Kenneth K. Kuo The Pennsylvania State University University Park, PA 16802

Transcription

1 Macroscale Characterization of Reactive & Mechanical Behaviors of Nano-Structured Energetic Materials Kenneth K. Kuo The Pennsylvania State University University Park, PA Presented at Nano-Engineered Energetic Materials (NEEM) MURI Kickoff Meeting University Park, PA September 14,

2 Characterization of Important Burning Behavior of a Solid Propellant SYMBOL DESCRIPTION a (T i ) n Pre-exponential factor of the Saint Robert s burning rate law rb = a( Ti) P for propellant at an initial temperature of T i n Pressure exponent in the above burning rate law a o Pre-exponential factor of the Saint Robert s burning rate law for propellant at an initial reference temperature, T i,ref i.e., at ( i) = aoexp σ P( Ti Ti, ref) σ P Temperature sensitivity, σ P 1 r b rb Ti P r = Aexp E / RT A Arrhenius pre-exponential factor [ ] E a Q s λ P b b a u s Activation energy Net heat release from the burning surface reaction Thermal conductivity of the propellant Coefficient in the following surface temperature vs. pressure relationship: ( T T ) = b( P P ) m s s, ref ref m Exponent in the above surface temperature vs. pressure relationship 2

3 Schematic Diagram of Solid Propellant Strand Burner (SPSB) Up to 9,500 psi capability -60 o C <T i < 80 o C Optically accessible 3

4 Solid Propellant Strand Burner (SPSB) Surge Tank SPSB To exhaust system Setra Pressure Transducer Window for optical access SPSB capabilities/features Optically accessible Up to 9,500 psi capability Temperature control 60 o C < T < 80 o C Active pressure control Constant N 2 purge entrains and cools exhaust products Surge tank limits pressure excursions N 2 inlet 4

5 Ultra High Pressure Strand Burner (UHPSB) High Pressure Combustion Lab (Control Room) TV set (P1) Compressor Building (Test Cell) Manual Remote OFF High Pressure Compressor HV9 Water Out Water In HV3 HV1 HV5 HV2 Air To lab Solenoid Valve Test Sample TC/BW Continuity Continuity FIRE Exhaust SV1 Cylinder A: Test Chamber (Pmax=30,000 psi) Compressor OFF ON ON Power OFF Exhaust ON OFF HV8 Cylinder B: Storage Tank (Pmax=30,000 psi) HV6 HV7 Up to 30,000 psi capability Constant temperature control Not optically accessible Large N 2 mass limits pressure excursion Remote controls No purge flow 5

6 Propellant Sample Preparation Propellant samples can be prepared with embedded breakwires and thermocouples Breakwires in a propellant strand are used in determining burn rate of a given propellant Micro-thermocouples are used to monitor propellant strand initial temperature and the thermal profile adjacent to the burning surface Igniter BW #2 Thermocouple BW #1 Curved Cut 6

7 Micro-thermocouple for Temperature Measurements Thermocouples down to a few microns in thickness can be embedded in solid propellant strands, using the cone and cup configuration. The R- or S-type hightemperature thermocouples can measure temperature up to ~2000 K. 7

8 Typical Temperature Profile Measured by Using Micro-thermocouples P = 640 psia r b = 1.52 cm/s Solid Phase T surface = K Distance From Surface [ µm] Gas Phase This figure shows a typical thermocouple trace of a propellant As seen in the figure, the surface temperature is 751 K and the thermal wave thickness is approximately 60 micrometers 8

9 Video images for Burning Rate Determination 1 mm Time [ms]: Propellant burning at 8,000 psi 9

10 SEM Micrographs of Two RDX-based Composite Propellants with Same Formulation but Different Particle Sizes Advanced Moderate Energy (AME) Propellant with micronsized RDX particles (2000X) Advanced Moderate Energy (AME) Propellant with nanosized RDX particles (2000X) 10

11 Measured and Correlated Burning Rate and r b Ratio for AHE and AME Propellants Burn Rate AHE/AME AHE/Nano-RDX AME - RDX/BBA/Alex Nano-RDX/BBA/Alex AHE - HNF/RDX/BBA/AL Pressure [psig] Burning Rate Ratio Burning rate of the AME Propellant with nano-sized RDX is similar to that with micron- sized RDX; however, the shock and impact sensitivities are expected to be lower for the propellant with nano-sized RDX particles High burning rate ratio was achieved using the AHE and AME propellants 11

12 Burning Rate vs. Initial Temperature The temperature sensitivities of this propellant are determined from the slopes of these plots for two different pressures. 12

13 Temperature Sensitivity versus Pressure for Two Selected Propellants 13

14 Temperature Sensitivity of a Gun Propellant Pressure [MPa] The temperature sensitivity is defined using the following equation: σ p ln r b = Ti This parameter can be used to find the Novozhilov κ- stability factor p Pressure [psia] κ σ p Τ s - Τ i ( ) 14

15 Arrhenius Burning Rate Law 15

16 Novozhilov Stability Parameters The two Novozhilov stability parameters are the κ-stability factor and the γ-stability parameter and are defined below T s κ σ p ( Ts Ti), γ Ti p Stability using the Novozhilov parameters is defined as: К < 1 or К > 1 and γ > γ* where 2 ( κ 1) ( κ + 1) By using the surface temperature measurements, these two parameters can be used to determine the stability of a propellant γ* = 16

17 Stability Plot for MURI #1a Propellant Small unstable combustion regime was identified 17

18 Characterization of New Propellants and Nano Energetic Materials Physical Properties Density, particle size distribution, etc. Micro and Macroscopic Imaging Particle shape, size, and their distribution in propellants Surface features of original and partially-burned propellants Thermal Analysis Amount of unreacted ( active ) material present based on mass gained during oxidation Reactivity and stored energy based on exotherm and onset temperature Other Physical & Chemical Analysis Combustion Analysis Compare and correlate particle and propellant properties to combustion results and performance 18

19 Particle Characterization Capability Using PSU s PCL Facilities Characteristics such as particle size, surface area,particle density, etc. can be measured and quantified. The particle characteristics of a material greatly influence many other chemical and physical characteristics including: stability, chemical reactivity, and material strength. Helium Autopycnometer calculates particle densities BET can perform a multipoint surface area analysis Microtrac/Ultra Fine Particle Analyzer - particle size measurements can be made ranging from to 6.5 microns. Horiba Particle Size Distribution Analyzer - particle size measurements can be made ranging from 0.01 µm to 300 µm. Laser Diffraction Particle Size Analyzer - provides particle size data ranging from 0.03 µm to 280 µm. Malvern Mastersizer - utilizing the wet technique, particle sizes throughout a dynamic size range of 0.05 µm to 900 µm can be measured, while the dry technique allows the user to quickly measure dry powders ranging from 0.5 µm to 900 µm. 19

20 Various Types of Electron Microscopy Scanning Electron Microscopy (SEM) uses a focused electron beam to scan small areas of solid samples. Spatial resolution of 4 nm is typical. Environmental Scanning Electron Microscopy (ESEM) has the capability for using different gases under controlled temperature or controlled rate of temperature increase. Energy Dispersive Spectroscopy (EDS) is a standard procedure for identifying and quantifying elemental composition of sample areas as small as a few cubic micrometers. Characteristic X-rays are produced when a material is bombarded with electrons in a SEM. Detection of these x-rays can be accomplished by an energy dispersive spectrometer to yield 2 dimensional elemental mapping of micron-sized features. Transmission electron microscopy (TEM) - A high voltage electron beam is passed through a thin ( nm) solid sample. Contrast is derived by electrons scattering from atoms in the material. Atomic scale imaging is possible in MCL s field emission instrument. In addition to the shape and size of the particles, phase identification and separation, chemical analysis at the sub-10 nm level, and characterization of microstructures, defects and chemical compositions can be made. 20

21 SEM Images of Aluminum Powder 2 µm 500 nm 20,000 times magnification 100,000 times magnification For Alex aluminum powder: Extremely spherical particles Size ranges from 50 to 250 nm Other particles: Varying degrees of uniform spheres and agglomeration Average diameter from 30 to 150 nm 21

22 Geometry of Aluminum Flakes (Photos courtesy of Dr. May Chan of NSWC-China Lake) Approximate dimensions of flake: 4 to 50 µm in width 50 to 200 nanometers in thickness 22

23 TEM of Aluminum Nano-Rods (image courtesy of NanoMat, Inc., North Huntingdon, PA) 23

24 Thermal Analysis Capability Using PSU s TAL Facilities The Thermal Analysis Laboratory (TAL) contains several instruments designed to characterize materials based on their behavior under various heat conditions. Differential Scanning Calorimetry (DSC) measures the temperatures and heat flows associated with transitions in materials to provide information about physical and chemical changes that involve endothermic and exothermic processes. Thermogravimetric Analysis (TGA) measures changes in weight of a sample with increasing temperature. Differential Thermal Analysis (DTA) measures the difference in temperature between a sample and a thermally inert reference as the temperature is raised, providing information on exothermic and endothermic reactions taking place in the sample. Typical applications Composition of multicomponent systems Thermal and oxidative stability Effect of reactive atmospheres on materials Melting point and phase transitions Heat capacity 24

25 DSC/TGA Curves of Silberline Flakes HR = 5 o C/min in O 2 Environment DSC Analysis 174% Heat Flow [W/g] TGA Analysis T MELT = 660 o C (aluminum) Weight % % Temperature [ o C] Weight gain due to oxidation from 97 to 174% of original mass Two-stage energy release a portion below T melt 25

26 DSC/TGA Curves of NTECH HR = 5 o C/min in O 2 Environment DSC Analysis 151% TGA Analysis 140 Heat Flow [W/g] 20 0 T MELT = 660 o C (aluminum) Weight % % Temperature [ o C] Weight gain due to oxidation from 97 to 151% of original mass Two-stage energy release most below T melt 26

27 Other Available Analysis Tools Field emission Auger electron spectroscopy - a finely focused electron beam ionizes atoms in the near surface by the production of a core hole. The ion loses energy by filling this core hole with an electron from a shallower level combined with ejection of an electron. The energy of this Auger electron is characteristic of the atom from which it was emitted and the number of electrons is proportional to the concentration of that element in the sample. The relatively low energy makes the technique inherently surface sensitive with the majority of the Auger electrons in a given sample originating from the outer 5-10 nm. In certain elements (Al, Mg, Si, In, Cu) the energy is a function of the local environment of the atom yielding a chemical (or oxidation) state sensitive tool. X-ray diffraction (XRD) - X-rays with wavelength on the order of lattice spacing are elastically scattered (i.e., diffracted) from the atomic planes in a crystalline material yielding diffraction peaks. Using Bragg s Law, the resultant diffraction pattern can be used to identify crystalline phases, determine residual stresses, preferred orientation or grain size. 27

28 Additional Analysis Tools Atomic Force Microscopy (AFM) - provides 3-dimensional topographic information about a sample by probing its surface structure with a very sharp tip. The lateral resolution of the image can be as small as the tip radius (typically 5-15 nm), and the vertical resolution can be on the order of angstroms. Secondary Ion Mass Spectrometry (SIMS) - primary ions with moderate energy bombard the sample surface and remove material by sputtering. A fraction of the sputtered material consists of positive and negative ions. These secondary ions are drawn into a mass spectrometer where they are analyzed according to their mass-to-charge ratio. Elements H-U (including isotopes) can be detected at sensitivity levels of 1-10 ppm (atomic) for most elements. 28

29 Active Content Analysis of Al Particles Chemical hydrolysis analysis Sample placed into aqueous KOH solution where Al reacts with KOH to form Al(OH) - 4 and hydrogen gas The quantity of hydrogen is measured and compared to the amount generated from a known standard (Valimet H-2 Al powder) to find active Al content Performed by Dr. Curtis E. Johnson of NAWC-China Lake Thermogravimetric analysis (TGA) Sample heated in an oxygen atmosphere until completely oxidized Active Al content determined from measured mass gain and assuming all weight gain due to reaction to stable oxide compound 29

30 Active Content Results In general, good agreement between the two methods for Al Significant differences found among the different particles (unreacted content ranged from 33.5 to 88.8 Active Material Content [wt%] KOH TGA % by weight) 0 Alex WARP-1 SILBAL CLAL TECHAL Boron C-Alex IHD-AR IHD-HE NTECH-80 NTECH-50 AVAL C-Boron 30

31 Derived Parameters of Interest for Various Nano-sized Particles Effective density (ρ effective ) is useful for determining density enhancement of solid fuel/propellant formulations containing particles. Higher density is not necessarily better because oxide density greater than base material. Particle Label Alex WARP-1 SILBAL CLAL TECHAL Boron Coated-Alex IHD-AR IHD-HE NTECH-80 NTECH-50 AVAL C-Boron Average Dia. [nm] flakes flakes Average Oxide Thickness [nm] assumed same as Alex assumed same as Boron ρ effective [g/cm 3 ]

32 Evaluation of Combustion Enhancement by Nanoparticles Using Hybrid Rockets The hybrid rocket facility at the HPCL has been used to evaluate the propulsion performance of many energetic nano-sized particles All particles tested in same equipment under the same conditions Test motor is scaled-down version of flight motor so results and trends should be directly applicable to large-scale systems Hybrid rockets are very promising technologies for future space systems due to inherent safety and operability advantages over current systems One major disadvantage of hybrid rockets (low fuel regression rate) can be addressed by use of nanoparticles 32

33 LGCP Hybrid Motor Layout End Plug Retainer Cradle Clamps Motor Wall Phenolic Tube Solid-fuel Grain Protective Graphite Liner Interchangeable Graphite Nozzle Load Cell Load Cell Support Grain Length = 16 inches Grain Diameter = inches CP Bore = 0.35 inches Linear Guide Platform Linear Bearing Guide Support Blocks Test Stand 33

34 Clean-Burning Plume Jet from a Hybrid Rocket Fuel Type: SF19 (5.65% boron) Obtained clean burning plumes from solid fuels containing nano-sized boron particles (with no visible particle streaks) SF19 (5.65% Boron) 34

35 Aluminized HTPB Fuel Mass Burning Rates 0.04 Average Mass Burning Rate [kg/s] Pure HTPB (SF1) 13%ALEX (SF2) 6.5%WARP-1 (SF4) 13%SILBAL (SF7) 13%CLAL (SF8) 13%WARP-1 (SF9) 13%TECHAL (SF11) 13%Al325 (SF12) 13%C-ALEX (SF13) 13%AVAL (SF15) 13%IHD-AR (SF16) 13%NTECH80 (SF17) 13%NTECH50 (SF18) Average Oxidizer Mass Flux [kg/m 2 -s] 35

36 Burn Rate of Two Different Aluminized Propellants Standard Aluminized Propellant T = 0 C i T i = 25 C T i = 50 C Alex Propellant T = 0 C i T i = 25 C T i = 50 C This plot compares burning rates of two Army propellants at pressures between 500 and 2000 psia and initial temperatures of 0 C, 25 C, and 50 C. Mench, Yeh, and Kuo (1998) showed substantial increase of burn rate using nano-sized aluminum particles. Average Pressure [psia] 36

37 Energetic Materials Presser Capabilities Used to consolidate propellant and explosive powders into sample pellets or strands for combustion testing. Safety features to protect the operator include heavy steel plate construction, pressure release ports, shear pins, and remote computer-controlled operation. Interchangeable die system allows pellets of varying diameters to be produced (typically ¼ ). Pressures of up to 40,000 psi have been achieved with RDX, producing a sample pellet with a density greater than 94 % of the theoretical maximum density. 37

38 Partially-Confined Hot Fragment Conductive Ignition (HFCI) Experiments This setup was specifically designed to study the spall fragment induced ignition of gun propellants. The HFCI ignition data are useful to guide the development of IM propulsion systems. 38

39 Go/No-Go Ignition Boundaries Under a Weakly Confined Environment The two propellants studied were M43 and XM39 39

40 Go/No-Go Ignition Boundaries Under a Highly Confined Enclosure The trend was reversed for these two propellants. 40

41 CO 2 Laser Ignition Test Setup Everlase CO 2 laser with 300 to 800 W continuous wave power Maximum peak pulse power of 3500 W Minimum pulse length of 100 µs Maximum pulse rate of 2.5 khz This laser system will be used for propellant ignition study 41

42 Laser Ignition Characteristics of New Propellants with Nanosized Energetic Particles Various ignition phenomena will be examined. The parameters of interest include the times for the onset of gas evolution, light emission, and self-sustained ignition as a function of heat flux. A high-powered CO 2 laser will be employed, which may operate either in a pulsed wave mode with a maximum of 3,500 watts or a continuous wave mode with a maximum of 800 watts. Heat flux delivered to the propellant surface will range from 30 to 250 W/cm 2 42

43 Double-Ended Strand Burner This special strand burner was designed for studying the gap-distance effect on propellant burning rate. 43

44 Burning Rate Measurement of Newly Processed Propellants Several windowed strand burners will be utilized to characterize the combustion behavior of solid propellants. The chamber can be operated at pressures up to 207 MPa and propellant initial temperature from 60 to +80 o C. Video data can be used to deduce the burning rate. In order to properly measure the burning rate as a function of pressure and web thickness, three techniques (acoustic methods, and real time x-ray radiography (RTR), and a windowed strand burner) appear to have the most promise. RTR offers the ability to monitor the instantaneous location of the propellant s burning surface as a function of time. 44

45 Burning Surface Observation of Propellants with Energetic Nano-Particles A copper-vapor laser will be utilized to observe the burning surface phenomena, including particle ejection, average particle burning time in the gas-phase zone, particle agglomeration, etc. 45