CA2052662A1 - Food grain sensitized emulsion explosives - Google Patents

Abstract

ABSTRACT
"Food Grain Sensitized Emulsion Explosives"
An emulsion explosive is provided wherein a base emulsion explosive composition is modified by the addition of a food grain, and preferably an expanded food grain, to the composition. The resultant explosives detonate at lower velocity and with lower pressure than typical bubble sensitized emulsions and/or are more resistant to dynamic pressure desensitization.

Description

20~2~ ' "Food Grain Sensitized Emulsion Explosives"
FIELD OF TH~ INVENTION
The present invention relates to emulsion explosives and, in particular, to emulsion explosives having modified explosive properties.

DESCRIPTION OF THE REL~l'EI) ART
Emulsion explosives have become well known in commercial blasting. These blasting agents, as described by ~luhm in U.S. Patent No. 3,447,978, typically comprise a discontinuous aqueous oxidizer salt phase and a continuous phase of a water-insoluble liquid or liquefiable fuel as a continuous phase. ~he emulsion is typically 6tabilized by the addition of a suitable emulsifying agent. This base emu~sion explosive composition will detonate under suitable conditions. However, additives are frequently ~ncluded in the composition to increase the sensitivity of the base composition.
In order to increase the sensitivity of emulsion explosive6, it is common practice to add materials to the emulsion which will provide ~uitable sized gas void~ within the emul~ion. For example, gas voids can be generated ~n situ by the reaction of various material~, such as, sodium nitrite, to form gas bubbles wh~ch are entrained within the emulsion (termed as chemical gas6ing). Further, gas voids can be generated in the emulsion explosi~e by the addition of void-containing materials to the emulsion to form a bubble ~ensitized emulsion explosive. Void-cont3ining materials used to date include glass micro~alloons, perlite, pclymeric void-containing mater~als, foams, and the like.

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Bubble sensitized emulsions are characterized by a high detonation velocity (5.0 to 5.8 km/sec) and a high detonation pressure (100 to 120 kbars). They are al80 more sensitive to desensitization by dynamic pressure than convention chemically sensitized explosives, i.e., the emulsion explosive can be desensitized by the shock wav~
from an ad~acent explosion, which can result in a misfire of the explosive.
With these inherent characteristics, bubble sensitized emulsions have been found to be advantageous in blasting hard rock or competent ground, where high brisance i6 required. However, in poor rock, weak ground or in shear blasting where high heave and resistance to pressure desensitization are needed, bubble sensitized emulsion explosives are far from satisfactory.
To minimize the effect of pressure desensitization, emulsion explosives comprising an energy-absorbing cushioning material have been suggested. In particular, the use of a variety of polymeric and flexible air void-containing materials as emulsion sensitizers is discussed in U.S. Patent No. 4,732,626. ~he cushioning materials described are synthetic materials, such as, polymeric foams which must be produced or are naturally occurring materials, such as, cork or rubber.
However, it i8 still desirable to provide emulsion explosives wherein the present weaknesses in bubble sensitized emulsion explosives are overcome by providing an emulsion explosive having a lower velocity of detonation and a lower detonation pressure and which explosives are more 0 resistant to dynamic pressure desensitization.
SUMMARY OF TH~ INVENTION
Accordingly, the present invention provides an emulsion explosive composition comprising an oxygen-supplying ~alt as a ~iscontinuous phase, a water insoluble liquid or liquefiable fuel as a continuous phase, an emulsifying 2 O ~

agent, and particles of a food grain distributed throughout said composition.
Suitable food grains of u~e in the present invention include any food grains which can act as a fuel in the explosive reaction or which contain air voids within the structure of the grain, depending on the desired properties of the emulsion explosive. Examples of suitable food grains include corn, wheat, soybean, bean and rice, or mixtures thereof. The food grain may be used as is or, preferably, as a void-containing expanded food grain. The food grain may be expanded by heating of the grain as, for example, in the case of corn as popcorn.
The food grain used should be sufficiently stable, under the processing conditions used to produce the emulsion explosive, to avoid substantial degradation of the cell structure of the grain. This is particularly true when expanded food grains are used to provide sensitivity in the emulsion explosive composition.
The food grain is, preferably, cut into or ground to a size suitable for incorporating into the emul~ion explosive in order to produce an essentially homogeneous mixture.
Preferably, the food grain is ground to a size of between 0.1 mm and 30 mm and, more preferably, between 0.5 mm to 5.0 mm.
The level of food grain added to the emulsion explosive depends on the desired properties of the emulsion explosive composition and on the type of food grain utilized.
Preferably, the level of food grain is between 0.1 and 15%, more preferably, between 1 and 10%, and, still more preferably, between 2 and 7%, by weight.
The different ground food grains will have different bulk densities depending on the particle fiize to which the food grain is ground and on the type of food grain utilized.
Typically, however, the bulk densities will vary from between 0.04 and 0.9 g/cc.

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The use of expanded food grains having air voids in the cell structure of the expanded grain has been found to increase the sensitivity of the base emulsion explosive.
This increase in 6ensitivity i8 related to the void size of the expanded food grain and to the level of expanded food grain added to the composition. Typical food grain void size6 range, preferably, from 40 to 200 microns. However, the void size of the particular food grain may be non-homogeneous and may extend beyond this range.
The emulsion explosives containing the expanded food grains are also more resistant to the effects of dynamic pressure (i.e. pressure desensitization) than microballoon containing emulsion explosives. This is believed to ~e due to the flexible nature of the cell wall surrounding the air void. In contrast, the rigid wall of the glass microballoon can be broken by the shock wave from an explosion which would occur, for example, in an ad~acent borehole.
Accordingly, the present invention provides an emulsion explosive which is more resistant to pressure desensitization. Preferably, the emulsions of the pressnt invention may be detonated by an A-3 primer, 4 seconds after a 250 g Pentolite charge has been detonated one metre away from the test sample of emulsion.
The use of non-expanded food grains aids in producing emulsion explosives ~aving a lower velocity of detonation (VOD). Preferably, the emulsion contains sufficient food grain to provide an emulsion explosive having a VOD of less than 3000 m/sec, more preferably, less than 2000 m/sec and, yet still more preferably, less than 1500 m/~ec.
Accordingly, depending on the desired properties of the emulsion explosi~e, the food grain component of the emulsion explosive may comprise a mixture of expanded and unexpanded food grainsO
The use of food grains in the preparation of water gel or slurry explosives has been described by Atadan et al in ~ ~ 5 ~ ~,5 ~) U.S. Patent No. 3,397,097. However, the use of these food grains was in water gel explosiYes.
It is believed that the ma~ority of the food grain added to either of the emulsion or water gel explosive~
remains in the continuous phase. In water gel explosive~, the stability of the food grain is adversely affected by absorption of water by the food grain in the continuous aqueous phase. In contrast, the food grain added in the present invention is primarily present in the non-aqueous fuel phase and, therefore, the raté of water absorption i8 greatly decreased. This results in improved stability of the food grain modified emulsion explosives of the present invention over the water gel explosives of the prior art.
The oxidizer ~alt for use in the discontinuous phase of the emulsion is, preferably, ~elected from the group consisting of alkali ~nd alkaline earth metal nitrates, chlorates and perchlorates, ammonium nitrate, ammoni~m chlorates, ammonium perchlorate and mixtures thereof~ It is particularly preferred that the oxidizer salt is ammonium O nitrate or a mixture of ammonium and sodium nitrate.
A preferred oxidizer salt mixture comprises a solution of 77% ammonium nitrate, 11% sodium nitrate and 12% water.
The oxidizer salt is, typically, ~ concentrated aqueous solution o~ the salt or mixture of salts. ~owever, the 'j oxidizer salt may also be a liquefied, melted solution of the oxidizer salt where a lower water content is desired.
It is particularly preferred that the discontinuous phase of the emulsion explosive be a eutectic compositlon.
By eutectic composition is meant that the melting point of the composition i6 either at the eutectic or in the region of the eutectic or the components of the composition.
The present invention also provides a method for the production of sn emulsion explosive having modified properties over typical emulsion explosives. Accordinqly, in a further aspect, the present invention provides a method ~05~6~
I~ICAN 797 of producing an emulsion explosive comprising emulsifying a discontinuous oxidizer salt in a continuous fuel phase to form a base emulsion explosive and adding a food grain to said base explo~ive.
In a preferred embodiment, the present invention allows for the production of emul~ion explosives which are sensitized but which have improved resistance to pressure desensitization over t pical microballoon-containing sensitized emulsion explosives of the prior art.
Accordingly, the present invention also provides a method of improving the resistance of a sensitized emulsion explosive to pressure desensitization comprising emulsifying a discontinuous oxidizer salt in a continuous fuel phase to form a base emulsion explosive and adding an expanded food grain to said base explosive.
The oxidizer salt for use in the discontinuous phase of the emulsion may further comprise a melting point depressant. Suitable melting point depressants for use with ammonium nitrate in the discontinuous phase include inorganic salts, such as, lithium nitrate, silver nitrate, lead nitrate, sodium nitrate, potassium nitrate; alcohols, such as, methyl alcohol, ethylene glycol, glycerol, mannitol, sorbitol, pentaerythritol; carbohydrates, such as, sugars, 6tarches and dextr$ns; aliphatic carboxylic acids and their salts, such as, formic acid, acetic acid, ammonium formate, sodium formate, sodium acetate, and ammonium acetate; glycine; chloracetic acid; glycolic acid; succinic acid; tartaric acid; adipic acid; lower aliphatic amides, such as, formamide, acetamide and urea; urea nitrate;
nitrogenous substances, such as, nitroguanidine, guanidine nitrate, methylamine, methylamine nitrate, and ethylene diamine dinitrate; and mixtures thereof.
Typically, the discontinuous phase of the emulsion comprises 60 to 97% by weight of the emulsion explosi~e and, preferably, 86 to 95% by weight of the emulsion explosive.

~ 5 ~ ICICAN 797 The continuous water-immiscible organic fuel phase of the emulsion explosive comprises an organic fuel. Suitable organic fuels for use in the continuous phase include aliphatic, alicyclic and aromatic compounds and mixtures thereof which are in the liquid 6tate at the formulation temperature. Suitable organic fuels may be chosen from fuel oil, diesel oil, distillate, furnace oil, kerosene, naphtha, waxes, (e.g., microcrystalline wax, paraffin wax and slack wax), paraffin oils, benzene, toluene, xylenes, asphaltic materials, polymeric oil8, such as, the low molecular weight polymers of olefins, animal oils, fish oils, and other mineral, hydrocarbon or fatty oils, and mixtures thereof.
Preferred organic fuels are liquid hydrocarbons, generally referred to as petroleum distillate, such as, gasoline, kerosene, fuel oils and paraffin oils. More preferably, the organic fuel is para~fin oil.
~ ypically, the continuous water-immiscible organic fuel phase of the emulsion explosive comprises 3 to 30% by weight of the emulsion explosive and, preferably, 5 to 15~ by weight of the emulsion explosive.
The emulsion explosi~e comprises an emulsifier component as an emulsifying agent to aid in the formation to the emulsion and to improve the stability of the emulsion.
The emulsifier component may be chosen from the wide range of emulsifying agents known in the art to be suitable for the preparation of emulsion explosive compositions.
Examples of such emulsifying agents include alcohol alkoxylates, phenol alkoxylates, poly(oxyalXylene) glycols, poly(oxyalkylene) fatty acid esters, amine alkoxylates, fatty acid esters of 60rbitol and glycerol, fatty acid salts, sorbitan esters, poly(oxyalkylene) sorbitan ester~, fa~ty amine alkoxylates, poly(oxyalkylene)glycol esters, ~atty acid amides, fatty acid amide alkoxylates, fatty amine, quaternary amines, alkyloxazolines, alkenyloxazolines, imidazolines, alkylsulfonates, 2 ~ 2 ICICAN 797 alkylarylsulfonates, alkylsulfosuccinates, alkylphosphates, alkenylphosphates, phosphate esters, lecithin, copolymers of poly(oxyalkylene) glycols and poly(l2-hydroxystearic acid), condensation products of compounds comprising at least one primary amine and poly~alk(en)yl]6uccinic acid or anhydride, and mixtures thereof.
Among the preferred emulsifying agents are the 2-alkyl-and 2-alkenyl-4,4'-bis~hydroxymethyl)oxazoline6, the fatty acid esters of ~orbitol, lecithin, copolymers of poly(oxyalkylene)glycols and poly(l2-hydroxystearic acid), condensation products of compounds comprising at least one primary a~ine and polytalk(en)yl~succinic acid or anhydride, and mixtures thereof.
More preferably, the emulsifier component comprises a condensation product of a compound comprising at least one primary amine and a polytalk(en)yl]succinic acid or anhydr$de. A preferred emulsifier is a polyisobutylene succin~c anhydride (PIBSA) based 6urfactant, which surfactants are described in Canadian Patent No. 1,244,463 (Baker). Australian Patent Application No. 40006/85 (Cooper and Baker) discloses emulsion explosive composition~ in which the emulsifier is a condensation product of a polytalk(en)yl]succinic anhydride and an amine, such a~, ethylene diamine, diethylene triamine and ethanolamine.
Further examples of preferred condensation products may be found in Australian Patent Application Nos. 29933/39 and 29932/89.
Typically, the emulsifier component of the emul~ion explosive comprises up to 5% by weight of tbe emul~ion explosive compogition. Higher proportions of the emulsifier component may be used and may serve as a supplemental fuel for the composition but, in general, it i6 not neces~ary to add more than 5% by weight of emulsifier component to achieve the desired effect. Stable emulsions can be formed using relatively low levels of emulsifier component and, for ~ ~ ICICAN 797 _g_ reasons of economy, it i8 preferable to keep to the minimum amounts of emulsifier necessary to achieve the desired effect. The preferred level of emulsifier component used i8 in the range of from 0.4 to 3.0~ by weight of the emulsion S explosive.
If desired, other optional fuel materials, hereinafter referred to as secondary fuels, may be incorporated into the emulsion explosives. Examples of such secondary fuels include finely divided solids. Examples of solid secondary fuels include finely divided materials, such as, sulphur;
aluminum; carbonaceous materials, such as, gilsonite, comminuted coke or charcoal, carbon blacX, resin acids, such as, abietic acid, sugars, such as, glucose or dextrose and other vegetable products, such as, starch, nut meal, grain lS meal and wood pulp; and mixtures thereof.
Typically, the optional secondary fuel component of the emulsion explosive comprises from 0 to 30% by weight of the emulsion explosive.
The explosive composition is, preferably, oxygen balanced. This may be achieved by providing a blend of components which are, themselves, oxygen balanced or by providing a blend which, while having a net oxygen balance, comprises components wh~ch are not, themselves, oxygen balanced. This provides a more efficient explos~ve composition which, when detonated, leaves fewer unreacted components. Additional components may be added to the explosive composition to control the oxygen balance of the explosive composition.
The food grain sensitized emul~ion explosive composition may also comprise an additional discontinuou~
~aseous component w~ich gaseous component can be utilized to further vary the density and/or the sensitivity of the explosive composition.
The methods of incorporating this gaseous component and the enhanced sensitivity of explosive compositions ~ ~ ~ 2 `~ CICAN ,9, comprising gaseous components are well known to those skilled in the art. The gaseous components may, for example, be incorporated into the explosive composition as fine gas bubbles dispersed through the composition, as hollow particles which are often referred to as microballons or as microspheres, as porous particles, or mixtures thereof.
A discontinuous phase of fine gas bubbles may be incorporated into the explosive composition by mechanical agitation, injection or bubbling the gas through the composition or by chemical generation of the gas in situ.
Suitable chemicals for the in situ generation of gas bubbles include peroxides, such as, hydrogen peroxide, nitrates, such as, sodium nitrate, nitrosoamines, such as, N,N'-dinitrosopentamethylenetetramine, alkali metal borohydrides, such as, sodium borohydride, and carbonates, such as, sodium carbonate. Preferred chemical for the in situ generation of gas bubbles are nitrous acid and its salts which decompose under conditions of acid pH to produce gas bubbles. Preferred nitrous acid salts include alkali metal nitrites, such as, sodium nitrite. Catalytic agents, such as, thiocyanate or thiourea may be used to accelerate the decomposition of a nitrite gassing agent. Suitable small hollow particles include small hollow microspheres of glass or resinous mater~als, such as, phenol-formaldehyde, urea-formaldehyde and copolymers of vinylidene chloride and acrylonitrile. Suitable porous materials include expanded minerals, such as, perlite and expanded polymers, such as, polystyrene.
EXAMPLES
The present invention will now ~e described, by way of example only, with reference to the following examples.
In all of the following examples, the emulsion explosives were prepared according to the following procedure. The emulsion was prepared in a Hobart* mixer * Trade Mark ~ ~3 ~ 2 ttnj ~j ~ ICICAN 797 equipped with a steam jacked 5-litre capacity mixing bowl and a standard whisk-shaped stirrer. A mixture of surfactants as emulsifying agents and paraffin o$1 as a fuel phase were weighed in the mixing bowl and heated to 9O to 100-C. An oxidizing salt liquor was prepared separately and was added to the heated oil phase while mixing at low speed (285 rpm) on the mixer to form a coarse emulsion. After the coarse emulsion had formed, it was ref$ned at high mixing speed (591 rpm) for 3 minutes.
Unless otherwise noted, the formulation of the base emulsion explosive is as set out in Table 1.

Emulsion Ex~losive Composition . .

PIBSA-based surfactant 1.2%
Sorbitan oleate 0.6 Paraffin oil 3.9 Oxidizing salt liquorl 94.3 100 . O
.
lAmmonium nitrate 77%, sodium nitrate 11% and wat~r 12~.

The sensitizing bubbles, which were expanded food grains, non-expanded food grains, or their mixtures with glass microballoons, were blended into the emulsion manually before packaging for testing.
The food gra$ns used in the examples were expanded or unexpanded and were ground to varying particles sized as noted for each example. The bulk density of the food grains used is set out in Table 2.

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TABLT~ 2 Bulk DensitY of Food Grains Type ~ Bulk Density (g~cc~
Rice 0.83 Soybean 0.68 Corn (grain) 0.84 Expanded corn (popcorn)l 0.025 Ground popcorn 0.10 Puffed wheat 0.044 Puffed rice 0.11 ...
11 to 2 cm in diameter 2 o . 5 to 5 mm in diameter ____ _ __ _ In the examples, the following test procedures were utilized, unless otherwise noted.
a) DensitY: the cartridge density of the experimental emulsions were determined by the weight to volume ratio.
b) Sensitivity: sensitivity was measured by determining the minimum detonator necessary for detonation from a series of detonator caps and primers with increasing strength, as follows:

Detonator/Primer Base Charge ta PETN or eouivalent~

R-6 0.15 R-7 . 0.20 R-8 0.25 EB 0.78 A-3 Primer 2.30 Anodet* 15.0 * Trade ~ark c) Detonation velocity (VOD): the VOD was determined by the time which the detonation wave takes to travel 2.5 or 5.0 inches.
d) ~nderwater test: the shock and bubble energy generated by the explosive is measured based on the measured pressure and size of bubbles formed when the explosive is detonated underwater.
e) Detonation pressure: the detonation pressure was determined by the dent produced by an explosive charge of 500 g in 50 mm diameter fired standing up on a cold rolled steel plate calibrated by the dent value for Pentolite.

To demonstrate the effect of food grains in sensitizing emulsion explosives, a series of emulsions was made with increasin~ popcorn content and tested for sensitivity and VOD in 50 mm diameter cartridge sizes. The popped corn used was 1 to 2 cm in diameter and had a bulk density of 0.025 g/cc. The compositions tested and the results are shown in Table 3.

Po~corn Sensitized Emulsion Explosives Exampl~ No.1 _ _ 4 5 _ Emulsion1~100 99 98 97 96 95 Popcorn % _ 1 2 3 4 5 Density (g/cc)1.43 1.14 1.01 0.940.91 0.~9 Sensit~vityFailed Anodet A-3 A-3 A-3 A-3 with Anodet VOD (m/sec in 50 mm diameter i 4019 1417 1763 1841 1901 Emulsion explosive composition as in Table 1 , 2 ~

Without the sensitizing bubbles, th~ emulsion i6 not sensitive, as indicated by Example 1. With the inclusion of t~e popped corn, the emulsions became sensitive and could be detonated. In Example 2, the sensitized emulsions could be detonated but required a 15 g c~arge of PETN. However, compositions containing 2~ popped corn could be initiated with 2.5 g ~ETN, as shown in Examples 3 to 6.
The detonation velocity of popped corn sensitized emulsions is from 1.4 to 1.9 km~sec, for Examples 3 to 6, 10 which is much lower than the normal velocity of 5.0 to 5.8 km/sec of typical microballoon sensitized emulsions.
The sensitizing effect of popped corn i8 due to its honeycomb structure with individual cells of 40 to 50 microns in size. It is believed that its ability to reduce the detonation velocity is derived from the large unit size of 1 to 2 cm of popcorn.
ExAMpLEs 7 To 11 A serie~ of food grain sensitized emulsions was again prepared using popped corn. However, in this ~eries, grcund popcorn of 0.5 to 5 mm diameter having a bulk den~ity of 0.10 g/cc was used. ~he emulsion compositions and blasting results are shown in Table 4.

Ground PoDcorn Sensitized Emulsion ExDlosives Exam~le No. 7 - 2 - -Emulsion S 98 97 96 95 93 Ground popcorn % 2 3 4 5 7 Density (g/cc) 1.08 1.03 0.99 0.88 0.74 Sensit~vity A-3 A-3 A-3 A-3 A-3 VOD (m/sec in 50 mm diameter)2197 2276 2461 2414 2490 s~

In general, it was found that emulsions sensitized by ground popcorn detonated with higher VOD than those sensitized by the larger diameter popcorn. The VOD is similar to conventional water gel ~lurries and is lower than conventional bubble sensitized emulsions.
The higher ~OD of ground popcorn compared to those with larger pieces of popcorn i~ probable due to the smaller particle of the ground material, making it less effective in reducing the detonation reaction rate.

A series of emulsion explosives was prepared which were 6ensitized by a mixture of glass microballoons and popcorn or ground popcorn. Ihe compositions and detonation results are shown in Table 5 TAT3~E 5 Glass M~croballoon - Po~corn Sensitized Emuls~on Explosives Example No. 1~ l~ 14 Emulsion % 97.5 95.5 93.0 Glass microballoons ~B23) % 2.5 2.5 2.5 Popcorn ~ _ 2.0 Ground popcorn % _ _ 2.5 Density (g/cc) 1.25 1.01 0.97 Sensitivity (32 mm) R-6 R-8 R-7 ~OD m/~ec in 32 mm diameter 4400 3489 3290 50 mm diameter 5000 3825 3390 Without popcorn or, in general, without a food grain sensitizer, as in Example 12, the microballoon sensitized product is sensitive to R-6 and detonates with a high YOD.
With popcorn, as in Examples 13 and 14, the emulsions retain their cap sensitivity, while their VOD is significantly reduced, even though the level of glass microballons remains constant.
Accordingly, emulsions with equivalent sensitivity and lower VOD compared to microballoon sensitized products could be o~tained by a mixture of microballoons and food grain materials.
EXAMPLES 15 and 16 Emulsion explosives were prepared which were sensitized by commercially available puffed wheat and puffed rice. The bulk densities of the puffed wheat and puffed rice were 0.04 and 0.11 g/cc, respectively. The compositions and blasting results are shown in Table 6.

~AB~E 6 Puffed Grain Sensitized Emulsions ¦Exam~le No. IlS 1 Emulsion % 96.0 94.0 Puffed Wheat ~ 4.0 __ Puffed Rice % __ 6.0 Density (g/cc) 1.03 1.10 Sensitivity 100 g Primer A-3 VOD m/sec in 50 mm diameter 1300 1293 The emulsion explosive of Example 15 was les5 sensitive than those ~ensitized with popcorn and, thus, required a larger detonator. This i~ believed to be due to the larger cell size in puffed wheat (180 to 200 micron) in comparison to popcorn (40 to 50 micron). ~owever, the grain size of the puffed wheat utilized (15 mm) was effective in reducing VOD.

2~ ICICAN 797 The puffed rice used in Example 16 was characterized by its non-homogeneous purous structure and its smaller grain size (9-10 mm). Therefore, it is efficient in reducing VOD
with a satisfactory sensitizing effect.

A series of emulsion explosives were prepared which illustrate the effect of food grains on emulsion explosives.
In order to ensure sensitivity of the emulsions, a mixture of glass microballoons and food grains was used. The 10 compositions and blasting results are shown in Table 7.

t TABLE 7 Emulsions Containing Food Grains Example No. 17 1~
Emulsion % 74.3 74.3 74.3 Glass microballoons (B23) ~ 2.7 2.7 2.7 Corn grain % 23.0 _ Rice grain % _ 23.0 Soybean grain % _ _ 23.0 Density (g/cc) 1.22 1.24 1.19 Sensitivity - R-7 R-6 R-6 VOD m/sec in 25 mm diameter 4123 3848 3207 Since the corn, rice and soybean grains did not have the necessary porous structure to sensitize the emulsion, glass microballoons were present in all examples to assure that the compositions would have adequate sensitivity.
Accordingly, the food grains used in Examples 17, 18 and 19 were used primarily to reduce the detonation velocity.

~ ICICAN 797 As shown in these examples, the emulsions containing the various food qrains did show lower VOD than conventional emulsion explosives. However, due to their high bulk density, a high content of food grain was required to have an appreciable effect on VOD.
EXAMPLES 20 to 24 A series of emulsions were prepared and were used to demonstrate the advantageous properties of emulsion explosives sensitized by expanded food grains. The formulations and blasting results are shown in Table 8.
Example 20 was a conventional emulsion explosive sensitized by 5% glass microballoons, typical of those used in the prior art, and was used for comparison purposes.
The same emulsion was used for all of the emulsion explosive compositions. Ground popcorn was in combination with puffed wheat in Example 24 to enhance sensitivity.
In Table 8, the results of the underwater test and the Plate Dent test are shown. All samples were initiated with an A-3 primer.

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The emulsions sensitized by the expanded food grains, as in Examples 21 to 24, were higher in bubble or gas energy than the conventional glass microballoon sensitized emulsion of Example 20. The ground popcorn composition of Example 22 yielded the highest gas energy efficiency of 67%.
All of the expanded food grain sensitized emulsions were low in detonation pressure compared to the glass microballoon sensitized emulsions. Further, all of the expanded food grain sensitized emulsions were resistant to dynamic pressure desensitization under conditions where the conventional glass microballoon sensitized emulsion failed.
Accordingly, from the examples described hereinabove, it can be noted that food grains and, preferably, expanded food grains, such as, for example popcorn, puffed wheat, puffed rice and the like, are efficient in reducing the detonation velocity of emulsion explosives. Further, the expanded food grains are capable of sensitizing and lowering the detonation velocity of emulsion explosives. This sensitizing effect of the expanded grain increases with decreasing particle size.
Further, emulsion explosives with eguivalent sensitivity to that of conventional microballoon sensitized products but with lower detonation velocity can be obtained by a hybrid system of expanded grains and glass microballoons. It should also be noted that emulsions sensitized by expanded grains are high in gas energy (heave), low in detonation pressure and have improved resistance to pressure desensitization than conventional glass microballoon sensitized emulsions.
Having described specific embodiments of the present invention, it will be understood that modifications thereof may be suggested to those skilled in the art and it i~
intended to cover all such modifications as fall within the scope of the appended claims.

Claims (10)

1. An emulsion explosive composition comprising an oxygen-supplying salt as a discontinuous phase, a water insoluble liquid or liquefiable fuel as a continuous phase, an emulsifying agent and particles of a food grain distributed throughout said composition.

2. An emulsion explosive as claimed in Claim 1 wherein said food grain is a void-containing expanded food grain.

3. An emulsion explosive as claimed in Claim 1 wherein said food grain is corn, wheat, soybean, bean or rice.

4. An emulsion explosive as claimed in Claim 2 wherein said void-containing food grain is popcorn, puffed wheat or puffed rice.

5. An emulsion explosive as claimed in Claim 1 comprising 0.1 to 15% by weight of said food grain.

6. An emulsion explosive as claimed in Claim 5 comprising 2 to 7% of said food grain.

7. An emulsion explosive as claimed in Claim 1 wherein said particle of food grain has a diameter of between 0.1 to 30 mm.

8. An emulsion explosive as claimed in Claim 7 wherein said diameter is between 0.5 mm and 5 mm.

9. A method of producing an emulsion explosive comprising emulsifying a discontinuous oxidizer salt in a continuous fuel phase to form a base emulsion explosive and adding a food grain to said base explosive.

10. A method of improving the resistance of a sensitized emulsion explosive to pressure desensitization comprising emulsifying a discontinuous oxidizer salt in a continuous fuel phase to form a base emulsion explosive and adding an expanded food grain to said base explosive.