Nanoscale cocrystalline explosives

Abstract

A method of manufacturing a CL-20/HMX cocrystalline explosive which is coated in a polymeric binder, so as to be useful as an explosive molding powder. The cocrystalline material having a desirable average crystal size of from about 300 nm to about 1000 nm, which crystals are intimately coated with a polymeric binder and are produced as granular agglomerates that are less than on average 5 microns in size, and which crystals are relatively easy and safe to handle, transport, store and use. The method involving spray drying a CL-20 and HMX solvent solution containing a polymeric binder to form an intermediary amorphous material—which intermediary is then heated to cocrystallize the CL-20/HMX into the desired size cocrystals and aggregates thereof—which are coated in said polymeric binder.

Claims

1. A method of manufacturing a CL-20/HMX cocrystalline powder material comprising: (a) dissolving a 2:1 molar ratio of CL-20 and HMX in a low boiling point solvent to form a solution; (b) adding to and dissolving within said solution a quantity of about 5 to about 30 weight percent of a polymeric binder; (c) spray drying the solution containing the dissolved polymeric binder to obtain an amorphous intermediary material; (d) after spray drying, heating said amorphous intermediary for an effective period of time to obtain the CL-20/HMX cocrystals which are coated in said polymeric binder; (e) wherein the mean crystal size of the CL-20/HMX cocrystals are from about 300 nm to about 1000 nm, and wherein said cocrystals are in a granular agglomerate form having a mean granule size of below 5 microns.

2. The method of claim 1, wherein said low boiling point solvent is acetone.

3. The method of claim 1, wherein said polymeric binder is selected from the group consisting of PVAc and VMCC.

4. The method of claim 1, wherein said amorphous intermediate is oven heated at a temperature of 100° C.

5. The method of claim 1, wherein said cocrystalline CL-20/HMX powder is used as an explosive molding powder and pressed into a desired configuration.

6. The method of claim 1, wherein the said effective period of time to obtain the CL-20/HMX cocrystals is about 5 hours.

7. The method of claim 1, wherein the quantity of polymeric binder is 10 weight percent.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) A more complete understanding of the present invention disclosure may be realized by reference to the accompanying drawings in which:

(2) FIG. 1 shows the Powder X-ray Diffraction (PXRD) patterns for 1) the amorphous CL-20/HMX/PVAc amorphous precursor prepared by spray drying marked as (a), 2) the product material of the subject invention consisting of CL-20:HMX (2:1) cocrystalline powder containing 10 wt % PVAc marked as (b), and c) triangular reference markers for PXRD peaks of the CL-20:HMX (2:1) cocrystal. See, Bolton et al., Cryst. Growth Des. 2012, 12, 4311-4314.

(3) FIG. 2 is a Scanning Electron Microscopy (SEM) image of the granular agglomerates of the CL-20:HMX (2:1) cocrystalline powder of the subject invention containing 10 wt % PVAc.

DETAILED DESCRIPTION

(4) As detailed above, the present invention provides a method of production for a new cocrystalline Cl-20:HMX with a 2:1 molar ratio material, which is readily useful in current military munitions, as a replacement for such munitions' main charge, boosters, and detonator output charges, and the like. Further, as also stated above, the subject cocrystalline explosive material offers significant handling and safety benefits over similar cocrystalline materials manufactured by prior art methods—such methods not capable of providing the present invention's polymeric coated cocrystals, which cocrystals have a mean crystal size of from about 300 nm to about 1000 nm, which crystals agglomerate into granules that are less than, on average, about 5 microns in size, i.e. desirable, as being relatively easily handled/transported/stored and exhibiting needed safety characteristics.

(5) The new CL-20/HMX (2:1) material of the present invention was collected and analyzed by Powder X-ray Diffraction (PXRD). And, referring to FIG. 1, the intermediate material of the present invention shown in the upper pattern (a)—with no distinct peaks is thereby proven to be amorphous. And, further, this intermediate material after further heating, per the present invention, subsequently converts to the desired crystalline form—as proven by the distinct peaks shown in the middle pattern (b) thereof which matches the published reference pattern of the CL-20:HMX (2:1) cocrystalline material as disclosed by Bolton et al, Cryst. Growth Des. 2012, 12, 4311-4314.

(6) Further, the final CL-20/HMX (2:1) cocrystalline powder product of the present invention was analyzed by Scanning Electron Microscope as seen in FIG. 2. In this figure, the product appears in a granular form of plate-like crystals—with a mean crystal size below 1 micron and with the mean size of the granules below 5 microns.

(7) Preferably, any form of CL-20 and HMX can be used in the present invention—the CL-20 being available from Alliant Techsystems Inc. (aka ATK), located in Arlington, Va., and the HMX from BAE Systems, Inc., Arlington, Va. Alternative binders useful in the present invention include vinyl resins, acrylic resins, cellulose resins, phenolic resins, epoxy resins—wherein a particularly preferred binder is PVAc, which is available from Sigma-Aldrich, St. Louis, Mo., as is the preferred acetone solvent. The particularly preferred PVAc binder has a molecular weight of from about 10,000 to about 1,000,000, preferably about 100,000. An alternatively preferred binder is VMCC, which is a resin binder composed of a carboxy-functional terpolymer consisting of vinyl chloride (83%), vinyl acetate (18%), and maleic acid (1%). The VMCC resin binder has a 19,000 MW and a 1.34 g/cc density.

(8) To aid in the understanding of the subject invention, the following example of the inventive process is provided as illustrative thereof; however, it is merely an example thereof and should not be construed as limitations on the claims:

Example

(9) A solution was prepared by dissolving 5.4 g of CL-20, 1.8 g of HMX, and 0.8 g of polyvinyl acetate (PVAc) 100,000 M.W. in 100 g of acetone at ˜20° C. Next the solution was spray dried using a Buchi model B-290 laboratory spray dryer, available from Buchi Labortechnik AG, Melerseggstrasse-40, Postfach, 9230 Flawil, Switzerland, which spray dryer was equipped with a two-fluid gas nozzle (0.7 mm diameter), i.e. a typical commercially available lab scale spray dryer. N.sub.2 was used for atomization as well as the drying gas—though any inert gas will suffice. The spray drying gas inlet temperature was set to 90° C. The spray drying gas flow rate was set to ˜35 m.sup.3/hour. The liquid feed rate was set to 5 ml/min. The intermediate amorphous product was collected using a cyclone separator and then placed in an oven to provide a hot environment, about 100° C. for a period of about 5 hours—to obtain the desired cocrystalline product coated in the polymeric binder. The intermediate amorphous spray dried material and the final CL-20/HMX cocrystalline product were, as stated above, assessed using PXRD to show the amorphous nature of the intermediate product and the cocrystalline nature of the final inventive product. Further, as detailed above, the final polymer coated product was analyzed by SEM to establish the agglomerated cocrystals into granules of below 5 microns, composed of CL-20/HMX (2:1) with a mean crystal size in the about 300 to about 1000 nm range.

(10) Although the invention has been described in-part above in relation to embodiments thereof, it will be understood by those skilled in the art that variations and modifications can be effected in these preferred embodiments without departing from the scope and spirit of the invention as claimed below.