You are here

Metal Composite Flakes Containing Novel 2D Materials for Advanced Obscuration

Description:

TECHNOLOGY AREA(S): Materials 

OBJECTIVE: To develop a low-cost manufacturing process for the production of metal composite flakes/discs for use as visible and infrared obscurants. The composite flakes/discs shall incorporate a two-dimensional (2D) material that: 1) enhances/retains the conductivity of the metal flake/disc, 2) provides a degree of attenuation in the visible region, and 3) provides a means of enhancing deagglomeration, dispersion, and aerosolization. Potential 2D material candidates may include but are not limited to graphene, Xenes (phosphorene, silicene, borophene, germanene, stanene), MXenes (Ti2C, Ti3C2, Ti4C3, and others), MAX phases (conducting carbides and nitrides), and transition metal dichalcogenides (MoS2, WS2, MoSe2, WSe2, and MoTe2). These composite flake/disc materials shall have an electrical conductivity on the order of iron, although a conductivity on the order of copper is preferred. 2D materials have been extensively researched in the last decade due their excellent electronic properties. These properties are attributed to the electrons having confined movement in the lateral 2D plane, while movement in the z-direction is restricted. The inherent conductivity provided by the 2D material shall serve to enhance the infrared obscuring capabilities of the flake/disc. Additionally, the 2D material should be appropriately chosen so as to provide attenuation in the visible region of the spectrum, i.e. via absorption. Finally, the 2D material should provide a means of mitigating particle agglomeration, so that aerosolization is maximized during the dissemination process. Dissemination approaches for the newly developed material shall include pneumatic (e.g. smoke generator) or explosive (e.g. grenade) techniques. In terms of the flake/disc design, the 2D material shall be an integrated component with the metal flake/disc. There are two essential dimensional requirements for the flakes produced. First, the length requirement is vital for achieving the desired electromagnetic properties. The distribution must be relatively narrow with a major lateral dimension of about 3 µm (D50, with a D10 of 2 µm and D90 of 4 µm) in order to produce a strong resonance within the FIR atmospheric transmission window (8 to 12 µm). Second, flake thicknesses should be as thin as possible within the constraints of flake production. This may prove to be in the vicinity of 20-50 nm, although an ideal thickness of 1-2 nm is desired. 

DESCRIPTION: Smoke and obscurants play a crucial role in protecting the Warfighter by decreasing the electromagnetic signature that is detectable by various sensors, seekers, trackers, optical enhancement devices and the human eye. Recent advances in materials science now enable the production of precisely engineered obscurants with nanometer level control over particle size and shape. Numerical modeling and many measured results on metal flakes affirm that more than order of magnitude increases over current performance levels are possible if high aspect-ratio conductive flakes/discs can be effectively disseminated as an un-agglomerated aerosol cloud. CURRENT STATUS: In spite of numerous publications, no one has yet demonstrated the IR optical attenuation efficiencies that would result from high conductivity coatings that are continuous along any metallic flake substrate having an appropriate narrow length distribution. Currently, the best obscurants for IR attenuation are comprised of brass flakes, which have an extinction cross-section/unit mass of 1.4 m2/g. 

PHASE I: Demonstrate with samples an ability to produce metal composite flakes with major dimensions of 3 µm (D50, with a D10 of 2 µm and D90 of 4 µm) in length, thicknesses of 20-50 nm (though 1-2 nm would be ideal), and conductivity of iron or better (>10^5 mho/cm). Demonstrate that considerations have been made to effectively disseminated as an un-agglomerated aerosol cloud. No less than (5) 1-gm samples shall be provided to ECBC for evaluation. 

PHASE II: Demonstrate that the process is scalable by providing 5 single manufacturing batches of 1-kg samples with no loss in performance, no increase in agglomeration, and no increase in dispersion capability from that achieved with the Phase I samples. Explore additional 2D materials that may enhance performance capabilities, using lessons learned from Phase I research. In Phase II, a design of manufacturing process to commercialize the concept should be developed. Cost considerations should be addressed to ensure that materials are competitive with or less expensive than existing Eckhart Richgold 4000 flakes. 

PHASE III: The techniques developed in this program can be integrated into current and future military obscurant applications. Improved grenades and other munitions are needed to reduce the current logistics burden of countermeasures to protect the soldier and associated equipment. This technology could have application in other Department of Defense interest areas including high explosives, fuel/air explosives and decontamination. Improved separation techniques can be beneficial for all powdered materials in the metallurgy, ceramic, pharmaceutical and fuel industries. Industrial applications could include electronics, fuel cells/batteries, furnaces and others. 

REFERENCES: 

1: Bohren, C.F.

2:  Huffman, D.R.

3:  Absorption and Scattering of Light by Small Particles

4:  Wiley-Interscience, New York, 1983.

5:  Huang, Wenjuan, Lin Gan, Huiqiao Li, Ying Ma, and Tianyou Zhai. "2D layered group IIIA metal chalcogenides: synthesis, properties and applications in electronics and optoelectronics." CrystEngComm 18, no. 22 (2016): 3968-3984.

6:  Embury, Janon

7:  Maximizing Infrared Extinction Coefficients for Metal Discs, Rods, and Spheres, ECBC-TR-226, Feb 2002, ADA400404, 77 Page(s)

8:  Obscurant Applications, S. Johnson, ISN Review, MIT, June 2012.

9:  Carvalho, A., Wang, M., Zhu, X., Rodin, A.S., Su, H. Neto, "Phosphorene: from theory to applications", Nature Reviews Materials 1, 16061, 2016.

10:  Chen, Y., Zhang, X., Liu, E., He, C., Shi, C., Li, J., Nash, P., Zhao, N., "Fabrication of in-situ grown graphene reinforced Cu matrix composites", Scientific Reports 6, 19363, 2016.

KEYWORDS: Graphene, Phosphorene, Dichalcogenides, Composites, Infrared Obscuration 

CONTACT(S): 

Zachary Zander 

(410) 436-3509 

zachary.b.zander.civ@mail.mil 

Brendan DeLacy 

(410) 436-5282 

US Flag An Official Website of the United States Government