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Novel Flame Inhibiting Materials to Increase Red Phosphorus Obscurant Safety

Description:

TECHNOLOGY AREA(S): Materials 

OBJECTIVE: To develop safe, non-toxic flame inhibiting materials or retardants and associated application processes that will significantly reduce the flame size and flame temperature of red phosphorus obscurants while not reducing burn rates, obscurant cloud yield, screening performance, or contributing to phosphine production. 

DESCRIPTION: The defense industry frequently leverages commercially-available materials for use in military applications. These materials as-packaged or prepared for the commercial or industrial sectors may not be in the best configuration for use in military-unique items. Some of these dual-use materials, such as those frequently used in high-performance visible and infrared obscurants, may produce large flames or high heat when burned to generate obscurant clouds. Military end items utilizing Red Phosphorus (RP) for obscuration, such as the KM03 manufactured by Diehl BGT Defence GmbH (Uberlingen, Germany), can produce flames during function that exceed one-foot in height.1 Large flames and high flame temperatures generated by burning RP create incendiary effects that may ignite dry vegetation, buildings or other materials in densely populated areas with unintended consequences. Traditional flame inhibitors have primarily focused on using halide salts or halogenated gases to modulate ion and free radical formation in the gas phase, materials to promote char layer creation when applied to polymers, or transition metal complexes to promote inhibition.2-6 The National Institute of Standards and Technology maintains an extensive online library of publications detailing traditional and other approaches to flame chemistry and inhibition.7 A novel approach is sought to reduce flaming since traditional approaches, such as formation of a char layer, may interfere with the burn rate or not offer a direct solution. The proposed approach may include novel coatings, additives, and the associated application processes to reduce flame size and resulting incendiary effects of burning RP. The rapid oxidation of hot, vaporized phosphorus in air is the primary flame component, this combustion mechanism may reduce the applicability of some traditional flame-suppressing materials. Slowing this vapor-phase reaction may lower flame size and temperature while not affecting burn rates or performance characteristics. Candidate materials and application processes must eliminate flaming and high flame temperatures generated in both the bulk material and pyrotechnic formulations, while maintaining the same compatibility and performance characteristics, e.g. oxidizer compatibility, burn rates, obscurant cloud yield, and mass extinction coefficients for visible (>=2.9 m2/g), near IR (>=1.4 m2/g), mid IR (>=0.27 m2/g) and far IR (>=0.32 m2/g), when compared to untreated red phosphorus. 

PHASE I: Develop materials and application techniques to reduce flaming and high flame temperatures created by burning RP. Candidate material coatings shall not affect RP burn rates, reduce the yield, optical (e.g. visible or infrared) screening performance or adversely affect mechanical properties when pressed into pellets.8 Care must be taken to select chemicals and formulations that are compatible with RP and oxidizers, such as NaNO3, CsNO3, SrNO3, and KNO3. 9-11 Candidate materials and application processes shall not create additional hazards such as degrading RP or increasing the formation of phosphine gas while in storage, and both the materiel solution and combustion byproducts shall not increase the toxicity of RP.11 The materials and process developed under Phase I shall result in two pounds of bulk, treated RP. Materials developed under Phase I shall be delivered to the Edgewood Chemical Biological Center for material testing and further study. An extensive review of candidate materials and application technologies shall be presented along with an analysis of alternatives for the top three candidate materials. The analysis of alternatives shall address issues such as: technological barriers and factors affecting application, material and process costs, material performance, durability, feasibility to scale up and cost. The decision path to select the top alternative material and process solution shall be presented. Highly-rated proposals are anticipated to provide the necessary details and mechanism of operation for evaluators to fully understand the proposed approach, including any literature references and similar or preliminary work that would demonstrate a successful application. The materials and processes developed under Phase I shall result in two pounds of bulk, treated RP. 

PHASE II: Scale up the process to produce batches of one-hundred pound increments or greater within a 24-hour period, or as a continuous process producing one-hundred pounds within a 24-hour period, while maintaining the same or better performances and efficiencies developed and demonstrated in Phase I. A successful Phase II will demonstrate scale-up to production of the processes and materials that were proven in Phase I. This phase shall produce as a deliverable a minimum of one-hundred pounds of treated, bulk RP. This production process must be representative of the final industrial process. 

PHASE III: The techniques developed in this program can be integrated into current and future military obscurant applications. Inhibitors to reduce flame and incendiary effects of RP munitions will improve safe deployment, reduce potential personnel hazards and increase the locations where RP obscurants may be used. RP flame inhibitors will further reduce hazards related to handling, transportation and manufacture of this necessary obscurant. This technology could have application in other DoD interest areas including high explosives, fuel/air explosives and decontamination. Industrial applications are immediately realizable to improve the safety of bulk RP used in the manufacture of flame retardant plastics, chemical processes, flame inhibitors for electronics, and others. 

REFERENCES: 

1: Anthony, J. Steven, et al. No. ECBC-TR-511. Edgewood Chemical Biological Center, Aberdeen Proving Ground MD, (2006).

2:  Hastie, J. W. Molecular basis of flame inhibition. Journal of Research

3:  77, (1973), 733-754.

4:  Brown, N. J. Halogen kinetics pertinent to flame inhibition: A Review. ACS Symposium Series

5:  16, (1975), 341-75.

6:  Babushok, V. I., Deglmann, P., Krämer, R., & Linteris, G. T. Influence of Antimony-Halogen Additives on Flame Propagation. Combustion Science and Technology, (2016).

7:  Morgan AB. A review of transition metal-based flame retardants: transition metal oxide/salts, and complexes. ACS Symposium

8:  1013, (2009), 312–28.

9:  Weaver, David P., and T. Singh. Kinetic Mechanisms for Ionization and Afterburning Suppression. Ft. Belvoir: Defense Technical Information Center

10:  (1987). http://handle.dtic.mil/100.2/ADA189219.

11:  National Institute of Science and Technology, publications library: https://www.nist.gov/publications

12:  Bohren, C.F.

13:  Huffman, D.R.

14:  Absorption and Scattering of Light by Small Particles

15:  Wiley-Interscience, New York, (1983).

16:  Ramsey, R. S.

17:  Moneyhun, J. H.

18:  Holmberg, R. W.

19:  Chemical and physical characterization of XM819 red phosphorus formulation and the aerosol produced by its combustion. ORNL/TM-9941

20:  (1985), Order No. 86007079.

21:  Zheng, Fu-xing

22:  Wang, Xuan-yu

23:  Song, Li

24:  Wang, Xiao-yang

25:  Effects of oxidants of RP smoke to anti-10.6 µm laser. Hanneng Cailiao

26:  15(2), (2007), 155-157.

27:  Gautam, G. K.

28:  Joshi, A. D.

29:  Joshi, S. A.

30:  Arya, P. R.

31:  Somayajulu, M. R.

32:  Radiometric screening of red phosphorus smoke for its obscuration characteristics. Defence Science Journal

33:  56(3), (2006), 377-381.

34:  Marrs, T.C.

35:  Colgrave, H.F.

36:  Edginton, J.A.G.

37:  Rice, P.

38:  Cross, N.L.

39:  The toxicity of a red phosphorus smoke after repeated inhalation

40:  Journal of Hazardous Materials

41:  22 (3), (1989), 269-82.

KEYWORDS: Visible And Infrared Obscuration, Safety, Phosphorus, Obscurants, Flame Inhibition, Flame Retardation, Incendiary 

CONTACT(S): 

Zachary Zander 

(410) 436-3509 

zachary.b.zander.civ@mail.mil 

Shaun Debow 

(410) 652-0812 

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