composition which is classified as being a booster sensitive explosive. Accordingly, a substantial portion of the ingredients for the explosive composition may be stored at site as a non-explosive thereby simplifying the storage of substantial quantities of the explosive composition at site.  
         [0058]     In one embodiment, the pumpable watergel explosive composition also comprises an insoluble sensitizer, the liquid chemical sensitizer solution is a booster sensitive explosive and the method further comprises transporting the liquid chemical sensitizer solution as a booster sensitive explosive to the second location and transporting the solid phase as a non-explosive to the second location.  
         [0059]     In another embodiment, the second location is a location at which the watergel explosive composition will be used and the method further comprises adding a crosslinking agent to the explosive composition contemporaneous with loading the watergel explosive composition into a borehole.  
         [0060]     In another embodiment, the method further comprises selecting as the gelling agent a guar gum which, 60 minutes after 9.00±0.01 g of the guar gum is added to a solution of 702 g of AN, 240 g of sodium nitrate and 258 g of distilled water at 43° C. and stirred for 2 minutes, has a viscosity of 7,000-12,000 cps at 25° C.  
         [0061]     In another embodiment,.the method further comprises adding at least one of (a) an organic combustible fuel, (b) at least one additional alkali metal nitrates and perchlorates, alkaline-earth metal nitrates and perchlorates and mixtures thereof; and mixtures of (a) and (b).  
         [0062]     In another embodiment, the method further comprises selecting ammonium nitrate particles having a tapped bulk density of 0.9-1.05 g/cc as the particulate oxidizer salt.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0063]     In accordance with this invention, the explosive composition comprises a blend of a liquid phase and a solid phase. The liquid phase comprises the continuous phase of the explosive composition and the solid phase comprises a discontinuous phase of the explosive composition. Preferably, the liquid and solid phases are combined so that the liquid phase at least essentially fills the interstitial spaces between the particles of the solid phase of the explosive composition.  
         [0064]     The explosive composition may comprises from about 10 to about 40, preferably from about 15 to about 35 and more preferably about 20 to about 30 wt. % of the continuous liquid phase and from about 60 to about 90, preferably from about 85 to about 65 and more preferably about 80 to about 70 wt. % of the discontinuous solid phase, based upon the total weight of the pumpable explosive composition.  
         [0065]     The liquid and solid phases may be combined by any means known in the art. Preferably, the explosive composition is prepared by adding the liquid phase to a mixing vessel, followed by addition of the solids, oil, and particulate oxidizer phase.  
         [0066]     The liquid phase comprises a solvent, a solubilized chemical sensitizer and a gelling agent. In addition, the liquid phase may also include an insoluble sensitizer and a cross linking agent. Optionally, the liquid phase may also include other additives known in the art such as additives for control of the pH such as fumaric acid or organic fuels such as oil.  
         [0067]     The solid phase comprises particulate oxidizer salt particles and may optionally include an organic combustible fuel, an insoluble sensitizer as well as other additives known in the art including microspheres, perlite, non-soluble fuels such as aluminum or rubber, non-soluble explosives such as TNT, PETN, or black powder.  
         [0068]     Solubilized Chemical Sensitizer  
         [0069]     The chemical sensitizer may be any sensitizer known in the explosive art which is soluble in a solvent. The chemical sensitizer may be a water-soluble explosive, preferably nitric or perchloric acid salts derived from organic amines, including the nitrates and perchlorates of aliphatic amines, more preferably an organic salt such as nitrogen-based salts of inorganic oxidizing acids, preferably amine nitrates, and most preferably nitrates of 1-3 carbon aliphatic amines, such as monomethylamine nitrate (MMAN) ethylamine nitrate, ethanolamine nitrate, propanolamine nitrate and ethylenediamine dinitrate. Other amine nitrates may be utilized such as hexamine nitrate.  
         [0070]     The chemical sensitizer preferably comprises from about 30 to about 85, more preferably from about 50 to about 80 and, most preferably from about 60 to about 70 wt. % of the liquid phase, based upon the total weight of the liquid phase. Accordingly, the amine nitrate will comprise from about 10 to about 30, more preferably from about 15 to 25 and, most preferably from about 12 to about 18 wt. % of the watergel explosive composition, based upon the total weight of the water gel explosive composition.  
         [0071]     Solvent  
         [0072]     The solvent may be any liquid in which the chemical sensitizer may be solubilized. Preferably, the solvent is selected from the group consisting of water, alcohol, glycol and mixtures thereof. More preferably, the solvent comprises water and, more preferably consists essentially of water.  
         [0073]     The solvent may comprise from about 15 to about 40 wt. %, more preferably from about 18 to about 27 wt. % and most preferably from about 20 to about 25 wt. % of the liquid phase, based upon the total weight of the liquid phase. This corresponds to the solvent comprising from about 5 to about 15 wt. %, preferably from about 7 to about 12 and, most preferably from about 7 to about 10 wt. % of the explosive composition based upon the total weight of the explosive composition. Accordingly, while the explosive composition may comprise less than about 15 wt. % water, and may comprise a majority of particulate ammonium nitrate, the explosive composition is still pumpable as a fluid.  
         [0074]     Gelling Agent  
         [0075]     The gelling agent may be any thickening agent known in the art for water gels. For example, the gelling agent may be one or more of guar gum, xanthan gum, locust bean gum, polyvinyl acetate, polyethylene oxides, polyacrylamide or starch. Preferably, the gelling agent comprises guar gum and, most preferably, consists essentially of guar gum.  
         [0076]     The gelling agent may comprise from about 0.3 to about 1 wt. % and, preferably, from about 0.3 to about 0.6 wt. % of the explosive composition, based upon the total weight of the explosive composition. This corresponds to the gelling agent comprising about 1-2 wt. % of the liquid phase, based upon the total weight of the liquid phase.  
         [0077]     Preferably, the guar gum which is utilized is a low viscosity guar gum. In this application, a low viscosity guar gum refers to a guar gum which meets the requirements of the following test. First, a test liquor is prepared utilizing 702 g of ammonium nitrate, 240 g of sodium nitrate and 258 g of distilled water. The nitrates are dissolved in the distilled water at an elevated temperature, but below 85° C. to prevent ammonia from being lost. When all of the nitrate salts have been dissolved, the test liquor is cooled to about 47° C. Make up water is added to account for any evaporative loss so as to obtain 1,200 g of test liquor. The test liquor is brought to 43° C. and 9 g of guar gum are added to the test liquor. The guar gum is added in about 7 seconds while mixing at 1650 rpm. The guar gum and test liquor are mixed for two minutes from the initial addition of the guar gum. A Brookfield R.V. viscometer with a number 5 spindle is utilized to determine the viscosity of the test liquor. The test liquor is allowed to cool to about 25° C. At 60 minutes, the viscosity of the mixture is measured. The viscosity of the mixture is preferably 7,000-17,000 cps, more preferably 7,000-12,000 cps and, most preferably 7,000-10,000 cps at 20 rpm.  
         [0078]     The guar gum will commence to hydrate upon addition to the liquid phase and will therefore commence to thicken the liquid phase. A portion of the crosslinking system (e.g., a system which requires two or more components to produce a crosslinking effect, such as potassium antimony tartrate and sodium dichromate) may be added to the liquid phase if the portion that is aged does not affect or does not markedly affect the viscosity of the liquid phase to a point at which the liquid phase cannot be pumped or mixed with the solid phase. This crosslinker, such as from about 0.005 to about 0.01 wt % of potassium antimony tartrate, will not generally affect the viscosity of the liquid phase until the remainder of the crosslinking system (i.e. the sodium dichromate) is added to the explosive composition during delivery of the explosive composition into the borehole. The remainder of the cross linker, if any, e.g., sodium dichromate, is preferably added immediately prior to the end of the hose which loads the explosive composition into a bore hole (e.g. within about the last ten to fifty feet of the hose).  
         [0079]     Insoluble Sensitizer  
         [0080]     Optionally, the explosive composition may also include an insoluble sensitizer. The insoluble sensitizer may be incorporated in to the liquid phase prior to combining the liquid phase with the solid phase. Alternately, the insoluble sensitizer may be incorporated as part of the solid phase or may be a separate feed stream which is added to the liquid phase and the solid phase to produce the explosive composition.  
         [0081]     The insoluble sensitizer may comprise any material known in the art which will decrease the density of the explosive composition and include air or other gasses in the explosive composition. Preferably, the insoluble sensitizer comprises one or more of perlite, microspheres and a gassing agent and, more preferably, one or more of perlite and microspheres.  
         [0082]     In accordance with a particularly preferred embodiment of the instant invention, the liquid phase fills, or at least essentially fills, the interstitial spaces between the particles of the solid phase. In such a case, it is particularly preferred to include an insoluble sensitizer as part of the explosive composition.  
         [0000]     Particulate Oxidizer Salt Particles  
         [0083]     Particulate oxidizer salt particles are known in the explosives art. In accordance with the instant invention, the particulate oxidizer salt particles are preferably selected from the group consisting of ammonium, alkali metal nitrates and perchlorates, ammonium, alkaline-earth metal nitrates and perchlorates and mixtures thereof. The oxidizer salt particles may comprise or consist essentially of ammonium nitrate particles.  
         [0084]     A portion of the ammonium nitrate particles may be replaced by other inorganic oxidizer salts known in the art including alkaline metal nitrates and perchlorates (such as sodium nitrate and potassium nitrate) or alkaline-earth metal nitrates and perchlorates (such as calcium nitrate) or other oxidizer salts. Preferably, the replacement inorganic salts are sodium nitrate and/or calcium nitrate. These additional nitrates may be added in an amount up to 20 wt. %, and preferably, up to 15 wt. %, base upon the weight of the ammonium nitrate particles in the solid phase.  
         [0085]     The oxidizer salt oxidizer salt particles preferably comprise and may consist essentially of high density oxidizer salt particles. It will be appreciated that the density of a particle will depend upon the salt which is utilized. High density ammonium nitrate particles, also known as “miniprills” have a tapped bulk density of 0.9-1.05, preferably 0.9-1 and, most preferably, about 0.95 g/cc.  
         [0086]     Miniprills may be prepared by any conventional means known in the art such as spraying molten nitrate containing very little moisture (e.g. 0.1-0.4 wt. % water, and preferably less than about 0.28 wt. % water) at elevated temperatures (e.g. 175° C. or higher) into a prilling tower countercurrent to cooling air. The cooling air solidifies the droplets into prills which are cooled to ambient temperature. This results in the production of miniprills which are generally round.  
         [0087]     Miniprills have a smaller void volume than low density ammonium nitrate particles (i.e. those with a density less than 0.85 g/cc). For example, the void volume of miniprills may be up to 12% lower than the void volume for low density prills.  
         [0088]     In accordance with a particularly preferred embodiment of the instant invention, the liquid phase and the solid phase are combined so that the liquid phase essentially fills and, preferably, completely fills the interstitial spaces (the void volume) of the particulate oxidizer salt particles. Despite the low water content of the liquid phase, and the relatively small amount of the liquid phase which is utilized in preparing the explosive composition, the explosive composition still exhibits fluid like characteristics (i.e. it is not a paste or too thick to pump at a reasonable rate and a safe pressure).  
         [0089]     In some embodiments, some particulate oxidizer salt may be added to the liquid phase in addition to the solubilized sensitizer. In such a case, the particulate oxidizer salt will be solubilized in the solvent. For example, the liquid phase may comprise up to about 30 wt. % solubilized oxidizer salt, particularly if the liquid phase has a low content of MMAN. Preferably the oxidizer salt which is utilized in such cases is ammonium nitrate. Accordingly, the liquid phase may comprise about 30 wt % MMAN, about 30 wt % AN, about 0.5 wt % guar gum and the balance water.  
         [0000]     Organic Combustible Fuel  
         [0090]     The organic combustible fuel may be selected from any fuel known in the art. The fuel may be a solid (e.g. a wax, ground rubber) or a liquid (e.g. fuel oil, heating oil, diesel oil, jet fuel, kerosene, mineral oils, saturated fatty acids such lauric acid and stearic acid, alcohol such as cetyl alcohol, corn oil, soy bean oil and the like) or a mixture of solid and liquid fuels. Preferably, the organic combustible fuel is a liquid fuel and may comprise fuel oil such as No. 2 fuel oil. The organic combustible fuel may also be supplemented with fuel-soluble ingredients such as glucose, mannose, fructose, waxes, such as microcrystalline wax, paraffin wax, petroleum wax and the like.  
         [0091]     The organic combustible fuel may be associated with the particulate oxidizer salt in accordance with any method known in the explosives art. Preferably, the organic combustible fuel is combined with the particulate oxidizer salt to form the solid phase that is then combined with the liquid phase. In a particular preferred embodiment, the solid phase comprises an ANFO blend. The ammonium nitrate and fuel oil may be blended in any ratio known in the art and, preferably, the fuel oil is blended at a rate of 2-4 wt. %, based upon the total weight of the explosive composition, with the amount reduced appropriately when other solid fuels are added, to maintain the desired oxygen balance.  
         [0092]     Preferably, the explosive composition contains sufficient organic combustible fuel so that the explosive composition has a slightly negative oxygen balance, taking into consideration the total oxidizing salts, fuel, sensitizers and other additives present in the explosive composition. Preferably, the negative oxygen balance is in the range of about −1 to −3.  
         [0000]     Cross Linking Agent  
         [0093]     Preferably, the explosive composition also comprises a cross linking agent. The cross linking agent may be selected from those known in the art. Preferably, the cross-linking agent is a metal salt, such as potassium antimony tartrate, potassium pyroantimonate, sodium dichromate, boric acid, ferric chloride, zirconium and titanium complexes or other metal compounds.  
         [0094]     Preferably, the cross-linking agent, or the final portion of the crosslinking system, is incorporated into the explosive composition subsequent to the explosive composition being passed through a pump that is used to load the explosive composition into the borehole. However, a portion of the crosslinking system (preferably potassium antimony tartrate) may be added to the liquid phase. It will be appreciated that the cross-linking agent may be added by any means known in the art.  
         [0095]     The cross linking agent may be added at a rate of 0.01-0.10, preferably about 0.05 wt. %, based upon the total weight of the explosive composition.  
         [0096]     The explosive composition may also include other additives that are known in the explosive art such as potassium iodide and stearic acid. Preferably, the explosive composition comprises less than about 15 wt. % aluminum, more preferably less than 5 wt. % aluminum and, most preferably, essentially no aluminum.  
         [0097]     In one embodiment, the explosive composition may have a pH from 3 to 7, preferably from 4 to 6 and, most preferably from 4.5 to 5.5. If the pH is less than about 4, then the gelling action of the guar gum is reduced due to acid hydrolysis and additional amounts of guar gum must be utilized. If the pH is greater than about 6, then premature gellation of the guar will commence and increased microbial attack of the guar is possible.  
         [0098]     The explosive composition utilizing these ingredients preferably has a density from about 1.05 to. 1.4 g/cc, more preferably 1.15 to 1.30 g/cc and, most preferably 1.22 to 1.28 g/cc.  
         [0099]     The explosive composition has a viscosity that is sufficiently low to render the watergel explosive composition pumpable when passed through a pump. This explosive composition exhibits a shear thinning rheology. When the explosive composition is essentially stagnant (e.g. at 2 rpm and 21° C.) the explosive composition has a viscosity from about 50,000 to 300,000 cps, preferably from 75,000 to 200,000 cps and, most preferably from 100,000 to 150,000 cps. When passed through a pump, the viscosity is reduced to render to composition pumpable. It is well understood by those skilled in the art whether an explosive composition is pumpable. Preferably, the explosive composition has a viscosity of less than 35,000 cps at 20 rpm and 21° C., preferably less than 20,000 cps and, more preferably less than 15,000 cps. Such explosive compositions can be passed through pumps that are utilized to load boreholes without the pump being overstressed and without excessive pressure being applied to the explosive composition. After being passed through a pump, the crosslinking agent, or the final portion of the crosslinking system, is preferably added prior to the end of the hose.  
         [0100]     In accordance with one embodiment of the instant invention, all of the feed materials may be combined at one particular location to produce the explosive composition. Alternately, the liquid phase may be prepared separately and stored for use later or transported to an alternate location. For example, the liquid phase, which is classified as an explosive composition may be prepared at a central facility and then shipped to various sites, such as blasting sites or secondary manufacturing locations, whereat the liquid phase is combined with, e.g., miniprills or ANFO to produce the final explosive composition.  
         [0101]     If the liquid phase is prepared separately, then the liquid phase may comprise a mixture of the solubilized chemical sensitizer, the solvent and the gelling agent, and optionally up to 30 wt. % ammonium nitrate or other inorganic oxidizing salt. Alternately, the liquid phase may also have incorporated therein some cross linking agent and/or some insoluble sensitizer (e.g. perlite and/or ceramic microspheres) and, more preferably, insoluble sensitizer and the cross linking agent. Accordingly, the explosive composition may be prepared by blending miniprills or ANFO with a liquid phase comprising the remaining reagents.  
       EXAMPLE  
       [0102]     An explosive composition was prepared according to the instant invention by combining the following ingredients which are set out in Table 1.  
                                         TABLE 1                                   Feed material   Weight %                                        Aqueous MMAN Solution (69 wt. %) MMAN)   21.67           Water   2.50           Potasium antimony tartrate   0.01           Ceramic Microspheres   2.00           Guar Gum   0.36           Perlite   0.15           ANFO (95.9 wt. % miniprills/4.1 wt. % fuel oil)   73.31           Total   100.00                      
 
         [0103]     The explosive composition was prepared by initially preparing the aqueous MMAN solution. The aqueous MMAN solution, additional water and the potassium antimony tartrate were added to a tank and stirred to blend the ingredients. The ceramic microspheres was added while the ingredients were being stirred in the tank. Subsequently, the guar gum was added and the mixing was continued for two minutes. At the end of two minutes, the perlite and ANFO were added and the mixing continued until the explosive composition had a uniform consistency.  
         [0104]     The explosive composition had a pH of 4.9 and a density of 1.28 g/cc. The viscosity of the explosive composition was then measured as made and after storing the explosive composition overnight and for four days. The results are set out in Table 2.  
                               TABLE 2                                   Mix   Units                               As Made       15 C.           pH   none   4.9           Density   g/cc   1.28           Visc@2 rpm and 15° C.   cps   110,000           Visc@20 rpm and 15° C.   cps   16,000           Overnight       24 C.           pH   none   4.9           Density   g/cc   1.28           Visc@2 rpm and 24° C.   cps   135,000           Visc@20 rpm and 24° C.   cps   19,500           Four Day       20 C.           pH   none   4.8           Density   g/cc   1.32           Visc@2 rpm and 20° C.   cps   107,500           Visc@20 rpm and 20° C.   cps   18,500                      
 
         [0105]     As can be seen from the forgoing, the viscosity of the explosive composition at low rpm was over 100,000 cps. However, at 20 rpm (i.e. simulating being passed through a pump), the viscosity reduced substantially thereby exhibiting a shear thinning rheology.  
         [0106]     The explosive composition was then crosslinked by adding 0.04 wt. % sodium dichromate before being detonated. The explosive composition was tested by loading it into a steel pipe, inserting the appropriate booster, initiating the booster, and measuring the velocity of detonation.  
         [0107]     The results are set out in Table 3.  
                                     TABLE 3                       Diameter   Booster   Velocity of       (mm)   Weight (grams)   Detonation (m/s)                                100   454   4900       75   227   4100       50   227   2800