Development of Ultra-High Pressure Supercritical Fluid Processing of Nano-sized Energetic Oxidizers

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1 Development of Ultra-High Pressure Supercritical Fluid Processing of Nano-sized Energetic Oxidizers Kenneth K. Kuo Kristen A. Clark, Peter J. Ferrara, and Robert B. Wehrman The Pennsylvania State University University Park, PA Presented at ARO Review of Nanoenergetic Materials Initiatives MURI/DURINT Review Aberdeen, MD November 16-17,

2 Acknowledgements Our thanks to the following people for their support and insight Dr. David Mann, ARO Prof. Rich Yetter, MURI Project PI Dr. Jeff Morris, ARL Prof. Lev Krasnoperov and Mr. Victor Stepanov, NJIT and ARDEC Our team is looking forward to working with Dr. Kevin McNesby, ARO Thanks for the participation of Scott Blakeslee and Erik Turner at PSU 2

3 Overview Motivation and Objectives RESS parameters Design of Experimental setup and Design Calculations Summary Future work 3

4 Motivation for Nano-particle Synthesis The reduction of oxidizer particle size in solid propellants has shown to decrease the propellant sensitivity for hot-spot initiation by mechanical forces (van der Steen, 1995, Armstrong, 2005). This reduced sensitivity is attractive for the development of insensitive munition (IM) solid propellants. IM characteristics are desirable due to their safe storage and handling. Thus, it is important produce nano-sized energetic particles (such as RDX) to be used as the oxidizer in the manufacturing of IM solid propellants. Physical grinding or milling to achieve nano-sized particles is: Challenging to create and control desirable size distribution Dangerous due to the force applied to fragment crystals of reactive material Thus, we prefer the RESS process. 4

5 Objectives for Nano-particle Synthesis The overall objective of this study is to produce nano-sized RDX particles by means of the rapid expansion of supercritical solutions (RESS) technique. The specific objectives are: Select an adequate solvent and co-solvent for the RESS process, Determine the desirable operating conditions for the RESS system, Design, fabricate, and set up an ultra-high pressure RESS system for a broad range of operating conditions, Design and fabricate an efficient nozzle for the expansion of the supercritical fluid mixture and particle extraction system for separating the nano-sized RDX particles from the supercritical fluid, Characterize the nano-sized RDX particles obtained from the RESS process 5

6 What is RESS? RESS stands for Rapid Expansion of a Supercritical Solution First used in pharmaceutical field for making nano-sized medical particles by Coffey and Krukonis in 1989 High-pressure supercritical solution forced through micron-sized nozzle to low pressure chamber to create nano-sized particle Potentially clean, recyclable, and environmentally-friendly technique 6

7 Required Chemical Ingredients for RESS Processing Supercritical fluids have solvating properties similar to liquid and mass-transfer properties like gases Carbon dioxide used as supercritical solvent Others ideal solvents investigated: Nitrous oxide considered too unstable Chlorofluorocarbons not acceptable due to environmental concerns Co-solvent [dimethylsulfoxide (DMSO, C 2 H 6 OS) or acetonitrile, (CH 3 )CN] can be used to increase solubility of solute in solvent RDX used as solute 7

8 Why was RESS Selected for Nano-sized Particle Creation? Mechanical grinding of energetic particles can be avoided SAS (Supercritical fluid Anti-Solvent) precipitation can produce micron-sized RDX particles but not for large quantities of nano-particles Thar Technologies RESS equipment has been used to produce small quantities of nano-sized RDX particles by NJIT/ARDEC group In order to increase the through put, commercial RESS systems were not selected due to their relatively low working pressures (below 10,000 psi); PSU design is rated up to 30,000 psi working pressure 8

9 Solvents chosen for PSU RESS Solvent: Carbon Dioxide, chosen for its documented solubility with RDX (through interaction with Dr. Jeff Morris of ARL) also low critical temperature and pressure (31.2 C and 7.38MPa or 87.9 F and psia) Possible Co-Solvents: Acetonitrile, DMSO, and DMF (dimethylformamide) for increasing solubility; DMSO showed up to 16x increase to that of neat carbon dioxide Phase diagrams of carbon dioxide and possible cosolvents were studied and superimposed 9

10 Superimposed Phase Diagram of Solvent & Co-Solvent Materials for RESS Process Pressure (psi) S CO 2 L CO 2 CO 2 Phase S DMSO V CO 2 Solid RDX L DMSO V DMSO Super Critical Region L Aceto V Aceto Max Operating Temp 176 F Aceto phase Decomposition region of RDX Melting of RDX F DMF phase DMSO phase Compression Expansion Temperature (F) 10

11 Flow Process Diagram of the Ultra-High Pressure RESS System 11

12 Calculated Nozzle Flow Rates as a Function of Stagnation Pressure For a 100-μm diameter nozzle, the predicted flow rate ranges from to kg/s at pressures 1000 to 30,000 psi respectively. Mass Flow Rates through Nozzle Mass Flow Rate (kg/s) Pressure (psig) 12

13 Mach Disk Stand-Off Distance as a Function of Pressure Change Mach disk will form beyond the exit plane of the expansion nozzle Stand-off distance calculated using: P dstandoff = 0.67 dnozzle throat P to determine the location for particle collector stagnation chamber Mach Disk Stand-Off Distance (in) P stagnation /P chamber Pressure Difference (Pstagnation/Pambient) 13

14 RESS Experimental Setup Saturation Vessel with Jacket Heater Expansion Vessel Saturation Vessel Stand High Pressure Solenoid Valve to Surge Tank High Pressure Solenoid Valve to Expansion Vessel Hydro-Pac Compressor Expansion Vessel Stand Surge Tank Air Supply for Ball Valves 14

15 Control Area for RESS Processing HiP High Pressure Pump CO2 Supply Computer Control NESLAB Heat Exchanger 15

Control Panel Exhibited overall process flow design Main power and emergency stop switches easily accessible Flow meter display Temperature controls at

16 Control Panel Exhibited overall process flow design Main power and emergency stop switches easily accessible Flow meter display Temperature controls at various stations with display Compressor and pump controls are visible BNC pass-thru for pressure transducer data Needle valve control for expansion vessel exhaust 16

17 Hydro-Pac 30,000 psi Compressor Capable of working pressure of 30,000psi Dual piston pump with water active cooling 5 horse power motor ¼ NPT fitting on inlet ¼ HiP fittings on outlet System Pressure Gauge Outlet Inlet Motor Dual piston 17

18 Saturation Vessel with Heating Jacket 30,000 psi HiP Clover leaf pressure vessel Heater Jacket 1/16 K-type thermocouple ¼ HiP Tubing 18

19 Windowed Expansion Vessel 200 psi expansion vessel Four 11 windows 2 Glass 2 Acrylic Four ¼ NPT exhaust ports Sixteen ¾ holes in flange to secure top and bottom flange 19

20 High Pressure Nozzle Assembly 316 SS Designed for working pressure of 30,000psi Equipped with 2 thermocouple ports and 1 pressure transducer port 20

21 Nozzle Assembly Exploded View Nozzle Retainer Ring Nozzle Spacer HiP Fitting for Pressure measurement Top Flange Nozzle exit Buna-N O-rings 21

22 High Pressure RESS Nozzle 316 SS Nozzle orifice size = 100 microns (0.004 ) 22

23 Schlieren System Set-Up Folding Mirror 2 Folding Mirror 1 Schlieren Field Mirror 2 Camera Knife Edge Schlieren Field Mirror 1 Light Source, Focusing Lens, and Slit under black cloth - Covers kept on Schlieren mirrors to reduce flash and reflection in the picture. 23

24 Schlieren System Utilizing a Schlieren Mirror system, density gradients in the expansion jet will be photographed. The hypothesis that larger regions of turbulent flow in the expansion jet can lead to higher rate of nano-sized particle formation will be examined. Due to space limitations, Z-Type folding technique has been adopted. Two12.5 -diameter Schlieren field mirrors and two 8.5 diameter folding mirrors are utilized. 24

25 Safety Features Incorporated in the RESS Design Emergency Stop button on control panel Opens all vents to relieve pressure All power will be cut off to stop both the compressor and pump Two high-pressure burst disks with vented exhaust in case of pressure spike Remotely controlled solenoid valve on expansion vessel in case of filter clogging The test room is surrounded by steel walls with a blow-out door, which will be open during the RESS processing 25

26 Summary RESS is the best and safest method for producing nano-sized energetic particles. Carbon dioxide is the best known solvent for RESS processing of RDX particles. By increasing the working pressure in the RESS system, we hope to increase the solubility and rate of throughput of nano-sized particles which are less sensitive to impact or mechanical stress loading. A Schlieren system has been set up and will be used for observing the flow field structure during the expansion process. The designed RESS system is fully constructed and ready for system checkout tests. 26

27 Future Work Planned system checkout test runs will start with lower pressure and gradually step up in pressure: 100 psi test with only CO psi test with only CO psi test with only CO psi test with only CO psi test with only CO 2 10,000 psi test with only CO 2 until reaching 30,000 psi Add RDX after pure CO 2 tests and perform tests at different pressures Stepwise addition of co-solvents Pre and post SEM particle characterization ADN will be considered for future RESS processing 27

28 Thank you! Questions? 28

Presser for Remote Consolidation of Solid Stands Consolidation of propellant ingredients into a solid strand can be achieved by remote pressing.

29 Presser for Remote Consolidation of Solid Stands Consolidation of propellant ingredients into a solid strand can be achieved by remote pressing. Designed to create highdensity propellant ingredient samples Remote computer control can discern actuator displacement steps down to inches System can also press premixed multiple solid propellant ingredients into a strand. Loading gauge Actuator Press Action Extra-Heavy Wall Chamber Displacement Control Sensors Presser cylinder Loading Port with Mandrel Manual Control Switches 29

After propellant sample is made, characterization can be preformed by burning strands Embed fine-wire thermocouple coated by inert silicon nitride (with bead size on order of micrometers) to measure

30 After propellant sample is made, characterization can be preformed by burning strands Embed fine-wire thermocouple coated by inert silicon nitride (with bead size on order of micrometers) to measure thermal profile in the strand and flame zone High-temperature chemical vapor deposition process under a relatively low pressure condition has been used to coat platinum thermocouples Custom-made components with a special electric circuit to control the temperature Chemical Vapor Deposition Thermocouple Coating Sample holder Temperature indicator Hot water bath (SiCl 4 evaporator) 12 VDC power supply Reactor Temperature controller 4-channel operational switches Hot water source Fan-mixture in reactor 30

Cover Page for Lab Report Group Portion. Compressible Flow in a Converging-Diverging Nozzle

Cover Page for Lab Report Group Portion Compressible Flow in a Converging-Diverging Nozzle Prepared by Professor J. M. Cimbala, Penn State University Latest revision: Prof. Steve Lynch, 14 February 2017