Principal Investigator: Dhanesh Chandra

Sub-surface Corrosion Research on Rock Bolt System
The objective of the proposed investigation is to conduct corrosion research and predict the durability of rock-bolts and other underground metallic subsurface supports.  In critical areas, it is possible to use highly corrosion resistant steels for rock bolts at Yucca Mountain (YM) repository, such as rock bolts made of ordinary and as well as other special materials in form of  I-beam, sheets, and others for tunnel reinforcement at YM site.  In addition, there is a propensity for stress corrosion cracking (SCC) as well as hydrogen induced cracking (HIC) in rock bolts likely to occur in YM repository emplacement under drift conditions.  As corrosion of these underground support structure materials depends on the YM environmental constraints, loading, and temperatures, it is necessary to evaluate different materials with a wide range of corrosion rates for the rock bolts, particularly important for SCC and HIC resistance, which incorporate these conditions.  Thus these studies will enable DOE to more accurately model for long-term predictions of drift stability during YM repository service.  In this, we will perform studies on new alloys, commercial, as well as alloys in service at YM test site.  We will have a database for corrosion rates of materials important for repository as the work progresses.   The research is mainly on testing rock bolts and other related materials using potentiodynamic polarization test, EIS measurements, stress corrosion/hydrogen embrittlement studies, oxidation of steels, crystal structure and microscopic characterization studies. [DOE]

Zr₂Fe Hydrides for Gettering Systems
The objective of this program is to perform crystal structure and thermodynamic studies on gettering alloys used in nuclear processing facilities at Los Alamos National Laboratory.  These are primarily designed for tritium applications, but the majority of the experiments are performed using hydrogen gas.  The major gettering phase in this alloy is the intermetallic Zr₂Fe, which is a non-equilibrium phase at room temperature and transforms to Zr₃Fe phase and other phases between 723 and 1123 K.  Annealing studies performed by in-situ x-ray diffractometry showed that Zr₂Fe ® Zr₃Fe, but the other associated phases such as ZrFe₂, (or any Zr₆Fe₃O) phases remain after processing.  Neutron scattering studies on these gettering materials are also performed that revealed that ~80% Zr₂Fe transforms to Zr₃Fe when annealed in vacuum at 953 K for 72 hours.  The existing phase diagrams of Zr-Fe system have discrepancies, and this system needs to be re-evaluated from 20 to 65 at. %Fe, based on results on this study.  Thermodynamic and structural studies of hydriding of metastable Zr₂Fe (BCT-I4mcm) intermetallic, at low temperatures (303-473 K), the structure transform primitive tetragonal hydride with a space group (P4/ncc.  The structure of Zr₃Fe and Zr₃FeH_x remains orthorhombic (Cmcm). Thermodynamic results showed partial disproportionation of Zr₂FeH_x resulting in formation of ZrH_x at 773 K, in pure hydrogen environment.  The nitrogen gas used in nuclear processing streams does not affect the hydriding process up to 633K; however, significant nitriding occurs above 973K, forming ZrN and -Fe phases. [Los Alamos National Laboratory Program]

Effect of Trace Elements on Long-Term Cycling and Aging Properties of Hydrides for Hydrogen Storage
Hydrogen storage in metal hydrides has a great potential for on-board vehicular applications. The effects of thermal cycling are important for long-term reliability of metal hydrides, during refueling with of hydrogen with small amounts of impurities. This program is part of Center of Excellence for Metal Hydrides for US DOE. These impurities can potentially cause problems due to disproportionation of hydrides, surface contamination, and possibly other bulk related affects, during numerous recharges.   In this research, we propose to investigate the effect of trace impurities in complex hydrides, which can be potentially used for fuel cell and other applications and aid in the development of materials solutions to potential hydrogen sorption degradation problems.  The stability of hydrides and thermodynamics and characterization of these hydrides under various condition using neutron scattering methods using deuterium gas, synchrotron x-ray studies, TEM,  and  x-ray photoelectron spectroscopy. [DOE]

Fe-U Interactions and formation of Intermetallic Compounds in Inert and Hydrogen Atmospheres
The goal of the proposed research is to obtain kinetics of formation of intermetallic compounds in Fe-U binary system as a function of composition and temperature in inert and in hydrogen environment.  We designed and fabricated diffusion couple die to produce samples for these interdiffusion studies. Characterization of the diffusion interfaces will be performed with Scanning Electron Microscopy (SEM) and/or Electron Probe Micro Analysis (EPMA).  A Fe-U-Fe diffusion couple will be prepared with thin plates.  The diffusion couple will be compressed in a stainless steel holder.  We propose to use the well known BM method to solve the inverse problem of determining interdiffusion coefficient (D) in Fe-U system from the experimentally determined concentration gradient (dx/dC). The solution to the inverse problem using BM method is:

where, C’ is the concentration, X_M is the Matano interface, and x is the distance.  The effect of temperature on interdiffusion coefficient will also be determined.  The concentration data will be obtained either using Hitachi FESEM or Cameca Electron microprobe at the University of Nevada, Reno. We plan to use Prof. Oishi’s numerical code to simulate diffusion profiles in multicomponent non-ideal systems.  This code will be modified and adapted for MATLAB for our research. [Los Alamos National Laboratory Program]

Los Alamos National Laboratory Program “Hydrogen Permeation in Metals and Alloys
It is proposed to perform hydrogen diffusion studies on Vanadium and Vanadium copper alloys using Devanathan and Stachurski electrochemical method.   This will allow the examination of hydrogen diffusion and trapping effects at moderate temperatures to verify the usefulness of vanadium as a hydrogen storage/transport medium.  The details of permeation calculations are described elsewhere but current produced at the anodic cell is monitored to obtain the flux using the following equation:

J L = i L/nF and   D_eff = L²/6t_lag

where, J is the flux, L the specimen thickness, i the current density, n the number of electrons transferred and F is Faraday’s constant, , D_eff the effective diffusivity and t_lag is the lag time.  The steady state flux (J_ss) is then determined from the data. The effective diffusivity can then be determined by one of several methods, the most common of which is the lag time method. Preliminary work has already been performed on membrane specimens of vanadium.