Compatibility of Diaminoazofuraz (Daazf) With Other Energetic Materials Using Differential Scanning Calorimetry (Dsc)

Background:

Energetic materials are chemicals that can release massive amounts of energy upon external stimulations, such as shock, heat, or electric current. Based on how energetic material is used, it can be classified into three different categories: explosives, propellants, and pyrotechnics. Explosives release large energy generating shockwaves that travel at supersonic speeds, also known as detonating. Characterized by their sensitivity, explosives can further be classified as either primary or secondary. Primary explosives are more sensitive than secondary, but secondary explosives are much more powerful. Propellants, on the other hand, do not detonate like explosives, but combust. From the combustion, propellants try to generate impulse to move objects. Some explosives can be used in propellant mixtures, as long as a shockwave doesn’t form to turn the combustion into ignition3. Finally, pyrotechnics are meant to generate light, heat, sound, or smoke.

The homogenous mixture that solidifies into a single solid is called a eutectic system. A eutectic system is helpful because it has a lower melting point than its individual components.4 The reason why eutectics are not considered a solid structure, even though it has a crystalline arrangement, is that the components that make up the mixture have different structural integrities.4 Meaning, each component still retains their initial properties, except melting point, within the structure. In addition, eutectics have the ability to eliminate undesirable properties such as hygroscopicity, reacting to the moisture content of the air by absorbing or releasing water vapor, or enhance properties of an individual constituent5. Comment by Mindy Levine: define what this is

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Binary mixtures are almost identical to eutectic mixtures, the only difference is classification. As in, all eutectics are binary mixtures, but not all binary mixtures are eutectics. As mentioned previously, a eutectic mixture melts at a lower melting point than any of the mixture components. This is not always the case for binary mixtures.

Differential scanning calorimetry (DSC) is an instrument that measures the energy absorbed or released by a sample when heated or cooled, otherwise known as the enthalpy. Calorimeters do this by measuring the difference in heat flow between a sample and a reference; in most cases the reference is air. Samples are placed in separate crucibles that have good thermal conductivity and a high melting point. Example materials for a crucible would be: aluminum, platinum, or copper. Although the capabilities of calorimeters are expanding, their main function is to perform experiments that involve temperature ramping, isothermal environments, or temperature modulation in a closed system.6 Comment by Mindy Levine: no random capitalizations Comment by Mindy Levine: this is ambiguous. isothermal what? what are they measuring? try to clarify

Summary:

Diaminoazofuraz (DAAzF), Figure 12, is a secondary, insensitive, explosive, meaning it won’t easily detonate when exposed to external stimulation. For this reason the possibility to use it as a solid propellant or high explosive is being considered. It has been classified this way because it has, “H50 of 320 cm (hammer weight of 2 kg), the critical diameter of 3 mm, and is insensitive to friction and static.”1 H50 is the impact sensitivity where there is a 50% chance of the material detonating and the critical diameter is the minimum diameter of the energetic material for it to detonate, anything smaller will not detonate reliably. Having a detonation velocity of 7420 m/s classifies it as a powerful secondary explosive. That is why it is being considered for use as a solid propellant or high explosive. Based on previous studies it has shown that binary mixtures of 50/50 wt% mixtures of DAAzF/triaminotrinitrobenzene(TATB) have better safety properties compared to hexanitrostilbene(HNS)/TATB 50/50 wt%. Using this as a basis, the paper shows the compatibility of DAAZF with other energetic materials. Comment by Mindy Levine: this is not plagiarism because you put it in quotes but it also does not make it clear that you understand what is going on here.

The compatibility and interaction were tested by creating various 50/50 wt% mixtures with DAAzF and other energetic material and checking the thermal decomposition point of said mixtures. The experiment was performed using a DSC with the mass of each sample at 2.0 mg (DAAzF/energetic material -1.00 mg/1.00 mg) . The atmospheric conditions heating at 10oC/minute, with static nitrogen at 1.0 MPa inside sealed aluminum cells. The samples used to mix with DAAzF were cyclotetramethylene-tetranitramine (HMX), trimethylenetrinitramine (RDX), nitrocellulose (NC), nitroglycerin (NG), NC+NG, aluminum powder, dinitroxydiethylnitramine (DINA), and 3,4-dinitrofurazanofuroxan (DNTF). The DSC curves of the binary mixtures are shown in Figure 1, along with collected data in Figure 2. The data collected was the temperature (oC) of the maximum exothermic peaks of the 50/50 mixture, Tp1, and the energetic material mixed with the DAAzF,Tp2. Using the formula ΔTP = TP1 - TP2, comparing ΔTP to the evaluated standards for explosives and contact materials, Figure 3, to classify how compatible DAAzF is with the other substances. From this the stability of the tested binary mixtures are DAAzF/NG > DAAzF/(NC + NG) > DAAzF/Al > DAAzF/NC > DAAzF/RDX > DAAzF/DINA > DAAzF/HMX > DAAzF/DNTF.

Using the standards of compatibility provided in the article, the mixtures with good compatibility, (ΔTP/ oC) ≤ 2, are DAAzF/(NC + NG), DAAzF/NG, DAAzF/Al, DAAzF/NC; meaning they are safe to use together. The only substance that is slightly compatible, 3 ≤ (ΔTP/ oC) ≤ 5 is DAAzF/RDX, meaning that it should only be used for short periods of time. Mixtures that have poor compatibility, 6 ≤ (ΔTP/ oC) ≤ 15 with each other are DAAzF/DINA and DAAzF/HMX, which are not recommended to use together. Finally, the mixture tested that is hazardous, (ΔTP/ oC) >15, to use together is DAAzF/DNTF.

There are some notables from the DSC curves shown in the paper. The first is that as a pure DAAzF decomposed to gas from 323-328 oC, with exothermic peak at 327.3 oC. Every mixture had a lower decomposition point than pure DAAzF. In order from highest to lowest decomposition points of the mixtures were DAAzF/Al > DAAzF/HMX > DAAzF/DNTF > DAAzF/RDX > DAAzF/NC ≈ DAAzF/(NC + NG) ≈ DAAzF/NG > DAAzF/DINA.

Commentary:

The purpose of the paper was to measure the compatibility of DAAzF with other energetic materials. Despite using two other sources with the Standard Compatibility Chart, Figure 4, it stemmed from a report titled Compatibility of Explosives with Polymers (II) by Norman Beach And Vincent Canfield. This report is a compilation of data from 1959-1967 of many energetic materials and plastics, and describes how compatible they are. The Compatibility Standard Chart is not used in this report but rather a similar test called the Vacuum Stability Test is used. It is a similar concept that tests the degree of reactivity of the polymer and energetic material mixtures by measuring the amount of gas released and using the equation R = C – (A+B), Figure 57, to determine how reactive the components are with each other. The paper written does not reference the equation, or how the standard chart was derived from it. Not to mention, the report is about compatibility between energetic material and plastics, not energetic material and energetic materials. The question remains whether the same type of measurement even works.

References:

1. Ji-Zhen, L.; Bo-Zhou, W.; Xue-Zhong, F.; Hong-Jian, W.; Xiao-Long, F.; Cheng, Z.; Huan, H. Defence Technology 2013, 9 (3), 153–156.

2. Hiskey, M. A.; Chavez, D. E.; Naud, D. L. Researchgate 2014.

3. Naik, V.; Patil, K. C. Resonance 2015, 20 (5), 431–444.

4. Cherukuvada, S.; Nangia, A. ChemInform 2014, 45 (10).

5. Oxley, J. C.; Smith, J. L.; Brown, A. C. The Journal of Physical Chemistry C 2017, 121 (30), 16137–16144.

6. Rawlinson, C. Differential Scanning Calorimetry 2006.

7. Beach, N. E.; Canfield, V. K. New Jersey: Dover April 1968.

Figures:

1. DAAzF figure

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2. DSC curves

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3. Maximum exothermic peaks of 50/50-DAAzF/energetic material

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4. Standard of compatibility for explosives and contacts materials

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5. Reactivity Test Details

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