Next Generation Munitions: Nano Propellants for 3D Printing Arthur - - PowerPoint PPT Presentation

Next Generation Munitions: Nano Propellants for 3D Printing

Arthur Provatas (Lead) & Liam Stephenson Advanced Warhead Technologies Weapons & Combat Systems Division PARARI 2019

E: arthur.provatas@dst.defence.gov.au

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Introduction

• DST plays a key role in positioning the ADF to fully exploit

capabilities afforded by emerging weapons concepts Transformative Energetics

Enabling advanced weapons systems that offer disruptive performance gains and increasing the agility, safety and efficiency of munitions manufacture.

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Transformative Energetics

Enabling advanced weapons systems that offer disruptive performance gains and increasing the agility, safety and efficiency of munitions manufacture.

Advanced Materials

• Nano-technology

Processing Technology

• Resonant Acoustic Mixing

3D Printing of Energetics Next Generation Munitions

Transformative Energetics Lines of Effort

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Nano-Energetics

• Material properties change significantly at nano-scale (<0.1 mm)

– Higher surface area – Increased chemical reactivity – Enhanced mechanical properties – Higher solubility – Improved heat dissipation – Smaller void sizes – Reduction in defects

Nano Energetics

Performance Sensitivity

Traditional Materials

Enhanced performance and safety

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Safety Processing pathways Burn Rate

Nano Processes

Top-Down Bottom-Up

Spray Drying

• Evaporative

Crystallisation Process

• Binder Encapsulated
• Simple and Scalable
• Best Polymorph Not

Always Retained

Bead Milling

• Comminution

Process

• Utilises Ceramic

Beads (<500 nm)

• Single Polymorph
• Scalable

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3D Printing of Propelling Charges

Performance Benefits

• Tuneable geometry and integrated charge design

– Greater range – Enhanced muzzle velocity – Increased precision – Charge Uniformity – Longer weapon life

Production Benefits

• Manufacturing agility (on-demand production)
• Reduced manufacturing footprint

22% m.v increase

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3D Printing Methods

Directed Energy Deposition

Focused thermal energy is used to fuse materials by melting as they are being deposited

Powder Bed Fusion

Thermal energy selectively fuses regions of a powder bed

Sheet Lamination

Sheets of material are bonded to form an object

Material Extrusion

Material is selectively dispensed through a nozzle

• r orifice

Binder Jetting

Liquid bonding agent is selectively deposited to join powder materials

Material Jetting

Droplets of build material are selectively deposited

Vat Photopolymerisation

Liquid photopolymer in a vat is selectively cured by light- activated polymerisation High Energy

Digital Light Processing UV Paste

Images from Hybrid Manufacturing Technologies

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Energetic Feedstock Challenges

• High solids loading (> 60 vol. %)
• Compositional homogeneity
• Compatibility with printing method
• Curability (UV Photopolymers)
• Physicochemical stability

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Work Program

• Initial studies focused on formulations of RDX and cellulose acetate butyrate (CAB) 

capable of producing spherical sub-micron particles

• Sensitiveness and mechanical testing revealed that these particles were slightly more

insensitive and mechanically superior to that of micron-sized RDX

• Transitioned to propellant relevant formulations with different polymer binders
• Current focus on spray drying experiments

The development of nano-propellant material suitable for use as 3DP feedstock

50 100 150 200 250 Max Load Modulus Yield Stress Normalisd Values (%) RDX Bulk n(RDX/CAB)

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Spray Drying: Büchi 290 closed loop system

Rapid Co-precipitation Yields Nanocomposite Granules EM + Binder Dissolved in Organic Solvent Atomisation Of Solution

Drying Cyclone Outlet Chamber Separator Filter Aspirator Process Variables Solution Feed Rate Atomizing Gas Rate Drying Temperature Solvent Type Concentration of Solute Heating Coil Nozzle Product

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RDX Type 1 Class 1, d50 200 mm Spray dried nRDX Type 1 Class 1

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Nano Propellant Formulations

• RDX Class 1
• nRDX Class 1
• n(RDX/NC)
• n(RDX/NC/P1)

RDX: Cyclotrimethylenetrinitramine NC: Nitrocellulose P1: Polymer 1 Comparison Cases Propellant Formulations

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Morphological Characteristics

Qiu et al, Powder Tech., 2015, 274, 333-337

Increasing Crystal Size

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Spray Dried RDX/NC

RDX / NC*_Ethyl Centralite

*NC stabilised with ethyl centralite (EC)

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Spray Dried RDX/NC/Polymer 1

RDX / NC / P1

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Mechanical Sensitiveness Testing

Compared with Class 1 RDX, nRDX variants are:

• Significantly less sensitive to friction;
• Exhibit lower ignition temperature;
• Other parameters are comparable

nRDX n(RDX/NC) n(RDX/NC/ P1) RDX Type 1 Class 1 Rotter Impact 90 80 90 80 BAM Friction (N) 168 240 360 96 Static Discharge (J) 4.5 4.5 4.5 4.5

• Temp. Ignition (oC)

206 205 215 219

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Burn Testing

Burn Times

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Formulation Time RDX, normal (bulk) > 1 min nRDX 13 s n(RDX_NC) 10 s n(RDX_NC_P1) 7 s (residue)

X-Ray Diffraction Analysis

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Nano-RDX-NC-P1 Nano-RDX RDX

α-RDX

• RDX can exist as several polymorphs (α, β, γ …)

– The α polymorph is stable at STP for bulk-form RDX

XRD Analysis

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Kumar et al, Propellants Explos. Pyrotech., 2014, 39: 383-389 RDX during spray drying, 2011, ARDEC

Future Testing

• Scale up
• 3D printing
• Burn rate testing
• Optimisation
• New formulations

Other Avenues of Nano-Energetic Production

• Bead milling

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Next Generation Munitions: Nano Propellants for 3D Printing

Arthur Provatas (Lead) & Liam Stephenson Advanced Warhead Technologies PARARI 2019

E: arthur.provatas@dst.defence.gov.au

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