Comminution of Energetic Materials in Binder Components with High Solid Loadings for Direct Application in Formulations

Transcription

1 Comminution of Energetic Materials in Binder Components with High Solid Loadings for Direct Application in Formulations Thomas Heintz, Alexander Dresel, Peter Gerber Fraunhofer - Institute for Chemical Technology (ICT) Pfinztal, Germany thomas.heintz@ict.fraunhofer.de 3 rd New Energetics Workshop (NEW) May 29-30, 2018 Stockholm, Sweden

2 Outline Introduction and motivation Comminution technology Materials and experiments Results: Particle size, microscopy, rheology Application: PBX formulations, detonation tests, mechanical analysis Conclusions and future work

3 Introduction Very fine particles < 3 µm, or even down to the sub-micron rage, are applicable as very fine fraction in propellant or explosive formulations. Expected advantages: High solid loading with acceptable viscosity for processing Less sensitivity Influence on the burn rate EDA project RSEM : Higher performance and more homogeneous detonation reaction zone of RS-PBX EDA-Partners: ADAI / LEDAP, Dept. of Mechanical. Engineering, University of Coimbra, Portugal Laboratório de Explosivos da Marinha, Almada, Portugal French-German Research Institute of Saint Louis ISL, Saint-Louis, France MBDA ITALIA S.P.A, La Spezia, Italy Segretario Generale della Difesa /Diverzione Nazionale degli Annamanti, Italy Fraunhofer ICT, Pfinztal, Germany WTD91, Meppen, Germany Prof. Igor Plaksin 2016 created the term Dirty Binder Suspension of an uncured binder enriched with ultra fine energetic particles * picture taken from: LOOKING FOR THE RS-PBXS ALLOWING FOR HIGHER PERFORMANCE OF INERTIAL CONFINEMENT: EDA RESEARCH AND TECHNOLOGY PROJECT RSEM, Ricardo Mendes et al., ICT-Conference 2017

4 Introduction Fine particles can be created by milling, precipitation, spray drying, flash evaporation and some other. Comminution techniques like wet and dry milling are common processes: Dry processes are effective, but may be more dangerous and produce more dust higher safety requirements Wet processes normally need additional steps: solid/liquid-separation, washing and drying Additives like anticaking agents may be needed for storing Usually the dry particles are mixed with the other components of the formulation during the kneading process. Idea: production of fine particles directly in a fluid that is used for later application Dirty Binder no dust, no solid/liquid separation, no washing, no drying, no anticaking agent

5 Comminution technology Requirements on wet milling technology: Processing of high viscous suspensions High performance comminution technique Resident against organic solvents, binder components and fluids e.g. plasticizers Explosion proof and remote controllable Placed in a safety working room

6 Comminution technology Combination of dissolver and bead mill (Dispermat AE06-C1, VMA-Getzmann GmbH, Germany) Technical Data: drive power 2.2 kw; rotation speed rpm; working volume liter zirconium oxide grinding beads: diameter mm

7 Materials and experiments Energetic Material: HMX, Grade B, µm, Lot. NSI00E00E0004 Inert binder: HTPB (hydroxyl-terminated polybutadiene) R-45HTLO, Lot First feasibility and curing tests at 60 C

8 Development of the particle size distribution in dependence of the milling time HMX in HTPB with a mass fraction of 20 wt.%

9 Progress of the comminution process After dispersing Comminution process 2-step process: 1. Dispersing 2. Comminution HMX-starting material: µm Final particle size measured by laser light diffraction: Mean particle size: 1.3 µm Particle size range: µm

10 Morphology and sensitivity Sample preparation for SEM and sensitivity tests: washing and drying HMX starting material Milled product: 9 wt. % Milled product: 20 wt. % 10 µm 1 µm 1 µm Impact sensitivity [Nm] Friction sensitivity [N] HMX 5,5 128 HMX (9%) HMX (20 %) HMX/HTPB_9 % 20 - HMX/HTPB_20 % 25 - rounding reduction of defects

11 Rheological behavior of HMX/HTPB-suspensions viscosity in dependence of the shear rate at constant temperature of 20 C

12 Rheological behavior of HMX/HTPB-suspensions temperature influence on the viscosity at a constant shear rate of 50 s -1

13 Detonation capability test Safety test for Dirty Binder with 20 wt.% solid load Dirty Binder mixed with IPDI and cured under vacuum at 60 C for five days Manufactured PBX test samples: diameter 21 mm and length 110 mm Initiation with pressed HWC Booster (Hexogen / Wax / Graphite 94.5 / 4.5 / 1) Detonation capability test result: no go PBX made of Dirty Binder with a total solid load of 18.6 wt.% after initiation with a pressed booster

14 Application: Plastic Bonded Explosive (PBX) formulations Two formulations HX 479 and HX 481 were manufactured and tested: HX 481 based on a standard HTPB binder HX 479 contains Dirty Binder 90/10 HTPB/HMX milled. The HMX amount of dirty binder was recalculated to 85 wt.% total solid load PBX formulation HX 481 HX 479 Total solid load 85 wt.% 85 wt.% (HMX bimodal) HTPB based binder system 15 wt.% 15 wt.% (Dirty Binder, HTPB with 10 wt.% HMX milled 1.3 µm) Detonation velocity ± 17.2 m/s ± 17.3 m/s

15 Mechanical analysis of Dirty Binder formulations Torsion-DMA measurements were performed with the HMX/HTPB formulations (with and without Dirty Binder) The loss factor can be determined with forced periodical deformation of the sample best obtained with DMA (dynamic mechanical analysis). loss factor tanδ = loss modulus G storage modulus G The formulations with Dirty Binder showed differences in loss factor shape. Find more information at ICT conference: Poster 108: Effect of HMX distribution and plasticizer content variations on the DMA loss factor of HTPB-IPDI binder Manfred A. Bohn, Peter Gerber, Thomas Heintz, Michael J. Herrmann Scientific work of Dr. Manfred Bohn, Fraunhofer ICT

16 Conclusions and future work Particle sizes in the range of 1-2 µm and narrow size distributions are possible Dirty Binders are processable and curable A lot of material combinations seem to be possible: Solids Future work: HMX, RDX ADN, GUDN FOX-7 non energetic materials Liquids HTPB GAP plasticizers anti solvents Increasing of the HMX content up to 30 wt.% Consideration of safety aspects and curing characteristics Production of ADN/GAP-Dirty Binder in kg-scale

17 Acknowledgement Alexander Dresel Christian Roßmann Karlfred Leisinger Werner Reinhard Christoph Birke Dirk Herrmannsdörfer Dr. Peter Gerber Dr. Manfred Bohn Dr. Manfred Kaiser (WTD91)