Patent Application
20050183803
The present invention relates to processing of an explosive molding powder. More specifically, the present invention relates to processing the explosive molding powder using a lacquer system and a nonaqueous slurry.
Explosive molding powders are known in the art and are used in various types of ordnance, such as grenades, land mines, missile warheads, and demolition explosives. The explosive molding powder is extrudable or pressable into a desired shape for use in the ordnance. Typically, the explosive molding powder is formed by adding a filler, such as a nitramine, to water to form an aqueous slurry. The aqueous slurry is stirred to suspend the filler in the water. A binder is then dissolved in an organic solvent to form a lacquer, which is added to the aqueous slurry. As the lacquer contacts the filler, particles of the filler agglomerate and a coating of the binder forms on the filler. The organic solvent is subsequently removed using heat and an air purge to enhance coating of the filler by the binder. The explosive molding powder is then filtered from the aqueous slurry and dried to produce hard granules.
One problem with producing explosive molding powders by this process is that nitramine-based molding powders are prone to agglomeration, or crashing. While some agglomeration of the filler is necessary to form the granules, too much agglomeration causes the nitramine-based molding powders to stick to surfaces of processing equipment, which results in low yields and reduced molding powder quality of the nitramine-based molding powders. Therefore, to form granules of a desired size, the agglomeration of the filler must be controlled.
Recently, there has been interest in forming aluminized, explosive molding powders, which incorporate aluminum particles into the explosive molding powders. Since aluminum particles smaller than 2 μm are generally water-reactive, nonaqueous media, rather than aqueous slurries, have been investigated to process the aluminized, explosive molding powder. For instance, fluorocarbon media have been used to process explosive molding powders, as disclosed in U.S. Pat. No. 5,750,921 to Chan et al. To form the explosive molding powder, a high explosive is suspended in the fluorocarbon medium. A lacquer of ethyl acetate and a binder is then added to the suspended high explosive to form the molding powder, which is filtered, dried, and pressed into explosive pellets. In this process, the single solvent lacquer does not provide a mix cycle that allows easy isolation of the explosive molding powder. Therefore, the yield and, potentially, the quality of the explosive molding powder are reduced.
It would be desirable to provide a repeatable method of processing an explosive molding powder from a nonaqueous slurry to produce a high yield of a quality explosive molding powder.
The present invention relates to a method of processing an explosive molding powder. The method comprises providing a nonaqueous slurry comprising at least one nitrate compound in an inert fluorocarbon medium. As used herein, the term “nitrate compound” refers to at least one nitramine, at least one nitrate ester, at least one nitrated aromatic, or mixtures thereof The nitrate compound may be selected from the group consisting of hexanitrohexaazaisowurtzitane (“CL-20”), cyclotetramethylene tetranitramine (“HMX”), pentaerythritol tetranitrate (“PETN”), hexanitrostilbene (“HNS”), 2,4,6-trinitro-1,3,5-benzenetriamine (“TATB”), cyclo-1,3,5-trimethylene-2,4,6-trinitramine (“RDX”), and mixtures thereof in the inert fluorocarbon medium. The inert fluorocarbon medium may be selected from the group consisting of perfluoroheptane (C7F16), perfluorooctane (C8F18), perfluorotributylamine, perfluorocyclic ether, and mixtures thereof. The nonaqueous slurry may optionally include a water-reactive additive, such as aluminum, boron, or magnesium.
A lacquer system comprising at least two organic solvents and at least one binder is also provided. The at least two organic solvents of the lacquer system may include at least one binder-soluble organic solvent and at least one binder-insoluble organic solvent. In one embodiment, the binder-soluble organic solvent may be ethyl acetate and the binder-insoluble organic solvent may be ethanol. The at least one binder may be selected from the group consisting of cellulose acetate butyrate (“CAB”), a fluoroelastomer, ethyl vinyl acetate, polyisobutylene polymer, nylon, a thermoplastic polyester elastomer, and a polyether block amide. The lacquer system may optionally comprise a plasticizer selected from the group consisting of bis-dinitropropyl acetal and bis-dinitropropyl formal (“BDNPA/F”), isodecyl pelargonate (“IDP”), dioctyl adipate (“DOA”), dioctyl sebecate (“DOS”), a glycidyl azide polymer (“GAP”), and mixtures thereof
The lacquer system and the nonaqueous slurry are combined to form granules of the explosive molding powder. The granules may comprise particles of the nitrate compound coated with the binder. At least one rinse solution may also be added to the combined lacquer system and the nonaqueous slurry to form the granules. The rinse solution may comprise at least one binder-soluble organic solvent and at least one binder-insoluble organic solvent. The lacquer system, the inert fluorocarbon medium, and the rinse solution(s) may be removed to form the granules.
The present invention also relates to a lacquer system for processing an explosive molding powder. The lacquer system comprises at least two organic solvents and at least one binder. A first organic solvent of the at least two organic solvents is formulated to solubilize the binder and a second organic solvent is formulated so that the at least one binder is insoluble. The first organic solvent may be present from approximately 25% to approximately 75% of a total volume of the lacquer system while the second organic solvent may be present from approximately 25% to approximately 75% of the total volume. In one embodiment, the first organic solvent may be ethyl acetate and the second organic solvent may be ethanol. The binder may be selected from the group consisting of cellulose acetate butyrate, a fluoroelastomer, ethyl vinyl acetate, polyisobutylene polymer, nylon, a thermoplastic polyester elastomer, and a polyether block amide.
The present invention also relates to solutions used in processing an explosive molding powder. The solutions comprise a lacquer system comprising at least two organic solvents and at least one binder and a nonaqueous slurry comprising at least one nitrate compound in an inert fluorocarbon medium. The at least one binder may be soluble in a first organic solvent of the at least two organic solvents and may be insoluble in a second organic solvent of the at least two organic solvents. The first organic solvent may be present from approximately 25% to approximately 75% of a total volume ofthe lacquer system while the second organic solvent may be present from approximately 25% to approximately 75% of the total volume. In one embodiment, the first organic solvent may be ethyl acetate and the second organic solvent may be ethanol. The at least one binder may be selected from the group consisting of cellulose acetate butyrate, a fluoroelastomer, ethyl vinyl acetate, polyisobutylene polymer, nylon, a thermoplastic polyester elastomer, and a polyether block amide. The lacquer system may also comprise at least one plasticizer selected from the group consisting of BDNPA/F, IDP, DOA, DOS, GAP, and mixtures thereof.
The nitrate compound in the nonaqueous slurry may be at least one nitramine, at least one nitrate ester, at least one nitrated aromatic, or mixtures thereof and may be selected from the group consisting of CL-20, HMX, PETN, HNS, TATB, RDX, and mixtures thereof The inert fluorocarbon medium may be selected from the group consisting of perfluoroheptane (C7F16), perfluorooctane (C8F18), perfluorotributylamine, perfluorocyclic ether, and mixtures thereof. The nonaqueous slurry may also comprise a water-reactive additive, such as aluminum, magnesium, or boron.
A lacquer system is disclosed for processing an explosive molding powder. As used herein, the term “lacquer system” refers to a mixed solvent lacquer system that includes at least two organic solvents and at least one binder, which is dissolved in at least one of the organic solvents. The lacquer system is added to a nonaqueous slurry that includes at least one nitrate compound in a nonaqueous medium. As used herein, the term “nitrate compound” refers to at least one nitramine, at least one nitrate ester, at least one nitrated aromatic, or mixtures thereof. Optionally, the nonaqueous medium may include at least one water-reactive additive. Since the lacquer system and the nonaqueous slurry do not include water, the lacquer system may be used to process explosive molding powders having water-reactive additives. The lacquer system may produce a high yield of the explosive molding powder, which has good safety properties and a low void content. Effective and repeatable processing of the explosive molding powder is based on the solubility of the binder(s) in the lacquer system.
The nonaqueous slurry may be formed by suspending the nitrate compound in the nonaqueous medium. The nitrate compound may include, but is not limited to, CL-20, HMX, PETN, HNS, TATB, RDX, or mixtures thereof. The nitrate compound may have a low solubility in the nonaqueous medium to provide effective processing. The nitrate compound used in the nonaqueous medium may have a particle size ranging from a submicron particle size (less than approximately 1 μm) to a particle size of several hundred μm. For instance, the nitrate compound may have a fine particle size of approximately 2 μm, or a coarse particle size, such as a particle size ranging from approximately 100 μm to approximately 400 μm. In one embodiment, the nitrate compound is CL-20 having a 2 μm particle size, or HMX. The nitrate compound may be present in the nonaqueous medium in an amount sufficient to produce a desired amount of the nitrate compound in the explosive molding powder. For instance, the nitrate compound may be present in the nonaqueous medium from approximately 10% to approximately 30%.
The water-reactive additive, if present, may also be suspended in the nonaqueous medium. The water-reactive additive may include, but is not limited to, a water-reactive metal, such as aluminum, magnesium, boron, or mixtures thereof. The water-reactive additive used in the explosive molding powder may have a small particle size, such as a particle size of less than approximately 2 μm. The water-reactive additive may be present in the nonaqueous slurry in an amount sufficient to produce an explosive molding powder having from approximately 1 weight percent (“wt %”)to approximately 30 wt % of the water-reactive additive. In one embodiment, the water-reactive additive is aluminum. The aluminum may be fine aluminum, having a particle size from approximately 1 μm to approximately 5 μm, or ultra-fine aluminum, having a particle size of less than approximately 1 μm. In one embodiment, the aluminum is Alex®, an ultra-fine, nano-aluminum powder having an average particle size of approximately 210 nm. Alex® is available from Argonide Corp. (Sanford, Fla.).
The nonaqueous medium may be an inert fluorocarbon medium in which the nitrate compound has a low solubility. The inert fluorocarbon medium may include, but is not limited to, a perfluoropolyether, perfluoroheptane (C7F16), perfluorooctane (C8F18), perfluorotributylamine, perfluorocyclic ether, or mixtures thereof. The inert fluorocarbon medium may also have a low boiling point so that the inert fluorocarbon medium is easily removed under drying conditions used in processing the explosive molding powder. For instance, the inert fluorocarbon medium may have a boiling point ranging from approximately 60° C. to approximately 100° C. Inert fluorocarbon media are known in the art and are available from numerous sources, such as from 3M (Maplewood, Minn.). In one embodiment, the nonaqueous medium is Fluoroinert™ Electronic Liquid FC-77, which is a thermally stable, fully fluorinated fluoroinert liquid that is available from 3M. Fluoroinert™ Electronic Liquid FC-77 is nonflammable, relatively nontoxic, and is not regulated as a volatile organic compound. Fluoroinert™ Electronic Liquid FC-77 includes 75% perfluorooctane and 25% perfluorocyclic ether, has a boiling point of 97° C., a density of 1.78 g/cc, and a dielectric constant of 1.86.
Other inert fluorocarbon media having similar properties and a boiling point within the range of from approximately 60° C. to approximately 100° C. are known in the art and may be used as the nonaqueous medium. Inert fluorocarbon media having higher boiling points may also be used as the nonaqueous medium. However, more stringent drying conditions may be necessary to remove the inert fluorocarbon medium if it has a higher boiling point. A sufficient amount of the inert fluorocarbon medium may be present in the nonaqueous slurry so that when the lacquer system and the nonaqueous slurry are combined, the lacquer system is diluted by the inert fluorocarbon medium, preventing particles of the nitrate compound from growing quickly and agglomerating to surfaces of the processing equipment. However, the amount of the inert fluorocarbon medium should not be so high as to impede the growth rate of the nitrate compound particles, which would result in the formation of small and highly sensitive granules of the explosive molding powder.
The lacquer system may include at least two organic solvents that are miscible, or at least partially miscible, with each other. The lacquer system may be immiscible, or at least partially immiscible, with the inert fluorocarbon medium. The effectiveness of the lacquer system to process the explosive molding powder may directly depend on solubility of the binder in the lacquer system. The binder may be soluble in at least one of the organic solvents of the lacquer system and insoluble in another of the organic solvents. The organic solvent in which the binder is soluble is referred to herein as the “binder-soluble organic solvent.” Examples of binder-soluble organic solvents include, but are not limited to, esters, ketones, alcohols, alkanes, ethers, amides, nitrites, and aromatics, such as ethyl acetate, acetone, isopropyl acetate, propyl acetate, methyl propyl ketone, and methyl ethyl ketone. The binder may be substantially soluble in the binder-soluble organic solvent, such as being at least approximately 80% soluble. The organic solvent in which the binder is insoluble is referred to herein as the “binder-insoluble organic solvent.” Examples of binder-insoluble organic solvents include, but are not limited to, esters, ketones, alcohols, alkanes, ethers, amides, nitrites, and aromatics, such as ethanol, methanol, propanol, and butanol. The binder may be substantially insoluble in the binder-soluble organic solvent, such as being at least approximately 80% insoluble.
The organic solvents of the lacquer system may be volatile so that they are easily removed under conditions used to dry the explosive molding powder. The binder-insoluble organic solvent may be more volatile than the binder-soluble organic solvent. However, the binder-insoluble organic solvent may be less volatile than the binder-soluble organic solvent. While the Examples herein describe a lacquer system having two organic solvents, the lacquer system may include more than two organic solvents, provided that the binder is soluble in at least one of the organic solvents and is insoluble in at least one of the organic solvents.
The binder-soluble organic solvent may be present in the lacquer system in an amount sufficient to dissolve the binder. However, the amount of the binder-soluble organic solvent may not be so great as to cause the nitrate compound to agglomerate and stick to the surfaces of the processing equipment. The amount of the binder-soluble organic solvent may also be sufficient to allow the binder to uniformly coat the nitrate compound particles during formation of the granules. The binder-insoluble organic solvent may be present in an amount sufficient to soften the granules on their outer surfaces and make the granules moldable. However, the binder-insoluble organic solvent may not soften the granules to such an extent that the granules agglomerate and stick to the surfaces of the processing equipment. The binder-insoluble organic solvent may also produce a smooth surface on the granules. Relative amounts of the binder-soluble organic solvent and the binder-insoluble organic solvent that are used in the lacquer system depend on the nature of the binder that is used. For sake of example only, the binder-soluble organic solvent may be present from approximately 25% to approximately 75% of a total volume of the lacquer system, while the binder-insoluble organic solvent may be present from approximately 25% to approximately 75% of the total volume. In one embodiment, the binder-soluble organic solvent and the binder-insoluble organic solvent are each present at approximately 50% of the total volume of the lacquer system.
The binder may be CAB; a fluoroelastomer, such as Viton® (available from Dupont Dow Elastomers, LLC) or FLUOREL® from 3M; Estane® (C5.14H7.5N0.187O1.76) (available from Noveon, Inc. (Cleveland, Ohio)); ethyl vinyl acetate; polyisobutylene polymer; nylon; a thermoplastic polyester elastomer, such as HyTrel® 8184 (available from E.I du Pont de Nemours and Company); or a polyether block amide, such as PEBAX® (available from Atofina Chemicals Inc.). The binder may be present in the lacquer system in an amount that is sufficient to bind together particles of the nitrate compound in the explosive molding powder. For instance, the binder may be present from approximately 1 wt % to approximately 50 wt %.
Additional components may be present in the lacquer system or in the nonaqueous slurry, such as plasticizers, surfactants, antioxidants, or bees' wax, depending on the desired properties of the explosive molding powder. The plasticizer may be BDNPA/F, IDP, DOA, DOS, GAP; or mixtures thereof. If the plasticizer is BDNPA/F, the bis-dinitropropyl acetal and the bis-dinitropropyl formal may be present in a weight ratio of the bis-dinitropropyl acetal to the bis-dinitropropyl formal ranging from approximately 45:55 to approximately 55:45. The surfactant may include, but is not limited to, a low molecular weight alcohol, such as 1-butanol or isopropanol. The antioxidant may include, but is not limited to, diphenylamine, an n-alkylnitroaniline, such as n-methylnitroaniline or n-ethylnitroaniline, or mixtures thereof.
In one embodiment, CAB is used as the binder, the binder-soluble organic solvent is ethyl acetate, ethanol is used as the binder-insoluble organic solvent, and the inert fluorocarbon medium is Fluoroinert™ Electronic Liquid FC-77.
To process the explosive molding powder, the nitrate compound, the inert fluorocarbon medium, and, optionally, the water-reactive additive may be combined to form the nonaqueous slurry. To avoid electrostatic discharge (“ESD”)hazards, the water-reactive additive may be wetted with the inert fluorocarbon medium before it is mixed with the nitrate compound. The nitrate compound, the water-reactive additive, and the inert fluorocarbon medium may be combined in a first reaction vessel with stirring and heating to keep the nitrate compound suspended. During processing of the explosive molding powder, the first reaction vessel may be continuously stirred at a speed ranging from approximately 200 revolutions per minute (“RPM”)to approximately 800 RPM. The first reaction vessel may be maintained at a temperature below the boiling points of the inert fluorocarbon medium, the binder-soluble organic solvent, and the binder-insoluble organic solvent, such as from approximately 20° C. to approximately 60° C.
The binder-soluble organic solvent and the binder-insoluble organic solvent may be mixed with the binder in a second reaction vessel to form the lacquer system. Additional components, such as one or more of the plasticizer, the surfactant, or the antioxidant may be added to the lacquer system. The lacquer system may then be added to the nonaqueous slurry with continuous stirring and heating. Upon addition of the lacquer system, particles of the nitrate compound may begin to agglomerate. The binder and any additional components may then precipitate on the nitrate compound particles, forming hard, round granules of the explosive molding powder. In other words, the binder and any additional components may form a coating on the nitrate compound particles. Desirably, a uniform coating of the binder and the additional components is applied to the nitrate compound particles. Uniform coating of the nitrate compound particles may be determined by viewing the granules by scanning electron microscopy.
The lacquer system may be added to the first reaction vessel at a lacquer addition rate sufficient to produce the hard, round granules. Depending on the binder and the nitrate compound that are used, the lacquer addition rate may be adjusted to produce the granules of a desired size. The lacquer addition rate may also affect the void content of the granules. Generally, a fast lacquer addition rate, such as addition of the lacquer over a time period of approximately 1 minute to approximately 5 minutes, grows the nitrate compound particles quickly and produces granules having a low void content. In contrast, a slow lacquer addition rate, such as addition of the lacquer over a time period of greater than approximately 10 minutes, grows small nitrate compound particles having a high void content. Desirably, the granules have a size from approximately 0.85 mm to approximately 4 mm. The lacquer addition rate may be adjusted from approximately 1 minute to approximately 15 minutes to produce the granules in this desired size range.
Small granules may be produced when the lacquer system is initially added to the nonaqueous slurry. However, small granules are undesirable because they have reduced safety properties. Therefore, to increase the size of the granules, at least one rinse solution may be added to the combined nonaqueous slurry and the lacquer system. The rinse solution may include organic solvents that are selected based on the nitrate compound used in the nonaqueous slurry. The rinse solution may include the same organic solvents as are used in the lacquer system. However, the relative amounts of each of the organic solvents in the rinse solution may differ from the relative amounts in the lacquer solution. The binder-soluble organic solvent may be present in the rinse solution from approximately 10% to approximately 90% of the total volume while the binder-insoluble organic solvent may be present from approximately 10% to approximately 90% of the total volume. For sake of example only, if CL-20 is used as the nitrate compound, the rinse solution may include 25% ethyl acetate and 75% ethanol. If HMX is used, the rinse solution may include 17% ethyl acetate and 83% ethanol. After the rinse solution is added, the mixture of the nonaqueous slurry and the lacquer system may be stirred for approximately 10 minutes to approximately 50 minutes until the granules grow to the desired size.
The inert fluorocarbon medium and the organic solvents of the lacquer system may be gradually removed from the first reaction vessel. The order in which the inert fluorocarbon medium and the organic solvents are removed may depend on the relative boiling points of the inert fluorocarbon medium and the organic solvents of the lacquer system. After removal, one or more of the inert fluorocarbon medium, the binder-soluble organic solvent, or the binder-insoluble organic solvent may be collected for recycling or reuse. The inert fluorocarbon medium and the lacquer system may be removed by one or more of heating the first reaction vessel, drawing a vacuum over the first reaction vessel, or flowing a gas over the first reaction vessel. For sake of example only, the first reaction vessel may be heated to a temperature ranging from approximately 30° C. to approximately 60° C. The first reaction vessel may also be continuously stirred to assist in removing the inert fluorocarbon medium and the lacquer system. Since the binder-insoluble organic solvent may be more volatile than the binder-soluble organic solvent, the binder-insoluble organic solvent may be removed from the first reaction vessel before the binder-soluble organic solvent. If surfactants or a rinse solution were used in the process, they may also be removed under these conditions.
After the inert fluorocarbon medium and the lacquer system are removed, the granules of the explosive molding powder may be filtered and dried. The granules may be dried by placing them in a vacuum oven for approximately 12 hours to approximately 24 hours at a temperature ranging from approximately 120° F. (48° C.) to approximately 140° F. (60° C.). The resulting granules may be pressed or extruded into pellets, grains, or billets that are used in grenades, land mines, missile warheads, demolition explosives, or other ordnance.
The reaction vessels used to process the explosive molding powder may be conventional reaction vessels, such as slurry kettles or slurry mixers. The reaction vessel may be equipped with a stirrer, such as an impeller, and a heat source, such as a heating jacket, to provide stirring and heat during processing of the explosive molding powder.
In addition to producing the explosive molding powder from the nonaqueous slurry, the lacquer system may also be used to produce an explosive molding powder from an aqueous slurry that includes at least one nitrate compound. To process the explosive molding powder from the aqueous slurry, the binder-soluble organic solvent and the binder-insoluble organic solvent may be insoluble in water. Since the lacquer system may be used with the aqueous slurry, it may also be used to process explosive molding powders that do not include water-reactive additives, such as non-aluminized explosive molding powders or aluminized explosive molding powders having an aluminum particle size of greater than approximately 2 μm. The lacquer system may also be used to process explosive molding powders that have an increased solubility in the inert fluorocarbon medium compared to their solubility in an aqueous medium.
The explosive molding powder formed by the method of the present invention may include at least one binder and at least one nitrate compound. The nitrate compound may be present in the explosive molding powder from approximately 50 wt % to approximately 98 wt %. Desirably, the nitrate compound is present from approximately 70 wt % to approximately 80 wt %. The binder may be present in the explosive molding powder at less than approximately 10 wt %. The explosive molding powder may also include the one or more of the water-reactive additive or the plasticizer.
The explosive molding powder processed by the method of the present invention has a high bulk density and improved impact properties compared to explosive molding powders processed by conventional methods. It is believed that the improvement in the bulk density and the impact properties is the result of producing the explosive molding powder to be substantially free of voids. For instance, the explosive molding powder may have a void volume of less than approximately 3%.
The following includes an example of an aluminized explosive molding powder that was formed by the process of the present invention. This example is merely illustrative and is not meant to limit the scope of the present invention in any way.
All three Examples used the same percentages of four ingredients (CL-20, aluminum, CAB, and BDNPA/F) to form 70 g mixes of the molding powder. The mixes produced in all three Examples were conducted in the same one-liter mixer. The mixes described in Examples 1 & 2 used a micron-sized aluminum, while the mix in Example 3 used a nano-sized aluminum.
Mix RH-1803-31 (Comparative Example) of a CL-20 explosive molding powder was processed using a lacquer having one organic solvent. To prepare the CL-20 explosive molding powder, 3.2% CAB was dissolved into 22 g ethyl acetate to form the lacquer. 4.8% of the BDNPA/F was then added to the lacquer. To form the non-aqueous slurry, 77% CL-20 and 15% Valimet H-2 aluminum were added to 400 g of FC-77 in a one-liter mixer. The Valimet H-2 aluminum was then wetted with FC-77 to avoid ESD hazards. The CL-20 used in the formulation had a 3.5 μm particle size. The non-aqueous slurry was then stirred at 400 RPM to 600 RPM and heated to a temperature of 25° C.-30° C. The lacquer was then added to the non-aqueous slurry over 5-15 minutes. An ethyl acetate rinse of 8 g was added slowly and the mixture was stirred for 15 minutes to 30 minutes to remove the ethyl acetate. During mixing, a small amount of molding powder adhered to the mixer, and the granules were small and had voids. Once the ethyl acetate was removed, the granules were filtered through a #4 Whatman filter and were dried overnight in a vacuum oven at a temperature of 120° F.-140° F.
The granules produced from mix RH-1803-31 had a high void content and a yield of 87%. The safety properties of mix RH-1803-31 are shown in Table 1. Impact properties of Mix RH-1803-31 were measured using an impact test developed by the Bureau of Explosives (“BOE”). Friction properties of Mix RH-1803-31 were measured using a friction test developed by Allegheny Ballistics Laboratory (“ABL”). Electrostatic discharge of Mix RH-1803-31 was measured using an ESD test developed by Thiokol Corporation (“TC”). The BOE Impact Test, the ABL Friction Test, and the TC ESD Test are known in the art and, therefore, details of these tests are not included herein. Because of the high void content of Mix RH-1803-31, the BOE Impact was undesirably sensitive.
Mix RH-1803-38 of a CL-20 explosive molding powder was processed using a lacquer having two organic solvents. To prepare the CL-20 explosive molding powder, 3.2% CAB was dissolved into a mixture of 50% (11 g) ethyl acetate and 50% (11 g) ethanol to form the lacquer system. 4.8% of the BDNPA/F was then added to the lacquer. To form the nonaqueous slurry, 77% CL-20 and 15% Valimet H-2 aluminum were added to 400 g of FC-77 in a one-liter mixer. The Valimet H-2 aluminum was wetted with FC-77 to avoid ESD hazards. The CL-20 used in the formulation had a 3.5 μm particle size. The non-aqueous slurry was then stirred at 370 RPM to 500 RPM and heated to a temperature of 25° C.-30° C. The lacquer was then added to the non-aqueous slurry over 5-15 minutes. Two 4 g rinses, each composed of 75% ethanol & 25% ethyl acetate, were added slowly and the mixture was stirred for 15 minutes to 30 minutes to remove the ethyl acetate and ethanol. During stirring, mix RH-1803-38 did not adhere to the mixer as did the granules in mix RH-1803-31. In addition, the granules of mix RH-1803-38 were larger and did not have voids. Once the ethyl acetate and ethanol were removed, the granules were filtered through a #4 Whatman filter and dried overnight in a vacuum oven at a temperature of 120° F.-140° F.
The granules produced from mix RH-1803-38 had a low void content and a yield of 99%. The safety properties of mix RH-1803-38 are shown in Table 2. Because of the low void content of mix RH-1803-38, the BOE impact was substantially less sensitive than mix RH-1803-31. In addition, the yield of mix RH-1803-38 was increased because there was not as much molding powder adhering to the mixer.
Mix JA-1878-20 of a CL-20 explosive molding powder was processed by dissolving 3.2% CAB into a mixture of 11 g (50%) ethyl acetate and II g (50%) ethanol to form the lacquer system. 4.8% BDNPA/F was added to the lacquer system. In a one-liter slurry mixer, 77% CL-20 and 15% Alex® were added to 400 g of FC-77 to form the nonaqueous slurry. The Alex® was wetted with FC-77 to avoid ESD hazards. The CL-20 used in the formulation had a 3.5 μm particle size. The nonaqueous slurry was stirred at 250 RPM for 3 minutes. Then, the lacquer system was added over 5.5 minutes and the stirring rate was increased to 370 RPM.
A vacuum was applied to the slurry mixer and the stirring rate was increased to 400 RPM. After 5 minutes of stirring, a rinse solution of 4 g of 75% ethanol and 25% ethyl acetate was added to the slurry mixer over 3 minutes at 410 RPM. The stirring speed was then increased to 430 RPM. After 2 minutes, an additional 4 g of 1:3 ethyl acetate/ethanol was added to the slurry mixer over 2 minutes and the stirring speed increased to 440 RPM. After 1 minute, an additional 4 g of 75% ethanol and 25% ethyl acetate was added to the slurry mixer over 1.5 minutes. After 4 minutes, a 3 g rinse solution of 75% ethanol and 25% ethyl acetate was added to the slurry mixer and the stirring speed increased to 480 RPM. The mixture was stirred for 50 minutes at a stirring speed of 270 RPM to 470 RPM to remove the ethyl acetate and the ethanol. Then, the granules were filtered through a #4 Whatman filter and the granules were dried in a vacuum oven at 120° F.-130° F. overnight. The yield of Mix JA-1878-20 was 97.3%. Mix JA-1878-20 produced uniform granules of the CL-20 explosive molding powder and had no voids. The safety properties for Mix JA-1878-20 are shown in Table 3.
The mixes prepared using the mixed solvent lacquer system, as described in Examples 2 and 3, exhibited improved impact properties and improved yields compared to the mix prepared using one solvent in the lacquer system, as described in Example 1.
While the invention may be susceptible to various modifications and alternative forms, specific embodiments have been described in detail herein. However, it should be understood that the invention is not intended to be limited to the particular forms disclosed. Rather, the invention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the following appended claims.
The U.S. Government has a paid-up license in this invention and the right in limited circumstances to require the patent owner to license others on reasonable terms as provided for by the terms of Contract No. DAAE30-00-9-0806.
