US 2989389 A
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. 2,989,389 PRIMER CHARGE FOR DETONATORS Josef Prior, Troisdorf, and Aloys Florin, Spich, Germany,
assignors to Dynamit-Actien-Gesellschaft vormals Alfred Nobel & Co., Troisdorf, Germany, a German corporation No Drawing. Filed Apr. 19, 1957, Ser. No. 653,754
Claims priority, application Germany Apr. 27, 1956 4 Claims. (Cl. 52-2) This invention relates to a primer charge for detonators and to a process for preparing the same.
In the explosive and ordnance field, the main explosive charge is exploded by means of an initial primer charge in a detonator, as for example a fuse or primer etc. The primer charge in the detonator may initially be fired electrically, by flame, percussion or the like, and, in certain cases, initiates the explosion of the main charge through an intermediate booster charge.
As the primer charge in connection with detonators, mixtures of technical lead azide with materials which increase the ignition sensitivity without themselves having the character of an initiating explosive, as for example, lead salts of picric acid, aluminium or magnesium powder and, in particular, lead salts of styphnic acid have been used. These materials, and in particular the mixtures of lead azide with lead salts of styphnic acid, have the disadvantage of being over sensitive to ignition and may he accidentally fired by small stray electrostatic charges or the like so that their use is very hazardous. In spite of this hazard, however, these mixtures have found wide spread use due to the lack of a suitable substitute and since technical lead azide itself is not sufliciently sensitive to ignition by flame or electric spark for this purpose.
One object of this invention is a novel primer charge composition for detonators which overcomes the above mentioned disadvantages and which is characterized by adequate flame sensitivity without an over sensitivity as to cause danger by accidental ignition, as for example, by electrostatic charges etc. This, and still further objects, will become apparent from the following description:
The primer charge for detonators, in accordance with the invention, comprises lead azide having an oxidizing agent selected from the group consisting of chromates, and preferably in finely divided form bound to at least the surface thereof.
The lead azide is preferably technical lead azide which may, for example, be prepared in the conventional manner from aqueous solutions of lead salts and salts of hydrazoic acid with the addition of dextrine and inorganic or organic water-soluble bases. This lead azide, having a purity of above 80% lead azide has the granulation size of a free flowing product in loading-machines.
The chromates may be incorporated on the surface of the mass or may form a firmly adherent surface coating on the mass.
In order to produce the primer charge having the oxidizing agent at the surface, a technical lead azide is formed which has an increase of content of base. Such a lead azide may be obtained, for example, either by using a larger addition of water soluble base during the precipitation of the lead azide or by treating the conventionally formed technical lead azide with an aqueous base after it has been produced. The oxidizing agent is then formed on the surface of the basic lead azide by chemical reaction. A solution of a water soluble salt to the oxidizing agent such as potassium sodium or ammonium bichromate is contacted with the basic lead azide causing a reaction in which connection the oxidizing agents, such as lead chromate, is produced on the surface of the lead Patented June 20, 1961 "ice azide In this manner, a strongly adherent surface coating of the oxidizing agent may be built up on the lead an e.
In another manner, the technical lead azide may be treated with the solution of the chromate-compound in a pH-range of between 1 to 5. l
The primer charge formed in accordance with the invention, comprising the lead azide having the bound chromate preferably at the surface, in quantities of 5 to 50%, is characterized by an excellent sensitivity to ignition by flame which is equal to that of the conventional mixtures of lead azide with netural or basic salts of styphnic acid while being inherently safer than the lead azide styphnic acid salt mixtures.
The sensitivity of the charge to ignition by flame or electric spark is essentially determined by the nature of the surface of the charge to be ignited so that the particles of the oxidizing agent located within the mass play a less important role than the particles at the surface. The charge consisting of the lead azide mass having the coating of oxidizing agent is therefore preferable in accordance with the invention.
For the formation of percussion detonators such as percussion primers, mixtures of lead azide with tetrazene and oxygen carriers such as barium chromate, lead chromate, red lead, lead oxide, and the like, and preferably with an abrasive such as powdered glass, silicone, carbide or calcium silicide have been conventionally used. Mere mechanical mixtures of lead azide with the oxidizing agent i.e. lead chromate or products obtained by treating the lead azide with aqueous dispersions of lead chromate, however are not the equivalents of the products in accordance with the invention and are not characterized by the increased flame ignitability of the charge in accordance with the invention. 7
While the invention has been described with reference to certain specific embodiments, various changes and modifications will become apparent to the skilled artisan which fall within the spirit of the invention and scope of the appended claims.
Examples (1) 15 g. of lead azide (92% PbN are stirred within a solution of 3 g. of chromic acid (CrO in 200 cm. water for 15 minutes (pH-value=3). The product obtained consists of a free flowing mass of orange-yellow color consisting of 78% of lead-azide. The sensitivity to a flame is equal to a mixture of 60% lead-azide and 40% lead styphnate.
(2) 15 g. of lead azide (92% PbN are stirred in a solution of 4 g. of sodium dichromate (Nagcl'goq) in 200 cm. water for 15 minutes (pH-value=4-5). The obtained product consists of a free flowing powder of orange-yellow color. Lead azide content: 80%. The sensitivity to a flame is equal to a mixture of 60% leadazide and 40% lead-styphnate.
(3) 15 g. of lead-azide (92%) are treated with a solution of 0,5 g. sodium hydroxide in cm. water. The obtained product has a lead-azide content of 83%. This product is stirred with 200 cm. of a solution of 4 g. sodium-dichromate. A free flowing mass of orangeyellow color is obtained. The sensitivity to a flame is better than a mixture of lead-azide and lead-styphnate 60/40.
1. A primer charge for a detonator consisting essentially of lead-azide having lead chromate bound to at least the surface thereof, said lead chromate being present in an amount of from 5 to 50%.
2. Primer charge according to claim 1 in which said 3 .l adzaz ld a le te hnic le -azid ha ia a p r ty above 80% PbN,.
3. Process for the production of a primer charge which -eomprises contacting a; granular free-flowing *bflSiCflfiQ-d' gazide ;with;an=aqueous;solution of a rnember selected from the group consisting of potassium bichiomate,
vsodium bichromate,ammoniumhichromate and chromic ,acid and V recovering lead-azide having -l ead chromate formed in said contacting firm1y adhering to the surface thereof, in the form of;a free-flowing powder containing .at 1east-50% lead-azide.
*4. Process for the production of; a primer charge which 1 comprises contacting a 1 granular free-flowing bas ic lead- .azidevwith anaqueous solution of 'a-member selected from the group consisting of;potassium bichron ate, sodium bichromate,t ammonium bichrornate .and chromic acid at a pH within the range of from: 1 to S-and recovering 4 leadazide having lead chromate formed in said contacting firmly adhering to the surface thereof, in the form of a free-flowing powder containing at least 50% leadazide.
References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES Mellors Modern Inorganic Chemistry, 1951, page '743-744, -QD151M52,- 1951 (copy in Scientific Library).