REPORT DOCUMENTATION PAGE OMB NO. 0704-0188 MURI 2005 ARO Annual Report.pdfformulations with control...

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2. REPORT DATE August 31, 2005

3. REPORT TYPE AND DATES COVERED Interim Progress Report, August 01, 2004 to July 31, 2005

4. TITLE AND SUBTITLE Nano Engineered Energetic Materials (NEEM)

5. FUNDING NUMBERS W911NF-04-1-0178

6. AUTHOR(S) David Allara, Dana Dlott, Rajiv Kalia, Kenneth Kuo, Aiichiro Nakano, Ralph Nuzzo, Priya Vashishta, Vigor Yang and Richard Yetter

7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) The Pennsylvania State University, University Park, PA The University of Illinois at Urbana-Champaign, Urbana, IL University of Southern California, Los Angeles, CA

8. PERFORMING ORGANIZATION REPORT NUMBER

9. SPONSORING / MONITORING AGENCY NAME(S) AND ADDRESS(ES) U. S. Army Research Office P.O. Box 12211 Research Triangle Park, NC 27709-2211

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11. SUPPLEMENTARY NOTES The views, opinions and/or findings contained in this report are those of the author(s) and should not be construed as an official Department of the Army position, policy or decision, unless so designated by other documentation. 12 a. DISTRIBUTION / AVAILABILITY STATEMENT Approved for public release; distribution unlimited.

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13. ABSTRACT (Maximum 200 words) The Nano Engineered Energetic Materials (NEEM) MURI program is exploring new methodologies for development of energetic material formulations with control of all constituents over a wide range of length scales from 1 nm to 1 mm and larger. In particular, new methods employing the latest techniques in molecular self-assembly and supramolecular chemistry for synthesizing and assembling nano-structured energetic materials are under study. The synthetic efforts of the program are guided by state-of-the-art theoretical calculations and advanced dynamic performance testing methodologies that also operate on all length scales. During the past year, progress has been made on the development of both model systems and new synthesis processes for Al clusters and their passivation with self assembled monolayers. A system for supercritical fluid processing of nano RDX has been designed and numerical codes for modeling the nucleation and particle growth of RDX have been developed. To study the stability, structure and reaction dynamics of nano energetic materials, large (billion atoms) multiscale simulations that couple quantum-mechanical (QM) to molecular dynamics (MD) calculations have been performed. A scalable parallel algorithm for reactive forcefield MD simulations was developed, and simulations of the reactivity of RDX molecules on aluminum were analyzed. Dynamic performance characterization of small quantities of NEEMs has been conducted using flash laser heating and laser-generated shock waves. Propagation of reaction fronts through energetic materials containing nano aluminum is reported. 14. SUBJECT TERMS Energetic materials, nanotechnology, nano aluminum, self-assembly, supercritical fluid processing, atomistic and molecular dynamics modeling, ultra-fast molecular spectroscopy, combustion

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Table of Contents

Introduction 3 Objectives and Approach 3 Organization 4 Scientific Progress and Accomplishments 4 Synthesis and Assembly 4 Theoretical Modeling and Simulation 11

Experimental Characterization and Diagnostics 16 Technology Transfer and Interactions 20 List of Papers Submitted or Published under ARO Sponsorship 21 Demographic Data 23 References 23

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Introduction

Novel energetic materials science and nanotechnology are recognized as critical enablers in support of a changing armed-force structure that will require new and advanced explosives and propellants. Much of the previous research on nanoscale energetic materials has emphasized the preparation and characterization of nanoscale energetic metallic particles. To evaluate the use of energetic nanoparticles in explosives and propellants, the nano material has typically been included as ingredients in otherwise conventional formulations using standard fabrication techniques. While some performance improvement has been demonstrated, the full extent of the anticipated gains from nanoscale energetic materials has not been realized in large part due to the incompatibility of length scales.

External to the energetic materials community, there has been tremendous progress in the molecular sciences toward the total command of chemistry at all length scales (supramolecular chemistry). This progress has been inspired primarily by advances in structural determination of biological systems, for instance the chromosome, where meter-long individual DNA molecules are intricately wound around protein spools to fit into micron-long cells, and the abalone shell, which consists of millions of intricate biological layers that provide scaffolds for the assembly of hard inorganic layers. Similar advancements in assembly of molecular and nanoscale elements have been made in the pharmaceutical and microelectronics fields as well. These developments make it clear that in the foreseeable future it will be possible to synthesize any desired macroscopic structure with precise location of every atom.

With this in mind, there are two critical issues relevant to the future development of nanostructured energetic materials: (1) self-assembly and supramolecular chemistry of the fuel and oxidizer elements of energetic materials has lagged far behind other chemistries, and (2) there is no fundamental understanding of exactly what supramolecular structures provide desirable performance, mechanical, and hazard characteristics. With advancements on these two issues, it is conceivable that macroscale formulations of energetic materials could be designed to preserve the intrinsic nanoscale structure of the individual components, thus achieving the true potential of nanoscale energetic materials.

To address these issues, the present MURI program on Nano Engineered Energetic Materials (NEEM) is exploring new methodologies for development of energetic material formulations with control of all constituents on all length scales from 1 nm to 1 mm and larger. In particular, new methods employing the latest techniques in molecular self-assembly and supramolecular control for synthesizing and assembling nano-structured energetic materials are understudy. The synthetic efforts of the program are guided by state-of-the-art theoretical calculations and advanced dynamic performance testing methodologies that also operate on all length scales.

Objectives and Approach

Two overall objectives of the NEEM MURI program are:

• The development of new methodologies for synthesis and assembly of nano-engineered energetic materials (NEEMs), which will also provide concurrent improvement in performance and managed energy release while providing reduced sensitivity and ease of processing and handling.

• The fundamental understanding of the relationship between the structures of NEEMs and their reactive and mechanical behavior, particularly with regard to sensitivity, ignition, burning characteristics, mechanical properties, and optimum loading density, thus enabling design optimization of NEEMs.

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To accomplish these objectives, the program makes use of a combination of novel nanotechnology fabrication techniques, state-of-the-art theoretical modeling techniques that can interrogate events occurring from the atomistic/molecular scale through the mesoscale to the macroscale, and experimental diagnostic techniques that can capture the reactive dynamics at femtosecond timescales to those that evaluate overall combustion performance.

Organization

Scientists and engineers from three universities are included in the program: the Pennsylvania State University (PSU), the University of Illinois at Urbana-Champaign (UIUC), and the University of Southern California (USC). The team consists of chemists with expertise at the juncture of organic and inorganic chemistry who were among the original developers of molecular self-assembly (Allara, Nuzzo), mechanical engineers with expertise in the formulation of real, practical propellants (Kuo, Yetter), theoreticians who use teraflop supercomputers to understand the chemical reactions of fuels and oxidizers from the level of individual atoms (Vashishta) to the macroscale (Nakano, Kalia, Yang), a physical chemist who pioneered the use of ultrafast laser spectroscopy to study initiation of energetic materials (Dlott), and mechanical engineers with expertise in the experimental and theoretical characterization of real-world performance parameters of energetic materials (Kuo, Yetter, Yang).

The overall research program is divided into three major inter-related areas: (1) synthesis, self-assembly and supramolecular chemistry of NEEMs, (2) theoretical modeling of the physiochemical processes and mechanical behavior of NEEMs, and (3) experimental characterization of the reaction dynamics of NEEMs (Fig. 1).

The kickoff meeting for the MURI program was held on September 14, 2004 at the Pennsylvania State University. A summary of the meeting can be found at the MURI website (www.neem.psu.edu). The present report provides a brief description of scientific progress and accomplishments over the last year. In addition, interactions and technology transfer among the team members and with DoD and DoE scientists are described. Finally, publications, presentations, and demographics of the program are reported.

Scientific Progress and Accomplishments Synthesis and Assembly

During the present reporting period, research has centered on the development of both model systems and new synthetic processes—ones that provide materials for fundamental studies that will allow the development of deep new understandings of nanoscale energetic materials.

As part of the synthetic efforts, the Nuzzo group in collaboration with Girolami at UIUC

has reexamined previous literature reports that describe the successful isolation of discrete aluminum clusters. The reports of such (non-gas-phase) clusters in the literature are in fact quite limited, being largely restricted to the leading work of Schnockel. The clusters in this approach are all synthesized by reacting aluminum(I) halides with LiN(SiMe3)2 and, with one exception, are generally obtained in very low yields. The limiting feature here is likely related to the metastable nature of the complex Al(I)X intermediate (X=iodide) used to prepare them

Synthesis & Assembly

Theoretical Modeling &Simulation

Experimental Characterization &

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mac

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Figure 1. NEEM MURI program structure.

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(Al(I)halides spontaneously disproportionate to Al metal and AlX3 complexes). By varying the halide and temperature of reaction, Schnockel was able to prepare and isolate clusters ranging from 7 to 77 aluminum atoms in size with each cluster “capped” by the N(SiMe3)2-ligand. Many attempts were made to repeat these syntheses—to develop models to guide the microscopy studies (see below)—but all were unsuccessful. Therefore, this approach was abandoned.

The other aluminum clusters described in the literature are exclusively tetramers apart

from an Al12 icosahedral cluster capped by i-Bu groups reported by Uhl (Fig. 2). The synthetic procedure used to prepare this cluster is shown in Eq. 1. The cluster was obtained as the by-product in the synthesis of another species, hence the yield for this reaction is quite low (1.5 % based on aluminum; 8.5 g of chlorodiisobutylaluminum yields 62 mg of product). To try and improve upon the yield, reaction of 2 equivalents of potassium with dichloroisobutylaluminum was attempted (Eq. 2). This produced an uncharacterized orange oil, which resisted attempts at crystallization. Elemental analysis showed the oil contained a low concentration of aluminum (7 % vs. ca. 30 % for the Al12 cluster).

Al(i-Bu)2Cl + K → K2Al12 (i-Bu)12 (Eq. 1) Al(i-Bu)Cl2 + 2K → ? (Eq. 2)

Further reactions were carried out using the proportions of the literature synthesis of

K2Al12(i-Bu)12 and dark red crystals of this material were obtained. These organometallic clusters are exceptionally reactive and are currently being examined as target materials for shock experiments being carried out by Dlott. They also provide a metric against which to compare results from similar experiments carried out using SAMs on Al thin films as a target material. The Nuzzo group in collaboration with the Dlott group has begun to examine these SAMs (an example of the structure is shown in schematic form in Fig. 3) in a series of laser shock experiments. The monolayers were grown using literature procedures first reported by the Nuzzo group some years ago. These studies are expected to provide new understandings of the molecular dynamics of well defined models of the surface passivants of interest to this program and the manner in which they respond under high energy density conditions.

Studies by the Nuzzo group have also begun that are examining the synthesis of size selected Al clusters using metal hydride precursors as source reagents. The approach follows from the observation of Buhro et al. that the decomposition of AlH3 under suitable conditions leads to the formation of nanocrystalline aluminum. These unpassivated aluminum nanoparticles, however, are exceptionally prone to oxidation in air.

In an attempt to form aluminum nanoparticles with a protective “capping” ligand, dihydride aluminum species of the type RAlH2 have been targeted. The R group -N(SiMe3)2 has been selected because of the stability it provides against agglomeration in Schnockels cluster

Figure 3. Schematic representation of the structure of the SAM formed by Palmitic Acid on an Aluminum thin film surface.

Figure 2. Al12 icosahedron capped with i-Bu groups.

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compounds. [(Me3Si)2NAlH2]·Et2O was synthesized in acceptable yield by the route described in Scheme 1 (Fig. 4).

The complex [(Me3Si)2NAlH2]·Et2O can be converted to clusters via direct thermolysis in solution (e.g., toluene). The thermolytic condensation of this reagent produces a very dark solution, and on prolonged heating, a fine gray/black precipitate. The appearance of the materials is consistent with the properties of the nanoscale materials described by Buhro. There is precedence for this reaction in the work of Janik et al. who refluxed the related complex [(Me3Si)2NAlH2]·NMe3 in toluene with the same observations as above (Fig. 5).

Janik et al. did not analyze the structures of the solids produced. Nuzzo and colleagues have begun detailed investigations using STEM-based protocols to characterize these materials further. An anerrobic sample transfer protocol is being developed to allow these materials to be sampled without decomposition due to oxidation.

The Nuzzo group has also begun a collaboration with Petrov and Donchev to examine the structure of clusters that are prepared directly in the analytical region of a UHV STEM (HB501) instrument. This study will allow the development of atomic level structural information for the clusters of extremely small sizes (< 2 nm). The purpose of this effort is to establish the nature of bond relaxations in these materials. It has been noted in several reports that aluminum clusters are subject to very substantial reconstructions—that is to say that bond relaxations substantially contract the metal-metal bond distances in these systems. The magnitude of this effect appears unprecedented in character and, if confirmed, would require a substantial revision of current predictions of theory.

The foundation for this effort is found in the recent development of a highly novel plasma

cluster source. This device (Fig. 6) represents a massive advance in the technology of plasma assisted physical vapor deposition. The compact size and low gas-load and field characteristics at the sample are crucial for allowing in-situ cluster growth in the TEM while preserving near atomic resolution. This device has begun to be tested and Fig. 7 shows—in the form of a dark field TEM image—an example of the growth of a model nanoscale cluster sample. To simplify the testing, Ag

MKS Baratron

LN2 trap

Cluster generator

Connection to the deposition chamber

Differential turbo pumpMKS Baratron

LN2 trap

Cluster generator

Connection to the deposition chamber

Differential turbo pump

Figure 6. A novel compact UHV source for the in-situ growth of clusters of pure metals and alloys.

LiAlH4 + AlCl3 AlH3 . Et2OEt2O HN(SiMe3)2

[(Me3Si)2NAlH2].Et2O

RefluxToluene

-H2

Aluminum nanoparticles capped by the bulky(Me3Si)2N ligand.

Figure 4. Scheme 1: One pot synthesis of an aluminum dihyride and subsequent “decomposition”.

2[(Me3Si)2NAlH2].NMe3

reflux

tolueneAlH3 . NMe3 + 1/n{HAl[N(SiMe3)2]2}n

Al + 3/2H2 + NMe3Figure 5. Scheme 1: Reflux of [(Me3Si)2NAlH2].NMe3.

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was used in this case. Modifications in the design are being made to enable cluster deposition using an Al target.

The Allara group (which moved its laboratories from the MRI Building to the new Chemistry Building on the Penn State campus during the past year) has developed new experimental methodologies for Al atom deposition on self-assembled monolayers with in-situ vibrational spectroscopy diagnostics. The group is in the process of making self assembled monolayers (SAMs) with 1, 2 and 3 nitro groups on model TNT type molecules. Methods to control the sample temperature and maintain it near room temperature were studied. To achieve sample temperature control, different atom vapor sources are required. In particular, 2-3 Knudsen sources for highly controlled deposition of Al atoms are needed. Additional funding for these Knudsen sources is currently being investigated.

Companion experiments using in-situ x-ray

photoemission and atomic force microscopy (AFM) have also been started. (Interestingly, with the AFM, a pulsed current through the Al-SAM composite may be used to trigger rapid reaction). The next series of experiments will involve looking at the chemical pathways of Al atoms on TNT models as a function of sample temperature to determine whether there is a reaction threshold for Al oxidation by the nitro groups. Some of the structures are expected to be a composite Al/Al2O3(~1 nm)/NitroSAM/Al assembly from which Al type sandwiches may be obtained. These samples will be provided to the Dlott group for reaction dynamics analysis and model configurations will be provided to the USC group for reactive simulation studies.

In addition to the synthesis and assembly of nanoscale energetic materials based on aluminum, other elements such as boron (clusters) are also of interest [1]. In many heterogeneous energetic materials, sensitivity properties are determined mainly by the energetic crystalline oxidizer, since it makes up a large percentage of the material. A reduction in sensitivity of the oxidizer ingredients should result in the formation of less sensitive materials [2,3]. Thus, the synthesis of nanoscale energetic oxidizers is also important and the Kuo group is studying supercritical fluid methods to produce nano RDX while the Yang group is numerically modeling the detailed fluid mechanics during the rapid expansion process, including nucleation and particle growth to enable optimization of the particle fabrication process.

The supercritical fluid (SCF) method being investigated for application to energetic materials is Rapid Expansion of Supercritical Solutions (RESS). In RESS, the material of interest is dissolved in a SCF at high pressures and increased temperatures. A co-solvent may also be used to increase the solubility of the material. The use of a co-solvent results in additional difficulties in handling and recovery. The solution is then expanded rapidly into a low-pressure chamber causing rapid nucleation of fine particles. Current research on nitramines shows very promising results, with mean particle sizes of ~130 nm and narrow size distribution. Parameters that control particle size in distribution can include the type of solvent and co-solvent, the concentration of solute in the solvent, pressure, temperature, and nozzle geometry. These parameters will be investigated during the period of this study for producing nano-sized RDX

Figure 7. Dark-field TEM image and particle-size distribution of Ag nanoclusters deposited using an in-situ UHV growth source.

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oxidizer crystals. The first application of using supercritical fluid to nucleate particles was performed in 1986 by Smith, Matson, and Peterson [4]. The first set of experiments was conducted with carbon dioxide as a solvent and metal oxides and polymers as the solutes. In 1989, Coffey and Krukonis developed this process for the pharmaceutical industry.

The RESS system follows the general process of solvent saturation by the solute during

the solution expansion process. Normally the solvent is carbon dioxide, but other materials have been explored as well. The solute can be any type of material as long as it is soluble in the solvent. In general, the solvent and co-solvent are brought to the solvent’s critical point or beyond in a saturation vessel. The solute is placed in the saturation vessel and becomes absorbed in the supercritical solvent and co-solvent mixture. The solution is then expanded through a nozzle orifice to atmospheric temperature and pressure. This expansion creates micro- or nano-sized particles, which can then be collected [5]. Carbon dioxide is a common solvent for the RESS process due to its relatively low critical temperature and pressure, 31.2 °C and 7.38MPa (87.9 °F and 1070.6 psia), respectively [6]. Other solvents considered were nitrous oxide, water, neon, and different types of Freon. However, it was determined that carbon dioxide is the best solvent for RESS due to it’s safe handling characteristics and its lower critical pressure and temperature. For this study, the solute is cyclotrimethylenetrinitramine or RDX [7]. RDX has a melting point of 204.1 °C (399.4 °F) at 14.7 psi [7]. This is important to know because decomposition of RDX by way of melting during RESS should be avoided at all costs. RDX can react very violently at temperatures slightly beyond its melting point. Solubility of RDX in carbon dioxide has been studied and reported up to 50.3 MPa (7,300 psi). It has been reported by Morris [8] that solubility of RDX in CO2 greatly increases from 3,000 to 5,800 psi; beyond that, the increase of solubility of RDX with pressure is less pronounced. As a matter of fact, without further investigation at higher pressures, the solubility of RDX in CO2 is not fully known.

While solubility has been studied experimentally at pressures lower than 50MPa, much is

still not known experimentally about the vapor pressure of RDX from its solution in CO2. Also, modeling has been difficult to perform due to the lack of knowledge in this area. The most recent work has been conducted by Damavarpu, Boddu, and Toghiani [9]. By using the Peng-Robinson equations, the fugacity of RDX in CO2 can be approximated [10]. In their modeling work, they claim that the solubility cannot be modeled within an accuracy of an order of magnitude due to the insufficient vapor pressure information.

The current research will lead to better understanding of the RDX vapor pressure

variations with temperature and its concentration in CO2. Also, the experimental set up of the present study at ultra-high pressures (up to 30,000 psi) will provide opportunity for examining the advantages for operating the RESS system at elevated pressures in the formation of nano-sized particles. Knowing what phase the materials are in when operating the experiment is critical to nano-particle formation. Carbon dioxide must be supercritical to be considered a credible solvent for RDX. The phase of RDX must be known to keep it from decomposition, liquefaction, or ignition. Also knowing what phase carbon dioxide and the co-solvent are in after the expansion is necessary for designing the particle filtration system. A co-solvent can be added to improve the solubility of RDX in carbon dioxide. The two co-solvents being considered are acetonitrile and dimethyl sulfoxide (DMSO). Adding 6.1 mol % of acetonitrile to carbon dioxide increases the solubility by 16 times while adding 5.6 mol % of DMSO to carbon dioxide increases the solubility by 120 times [11].

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Figure 8 is a superimposed phase diagram for carbon dioxide, RDX, and the two co-solvents DMSO and acetonitrile. The supercritical range for carbon dioxide is labeled in bold and outlined with bold blue lines as the region that should be targeted for experimental operation in the saturation vessel. The dashed thick arrow indicates the change of state of the solvent and the co-solvent mixture through the compression process, which will be preformed through two separate compressors shown in Fig. 9. The thick curved solid arrow represents the state change from heating of the solvent mixture to the expansion of the RDX dissolved mixture through the nozzle located in the expansion vessel. From Fig. 8, it can be determined that there is a suitable supercritical region which is ideal for the RDX particles to be dissolved in the solvent mixture. By expanding the mixture through a specially designed nozzle under well-controlled temperature conditions, one can expand the mixture to a much lower pressure level (e.g., 1 atm) at which both the solvent (CO2) and co-solvent (acetonitrile) are in the gas phase while nano-sized RDX particles can be formed. If the co-solvent is DMSO, it will not vaporize to the gas phase during the expansion to 1 atm. It is worthwhile to note that the decomposition region of RDX is shown with bold green horizontal line on Fig. 8. For safety purposes, it is beneficial to keep the maximum operating temperature far below the melting temperature of RDX. In order to avoid ignition, the existing RESS work by Stepanov et al. [5] have utilized T = 80 °C (176 °F) as the maximum operating temperature. This vertical line is also shown in Fig. 8. The designed ultra-high pressure RESS system is shown in Fig. 9. This facility will have the unique capability for operating at a broad range of pressure and temperature conditions. In terms of operation, the RDX or other energetic crystalline material is first loaded into the saturation chamber. Then the liquid CO2 is compressed to an elevated pressure beyond critical pressure before mixing with the compressed co-solvent. The liquid-phase co-solvent is supplied through a separate pump system prior to its mixing with liquid CO2. After combining the two solvent materials, the mixture will be heated to a desirable temperature before entering into the saturation vessel. They are heated further in the saturation vessel to the selected operating

Figure 9. Process flow diagram of the designed RESS system.

CompressionExpansion

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Figure 8. Phase Diagram of Carbon Dioxide, RDX, Dimethyl Sulfioxide, and Acetonitrile.

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temperature, while the RDX particles are dissolved in the mixture of solvents. The chamber pressure is also controlled in the saturation vessel. The pressure control is achieved by a computer-operated system for actuating a ball valve to bleed any excess amount of gas into a surge tank. Finally, the supercritical fluid (with RDX dissolved in the solvents) is fed into the expansion vessel through a ball valve controlled line. In the expansion vessel, this supercritical fluid expands through a specially designed nozzle. This nozzle has several interchangeable units; each unit corresponds to a different nozzle throat diameter ranging from 1-100 microns. The rapid expansion of this supercritical fluid mixture through the nozzle will cause the formation of nano-sized particles, in the mean time the co-solvent will go through a phase change from the liquid phase to the gas phase while CO2 will change from the supercritical condition to the gas phase (Fig. 8). Shadowgraph and Schlieren photography techniques are planned to observe the mixture expansion process.

In order to achieve a high chamber pressure on the order of 206.8 MPa (30,000 psi), a

means of compressing the CO2 and co-solvent is required. A Hydro-Pac Li’l Critter high-pressure compressor and HiP pneumatically activated hydraulic pumping system have been ordered for the CO2 and co-solvent, respectively. It is critical to make sure that the CO2 entering the Hydro-Pac compressor is in the liquid phase. In order to achieve this, a NESLAB cooling bath, which can cool the CO2 to -20 °C (-4°F), is being utilized. To determine if the CO2 is a liquid before the compressor, a pressure transducer and a K-type thermocouple probe will be used. A flow meter attached to the Hydro-Pac Compressor, has been incorporated into the system to determine the flow rate of the CO2. Also, the co-solvent pump has a flow meter in line, made by Omega (Fig. 9). The mixture of the two fluids entering the saturation vessel will be preheated using a temperature controlled heating tape that wraps around the tubing.

The saturation vessel is a HiP cloverleaf pressure vessel, rated to 206.8 MPa (30,000 psi).

A jacket heater, also made by HiP, is used to heat the vessel and the enclosed CO2 up to 80 °C (176 °F) using an Omega temperature controller. A safety head is being installed to ensure no over pressurization of the system can occur. There is also a computer-controlled pneumatically actuated solenoid valve (BV2) that will be used to control the pressure in the system. This valve will be activated to open when the pressure in the chamber becomes higher than the desired upper threshold, and similarly activate to close when the chamber pressure dropped below the lower threshold for a given experiment. For example, if a pressure of 103.4 MPa (15,000 psi) is needed for a given test, the thresholds will be set to +/- 0.69 MPa (100 psi) from the target chamber pressure. When the pressure reaches 104.1 MPa (15,100 psi), the solenoid valve will open, releasing CO2 into the surge tank. With this valve in the open position, the pressure in the saturation chamber will drop until it reaches 102.7 MPa (14,900 psi). At this point, the solenoid valve (BV2) will close, allowing the chamber to build up in pressure again. The gas that exhausts from the surge tank to the atmosphere will be filtered, picking up any RDX particles that are entrained in the flow, and releasing the rest of the CO2 into the atmosphere.

Another major component of the system is the

expansion vessel, where the components of the mixture will be separated, and RDX nano-particles will be recovered. Two major design issues involved with the expansion vessel are the nozzle and particle collector. The nozzle needs to be designed in such a way that nano-sized particles will be produced, and the expansion itself would take place in a portion of the vessel as to be accessible for flow visualization techniques. This requirement dictated that the nozzle

Expansion Chamber

HiP fitting inlet

Heater

Nozzle

Expansion Chamber

HiP fitting inlet

Heater

Nozzle

Figure 10. Cross-sectional view of the expansion vessel and nozzle assembly.

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diameter be on the order of a tenth of a µm. While particle size has not been conclusively proven as a function of nozzle size, RDX nano-particles produced up to this point have used nozzles with a diameters ranging from 100-125µm [5]. Figure 10 shows a cross-sectional view of the expansion vessel, and the nozzle assembly in greater detail. The collection of the RDX particles will take place mostly in the expansion vessel. There are ports in the annular space region for venting the CO2 gas and co-solvent vapor to the exhaust line. A particle collector is being designed to allow particles to be accumulated near the bottom of the collector, while the CO2 gas and co-solvent vapor can still leave its lateral surface. The design process is being completed for the ultra-high pressure RESS system. All RESS system components discussed have been ordered and the system will be assembled and constructed as the parts arrive at the High Pressure Combustion Lab of PSU. The system is designed for pressures higher than have ever been tested for RESS. Therefore, broad range experiments will be conducted at a minimum of 34.5 MPa (5,000 psi) and a maximum pressure up to 172.4 MPa (25,000 psi). The dependency of solubility and nano-sized particle formation on pressure and temperature in the saturation and expansion vessels will be investigated, respectively. Also dependency of nozzle size on nano-sized particle formation in the expansion vessel will be studied as testing proceeds. The advantages of the addition of a solvent and co-solvent filtration will be another aspect that will be further explored. When nano-particles are created their size will be examined under a SEM microscope and other laser-based characterization instruments. Theoretical Modeling and Simulation

A goal of this portion of the MURI project is to study nano-engineered energetic materials using large (billion atoms) multiscale simulations that couple quantum-mechanical (QM) calculations to molecular dynamics (MD) calculations. The USC group (Vashishta, Kalia, and Nakano) is calculating the stability, structure and energetics of metallic nanoparticles with a special focus on the relationships between particle size, shape and excess surface free energy. Multiscale modeling of the thermo-mechanical properties and microscopic mechanisms of detonation and deflagration processes of NEEMs is also being studied. These calculations couple directly to the synthesis, fabrication, and materials characterization studies of Allara and Nuzzo as well as to the dynamical characterization studies of Dlott and Yetter. Theoretical studies by Yang will couple to the studies of the USC group at the meso/macro scale. As mentioned in the previous section, Yang is also modeling the supercritical fluid processing techniques understudy by Kuo and colleagues.

To seamlessly couple QM and MD simulations, the USC group has found it necessary to introduce an intermediate layer. The first principles-based reactive force field (ReaxFF) MD simulation approach, developed at Goddard’s group at Caltech, describes chemical bond breakage and formation through reactive bond orders and charge transfer through the charge-equilibration (QEq) scheme. Goddard and co-workers have demonstrated that ReaxFF is capable of reproducing the energy surfaces, charge distributions, structures, and barriers from accurate QM calculations for reactive systems. This method is several orders of magnitude faster than QM methods.

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To perform multimillion atom simulations of chemical reactions in NEEMs, the USC group has developed a scalable parallel algorithm for ReaxFF MD simulations using spatial decomposition. The bond order, Bij, is an attribute of an atomic pair, (i, j), and changes dynamically depending on the local environment. In ReaxFF, the interatomic potential energies between atomic pairs, triplets, and quartets depend on the bond orders of all constituent atomic pairs. Force calculations in ReaxFF MD thus include up to atomic 4-tuples explicitly, and require information on 6-tuples implicitly through the bond orders. To efficiently handle the resulting multiple interaction ranges, the parallel reactive force field (P-ReaxFF) algorithm employs a multilayer cellular decomposition (MCD) scheme for caching atomic n-tuple (n = 2-6) information.

Scalability test of the P-ReaxFF algorithm has been performed on an 800-processor Power4 system at DoD’s Arctic Region Supercomputing Center (ARSC), where each compute node is an 8-way 1.5GHz Power4 system. Figure 11 shows the parallel efficiency (circles) and communication overhead (squares) of the P-ReaxFF MD algorithm with scaled workloads—86,016P-atom RDX (1,3,5-trinitro-1,3,5-triazine) systems on P processors (P = 1, ..., 512). The computation time includes 3 conjugate gradient iterations to solve the QEq problem for determining atomic charges at each MD time step. The execution time increases only slightly as a function of P, and the parallel efficiency is 0.987 for a 149 million-atom system on 512 processors.

In order to validate ReaxFF MD simulations of Al nanoparticles embedded in an energetic crystal, the USC group has performed an MD simulation to study the decomposition of an RDX molecule on Al (111) surface, in which interatomic forces are computed quantum-mechanically using the Hellmann-Feynman theorem in the framework of DFT (Fig. 12). The DFT calculation is based on the norm-conserving pseudopotentials by Troullier and Martins and the generalized gradient correction by Perdew, Burke and Ernzerhof, and it is implemented on a real-space grid and accelerated with the multigrid method. The simulation shows the decomposition of NO2 fragments in RDX and subsequent formation of Al-O bonds on the Al surface. This suggests that, to stop the premature reaction of RDX with pure Al surface, a nanoscale buffer layer may be necessary on the Al surface.

Figure 13 shows the charge distribution of each oxygen atom as a function of time. Since O2, O3 and O6 atoms are bonded with aluminum atoms, these oxygen atoms attract more electrons from the surrounding aluminum atoms. As a result, the absolute value of charges on oxygen atoms suddenly increases after the onset of O-Al bond formations, i.e., 100 fs for O2, 400 fs for O3, and 360 fs for O6. On

Figure 11: Parallel efficiency (circles) andcommunication overhead (squares) as a function ofthe number of processors for the P-ReaxFF MDalgorithm with scaled workloads—86,016 P atomRDX systems on P processors (P = 1, ..., 512) of theIceberg Power4 system.

Figure 12. DFT-based MD simulation of the decompositionof an RDX molecule on an Al (111) surface.

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the other hand, aluminum atoms are positively charged because of the oxidization. Figure 13 also shows the sum of charges for all 64 aluminum atoms. The increase of Al charges reflects electron transfer from aluminum atoms to oxygen atoms. These electron-transfer processes cause N-O bonds breakage and Al-O bonds formation.

An interesting study reported on by the USC group was the oxidation of aluminum single crystals using molecular dynamics simulations with dynamic charge transfer between atoms. The simulations were performed on three aluminum low-index surfaces ((100), (110), and (111)) at room temperature. The results showed that the oxide film growth kinetics was independent of the crystallographic orientation under the conditions studied. Beyond a transition regime (100 ps), the growth kinetics followed a direct logarithmic law resulting in a limiting thickness of ~ 3 nm. The obtained amorphous structure of the oxide film had initially Al excess (compared to the composition of Al2O3) and evolves, during the oxidation process, to an Al percentage of 45%. The presence of an important mobile porosity was also observed in the oxide. Analysis of atomistic processes indicated that the growth proceeds by oxygen atom migration and, to a lesser extent, by aluminum atom migration. In both cases, a layer-by-layer growth mode was observed. The movement and creation/annihilation of these pores was an important factor for the development of the oxide film. The presence of mobile pores may also be important for higher temperature oxidation, where the amorphous oxide transitions through various polymorphs of aluminum oxide. As shown by Dlott in the next section, the thickness of the oxide layer also has important implications on the use of nano aluminum in explosives and propellants.

The Yang group in collaboration with Yetter is developing meso and macro scale

reactive models for the combustion of nano-aluminum. During this period of the project, an extensive literature survey on aluminum particle combustion was completed. Prior to performing a full multiscale simulation of the generation, transport, and combustion of nanosized energetic materials in flow environments, understanding of the combustion of single particles in quiescent medium is required. Moreover, the theories developed for micron-sized particles cannot be directly applied to the ignition and combustion behavior of nano-sized particles. With this point of view, a comprehensive review of work done on aluminum particles at the micro scale and nano scale has been performed [12-33]. An attempt has been made to develop a unified theory for aluminum particle combustion, which is applicable at all scales. The results of the USC group on nanoparticle oxidation are being used towards the development of this particle combustion model. This interactiong will provide a unique opportunity to couple the USC modeling at the atomistic level to the macroscale modeling of Yang and co-workers.

During the past year, Yang and his group have also developed a unified numerical

simulation scheme to model the nucleation process during the rapid expansion of supercritical fluids. Process optimization will be performed for the production of nano RDX crystals.

Figure 13. Time variation of charge distribution on eachoxygen atom and sum of charges of all 64 aluminum atoms.As a result of O2-Al, O3-Al and O6-Al bonds formation,absolute values of charges for O2, O3 and O6 are increasedby electron transfer from aluminum atoms to these oxygenatoms. On the other hand, aluminum atoms are positivelycharged because of the oxidization.

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To characterize fluid injection and mixing process, a unified model that accommodates

full conservation laws and real-fluid thermodynamics and transport phenomena over the entire thermodynamic regime of concerned has been established for single phase. Several computational and modeling challenges must be overcome in order to perform numerical simulation on high-pressure fluid injection system. First, thermodynamic non-idealities and transport anomalies occur as the fluid transits through the transcritical regime. Thus treating these phenomena in a manner consistent with the intrinsic characteristics of a numerical algorithm presents a main obstacle. Second, the rapid variation of fluid state and the wide disparities in the characteristic time and length scales impose the well-known stiffness problem. In order to overcome all these difficulties, a unified treatment of general fluid thermodynamics is developed. Thermodynamic properties including enthalpy, internal energy and heat capacity are directly calculated by means of fundamental thermodynamic theories and a modified Soave-Redlich-Kwong (SRK) equation of state, which is reasonably accurate over the high-pressure and low temperature regime in the present study and easy of implementation. A highly accurate 3D temperature-internal energy curve fit is employed to avoid computationally intensive iterations over the entire fluid state of concern. Transport properties including viscosity and thermal conductivity are estimated by means of the corresponding state principles along with the use of the 32-term Benedict-Webb-Rubin (BWR) equation of state. Turbulence closure is achieved using a compressible version of Smagorinsky SGS model. The theoretical formulation outlined above is solved by means of a density-based, finite volume methodology. The spatial discretization employs a fourth-order, central-difference scheme in generalized coordinates. A fourth-order scalar dissipation with a total-variation-diminishing switch developed by Swanson and Turkel is implemented to ensure computational stability and to prevent numerical oscillations in regions with steep gradients. Temporal discretization is obtained using a four-step fourth-order Runge-Kutta scheme. A multiblock domain decomposition technique, along with static load balance, is employed to facilitate the implementation of parallel computation with message passing interfaces at the domain boundaries. The SUPERTRAPP package will be used to generate a table containing the dew-point pressure, saturated liquid/vapor density, saturated liquid/vapor composition. Flow density and temperature will be achieved by solving Navier-Stokes code for the binary mixture system. Pressure will be achieved by SRK-EOS at determined temperature and density. When the local temperature is less than the mixture critical temperature and the local density is between the saturation-state values, the homogeneous equilibrium model is activated and will replace SRK-EOS to get the local pressure instead.

The model was initially employed to study the mixing of coaxial nitrogen jets. Effect of

transverse acoustic on coaxial jet evolution is investigated. The model simulates the experiments by Davis et al. [34]. The injector used in their study produces a cryogenic jet that is injected through a sharp-edged stainless steel inner tube having a length of 50 mm, an inner diameter 0.508 mm and an outer diameter of and 1.59 mm. The annular region was 0.415 mm between inner and outer tubes (Fig. 14). A cuboid computational domain is generated (Fig. 15). The entire grid system besides the inlet part has 141×81×301 (3.44 million) points along the axial, radial and azimuthal direction, respectively. In order to avoid the singular point in the center region of computation domain, and on the mean time increase the time step, central square grids are introduced in the center part. The grid resolution is chosen based on the inlet Reynolds number such that the largest grid size falls in the inertial sub-

LN2 R1 = 0.254mm R2 = 0.795mm

GN2

R3 = 1.21mm

Figure 14. Schematic of the coaxial injector employed for the high-pressure LN2/GN2 mixing simulation.

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range of the turbulent energy spectrum. The analysis is conducted on an in-house distributed-memory parallel computer. The computation domain is divided into 72 blocks, and a total number of 57 processes are used.

Contours of streamwise velocity are shown in Fig. 16. There is a strong back-flow region exists which can be seen through blue contours of u(x,y), corresponding to a region of u less than zero. Just as Silvo et al. [35] have mentioned in there work, similar back-flow region were observed in experimental studies of coaxial jets with high velocity ratios and are always present in co-annular jet, where no inner jet exists and therefore can be seen as a coaxial jet with velocity ratio equals to infinity. From the snapshot of the instantaneous temperature and vorticity field, three shear layers were observed obviously. The evolution and interaction of large structures strongly influence the mixing and entrainment of a mixing layer. Large flow structure was found to be dominated by the gaseous nitrogen in annular region. The vortex shedding process can be clearly observed in temperature field. Due to hydrodynamic instability, small ripples appear in the jet surface near the injector exits. As those instability waves move downstream, they grow up and roll into a succession of ring vortices. The vortex may interact with the wave behind it and merge together, a process called vortex paring. As a result, the length scales of vortices increase.

Future work will focus on the homogeneous nucleation model. This implementation includes two steps: (1) extension of the model to a binary mixing system (for mixtures, the equation of state, transport properties and related thermodynamic properties will be modified by operating with mixing rules), and (2) establishment and inclusion of a homogeneous nucleation model.

Figure 15. Schematic of grid system,total grid points, 141×81×301 = 3.44million. (The presented grid has fewerpoints than these used in thecalculations, but the distributions of gridpoints are similar).

Figure 16. Contours of velocity in x and y direction, temperature and vorticity magnitude in plane z=0. (p∞ = 4.94 MPa, T∞ = 233 K, ULN2 = 3.6 m/s, UGN2 = 22.5 m/s, TLN2 = 132 K, TGN2 = 191 K, no acoustic excitation).

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An intricate feature in the simulation of transcritical fluid injection is that processes will transverse the dew-point line for a binary mixture. The single-phase fluid may be in a quasi-steady state, where the EOS can still be applied, or in an unstable state, where the homogeneous equilibrium model will be introduced to handle two-phase flow. Currently, the homogeneous equilibrium model discussed in the work of Edwards et al. [36] will be used because its simplicity to implement. Experimental Characterization and Diagnostics

Dlott and his group are studying fundamental mechanisms of the reactive behavior of energetic materials containing nanoparticles using new methods specifically developed to probe events on short time scales and at small length scales. Materials engineering and science is used to create nanoenergetic materials with well-understood structural elements in order to deduce the relationships between these structural elements and performance. In particular, dynamic performance characterization of small quantities of NEEMs is conducted using flash laser heating or laser-generated shock waves (to mimic combustion or shock wave initiated detonation) combined with ultra-fast molecular spectroscopy. Because virtually every facet of nano-energetic performance involves heterogeneous interfacial effects (e.g., between metal cores and SAMs or oxidizers), ultra high-speed surface-selective techniques, such as femtosecond vibrational sum-frequency generation (SFG), are applied. SFG measurements in real time (10-15 - 10-6 s) can detect the disappearance of SAM bonds and the highly exothermic appearance of oxidized metal.

Recent progress has been made in a number of areas. Time-resolved CARS was used to study reaction propagation over nanometer length scales using size-selected nanoparticles embedded in an oxidizing matrix. A mathematical model was developed for this short-ranged reaction propagation process. An experimental system that acquires emission spectra with spectral and 30 ps time resolution has been developed and initial experiments are now underway. An experimental system is also being developed that uses femtosecond IR pulses and a new IR array detector to study chemical reactions in real time.

In addition, an experimental system has

been developed that combines picosecond laser flash-heating pulses with a 1 ns high-speed microscope to look at nanoenergetic material chemistry with ultrafast photography (Fig. 17). Physical analysis of the blast wave emanating from a flash-heated region is used to quantitatively determine the energy released in chemical reactions (Fig. 18). A number of Al/fluorocarbon composite systems have been manufactured and preliminary experiments are underway. With other UIUC collaborators (Nuzzo and Girolami), who have synthesized a variety of Al cluster molecules, the group is working on preparing samples with monodisperse Al clusters in the size range of 10-70 atoms. Dlott and Vashishta have been interacting and discussing future simulations of nanoparticle combustion that could be coupled to his experiments.

laser pulse(invisible)

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debris Figure 18. Schematic of the microexplosion process.

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Figure 17. Experimental configuration for investigation of microexplosions of nanoenergetic materials.

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As an illustration of a recent set of experiments on comparing the chemistries of two samples of 10 wgt % 30 nm Al in either nitrocellulose or Teflon A, a 100 ps duration near-infrared flash heating pulse was focused to 100 µm diameter on the surface of each sample. The samples are about 3 microns thick on a glass substrate (Fig. 18). The results of time resolved microscopy for the tiny explosions of the two samples are shown in Figs. 19 and 20. There is a reflection from the glass substrate, and therefore the images of the reflected surface on the left hand side should be ignored. By measuring the kinetic energy of the fragments and shock wave, the energy of explosion is determined. Note that 100 µm travel in 100 ns corresponds to 1 km/s.

A number of key findings have been obtained from the Dlott group research during this reporting period. In particular, a nanoparticle reacting with its surroundings was observed to exhibit two stages: the reaction of the nanoparticle with adjacent oxidizer and the subsequent propagation of reactions between adjacent particles. Furthermore, the propagation of the chemical reactions was measured over the length scale of a few nanoparticle diameters.

A particularly interesting and important finding obtained from the Dlott group concerns

the thickness of the oxide shell on nano aluminum and its role in the dynamics of the reaction. In this research, the dynamical effects of the aluminum nanopowder oxide layer were investigated in nanoenegetic materials consisting of nitrocellulose oxidizer containing embedded ~60nm diameter Al having thinner (2.5nm) or thicker (6nm) oxide layers. Following flash heating, a hot spot was formed near each Al particle. The mean distance of reaction propagation (drxn) from the hot spot through the nitrocellulose was determined with ~100 nm resolution. With 100 ps pulses a shock propagation mechanism was dominant, and with 10-25 ns pulses, a thermal explosion mechanism was dominant. When higher energy picosecond pulses were used, drxn was observed to be significantly increased with thicker oxide layers, but using nanosecond pulses drxn was slightly decreased with thicker oxide layers. This oxide layer enhancement of drxn with picosecond pulses is attributed to the thicker oxide layer confining the hot Al for several tens of picoseconds, resulting in a stronger shock wave (larger pressure build-up). This work supports the view of the oxide layer as deadweight for slower heating rate processes such as combustion, but it suggests a thicker oxide layer may be of some benefit for extremely high heating rate processes involved in detonation or high-speed deflagration of nanoenergetic materials.

50 ns

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660 µmFigure 19. Microexplosion of the nanoenegetic material consisting of 10% 30.2 nm Al in nitrocellulose.

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Figure 20. Microexplosion of the nanoenergetic material consisting of 10% 30.2 nm Al in Teflon.

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Finally, the Dlott group has shown how the optical absorption spectrum of Al and B nanoparticles depends on particle size and the surrounding dielectric oxidizer. In particular, energetic nano-particles were found more strongly absorbing than bulk Al or bulk B. Owing to the large absorption cross section of nanoparticles in the visible and near-IR, in laser ignition and laser initiation experiments only modest powers are needed to produce the high temperatures needed for ignition. However, the cross section data also indicate that caution should be used when comparing the performance of different nanoparticles in laser heating experiments.

The Yetter group in collaboration with Son (on sabbatical leave from LANL) has been developing and conducting research in three areas: flame propagation across the surface and through packed layers of nano aluminum particles, the reaction propagation and analysis of metastable intermolecular composites (MICs) in narrow channels, and fabrication and dynamic analysis of nano-silicon based composite energetic materials. Microscale diagnostics to analyze the combustion of the nano energetic materials are being developed. These experiments will also make use of the nano energetic materials developed by Allara, Nuzzo, and Kuo. The present experiments and diagnostics are designed to be complementary to those of Dlott.

An understanding of the reactive and transport

mechanisms in energetic systems with nano-particulate ingredients is important to deflagration and detonation phenomena of energetic materials. The group has been investigating reaction front propagation during the combustion of heterogeneous condensed phase systems based on nano-aluminum in various gaseous oxidizers (Fig. 21). In air, the complex burning process of nano-aluminum exhibits a rich but controllable pattern. The combustion front in a quasi-two-dimensional geometry exhibits directional fingering instability with two length scales that are determined differently – the finger width and the finger spacing (Fig. 22). The non-dimensional control parameter is the Péclet number (Pe), which measures the relative importance of molecular advection and diffusion. Such phenomena have been observed in the flame propagation through other condensed phase media [37-39].

The results of the above nanoparticle studies will be compared and used to assist the

understanding of the reaction propagation of MIC systems in vacuum, air and under pressure in various environments. In the present research, a series of experimental configurations are being produced to study the combustion dynamics of MICs including a high pressure optical closed combustion chamber, an open-ended acrylic tube experiment (ID = 3.175 mm), and micron-sized (submillimeter) channels to measure propagation speeds and transient pressures and temperatures. The initial design of the first two of these systems is similar to those of Son and colleagues at LANL [40-42]. The latter experiments are being developed for microscopic diagnostics, which will initially include high-speed photography and emission spectroscopy. The group has also developed a micro-PIV system this past year, which may be used for digital speckle photography, and is currently setting up a 5m spectrometer to an inverted microscope with an intensified CCD camera for spectroscopy measurements.

Figure 22. Photograph of fingering instability for nano aluminum combustion reacting in stagnant air.

particle bed

oxidizer flow

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Figure 21. Schematic representation of the experimental setup for nano aluminum propagation studies.

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A limited amount of research has been performed on porous silicon as a fuel in composite energetic systems [43-45]. Adiabatic flame temperatures of silicon reacting with stoichiometric oxygen are approximately 3100 K at 1 atm. Reaction of silicon with AP yields a flame temperature of 2900 K at 1 atm. The group is looking at binary systems based on porous silicon layers with their pores filled with solid oxidizers. The porous layers are produced by standard electrochemical etching processes. The internal surface areas of porous silicon can be as large as 103 m2/cm3. The pore size and porosity are controllable during the fabrication process to achieve the desired Si/oxidizer ratio. The surface is stabilized against natural oxidation by annealing the porous silicon after etching. Prior to fabrication of the wafer composites, silicon powder has been acquired and tests are currently underway investigating different oxidizers and propagation rates through the particulate silicon oxidizer mixtures. These systems may be useful by themselves, e.g., as initiators, and will also be important to the model systems underdevelopment by Nuzzo using lithography techniques. In the area of experimental characterization and diagnostics, the Kuo group has developed techniques to integrate nano-energetic materials into solid fuels and composite propellant formulations. Provided sufficient quantities of the nano-material are obtained, experiments are also planned on evaluating the combustion and ignition characteristics of the bulk material.

In order to characterize the combustion behavior of certain nitramine propellants containing nano-sized RDX particles, it is beneficial to consolidate the propellant mixed into a solid propellant strand. The propellant mix can be compressed to form a cylindrical strand in an upgraded propellant presser (Fig. 23). This propellant presser has designed specially to consolidate propellant ingredients to create high-density propellant samples. Since pressing propellants is could be hazardous, the presser is located in a reinforced concrete test cell and is fully controlled by a computer that is outside the cell for safety operation. The computer can discern actuator displacement steps down to 0.001 inches.

Once the propellant sample is made, strand-

burning experiments can be conducted. One of the measurement techniques for the thermal profile in the solid propellant and its flame zone is to employ an embedded fine-wire thermocouple (with bead size on the order of a few micrometers) in the solid strand. In order to avoid any catalytic effect caused by thermocouple bead material, the fine-wire thermocouple can be coated with a very thin layer (from 5 to 10 micrometers) of silicon nitride (Si3N4), which is a chemical inert material. This is a challenging work, since it requires the use of high-temperature (over 1472 °F) chemical vapor deposition process under a relatively low-pressure condition to coat the platinum fine-wire thermocouples. The reagents for the coating are silicon-tetrachloride (SiCl4) and ammonia (NH3). This setup was constructed with custom-made components and with a special electric circuit to control the temperature to

Press Action

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Figure 23. Propellant presser with computer controlled precision loading and displacement process.

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Figure 24. Hot chemical vapor deposition system for ceramic coating of fine-wire thermocouples.

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ensure that the required temperature of the coating process inside of the reactor has been reached. Figure 24 is a picture of the thermocouple coating system for fine-wire thermocouples coated with silicon nitride (Si3N4). This technology has proven to be better than conventional coating technologies. Propellant formulations using nano-sized RDX will be investigated through combustion characterization of potentially interesting propellant strands. Thermal profiles will be recorded through the use of ceramic-coated fine-wired thermocouples embedded in propellant strands.

Technology Transfer and Interactions

As discussed throughout the report, the team has been developing strong interactions

among themselves. In addition, all team members have had close working relationships with various DoD and DoE laboratories. Several collaborative programs with scientists and engineers at ARL, ARDEC, NAVSEA-IH, and LANL have been or are in the process of being initiated. These collaborations are expected to grow during the second year of the program.

At Penn State, Dr. Steven F. Son has taken a year sabbatical from Los Alamos National

Laboratory (LANL) to conduct collaborative research with Yetter, Kuo, Yang, and Allara on the MURI program. This collaboration will be continued through the duration of the program via graduate students spending summers at LANL. In addition, Kuo and Yetter have an existing program with Dr. Lee Harris at ARDEC on the development of advanced layered gun propellants. Nano energetic materials fabricated as part of this MURI will be used as ingredients in future formulations of these propellants.

Before the RESS system design was fully developed, Kuo and several members of his

group as well as Yetter visited Picatinny Arsenal to confer with Mr. Victor Stepanov of New Jersey Institute of Technology (NJIT) and ARDEC about the RESS process. While Mr. Stepanov’s system was rated to a lower pressure of 10,000 psi, the concept for nano-sized particle formation in his system is quite similar to the one adopted for the Penn State design process. His advice and input was very helpful to the current work and collaborative interactions are planned for the future. During the 6th International Symposium on Special Topics in Chemical Propulsion, held in Santiago, Chile in March 2005, Kuo spoke with Professor Lev Krasnoperov of NJIT for the detailed operational process in the production of nano-crystalline RDX. The Kuo group also consulted Dr. Jeff Morris of ARL this past year on solubility aspects for the RESS process. His familiarity with carbon dioxide and RDX reactions at elevated pressures were helpful in determining the pressure and temperature limits which were placed on the Penn State RESS system. While a visit was not made to his facility to see his Thar Technologies setup, photographs of his experimental facility were obtained and discussed. Dr. Morris also directed the team to past research on RESS systems and the most recent progress on the theoretical modeling of RDX solubility.

To increase communication and collaboration between the CACS group at USC and the

theoretical chemistry group at ARL, Dr. Brad Forch and Dr. Kevin McNesby visited the CACS facilities, including a tour of the Data Visualization Center and the parallel computing labs. Dr. McNesby also gave a seminar on his research during the visit.

The CACS graduate student, Richard Clark, visited ARL in Maryland during August 2005. During his weeklong visit, he gave a presentation to the theoretical chemistry group and met with most of the group’s researchers individually. Richard Clark enjoyed the opportunity to discuss areas of future research collaborations with Dr. Brad Forch, Dr. Maggie Hurley, and

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Dr. Betsy Rice. The relationships developed during the visit will increase regular communications between CACS and ARL and will enhance opportunities for future collaborations. Another graduate student, Richard Seymour, will spend the 2006 summer at ARL as part of the continuing collaborations. CACS researchers and graduate students are using DoD supercomputing facilities including the supercomputer at ARL for large-scale simulations for NEEM research. The USC group has also been collaborating with the Goddard group at Caltech on modeling of energetic materials.

At UIUC, Dlott has discussed his research extensively with collaborators at the DOE labs

LANL and Argonne. Dr. Jason Jouet of NAVSEA-IH has been contacted with regards to his research on SAM/aluminum particles and interactions are expected to develop with him in the future. Natural collaborations are also emerging by exchange of energetic materials for analysis between the team members and the DoD/DoE laboratories.

List of Papers Submitted or Published under ARO Sponsorship during this Reporting Period

Manuscript submitted, but not published

1. “Time and space resolved studies of shock compression molecular dynamics”, J. E. Patterson, A. S. Lagutchev, S. A. Hambir, W. Huang, H. Yu, and Dana D. Dlott, Shock Waves (submitted 2/04).

2. “Nanotechnology energetic material dynamics studied with nanometer spatial resolution and picosecond temporal resolution”, Dana D. Dlott, Selezion A. Hambir, Hyunung Yu, Proceedings of 6ISICP conference (3/05).

3. “Thinking big (and small) about energetic materials”, Dana D. Dlott, Materials Science and Technology (submitted 5/5/05).

Papers published in peer-reviewed journals

1. “Large-scale molecular dynamics simulations of alkanethiol self-assembled monolayers,” S. Vemparala, B. B. Karki, R. K. Kalia, A. Nakano, and P. Vashishta, Journal of Chemical Physics 121, 4323-4330 (2004)

2. “Electric field induced switching of poly (ethylene glycol) (PEG) terminated self-assembled monolayers: a parallel molecular dynamics simulation,” S. Vemparala, R. K. Kalia, A. Nakano, and P. Vashishta, Journal of Chemical Physics 121, 5427-5433 (2004)

3. “Molecular dynamics simulations of the nano-scale room-temperature oxidation of aluminum single crystals,” A. Hasnaoui, O. Politano, J. M. Salazar, G. Aral, R. K. Kalia, A. Nakano, and P. Vashishta, Surface Science 579, 47-57 (2005)

4. “Oxidation of aluminum nanoclusters,” T. J. Campbell, G. Aral, S. Ogata, R. K. Kalia, A. Nakano, and P. Vashishta, Physical Review B 71, 205413:1-14 (2005)

5. “Embedded divide-and-conquer algorithm on hierarchical real-space grids: parallel molecular dynamics simulation based on linear-scaling density functional theory,” F. Shimojo, R. K. Kalia, A. Nakano, and P. Vashishta, Computer Physics Communications 167, 151-164 (2005)

6. “Dynamical Effects of the Oxide Layer in Aluminum Nanoenergetic Materials”, Shufeng Wang, Hyunung Yu, Yanqiang Yang and Dana D. Dlott, Propellants, Explosives and Pyrotechnics, 30, pp. 148-155 (2005).

7. “Near-infrared and Visible Absorption Spectroscopy of Nanoenergetic Materials Containing Aluminum and Boron”, Yanqiang Yang, Shufeng Wang, Zhaoyong Sun and Dana D. Dlott, Propellants, Explosives and Pyrotechnics 30, pp. 171-177 (2005).

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8. “Time and space resolved studies of shock compression molecular dynamics”, J. E. Patterson, A. S. Lagutchev, S. A. Hambir, W. Huang, H. Yu, and Dana D. Dlott, Shock Waves (submitted 2/04).

Papers published in non-peer-reviewed journals or in conference proceedings

1. “Nanotechnology energetic material dynamics studied with nanometer spatial resolution and picosecond temporal resolution”, Dana D. Dlott, Hyunung Yu, Shufeng Wang, Yanqiang Yang, Selezion A. Hambir, in “Advances in Computational & Experimental Engineering & Sciences ’04”, S. N. Atlurl and A. Tadeu, eds., pp. 1427-1432 (2004).

2. “Nanotechnology energetic material dynamics studied with nanometer spatial resolution and picosecond temporal resolution”, Dana D. Dlott, Selezion A. Hambir, Hyunung Yu, Proceedings of 6ISICP conference (3/05).

Papers presented at meetings, but not published in conference proceedings

1. USC group, “High-end multiscale simulations of nanomaterials,” ECCOMAS (European Congress on Computational Methods in Applied Sciences and Engineering) 2004 Symposium on “Bridging Multiscale Methods for Nano Mechanics and Materials” (Jyvaskyla, Finland, July 25, 2004,)

2. USC group, “Large-scale atomistic simulations of nanosystems on parallel computers,” International Conference on Computational Engineering and Science, (Madeira, Portugal, July 27, 2004)

3. USC group, “Multimillion atom simulations and visualization of oxidation and hypervelocity impact damage,” Advanced Computing and Simulation, 24th Army Science Conference (Orlando, FL, November 30, 2004)

4. USC group, “Large space-time multiscale simulations of nanosystems,” PRETISSIMO Workshop on “Molecular Simulation: Algorithmic and Mathematical Aspects” (Paris, France, December 3, 2004)

5. USC group, “Multimillion-atom molecular dynamics simulation of chemical reactions,” International Conference on Scientific Computing and Differential Equations (Nagoya, Japan, May 25, 2005)

6. USC group, “Hierarchical atomistic simulations of fracture in nanostructured materials,” Lorentz Workshop on the Statistical Physics of Pattern Formation and Fracture in Disordered Materials, Leiden, The Netherlands, November 15-19, 2004.

7. USC group, “Large-scale atomistic simulation of hypervelocity impact and crack propagation under compression,” 2004 MRS Fall Meeting, Boston, MA, November 29 – December 3, 2004.

8. USC group, “Multimillion atom fracture and shock simulations,” 45th Sanibel Symposium, St. Simons Island, Georgia, March 5 - 11, 2005.

9. Dlott, (invited) Gordon Conference on Energetic Materials, Tilton, NH (June ’04), “Time and space resolved ultrafast spectroscopy of nanoenergetic materials”.

10. Dlott, (invited, keynote address), International Conference on Computational & Experimental Engineering and Sciences, Madeira, Portugal, (July ’04). “Nanotechnology energetic material dynamics studied with nanometer spatial resolution and picosecond temporal resolution”.

11. Dlott, (invited) Argonne National Laboratory Chemistry Division, Argonne, IL (Sept. ’04), “Vibrational energy at interfaces”.

12. Dlott, (invited) Los Alamos National Laboratory, Physics Division (Feb. ’05), “Ultrafast nonlinear spectroscopy of molecular shock compression”.

13. Dlott, (invited) 2nd International Symposium on Interdisciplinary Shock Wave Research, Sendai, Japan (Mar. ’05), “Shock compression of molecules with picosecond time and 1.5 angstrom spatial resolution”.

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14. Dlott, (invited, plenary talk) Sixth International Symposium on Special Topics in Chemical Propulsion, Santiago, Chile (Mar. ’ 05). “Nanotechnology energetic material dynamics studied with nanometer spatial resolution and picosecond temporal resolution”.

15. Dlott, (invited) University of Southern California Department of Physics (Apr. ’05), “The new wave in shock waves”.

16. Dlott, (invited) Air Force Office of Scientific Research Molecular Dynamics Conference (May ’05), “Vibrational energy with high time and space resolution”.

17. Yetter, “Nano-Engineered Energetic Materials (NEEM) MURI,” 2004 Army Energetic Materials MURI and DURIT Review Meeting, Picatinny Arsenal Officers’ Club, 27-28 October, 2004.

18. Yetter, “An Overview of the Nano-Engineered Energetic Materials (NEEM) MURI,” 2005 Energetic Materials Technology Exchange, Marriott Crystal City at Reagan National Airport, Arlington, VA, 12-14 July 2005.

Demographic Data

Demographic Data for this Reporting Period: • Number of Manuscripts submitted during this reporting period: 6 • Number of Peer Reviewed Papers submitted during this reporting period: 2 • Number of Non-Peer Reviewed Papers submitted during this reporting period: 4 • Number of Presented but not Published Papers submitted during this reporting period: 0

Demographic Data for the life of this agreement: • Number of Scientists Supported by this agreement (decimals are allowed): 23 • Number of Inventions resulting from this agreement 0 • Number of PhD(s) awarded as a result of this agreement: 0 • Number of Bachelor Degrees awarded as a result of this agreement: 0 • Number of Patents Submitted as a result of this agreement: 0 • Number of Patents Awarded as a result of this agreement: 0 • Number of Grad Students supported by this agreement: 4 • Number of FTE Grad Students supported by this agreement: 1 • Number of Post Doctorates supported by this agreement: 7 • Number of FTE Post Doctorates supported by this agreement: 1 • Number of Faculty supported by this agreement: 8 • Number of Other Staff supported by this agreement: 2 • Number of Undergrads supported by this agreement: 1 • Number of Master Degrees awarded as a result of this agreement: 0

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