WO2023012787A1 - Burning rate enhancement of solid propellant for rocket motors using energetic formulations containing ammonium perchlorate and high concentration graphene oxide or epoxy-modified graphene oxide - Google Patents

Abstract

A method for enhancing the burning rate of a solid propellant for a rocket motor includes: forming a composite of graphene oxide (GO) or epoxy modified graphene oxide (EMGO) and ammonium perchlorate (AP), wherein the composite is comprised of APGO or APEMGO particles having a diameter of 5-60 microns in which GO or EMGO is coated onto AP, and the composite includes GO or EMGO in a weight percentage of at least 10%; and dispersing the composite in a solid propellant, said solid propellant also including neat AP and hydroxyl terminated polybutadiene (HTPB).

Description

BURNING RATE ENHANCEMENT OF SOLID PROPELLANT FOR ROCKET MOTORS USING ENERGETIC FORMULATIONS CONTAINING AMMONIUM PERCHLORATE AND HIGH CONCENTRATION GRAPHENE OXIDE OR EPOXY-MODIFIED GRAPHENE OXIDE

Related Applications

This Application claims priority to Israeli Patent Application No. 285,325, filed August 2, 2021, entitled "Energetic Formulations Containing Epoxy-Modified Graphene Oxide," and Israeli Patent Application No. 290,296, filed February 1, 2022, entitled "Burning Rate Enhancement of Solid Propellant for Rocket Motors Using Energetic Formulations Containing Ammonium Perchlorate and High Concentration Graphene Oxide or Epoxy-Modified Graphene Oxide," the contents of which are incorporated by reference as if fully set forth herein.

Field of the Invention

The present disclosure, in some embodiments, concerns burning rate enhancement of propellants for rocket motors, and more specifically to burning rate enhancement by the use of energetic formulations based on ammonium perchlorate (AP) coated with graphene oxide (GO) or by epoxy-modified graphene oxide (EMGO), in a high weight percentage.

Background of the Invention

The burning rate of a solid propellant is one of the more important properties of the propellant, in addition to its energetic content. Burning rate refers to a measure of the linear combustion rate of a compound or substance. Higher burning rates increase the pressure in a rocket's combustion chamber, resulting in a much higher thrust, essential for powerful boosters. In addition, high burning rates also save weight of the rocket motor by providing a given thrust when needed, but at reduced pressures, enabling reduction of casing thickness and overall weight.

Ammonium perchlorate (NH₄CIO₄) is a water-soluble solid that is a powerful oxidizer, and the main ingredient of many high-energy composite propellants. One common solid rocket propellant is based on ammonium perchlorate (AP) as an oxidizer, HTPB (Hydroxyl Terminated Polybutadiene) as a binder and fuel, and other additives like plasticizers, surface active agents, burning rate catalysts like iron oxide, and curative agents. In some cases, there is also use of aluminum powder to increase the energy content of the propellant. Generally, combustion of solid rocket propellants within a pressure combustion chamber of a solid rocket motor generates high flow rates of combustion gases, increasing the pressure and temperature. Through release of the high-pressure gases via a well-designed nozzle, thrust is created and moves the rocket.

Common methods for achieving high burning rates in propellants include increasing the percentage of solids such as ammonium perchlorate, particularly in smaller sized crystals thereof, and using burning rate enhancers that catalyze the combustion process. The commonly used burning rate enhancers consist of fine grains of metal oxides like Fe₂O₃, or similar. In some cases, there is also use of organometallic molecules having iron (Fe) atoms. These metal-based materials enhance the burning rate by increasing the heat conductivity of the propellant.

Graphene oxide (GO) is a material made of carbon, hydrogen, and oxygen molecules, produced through oxidation of graphite. Graphene oxide may exist as a sheet having a thickness of a single atomic layer, or as a multi-layered structure of multiple sheets. Graphene oxide is formed through reaction of graphene sheets with oxygen-containing groups. Following such reactions, carboxyl groups are arranged on the edges of the sheets, and hydrophilic oxygen groups, such as hydroxyl, epoxy, and carbonyl groups, are arranged on the surface of the sheets. These oxygen-containing groups may then be functionalized with different materials. As used in the present disclosure, the term "functionalized graphene oxide" refers to graphene oxide whose oxygen-containing groups have been further functionalized, whereas the term "non-functionalized graphene oxide" refers to graphene oxide whose oxygen groups have not undergone further functionalization.

Functionalized graphene oxide has previously been introduced into solid or liquid fuels, for the purpose of improving the combustion characteristics of those fuels. For example, it has been observed that the presence of GO functionalized with organic molecules having nitro- and amino-groups serves as a burning rate catalyst.

Summary of the Invention

Research to date on the use of non-functionalized graphene oxide as a burning rate catalyst has generated contradictory results. In 2016, Memon et al. reported results of experiments in which flakes or particles of GO were coated around fine crystals of ammonium perchlorate (AP). These nanocomposites were prepared from mixtures having a weight ratio of AP:GO of 50:1 (1.5 g of ammonium perchlorate with 0.03 g of GO), with a resulting weight ratio of AP:GO of 19:1 (5% GO). The resulting composites had a reduced decomposition temperature of 403 °C, as compared to 435 °C for chemical grade ammonium perchlorate. In addition, using this material, bimodal ammonium perchlorate / hydroxyl- terminated polybutadiene solid propellants were prepared, in which the total weight percentage of GO was 2%. The combustion behavior of these propellants was investigated. The solid propellant containing the AP coated with GO exhibited an increase in burning rate of approximately 15% at 80 atm, compared to a propellant containing AP prepared according to the same methods but without the GO.

The authors considered these results to be generally positive, but recognized that the decomposition temperature of 403 °C was not particularly impressive, especially compared to temperatures available using catalysts such as iron oxide, which resulted in decomposition temperatures of 360 °C. The authors' only suggestion for further enhancing the burning rate was to combine (functionalize) graphene oxide with metals or metal oxides. [Memon, N.K., Mcbain, A.W., Son, S.F., Graphene Oxide / Ammonium Perchlorate Composite Material for Use in Solid Propellants, J. Propuls. Power 2016, 32, 682-686, https://doi.Org/10.2514/l.B35815.1

More recent literature has taught away from the use of non-functionalized GO as a burning rate catalyst or enhancer. Cheng et al. found that non-functionalized GO showed weaker or no catalytic activities" because the GO was sensitive to heat at between 200 - 300 °C, which "left behind vacancies and topological defects throughout the nanosheets of reduced GO." This in turn, "inevitably affected its electronic and mechanical properties and catalytic activity on the thermal decomposition of AP." [Cheng, J., Yan, J., Wang, L. et al. Functionalization Graphene Oxide with Energetic Groups as a New Family of Metal-Free and Energetic Burning Rate Catalysts and Desensitizers for Ammonium Perchlorate. J Therm Anal Calorim 140, 2111-2122 (2020). https://doi.Org/10.1007/sl0973 019 08938-7.1 In their experimental data, Cheng et al. reported that "when GO was added, the thermal decomposition behavior of AP catalyzed by GO had no obvious changes compared with that of pure AP." Cheng et al. further reported that the thermal decomposition of the APGO mixture actually started at higher temperatures than that of pure AP. Cheng et al. accordingly recommended catalyzing the decomposition of AP with a functionalized GO.

Accordingly, there exists a need for a burning rate catalyst or enhancer based on non-functionalized GO that succeeds at reducing the decomposition temperature of AP to well below 400 °C. This burning rate catalyst or enhancer should ideally have reduced temperature of decomposition and increased enthalpy. When incorporated into the AP within the propellant in a proper manner, the catalyst or enhancer enhances the decomposition of ammonium perchlorate within the propellant, and increases the burning rate of the propellant by at least 20%, all without requiring the use of metal-based additives or functionalization of the GO.

The present application discloses that combining non-functionalized GO with AP, where the GO is in high relative concentration, well above typical catalytic ratios, and using the combination (APGO) as a burn-rate enhancer, produces significant burning rate enhancement results. In particular, the present disclosure presents that APGO in relative ratios of such as 10-20% by weight achieves significant reduction in decomposition temperature and increase in exothermic enthalpy.

The present application further discloses that contrary to Memon et al.'s only suggestion for further enhancing the burning rate, i.e., by combining graphene oxide with metals or metal oxides, the use of epoxy-modified graphene oxide EMGO (which may be free of metals and/or metal oxides) as a coating for ammonium perchlorate, in place of regular graphene oxide, also achieves significant results. These results include improvements both with respect to reduction of temperature of decomposition and with regard to increase of exothermic enthalpy.

It is expected that the use of the high concentration graphene oxide (GO) or epoxy modified graphene oxide (EMGO) coating the AP, and substituting the resulting APGO or APEMGO as a certain part of the AP in a preparation of a solid propellant including AP and HTPB, results in burning rate enhancement of between 20-40%, as determined by preliminary empirical testing.

According to a first aspect, a method for enhancing the burning rate of a solid propellant for a rocket motor is disclosed. The method includes: forming a composite of graphene oxide (GO) or epoxy modified graphene oxide (EMGO) and ammonium perchlorate (AP) by coating GO or EMGO onto AP, wherein the composite is comprised of APGO or APEMGO particles having a diameter of 5-60 microns, and the composite includes GO or EMGO in a weight percentage of at least 10%; and dispersing the composite in a solid propellant, said solid propellant also including neat AP and hydroxyl terminated polybutadiene (HTPB).

In another implementation according to the first aspect, the forming step includes coating the GO or EMGO onto the AP in a weight percentage of between approximately 10- 20%. In another implementation according to the first aspect, following the dispersing step, the total weight percentage of the GO or EMGO in the solid propellant is between 0.3% and 6%.

In another implementation according to the first aspect, the method further includes burning the solid propellant at a burning rate that is at least 20% higher than a burning rate of an equivalent solid propellant having the AP without the GO or EMGO.

According to a second aspect, a burning rate enhancer is disclosed. The burning rate enhancer includes a composite of graphene oxide (GO) or epoxy-modified graphene oxide (EMGO) coated onto ammonium perchlorate (AP) to form APGO or APEMGO particles having a diameter of between 5-60 microns, wherein the composite includes GO or EMGO in a weight percentage of at least 10%.

In another implementation according to the second aspect, the GO or EMGO is present in a weight percentage of between approximately 10-20%.

In another implementation according to the second aspect, a solid propellant for a rocket motor includes the burning rate enhancer, neat AP, and hydroxyl terminated polybutadiene (HTPB).

In another implementation according to the second aspect, the total weight percentage of the GO or EMGO in the solid propellant is between 0.3 and 6%.

In another implementation according to the second aspect, the solid propellant is metal-free.

In another implementation according to the second aspect, the solid propellant incudes aluminum powder for increasing energy content of the solid propellant.

In another implementation according to the second aspect, the solid propellant includes a metal-based burn-rate enhancer.

Detailed Description of the Invention

The present disclosure, in some embodiments, concerns burning rate enhancement of solid propellants for rocket motors, and more specifically to burning rate enhancement by use energetic formulations based on ammonium perchlorate (AP) coated with GO, or by EMGO, in a high weight percentage.

Before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not necessarily limited to the details set forth in the following description and illustrated in the Examples. The invention is capable of other embodiments or of being practiced or carried out in various ways. Preparation of Solid Propellant with APGO or APEMGO in High Weight Ratios

Solid propellants may be prepared by dispersing the following components amongst each other: crystals of AP coated with GO or EMGO (hereinafter, APGO or APEMGO), crystals of neat AP that are not coated with GO or EMGO additional components including HTPB (hydroxyl terminated polybutadiene) as a binder and fuel, and other additives like plasticizers, surface active agents, curative agents, and, optionally, aluminum as an energy enhancement additive.

The crystals of neat AP that are used in the solid propellant in addition to the APGO or APEMGO may be of any size or diameter typically found in solid propellants. The neat AP may also be in more than one size or fraction.

The specific methods of preparation of the APGO and APEMGO will be described in the "methods of preparation" section at the end of this disclosure.

Within the APGO and APEMGO, the weight percentage of the GO or EMGO may be between 5-50%. In preferred embodiments, the weight percentage of the GO or EMGO is at least 10%. The total concentration (by weight) of GO or EMGO within the propellant may be between 0.3% and 6%.

Heat Flow and Enthalpy Data

Table 1 summarizes energetic values for AP and AP coated by GO and EMGO at specific concentrations.

Table 1 - Comparison of Energetics for AP, APGO, and APEMGO

The data for neat AP was taken from published literature values, and the data for APGO and APEMGO was obtained through standard experimental procedures.

While the data generally speaks for itself, it is observed that all five experimental results achieved a temperature of the largest exotherm between 360 °C and 370 °C, as compared to 465 °C for neat AP. The enthalpy of the largest exotherm was 77% higher than that of neat AP in the case of 10% APGO, and more than 200% greater than that of neat AP in the case of the other three tested composites. In addition, the heat flow rate of the exotherm was nearly twice as high in the case of the 20% APGO or APEMGO vs. the 10% APGO or APEMGO. The improvements in performance were even greater for 30% APGO, which achieved the best results both for exotherm temperature and for heat flow rate.

Burning Rate Enhancement for Propellants Having APGO and APEMGO

It is expected that solid propellants prepared using the APGO or APEMGO composites discussed herein, in place of part of the AP particles in a solid propellant, will exhibit a 20-40% enhancement in burning rate. This expectation is based on preliminary data as well as the corresponding improvements in enthalpy and a lower decomposition temperature that are reported above. The lowering of the decomposition temperature, the increase in the enthalpy released during such decomposition, and the high heat flow rate during the composition, directly result in an increase in burning rate, as is known to those of skill in the art.

The energetic improvements of APGO caused by the high relative concentration of GO may be explained based on properties of GO. GO is considered to have unique energetic properties for improving the thermal decomposition of ammonium perchlorate in high percentages for at least the following reasons:

First, GO itself is a kind of energetic material with self-sustained combustion ability, because the oxygen groups on the graphene oxide sheet can oxidize the carbon moiety of the graphene and generate a large amount of heat at a relatively low temperature (approximately 200°C), which can form a positive thermal effect on the AP.

Second, GO has a nanometric structure, that is, it comprises lamellae and lamellar particles which are roughly three to four orders of magnitude smaller than the AP crystallites, the latter usually being in the range of 10 to 200 microns. The nanometric dimensions allow intimate contact with the AP crystals and deliver very large surface areas of contact. This intimate contact accelerates the local heat transfer and deflagration processes, also driven by the excellent dispersion of the GO at a nanometric level and distribution of the particles within very short ranges from one another.

Last, GO can promote high rate of localized heat transfer in an energetic composite system, due to the nanometric dispersion and effective distribution of GO, resulting in rapid and thorough thermal reactions, leading to localized temperature increase that initiates AP decomposition. This localized temperature may be higher than the average temperature of the propellant, because of the low thermal conductivity, thus promoting early energy release with high energy flux that enhances the oxidation effect, at lower effective temperatures, on the remaining carbon moiety of the graphene.

In addition, reduced graphene oxide, produced by the decomposition of oxygen groups in the graphene oxide, possesses high thermal conductivity, and is highly combustible, thus further enhancing energy propagation and increasing the flux by the formation of nanometric carbon-rich fuel and the fast heat transfer.

In sum, GO is preferred over commonly used metal-oxide based burning rate enhancers, due to its low temperature energy release (200°C), large surface area (hundreds of square meters per gram) and combustion attributes based on its carbon content. The positive energetic results are particularly expected when GO is present in sufficient quantity to provide heat transfer and enhanced energy input.

The energetic improvements based on the use of EMGO as a burning rate catalyst or enhancer are based on the factors discussed above with respect to GO, as well as the high exothermic enthalpies and heat flows in EMGO compared to neat GO.

Improvements in the energetic performance during decomposition of APEMGO relative to APGO may be seen in table 1. The higher enthalpy during the decomposition of EMGO contributes to the oxidizing effect of the AP and the resulting burning rate enhancement.

In the examples illustrated in Table 1, the positive energetic data was exhibited in APGO and APEMGO having weight percentages of the GO or EMGO of between 10-30%. In view of the explanations discussed above and the data of Table 1, it is expected that the advantageous effects described herein would pertain even to a weight percentage of GO or EMGO of up to 50%, i.e., a 1:1 ratio. In particular, the data of Table 1 show an increase in effectiveness of the GO and EMGO when the concentration of GO or EMGO is increased, and do not show any peak or decrease in effectiveness. In certain embodiments, the solid propellant containing the APGO or APEMGO composite is metal-free. In particular, the solid propellant need not contain any metal oxide catalysts such as iron oxide. The use of metals in rocket propellants is disfavored. Combustion of metals produces environmentally unfriendly emissions, combustion of metals leaves a detectable signature, and the metal oxides in some cases, when passing through the exhaust tube and the nozzle of the motor, cause erosion and may decrease the performance of the motor.

In alternative embodiments, the solid propellant may include metal oxides. In particular, as the APGO or APEMGO in high ratios generates the energetic enhancements by a process which is at least partially based on heat transfer at relatively low temperatures, as discussed above and, by contrast, the burning rate enhancement of metal oxides with AP operates using a traditional catalytic process, the two additives complement each other. Given that the two additives operate based on different processes, it is expected that the combination of additives would result in an even higher burning rate enhancement than the use of either additive alone.

The solid propellant may also include aluminum powder in order to increase its energy content, as discussed above.

Preparation of APGO and APEMGO

The following section illustrates various methods by which APGO and APEMGO were prepared, for purposes of analysis of their energetic properties, as detailed above. The following methods of preparation are merely exemplary, and any method of preparation may be used to generate the APGO and APEMGO included in the solid propellants described above, without departing from the scope of the present invention.

Ammonium perchlorate (AP) coated by graphene oxide (GO) was prepared using a fast crash sedimentation method, similar to that described in Example 4 of Israeli patent application 285,325. In a first flask, powdery GO was dispersed in acetone by sonication, for a period of up to 24 hours. In a second flask, AP was dissolved in acetone, in an ice bath. The AP mixture was added to the GO dispersion, and the mixture was sonicated for 15 minutes. The mixture was then slowly added to a third flask containing ethyl acetate, while rapidly stirring. The ethyl acetate caused the AP to precipitate in a fast-crash sedimentation process, forming 10-60 micron-sized crystals of APGO comprised of AP crystals with GO adhered to their surfaces. The composite of AP and GO was then removed from the suspension. After decantation, the solids were filtrated with a Buchner funnel using either Teflon or cellulose filter. The material was allowed to dry at room temperature for 24 hours, and then dried out in a vacuum oven.

The morphology of the APGO solid deposit was characterized by scanning electron microscopy (SEM), showing micron-sized (typically 10-60 microns) AP crystals coated by GO nano-particles. It is expected that the advantageous results described herein would pertain for APGO crystals of different diameters as well, including those sized between 5 and 100 microns.

Generally speaking, the initial concentration of the GO directly correlated to the final concentration of the GO. However, the exact final composition of the APGO solid deposit may vary based on factors including rate and order of addition of the components, mixing speed, temperature, etc. In addition, certain steps in the process may be bypassed, such as sonication of the APGO dispersion or the use of a cooling bath.

The preparation process described above may be performed at a relatively low temperature, and with industrial solvents that may be recycled by a simple distillation setup.

Alternatively, the composite may be prepared through spray-coating a dispersion of the GO onto the AP. The spray coating process may be done with organic solvents or with water. A water-based spray-coating process may be beneficial regarding the handling, dissolution rates, available equipment, disposal of waste water and/or reuse of waste water, and the safety issues related to work with other solvents. In still another possibility, the ammonium perchlorate may be coated by a sol-gel using a graphene oxide aerogel. These alternative processes may be preferred in certain circumstances insofar as they avoid the use of a large amount of organic solvents.

In order to prepare AP coated with EMGO, GO was functionalized with an epoxycontaining compound to thereby produce EMGO. The epoxy group that is functionalized onto the GO to produce the EMGO may be combined with the GO sheet, for example, through reaction of GO with an epoxysilane, epichlorohydrin, or a hydrocarbon compound containing a plurality of epoxy groups, such as 1,3 butadiene diepoxide or 1, 2,7,8 diepoxyoctane. Examples of such reaction processes are disclosed in Israeli patent application No. 285,325, referenced above, and are repeated below, in an abridged presentation, as an addendum to the present disclosure. The epoxy-modified graphene oxide (EMGO) was then coated onto the ammonium perchlorate using the fast crash sedimentation process described above. Alternatively, the APEMGO composite may be prepared through the same alternative methods mentioned above for the APGO.

Addendum - Preparation of EMGO

Below, various experimental methods are described for functionalizing GO with molecules containing one or more epoxy groups. One guiding principle common to the experimental strategy is that the epoxy groups that are directly bonded to the graphene oxide sheets are highly energetic. Thus, it would be counterproductive to replace or sacrifice these epoxy groups. Thus, addition of new functional groups is preferably performed through the hydroxyl or carboxyl groups of the GO. In each of the reactions described below, it is assumed that the functional groups are added at the hydroxyl groups of the GO.

Each of the reactions described below was performed on graphene oxide prepared according to any known method, such as Hummer's method. The oxygen functionality may be up to 50% by weight. The specific makeup of each graphene oxide sheet may be determined by x-ray photoelectron spectroscopy (XPS), although this is not required for preparation of the energetic material.

Advantageously, each of the reactions described below may be performed dispersing the graphene oxide preferably in water, while other non-toxic, non-explosive solvents are also useful. The functionalization reactions may be generally short, being performed in a single-step of approximately 30 minutes, and at relatively low temperatures. Thus, the methods of synthesis achieve high energy benefits using safe and "green" chemistry practices.

Example 1 - Epoxysilane

An exemplary epoxysilane is a silane bonded to three methoxy groups and a fourth group with the formula (CH₂)₃-O-CH₂-epoxy. As may be recognized by those of skill in the art, any of the three methoxy groups may be replaced by another suitable "R" group, such as an ethoxy group.

Epoxysilane modified GO was prepared according to the following steps. In a first flask, 0.5 g GO were dispersed in 250 ml water. In a second flask, 2 ml of epoxysilane and 2 ml of water were dissolved in 200 ml isopropyl alcohol (IPA). Acetic acid was added to the second flask, until pH reached 3-4. IPA and the silane mixture (flask 2), were stirred at room temperature for 30 min and then added to the GO/water dispersion (flask 1). Afterward, the mixture was heated to 70°C for 30 min. Upon cooling to room-temperature the suspension was filtered, washed and dried.

Example 2 - 1,3, Butadiene Epoxide

Graphene oxide may be reacted with 1,3 butadiene epoxide in a condensation reaction, catalyzed by stannous chloride (SnCI₂). SnCI₂ is a well-known catalyst for catalyzing condensation reactions, although it is not known for catalyzing functionalization of GO. In one embodiment, a hydroxyl group on the graphene oxide is reacted with 1,3 butadiene epoxide. An oxygen from the alcohol group of GO is bonded to one of the carbons from one of the epoxy groups of 1,3 butadiene epoxide, to form an ether. That epoxy group opens up, and its oxygen bonds with the hydrogen that had been removed from the hydroxyl group of the GO, to form a new hydroxyl group. The other epoxide group of the 1,3 butadiene epoxide remains unreacted.

An experimental procedure for conducting this condensation was performed as follows. In a first flask, 300 mg of GO were dispersed in 50 ml acetone. In a second flask, 32 mg of SnCI₂ were dissolved in 5 ml acetone. The content of the second flask was added to the first flask. 270 ml of 1,3 butadiene diepoxide were added to the first flask. The mixture was stirred at room temperature for 30 minutes. Following the reaction, the suspension was filtered, washed, and dried.

Example 3 - 1, 2,7,8 diepoxyoctane

Graphene oxide may be reacted with 1,2, 7, 8 diepoxyoctane in a condensation reaction, catalyzed by stannous chloride (SnCI₂). An oxygen from an alcohol group of GO is bonded to one of the carbons from one of the epoxy groups of 1,2, 7, 8 diepoxyoctane, to form an ether. That epoxy group opens up, and its oxygen bonds with the hydrogen that had been removed from the hydroxyl group of the GO, to form a new hydroxyl group. The other epoxide group remains unreacted. The experimental procedure of this reaction was the same as that of GO-1,3 butadiene epoxide in Example 2.

Other sources of epoxide may include: epichlorohydrin, which produces an epoxymodified GO without any alkyl groups between the ether and the epoxide; polyglycol diepoxides, epoxidized pentaerythritol, epoxy-amine compounds, and other di- and multiepoxy compounds.

In addition, other experimental parameters are expected to produce equivalent, or even superior, energetic results. For example, the GO may be suspended in water with a weight percent ranging from 0.5% to 10%. Likewise, the concentration of the epoxy- containing compound and the catalyst may be increased up to a saturation point of the epoxy-containing compounds relative to the hydroxyl groups of the graphene oxide.

Furthermore, it may be possible to increase the energetic qualities of the graphene oxide sheets even further by further functionalizing other oxygen atoms of the graphene oxide with oxidizing agents such as nitric acids or sulfuric acids, or other oxoacids. Nitrogroups may be introduced in the form of the nitronium ion. Alternatively, nitro-groups or amino groups may be inserted through a two-step process of acylating the carboxyl groups of the graphene oxide, and substituting functional groups containing the nitro- or aminogroups for the chloride of the acyl groups. Similarly, any of the above-described epoxy- containing compounds may be modified with oxidizing agents containing nitrogen. In such embodiments, the nitrogen is located between the graphene sheet and the epoxy groups.

Claims

Claims What is claimed is:

1. A method for enhancing the burning rate of a solid propellant for a rocket motor, comprising: forming a composite of graphene oxide (GO) and ammonium perchlorate (AP)by coating GO onto AP, wherein the composite is comprised of APGO particles having a diameter of 5-60 microns and the composite includes GO in a weight percentage of at least 10%; and dispersing the composite in a solid propellant, said solid propellant also including neat AP and hydroxyl terminated polybutadiene (HTPB).

2. The method of claim 1, wherein the forming step comprises coating the GO onto the AP in a weight percentage of between approximately 10-20%.

3. The method of claim 1, wherein the forming step comprises coating the GO onto the AP in a weight percentage of between approximately 20-30%.

4. The method of claim 1, wherein, following the dispersing step, the total weight percentage of the GO in the solid propellant is between 0.3% and 6%.

5. The method of claim 1, further comprising burning the solid propellant at a burning rate that is at least 20% higher than a burning rate of an equivalent solid propellant having the AP without the GO.

6. A method for enhancing the burning rate of a solid propellant for a rocket motor, comprising: forming a composite of epoxy-modified graphene oxide (EMGO) and ammonium perchlorate (AP) by coating EMGO onto AP, wherein the composite is comprised of APEMGO particles having a diameter of 5-60 microns, and the composite includes EMGO in a weight percentage of at least 10%; and dispersing the composite in a solid propellant, said solid propellant also including neat AP and hydroxyl terminated polybutadiene (HTPB).

7. The method of claim 6, wherein the forming step comprises coating the EMGO onto the AP in a weight percentage of between approximately 10-20%.

8.The method of claim 6, wherein, following the dispersing step, the total weight percentage of the EMGO in the solid propellant is between 0.3% and 6%.

9. The method of claim 6, further comprising burning the solid propellant at a burning rate that is at least 20% higher than a burning rate of an equivalent solid propellant having the AP without the EMGO.

10. A burning rate enhancer, comprising a composite of graphene oxide (GO) coated onto ammonium perchlorate (AP) to form APGO particles having a diameter of between 5-60 microns, wherein the composite includes GO in a weight percentage of at least 10%.

11. The burning rate enhancer of claim 10, wherein the GO is present in a weight percentage of between approximately 10-20%.

12. The burning rate enhancer of claim 10, wherein the GO is present in a weight percentage of between approximately 20-30%.

13. A solid propellant for a rocket motor, comprising the burning rate enhancer of any of claims 10-12, neat AP, and hydroxyl terminated polybutadiene (HTPB).

14. The solid propellant of claim 13, wherein the total weight percentage of the GO in the solid propellant is between 0.3 and 6%.

15. The solid propellant of claim 13, wherein the solid propellant is metal-free.

16. The solid propellant of claim 13, further comprising aluminum powder for increasing energy content of the solid propellant.

17. The solid propellant of claim 13, further comprising a metal-based burnrate enhancer.

18. A burning rate enhancer, comprising a composite of epoxy-modified graphene oxide (EMGO) coated onto ammonium perchlorate (AP) to form APEMGO particles having a diameter of between 5-60 microns, wherein the composite includes EMGO in a weight percentage of at least 10%.

19. The burning rate enhancer of claim 18, wherein the EMGO is present in a weight percentage of between approximately 10-20%.

20. A solid propellant for a rocket motor, comprising the burning rate enhancer of claim 18 or 19, neat AP, and hydroxyl terminated polybutadiene (HTPB).

21. The solid propellant of claim 20, wherein the total weight percentage of the EMGO in the solid propellant is between 0.3 and 6%.

22. The solid propellant of claim 20, wherein the solid propellant is metal-free. - 16 -

23. The solid propellant of claim 20, further comprising aluminum powder for increasing energy content of the solid propellant.

24. The solid propellant of claim 20, further comprising a metal-based burnrate enhancer.