Engineering topics

Dinh, L. N.

Publications and source records attributed to Dinh, L. N..

5 records

DOE OSTI2023

Refined Outgassing Model for the LiH/LiOH System

Previous models for H 2 and H 2 O outgassing from moisture exposed LiH specimens were based on temperature programmed desorption/decomposition (TPD) experiments and analyses that yielded kinetic descriptions which were specific to defined sets of initial conditions. Subsequently the inputs to the kinetic models were refined to correlate with infrared spectra of the adsorbed species. In this current enhancement, better agreement between prediction and experiment was obtained through: 1) refining the reaction mechanisms for some of the decomposition reactions; 2) developing the potential range of kinetic parameters by simultaneous fitting of all the TPD outgassing curves obtained at different heating rates; and, 3) limiting the scope of possible kinetic parameters to an optimized subset by matching the outgassing prediction curves at 3 different temperatures to the outcomes from the accurate but cumbersome, non-intuitive, and effort demanding isoconversional analysis.

36 MATERIALS SCIENCE↗

DOE OSTI2023

The kinetics of the PuO 2 to Pu 2 O 3 conversion

Here in an oxidizing environment, the oxide formed on plutonium (Pu) metal is composed of a plutonium dioxide (PuO 2 ) top layer and a thin cubic plutonium sesquioxide (Pu 2 O 3 ) middle layer. In a reducing environment, the PuO 2 layer auto-reduces to cubic Pu 2 O 3 . The speed and extent of this conversion depend on the combination of temperature and time. While PuO 2 provides a strong diffusion barrier against unwanted Pu corrosion by gaseous species (like hydrogen), Pu 2 O 3 does not, since its crystal structure has chains of oxygen vacancies. The kinetics of the PuO 2 reduction are, therefore, of fundamental interest and enable researchers to better protect Pu from corrosion. In this report, the oxygen-diffusion-limited kinetics of the dioxide to sesquioxide conversion were obtained by dynamically heating a PuO 2 -covered Pu sample from 294 to 418 K in a high-vacuum vessel equipped with an in situ spectroscopic ellipsometer. The physical/chemical constraints in the conversion process were combined with the ellipsometry method of multi-sample analysis to track the percentage of PuO 2 and to compute the extent of Pu 2 O 3 formation. The resulting diffusion coefficients were compared against and then combined with complementary literature data to produce a comprehensive set of kinetic parameters for reliably modeling oxide conversion over a larger temperature range than spanned by prior studies. The extracted thermal activation energy barrier (43.7 kJ/mol) and pre-exponential factor (5.0 × 10 -10 cm 2 /s) for the oxygen-diffusion-limited process can be used to accurately model the PuO 2 to Pu 2 O 3 transformation in vacuum and/or inert gas applications.

36 MATERIALS SCIENCE↗

DOE OSTI2021

Develop low-temperature diffusional moisture outgassing model for silica-filled silicones

A universal outgassing model for all silica-filled silicones would allow researchers to make moisture outgassing predictions for many different silica-filled silicones using the same sets of kinetic parameters (but with different intensities for the outgassing constituents). In FY 2020, we succeeded in developing such a model for outgassing in a vacuum/dry environment after ~ 1-2 hours of room temperature vacuum pump. That means the FY2020 model does not account for the low temperature diffusional moisture outgassing during the first few hours under vacuum pump. In FY 2021, we have used the experimental technique of dynamic vapor sorption together with the modified Page diffusion model to measure and quantify the low temperature (i. e. room temperature) diffusional moisture release to complete our universal moisture outgassing model for silica-filled silicones from low temperatures to high temperatures.

36 MATERIALS SCIENCE↗

DOE OSTI2021

Design of Sample Holder for Plutonium Coupon Studies

In order to gain better understanding of the plutonium (Pu) corrosion behaviors and reaction kinetics, it is imperative that coupon experiments must be performed on well-defined surfaces. The reactions at the samples’ surfaces have to be properly monitored in terms of reactive gaseous pressures and temperatures. The pressure can be measured by using a pressure gauge, the temperature can be detected with calibrated thermal couples and/or pyrometric camera. These devices do not interfere with the chemistry of the surface reaction. However, to obtain information from the surface reaction, the aggressively machined edge and the back side of the Pu coupons need to be shielded from the applied gases. The coupons are typically made to 5/8 inch in diameter and 0.065 inch in thickness. To this end, a sample holder was designed which can seal the machined edge and the back side of coupons from the exposed gases, thus allowing proper surface reaction. The holder design was fabricated and had been tested with several coupon samples. We have achieved perfect sealing of the machined edge and the back side of the coupons, even when the coupons’ thicknesses are vastly different than the nominal thickness for which the sample holders were fabricated for. This write-up is to document the design of the holder and provide a description of the procedures to properly put the components together.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2020

Proper use of HHDRIFT in surveillance and production conditions

With higher quality optics, newer benchtop DRIFT (diffuse reflectance infrared Fourier transform) spectroscopy systems with modern electronic circuitries should be the preferred choice if detection sensitivity, intensity, and reliability are top priorities. However, when space consideration or other restrictions require the use of a HHDRIFT (handheld DRIFT), it is possible to convert the measurements of the HHDRIFT to those obtained from any benchtop DRIFT and vice versa. In this report, the conversion of the measurements between a HHDRIFT and a benchtop DRIFT at LLNL (Lawrence Livermore National Laboratory) are shown to be linear in both production and surveillance conditions. A similar methodology can be used to obtain the measurement correlations between any HHDRIFT and any benchtop DRIFT at other sites.

36 MATERIALS SCIENCE↗