Thermally-Expandable Microspheres in Explosives and Propellants for Tunable Detonation and Deflagration Control

Abstract

The present disclosure describes compositions combining 1,3,5-trinitro-1,3,5-triazinane (RDX)-based rubberized explosive and thermally-expandable microspheres (TEMs), to create explosive and or propellant compositions which are switchable in detonation properties, and methods for making and using such compositions.

Description

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This Application relates to and claims the benefit of U.S. Provisional Patent Application No. 63 / 620,341, filed on Jan. 12, 2024. The contents of which are expressly incorporated herein by reference in its entirety into this present disclosure.GOVERNMENT SUPPORT CLAUSE

[0002] This invention was made with government support under grant W911NF-22-2-0170 awarded by the U.S. Army Research Office. The government has certain rights in the invention.FIELD OF INVENTION

[0003] This disclosure relates generally to the area of explosive and propellant compositions, methods for manufacture and use. The present disclosure more particularly addresses methods for making and using compositions of explosive or propellant which incorporate microspheres to desensitize, modify or control detonation. In particular, the present disclosure describes compositions combining 1,3,5-trinitro-1,3,5-triazinane (RDX)-based rubberized explosive and thermally-expandable microspheres (TEMs), and methods for the use of microspheres to prevent explosion and compositions which act as switchable explosive material.BACKGROUND

[0004] Improving the safety of explosive materials through the synthesis of insensitive explosives has been studied extensively. However, little work has focused on creating switchable explosives. A switchable explosive is normally insensitive to detonation, and therefore safe to handle and transport, but can be sensitized when needed to create a functional explosive. Similarly, it may be desired to desensitize an explosive to prevent its function.

[0005] The present disclosure describes the ability to create a switchable 1,3,5-trinitro-1,3,5-triazinane (RDX)-based rubberized explosive using thermally-expandable microspheres (TEMs). The addition of TEMs to the explosive formulation allowed for microstructural changes and potential hot spot locations such as voids to form as the microspheres expanded. Small voids (less than about 10 μm) are more likely to be critical hot spots when shocked, and likewise larger voids are less likely to ignite successfully (sub-critical) when shocked. Consequently, both sensitization and desensitization are possible. The rubberized explosive considered here with unexpanded microspheres was unable to sustain a detonation for the size used, but after specific heating followed by cooling to produce small voids, a detonation was achieved. That is, the TEMs addition to the RDX-based rubberized explosive resulted in an explosive that is detonation insensitive when unheated but becomes a functional explosive after it is sensitized through heating. This paves the way to create insensitive explosive formulations with on-demand switchable detonation function through the incorporation of thermally-expandable microspheres. Desensitization was also demonstrated with specific heating of TEMs in an initially detonable explosive charge. And finally, we also demonstrated that deflagration can be affected by heating TEMs.BRIEF SUMMARY OF THE INVENTION

[0006] The present disclosure provides a method of controlling the detonation properties of an explosive composition comprising combining 1,3,5-trinitro-1,3,5-triazinane (RDX)-based rubberized explosive with thermally-expandable microspheres (TEMs) such that the detonation properties of the resulting composition is different than that of the original explosive or propellant composition.

[0007] The present disclosure provides for a method for tuning deflagration properties of an explosive composition comprising combining 1,3,5-trinitro-1,3,5-triazinane (RDX)-based rubberized explosive with thermally-expandable microspheres (TEMs).

[0008] The present disclosure provides for a method of making an explosive composition comprising combining 1,3,5-trinitro-1,3,5-triazinane (RDX)-based rubberized explosive with thermally-expandable microspheres (TEMs) wherein said combination formulation allows for tuning detonation properties of the explosive composition.

[0009] The present disclosure also provides for a method of making an explosive composition comprising combining 1,3,5-trinitro-1,3,5-triazinane (RDX)-based rubberized explosive with thermally-expandable microspheres (TEMs) wherein said combination formulation allows for where the explosive composition is switchable between sensitive to detonation (sensitizing, sensitized) or insensitive to detonation (desensitizing, desensitized).

[0010] The present disclosure further provides for making an explosive composition that is desensitized, where the explosive composition was treated with an about 95° C. heating cycle.

[0011] The present disclosure provides for making an explosive composition where the explosive composition is further treated by sensitizing for detonation. The present disclosure provides for making a desensitized explosive composition as described above, sensitized to detonation. The present disclosure provide for sensitizing an explosive composition as described where the explosive composition is subject to an about 125° C. heating cycle.

[0012] Thus the present disclosure provides for a method of making an explosive composition comprising combining 1,3,5-trinitro-1,3,5-triazinane (RDX)-based rubberized explosive with thermally-expandable microspheres (TEMs) wherein said combination formulation where the explosive composition is made detonable by heat treatment.

[0013] Thus the present disclosure provides for a method for transforming a detonable material to a non-detonable material by heating the detonable material to create voids that are too large to function as critical hot spots. Thus the present disclosure provides for a method of making a detonable explosive composition where the weight ratio of coarse to fine weight of rubberized RDX is at least about 1:1.

[0014] The present disclosure provides for tuning deflagration properties of the explosive composition, tuning detonation properties of a propellant composition, or tuning deflagration properties of a propellant composition.

[0015] The present disclosure provides for an explosive composition made by a method as described above. Thus the present disclosure provides for an explosive composition comprising 1,3,5-trinitro-1,3,5-triazinane (RDX)-based rubberized explosive and thermally-expandable microspheres (TEMs). The present disclosure provides for the explosive composition made by the method described, which is desensitized to detonation, which has about a 1:1 coarse to fine weight ratio rubberized RDX explosive.

[0016] The present disclosure provides for a method for making 1,3,5-trinitro-1,3,5-triazinane (RDX)-based rubberized explosive switchable, comprising making an explosive composition by combining 1,3,5-trinitro-1,3,5-triazinane (RDX)-based rubberized explosive and thermally-expandable microspheres (TEMs), subjecting the explosive composition to heat treatment at about 95° C.

[0017] The present disclosure provides for a method for making 1,3,5-trinitro-1,3,5-triazinane (RDX)-based rubberized explosive switchable, comprising making an explosive composition by combining 1,3,5-trinitro-1,3,5-triazinane (RDX)-based rubberized explosive and thermally-expandable microspheres (TEMs), manufacturing the explosive composition to be below the material's critical thickness.

[0018] The present disclosure provides for a method for making 1,3,5-trinitro-1,3,5-triazinane (RDX)-based rubberized explosive desensitized for detonation, comprising making an explosive composition by combining 1,3,5-trinitro-1,3,5-triazinane (RDX)-based rubberized explosive and thermally-expandable microspheres (TEMs); treating the explosive composition to heat treatment at about 95° C.

[0019] The present disclosure provides for a method for making a switchable explosive composition comprising;

[0020] first making an explosive composition that is desensitized to explosion by combining 1,3,5-trinitro-1,3,5-triazinane (RDX)-based rubberized explosive and thermally-expandable microspheres (TEMs), subjecting the explosive composition to about 95° C. heat treatment, creating a desensitized explosive composition;

[0021] second, subjecting the desensitized explosive composition to about 125° C. heat treatment, creating a sensitized explosive composition.

[0022] In particular, the present invention provides for methods of making a switchable explosive composition comprising a mixture of RDX comprising Class 5 RDX, Class 3 RDX, and an appropriate binder, and combining the mixture of RDX with TEM. A preferred binder is hydroxyl-terminated polybutadiene (HTPB)-based binder. A preferred TEM is Expancel® 031DU40.

[0023] The explosive composition of the present invention combines a fine and coarse RDX into an explosive mixture with appropriate binder. In particular, fine RDX is represented by Class 5 RDX, and coarse RDX is represented by Class 3 RDX.

[0024] The present disclosure provides for a mixture of RDX that is about 85% total RDX weight to about 15% binder by weight (RDX85.0). In particular it is preferable to have the RDX85.0 mixture to comprise about 68% Class 3 RDX, about 17% Class 5 RDX and about 15% binder, by weight. The present disclosure illustrates various RDX85.0 mixtures, as for example in Table 1. Thus the present disclosure provides for RDX85.0 mixtures which combine from about 63% to 69% coarse RDX with fine RDX and TEMs. The present disclosure also provides for explosive mixtures whish combines about 12% to about 18% fine RDX. It is further encompassed an explosive mixture that is 1:1 by weight fine to coarse RDX.

[0025] The present invention encompasses the mixing of RDX with TEMs in the explosive mixture, with the weight of TEMs replacing an equal weight of RDX and the result combined with the appropriate 15% by weight binder. The present disclosure illustrates mixtures of RDX and TEM as illustrated by the data in Table 1. Thus the present disclosure encompasses explosive mixtures of RDX and TEMs that have from about 0.21 to about 8.5 by weight TEMs.

[0026] The present invention provides for the preparation of an explosive mixture which can be desensitized to detonation by heat cycle treatment to expand the TEM content. Thus the present disclosure provides for treatment of the explosive mixture by a heating cycle that has a profile with a ramp from about 40° C. to about 95° C. in 25 minutes, a 30 minute isotherm at about 95° C., and a cooldown to about 30° C. in 25 minutes.

[0027] The present invention provides for a method for sensitizing explosive mixture (either raw or after desensitizing) for detonation by heat cycle treatment to minimize the TEM expansion. Thus the present disclosure provides for the treatment of the explosive mixture by a heating cycle that has a profile with a ramp from about 40° C. to about 125° C. in 45 minutes, a 30 minute isotherm at about 125° C., and a cooldown to about 30° C. in 45 minutes.

[0028] These and other features, aspects and advantages of the present invention will become better understood with reference to the following figures, associated descriptions and claims.BRIEF DESCRIPTION OF THE DRAWINGS

[0029] A better understanding of the present disclosure will be obtained upon reference to the following description in conjunction with the accompanying drawings.

[0030] FIG. 1. Illustrates a schematic for the brass witness plate and high-speed camera experiment.

[0031] FIG. 2. (FIG. 2A-C) Shows Micro x-ray computed tomography for a) unheated, b) unheated magnified view and c) 95° C. heated, and d) 95° C. heated magnified view of a TEMS1.70 sample.

[0032] FIG. 3 (FIG. 3A-B) Shows Micro x-ray computed tomography for a) unheated and b) 125° C. heated TEMS1.70 samples.

[0033] FIG. 4. (FIG. 4A-C) Shows High speed imaging of a) RDX85.0 unheated, b) TEMS0.85 unheated and c) TEMS0.85 heated at 95° C.

[0034] FIG. 5. (FIG. 5A-B) Shows High speed imaging of a) RDX85.0 unheated and b) RDX85.0 heated at 125° C.

[0035] FIG. 6. (FIG. 6A-C Upper low mag / Lower high mag) Shows Scanning electron microscope images of RDX85.0 samples that were a) unheated, b) heated at 95° C., and c) heated at 125° C.

[0036] FIG. 7. (FIG. 7A-B) Shows High speed imaging of a) TEMS0.85 unheated and b) TEMS0.85 at 125° C.

[0037] FIG. 8. (FIG. 8A-B) Shows High speed imaging of a) TEMS1.70 unheated and b) TEMS1.70 heated at 125° C.

[0038] FIG. 9. (FIG. 9A-B) Shows High speed imaging of a) RDX1:1 unheated and b) RDX1:1 heated at 95° C.

[0039] FIG. 10. Shows a plot of Mass burning rate of unheated, heated at 95° C., and heated at 125° C. TEMS1.70 propellant samples.DETAILED DESCRIPTION

[0040] While the concepts of the present disclosure are illustrated and described in detail in the figures and the description herein, results in the figures and their description are to be considered as exemplary and not restrictive in character; it being understood that only the illustrative embodiments are shown and described and that all changes and modifications that come within the spirit of the disclosure are desired to be protected.

[0041] Unless defined otherwise, the scientific and technology nomenclatures have the same meaning as commonly understood by a person in the ordinary skill in the art pertaining to this disclosure.

[0042] As used herein: “Explosive” or “explosives” incorporates any related incendiary or otherwise exploding material which can be used as a destructive explosive or as a propellant, such as for a projectile. When referring to “controlling” the detonation process, “controlling” is meant to encompass modulating, inhibiting, delaying, modifying or otherwise altering from the unaltered properties of an explosive composition.

[0043] In the present disclosure the term “about” can allow for a degree of variability in a value or range, for example, within 20%, within 10%, within 5%, or within 1% of a stated value or of a stated limit of a range.

[0044] In the present disclosure the term “substantially” can allow for a degree of variability in a value or range, for example, within 80%, within 90%, within 95%, or within 99% of a stated value or of a stated limit of a range.

[0045] The present disclosure provides a method of controlling the detonation properties of an explosive composition comprising combining 1,3,5-trinitro-1,3,5-triazinane (RDX)-based rubberized explosive with thermally-expandable microspheres (TEMs) such that the detonation properties of the resulting composition is different than that of the original explosive or propellant composition.

[0046] The present disclosure provides for a method for tuning deflagration properties of an explosive composition comprising combining 1,3,5-trinitro-1,3,5-triazinane (RDX)-based rubberized explosive with thermally-expandable microspheres (TEMs).

[0047] The present disclosure provides for a method of making an explosive composition comprising combining 1,3,5-trinitro-1,3,5-triazinane (RDX)-based rubberized explosive with thermally-expandable microspheres (TEMs) wherein said combination formulation allows for tuning detonation properties of the explosive composition.

[0048] The present disclosure also provides for a method of making an explosive composition comprising combining 1,3,5-trinitro-1,3,5-triazinane (RDX)-based rubberized explosive with thermally-expandable microspheres (TEMs) wherein said combination formulation allows for where the explosive composition is switchable between sensitive to detonation (sensitizing, sensitized) or insensitive to detonation (desensitizing, desensitized).

[0049] The present disclosure further provides for making an explosive composition that is desensitized, where the explosive composition was treated with an about 95° C. heating cycle.

[0050] The present disclosure provides for making an explosive composition where the explosive composition is further treated by sensitizing for detonation. The present disclosure provides for making a desensitized explosive composition as described above, sensitized to detonation. The present disclosure provides for sensitizing an explosive composition as described where the explosive composition is subject to an about 125° C. heating cycle.

[0051] Thus the present disclosure provides for a method of making an explosive composition comprising combining 1,3,5-trinitro-1,3,5-triazinane (RDX)-based rubberized explosive with thermally-expandable microspheres (TEMs) wherein said combination formulation where the explosive composition is made detonable by heat treatment.

[0052] The present disclosure provides for a method for transforming a detonable material to a non-detonable material by heating the detonable material to create voids that are too large to function as critical hot spots.

[0053] The present disclosure provides for tuning deflagration properties of the explosive composition, tuning detonation properties of a propellant composition, or tuning deflagration properties of a propellant composition.

[0054] The present disclosure provides for an explosive composition made by a method as described above which provides for an explosive composition comprising 1,3,5-trinitro-1,3,5-triazinane (RDX)-based rubberized explosive and thermally-expandable microspheres (TEMs) which is desensitized to detonation, which has about a 1:1 coarse to fine weight ratio rubberized RDX explosive.

[0055] The present disclosure provides for a method for making 1,3,5-trinitro-1,3,5-triazinane (RDX)-based rubberized explosive switchable, comprising making an explosive composition by combining 1,3,5-trinitro-1,3,5-triazinane (RDX)-based rubberized explosive and thermally-expandable microspheres (TEMs), subjecting the explosive composition to heat treatment at about 95° C.

[0056] The present disclosure provides for a method for making 1,3,5-trinitro-1,3,5-triazinane (RDX)-based rubberized explosive switchable, comprising making an explosive composition by combining 1,3,5-trinitro-1,3,5-triazinane (RDX)-based rubberized explosive and thermally-expandable microspheres (TEMs), manufacturing the explosive composition to be below the material's critical thickness.

[0057] The present disclosure provides for a method for making 1,3,5-trinitro-1,3,5-triazinane (RDX)-based rubberized explosive desensitized for detonation, comprising making an explosive composition by combining 1,3,5-trinitro-1,3,5-triazinane (RDX)-based rubberized explosive and thermally-expandable microspheres (TEMs); treating the explosive composition to heat treatment at about 95° C.

[0058] The present disclosure provides for a method for making a switchable explosive composition comprising;

[0059] first making an explosive composition that is desensitized to explosion by combining 1,3,5-trinitro-1,3,5-triazinane (RDX)-based rubberized explosive and thermally-expandable microspheres (TEMs), subjecting the explosive composition to about 95° C. heat treatment, creating a desensitized explosive composition;

[0060] second, subjecting the desensitized explosive composition to about 125° C. heat treatment, creating a sensitized explosive composition.

[0061] In particular, the present invention provides for methods of making a switchable explosive composition comprising a mixture of RDX comprising Class 5 RDX, Class 3 RDX, and an appropriate binder, and combining the mixture of RDX with TEM. A preferred binder is hydroxyl-terminated polybutadiene (HTPB)-based binder. A preferred TEM is Expancel® 031DU40.

[0062] The explosive composition of the present invention combines a fine and coarse RDX into an explosive mixture with appropriate binder. In particular, fine RDX is represented by Class 5 RDX, and coarse RDX is represented by Class 3 RDX.

[0063] The present disclosure provides for a mixture of RDX that is about 85% total RDX weight to about 15% binder by weight (RDX85.0). In particular it is preferable to have the RDX85.0 mixture to comprise about 68% Class 3 RDX, about 17% Class 5 RDX and about 15% binder, by weight. The present disclosure illustrates various RDX85.0 mixtures, as for example in Table 1. Thus the present disclosure provides for RDX85.0 mixtures which combine from about 63% to 69% coarse RDX with fine RDX and TEMs. The present disclosure also provides for explosive mixtures whish combines about 12% to about 18% fine RDX. It is further encompassed an explosive mixture that is 1:1 by weight fine to coarse RDX.

[0064] The present invention encompasses the mixing of RDX with TEMs in the explosive mixture, with the weight of TEMs replacing an equal weight of RDX and the result combined with the appropriate 15% by weight binder. The present disclosure illustrates mixtures of RDX and TEM as illustrated by the data in Table 1. Thus the present disclosure encompasses explosive mixtures of RDX and TEMs that have from about 0.21 to about 8.5 by weight TEMs.

[0065] The present invention provides for the preparation of an explosive mixture which can be desensitized to detonation by heat cycle treatment to expand the TEM content. Thus the present disclosure provides for treatment of the explosive mixture by a heating cycle that has a profile with a ramp from about 40° C. to about 95° C. in about 25 minutes. It is further provided for a subsequent about 30 minute isotherm at about 95° C. Further it is provided for a further cooldown to about 30° C. in about 25 minutes.

[0066] The present invention provides for a method for sensitizing explosive mixture (either raw or after desensitizing) for detonation by heat cycle treatment to minimize the TEM expansion. Thus the present disclosure provides for the treatment of the explosive mixture by a heating cycle that has a profile with a ramp from about 40° C. to about 125° C. in about 45 minutes. It is further encompassed a subsequent about 30 minute isotherm at about 125° C. Further, there can be a subsequent cooldown to about 30° C. in about 45 minutes.INTRODUCTION

[0067] The development of switchable energetic materials is critical for increased safety and the prevention of accidents, especially for applications using high explosives (HE). Extensive research has been conducted to develop insensitive explosives such as triaminotrinitrobenzene (TATB) and ammonium nitrate at the expense of performance. However, accidents still occur with insensitive energetic materials such as the Beirut disaster in 2020. Unlike current insensitive energetic materials, an ideal switchable energetic material would be insensitive to unplanned initiation but perform well when sensitized. The energetic material would undergo a specific process to switch from insensitive to detonable when an application requires its use, creating an explosive that is safe from unplanned explosion until the material is used for its intended purpose. Likewise, a more sensitive explosive that could be desensitized on demand would be useful for some applications.

[0068] There is some previous work in switchable energetic materials. Switchable explosives have been created by tuning the explosive performance through fluid activation (Brown et al., 2023). The 1,3,5,7-tetranitro-1,3,5,7-tetrazocane (HMX)-based high explosive used in the study by Brown et al. was printed in strands below the material's critical diameter, meaning that the material would not sustain a detonation wave. Loss of energy in the gaps between the strands resulted in the failure of the detonation as it propagated through the material. However, the material was able to detonate after the 3D printed explosive lattice was filled with an activating fluid. The stronger confinement of the activating fluid increased the pressure of the shocks interacting between the 3D printed strands, allowing the material to sustain a detonation. Although the HMX-based explosive material was shown to be switchable, it required the addition of an activating fluid to tune the detonation performance as opposed to a switchable explosive material that is a single component. Likewise, the fluid will likely decrease performance significantly, especially if an inert is chosen.

[0069] Increasing the porosity and hot spot locations within an explosive material has been theorized as a mechanism to create switchable explosives (Duque et al., 2020). Porosity has been shown to sensitize HE due to the shock compression of hot spot locations (Parker et al., 2021). When a material is initiated by a shock, trapped gases within the hot spot locations are adiabatically compressed by the shock front. This leads to a localized temperature increase, which drives local chemical reactions leading to detonation. The formation of hot spots has been shown to increase explosive sensitivity, as a porous bulk explosive material was found to have higher shock sensitivity than the same bulk material at a higher theoretical maximum density. An increase in porosity can be accomplished in several ways; however, this study proposes the addition of thermally-expandable microspheres (TEMs) paired with thermal cycling as the means to increase porosity and hot spot locations (voids).

[0070] Thermal cycling of explosives has been shown to increase porosity and void size in 5-iodo-2′-deoxyuridine (IDOX), HMX, and TATB-based plastic bonded explosives (PBX) (Duque et al., 2020; Parker et al., 2021; Willey et al., 2006). The difference in thermal expansion between the explosive and the binder in a PBX can cause microstructural changes such as cracking, fracturing and debonding between the binder and explosive crystals, which sensitizes the material (Duque et al., 2020; Hu et al., 2017). The microstructural changes due to heating PBXs can be applied to switchable explosives as heating an explosive that is below the material's critical diameter / thickness may produce sufficient critical hot spot locations to sensitize the explosive, allowing it to detonate.

[0071] Thermally-expandable microspheres have a thermoplastic shell and are filled with a low boiling point hydrocarbon (Nouryon. Expancel® 031DU40). Heating TEMs results in the vaporization of the hydrocarbon and expansion of the microspheres. Unexpanded and expanded TEMs have been used to sensitize ammonium nitrate explosives. Expansion of TEMs have been shown to change the density and detonation velocity of a pressed RDX / polyethene wax explosive formulation (Busby et al., 2023). TEMs have also been incorporated into mock formulations of plastic-bonded explosives to demonstrate a potential method for on-demand control of an explosive material [3]. The TEMs contained within a PBX formulation allow for the microstructure of the explosive to be changed when heat is applied to the material. Specifically, the expansion of the microspheres creates voids, which can function as hot spot locations within the explosive material when shocked. Thermally-expandable microspheres within a cast mock PBX expanded when heated by Higginbothan Duque et al.; however, the hypothesis that this would increase the shock sensitivity was not confirmed experimentally since only inert materials were considered (Duque et al., 2020). That is, a fully switchable explosive without fluid additions has been theorized but has not been demonstrated yet. Further, no work on deflagrating energetic materials has been suggested or considered.

[0072] The objectives of this work are to i) fabricate an explosive composite matrix with TEMs and investigate the microstructural changes within the material when exposed to the heating, ii) investigate the behavior of a detonation as it propagated through samples with different concentrations of TEMs subjected to different heating cycles, and finally iii) determine if heating alone or in combination with thermally-expandable microspheres allowed for switchable explosive function in an 1,3,5-trinitro-1,3,5-triazinane (RDX)-based rubberized explosive.EXAMPLESMethods and Materials

[0073] The sample formulations tested in this work were based on an explosive of 85 wt. % RDX and 15 wt. % hydroxyl-terminated polybutadiene (HTPB)-based binder. The RDX was a bimodal formulation of class 3 RDX (Lot No. BAE13E011-101) and class 5 RDX (Lot No. BAE15D097-002), representing coarse and fine particles, respectively, at a 4:1 coarse-to-fine weight ratio. The binder consisted of HTPB resin (73.6 wt. %), modified isocyanate curative (MDI, 11.4 wt. %), and isodecyl pelargonate plasticizer (IDP, 15 wt. %), all procured from Rocket Motor Components. TEMs (Expancel® 031DU40) were added in partial replacement of RDX; the binder was kept consistent at 15 wt. %. The thermally-expandable microspheres are listed by the manufacturer to have a D50 particle size between 10-16 μm. All components were used as received. The rubberized explosive formulations are shown in Table 1. The solid particles were added to the binder and a LabRAM resonant acoustic mixer (Resodyn Acoustic Mixers, Inc.) was used to mix the samples for two cycles of three minutes at 70 g's. The material was then hand-packed into 9.1 mm (width)×6.8 mm (height)×66 mm (length) rectangular Teflon™ molds and was stored at room temperature for four days to allow the samples to cure. After removal from the molds, a precision wire saw (Princeton Scientific Model: WS25B) was used to cut all samples to a length of 25 mm.TABLE 1RDX-based rubberized explosive formulations.Class 3Class 5RDXRDXTEMsBinderFormulation(wt. %)(wt. %)(wt. %)(wt. %)RDX85.06817015TEMS0.2167.9016.890.2115TEMS0.4367.7916.780.4315TEMS0.8567.5816.570.8515TEMS1.7067.1516.151.7015TEMS8.5063.7512.758.5015

[0074] X-ray microcomputed tomography (CT) (Skyscan 1272) was used to quantify the microstructural changes and expansion of the TEMs within the polymer matrix for a TEMS1.70 sample. The sample was scanned before and after heating, and then used in the witness plate / high-speed video experiment. The response of the TEMs to changes in temperature was further investigated using hot-stage microscopy (Linkam T1000 hot-stage and a Hirox digital microscope) and differential scanning calorimetry / thermogravimetric analysis (DSC / TGA). Hot-stage microscopy was performed at a heating rate of 10° C. / min for both neat TEMs and a TEMS1.70 sample. DSC / TGA of the thermally-expandable microspheres was performed on a TA Instruments SDT Q600. Samples sizes of approximately 1.4 mg were heated in alumina crucibles at both 2.5° C. / min and 10° C. / min to a maximum temperature of 200° C. under a gas flow of 100 mL / min of 20 at. % oxygen / balance argon. The heating rates were selected to match the heating rate for the heating profile used for thermal cycling before detonation experiments and the heating rate used for hot-stage microscopy. The microstructure of the samples was investigated using a field emission scanning electron microscope (SEM) (FEI Nova NanoSEM) with an accelerating voltage of 3 kV. The samples were sputter coated with a 20 nm thick layer of palladium (Pd) and platinum (Pt) alloy using a sputter coater (Cressington, UK) before imaging. The density before and after heating was measured using Archimedes' principle for all formulations to quantify the effect of the heating and TEMs expansion on the density of the sample. Due to the extremely low density of samples with higher TEMs loadings, Archimedes' method proved unworkable since the sample will float in the liquids used, and geometric densities were calculated instead.

[0075] A combined witness plate and high-speed video experiment was used to evaluate the detonation propagation of each formulation. All formulations were tested with and without heating. RDX85.0 was tested without heating to confirm that the material would not sustain a detonation wave and with heating to determine if the increase in porosity from thermal cycling resulted in sufficient sensitization to sustain a detonation wave. Additional testing at coarse-to-fine weight ratios of 1:2, 1:1, 3:2, 2:1, 3:1, and 7:2 at the same dimensions was conducted to better identify the threshold of detonability. Testing formulations containing TEMs without heating was necessary as unexpanded TEMs have been shown to sensitize ammonium nitrate emulsion explosives and could sensitize the RDX-based rubberized explosive, allowing the material to detonate (Duque et al., 2020). The same formulations were tested after the samples were heated to evaluate the influence of the TEMs expansion and subsequent microstructural changes. Samples were heated with two different temperature profiles to evaluate the differences in expansion at different maximum temperatures. The first profile consisted of a ramp from 40° C. to 125° C. in 45 minutes, a 30 minute isotherm at 125° C., and a cooldown to 30° C. in 45 minutes. The second profile had a ramp from 40° C. to 95° C. in 25 minutes, a 30 minute isotherm at 95° C., and a cooldown to 30° C. in 25 minutes. All detonation experiments were conducted at room temperature after the samples had cooled completely. Samples tested after heating were only heated using one of the two specified temperature profiles. The samples were glued into 3D printed tough polylactic acid (PLA) holders using Barco Bond™ Epoxy. A Teledyne aluminum cup RP-80 detonator was centered, positioned to have intimate contact with the surface of the RDX-based rubberized explosive formulations, and glued into the 3D printed sample holder using cyanoacrylate glue. This was done to ensure a consistent shock input into the samples. Barco Bond™ Epoxy was then used to attach the samples to 3.18 mm thick brass witness plates. The high speed video of the detonation propagation was recorded using a Shimadzu HPV-X2 camera with a 105 mm, f / 2.8, Nikon AF Micro lens recording at 10 million fps. A turning mirror was used to view the samples within the detonation chamber, which was closed using two half-inch polycarbonate windows. A schematic of the experimental set up is shown in FIG. 1.

[0076] The mass burning rate was measured using a Crawford bomb strand burner at 6.89 MPa (1000 psi) nitrogen and a Phantom VEO high speed camera. Samples were ignited using 30 BNC nichrome wire and samples were inhibited on sides using nail polish. The propellant used in the burning rate experiments was the TEMS1.70 formulation and was tested for unheated, 95° C. heated, and 125° C. heated samples. Samples were allowed to cool prior to testing and three samples were tested for each TEMS1.70 formulation.Results and DiscussionCoarse to Fine Weight Ratio and Critical Thickness

[0077] RDX85.0 was tested at different coarse to fine weight ratios to evaluate when the explosive was below the material's critical thickness. Coarse to fine weight ratios of 1:2, 2:3, 1:1, 2:1, 3:1, and 7:2 were determined to be above the critical thickness for this material at the cross-section considered here (9.1 mm×6.8 mm), but the coarse to fine weight ratio of 4:1 has consistently proven unable to sustain a detonation. This indicates that the 4:1 formulation is only slightly below the material's critical thickness and as a result was selected as the baseline explosive.Micro X-Ray Computed Tomography

[0078] The X-ray micro-computed tomography results for the unheated and heated TEMS1.70 sample are shown in FIG. 2 for the 95° C. heating cycle. The results show an increase in sample size and porosity for the heated sample due to the expansion of the TEMs. This is most prevalent in the cracks that form due to debonding between the RDX crystals and the HTPB binder, as shown in FIG. 2 (c and d). This demonstrated the ability of thermally-expandable microspheres to be mixed into rubberized explosive formulations and increase the porosity / hot spot locations within the explosive. The same TEMS1.70 sample was used for both the unheated and heated micro x-ray computed tomography scans.

[0079] Micro x-ray computed tomography was performed for the 125° C. heating cycle as well. The results for both the unheated and 125° C. heated TEMS1.70 sample are shown in FIG. 3 (the same sample was used for both the unheated and heated scans). Unlike the 95° C. heating cycle, the results for micro x-ray computed topography for the 125° C. heating cycle showed minimal expansion and debonding within the sample compared to the unheated sample. The higher applied temperature apparently deflated / melted the thermally-expandable microspheres within the rubberized explosive, allowing the sample to then retract to a similar size to the sample prior to being heated.Differential Scanning Calorimetry, Thermogravimetric Analysis, and Hot-Stage Microscopy

[0080] Differential scanning calorimetry / thermogravimetric analysis of the thermally-expandable microspheres was performed to investigate the expansion and melting of the TEMs as the material is heated. At a heating rate of 2.5° C. / min, two endotherms were observed at 87° C. and 114-118° C. For the test at 10° C. / min, these endotherms were observed at 88° C. and 125° C. In addition, approximately 27% of the weight loss was observed from 90 to 125° C. for the neat TEMs. This weight loss is associated with the rupture of the thermoplastic and deflation of the microspheres. The first endotherm is the vaporization of the liquid hydrocarbon within the TEMs, and the second endotherm corresponds to the melting of the thermoplastic microspheres. This was confirmed visually using hot-stage microscopy for both neat TEMs and a TEMS1.70 sample.

[0081] The in-situ hot-stage microscopy results (supplementary material) for both the neat TEMs and TEMS1.70 sample showed visual expansion of the microspheres at 93-97° C. and deflation / melting from 127-153° C. The TEMS1.70 sample was observed to expand as the TEMs expanded and then retract to nearly the pre-heated dimensions as the TEMs deflated. This provides an explanation as to why little change was observed in the micro x-ray computed tomography scans of the 125° C. heating cycle. As the expandable microspheres within the rubberized explosive deflated, the sample retracted to close to its original size, but with damage in the form of thin gaps that will be seen to have a significant effect on the detonation. The rupture temperature of the thermoplastic spheres is above the maximum temperature of the 95° C. heating cycle, which results in the TEMs remaining expanded after heating and is the reason for the larger microstructural changes observed in samples from this heating cycle (FIG. 2).Density Measurements

[0082] The density for the 95° C. and 125° C. heating cycle was determined using Archimedes' principle, or geometric density when the density was too low to be measured with Archimedes' principle. The densities before and after heating for both heating cycles are listed in Table 2. For the 95° C. heating cycle, the decrease in density is attributed to the expansion of the TEMs that remained expanded after heating within the rubberized explosive. For the 125° C. heating cycle, the relatively small decrease in density is attributed to the expansion and subsequent rupture of the TEMs, and also the mass loss due to the melting of the TEMs thermoplastic and release of the enclosed hydrocarbon. The density decrease is likewise more substantial for the 95° C. heating cycle compared to the 125° C. heating cycle. This is expected as the 95° C. heating cycle does not deflate the TEMs, allowing the samples to remain expanded after the heating cycle is complete, increasing the volume of the sample.TABLE 2Density before and after heating to 95° C. and 125° C. heating cycles.DensityDensityBeforeAfterHeatingHeatingTemperatureFormulation(g · cm−3)(g · cm−3) 95° C.RDX85.01.5721.566TEMS0.211.5641.545TEMS0.431.5581.538TEMS0.851.5531.459TEMS1.701.5380.962TEMS8.501.4540.166125° C.RDX85.01.5721.557TEMS0.851.5531.512TEMS1.701.5381.496TEMS8.501.4541.052Detonation Propagation Experiments

[0083] An experimental study using both a brass witness plate and high-speed video was conducted to determine if heating alone or a combination of thermally-expandable microspheres and heating of an explosive formulation below its critical thickness would produce a material with switchable detonation function. The first formulation (RDX85.0) tested was an 85 wt. % solids loading explosive containing no TEMs that was determined to be below the critical thickness for this material. This formulation was tested for both an unheated sample and a sample heated at 95° C. The detonation wave was unable to propagate through either the unheated or 95° C. heated RDX85.0 sample. Formulations containing different concentrations of TEMs (0.21 wt. % to 8.50 wt. %) were each tested with and without a prior heating cycle to 95° C. All formulations with TEMs, unheated and heated, failed to detonate completely for the 95° C. heating cycle. Still images from high speed imaging of RDX85 unheated, TEMS0.85 unheated, and TEMS0.85 heated at 95° C. are shown in FIG. 4. The high speed images for the other tested formulations at 95° C. containing TEMs resembled the results shown in FIG. 4. The increased porosity due to the expansion of the TEMs likely created non-critical hot spots and, as a result, was unable to sensitize the rubberized explosive. Critical hot spots in polymer bonded explosives are typically between 0.1 to 10 μm to sensitize high explosive. The D50 of the thermally-expandable microspheres is 10-16 μm when unexpanded, which suggests that intact microspheres, both the unexpanded and expanded, may be too large to create a sufficient increase in critical hot spots to result in initiation.

[0084] The second heating cycle tested had a specified 30 minute isotherm at 125° C. to allow for the complete expansion and subsequent melting, rupture, and deflation of the TEMs within the explosive formulation. RDX85.0 was tested after heating to determine if the higher temperature heating cycle would result in a change in detonation function for the material. The results from the high speed imaging for the unheated and 125° C. heated RDX85.0 samples are shown in FIG. 5. The detonation was unable to propagate for the unheated RDX85.0, which was expected as this material was selected due to it being below critical thickness. However, the heated sample of RDX85.0 was able to sustain a detonation wave through the entire sample. This was confirmed by an indentation in the brass witness plate.

[0085] This switch in detonation function after heating is likely due to increased porosity from thermal cycling damage and possible debonding of the binder from the RDX crystals due to heating at 125° C. SEM imaging was performed to investigate debonding or cracking near the RDX crystal and binder interface. SEM images for RDX85.0 samples that were unheated, heated at 95° C., and heated at 125° C. are shown in FIG. 6. Debonding was not observed in the unheated RDX85.0 sample. Some debonding and cracking was noted for the 95° C. heating cycle; however, more prevalent debonding, pores, and cracking occurring near the RDX crystal and binder interface was observed for the 125° C. heating cycle. This suggests that the higher heating cycle results in more small-scale hot spot locations, leading to the sensitization of the 85 wt. % RDX rubberized explosive (RDX85.0).

[0086] The results from the high-speed video for TEMS0.85 unheated and TEMS0.85 heated at 125° C. are shown in FIG. 7. The detonation was unable to propagate through both the unheated and 125° C. heated TEMS0.85 samples. Although the heated sample for TEMS0.85 was unable to fully propagate the detonation wave through the sample, it sustained the detonation longer than unheated RDX85.0 or its unheated counterpart with TEMs before the detonation failed. This indicates that the heating process and expansion / deflation of the thermally-expandable microspheres do have a noticeable effect on detonation behavior. However, 0.85 wt. % of TEMs likely did not increase the porosity and number of critical hot spot locations sufficient to overcome the 0.85 wt. % of explosive that the TEMs replaced in the formulation.

[0087] The concentration of TEMs was increased to 1.7 wt. % in TEMS1.70, resulting in a higher porosity and number of potential hot spot locations compared to TEMS0.85. A comparison of the high speed imaging results of TEMS1.70 unheated, and heated at 125° C. are shown in FIG. 8. The unheated sample of TEMS1.70, like the previous results, failed to sustain a detonation wave. However, the heated TEMS1.70 sample was able to sustain the detonation wave fully through the material, demonstrating that TEMs, with a 125° C. heating cycle, can be used to produce a switchable rubberized explosive. The detonation of the heated TEMS1.70 sample was further confirmed by an indentation in the brass witness plate from the detonation wave. A formulation with 8.5 wt. % TEMs (TEMS8.50) was also tested with the 125° C. heating cycle, this formulation failed to sustain a detonation and the high speed imaging results appeared similar to those shown in FIG. 7.

[0088] The ability of a sample to sustain a detonation wave is likely due to the crack formation and debonding of the binder from the explosive crystals as the TEMs expand. That is, if the appropriately sized voids are created (smaller), sufficient critical hot-spot density is achieved for successful detonation propagation. Unlike the samples heated with the 95° C. heating cycle, the 125° C. heating cycle melts and deflates the microspheres after expansion, allowing the sample to retract to a similar size prior to heating. This allows the cracks and debonding that occurred during expansion to function as critical hot spots. That is, the hot spots are small enough. Conversely, the 95° C. heating cycle fails to sensitize the rubberized explosive as the increase in volume (decreased density) and larger-sized voids result in predominately non-critical hot spots. However, the 95° C. heating cycle could be used to desensitize a detonable explosive, which would have many possible applications also.

[0089] The expansion and melting / deflation of the TEMs is not the only factor for switchable detonation function. A table summarizing the go / no go results for the detonation propagation experiments is shown in Table 3. Importantly, the balance between explosives replaced with TEMs

[0090] also affects the detonation behavior as the concentration of TEMs was determined to be a factor in the switchable detonation function for the 125° C. heating cycle. For example, TEMS0.85 was unable to sustain a detonation wave after heating as the increase in critical hot spot formation was presumably unable to overcome the removal of 0.85 wt. % RDX. However, TEMS1.70 was found to detonate after heating as the increase in critical hot spot locations was sufficient to sensitize the rubberized explosive, despite the associated loss of energetic material. In contrast, TEMS8.50 was unable to sustain a detonation as the expansion / melting / deflation of the microspheres likely created non-critical hot spots as the change in density for the 125° C. heated TEMS8.50 was the most substantial of all samples for this heating cycle (Table 2).

[0091] The inability of the unheated TEMS1.70 sample to detonate implies that until the material is heated and the TEMs expand, the material will not detonate unintentionally, decreasing the safety risk of storage and transport of the material. The heated RDX85.0 sample successfully sustaining a detonation wave suggests that the expansion and deflation of the TEMs alone are not responsible for the switchable detonation function, but a combination of microstructural changes resulting from heating of the rubberized explosive and the expansion / deflation of the thermally-expandable microspheres.

[0092] To investigate the desensitization of a detonable explosive, an additional 1:1 coarse-to-fine weight ratio formulation (RDX1:1) containing 41.65 wt. % class 3 RDX, 41.65 wt. % class 5 RDX,

[0093] 1.70 wt. % TEMs, and 15 wt. % of the same binder as the previous formulations was tested without heating and after undergoing the 95° C. heating cycle. A comparison of the high speed imaging results of RDX1:1 unheated and heated at 95° C. are shown in FIG. 9. The unheated RDX1:1 sample was able to propagate a detonation, whereas the sample heated to 95° C. was unable to sustain a detonation. This demonstrates that the larger expanded microspheres are able to create non-critical hot spots and successfully desensitize a detonable explosive.TABLE 3Summary of detonation propagation experiment results.DetonationPropagationTemperatureFormulationResult 22° C.RDX85.0No GoRDX1:1GoTEMS0.21No GoTEMS0.43No GoTEMS0.85No GoTEMS1.70No GoTEMS8.50No Go 95° C.RDX85.0No GoRDX1:1No GoTEMS0.21No GoTEMS0.43No GoTEMS0.85No GoTEMS1.70No GoTEMS8.50No Go125° C.RDX85.0GoTEMS0.85No GoTEMS1.70GoTEMS8.50No GoBurning Rate Experiments

[0094] Mass burning rate experiments were done in a Crawford bomb strand burner at 6.89 MPa (1000 psi) nitrogen using the TEMS1.70 formulation. Three samples were tested for all heating cycles including the unheated TEMS1.70 formulation. The mass burning rates for TEMS1.70 unheated, heated at 95° C., and heated at 125° C. are shown in FIG. 10. The average mass burning rates for the unheated (0.79 g / cm2-s) and 125° C. samples (0.78 g / cm2-s) were similar; however, the average mass burning rate for samples heated with the 95° C. heating cycle (0.49 g / cm2-s) was significantly lower. The reduced mass burning rate of the 95° C. TEMS1.70 samples is likely due to the decreased density of the samples after the expansion of the TEMs. The unheated (1.538 g / cm3) and 125° C. (1.496 g / cm3) sample densities are similar, but the density for the 95° C. (0.962 g / cm3) samples is significantly lower. These results demonstrate that TEMs can be included in propellant formulations to alter the mass burning rate.CONCLUSION

[0095] The results of this study demonstrated that a combination of heating, expansion, and deflation of thermally-expandable microspheres can be used to create switchable RDX-based rubberized explosives (either sensitizing or desensitizing). The explosive formulations with the unexpanded TEMs and the formulations heated with a 95° C. heating cycle were unable to sensitize the explosive sufficiently to allow for the material to sustain a detonation due to the large size of the expanded TEMs. Unlike the 95° C. heating cycle, a 125° C. heating cycle was shown to produce a detonable explosive due to the resulting smaller voids. The change in detonation function between the 95° C. and 125° C. heating cycles is due to the deflation of the TEMs that occurs during the 125° C. heating cycle that, again, results in smaller voids that will more likely be critical hot spots. The lower temperature heating cycle likely creates non-critical hot spots (too large) that result in a localized temperature increase insufficient for the initiation of the explosive. The expansion of the TEMs for the higher heating cycle allows for small cracks to form and debonding to occur between the explosive crystals and binder, similar to the lower temperature cycle. The deflation of the TEMs allows the sample to retract to a comparable size to before heating. This deflation likely results in the formation of critical hot spots as the cracks and debonding remain, without the increase in volume observed with the 95° C. heating cycle.

[0096] Sensitizing a material to detonation for the 125° C. heating cycle is a balance between the relative amount of TEMs added (replacing RDX in the explosive formulation) and the sensitization with increased number of smaller voids (critical hot spots). As RDX is removed from the formulation, the critical thickness for the material will increase, while as TEMs are added, the number of critical hot spot locations increases. Balancing these effects was required to produce a detonable rubberized explosive with the 125° C. heating cycle. Heated TEMS1.70 was shown to sustain a detonation wave, whereas heated TEMS0.85 and TEMS8.50 were unable to propagate a detonation wave as not sufficient critical hot spot locations were produced to overcome the removal of explosive material for both TEMS0.85 and TEMS8.50 samples.

[0097] Adding TEMs to an explosive below the material's critical thickness can produce a switchable explosive, where the explosive is unable to detonate without the expansion / deflation of the TEMs. However, simply heating the explosive formulation without adding thermally-expandable microspheres can also result in switchable detonation function, as shown for the configuration and material considered. This is likely due to microstructural changes such as increased void volume, cracking, and debonding of the binder from the explosive crystal that is a result of thermal cycling. Both heating and the combination of expansion / deflation of TEMs created explosive materials that are safe to store and transport but are still usable for applications as the detonation function can be “switched on” by heating the material.

[0098] Also, a detonable material in a given configuration can be transformed to a non-detonable material if heating results in voids that are too large to function as critical hot spots. The formation of non-critical hot spots within the explosive charge and significant density decrease due to the expansion of the TEMs were shown to desensitize a detonable explosive for a 1:1 coarse to fine weight ratio rubberized RDX explosive. The expansion of TEMs and subsequent density decrease were also shown to alter the mass burning rate of a propellant. The measured mass burning rate for unheated and 125° C. TEMS1.70 samples were similar, but a significant decrease was observed for the 95° C. samples. This demonstrates that TEMs can be included in propellant formulations to alter the mass burning rate.REFERENCES

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[0102] L. Perry (2020). Novel PBX Formulations Containing Thermally-Expandable Microspheres for on-Demand Control of Explosive Behavior. AIP Conference Proceedings, vol. 2272, 2020, doi:10.1063 / 12.0000787.

[0103] 4. G. R. Parker, D. S. Eastwood, M. Storm, K. Vitharana, E. M. Heatwole, I. Lopez-Pulliam, R. M. Broilo, P. M, Dickson, A. Martinez, C. Rau, & N. K. Bourne (2021). 4D Micro-Scale, Phase-Contrast X-Ray Imaging and Computed Tomography of HMX-Based Polymer-Bonded Explosives during Thermal Runaway. Combustion and Flame, vol. 226, 2021, pp. 478-89, doi:10.1016 / j.combustflame.2020.12.025.

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[0107] 8. C. Miller, D. Kittell, C. Yarrington, & M. Zhou (2020). Prediction of Probabilistic Detonation Threshold via Millimeter-Scale Microstructure-Explicit and Void-Explicit Simulations. Propellants, Explosives, Pyrotechnics, 45(2), 254-269. https: / / doi.org / 10.1002 / prep.201900214

[0108] 9. J. R. Lawrence, G. A. Montoya, A. D. Koeblitz, & S. F. Son. Influence and Comparison of Cylindrical Engineered Defects on Detonation Waveshape in a Rubberized RDX Explosive. Propellants, Explosives, and Pyrotechnics. Accepted with revisions winter 2023.

[0109] 10. T. M. Willey, T. van Buuren, J. R. I. Lee, G. E. Overturf, & J. H. Kinney (2006). Changes in Pore Size Distribution upon Thermal Cycling of TATB-Based Explosives Measured by Ultra-Small Angle X-Ray Scattering. Propellants, Explosives, Pyrotechnics, vol. 31, no. 6, 2006, pp. 466-71, doi:10.1002 / prep.200600063.

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Examples

examples

Methods and Materials

[0073]The sample formulations tested in this work were based on an explosive of 85 wt. % RDX and 15 wt. % hydroxyl-terminated polybutadiene (HTPB)-based binder. The RDX was a bimodal formulation of class 3 RDX (Lot No. BAE13E011-101) and class 5 RDX (Lot No. BAE15D097-002), representing coarse and fine particles, respectively, at a 4:1 coarse-to-fine weight ratio. The binder consisted of HTPB resin (73.6 wt. %), modified isocyanate curative (MDI, 11.4 wt. %), and isodecyl pelargonate plasticizer (IDP, 15 wt. %), all procured from Rocket Motor Components. TEMs (Expancel® 031DU40) were added in partial replacement of RDX; the binder was kept consistent at 15 wt. %. The thermally-expandable microspheres are listed by the manufacturer to have a D50 particle size between 10-16 μm. All components were used as received. The rubberized explosive formulations are shown in Table 1. The solid particles were added to the binder and a LabRAM resonant acoustic mixer (Resodyn ...

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This Application relates to and claims the benefit of U.S. Provisional Patent Application No. 63 / 620,341, filed on Jan. 12, 2024. The contents of which are expressly incorporated herein by reference in its entirety into this present disclosure.GOVERNMENT SUPPORT CLAUSE

[0002] This invention was made with government support under grant W911NF-22-2-0170 awarded by the U.S. Army Research Office. The government has certain rights in the invention.FIELD OF INVENTION

[0003] This disclosure relates generally to the area of explosive and propellant compositions, methods for manufacture and use. The present disclosure more particularly addresses methods for making and using compositions of explosive or propellant which incorporate microspheres to desensitize, modify or control detonation. In particular, the present disclosure describes compositions combining 1,3,5-trinitro-1,3,5-triazinane (RDX)-based rubberized explosive and thermally-expandable microspheres (TEMs), and methods for the use of microspheres to prevent explosion and compositions which act as switchable explosive material.BACKGROUND

[0004] Improving the safety of explosive materials through the synthesis of insensitive explosives has been studied extensively. However, little work has focused on creating switchable explosives. A switchable explosive is normally insensitive to detonation, and therefore safe to handle and transport, but can be sensitized when needed to create a functional explosive. Similarly, it may be desired to desensitize an explosive to prevent its function.

[0005] The present disclosure describes the ability to create a switchable 1,3,5-trinitro-1,3,5-triazinane (RDX)-based rubberized explosive using thermally-expandable microspheres (TEMs). The addition of TEMs to the explosive formulation allowed for microstructural changes and potential hot spot locations such as voids to form as the microspheres expanded. Small voids (less than about 10 μm) are more likely to be critical hot spots when shocked, and likewise larger voids are less likely to ignite successfully (sub-critical) when shocked. Consequently, both sensitization and desensitization are possible. The rubberized explosive considered here with unexpanded microspheres was unable to sustain a detonation for the size used, but after specific heating followed by cooling to produce small voids, a detonation was achieved. That is, the TEMs addition to the RDX-based rubberized explosive resulted in an explosive that is detonation insensitive when unheated but becomes a functional explosive after it is sensitized through heating. This paves the way to create insensitive explosive formulations with on-demand switchable detonation function through the incorporation of thermally-expandable microspheres. Desensitization was also demonstrated with specific heating of TEMs in an initially detonable explosive charge. And finally, we also demonstrated that deflagration can be affected by heating TEMs.BRIEF SUMMARY OF THE INVENTION

[0006] The present disclosure provides a method of controlling the detonation properties of an explosive composition comprising combining 1,3,5-trinitro-1,3,5-triazinane (RDX)-based rubberized explosive with thermally-expandable microspheres (TEMs) such that the detonation properties of the resulting composition is different than that of the original explosive or propellant composition.

[0007] The present disclosure provides for a method for tuning deflagration properties of an explosive composition comprising combining 1,3,5-trinitro-1,3,5-triazinane (RDX)-based rubberized explosive with thermally-expandable microspheres (TEMs).

[0008] The present disclosure provides for a method of making an explosive composition comprising combining 1,3,5-trinitro-1,3,5-triazinane (RDX)-based rubberized explosive with thermally-expandable microspheres (TEMs) wherein said combination formulation allows for tuning detonation properties of the explosive composition.

[0009] The present disclosure also provides for a method of making an explosive composition comprising combining 1,3,5-trinitro-1,3,5-triazinane (RDX)-based rubberized explosive with thermally-expandable microspheres (TEMs) wherein said combination formulation allows for where the explosive composition is switchable between sensitive to detonation (sensitizing, sensitized) or insensitive to detonation (desensitizing, desensitized).

[0010] The present disclosure further provides for making an explosive composition that is desensitized, where the explosive composition was treated with an about 95° C. heating cycle.

[0011] The present disclosure provides for making an explosive composition where the explosive composition is further treated by sensitizing for detonation. The present disclosure provides for making a desensitized explosive composition as described above, sensitized to detonation. The present disclosure provide for sensitizing an explosive composition as described where the explosive composition is subject to an about 125° C. heating cycle.

[0012] Thus the present disclosure provides for a method of making an explosive composition comprising combining 1,3,5-trinitro-1,3,5-triazinane (RDX)-based rubberized explosive with thermally-expandable microspheres (TEMs) wherein said combination formulation where the explosive composition is made detonable by heat treatment.

[0013] Thus the present disclosure provides for a method for transforming a detonable material to a non-detonable material by heating the detonable material to create voids that are too large to function as critical hot spots. Thus the present disclosure provides for a method of making a detonable explosive composition where the weight ratio of coarse to fine weight of rubberized RDX is at least about 1:1.

[0014] The present disclosure provides for tuning deflagration properties of the explosive composition, tuning detonation properties of a propellant composition, or tuning deflagration properties of a propellant composition.

[0015] The present disclosure provides for an explosive composition made by a method as described above. Thus the present disclosure provides for an explosive composition comprising 1,3,5-trinitro-1,3,5-triazinane (RDX)-based rubberized explosive and thermally-expandable microspheres (TEMs). The present disclosure provides for the explosive composition made by the method described, which is desensitized to detonation, which has about a 1:1 coarse to fine weight ratio rubberized RDX explosive.

[0016] The present disclosure provides for a method for making 1,3,5-trinitro-1,3,5-triazinane (RDX)-based rubberized explosive switchable, comprising making an explosive composition by combining 1,3,5-trinitro-1,3,5-triazinane (RDX)-based rubberized explosive and thermally-expandable microspheres (TEMs), subjecting the explosive composition to heat treatment at about 95° C.

[0017] The present disclosure provides for a method for making 1,3,5-trinitro-1,3,5-triazinane (RDX)-based rubberized explosive switchable, comprising making an explosive composition by combining 1,3,5-trinitro-1,3,5-triazinane (RDX)-based rubberized explosive and thermally-expandable microspheres (TEMs), manufacturing the explosive composition to be below the material's critical thickness.

[0018] The present disclosure provides for a method for making 1,3,5-trinitro-1,3,5-triazinane (RDX)-based rubberized explosive desensitized for detonation, comprising making an explosive composition by combining 1,3,5-trinitro-1,3,5-triazinane (RDX)-based rubberized explosive and thermally-expandable microspheres (TEMs); treating the explosive composition to heat treatment at about 95° C.

[0019] The present disclosure provides for a method for making a switchable explosive composition comprising;

[0020] first making an explosive composition that is desensitized to explosion by combining 1,3,5-trinitro-1,3,5-triazinane (RDX)-based rubberized explosive and thermally-expandable microspheres (TEMs), subjecting the explosive composition to about 95° C. heat treatment, creating a desensitized explosive composition;

[0021] second, subjecting the desensitized explosive composition to about 125° C. heat treatment, creating a sensitized explosive composition.

[0022] In particular, the present invention provides for methods of making a switchable explosive composition comprising a mixture of RDX comprising Class 5 RDX, Class 3 RDX, and an appropriate binder, and combining the mixture of RDX with TEM. A preferred binder is hydroxyl-terminated polybutadiene (HTPB)-based binder. A preferred TEM is Expancel® 031DU40.

[0023] The explosive composition of the present invention combines a fine and coarse RDX into an explosive mixture with appropriate binder. In particular, fine RDX is represented by Class 5 RDX, and coarse RDX is represented by Class 3 RDX.

[0024] The present disclosure provides for a mixture of RDX that is about 85% total RDX weight to about 15% binder by weight (RDX85.0). In particular it is preferable to have the RDX85.0 mixture to comprise about 68% Class 3 RDX, about 17% Class 5 RDX and about 15% binder, by weight. The present disclosure illustrates various RDX85.0 mixtures, as for example in Table 1. Thus the present disclosure provides for RDX85.0 mixtures which combine from about 63% to 69% coarse RDX with fine RDX and TEMs. The present disclosure also provides for explosive mixtures whish combines about 12% to about 18% fine RDX. It is further encompassed an explosive mixture that is 1:1 by weight fine to coarse RDX.

[0025] The present invention encompasses the mixing of RDX with TEMs in the explosive mixture, with the weight of TEMs replacing an equal weight of RDX and the result combined with the appropriate 15% by weight binder. The present disclosure illustrates mixtures of RDX and TEM as illustrated by the data in Table 1. Thus the present disclosure encompasses explosive mixtures of RDX and TEMs that have from about 0.21 to about 8.5 by weight TEMs.

[0026] The present invention provides for the preparation of an explosive mixture which can be desensitized to detonation by heat cycle treatment to expand the TEM content. Thus the present disclosure provides for treatment of the explosive mixture by a heating cycle that has a profile with a ramp from about 40° C. to about 95° C. in 25 minutes, a 30 minute isotherm at about 95° C., and a cooldown to about 30° C. in 25 minutes.

[0027] The present invention provides for a method for sensitizing explosive mixture (either raw or after desensitizing) for detonation by heat cycle treatment to minimize the TEM expansion. Thus the present disclosure provides for the treatment of the explosive mixture by a heating cycle that has a profile with a ramp from about 40° C. to about 125° C. in 45 minutes, a 30 minute isotherm at about 125° C., and a cooldown to about 30° C. in 45 minutes.

[0028] These and other features, aspects and advantages of the present invention will become better understood with reference to the following figures, associated descriptions and claims.BRIEF DESCRIPTION OF THE DRAWINGS

[0029] A better understanding of the present disclosure will be obtained upon reference to the following description in conjunction with the accompanying drawings.

[0030] FIG. 1. Illustrates a schematic for the brass witness plate and high-speed camera experiment.

[0031] FIG. 2. (FIG. 2A-C) Shows Micro x-ray computed tomography for a) unheated, b) unheated magnified view and c) 95° C. heated, and d) 95° C. heated magnified view of a TEMS1.70 sample.

[0032] FIG. 3 (FIG. 3A-B) Shows Micro x-ray computed tomography for a) unheated and b) 125° C. heated TEMS1.70 samples.

[0033] FIG. 4. (FIG. 4A-C) Shows High speed imaging of a) RDX85.0 unheated, b) TEMS0.85 unheated and c) TEMS0.85 heated at 95° C.

[0034] FIG. 5. (FIG. 5A-B) Shows High speed imaging of a) RDX85.0 unheated and b) RDX85.0 heated at 125° C.

[0035] FIG. 6. (FIG. 6A-C Upper low mag / Lower high mag) Shows Scanning electron microscope images of RDX85.0 samples that were a) unheated, b) heated at 95° C., and c) heated at 125° C.

[0036] FIG. 7. (FIG. 7A-B) Shows High speed imaging of a) TEMS0.85 unheated and b) TEMS0.85 at 125° C.

[0037] FIG. 8. (FIG. 8A-B) Shows High speed imaging of a) TEMS1.70 unheated and b) TEMS1.70 heated at 125° C.

[0038] FIG. 9. (FIG. 9A-B) Shows High speed imaging of a) RDX1:1 unheated and b) RDX1:1 heated at 95° C.

[0039] FIG. 10. Shows a plot of Mass burning rate of unheated, heated at 95° C., and heated at 125° C. TEMS1.70 propellant samples.DETAILED DESCRIPTION

[0040] While the concepts of the present disclosure are illustrated and described in detail in the figures and the description herein, results in the figures and their description are to be considered as exemplary and not restrictive in character; it being understood that only the illustrative embodiments are shown and described and that all changes and modifications that come within the spirit of the disclosure are desired to be protected.

[0041] Unless defined otherwise, the scientific and technology nomenclatures have the same meaning as commonly understood by a person in the ordinary skill in the art pertaining to this disclosure.

[0042] As used herein: “Explosive” or “explosives” incorporates any related incendiary or otherwise exploding material which can be used as a destructive explosive or as a propellant, such as for a projectile. When referring to “controlling” the detonation process, “controlling” is meant to encompass modulating, inhibiting, delaying, modifying or otherwise altering from the unaltered properties of an explosive composition.

[0043] In the present disclosure the term “about” can allow for a degree of variability in a value or range, for example, within 20%, within 10%, within 5%, or within 1% of a stated value or of a stated limit of a range.

[0044] In the present disclosure the term “substantially” can allow for a degree of variability in a value or range, for example, within 80%, within 90%, within 95%, or within 99% of a stated value or of a stated limit of a range.

[0045] The present disclosure provides a method of controlling the detonation properties of an explosive composition comprising combining 1,3,5-trinitro-1,3,5-triazinane (RDX)-based rubberized explosive with thermally-expandable microspheres (TEMs) such that the detonation properties of the resulting composition is different than that of the original explosive or propellant composition.

[0046] The present disclosure provides for a method for tuning deflagration properties of an explosive composition comprising combining 1,3,5-trinitro-1,3,5-triazinane (RDX)-based rubberized explosive with thermally-expandable microspheres (TEMs).

[0047] The present disclosure provides for a method of making an explosive composition comprising combining 1,3,5-trinitro-1,3,5-triazinane (RDX)-based rubberized explosive with thermally-expandable microspheres (TEMs) wherein said combination formulation allows for tuning detonation properties of the explosive composition.

[0048] The present disclosure also provides for a method of making an explosive composition comprising combining 1,3,5-trinitro-1,3,5-triazinane (RDX)-based rubberized explosive with thermally-expandable microspheres (TEMs) wherein said combination formulation allows for where the explosive composition is switchable between sensitive to detonation (sensitizing, sensitized) or insensitive to detonation (desensitizing, desensitized).

[0049] The present disclosure further provides for making an explosive composition that is desensitized, where the explosive composition was treated with an about 95° C. heating cycle.

[0050] The present disclosure provides for making an explosive composition where the explosive composition is further treated by sensitizing for detonation. The present disclosure provides for making a desensitized explosive composition as described above, sensitized to detonation. The present disclosure provides for sensitizing an explosive composition as described where the explosive composition is subject to an about 125° C. heating cycle.

[0051] Thus the present disclosure provides for a method of making an explosive composition comprising combining 1,3,5-trinitro-1,3,5-triazinane (RDX)-based rubberized explosive with thermally-expandable microspheres (TEMs) wherein said combination formulation where the explosive composition is made detonable by heat treatment.

[0052] The present disclosure provides for a method for transforming a detonable material to a non-detonable material by heating the detonable material to create voids that are too large to function as critical hot spots.

[0053] The present disclosure provides for tuning deflagration properties of the explosive composition, tuning detonation properties of a propellant composition, or tuning deflagration properties of a propellant composition.

[0054] The present disclosure provides for an explosive composition made by a method as described above which provides for an explosive composition comprising 1,3,5-trinitro-1,3,5-triazinane (RDX)-based rubberized explosive and thermally-expandable microspheres (TEMs) which is desensitized to detonation, which has about a 1:1 coarse to fine weight ratio rubberized RDX explosive.

[0055] The present disclosure provides for a method for making 1,3,5-trinitro-1,3,5-triazinane (RDX)-based rubberized explosive switchable, comprising making an explosive composition by combining 1,3,5-trinitro-1,3,5-triazinane (RDX)-based rubberized explosive and thermally-expandable microspheres (TEMs), subjecting the explosive composition to heat treatment at about 95° C.

[0056] The present disclosure provides for a method for making 1,3,5-trinitro-1,3,5-triazinane (RDX)-based rubberized explosive switchable, comprising making an explosive composition by combining 1,3,5-trinitro-1,3,5-triazinane (RDX)-based rubberized explosive and thermally-expandable microspheres (TEMs), manufacturing the explosive composition to be below the material's critical thickness.

[0057] The present disclosure provides for a method for making 1,3,5-trinitro-1,3,5-triazinane (RDX)-based rubberized explosive desensitized for detonation, comprising making an explosive composition by combining 1,3,5-trinitro-1,3,5-triazinane (RDX)-based rubberized explosive and thermally-expandable microspheres (TEMs); treating the explosive composition to heat treatment at about 95° C.

[0058] The present disclosure provides for a method for making a switchable explosive composition comprising;

[0059] first making an explosive composition that is desensitized to explosion by combining 1,3,5-trinitro-1,3,5-triazinane (RDX)-based rubberized explosive and thermally-expandable microspheres (TEMs), subjecting the explosive composition to about 95° C. heat treatment, creating a desensitized explosive composition;

[0060] second, subjecting the desensitized explosive composition to about 125° C. heat treatment, creating a sensitized explosive composition.

[0061] In particular, the present invention provides for methods of making a switchable explosive composition comprising a mixture of RDX comprising Class 5 RDX, Class 3 RDX, and an appropriate binder, and combining the mixture of RDX with TEM. A preferred binder is hydroxyl-terminated polybutadiene (HTPB)-based binder. A preferred TEM is Expancel® 031DU40.

[0062] The explosive composition of the present invention combines a fine and coarse RDX into an explosive mixture with appropriate binder. In particular, fine RDX is represented by Class 5 RDX, and coarse RDX is represented by Class 3 RDX.

[0063] The present disclosure provides for a mixture of RDX that is about 85% total RDX weight to about 15% binder by weight (RDX85.0). In particular it is preferable to have the RDX85.0 mixture to comprise about 68% Class 3 RDX, about 17% Class 5 RDX and about 15% binder, by weight. The present disclosure illustrates various RDX85.0 mixtures, as for example in Table 1. Thus the present disclosure provides for RDX85.0 mixtures which combine from about 63% to 69% coarse RDX with fine RDX and TEMs. The present disclosure also provides for explosive mixtures whish combines about 12% to about 18% fine RDX. It is further encompassed an explosive mixture that is 1:1 by weight fine to coarse RDX.

[0064] The present invention encompasses the mixing of RDX with TEMs in the explosive mixture, with the weight of TEMs replacing an equal weight of RDX and the result combined with the appropriate 15% by weight binder. The present disclosure illustrates mixtures of RDX and TEM as illustrated by the data in Table 1. Thus the present disclosure encompasses explosive mixtures of RDX and TEMs that have from about 0.21 to about 8.5 by weight TEMs.

[0065] The present invention provides for the preparation of an explosive mixture which can be desensitized to detonation by heat cycle treatment to expand the TEM content. Thus the present disclosure provides for treatment of the explosive mixture by a heating cycle that has a profile with a ramp from about 40° C. to about 95° C. in about 25 minutes. It is further provided for a subsequent about 30 minute isotherm at about 95° C. Further it is provided for a further cooldown to about 30° C. in about 25 minutes.

[0066] The present invention provides for a method for sensitizing explosive mixture (either raw or after desensitizing) for detonation by heat cycle treatment to minimize the TEM expansion. Thus the present disclosure provides for the treatment of the explosive mixture by a heating cycle that has a profile with a ramp from about 40° C. to about 125° C. in about 45 minutes. It is further encompassed a subsequent about 30 minute isotherm at about 125° C. Further, there can be a subsequent cooldown to about 30° C. in about 45 minutes.INTRODUCTION

[0067] The development of switchable energetic materials is critical for increased safety and the prevention of accidents, especially for applications using high explosives (HE). Extensive research has been conducted to develop insensitive explosives such as triaminotrinitrobenzene (TATB) and ammonium nitrate at the expense of performance. However, accidents still occur with insensitive energetic materials such as the Beirut disaster in 2020. Unlike current insensitive energetic materials, an ideal switchable energetic material would be insensitive to unplanned initiation but perform well when sensitized. The energetic material would undergo a specific process to switch from insensitive to detonable when an application requires its use, creating an explosive that is safe from unplanned explosion until the material is used for its intended purpose. Likewise, a more sensitive explosive that could be desensitized on demand would be useful for some applications.

[0068] There is some previous work in switchable energetic materials. Switchable explosives have been created by tuning the explosive performance through fluid activation (Brown et al., 2023). The 1,3,5,7-tetranitro-1,3,5,7-tetrazocane (HMX)-based high explosive used in the study by Brown et al. was printed in strands below the material's critical diameter, meaning that the material would not sustain a detonation wave. Loss of energy in the gaps between the strands resulted in the failure of the detonation as it propagated through the material. However, the material was able to detonate after the 3D printed explosive lattice was filled with an activating fluid. The stronger confinement of the activating fluid increased the pressure of the shocks interacting between the 3D printed strands, allowing the material to sustain a detonation. Although the HMX-based explosive material was shown to be switchable, it required the addition of an activating fluid to tune the detonation performance as opposed to a switchable explosive material that is a single component. Likewise, the fluid will likely decrease performance significantly, especially if an inert is chosen.

[0069] Increasing the porosity and hot spot locations within an explosive material has been theorized as a mechanism to create switchable explosives (Duque et al., 2020). Porosity has been shown to sensitize HE due to the shock compression of hot spot locations (Parker et al., 2021). When a material is initiated by a shock, trapped gases within the hot spot locations are adiabatically compressed by the shock front. This leads to a localized temperature increase, which drives local chemical reactions leading to detonation. The formation of hot spots has been shown to increase explosive sensitivity, as a porous bulk explosive material was found to have higher shock sensitivity than the same bulk material at a higher theoretical maximum density. An increase in porosity can be accomplished in several ways; however, this study proposes the addition of thermally-expandable microspheres (TEMs) paired with thermal cycling as the means to increase porosity and hot spot locations (voids).

[0070] Thermal cycling of explosives has been shown to increase porosity and void size in 5-iodo-2′-deoxyuridine (IDOX), HMX, and TATB-based plastic bonded explosives (PBX) (Duque et al., 2020; Parker et al., 2021; Willey et al., 2006). The difference in thermal expansion between the explosive and the binder in a PBX can cause microstructural changes such as cracking, fracturing and debonding between the binder and explosive crystals, which sensitizes the material (Duque et al., 2020; Hu et al., 2017). The microstructural changes due to heating PBXs can be applied to switchable explosives as heating an explosive that is below the material's critical diameter / thickness may produce sufficient critical hot spot locations to sensitize the explosive, allowing it to detonate.

[0071] Thermally-expandable microspheres have a thermoplastic shell and are filled with a low boiling point hydrocarbon (Nouryon. Expancel® 031DU40). Heating TEMs results in the vaporization of the hydrocarbon and expansion of the microspheres. Unexpanded and expanded TEMs have been used to sensitize ammonium nitrate explosives. Expansion of TEMs have been shown to change the density and detonation velocity of a pressed RDX / polyethene wax explosive formulation (Busby et al., 2023). TEMs have also been incorporated into mock formulations of plastic-bonded explosives to demonstrate a potential method for on-demand control of an explosive material [3]. The TEMs contained within a PBX formulation allow for the microstructure of the explosive to be changed when heat is applied to the material. Specifically, the expansion of the microspheres creates voids, which can function as hot spot locations within the explosive material when shocked. Thermally-expandable microspheres within a cast mock PBX expanded when heated by Higginbothan Duque et al.; however, the hypothesis that this would increase the shock sensitivity was not confirmed experimentally since only inert materials were considered (Duque et al., 2020). That is, a fully switchable explosive without fluid additions has been theorized but has not been demonstrated yet. Further, no work on deflagrating energetic materials has been suggested or considered.

[0072] The objectives of this work are to i) fabricate an explosive composite matrix with TEMs and investigate the microstructural changes within the material when exposed to the heating, ii) investigate the behavior of a detonation as it propagated through samples with different concentrations of TEMs subjected to different heating cycles, and finally iii) determine if heating alone or in combination with thermally-expandable microspheres allowed for switchable explosive function in an 1,3,5-trinitro-1,3,5-triazinane (RDX)-based rubberized explosive.EXAMPLESMethods and Materials

[0073] The sample formulations tested in this work were based on an explosive of 85 wt. % RDX and 15 wt. % hydroxyl-terminated polybutadiene (HTPB)-based binder. The RDX was a bimodal formulation of class 3 RDX (Lot No. BAE13E011-101) and class 5 RDX (Lot No. BAE15D097-002), representing coarse and fine particles, respectively, at a 4:1 coarse-to-fine weight ratio. The binder consisted of HTPB resin (73.6 wt. %), modified isocyanate curative (MDI, 11.4 wt. %), and isodecyl pelargonate plasticizer (IDP, 15 wt. %), all procured from Rocket Motor Components. TEMs (Expancel® 031DU40) were added in partial replacement of RDX; the binder was kept consistent at 15 wt. %. The thermally-expandable microspheres are listed by the manufacturer to have a D50 particle size between 10-16 μm. All components were used as received. The rubberized explosive formulations are shown in Table 1. The solid particles were added to the binder and a LabRAM resonant acoustic mixer (Resodyn Acoustic Mixers, Inc.) was used to mix the samples for two cycles of three minutes at 70 g's. The material was then hand-packed into 9.1 mm (width)×6.8 mm (height)×66 mm (length) rectangular Teflon™ molds and was stored at room temperature for four days to allow the samples to cure. After removal from the molds, a precision wire saw (Princeton Scientific Model: WS25B) was used to cut all samples to a length of 25 mm.TABLE 1RDX-based rubberized explosive formulations.Class 3Class 5RDXRDXTEMsBinderFormulation(wt. %)(wt. %)(wt. %)(wt. %)RDX85.06817015TEMS0.2167.9016.890.2115TEMS0.4367.7916.780.4315TEMS0.8567.5816.570.8515TEMS1.7067.1516.151.7015TEMS8.5063.7512.758.5015

[0074] X-ray microcomputed tomography (CT) (Skyscan 1272) was used to quantify the microstructural changes and expansion of the TEMs within the polymer matrix for a TEMS1.70 sample. The sample was scanned before and after heating, and then used in the witness plate / high-speed video experiment. The response of the TEMs to changes in temperature was further investigated using hot-stage microscopy (Linkam T1000 hot-stage and a Hirox digital microscope) and differential scanning calorimetry / thermogravimetric analysis (DSC / TGA). Hot-stage microscopy was performed at a heating rate of 10° C. / min for both neat TEMs and a TEMS1.70 sample. DSC / TGA of the thermally-expandable microspheres was performed on a TA Instruments SDT Q600. Samples sizes of approximately 1.4 mg were heated in alumina crucibles at both 2.5° C. / min and 10° C. / min to a maximum temperature of 200° C. under a gas flow of 100 mL / min of 20 at. % oxygen / balance argon. The heating rates were selected to match the heating rate for the heating profile used for thermal cycling before detonation experiments and the heating rate used for hot-stage microscopy. The microstructure of the samples was investigated using a field emission scanning electron microscope (SEM) (FEI Nova NanoSEM) with an accelerating voltage of 3 kV. The samples were sputter coated with a 20 nm thick layer of palladium (Pd) and platinum (Pt) alloy using a sputter coater (Cressington, UK) before imaging. The density before and after heating was measured using Archimedes' principle for all formulations to quantify the effect of the heating and TEMs expansion on the density of the sample. Due to the extremely low density of samples with higher TEMs loadings, Archimedes' method proved unworkable since the sample will float in the liquids used, and geometric densities were calculated instead.

[0075] A combined witness plate and high-speed video experiment was used to evaluate the detonation propagation of each formulation. All formulations were tested with and without heating. RDX85.0 was tested without heating to confirm that the material would not sustain a detonation wave and with heating to determine if the increase in porosity from thermal cycling resulted in sufficient sensitization to sustain a detonation wave. Additional testing at coarse-to-fine weight ratios of 1:2, 1:1, 3:2, 2:1, 3:1, and 7:2 at the same dimensions was conducted to better identify the threshold of detonability. Testing formulations containing TEMs without heating was necessary as unexpanded TEMs have been shown to sensitize ammonium nitrate emulsion explosives and could sensitize the RDX-based rubberized explosive, allowing the material to detonate (Duque et al., 2020). The same formulations were tested after the samples were heated to evaluate the influence of the TEMs expansion and subsequent microstructural changes. Samples were heated with two different temperature profiles to evaluate the differences in expansion at different maximum temperatures. The first profile consisted of a ramp from 40° C. to 125° C. in 45 minutes, a 30 minute isotherm at 125° C., and a cooldown to 30° C. in 45 minutes. The second profile had a ramp from 40° C. to 95° C. in 25 minutes, a 30 minute isotherm at 95° C., and a cooldown to 30° C. in 25 minutes. All detonation experiments were conducted at room temperature after the samples had cooled completely. Samples tested after heating were only heated using one of the two specified temperature profiles. The samples were glued into 3D printed tough polylactic acid (PLA) holders using Barco Bond™ Epoxy. A Teledyne aluminum cup RP-80 detonator was centered, positioned to have intimate contact with the surface of the RDX-based rubberized explosive formulations, and glued into the 3D printed sample holder using cyanoacrylate glue. This was done to ensure a consistent shock input into the samples. Barco Bond™ Epoxy was then used to attach the samples to 3.18 mm thick brass witness plates. The high speed video of the detonation propagation was recorded using a Shimadzu HPV-X2 camera with a 105 mm, f / 2.8, Nikon AF Micro lens recording at 10 million fps. A turning mirror was used to view the samples within the detonation chamber, which was closed using two half-inch polycarbonate windows. A schematic of the experimental set up is shown in FIG. 1.

[0076] The mass burning rate was measured using a Crawford bomb strand burner at 6.89 MPa (1000 psi) nitrogen and a Phantom VEO high speed camera. Samples were ignited using 30 BNC nichrome wire and samples were inhibited on sides using nail polish. The propellant used in the burning rate experiments was the TEMS1.70 formulation and was tested for unheated, 95° C. heated, and 125° C. heated samples. Samples were allowed to cool prior to testing and three samples were tested for each TEMS1.70 formulation.Results and DiscussionCoarse to Fine Weight Ratio and Critical Thickness

[0077] RDX85.0 was tested at different coarse to fine weight ratios to evaluate when the explosive was below the material's critical thickness. Coarse to fine weight ratios of 1:2, 2:3, 1:1, 2:1, 3:1, and 7:2 were determined to be above the critical thickness for this material at the cross-section considered here (9.1 mm×6.8 mm), but the coarse to fine weight ratio of 4:1 has consistently proven unable to sustain a detonation. This indicates that the 4:1 formulation is only slightly below the material's critical thickness and as a result was selected as the baseline explosive.Micro X-Ray Computed Tomography

[0078] The X-ray micro-computed tomography results for the unheated and heated TEMS1.70 sample are shown in FIG. 2 for the 95° C. heating cycle. The results show an increase in sample size and porosity for the heated sample due to the expansion of the TEMs. This is most prevalent in the cracks that form due to debonding between the RDX crystals and the HTPB binder, as shown in FIG. 2 (c and d). This demonstrated the ability of thermally-expandable microspheres to be mixed into rubberized explosive formulations and increase the porosity / hot spot locations within the explosive. The same TEMS1.70 sample was used for both the unheated and heated micro x-ray computed tomography scans.

[0079] Micro x-ray computed tomography was performed for the 125° C. heating cycle as well. The results for both the unheated and 125° C. heated TEMS1.70 sample are shown in FIG. 3 (the same sample was used for both the unheated and heated scans). Unlike the 95° C. heating cycle, the results for micro x-ray computed topography for the 125° C. heating cycle showed minimal expansion and debonding within the sample compared to the unheated sample. The higher applied temperature apparently deflated / melted the thermally-expandable microspheres within the rubberized explosive, allowing the sample to then retract to a similar size to the sample prior to being heated.Differential Scanning Calorimetry, Thermogravimetric Analysis, and Hot-Stage Microscopy

[0080] Differential scanning calorimetry / thermogravimetric analysis of the thermally-expandable microspheres was performed to investigate the expansion and melting of the TEMs as the material is heated. At a heating rate of 2.5° C. / min, two endotherms were observed at 87° C. and 114-118° C. For the test at 10° C. / min, these endotherms were observed at 88° C. and 125° C. In addition, approximately 27% of the weight loss was observed from 90 to 125° C. for the neat TEMs. This weight loss is associated with the rupture of the thermoplastic and deflation of the microspheres. The first endotherm is the vaporization of the liquid hydrocarbon within the TEMs, and the second endotherm corresponds to the melting of the thermoplastic microspheres. This was confirmed visually using hot-stage microscopy for both neat TEMs and a TEMS1.70 sample.

[0081] The in-situ hot-stage microscopy results (supplementary material) for both the neat TEMs and TEMS1.70 sample showed visual expansion of the microspheres at 93-97° C. and deflation / melting from 127-153° C. The TEMS1.70 sample was observed to expand as the TEMs expanded and then retract to nearly the pre-heated dimensions as the TEMs deflated. This provides an explanation as to why little change was observed in the micro x-ray computed tomography scans of the 125° C. heating cycle. As the expandable microspheres within the rubberized explosive deflated, the sample retracted to close to its original size, but with damage in the form of thin gaps that will be seen to have a significant effect on the detonation. The rupture temperature of the thermoplastic spheres is above the maximum temperature of the 95° C. heating cycle, which results in the TEMs remaining expanded after heating and is the reason for the larger microstructural changes observed in samples from this heating cycle (FIG. 2).Density Measurements

[0082] The density for the 95° C. and 125° C. heating cycle was determined using Archimedes' principle, or geometric density when the density was too low to be measured with Archimedes' principle. The densities before and after heating for both heating cycles are listed in Table 2. For the 95° C. heating cycle, the decrease in density is attributed to the expansion of the TEMs that remained expanded after heating within the rubberized explosive. For the 125° C. heating cycle, the relatively small decrease in density is attributed to the expansion and subsequent rupture of the TEMs, and also the mass loss due to the melting of the TEMs thermoplastic and release of the enclosed hydrocarbon. The density decrease is likewise more substantial for the 95° C. heating cycle compared to the 125° C. heating cycle. This is expected as the 95° C. heating cycle does not deflate the TEMs, allowing the samples to remain expanded after the heating cycle is complete, increasing the volume of the sample.TABLE 2Density before and after heating to 95° C. and 125° C. heating cycles.DensityDensityBeforeAfterHeatingHeatingTemperatureFormulation(g · cm−3)(g · cm−3) 95° C.RDX85.01.5721.566TEMS0.211.5641.545TEMS0.431.5581.538TEMS0.851.5531.459TEMS1.701.5380.962TEMS8.501.4540.166125° C.RDX85.01.5721.557TEMS0.851.5531.512TEMS1.701.5381.496TEMS8.501.4541.052Detonation Propagation Experiments

[0083] An experimental study using both a brass witness plate and high-speed video was conducted to determine if heating alone or a combination of thermally-expandable microspheres and heating of an explosive formulation below its critical thickness would produce a material with switchable detonation function. The first formulation (RDX85.0) tested was an 85 wt. % solids loading explosive containing no TEMs that was determined to be below the critical thickness for this material. This formulation was tested for both an unheated sample and a sample heated at 95° C. The detonation wave was unable to propagate through either the unheated or 95° C. heated RDX85.0 sample. Formulations containing different concentrations of TEMs (0.21 wt. % to 8.50 wt. %) were each tested with and without a prior heating cycle to 95° C. All formulations with TEMs, unheated and heated, failed to detonate completely for the 95° C. heating cycle. Still images from high speed imaging of RDX85 unheated, TEMS0.85 unheated, and TEMS0.85 heated at 95° C. are shown in FIG. 4. The high speed images for the other tested formulations at 95° C. containing TEMs resembled the results shown in FIG. 4. The increased porosity due to the expansion of the TEMs likely created non-critical hot spots and, as a result, was unable to sensitize the rubberized explosive. Critical hot spots in polymer bonded explosives are typically between 0.1 to 10 μm to sensitize high explosive. The D50 of the thermally-expandable microspheres is 10-16 μm when unexpanded, which suggests that intact microspheres, both the unexpanded and expanded, may be too large to create a sufficient increase in critical hot spots to result in initiation.

[0084] The second heating cycle tested had a specified 30 minute isotherm at 125° C. to allow for the complete expansion and subsequent melting, rupture, and deflation of the TEMs within the explosive formulation. RDX85.0 was tested after heating to determine if the higher temperature heating cycle would result in a change in detonation function for the material. The results from the high speed imaging for the unheated and 125° C. heated RDX85.0 samples are shown in FIG. 5. The detonation was unable to propagate for the unheated RDX85.0, which was expected as this material was selected due to it being below critical thickness. However, the heated sample of RDX85.0 was able to sustain a detonation wave through the entire sample. This was confirmed by an indentation in the brass witness plate.

[0085] This switch in detonation function after heating is likely due to increased porosity from thermal cycling damage and possible debonding of the binder from the RDX crystals due to heating at 125° C. SEM imaging was performed to investigate debonding or cracking near the RDX crystal and binder interface. SEM images for RDX85.0 samples that were unheated, heated at 95° C., and heated at 125° C. are shown in FIG. 6. Debonding was not observed in the unheated RDX85.0 sample. Some debonding and cracking was noted for the 95° C. heating cycle; however, more prevalent debonding, pores, and cracking occurring near the RDX crystal and binder interface was observed for the 125° C. heating cycle. This suggests that the higher heating cycle results in more small-scale hot spot locations, leading to the sensitization of the 85 wt. % RDX rubberized explosive (RDX85.0).

[0086] The results from the high-speed video for TEMS0.85 unheated and TEMS0.85 heated at 125° C. are shown in FIG. 7. The detonation was unable to propagate through both the unheated and 125° C. heated TEMS0.85 samples. Although the heated sample for TEMS0.85 was unable to fully propagate the detonation wave through the sample, it sustained the detonation longer than unheated RDX85.0 or its unheated counterpart with TEMs before the detonation failed. This indicates that the heating process and expansion / deflation of the thermally-expandable microspheres do have a noticeable effect on detonation behavior. However, 0.85 wt. % of TEMs likely did not increase the porosity and number of critical hot spot locations sufficient to overcome the 0.85 wt. % of explosive that the TEMs replaced in the formulation.

[0087] The concentration of TEMs was increased to 1.7 wt. % in TEMS1.70, resulting in a higher porosity and number of potential hot spot locations compared to TEMS0.85. A comparison of the high speed imaging results of TEMS1.70 unheated, and heated at 125° C. are shown in FIG. 8. The unheated sample of TEMS1.70, like the previous results, failed to sustain a detonation wave. However, the heated TEMS1.70 sample was able to sustain the detonation wave fully through the material, demonstrating that TEMs, with a 125° C. heating cycle, can be used to produce a switchable rubberized explosive. The detonation of the heated TEMS1.70 sample was further confirmed by an indentation in the brass witness plate from the detonation wave. A formulation with 8.5 wt. % TEMs (TEMS8.50) was also tested with the 125° C. heating cycle, this formulation failed to sustain a detonation and the high speed imaging results appeared similar to those shown in FIG. 7.

[0088] The ability of a sample to sustain a detonation wave is likely due to the crack formation and debonding of the binder from the explosive crystals as the TEMs expand. That is, if the appropriately sized voids are created (smaller), sufficient critical hot-spot density is achieved for successful detonation propagation. Unlike the samples heated with the 95° C. heating cycle, the 125° C. heating cycle melts and deflates the microspheres after expansion, allowing the sample to retract to a similar size prior to heating. This allows the cracks and debonding that occurred during expansion to function as critical hot spots. That is, the hot spots are small enough. Conversely, the 95° C. heating cycle fails to sensitize the rubberized explosive as the increase in volume (decreased density) and larger-sized voids result in predominately non-critical hot spots. However, the 95° C. heating cycle could be used to desensitize a detonable explosive, which would have many possible applications also.

[0089] The expansion and melting / deflation of the TEMs is not the only factor for switchable detonation function. A table summarizing the go / no go results for the detonation propagation experiments is shown in Table 3. Importantly, the balance between explosives replaced with TEMs

[0090] also affects the detonation behavior as the concentration of TEMs was determined to be a factor in the switchable detonation function for the 125° C. heating cycle. For example, TEMS0.85 was unable to sustain a detonation wave after heating as the increase in critical hot spot formation was presumably unable to overcome the removal of 0.85 wt. % RDX. However, TEMS1.70 was found to detonate after heating as the increase in critical hot spot locations was sufficient to sensitize the rubberized explosive, despite the associated loss of energetic material. In contrast, TEMS8.50 was unable to sustain a detonation as the expansion / melting / deflation of the microspheres likely created non-critical hot spots as the change in density for the 125° C. heated TEMS8.50 was the most substantial of all samples for this heating cycle (Table 2).

[0091] The inability of the unheated TEMS1.70 sample to detonate implies that until the material is heated and the TEMs expand, the material will not detonate unintentionally, decreasing the safety risk of storage and transport of the material. The heated RDX85.0 sample successfully sustaining a detonation wave suggests that the expansion and deflation of the TEMs alone are not responsible for the switchable detonation function, but a combination of microstructural changes resulting from heating of the rubberized explosive and the expansion / deflation of the thermally-expandable microspheres.

[0092] To investigate the desensitization of a detonable explosive, an additional 1:1 coarse-to-fine weight ratio formulation (RDX1:1) containing 41.65 wt. % class 3 RDX, 41.65 wt. % class 5 RDX,

[0093] 1.70 wt. % TEMs, and 15 wt. % of the same binder as the previous formulations was tested without heating and after undergoing the 95° C. heating cycle. A comparison of the high speed imaging results of RDX1:1 unheated and heated at 95° C. are shown in FIG. 9. The unheated RDX1:1 sample was able to propagate a detonation, whereas the sample heated to 95° C. was unable to sustain a detonation. This demonstrates that the larger expanded microspheres are able to create non-critical hot spots and successfully desensitize a detonable explosive.TABLE 3Summary of detonation propagation experiment results.DetonationPropagationTemperatureFormulationResult 22° C.RDX85.0No GoRDX1:1GoTEMS0.21No GoTEMS0.43No GoTEMS0.85No GoTEMS1.70No GoTEMS8.50No Go 95° C.RDX85.0No GoRDX1:1No GoTEMS0.21No GoTEMS0.43No GoTEMS0.85No GoTEMS1.70No GoTEMS8.50No Go125° C.RDX85.0GoTEMS0.85No GoTEMS1.70GoTEMS8.50No GoBurning Rate Experiments

[0094] Mass burning rate experiments were done in a Crawford bomb strand burner at 6.89 MPa (1000 psi) nitrogen using the TEMS1.70 formulation. Three samples were tested for all heating cycles including the unheated TEMS1.70 formulation. The mass burning rates for TEMS1.70 unheated, heated at 95° C., and heated at 125° C. are shown in FIG. 10. The average mass burning rates for the unheated (0.79 g / cm2-s) and 125° C. samples (0.78 g / cm2-s) were similar; however, the average mass burning rate for samples heated with the 95° C. heating cycle (0.49 g / cm2-s) was significantly lower. The reduced mass burning rate of the 95° C. TEMS1.70 samples is likely due to the decreased density of the samples after the expansion of the TEMs. The unheated (1.538 g / cm3) and 125° C. (1.496 g / cm3) sample densities are similar, but the density for the 95° C. (0.962 g / cm3) samples is significantly lower. These results demonstrate that TEMs can be included in propellant formulations to alter the mass burning rate.CONCLUSION

[0095] The results of this study demonstrated that a combination of heating, expansion, and deflation of thermally-expandable microspheres can be used to create switchable RDX-based rubberized explosives (either sensitizing or desensitizing). The explosive formulations with the unexpanded TEMs and the formulations heated with a 95° C. heating cycle were unable to sensitize the explosive sufficiently to allow for the material to sustain a detonation due to the large size of the expanded TEMs. Unlike the 95° C. heating cycle, a 125° C. heating cycle was shown to produce a detonable explosive due to the resulting smaller voids. The change in detonation function between the 95° C. and 125° C. heating cycles is due to the deflation of the TEMs that occurs during the 125° C. heating cycle that, again, results in smaller voids that will more likely be critical hot spots. The lower temperature heating cycle likely creates non-critical hot spots (too large) that result in a localized temperature increase insufficient for the initiation of the explosive. The expansion of the TEMs for the higher heating cycle allows for small cracks to form and debonding to occur between the explosive crystals and binder, similar to the lower temperature cycle. The deflation of the TEMs allows the sample to retract to a comparable size to before heating. This deflation likely results in the formation of critical hot spots as the cracks and debonding remain, without the increase in volume observed with the 95° C. heating cycle.

[0096] Sensitizing a material to detonation for the 125° C. heating cycle is a balance between the relative amount of TEMs added (replacing RDX in the explosive formulation) and the sensitization with increased number of smaller voids (critical hot spots). As RDX is removed from the formulation, the critical thickness for the material will increase, while as TEMs are added, the number of critical hot spot locations increases. Balancing these effects was required to produce a detonable rubberized explosive with the 125° C. heating cycle. Heated TEMS1.70 was shown to sustain a detonation wave, whereas heated TEMS0.85 and TEMS8.50 were unable to propagate a detonation wave as not sufficient critical hot spot locations were produced to overcome the removal of explosive material for both TEMS0.85 and TEMS8.50 samples.

[0097] Adding TEMs to an explosive below the material's critical thickness can produce a switchable explosive, where the explosive is unable to detonate without the expansion / deflation of the TEMs. However, simply heating the explosive formulation without adding thermally-expandable microspheres can also result in switchable detonation function, as shown for the configuration and material considered. This is likely due to microstructural changes such as increased void volume, cracking, and debonding of the binder from the explosive crystal that is a result of thermal cycling. Both heating and the combination of expansion / deflation of TEMs created explosive materials that are safe to store and transport but are still usable for applications as the detonation function can be “switched on” by heating the material.

[0098] Also, a detonable material in a given configuration can be transformed to a non-detonable material if heating results in voids that are too large to function as critical hot spots. The formation of non-critical hot spots within the explosive charge and significant density decrease due to the expansion of the TEMs were shown to desensitize a detonable explosive for a 1:1 coarse to fine weight ratio rubberized RDX explosive. The expansion of TEMs and subsequent density decrease were also shown to alter the mass burning rate of a propellant. The measured mass burning rate for unheated and 125° C. TEMS1.70 samples were similar, but a significant decrease was observed for the 95° C. samples. This demonstrates that TEMs can be included in propellant formulations to alter the mass burning rate.REFERENCES

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[0102] L. Perry (2020). Novel PBX Formulations Containing Thermally-Expandable Microspheres for on-Demand Control of Explosive Behavior. AIP Conference Proceedings, vol. 2272, 2020, doi:10.1063 / 12.0000787.

[0103] 4. G. R. Parker, D. S. Eastwood, M. Storm, K. Vitharana, E. M. Heatwole, I. Lopez-Pulliam, R. M. Broilo, P. M, Dickson, A. Martinez, C. Rau, & N. K. Bourne (2021). 4D Micro-Scale, Phase-Contrast X-Ray Imaging and Computed Tomography of HMX-Based Polymer-Bonded Explosives during Thermal Runaway. Combustion and Flame, vol. 226, 2021, pp. 478-89, doi:10.1016 / j.combustflame.2020.12.025.

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[0107] 8. C. Miller, D. Kittell, C. Yarrington, & M. Zhou (2020). Prediction of Probabilistic Detonation Threshold via Millimeter-Scale Microstructure-Explicit and Void-Explicit Simulations. Propellants, Explosives, Pyrotechnics, 45(2), 254-269. https: / / doi.org / 10.1002 / prep.201900214

[0108] 9. J. R. Lawrence, G. A. Montoya, A. D. Koeblitz, & S. F. Son. Influence and Comparison of Cylindrical Engineered Defects on Detonation Waveshape in a Rubberized RDX Explosive. Propellants, Explosives, and Pyrotechnics. Accepted with revisions winter 2023.

[0109] 10. T. M. Willey, T. van Buuren, J. R. I. Lee, G. E. Overturf, & J. H. Kinney (2006). Changes in Pore Size Distribution upon Thermal Cycling of TATB-Based Explosives Measured by Ultra-Small Angle X-Ray Scattering. Propellants, Explosives, Pyrotechnics, vol. 31, no. 6, 2006, pp. 466-71, doi:10.1002 / prep.200600063.

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Examples

examples

Methods and Materials

[0073]The sample formulations tested in this work were based on an explosive of 85 wt. % RDX and 15 wt. % hydroxyl-terminated polybutadiene (HTPB)-based binder. The RDX was a bimodal formulation of class 3 RDX (Lot No. BAE13E011-101) and class 5 RDX (Lot No. BAE15D097-002), representing coarse and fine particles, respectively, at a 4:1 coarse-to-fine weight ratio. The binder consisted of HTPB resin (73.6 wt. %), modified isocyanate curative (MDI, 11.4 wt. %), and isodecyl pelargonate plasticizer (IDP, 15 wt. %), all procured from Rocket Motor Components. TEMs (Expancel® 031DU40) were added in partial replacement of RDX; the binder was kept consistent at 15 wt. %. The thermally-expandable microspheres are listed by the manufacturer to have a D50 particle size between 10-16 μm. All components were used as received. The rubberized explosive formulations are shown in Table 1. The solid particles were added to the binder and a LabRAM resonant acoustic mixer (Resodyn ...

Claims

1. A method of making an explosive composition comprising combining 1,3,5-trinitro-1,3,5-triazinane (RDX)-based rubberized explosive with thermally-expandable microspheres (TEMs) wherein said combination formulation allows for tuning detonation properties of the explosive composition.

2. The method of claim 1, where the detonation properties of the explosive composition is switchable between desensitized and sensitized.

3. The method of claim 1, where the detonation properties are tuned by heat treatment.

4. The method of claim 1, where the detonation property of the composition is desensitized.

5. The method of claim 4 where the explosive composition is made detonable by subsequent heat treatment.

6. The method of claim 3, where the explosive composition was heated with an about 95° C. heating cycle.

7. The method of claim 3, where the explosive composition is heated with an about 125° C. heating cycle.

8. A method for transforming a detonable material to a non-detonable material by heating the detonable material to create voids that are too large to function as critical hot spots.

9. The method of claim 8 where the weight ratio of coarse to fine weight of rubberized RDX is at least about 1:1.

10. The method of claim 1 where the explosive composition consisting of combining 1,3,5-trinitro-1,3,5-triazinane (RDX)-based rubberized explosive with thermally-expandable microspheres (TEMs), provides for tuning deflagration properties of the explosive composition, tuning detonation properties of a propellant composition, or tuning deflagration properties of a propellant composition.

11. An explosive composition made by the method of claim 1.

12. The explosive composition of claim 11 which is desensitized to detonation, which has about a 1:1 coarse to fine weight ratio rubberized RDX explosive.

13. A method for making 1,3,5-trinitro-1,3,5-triazinane (RDX)-based rubberized explosive switchable, comprising making an explosive composition by combining 1,3,5-trinitro-1,3,5-triazinane (RDX)-based rubberized explosive and thermally-expandable microspheres (TEMs), subjecting the explosive composition to heat treatment at about 95° C.

14. A method for making 1,3,5-trinitro-1,3,5-triazinane (RDX)-based rubberized explosive switchable, comprising making an explosive composition by combining 1,3,5-trinitro-1,3,5-triazinane (RDX)-based rubberized explosive and thermally-expandable microspheres (TEMs), manufacturing the explosive composition to be below the material's critical thickness.

15. A method for making 1,3,5-trinitro-1,3,5-triazinane (RDX)-based rubberized explosive desensitized for detonation, comprising making an explosive composition by combining 1,3,5-trinitro-1,3,5-triazinane (RDX)-based rubberized explosive and thermally-expandable microspheres (TEMs); treating the explosive composition to heat treatment at about 95° C.

16. A method for making a switchable explosive composition that is non-explosive, sensitized to be explosive comprising;first making an explosive composition that is desensitized to explosion by combining 1,3,5-trinitro-1,3,5-triazinane (RDX)-based rubberized explosive and thermally-expandable microspheres (TEMs), subjecting the explosive composition to about 95° C. heat treatment, creating a desensitized explosive composition;second, subjecting the desensitized explosive composition to about 125° C. heat treatment, creating a sensitized explosive composition.

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