GB2206574A

GB2206574A - Explosive

Info

Publication number: GB2206574A
Application number: GB08813578A
Authority: GB
Inventors: Andrew Victor Hearn; Pieter Stephanus Jaco Halliday
Original assignee: AECI Ltd
Current assignee: AECI Ltd
Priority date: 1987-06-29
Filing date: 1988-06-08
Publication date: 1989-01-11
Anticipated expiration: 2008-06-08
Also published as: MW1888A1; NO882865L; EP0297740A3; NO882865D0; GB8813578D0; GB2206574B; CA1330397C; ZW8688A1; AU616892B2; AU1831988A; EP0297740A2; NZ225094A

Description

:;7->. r 1 1\ C S] /'-\ /-\ 2 '12' 0 6 5 7 4 1 EXPLOSIVE THIS INVENTION

relates to an explosive. It relates in particular to the manufacture of an emulsion explosive comprising a discontinuous phase which forms an oxidizing salt-containing component and a continuous phase which is immiscible with the discontinuous phase and which forms a fuel 5 component.

Such explosives, when the oxidizing salt-containing component contains water and is in the form of an aqueous solution, are known as Uwater-infuel" emulsions, and when the oxidizing salt component contains little or no water, they can be regarded as "melt-in-fuel" emulsions.

According to the invention, in the manufacture of an emulsion explosive comprising a discontinuous phase which forms an oxidizing salt-containing component and a continuous phase which is immiscible with the discontinuous phase and which forms a fuel'component, there is provided a method of thickening or increasing the viscosity of the emulsion which comprises dispersing insoluble particulate bentonite or a derivative thereof in at least one of the components of the emulsion.

The bentonite or bentonite derivative is preferably added to the emulsion formed after admixture of said components, in a proportion of from about 1,0 to about 5,0% by mass based on the emulsion mass. The Applicant has found that the bentonite or derivative is thereby dispersed through the emulsion without dissolving in either of the components, and without causing crystallization.

The bentonite or bentonite derivative may be dispersed in the emulsion by admixture of the powder with the emulsion in a low shear blender.

The bentonite is preferably swellable sodium bentonite which is composed largely of the mineral montmorillonite. It may be of the so-called USA 5 tight-spec type having a degree of dry particle fineness as follows: 90% by mass minimum finer than US Sieve No. 40 and 10% by mass maximum finer than US Sieve No.200. In other words, at least 90% by mass of the bentonite particles may'have a particle size less than 425 microns and at most 10% by mass of the bentonite particles may have a particle size less than 75 microns. The average particle size of the bentonlite particles may be from about 75 microns to about 425 microns, preferably from about 75 microns to about 350 microns.

The sodium bentonite may be that which is commercially available in powder form under the trade name MX-80 VOLCLAY WESTERN BENTONITE-13T from the American Colloid Company, and whiJhas a water content of between 5 and 10% by mass, a dry particle fineness of 10% by mass maximum retained on US Sieve No.40 and 10% by mass maximum passing US Sieve No.200, and a wet particle fineness of at least 94% by mass being finer than US Sieve No. 200 and at least 92% by mass being finer than US Sieve No. 325.

Suitable bentonite derivatives include the quarternary ammonium bentonite salts especially those having at least one long chain alkyl group having at least 10 C atoms. (Commercially available bentones) which are swellab in methanol and are preferably pretreated therewith.

The discontinuous phase may comprise at least one oxidizing salt selected from the group consisting of ammonium nitrate, alkali metal i e 1 0 -anitrates, alkaline earth metal nitrates, ammonium perchlorate, alkali metal perchlorates, and alkaline earth metal perchlorates.

The discontinuous phase may comprise ammonium nitrate with at least one further compound selected from the group consisting of oxygen -releasing salts and fuels which, together with the ammonium nitrate, forms a melt which has a melting point which is lower than that of the ammonium nitrate. Said further compound may be sodium nitrate, calcium nitrate, urea, urea derivatives such as thiourea, or the like. The discontinuous phase may in certain cases comprise water, which is kept to a minimum to avoid wasted energy arising from steam generation, but which is employed to facilitate melting/dissolving of the oxidizing salt component to avoid excessive high processing temperatures during formation of' the base emulsion.

The fuel component of the emulsion may forn. from 21 to 25% by mass of the emulsion, preferably about 3 to 12% by mass.

The fuel of the fuel component will be immiscible with and insoluble L-1 water. Preferably, the fuel of the fuel component is non-self-explosive and is selected from at least one member of the group consisting of 0 hydrocarbons, halogenated hydrocarbons and nitrated hydrocarbons.

Typically, said fuel comprises at least one wax selected from the group consisting of paraffin waxes, mi crocrys tal line waxes and slack waxes, and it may comprise at least one member of the group consisting of mineral oils, fuel oils, lubricating oils, liquid paraffin, xy,lene, toluene, petrolatum and dinitrotoluene.

The fuel may comprise an emulsifier or a mixture Of suitable emulsifiers. The fuel component may thus comprise at least one emulsifier selected from the group consisting of sorbitan sesquioleate, sorbitan i,- ionooleate, sorbitan monopalmitate, sodium monostearate, sodium tristearate., the mono- and diglycerides of fat-forming fatty acids, soya bean lecithin, derivatives of lanolin, alkyl benzene sulphonates, oleyl acid phosphate, laurylamine acetate, decaglycerol decaoleate, decaglycerol decastearate, 2 -oleyl -4,4' -bis ChydroMethyl) - 2 -oxazo line, polymeric emulsifiers containing polyethylene glycol backbones with 10fatty acid side chains and derivatives of polyisobutylene succinic anhydride.

The emulsifiers act as surfactants and stabilizers to promote the formation of the emulsion and to resist crystallization and/or coalescence of the discontinuous phase.

The method may include the step of dispersing a density -reducing agent in the emul-cion to form an emulsion having a density of from 1,10 to 1, 15 g/cm3 at 250C.

The dens ity- reducing agent may be selectecl from the group consisting of microballoons, microspheres and gas bubbles. In one embodiment, the eventual emulsion may thus include glass microballoons, microspheres of polymeric material or another form of density-reducing agent, to proviele the emulsion with the final density of 1,10 to 1,15 g/cm3 at 250C. The emulsion may then comprise up to about 10% by mass of glass microballoons (eg C15/250 glass microballoons available from 3M South 25Africa (Pty) Limited) or microspheres of a polymeric material (eg EXCRkNCEL1 642 DE microspheres available from KemaNord AB, Sweden), which 4 0 can further act to sensitize the explosive. Although the mass of microballoons or microspheres included may be up to 10%, it is preferably less than 4,5% by mass, based on-the mass of the emulsion to which they are added. In another embodiment, the density-reducing agent may comprise air bubbles in the emulsion. The bubbles can then be mechanically induced eg by physical mixing or blowing, and/or chemically induced, eg by a chemical foaming agent such as sodium nitrite added to the emulsion.

The invention extends to an emulsion explosive whenever manufactured 10 according to the method described above.

The invention will now be described by way of example, with reference to the following non-limiting Examples.

EWIPLEPS Cartridged water-in-oil emulsion explosives were prepared having the 15 following compositions, in which all units are expressed as percentages 0 on a mass basis:

Constituent Sample 1 Sample 2 Ammonium nitrate 68,60 65,98 Sodium nitrate 12,81 12,32 Thiourea 0,1 - Water 1M1 9,73 P95 Oil M7 O93 Crill 4 (sorbitan monooleate emulsifier) 1,36 1,31 Paraffin Wax (Aristo) 1,98 1;90 Microcrystalline Wax (BE SQUARE Amber) 1298 1,90 Bentonite 2,00 2M Sodium nitrite (20% m/m aqueous solution) 0,09 - 3M B23/500 Microballoons - 393 TOTAL 100,00 100,00 Cold Density (g/cm,) lis 1,15 -6 The P95 (trade name) mineral oil was obtained from BP South Africa (Proprietary) Limited, and the Crill 4 (trade name) from CToda Chemicals South Africa (Proprietary) Limited. The parafiin wax was Aristo (trade name) wax obtained from Sasol Chemicals (Proprietary) Limited, and the microcrystalline wax was BE SQUARE Amber 175 (trade name) obtained from Bareco Inc. USA. The microballoons were 3M B23/500 (trade name) glass microballoons obtained from 31M South Africa (Proprietary) Limited. The bentonite was NDC-80 VOLCLAY WESTERN BENTONITE-13T (trade name) obtained from American Colloid Company, and typically having the following chemical analysis: SiO 2 60,0-62,0% m/m; A1 2 0 3 21,0-23,0% m/m; Fe 2 0 3 3,0-4,0% m/m; MgO 2,0-3,0% m/m; Na 2 0 2,0-3,0% m/m; CaO 0,1-0,7% m/ri; K 2 0 0,4-0,5% m/m; and having a pH value of 8,5-10,0.

The amount of water given includes the water used to make up the sodium nitrite solution.

The emulsion explosives were prepared by forming a premix of water, amonixz- nitrate, nitrate, and thiouTea at about 80 to WC, and a second preri-x of the mi crocrystal line wax, paraffin wax, P95 oil and Crill 4 at about 7.0 to WC. The first premix was then slowly added to the second premix with agitation to form a base emulsion. The bentonite was thereafter admixed with the base emulsion in a low shear blender for about 1 minute to provide a thickened emulsim. Samples 1 and 2 were prepared by respectively dispersing the sodium nitrite or the microballoons in the base emulsion in a blender at normal elevated working temperatures, followed by cartridging and rapid cooling.

Comparative samples, identical to Samples 1 and 2 save that they did not contain bentonite. were also made up.

1 0 Samples 1 and 2, with and without the bentanite, were tested according to the Stanhope cone penetrometer method (with 150 g cone), and the results obtained are set out in Table I.

TABLE 1

SAWLE =RATION (MM) without bentonite with bentonite Temperature 3VC Sample 1 22,5 18,0 Sample 2 13,5 7,8 Cii.) Temperature SO'C Sample 2 19,4 1614 (iii) Temperature 6CC Sample 2 23,4 17,3 The viscesity of Sample 2, with and without the bentonite, was measured at elevated temperatures, and the results are set out in Table II.

Temperature (12c) TABLE II

Viscosit-, (CP) Sample 2 without Sample 2 witn bentonite bentonite 26 800 76 SGO so 17 600 19 600 7 600 13 120 Sample 2, with and without the bentonite, was also tested for mini= initiation (M1) and velocity of detonation (VOD) at WC, and the results are set out in Table III. Table III also sets out the results of tests for bII and VOD at WC of a further sample termed Sample 3, which is a formulation essentially similar to Sample 2 but which contains 4% by mass of the bentonite based on the mass of the emulsion. In Table III, W indicates a misfire, and 13DI, 14D1 and 'SDI indicate that the explosive could be detonated with a detonator containing 45mg, 90mg, and 180mg pentaethyritol tetranitrate respectively.

TABLE III

SAMP125 Detonation Characteristics at 400C Initial After 4 months A ter 6 -m-o-nt-Fs-- Y75 m 11 OD 1 TD M1 VOD (km,Is) (km/s) (kmls) Sample 21 3D 4.99 SD 457 M8D (Without bentonite) Sample 2 (with 2% bentonite) Sample 3 (4% bentonite) 3D 4.17 A 3D 4,8 1 SD 4D 4,7 SD 4,9 4,7 M8D Sample 2, with and without bentonite, was tested for susceptibility to shock crystallization, and the results are set out in Table 1V (Temperature Rise on Shocking) and Table V (Bubble Energy after Shocking). Temperature rise on shocking was measured by placing a thermocouple in the centre of a cartridge suspended vertically at 6,7 m below the sur- face of water. A 150g booster was fired at the same depth at a distance of 2,8m. from the cartridge and the resultant temperature 25rise due to crystallisation was recorded. The average of three results is given in Table 1V. Bubble energy after shocking was measured by firing a 150g booster at varying distances from five cartridges suspended vertically at a water depth of 6,7m The cartridges were detonated 13 seconds later and their bubble energy recorded as given in Table V. The same method of shocking was used for Sanple 2 (without bentonite) and Sample 2 (with bentonite).

TABLE IV

TEMPERATURE RISE ON SHOCKING SAMPLE Temperature Rise Time taken to Reach (CC) blaximm Temperature (S) Sample 2 22P3 360 (without bentonite) Sample 2 21.90 360 (with bentonite) TABLE V

BUBBLE ENERGY AFTER SHOCKING SA1111PLI-i Distance rom. Booster Bubble Enerp, (M) (W/kg) Sample 2 - 210 (without bentonite) 5 l50 3 l48 2 1P45 1,8 1,40 1,75 Misfire Sample 2 - 2,10 (with bentonite) 5 1,55 3 1,50 2 1,45 1,8 1240 1,75 Misfire 10- Without wishing to be bound by theory, the Applicant believes that the desired increase in viscosity on addition of bentonite to emulsion explosives is obtained by the bentonite acting on components such as the waic on cooling, thereby causing swelling of these components (indicating modification of the crystal structure thereof) and hence thickening of the emulsion.

z The increased emulsion viscosity provides advantages such as higher degree of gas or air bubble retention and hence longer shelf life.

The addition of bentonite to emulsion explosives causes an increase- in rigidity at all temperatures, but the resistance to softening at high temperatures is increased considerably, as seen from the viscosity (see Table II) and cone penetration values (see Table I).

a

Claims

1. In the manufacture of an emulsion explosive comprising a discontinuous phase which forms an oxidizing salt-containing component and a continuous phase which is immiscible with the discontinuous phase and which forms a fuel component, a method of thickening or increasing the viscosity of the emulsion which comprises dispersing insoluble particulate bentonite or a derivative thereof in at least one of the components of the emulsion.

2. A method as claimed in Claim 1, in which the bentonite is added to the emulsion formed after admixture of said components, in a proportion of from about 1,0 to about 5,0% by mass based on the emulsion mass.

3. A method as claimed in Claim 1 or Claim 2, in which the bentonite is swellable sodium bentonite.

4. A method as claimed in Claim 1, Claim 2 or Claim 3, in which at least 90% by mass of the bentonite particles have a particle size less than 425 microns and at most 10% by mass of the bentonite particles have a particle size less than 75 microns.

5. A method as claimed in Claim 4, in which the average particle size of the bentonite particles is from about 75 microns to about 425 microns.

6. A method as claimed in any of the preceding claims, in which the discontinuous phase comprises at least one oxidizing salt selected from the group consisting of ammonium nitrate, alkali metal nitrates, alkaline earth metal nitrates, ammonium perchlorate, alkali metal perchlorates, and alkaline earth metal perchlorates.

7. A method as claimed in Claim 6, in which the discontinuous phase comprises ammonium nitrate with at least one further compound selected from the group consisting of oxygen-releasing salts and fuels which, together with the ammonium nitrate, form a melt which has a melting point which is lower than that of the ammonium nitrate.

8. A method as claimed in any one of the preceding claims, in which the fuel component forms from 2 to 25% by mass of the emulsion.

9. A method as claimed in any one of the preceding claims, in which the fuel of the fuel component is non-self-explosive and is selected from the group consisting of hydrocarbons, halogenated hydrocarbons and nitrated hydrocarbons.

10. A method as claimed in Claim 9, in which said fuel comprises at least one wax selected from the group consisting of paraffin waxes, microcrystalline waxes and slack waxes.

11. A method as claimed in Claim 9 or Claim 10, in which the fuel of the fuel component comprises at least one member of the group consisting of mineral oils, fuel oils, lubricating oils, liquid paraffin, xylene, toluene, petrolatum and dinitrotoluene.

12. A method as claimed in any one of the preceding claims, in which the fuel component comprises at least one emulsifier selected from the group consisting of sorbitan sesquioleate, sorbitan monooleate, sorbitan monopalmitate, sodium monostearate, sodium tristearate, the mono- and diglycerides of fat-forming fatty acids, soya bean lecithin, derivatives of lanolin, alkyl benzene sulphonates, oleyl acid phosphate, laurylamine acetate, decaglycerol decaoleate, decaglycerol decastearate, 2-oley]-4,4'bis(hydroxymethol)-2-oxazoline, polymeric emulsifiers containing polyethylene glycol backbones with fatty acid side chains and derivatives of polyisobutylene succinic anhydride.

13. A method as claimed in any one of the preceding claims, which includes the step of dispersing a density-reducing agent in the emulsion to form an emulsion having a density of from 1,10 to 1,15 g/cm 3 at 251C.

14. A method as claimed in Claim 13, in which the density-reducing agent is selected from the group consisting of microballoons, microspheres and gas bubbles.

15. In the manufacture of an emulsion explosive comprising a discontinuous phase which forms an oxidizing salt-containing component and a continuous phase which is immiscible with the discontinuous phase and which forms a fuel component, the method of thickening or increasing the viscosity of the emulsion, substantially as described herein. -

16. An emulsion explosive whenever manufactUred according to the method of any one of the preceding claims.

Published 19813 at The Pate-.t State 6671 High Hc-'borr.. London WC1R 4TP Rarther copies mk,, be obTainei froyn The Patent Office, mn %;--3 h, Mliltir)lex ech-Tuciaes ltd. St Mary Crkv,.Ker,.. Con. 1 87.