WO2004069771A1

WO2004069771A1 - Explosive composition

Info

Publication number: WO2004069771A1
Application number: PCT/IB2004/000292
Authority: WO
Inventors: Roger De Villiers
Original assignee: Metlite Alloys Gauteng (Pty) Ltd.
Priority date: 2003-02-05
Filing date: 2004-02-05
Publication date: 2004-08-19

Abstract

This invention relates to the use of a composition containing metal flakes and/or metal powder and metal oxide powder for enhancing the detonation pressure, blast impulse, power output and/or briscance of molecular explosives, booster and primer compositions. The metal, metal oxide composition may contain from 90 to 10%, by weight, metal in the form of aluminium or aluminium alloy such as Al/Mg and from 10 to 90%, by weight, metal oxide such as AI203, Fe203, Mn03, Mg02. The metal, metal oxide composition may comprise up to 40%, by weight, of the molecular explosives, booster or primer composition.

Description

EXPLOSIVE COMPOSITION

BACKGROUND OF THE INVENTION

THIS invention relates to explosive compositions.

South African Patent No. 96/3387 describes the use of metal and metal oxide flakes and powders and mixtures of metal powders as sensitisers in bulk explosives which comprise an oxidiser salt in the form of ammonium nitrate, and a fuel in the form of fuel oil or coal dust.

International Patent Publication No. WO 02/34696 discloses porous prills comprising a homogeneous mixture of metal flakes and/or metal powder and metal oxide powder and a binder, for use as a sensitiser or energiser in dry ANFO mixers and heavy ANFO mixers, doped emulsion blends and packaged explosives preparations.

Such formulations are ranked as tertiary explosives, due to a relatively low sensitivity to initiation, as opposed to primary and secondary formulations. These formulations are not cap-sensitive. This is attributed to the fact that such formulations are derived from mechanical mixing oxidisers and fuels such as ammonium nitrate and fuel oil. The exponential increase in distance between oxidiser and fuel components in tertiary blends as opposed to molecular structures clearly explains the lower sensitivities, detonation velocities, shock energy and resultant brisance of these formulations. Such formulations have a predominant application in commercial blasting environments. SUMMARY OF THE INVENTION

A first aspect of this invention relates to the use of a composition containing metal flakes and/or metal powder and metal oxide powder (from hereon referred to as a "metal, metal oxide composition"), in enhancing the detonation pressure, blast impulse, power output and/or briscance of molecular explosives, booster and primer compositions.

Typically, the metal,^" metal oxide composition replaces explosives components (such as PETN, TNT and RDX) in the molecular explosives, booster or primer compositions.

The metal, metal oxide composition may contain from 90 to 10%, by weight, metal in the form of aluminium or aluminium alloy such as Al/Mg and from 10 to 90%, by weight, metal oxide such as AI₂O₃, Fe₂O₃, MnO₃ or MgO₂, preferably AI₂O₃ and Fe₂O₃. Usually, the composition will contain 20 to 50%, by weight, aluminium, 1 to 30%, by weight, AI₂O₃, and 50 to 80%, by weight, Fe₂O₃.

The metal, metal oxide composition may comprise up to 40%, by weight, of a molecular explosive, booster or primer composition, typically from 5- 40%, by weight, of the molecular explosive, booster or primer composition.

A further aspect of the invention relates to molecular explosive, booster and primer compositions containing a metal and metal oxide, for enhancing detonation pressure, blast impulse, power output and/or briscance.

According to a preferred embodiment of the invention a booster composition includes PETN and TNT typically at a 60:40 ratio and the metal, metal oxide composition comprises 5 to 20%, by weight, of the booster composition. Typically, the metal, metal oxide composition contains 30 to 40%, by weight, aluminium, 1 to 10%, by weight, AI₂O₃, and 50 to 70%, by weight, Fe₂O₃. According to a further embodiment of the invention a plastic explosives composition includes RDX, polyiso-butylene and sebasic acid and the metal, metal oxide composition comprises 20 to 40%, by weight, of the plastic explosives composition. Typically, the metal, metal oxide composition contains 30 to 40%, by weight, aluminium, 1 to 10%, by weight, AI₂O₃, and 50 to 70%, by weight, Fe₂O₃.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a graph showing a VOD measurement for a booster composition containing 10%, by weight, metal, metal oxide composition; and

Figure 2 is a graph showing a VOD measurement for a booster composition containing 20%, by weight, metal, metal oxide composition.

DESCRIPTION OF PREFERRED EMBODIMENTS

In broad terms, this invention relates to the use of a metal, metal oxide composition to enhance the detonation pressure, blast impulse, power output and/or briscance of molecular explosives, boosters and primers.

Molecular explosives are explosives formulations that are derived by methods of chemical synthesis, yielding molecular structures that have structural molecular intimacy between the oxidiser and fuel components. These formulations are classed as secondary high explosives with respect to sensitivity. Examples of components of these compositions are TNT (2,4,6 Trinitro-Toluene) and PETN (Penta-Aerythritol-Tetra Nitrate) and RDX (cyclotrimethylenetrinitramine). Typical explosives compositions are Pentolite (comprising PETN and TNT), PE plastic explosive (comprising RDX, poly-isobutylene and sebasic acid) and PBX (plastic bonded explosive comprising RDX and plasticizer). Such formulations exhibit high velocities of detonation, high shock energy components, and typically superior brisance when compared to tertiary/commercial explosives formulations. Some of these formulations are cap-sensitive. These formulations are predominantly applied in military and explosives booster applications. Typical explosives compositions include Pentolite, PE (plastic explosives) and PBX (plastic bonded explosive).

The primary function of a booster is to provide an intermediate phase between a primary/highly sensitive initiator such as a detonator, and a less sensitive main charge, such as a tertiary formulation. The booster will detonate when exposed to a detonator (is cap-sensitive), and will enhance the detonation pressure to a level sufficient to effectively initiate the main charge, which is not cap-sensitive. The primary attribute of a booster is sensitivity and detonation pressure. The detonation pressure predominantly determines booster efficiency. For this purpose Pentolite is commonly used. Pentolite comprises PETN and TNT in a typical 60:40 ratio. The PETN component is the more sensitive, and higher detonation pressure yielding formulation. TNT is simply used as a casting medium, as it melts safely at a low and safe temperature (80°C), thereby binding and incorporating the PETN, which has a high melting point.

According to the invention, the inclusion of metal, metal oxide compositions in molecular explosives, boosters and primers increases the detonation pressure of the explosives dramatically. This is evidenced in the unexpectedly high increase in VOD (velocity of detonation measured in m/s) provided by the inclusion of the metal, metal oxide composition. The blast impulse of the explosive is also increased. At the same time, relatively expensive explosives components (such as PETN, TNT and RDX) are replaced with the relatively inexpensive metal, metal oxide composition. As will be explained in more detail below, the metal, metal oxide composition may be obtained from waste products. The metal, metal oxide composition comprises finely ground aluminium flakes and powder or an alloy of aluminium such as Al/Mg. The metal oxide is selected from AI₂O₃, Fe₂O₃, MnO₃ or MgO₂ powder, or a mixture thereof. Typical mixtures of metal, metal oxide compositions are described in South African patent no. 96/3387, the disclosure of which is incorporated herein by reference.

The Al flakes and AI₂O₃ powder are obtained from residues in the form of dross, skimmings, shavings and grindings from aluminium and aluminium production from primary and secondary operations which are often destined for landfill. The Fe₂O₃ powder is obtained from iron oxide fines obtained, for example, from processes carried out on the tailings from the mining of ore bodies or other production processes. The other metal oxides (MnO₃ and MgO₂) may also be obtained from waste. The production of metal, metal oxide compositions from dross is described in detail in International Patent Publication No. WO 02/34696, the disclosure of which is incorporated herein by reference.

The metal, metal oxide composition may contain from 90 to 10%, by weight, metal in the form of aluminium or aluminium alloy and from 10 to 90%, by weight, metal oxide. Usually, the composition will contain 20-50%, by weight, aluminium, 1-30%, by weight, aluminium oxide, and 50-80%, by weight, iron oxide. The composition may also contain other inert compounds such as magnesium chloride, other halide salts (NaCI and KCI), alloy metals (Cu, B, Mg, Si and Ti), and trace metals (Fe, Pb, Bi, Mn and Zn).

Table 1 below shows typical metal, metal oxide compositions. Table 1

The metal, metal oxide composition may be used in powder form or may be formed into porous prills, as described in International Patent Publication No. WO 02/34696, depending on the application.

Tests have been conducted to show that up to 40%, by weight, of a Pentolite booster can be substituted with the metal, metal oxide composition of the invention and the invention will now be described in more detail with reference to the following non-limiting examples.

In the tests, boosters, with the inclusion of the metal, metal oxide composition, were prepared by adding 60:40 Pentolite to a melting pot, and heating the pot to a temperature of 100°C (max) to melt the Pentolite until the fluid stage is reached. The metal, metal oxide composition (in powder form) was mixed into the molten Pentolite fudge to achieve consistent rheology, with the use of a mixing spatula. The molten mix was poured into a volumetric booster casing and, for the purposes of the test, a VOD probe was inserted to the center of the booster. The booster was allowed to chrystallise/solidify and cool to ambient temperature.

VOD (Velocity of Detonation) tests were performed on boosters using a Microtrap VOD/data recorder system with resistance type probe rod. The system was a portable one channel continuous explosives VOD recorder. Resolution = 14 bits, 1 part in 16,384. Recording speed was adjustable from 1 Hz to 2 MHz. Standard memory of 4,000,000 data points = 2 seconds recording time at a 2MHz recording speed. UP to 800m of resistance cable are supported and can be instrumented in blast holes.

In each test, the booster was placed on a witness plate, and connected to a VOD data recorder. A bridge of sighs was placed over the booster set-up and pressure transducers were placed. A detonator was then placed on top of the booster and the charged was fired.

Results of two tests, using the metal, metal oxide composition ho. 3 of Table 1 , are provide below:

Table 2

Copies of the VOD measurements for Tests 1 and 2, respectively, are provided in Figures 1 and 2.

The standard recorded VOD of Pentolite is 6100 m/s. The VOD of the 10% substitution of metal, metal oxide composition (7940 m/s), and of the 20% substitution metal, metal oxide composition (9396 m/s), is unexpectedly high.

HMX (a molecular explosive composition known as high molecular X derived as a byproduct during the nitration process is used to manufacture RDX) has a standard VOD of 9000 m/s. The inclusion of the metal, metal oxide composition in a pentolite booster has therefor increased the VOD of the booster to greater than that of HMX.

Tests were conducted where 30% of a TNT explosives composition was replaced with a metal, metal oxide composition No. 3 from Table 1. The velocity of detonation of 100% TNT was compared to the TNT with a 30% metal, metal oxide composition and the results of these tests are provided in Tables 3 and 4 below.

Table 3 100% TNT

Table 4

30% Composition No. 3 from Table 1 and 60% TNT

It will be seen from Tables 3 and 4 that the inclusion of the 30% metal, metal oxide composition had no negative effect on the VOD of the TNT explosives composition. This is very surprising, as one would expect the inclusion of a metal such as aluminium to detract from shock energy and boost secondary reaction and gas energy and thus to lower the VOD of a TNT explosives composition.

Further tests were conducted to determine the difference in blast impulse of pentolite boosters with various percentages of the metal, metal oxide composition. The tests were conducted in accordance with a procedure of operating of a bridge of sighs as depicted in Figure 3. The bridge of sighs 10 includes a plurality of pipes 12 each of which contains an aluminium gauge and a spike. After an explosion each spike is accelerated along a pipe and comes into contact with a gauge causing an indent in the gauge. Specifications of the gauges and spikes are provided in Tables 5 and 6 below respectively. Indents in the aluminium gauges were measured using a Starret™ micrometer. The comparison was made in terms of indent depth over the area covered by 17 gauges. The analysis was based solely on the depth of penetration, primarily of the central gauges. The gauges were calibrated to give a comparative valuation in terms of impulse (Ns). The impulse was deduced by the Hopkinson Bar and the unit Newton second (Ns) is used. The formula that was deduced from the calibration reads as follows: Y=3.728x+1.1827. Where y = indent in mm and x = in Ns.

Table 5:

Aluminium Gauge specifications

Table 6:

Spike specifications

A 350 g booster containing pentolite and metal, metal oxide granules was cast using the procedure described above. A resistance wire was cast into the booster to determine the VOD while the blast measurements were conducted. A 10 g ball of PE was inserted to the tube section of the booster assisting transfer from a Carrick 6D IED (Instantaneous Electric Detonator with 600mg charge size). The initiating current came from the mil-spec "Shrike" over a 35 m twin strand cable. The BOS (bridge of sighs) was set at 400mm from the central surface, and was kept there for the duration of the test. The bridge was weighted down by two 175 kg steel billets, on the sides of A and H. For the BOS results it must be noted that the detonation direction was central and upward in all cases. The maximum force would be therefore directed at the number 5 gauge. The BOS had two beams, for certainty about data capture the numbering system changes from numeric to alphanumeric. The main beam was numbered from 1 to 9 with 5 in the centre. The two secondary beams are bolted on perpendicular to the main beam. Number 5 became the common gauge for calculations. These beams were numbered A through H starting on the left hand side if the BOS is viewed from number 1. The tail section was set between two half bricks, ensuring that the charge is directly below No. 5. The charge setup was checked before every shot, and the cabling for the resistance wire was take along side number 5 and attached to the 5^th spike with masking tape. This set up did not interfere with the opening to the gauge. A steel plate (size 450 x 450 x 20mm) was embedded in the ground, 250 mm below the surface. The square hole was the size of the plate approximately 450 x 450 mm. The top of the charge then stood level with the ground. The spikes where then set from that level.

The results of the blast impulse tests on different percentages of pentolite and metal, metal oxide composition no. 3 from Table 1 for gauges D, E, 4, 5 and 6 are provided in Table 7 below. These gauges are grouped around the central core of the arced assembly of gauges. The boosters are plane wave generators and focus their energy distribution on the central core of the gauge assembly, i.e. at gauges D, E, 4, 5, and 6.- The values shown are the depth of indentations in the gauges, in mm.

Table 7

It will be seen from Table 7 that the inclusion of from 5%-40%, by weight, of the metal, metal oxide composition in each case led to improved blast impulse performance over 100% pentolite. The best performance is observed by the addition of 5%, by weight, metal, metal oxide composition. On direct comparison a depth of 50% greater was observed from 100% pentolite to the inclusion of 5%, by weight metal, metal oxide composition.

A complete set of results in Ns for all the gauges is provided in Table 8 below. Table 8:

It will be seen from Table 8 that the inclusion of 5-40%, by weight, of the metal, metal oxide composition in each case leads to improved impulse performance over 100% pentolite.

Tests have also been conducted with PE (RDX, poly-iso butylene and sebasic acid). -850+300 micron prills of the metal, metal oxide composition number 3 from Table 1 (30% inclusion of the metal, metal oxide composition with PE) yielded enhanced briscance and detonic power, by punching a superior hole through a 3-inch thick witness plate when compared to a standard 1 kg PE charge. A further test confirmed shock- induced reaction and detonic behavior of the substrate on its own. In this trial, 500g of PE was placed on top of 500g of the metal, metal oxide composition number 3 of Table 1 in a plastic container on top of a 5-inch thick witness plate. Without the prill reacting at a rate of 6-7 km/s, classic Shockwave theory would dispute any form of spalling in the witness plate. The outcome was a clean hole through the witness plate.

Without wishing to be bound to theory, the Arrhenius equation supports the increased VOD and detonation pressure observed by the inclusion of the metal, metal oxide compositions in molecular explosives, booster and primer explosive compositions.

The Arrhenius equation underlines detonation temperature as the highest contributing factor to the initiation process. Some of the formulations were able to achieve stable high order detonation in excess of their known critical densities.

= Ae ^Ea/RT

A = Arrhenius constant

Ea = Activation energy

R = Universal gas constant

T = Temperature in Kelvin

As Ea for military explosives carries a value of between 41.84 kj/mol and 418.4 kj/mol^"1, and R has a value of 8.314 x 10^"3 kj/mol^"1/K^"1, it becomes clear that a small percentage temperature change has a predominant effect on the rate of reaction. As an example, a typical detonation with an Ea of 41.84 kj/mol^"1 at 800°C has a reaction rate more than 10 x greater than the same reaction at 700°C.

It will be seen from the above that the inclusion of the metal, metal oxide composition in molecular explosives, booster and primer compositions yields unexpectedly high VOD's and thus vastly improved detonation pressures. The inclusion of the metal, metal oxide composition in molecular explosives, boosters and primer compositions also improves the blast impulse thereof. At the same time, costs are reduced because expensive explosive components are replaced with the relatively inexpensive metal, metal oxide composition which can be produced from waste.

Claims

1. The use of a metal, metal oxide composition in enhancing the detonation pressure, blast impulse, power output and/or briscance of molecular explosives, booster and primer compositions.

2. The use of claim 1, wherein the metal, metal oxide composition contains from 90 to 10%, by weight, metal and from 10 to 90%, by

- ^" weight, metal oxide. ■ ^{~ ' ■} ■

3. The use of claim 2, wherein the metal is aluminium or aluminium alloy and the metal oxide is AI₂O₃, Fe₂O₃, MnO₃ and/or Mg0₂.

4. The use of claim 3, wherein the metal is aluminium.

5. The use of claim 4, wherein the metal oxide is AI₂O₃ and Fe₂O₃.

6. The use of claim 5, wherein the metal, metal oxide composition contains 20 to 50%, by weight, aluminium, 1 to 30%, by weight, AI₂O₃ and 50 to 80%, by weight, Fe₂O₃.

7. The use of claim 1, wherein the metal, metal oxide composition comprises up to 40%, by weight, of the molecular explosive, booster or primer composition.

8. The use of claim 7, wherein the metal, metal oxide composition comprises from 5 to 40%, by weight, of the molecular explosive, booster or primer composition.

9. A molecular explosive, booster or primer explosive composition containing metal and metal oxide, for enhancing detonation pressure, blast impulse, power output and/or briscance of the molecular explosive, booster or primer composition.

10. The molecular explosive booster, or primer composition of claim 9 including Pentolite, plastic explosive or plastic bonded explosive.

11. A booster composition including PETN and TNT and a metal, metal oxide composition comprising 5 to 20%, by weight, of the booster composition.

12. The booster composition of claim 11, wherein the metal, metal oxide composition contains 30 to 40%, by weight, aluminium, ^~1 to 10%, by weight, AI₂O₃₎ and 50 to 70%, by weight, Fe₂O₃.

13. A plastic explosives composition including RDX, polyiso-butylene and sebasic acid and a metal, metal oxide composition comprising 20 to 40%, by weight, of the plastic explosives composition.

14. The plastic explosives composition of claim 13, wherein the metal, metal oxide composition contains 30 to 40%, by weight, aluminium, 1 to 10%, by weight, AI₂O₃, and 50 to 70%, by weight, Fe₂O₃.