"Two-color fluorescence thermometry under dynamic shock compression"

Speaker: Hergen Eilers, Research Professor (Washington State University)

Abstract: To determine the feasibility of temperature measurements in heterogeneous materials under dynamic compression, we designed and synthesized various sensor materials and investigated their properties. The sensors consist of molecular complexes containing trivalent lanthanide ions such as Dy3+ and various organic ligands. The 2-color fluorescence properties of Dy3+ provide the temperature sensing capability. The ligands serve to: enhance the absorption of UV light; allow for the growth of molecular crystals; and allow for dispersion in a polymer matrix. The sensors have been designed so that they can easily be excited by 355 nm laser light, have a high emission intensity over a wide range of temperatures, and have a fluorescence lifetime of at least 10 μs. Such a lifetime allows us to excite the sensor with a single laser shot and transfer all the energy to the lanthanide ion right before the shock hits and deforms the molecular ligand structure. Shock compression experiments were performed using a single-stage gas gun (2.5” bore), designed to reach peak stresses of up to 9 GPa. We observed photo-luminescence and were able to determine the 2-color intensity ratios for about 2 μs after the shock entered the sample, which is long enough for the proposed application of these temperature sensors. Assuming any potential effect of the dynamic compression impacts the two emitting lanthanide states equally, we can convert the fluorescence intensity ratio into temperature.

"Internal Fireball Emission Measurements Utilizing a Singular Sensor Hyperspectral Imager"

Speaker: Elliot Wainwright, Research Materials Engineer (US Army DEVCOM Army Research Laboratory)

Abstract: Snapshot hyperspectral imaging serves as a tool to garner more information from austere diagnostic environments with high-rate requirements. Here, we demonstrate two configurations of a custom snapshot hyperspectral imaging system which allow for simultaneous imaging, spectroscopy, and temperature measurements of the interior of a post-detonation fireball when used in combination with a transparent flat-plate, hemispherical detonation test. We present the efficacy of this system with these tests and characterize the internal emissions and reactions from surrogate aluminized and non-aluminized composition C-4 charges. The design, calibration procedures, and an assessment of the measurement system under a ‘spectroscopy’ and ‘pyrometery’ mode will be compared, and atomic and molecular spectra at various spatially-defined sampling points as well as temperature measurements via grey-body fitting will be presented, both sampled at rates >40 kHz. We provide examples of how hyperspectral imaging can be used to extract a wide variety spatially and temporally resolved information from post-detonation phenomena. Finally, we discuss limitations of the current system design and potential applications for computation fluid dynamics (CFD) model verification & validation, particularly for the characterization of novel combined effects explosives (CEX) formulations.

"CARS thermometry and species detection in inductively coupled plasma jets"

Speaker: Sean Kearney, Professor (University of Illinois Urbana-Champaign)

Abstract: Coherent anti-Stokes Raman scattering (CARS) is a well-established laser spectroscopic technique for multi-parameter gas-phase diagnostics in challenging environments. Its coherent, laser-like signal provides strong background rejection in luminous flows and near scattering boundaries such as wind-tunnel walls and material surfaces. Broadband implementations further enable simultaneous measurements of nonequilibrium temperatures and multi-species concentrations in reacting flows. The working principles of CARS and its advantages for high-temperature, high-background environments are briefly reviewed, with emphasis on the ability of the method to resolve temperature and species profiles in challenging application environments with high spatial resolution, and near surfaces.

Recent measurements in a high-enthalpy inductively coupled plasma jet, Illinois Plasmatron X, are presented. In these flows, high atomic oxygen concentrations at jet temperatures exceeding 5000 K produce an intensely reactive environment. With spatial resolution on the order of 100 μm, temperature and carbon monoxide profiles are mapped in the near-wall region, revealing the structure of the ablation boundary layer over graphite. When combined with surface recession measurements, these data provide a more complete experimental picture of air–carbon ablation processes. As a spatially resolved spectroscopic diagnostic, CARS also enables detailed characterization of nonequilibrium effects. Measurements of nitrogen vibrational and rotational temperatures in the boundary layer near a catalytic copper surface are discussed. Finally, ongoing efforts to extend CARS for simultaneous atomic oxygen detection in ablation environments are described, including recent demonstrations of O-atom spectra in laboratory-scale argon–oxygen plasmas.

"Bulk-Castable Reactive Alloy Structures"

Speaker: Atakan Peker, Research Professor (Washington State University)

Peker, A. and Gupta, Y. M.

Abstract: Reactive Materials (RM) are a class of energetic solids containing large amounts of enthalpic energy, which can be released using appropriate stimuli. A critical shortcoming of usual reactive materials is the lack of mechanical strength for structural durability. Prior to this work, most of the RMs included metal components in pure elemental form, whether they were sintered or otherwise processed. A new class of structurally suitable reactive materials, Reactive Alloy Structures (RAS), was developed using a systematic alloy design approach. The RAS system developed is based on high-density reactive metals and is produced by using a bulk-casting method. Homogenous microstructures having high strength exceeding 200 ksi are achieved, while preserving inherent enthalpic (combustion) energy and the ability to release it on demand. The metallurgy of the RAS along with its processing advantages and limitations will be discussed.

*Scheduled for joint session with the Reactive Material Technical Exchange on 8/12