GB2257135A

GB2257135A - Preparation of a hydrogel type safety explosive

Info

Publication number: GB2257135A
Application number: GB9213106A
Authority: GB
Inventors: Zabala Juan Antonio Andrio; Ocejo Agustin Gonzalez; Rodriguez Luis Antonio Vidal
Original assignee: Union Espanola de Explosivos SA
Current assignee: Union Espanola de Explosivos SA
Priority date: 1991-06-20
Filing date: 1992-06-18
Publication date: 1993-01-06
Anticipated expiration: 2012-06-18
Also published as: PL294937A1; FR2677978A1; FR2677978B1; GB2257135B; GB9213106D0; DE4219960C2; DE4219960A1; ES2047408B1; PL169556B1; ES2047408A1

Description

1 22371735 PREPARATION OF A HYDROGEL TYPE SAFETY EXPLOSIVE COMPOSITION

BACKGROUND

Hydrogel type explosive compositions, still widely used and employed in the explosives market for the intrinsic properties they provide, have, however, hardly found any place in the field of activity of safety or permissible explosives.

To obtain the safety characteristics of these compositions, it is usual to employ inhibitory agents such as sulphates, alkali metal and alkaline earth metal halides and ammonium salts.

In Spanish Patent No. 505,395/5 in the name of Ireco Chemicals, a hydrogel type explosive composition is described, based on the use as an oxidising salt of a minimum of fifteen per cent of calcium nitrate, which enables the sensitivity at lower temperatures to be increased, and at the same time avoids or decreases the use of other sensitisers which, on account of their characteristics, would affect the consideration of this composition as a safety or permissible explosive. Such explosive mixtures are considered to be safety explosives complying with the legislation and regulations of India and the USA.

The most characteristic aspect of West German Patent No. P-2350605.0-45 in the name of IDL Chemicals Limited is the use as a sensitiser of a passivated aluminium together with the use of a coolant salt. Passivation of the aluminium is obtained by means of a prior treatment with a mono- or polyhydric alcohol.

The safety explosive described in Patent No. 87/2089 in the name of AECI Limited of South Africa possesses the feature of the use of aluminium in amounts limited to 1.2 to 1.6% of the explosive mixture, at least 40% of the aluminium being pulverised aluminium which, in 2 addition to differing in form, size and properties with respect to paint- grade aluminium in flake form, possesses a smaller specific surface area.

Spanish Patent Application No. P-9001635 in the name of Dantex Explosives Limited describes a safety or permissible explosive complying with the regulations in force in South Africa, which is basically characterised in that it contains an appropriate amount of a paint grade aluminium in flake form, without any passivation treatment, and does not contain any other type of aluminium.

The basic idea of the present invention is the character of safety explosive based on the use of a halide/nitrate salt pair in its composition.

Owing to the possible existence of potentially inflammable atmospheres, the use of explosives in coal mines involves compliance with strict regulations and the passing of a series of specific tests. Thus, in Spain, they are required to be approved as safety explosives, for which purpose and according to Technical Specification No. ET 310-1-85, they have to pass some tests which, although they differ according to the type or class of explosive under consideration, consist in essence in their being detonated under different conditions of confinement and load, in two types of atmospheres, one in a mixture of methane in air and the other in an atmosphere of coal dust in air.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to the composition and to the process for the manufacture of an explosive aqueous suspension with the consistency of a gel, which possesses the characteristics of a safety or permissible explosive complying with the legislation and regulations in force in Spain.

3 This behaviour is obtained by the presence in the formulation of a pair of inorganic salts which react with one another at the time of detonation through the supply of energy by the other, non-inert constituents present in the composition, giving rise in the nascent state to another salt whose inhibitory power is much greater than that which it would have supplied to the composition if it had been incorporated directly therein.

The use, by direct addition, of alkali metal or alkaline earth metal halides as inhibitory agents in safety explosive compositions is known, but its coolant power is of the order of 30% of the theoretical value, compared with the 90% which is obtained when these halides occur in the nascent state.

Consequently, the basic idea of this invention is the use of ammonium halides, and more specifically ammonium chloride, preferably in an amount of 11-15% in combination with appropriate amounts, preferably 19-25%, of an alkali metal nitrate, especially sodium nitrate or potassium nitrate, and which on reacting produce on the one hand combustible and combustionsupporting gases which supply the energy required as an explosive, and on the other hand an inhibitory salt in the nascent state having maximal coolant and flame-suppressant power.

The process of manufacture involves the prior preparation of three mixtures, two in the liquid phase and the other in the solid phase. The first of these mixtures consists bf an aqueous solution of oxidising salts, with the object of obtaining a eutectic mixture with a relatively low crystallisation temperature in relation to the concentration of salts present therein. A single salt could also be used. It is advantageous to use a thickening agent in this solution with the object of giving the solution an appropriate viscosity, and gums originating from seeds, such as guar gums, or biosynthetic products such as xanthan gum, or fractions or 4 derivatives of starch or celluloses such as carboxymethylcellulose, or synthetic polymers such as polyacrylamide, may be employed in this capacity.

The salts to be employed in this solution are customarily inorganic compounds of alkali metals, alkaline earth metals and ammonia, although sodium or potassium nitrate and ammonium nitrate will preferably be employed, it being possible to employ other salts such as sodium, potassium or ammonium perchlorates or calcium nitrate or mixtures. The solution obtained should be kept hot, at a temperature of approximately ten degrees centigrade above its crystallisation temperature.

The second liquid phase of the formulation contains the basic provision of sensitising constituents, and consists of an aqueous solution of a monomethylamine, hexamine, ethanolamine, diethanolamine, triethanolamine, diethylenetriamine, diethylamine, ethylenediamine or dimethylamine nitrate or mixture thereof. This solution should be kept at a temperature of the order of ten degrees above its crystallisation temperature.

The solid phase is composed of the remainder of the integral components of the formulation, and which basically consist of three groups of products, ammonium chloride or other halide, the remainder of the oxidising salts not included in the first liquid phase, which will preferably be potassium, sodium or ammonium nitrate or a mixture thereof, it also being possible to employ other salts such as calcium nitrate or sodium, potassium and ammonium perchlorates, and the necessary additives of the density regulator, thickener and fuel type.

These fuels can be carbon-containing substances such as coal, products of vegetable origin such as starches, flour, sawdust, rubber, organic liquids such as glycols and, in general, any product among those known for this application, in amounts such as to enable a formulation with a good oxygen balance to be obtained.

The formulation can include a certain proportion, less than 2%, of an aluminium of high specific surface area, such as Paint-grade type aluminium. The products of physical nature which are customarily employed for regulating the density, such as glass or plastic microspheres (perlite), as well as part of the thickening agent employed, accompanied by a crosslinking agent which acts on the thickener, giving the final product a gel consistency, are also incorporated in this mixture. These products are customarily metal-containing ions such as dichromates or antimonates, the commonest being potassium pyroantimonate and potassium dichromate, which are used in very small proportions. Were chemical gasifying agents to be used for regulating the density, these would be added at the end of the preparation process.

These three prior preparations are made in appropriate separate mixers and in large amounts, a proportion thereof being measured out for relatively small amounts of explosive into a high-speed mixer, mixing being carried out in a short period of time, less than one minute, whence the mixture is emptied into a hopper and fed therefrom into the cartridging machines.

A hydrogel type safety explosive composition according to this invention would be composed of the following components: a first aqueous solution composed of 15 to 20% of water, 18 to 25% of sodium or potassium nitrate, 55 to 65% of ammonium nitrate and 0.1 to 0.5% of a thickening agent. The liquid fuels of the formulation may be totally or partially included in this solution. The latter would participate in the final explosive composition in a proportion of the order of 35 to 50%. A second solution of an amine nitrate, in water, in proportions of the order of 15 to 30%. Depending on these proportions, the amount of this solution to be employed in the explosive mixture will be variable, but it is always in such an amount as to provide between 20 and 30% of amine nitrate and an amount of water equivalent to 2.5 6 to 5-0.. The mixture consisting of the remainder of components would be composed of ammonium chloride in amounts of 40 to 60%, sodium or potassium nitrate from 40 to 65%, a starch in a proportion of 10 to 15%, a thickening agent with crosslinker, such as guar gum and potassium pyroantimonate, around 4 to 7%, and a density regulator such as perlite in proportions of 4 to 9% depending on the density which it is desired to obtain, and which can be between 0.85 and 1.35 g/cc. From this mixture of solids, an amount of between 20 and 45% should be taken to make the explosive mixture. When the formulation includes aluminium, this will be in an amount of 1 to 1.8%, and may be added in the f inal mixing process or to the prior mixture of solids.

EXAMPLES

The following table lists a few examples of formulations which illustrate the explosive compositions defined in this invention, which are nonlimiting in nature, many other possible formulations being able to exist:

CONTENTS IN 1 2 3 4 5 6 7 8 10.4 10.3 9.4 11.9 10.5 10.8 10.6 10.5 Water Ammonium chloride 15.0 12.0 15.0 11.0 12.8 14.0 11.0 12.0 Sod. nitrate 22.4 19.1 24.0 20.5 21.4 21.5 23.0 Pot. nitrate - - - 18.8 - - - - Cal. nitrate - 6.0 3.0 - - - 3.0 - Ammo. nitrate 24.0 22.0 22.0 29.0 26.7 25.0 24.3 24.3 Sod. chloride 5.0 - - Monomethyl amine nitrate 22.0 25.0 19.8 23.0 18.0 23.0 23.2 23.2 Aluminium 1.5 - 1.3 1.4 1.2 - 1.0 1.0 Additives 4.7 5.6 5.5 4.9 5.3 5.8 5.4 6.0 7 All the formulations were prepared according to the process described in this invention, employing amounts of the prior mixtures lying between the percentages defined, and in amounts such as to obtain fifty kilograms of explosive mixture. These formulations have densities which fluctuate between 1.05 and 1.24, plus a detonation velocity of between 2700 m/s and 3100 m/s. They were tested as type II safety explosives according to Technical Specification ET-310-1-85 of the Spanish regulations in the tests specified in the standard.

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Claims

1. A safety or permissible explosive composition which has the consistency of a gel and which consists of a solution of oxidising salts in a proportion of 35 to 50%, a solution of amine nitrate in a proportion of 18 to 25% and a mixture of solids in a proportion of 20 to 35%, in which composition a salt pair consisting of an ammonium halide and an alkali metal nitrate, which acts as an inhibitor, is included, thickening agents and density regulating agents being present in addition.

2. An explosive composition according to Claim 1, in which the salt pair consists of ammonium chloride and sodium nitrate, in a proportion of the former of between 11 and 15% and of the latter of between 19 and 25%, preferably.

3. An explosive composition according to Claims 1 and 2, which employs as a sensitiser an amine nitrate, which can be monomethylamine nitrate or nitrates of other amines such as hexamine, ethanolamine, diethanolamine, triethanolamine, diethylenetriamine, diethylamine, ethylenediamine or dimethylamine or a mixture thereof.

4. An explosive composition according to Claims 1 to 3, which employs as oxidising salts ammonium or alkali metal or alkaline earth metal nitrates or sodium or potassium or ammonium perchlorate or mixtures thereof.

5. An explosive composition according to Claims 1 to 4, which employs as density regulators products having a physical action such as glass or plastic microspheres, perlites or products which give rise to a chemical gasification.

1 9

6. An explosive composition according to Claims 1 to 5, which, in the mixture of solids, can include fuels or energy-rich substances of vegetable origin such as starches, flours, sawdust., rubber, coal and sugars, metals with aluminium, or alternatively liquid fuels such as products derived from petroleum, glycols, which are incorporated in the solution of oxidising substances.

7. An explosive composition according to Claims 1 to 6, which employs as a thickener products derived from seeds, such as guar gum, galactomannans, biosynthetic products such as xanthan gum or derivatives of starch or cellulose such as carboxymethyl cellulose, or synthetic polymers such as polyacrylamide.

8. A process for the manufacture of safety or permissible explosive compositions according to Claims 1 to 7, which, containing a salt pair generating inhibitory products, consists in a preparation of premixtures of oxidising substances, sensitisers and additives, one in the liquid phase and another in the solid phase, and in a subsequent combined processing to arrive at the composition which fulfils the desired requirements.