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13 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

A Simple Hydride Model for Cerium Ejecta Particles

Cerium ejecta particles form after a shock wave impacts a cerium plate with a known roughness or prescribed surface perturbation. When these particles are ejected into hydrogen or deuterium gas the material reacts exothermically and raises the temperature of the particle relative to the gas. A simple model is developed, assuming that the particle remains intact and spherical, to capture the heat and mass transfer that occurs during this process. Model performance is evaluated by comparing with cerium ejecta experiments where the particles are ejected into deuterium gas at initial pressures of 4 and 8 atm. Overall, the model is able to capture the approximately 400 K increase in particle temperature above the surrounding gas temperature.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

A simple hydride model for cerium ejecta particles

Cerium ejecta particles form after a shock wave impacts a cerium plate with a known roughness or prescribed surface perturbation. When these particles are ejected into hydrogen or deuterium gas the material reacts exothermically and raises the temperature of the particle relative to the gas. A simple model is developed, assuming that the particle remains intact and spherical, to capture the heat and mass transfer that occurs during this process. Model performance is evaluated by comparing with cerium ejecta experiments where the particles are ejected into deuterium gas at initial pressures of 4 and 8 atm. Overall, the model is able to capture the approximately 400 K increase in particle temperature above the surrounding gas temperature.

36 MATERIALS SCIENCE↗
DOE OSTI2022

A simple hydride model for cerium ejecta particles

Cerium ejecta particles form after a shock wave impacts a cerium plate with a known roughness or prescribed surface perturbation. When these particles are ejected into hydrogen or deuterium gas the material reacts exothermically and raises the temperature of the particle relative to the gas. A simple model is developed, assuming that the particle remains intact and spherical, to capture the heat and mass transfer that occurs during this process. Model performance is evaluated by comparing with cerium ejecta experiments where the particles are ejected into deuterium gas at initial pressures of 4 and 8 atm. Overall, the model is able to capture the approximately 400 K increase in particle temperature above the surrounding gas temperature.

36 MATERIALS SCIENCE↗
DOE OSTI2023

A hydride model for solid and liquid cerium ejecta particles

Cerium ejecta particles form after a shock wave impacts a cerium plate with a rough surface or prescribed surface perturbation. When these particles are ejected into hydrogen or deuterium gas the material reacts exothermically and raises the temperature of the particle. Two models are developed to capture the heat and mass transfer that occurs during this process. One model assumes that for larger solid ejecta particles, the loss of mass is negligible while for smaller liquid ejecta particles, the loss of mass during reaction is accounted for. The loss of mass is assumed to occur from the hydride layer being extremely brittle and the fact that it will be relatively easy for the hydride material on the outside of the particle to go into tension, crack and flake off. The model is tested by performing simulations similar to the original experiments that motivated the development of these models and comparing the particle temperatures. While the model is able to capture some general features of the flowfield, inaccuracies clearly exist that must be addressed and the results underscore the need for more isolated experiments where fewer assumptions and physical processes are present simultaneously.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2026

A point-particle-based hydride shell-shedding model for ejecta particle transport in reactive environments

A shock wave passing over a rough or perturbed metal surface will induce a limiting case of Richtmyer–Meshkov instability and will cause small particles to eject from the surface and transport into the surrounding medium. These particles are known as ejecta and can be either solid or liquid in nature. Recent experiments have shown that liquid cerium ejecta clouds exhibit unexpected non-monotonic acceleration behaviors as well as temperature plateaus after a brief temperature rise if they are transporting in a chemically reactive, hydrogen-based medium while they act as expected in an inert medium. This work details a point-particle model developed for reactive cerium ejecta transport, which attempts to account for these new physics through the behavior of a developing solid hydride shell, which is believed to form as a product of the reaction. The overall model incorporates the effects of the reaction on the particle properties as well as the effects of potential shedding of the shell into sub-micrometer scale flakes and potential phase change of the hydride if the ejecta particles reach the melt point of the hydride layer. The model is tested by performing simulations of the original motivating experiments and comparing quantities, such as ejected mass, velocimetry, and temperature profiles, against the experimental data. While the model is able to capture many general features of the observed anomalies, some inaccuracies still exist. These point to both missing physics in the model (such as a deuterium adsorption mechanism on the hydride layer) as well as a lack of knowledge of certain material properties (such as the strength of cerium hydride to determine dynamic fracture thicknesses) needed to fully reduce the uncertainties in the model by up to an order of magnitude and perform a true attempt at model validation.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2017

Gas-Phase Ion-Neutral Interactions of Cerium Ions with Deuterium, STL-002-17, Year 1 of 1

This presentation describes investigation of the gas-phase interactions of cerium (Ce) cations and deuterium neutrals using a temperature-dependent reaction cell embedded between two quadrupole mass analyzers. A negative temperature dependence is observed, indicating the reaction becomes less efficient as the temperature is increased. A combination of experimental and theoretical analyses suggests that the overall reaction is exothermic for insertion of Ce+ into the deuterium bond.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2026

A stress-based fracture model for reacting metal ejecta

The evolution of reacting metal ejecta continues to be a topic of interest at the forefront of metals in reactive and extreme environments. Ejecta are small particles formed when the surface of a metal undergoes Richtmyer–Meshkov instability from a strong shock. Experiments have shown that in the case where ejecta are in ambient conditions that induce a reaction, the ejecta behave irregularly. The ejecta temperature rises and then plateaus, and the acceleration profile shows unexpected jumps. These variations are assumed to be related to the exothermic heat release and particle mass loss caused by the reaction. To explain this phenomenon, efforts to model this in simulations have increased. While current models can capture many of these physical processes, they currently assign a constant reaction shell thickness with little physical reasoning. This work remedies this problem by assigning a dynamic physically informed shell thickness to the reacting particles, using solid analysis. The shell thickness of the particles impacts the rate of change of reacted mass in the system, as well as the rate at which the particles react. The model is based on a simple stress–strain relationship and gives a dynamic assignment for when the reacting particle should begin to fracture. We compare our model to the previous computational and simulation data to analyze the effects of different model parameters.

42 ENGINEERING↗
DOE OSTI2020

Understanding the transport and break up of reactive ejecta

This manuscript investigates reactive- versus hydrodynamic-breakup processes of ejecta. For this paper, the reactive metal is cerium (Ce) and the nonreactive metal is tin (Sn), the nonreactive gas is helium (He) and the reactive gas is deuterium (D 2 ) or hydrogen (H 2 ). Experiments were performed in vacuum and the reactive- and nonreactive-gases at various pressures, where we endeavored to match the post-shock gas densities to differentiate between reactive- versus hydrodynamic-breakup processes. Hydrodynamic breakup sensitively links to the Weber number (gas density, liquid fragment diameter, surface tension, and the square of the relative velocity between the fragment and the gas), whereas reactive breakup links to the reactive dynamics which includes two processes. In one case the reactive metal breaks up into smaller fragments as rapidly as the reaction rate, and in the other a crust grows on the liquid fragments as the reactions occur, a diffusion limited process. In the latter case, the particle diameters increase with time as the crust grows. In this process, which is indicated by the data, particles breakup as the CeD 2 loses strength with increasing temperature, leaving an exponentially increasing diameter.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Density functional theory study of cerium deuterides

Here, we present a density functional theory study of cerium deuterides, varying deuterium content and temperature. Results are discussed in relation to ejecta experiments recently described in [J. Dynam. Mat. Behav. 1, 12 (2017)]. Using quantum molecular dynamics, we calculate diffusion coefficients, radial distribution functions, and heat capacities of these materials. Properties are calculated over temperatures ranging from 500-4000K at near ambient pressure and at 2.37 fold compression. We find that deuterium diffusion occurs rapidly accross this temperature and compression region and that heat capacity calculations are in agreement with approximations made in experiments. For cerium metal, a comparison of self-diffusion coefficient and viscosity with experimental data and analytical models shows excellent agreement. Lastly, we discuss the stucture of cerium deuterides with respect to radial distribution functions and provide fitted equations for diffusion coefficients over temperature.

36 MATERIALS SCIENCE↗