Sensitive Low Water Emulsion Explosive Compositions

This invention relates to water-in-oil explosive compositions and, more specifically, to cap sensitive emulsion explosives. In another aspect, this invention relates to emulsion explosive compositions having increased sensitivity resulting from low water content.

Water-in-oil emulsion type blasting agents were first disclosed by Bluhm in U.S. Pat. No. 3,447,978. These emulsion type blasting agents contain an aqueous solution of inorganic oxidizer salts that is emulsified as the dispersed phase within a continuous carbonaceous fuel phase, and a uniformly distributed gaseous component. Later, cap sensitive emulsion explosive compositions were produced using explosive additives such as trinitrotoluene, and pentaerythritol tetranitrate, (see e.g., U.S. Pat. No. 3,770,522). Water-in-oil emulsion explosive compositions have also been made cap sensitive by the addition of nonexplosive detonation catalysts (see e.g., U.S. Pat. Nos. 3,715,247 and 3,765,964). Most recently, cap sensitive water-in-oil emulsion type explosive compositions, containing neither explosive ingredients nor detonation catalysts, have been disclosed in U.S. Pat. Nos. 4,110,134, 4,149,916 and 4,149,917.

While the cap sensitive emulsion explosive compositions disclosed in the above-identified patents satisfy a wide range of requirements, there are certain blasting applications in which even higher sensitivities than are available using such compositions would be advantageous. One recognized indication of increased sensitivity is the standard half cartridge air gap sensitivity test. Basically, this test measures sensitivity in terms of the length of the air gap across which one-half of a standard cartridge of explosive material can detonate a second half of a cartridge. Thus, for example, the preferred cap sensitive emulsion explosive materials, prepared according to the disclosures of U.S. Pat. No. 4,110,134, have an "air gap sensitivity" of about two inches. As noted above, cap sensitive compositions having sensitivities greater than those of heretofore available cap sensitive explosive emulsion compositions are desirable in certain blasting applications.

It has been discovered that by lowering the water content of the matrix of water-in-oil emulsion explosive compositions to below about 10%, the explosives, which basically comprise a continuous hydrocarbon phase, a discontinuous aqueous phase containing inorganic oxidizing materials, and closed cell void containing materials, attain increased explosive sensitivity. The compositions of the present invention comprise an emulsion matrix having from about 3.5% to about 8% by weight of the hydrocarbon fuel including an emulsifier; from about 4% to less than about 10% by weight of water; and from about 65% to about 85% by weight of inorganic oxidizing salt. To such materials are added from about 0.25% to about 15% by weight of closed cell void-containing materials; and, optionally, up to about 5% by weight nonexplosive detonation catalysts, up to about 20% lower alkylamine or alkanolamine nitrate sensitizing agents and up to about 20% by weight auxiliary fuels to form the explosive emulsion.

Thus, quite unexpectedly, it has been discovered that cap sensitive explosive emulsion compositions detonable by a number 6 cap at diameters of 1.25 inches and less can be substantially increased in sensitivity, as measured by the half cartridge air gap test, by reducing the water content of the matrix to below about 10%. The compositions of the present invention do not employ conventional high explosive sensitizers, are water resistant because of their emulsion characteristics, insensitive to initiation by fire, impact, friction or static electricity, exemplify good low temperature detonation characteristics and are stable enough for commercial utilization.

As used herein, the term "matrix" and/or "emulsion matrix" is defined as the water-in-oil emulsion including fuel, emulsifiers, water and inorganic oxidizing salts but excluding closed cell void-containing materials and auxiliary fuels (such as aluminum for example). Thus, I have discovered that by employing less than 10% by weight water in the emulsion matrix, the sensitivity of the emulsion explosive composition itself (prepared by admixing closed cell void-containing materials and, optionally, sensitizing agents with the matrix) is unexplainably increased.

The water-in-oil explosive emulsions of the present invention comprise, as a continuous phase thereof, from about 3.5% to about 8.0%, and preferably from about 4.5% to about 5.5% by weight of a carbonaceous fuel component, including an emulsifier. The carbonaceous fuel component can include most hydrocarbons, for example, paraffinic, olefinic, naphthenic, aromatic, saturated or unsaturated hydrocarbons. In general, the carbonaceous fuel is a water immiscible emulsifiable fuel that is either liquid or liquefiable at a temperature up to about 200.degree. F., and preferably between about 110.degree. F. and about 160.degree. F. At least about 2.0% by weight of the total composition should be either a wax or oil, or a mixture thereof. If a mixture of wax and oil is employed, the wax content can preferably range from about 1.0% to about 3.0% by weight and the oil content can range from about 3.0% to about 1.0% by weight (depending on wax content) of the total emulsion.

Suitable waxes having melting points of at least about 80.degree. F. such as petrolatum wax, microcrystalline wax, and paraffin wax, mineral waxes such as ozocerite and montan wax, animal waxes such as spermacetic wax, and insect waxes such as beeswax and Chinese wax can be used in accordance with the present invention. Examples of preferred waxes include waxes identified by the trade designations INDRA such as INDRA 5055-G, INDRA 4350-E, and INDRA 2119 sold by Industrial Raw Materials Corporation. Also suitable is ARISTO 143.degree. sold by Union 76. Other suitable waxes are WITCO 110X, WITCO ML-445, and X145-A, which are marketed by Witco Chemical Company, Inc. The most preferred waxes are a blend of microcrystalline waxes and paraffin, such as the wax sold under the trade designation INDRA 2119, identified above. In this regard, more sensitive emulsions can be obtained by using a blend of microcrystalline wax and paraffin rather than microcrystalline or paraffin wax alone.

Suitable oils useful in the compositions of the present invention include the various petroleum oils, vegetable oils, and various grades of dinitrotoluene; a highly refined white mineral oil sold by Whitco Chemical Company, Inc. under the trade designation KAYDOL and the like.

The carbonaceous fuel component of the subject invention will also include the emulsifier used to form the emulsion explosive composition. Any of a wide variety of water-in-oil emulsifiers can be employed and the following examples are not to be interpreted as limiting. Thus, suitable emulsifiers which can be employed in the emulsion explosives of the present invention include those derivable from sorbitol by esterification with removal of one molecule of water such as sorbitan fatty acid esters, for example, sorbitan monolaurate, sorbitan monooleate, sorbitan monopalmitate, sorbitan monostearate, and sorbitan tristearate. Other useful materials comprise mono- and diglycerides of fat-forming fatty acids, as well as polyoxyethylene sorbitol esters, such as polyethylene sorbitol beeswax derivative materials and polyoxyethylene(4)lauryl ether, polyoxyethylene(2)ether, polyoxyethylene(2)stearyl ether, polyoxyalkylene oleate, polyoxyalkylene laurate, oleyl acid phosphate, substituted oxazolines and phosphate esters, mixtures thereof and the like. In general, the emulsifiers should be present in an amount ranging from about 0.5% to about 2.0% by weight of the total composition, and preferably from about 0.8% to about 1.2% by weight of the total composition.

The discontinuous aqueous phase of the explosive emulsions of the present invention are unusual in that they contain less than about 10% by weight of the emulsion matrix of water. Thus, the emulsion matrixes of the compositions of the present invention contain a minimum of about 4.0% water, less than about 10% by weight water and preferably from about 6% to about 8% water. The precise amount of water employed will depend, to some extent, upon the mixture of inorganic oxidizing salts which are employed.

The inorganic oxidizing salts dissolved in this unusually low amount of water will generally comprise from about 65% to about 85% by weight of the emulsion explosive composition. A major proportion of the inorganic oxidizing salt content is preferably comprised of ammonium nitrate; however, mixtures of ammonium nitrate and other alkali and alkaline earth metal nitrates as well as alkali and alkaline earth metal perchlorates can be successfully employed as the inorganic oxidizing salt components of the emulsions of the present invention. Preferred inorganic oxidizing salts, in addition to ammonium nitrate, include sodium nitrate and sodium perchlorate. However, other nitrates and perchlorates, for example calcium nitrate, calcium perchlorate, potassium nitrate and potassium perchlorate can also be used.

The adjustment of the kinds and amounts of inorganic oxidizing salts to obtain an aqueous oxidizing salt solution phase for the emulsion matrix which contains reduced amounts of water is an important part of the subject invention. Especially preferred mixtures of inorganic oxidizing salts include from about 55% to about 70% ammonium nitrate in combination with from about 5% to about 20% sodium nitrate and up to about 10% ammonium or sodium perchlorate. Those skilled in the art will recognize that because of the varying solubility characteristics of suitable inorganic oxidizing salts such as, for example, ammonium perchlorate as compared to ammonium nitrate, adjustment of water content within the range specified may be necessary according to the particular mix of inorganic oxidizing salts employed.

Thus, both the mix of inorganic oxidizing salts and the precise water content below about 10% by weight of the emulsion matrix are variables which can be adjusted to achieve the increased sensitivity of the compositions of the subject invention.

In addition to the above-identified carbonaceous fuel phase and aqueous oxidizer solution phase, explosive emulsions of the present invention preferably include sensitizing agents selected from three categories. The first two categories of sensitizing agents, and mixtures of them can be employed in amounts ranging from about 0% to about 20% by weight of the total explosive emulsion composition. The first category of sensitizing agents are lower alkylamine and alkanolamine nitrates such as methylamine nitrate, ethylamine nitrate, ethanolamine nitrate, propanolamine nitrate, ethylenediamine dinitrate, and similar amine nitrates having from about one to about three carbon atoms. The preferred amine nitrate sensitizing agent for the emulsions of the present invention is ethylenediamine dinitrate. The second category of sensitizing agents are nonexplosive compositions which can be described as detonation catalysts. These detonation catalysts include inorganic metal compounds of atomic number 13 or greater, other than groups 1A and 2A of the periodic table and other than dioxides. Preferable detonation catalysts include compounds of copper, zinc, iron, or chromium, as these produce the greatest increase in sensitivity. Compounds of aluminum, magnesium, cobalt, nickel, lead, silver and mercury are also suitable. For the purpose of this invention, silicon and arsenic are not considered to be metals. Nitrates, halides, chromates, dichromates, and sulfates are preferred for their sensitivity and solubility. Oxides may also be used but oxides are not as convenient as the other compounds because of their low solubility. Mixtures of various detonation catalysts are also contemplated. One especially preferred detonation catalyst is copper chloride. From 0% up to about 5% by weight of the explosive composition of this second category of sensitizing agents can be employed in the explosive emulsions of the present invention. The soluble detonation catalysts can be added by admixing same with the inorganic oxidizing salt solution. Relatively insoluble oxide detonation catalysts can be added to the emulsion matrix.

The low water emulsion explosive compositions of the present invention also employ a third category of sensitizing agents in the form of closed cell void containing materials. Such materials can include any particulate material which comprises closed cell, hollow cavities. Each particle of the material can contain one or more closed cells, and the cells can contain a gas, such as air, or can be evacuated or partially evacuated. Sufficient closed cell void containing materials should be utilized to yield a density of the resulting emulsion of from about 0.9 to about 1.3 grams/cc. Generally, from about 0.25% to about 10% by weight of the explosive emulsion composition of such materials can be employed for this purpose.

The preferred closed cell void containing materials used in the compositions of the subject invention are discrete glass spheres having a particle size in the range from about 10 to about 175 microns. In general, the particle density of such bubbles can be within the range of about 0.1 to about 0.7 grams/cc. Some preferred types of glass microbubbles which can be utilized within the scope of the subject invention are the microbubbles sold by 3M Company and which have a particle size distribution in the range of from about 10 to about 160 microns and a nominal size in the range of from about 60 to 70 microns, and densities in the range of from about 0.1 to about 0.4 grams/cc. Preferred microbubbles sold by 3M Company are distributed under the trade designation B15/250. Further examples of such materials include those sold under the trade designation Eccospheres by Emerson & Cumming, Inc. and which generally have a particle size range of from about 44 to about 175 microns at a particle density of about 0.15 to about 0.4 grams/cc. Microbubbles sold under the designation Q-Cell 200 by Philadelphia Quartz Company are also suitable. When glass microbubbles are employed in the compositions of the subject invention, they can comprise from about 1% to about 5% by weight thereof.

Auxiliary fuels can also be employed. An excellent auxiliary fuel, which is nonexplosive, is particulate aluminum. Aluminum, and other nonexplosive auxiliary fuels, can be employed in amounts ranging from about 0% to about 20% by weight of the emulsion explosive composition. Of course, the second category of sensitizing agents discussed above also act as auxiliary fuels because of their negative oxygen balance.

The low water explosive emulsions of the subject invention can be prepared by premixing the water and inorganic oxidizer salts in a first premix, and the carbonaceous fuel and emulsifier in a second premix. The two premixes are heated, if necessary. The first premix is generally heated until the salts are completely dissolved (about 120.degree. to about 220.degree. F.) and the second premix is heated, if necessary, until the carbonaceous fuel is liquefied (generally about 120.degree. F. or more if wax materials are utilized). The premixes are then blended together and emulsified to form the emulsion matrix and thereafter the glass microbubbles, or other gas entrapping materials are added until the density is lowered to the desired range. In the continuous manufacture of emulsion explosive compositions, it is preferred to prepare an aqueous solution containing the oxidizers in one tank and to prepare a mix of the organic fuel components (excluding the emulsifier) in another tank. The two liquid mixes and the emulsifier are then pumped separately into a mixing device wherein they are emulsified. The emulsion matrix is next pumped to a blender where the glass microbubbles and insoluble auxiliary fuel, if desired, are added and uniformly blended to complete the water-in-oil emulsion explosive product. The resulting emulsion explosive is then processed through a Bursa filler or other conventional device into packages of desired diameters. For example, the emulsion explosives can be packaged in spiral wound or convoluted polymer laminated paper cartridges.

The following examples are given to better facilitate the understanding of the subject invention but are not intended to limit the scope thereof.

Examples set forth in Table I below were prepared in the following manner. A first premix of water and the inorganic oxidizers was prepared at about 220.degree. F. A second mix of the carbonaceous fuel and the emulsifier was prepared at a temperature of about 150.degree. F. The first premix was then slowly added to the second premix, with agitation, to obtain a water-in-oil emulsion. Thereafter, the glass microbubbles were blended into the emulsion to form the final emulsion explosive composition.

All of the compositions set forth in Table I were extruded or tamped into paper tubes having a 11/4 inch diameter, and sealed. The cartridges were then cut in half and tested according to the regulations set forth in 30 CFR 15 et seq., the standards used by the Bureau of Mines to determine the 1/2 cartridge gap sensitivity of permissible type explosives.

While the subject invention has been described in relation to its preferred embodiments, it is to be understood that various modifications thereof will be apparent to those of ordinary skill in the art upon reading the specification, and it is intended to cover all such modifications which fall within the scope of the appended claims.