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All sourcesNASA NTRSDOE OSTI
NASA NTRS2003

Measuring Diffusion of Liquids by Common-Path Interferometry

A method of observing the interdiffusion of a pair of miscible liquids is based on the use of a common-path interferometer (CPI) to measure the spatially varying gradient of the index refraction in the interfacial region in which the interdiffusion takes place. Assuming that the indices of refraction of the two liquids are different and that the gradient of the index of refraction of the liquid is proportional to the gradient in the relative concentrations of either liquid, the diffusivity of the pair of liquids can be calculated from the temporal variation of the spatial variation of the index of refraction. This method yields robust measurements and does not require precise knowledge of the indices of refraction of the pure liquids. Moreover, the CPI instrumentation is compact and is optomechanically robust by virtue of its common- path design. The two liquids are placed in a transparent rectangular parallelepiped test cell. Initially, the interface between the liquids is a horizontal plane, above which lies pure liquid 2 (the less-dense liquid) and below which lies pure liquid 1 (the denser liquid). The subsequent interdiffusion of the liquids gives rise to a gradient of concentration and a corresponding gradient of the index of refraction in a mixing layer. For the purpose of observing the interdiffusion, the test cell is placed in the test section of the CPI, in which a collimated, polarized beam of light from a low-power laser is projected horizontally through a region that contains the mixing layer.

Rashidnia, Nasser↗
DOE OSTI2022

A bi-layer barrier design for 122-type iron-based superconducting wires and tapes

Iron-based superconducting wires and tapes hold great promise for high-field magnet applications. A promising design for 122-type wires and tapes based on the powder-in-tube method is using silver and copper double-layer sheaths. For this design a heat treatment temperature below ~ 779 °C is required to prevent Ag-Cu liquid formation. However, this may be below the optimal heat treatment temperature for the critical current density, and still cannot prevent Ag-Cu interdiffusion occurring in the solid state. In this work we propose adding a niobium or tantalum or vanadium (or their alloys) barrier layer between the Ag and Cu to solve the Ag-Cu interdiffusion issue, given that the group-VB metals (vanadium, niobium, tantalum) are relatively inert to both Ag and Cu. To investigate the effectiveness of this design, BaFe 1.84 Co 0.16 As 2 wires and tapes with Ag/Cu and Ag/Ta/Cu sheaths, as well as Ba 0.6 K 0.4 Fe 2 As 2 wires and tapes with Ag/Cu and Ag/Nb/Cu sheaths, were fabricated. It was found that both the Ta and Nb layers kept integral after wire drawing, but after a large flat-rolling reduction the Ta layer broke while the Nb layer kept integral. In the tapes with Ag/Cu sheaths (without the Ta or Nb layer) Cu diffused through the Ag layer and into the powder cores during 740 °C heat treatment, while in the tapes with Ag/Nb/Cu sheaths the Nb layer effectively blocked Ag-Cu interdiffusion even at 900 °C. Further, this work demonstrates that Ta is a suitable barrier material for 122-type wires, while Nb is suitable for both wires and tapes. In this design using Ag/Nb (or Ta)/Cu sheaths, we can regard the outer Cu as the conductor matrix while the Ag and Nb (or Ta) serve as two layers of barriers that suppress reactions between the components. Thus, we call this design a “bi-layer barrier” design for 122-type wires and tapes.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Fuel-cladding chemical interaction of a prototype annular U-10Zr fuel with Fe-12Cr ferritic/martensitic HT-9 cladding

As an alternative fuel form, the annular metallic fuel design eliminates the liquid sodium bond between the fuel and the cladding, providing back-end fuel cycle and other benefits. The fuel-cladding chemical interaction (FCCI) of annular fuel also presents new features. In this work, state-of-the-art electron microscopy and spectroscopy techniques were used to study the FCCI of a prototype annular U-10wt%Zr (U-10Zr) fuel with ferritic/martensitic HT-9 cladding irradiated to 3.3% fission per initial heavy atom. Compared with sodium-bonded solid fuels, negligible amounts of lanthanides were found in the FCCI layer in the investigated helium-bonded annular fuel. Instead, most lanthanides were retained in the newly formed UZr 2 phase in the fuel center region. The interdiffusion of iron and uranium resulted in tetragonal ( U ,Zr) 6 Fe phase (space group I4/mcm) and cubic ( U ,Zr)( Fe ,Cr) 2 phase (space group Fd 3 ¯ m). The ( U ,Zr)( Fe ,Cr) 2 phase contains a high density of voids and intergranular uranium monocarbides of NaCl-type crystal structure (space group Fm 3 ¯ m). At the interdiffusion zone and inner cladding interface, a porous lamellar structure composed of alternating Cr-rich layers and U-rich layers was observed. Next to the lamellar region, the unexpected phase transformation from body-centered cubic ferrite (α-Fe) to tetragonal binary Fe-Cr σ phase (space group P4 2 /mnm) occurred, and tetragonal Fe-Cr-U-Si phase (space group I4/mmm) was identified. Due to the diffusion of carbon into the interdiffusion zone, carbon depletion inside the HT-9 led to the disappearance of the martensite lath structure, and intergranular U-rich carbides formed as a result of the diffusion of uranium into the cladding. These detailed new findings reveal the unique features of the FCCI behavior of annular U-Zr fuels, which could be a promising alternative fuel form for high burnup fast reactor applications.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2022

Density functional theory study of formation and diffusion of hydrogen, deuterium, and tritium in Pd-V intermetallic compounds

Permeation of hydrogen isotopes in palladium/vanadium bimetallic membranes is known to deteriorate over time because of Pd-V interdiffusion. Additionally, intermetallic compounds may form in the interdiffusion region. Density functional theory is employed to study how Pd-V compounds may affect the permeation. Three compounds Pd 8 V, alpha-Pd 2 V, and PdV 4 are explored in this study. Formation and migration energies of hydrogen, deuterium, and tritium are calculated and subsequently compared to the data in pure Pd and V metals. The calculations show that both the formation and migration energies in the compounds are higher than in the pure metals. Thus, the permeation of these isotopes in the compounds is lower than in the pure metals. In addition, the least permeable compound is the one near the middle of the composition range, i.e. the alpha-Pd 2 V. The results provide atomistic insight for the permeation reduction in Pd/V membranes as interdiffusion progresses.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Environmental degradation of electroplated nickel and copper coated SS316H in molten FLiNaK salt

Corrosion of nickel and copper electroplated coatings on SS316H in molten FLiNaK salt was studied. 500- and 1000-hour static corrosion tests were performed in molten FLiNaK at 700 degrees Celsius. Characterization of the coatings following corrosion indicated that they did not degrade in the molten salt during the corrosion experiment and fully protected the underlying SS316H from chromium dissolution. Interdiffusion between the copper coating and SS316H was extremely limited, interdiffusion between the nickel coating and SS316H. Diffusion modelling revealed that the nickel coatings still significantly reduced chromium dissolution over 60 years despite the interdiffusion.

36 MATERIALS SCIENCE↗
NASA NTRS1976

Macroscopic aspects of interfacial reactions

The extent of interdiffusion and formation of new phases is determined by the constitution diagram of the alloy system, the interdiffusion coefficients of the phases present, and the thermal conditions (temperature and time) associated with the bonding process and/or subsequent use of the bonded structure. In many instance, the kinetics of interdiffusion and phase formation can be predicted from known parameters using numerical methods and computer techniques. Predictions are compared with experimentally determined parameters for a variety of metallurgical alloy systems.

Heckel, R. W.↗
NASA NTRS1981

Stuffed MO layer as a diffusion barrier in metallizations for high temperature electronics

Auger electron spectroscopy was employed to characterize the diffusion barrier properties of molybdenum in the CrSi2/Mo/Au metallization system. The barrier action of Mo was demonstrated to persist even after 2000 hours annealing time at 300 C in a nitrogen ambient. At 340 C annealing temperature, however, rapid interdiffusion was observed to have occurred between the various metal layers after only 261 hours. The presence of controlled amounts of oxygen in the Mo layer is believed to be responsible for suppressing the short circuit interdiffusion between the thin film layers. Above 340 C, its is believed that the increase in the oxygen mobility led to deterioration of its stuffing action, resulting in the rapid interdiffusion of the thin film layers along grain boundaries.

Boah, J. K.↗
NASA NTRS1990

Characterization of Iridium Coated Rhenium Used in High-Temperature, Radiation-Cooled Rocket Thrusters

Materials used for radiation-cooled rocket thrusters must be capable of surviving under extreme conditions of high-temperatures and oxidizing environments. While combustion efficiency is optimized at high temperatures, many refractory metals are unsuitable for thruster applications due to rapid material loss from the formation of volatile oxides. This process occurs during thruster operation by reaction of the combustion products with the material surface. Aerojet Technical Systems has developed a thruster cone chamber constructed of Re coated with Ir on the inside surface where exposure to the rocket exhaust occurs. Re maintains its structural integrity at high temperature and the Ir coating is applied as an oxidation barrier. Ir also forms volatile oxide species (IrO2 and IrO3) but at a considerably slower rate than Re. In order to understand the performance limits of Ir-coated Re thrusters, we are investigating the interdiffusion and oxidation kinetics of Ir/Re. The formation of iridium and rhenium oxides has been monitored in situ by Raman spectroscopy during high temperature exposure to oxygen. For pure Ir, the growth of oxide films as thin as approximately 200 A could be easily detected and the formation of IrO2 was observed at temperatures as low as 600 C. Ir/Re diffusion test specimens were prepared by magnetron sputtering of Ir on Re substrates. Concentration profiles were determined by sputter Auger depth profiles of the heat treated specimens. Significant interdiffusion was observed at temperatures as low as 1000 C. Measurements of the activation energy suggest that below 1350 C, the dominant diffusion path is along defects, most likely grain boundaries, rather than bulk diffusion through the grains. The phases that form during interdiffusion have been examined by x ray diffraction. Analysis of heated test specimens indicates that the Ir-Re reaction produces a solid solution phase of Ir dissolved in the HCP structure of Re.

Stulen, R. H.↗
DOE OSTI2024

Surface Atomic Rearrangement with High Cation Ordering for Ultra-Stable Single-Crystal Ni-Rich Co-Less Cathode Materials

It is crucial to minimize cobalt content in Ni-rich layered single-crystal cathodes due to their high price and limited availability, yet it will inevitably lead to cation disordering, capacity degradation, and thermal issues. Herein, to overcome the intrinsic trade-off between performance and composition of Ni-rich Co-less single-crystal cathodes, a precursor engineering strategy with an epitaxially grown cobalt enrichment on the surface is innovatively proposed. In contrast to traditional coating modifications with random orientation and rigid surface-bulk boundary, the epitaxially enriched surface cobalt layer on the precursor undergoes rapid interdiffusion with the internal Ni 3+ during the optimized sintering process. This interdiffusion eliminates the surface-bulk boundary, promoting the uniform distribution of cobalt and synergistically addressing the Li/Ni intermixing. Moreover, an enhanced surface Li + diffusion is obtained, thereby suppressing the Li + concentration gradient and intragranular cracks generation. Consequently, the modified LiNi 0.7 Co 0.07 Mn 0.23 O 2 exhibits impressive cycling stability with increased capacity retention in both coin-type half-cells and pouch-type full-cells (91% after 1000 cycles), even under the harsh condition of high-temperature, surpassing the majority of previously reported Ni-rich cathodes. Finally, this work opens new avenues toward the low cost, high energy density, thermal stability, and long cyclic life for Ni-rich Co-less cathodes and sheds light on large-scale commercial production.

25 ENERGY STORAGE↗
DOE OSTI2022

Interlayer fusion bonding of semi-crystalline polymer composites in extrusion deposition additive manufacturing

This work focuses on the evolution of interlayer fracture toughness properties of fiber-reinforced, semi-crystalline polymers in the extrusion deposition additive manufacturing (EDAM) process. Further, this work bridges the gap between the additive process conditions (time-temperature history) and the effective layer-to-layer fracture properties developed within a printed component. This is the first step to predict delamination that can occur during printing, during cooling to room temperature after printing, and during service performance of an additively manufactured geometry. A phenomenological model is developed for fusion bonding of semi-crystalline polymer matrix composites by coupling the interdiffusion of polymer chains with the evolution of polymer crystallinity. While the interdiffusion is captured by reptation theory of polymer dynamics, the evolution of crystallinity is modeled by phenomenological crystallization kinetics and crystal melting dynamics. Further, a methodology is developed to determine the critical strain energy release rate, G IC of the interlayer interface and experiments are conducted utilizing the double cantilever beam fracture test geometry. In conclusion, predictions of GIC as a function of thermal history are compared with experiments.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Probing degradation at solid-state battery interfaces using machine-learning interatomic potential

Solid-state batteries featuring fast ion-conducting solid electrolytes are promising next-generation energy storage technologies, yet challenges remain for practical deployment due to electro-chemo-mechanical instabilities at solid-solid interfaces. These interfaces, which include homogeneous/internal interfaces such as grain boundaries (GBs) and heterogeneous/external interfaces between solid-electrolyte and electrode materials, can impede Li-ion transport, deteriorate performance, and eventually lead to cell failure. Here, in this study, we leverage large-scale molecular simulations, enabled by validated machine-learning interatomic potentials, to directly probe the onset of interfacial degradation at the garnet Li 7 La 3 Zr 2 O 12 (LLZO) solid-electrolyte/LiCoO 2 (LCO) cathode interface. By surveying different interfacial geometries and compositions, it is found that Li-deficient interfaces can lead to severe interfacial disordering with cation mixing and Co interdiffusion from LCO into LLZO. By contrast, Li-sufficient interfaces are less disordered, although elemental segregation with local ordering is observed. As a consequence of Co interdiffusion, Co-rich regions are formed at the GBs of LLZO due to cation segregation and trapping effects. This behavior is independent of the GB tilting axis, degree of disorder at the GBs, and Co concentration, which implies Co clustering at GBs is a general phenomenon in polycrystalline LLZO and can dictate its overall transport and mechanical properties. Our findings elucidate the underlying fundamental mechanisms that give rise to experimentally observed physicochemical properties and provide guidelines for interface design that can mitigate interfacial degradation and improve cycling performance.

25 ENERGY STORAGE↗
DOE OSTI2022

Application of the core shell model for strengthening polymer filament interfaces

While surface segregation has been intensively studied in thin films, relatively little has been investigated in filament geometries. In contrast to thin films, the filament surface forms a continuum, with interactions both at the free air and internal filament interface, which makes it difficult to achieve an equilibrium configuration. This asymmetry has become particularly apparent with the increasing use of additive manufacturing where entire structures are constructed via layered deposition of filamentous layers from a moving thermal nozzle. In addition, this process is highly non-equilibrated with poor thermal retention and is responsible for insufficient filament–filament interfacial fusion and internal pore formation along the printing direction. These features all contribute to poor mechanical and structural properties, which are exacerbated in semi-crystalline polymers, such as Polylactic Acid (PLA), where the melting point, T m , is much higher than the glass transition, T g . Even though system is liquid the molecules become ordered within the crystal structure and this ordering interferes with interdiffusion, which in turn prevents proper interfacial fusion. Capitalizing on the differential in surface tension, we show that addition of less than 1%, or trace amounts, of longer chain polymers, an oriented core shell structure, will be formed with a self-limiting thickness of three time the radius of gyration, R g , of the tracer chains. The lower T g of the tracers and their orientation makes them poised for interdiffusion when subsequent layers are deposited producing structures with significant improvement of the mechanical properties and internal structural integrity.

36 MATERIALS SCIENCE↗
DOE OSTI2025

TEM characterization of two variants of fuel cladding chemical interaction in a HT-9 Clad U-10Zr Fuel. Variant 1: FCCI with a Zr Rind

Here, this study investigated the fuel cladding chemical interaction (FCCI), a key factor that limits operational temperature and burnup, in an HT-9 clad U-10Zr nuclear fuel sample irradiated to a high burnup of 13.1 at.% at a time-averaged peak inner cladding temperature (PICT) of 530 °C. Previous results showed this fuel sample exhibited two distinct levels of FCCI at d. This paper analyzed the FCCI at an azimuthal position showing an interdiffusion layer of <10 µm using transmission electron microscopy to examine chemical and crystallographic nature of phases at the fuel-cladding interface at the nanoscale level. A ZrC layer and a Zr 3 Si phase were identified at the interface; these, along with the relatively low local temperature, potentially contributed to limit interdiffusion, behaving as inhibitors for deleterious interactions. Lanthanides (Ln) partially consumed the ZrC layer and interacted with Fe, forming a Zr-Ln compound and a (Zr,Ce)Fe 2+x phase while also infiltrating up to 4 µm into the cladding. Neither U nor Zr were observed in the cladding, whereas Fe diffused up to 3–5 µm in the fuel. Fe infiltration formed a ternary U-Zr-Fe ε-phase and likely promoted the precipitation of a Cr-rich α’ phase on the cladding interface. Additionally, a Cr-rich χ-phase, likely formed by the dissociation of pre-existing M 23 C 6 carbide precipitates, was identified about 2–5 µm from the fuel-cladding interface. Irradiation-induced nano-voids were also observed in the HT-9 bulk. These findings provide critical insights into FCCI mechanisms at representative irradiation conditions, essential for developing models simulating in-pile metallic fuel behaviors for next-generation reactors.

36 - MATERIALS SCIENCE↗
DOE OSTI2025

First-principles elucidation of the effects of Al-doping on Li-ion diffusion in LiCoO 2

Al-doped garnet Li 7 La 3 Zr 2 O 12 solid-electrolyte and LiCoO 2 cathode are promising choices as catholyte materials in all solid-state Li batteries, however, interdiffusion of Al is commonly evident during high-temperature processing and electrochemical cycling. Furthermore, to address the impact of Al interdiffusion on Li + transport properties in LiCoO 2 , we carried out a systematic evaluation of Al doping on Li + diffusion barriers in LiCoO 2 using first-principles based methods. Following the monovacancy diffusion mechanism, Al-doping (primarily at the Co site) is found to improve Li diffusion kinetics in the LiCoO 2 lattice due to favorable CoO 6 octahedral distortion experienced at the transition states. However, when considering the previously established dominant divacancy diffusion mechanism, slower Li diffusion is generally expected. In addition, a broad variation of Li diffusion barriers is observed upon Al doping, which suggests the system may suffer from non-uniform Li incorporation and diffusion that adversely affects its rate capacity during cycling. In summary, this work highlights, for the rational design of catholyte of all solid-state batteries, special attention may need to be paid to address the potential impact of non-intentional doping induced during processing on the overall electrochemical performance of the catholyte.

Al-doped LiCoO2↗
DOE OSTI2026

Task Sharing of Proton Incorporation in Vertically Aligned Nanocomposite Triple Conductors: Growth, Structure, and Surface Exchange Kinetics

As protonic ceramic electrolysis cells emerge for efficient H 2 production, there is a need to develop air electrode materials enabling fast, durable steam splitting and proton incorporation. Single-phase triple conductors may fail to satisfy the myriad performance/stability requirements, and their critical charge-carriers (holes, oxygen vacancies, and protons) are in competition, limiting their concentrations. Instead, we propose task-sharing, vertically aligned nanocomposites (VANs), comprising a proton conductor (BaZr 0.9 Y 0.1 O 3-δ ) and a redox-active mixed ionic electronic conductor (Ce 0.9 Pr 0.1 O 2-δ ), that may enable rapid proton surface exchange at the solid–gas interface and transport along the solid–solid heterointerfaces. We grew VANs by pulsed laser deposition and investigated the interplay between their processing conditions, structure, and proton and oxygen surface exchange kinetics. We varied the substrate temperature, laser repetition rate, laser fluence, and processing oxygen pressure. The crystallinity and phases were characterized by grazing-incidence X-ray diffraction, and the strain and structural order as a function of depth were evaluated by angle-dependent synchrotron X-ray pair distribution function analysis. To evaluate the potential for interdiffusion, the formation energies of substitutional defects were simulated with density functional theory. Corresponding structural analysis and elemental mapping were performed by scanning/transmission electron microscopy, energy-dispersive X-ray spectroscopy, and electron energy-loss spectroscopy, indicating distinct nanoscale compositional regions with a hierarchical structure embedded in individual VANs columns and minimal interdiffusion across a bilayer film. Proton and oxygen surface exchange coefficients (k H , k O ) and polarization resistances were evaluated by electrical and optical relaxations and impedance spectroscopy of VAN-incorporated protonic ceramic electrochemical cells, respectively, at 400–500 °C, demonstrating values comparable to some of the best-known triple and mixed conductors.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Neutron Reflectometry Reveals Diffusion in Contrast-Matched Brush Particle Bilayers

A material system for performing layer-spread experiments on brush particle bilayers is presented and used to determine the diffusion constant of brush particles in the melt state. Selective deuteration of the core and shell of organo-silica nanoparticles grafted with poly(methyl methacrylate) was used to match the scattering length density of the core and the polymer canopy layer. This subdued the scattering of particle cores (i.e., formfactor scattering) and enabled the analysis of the interdiffusion kinetics using neutron reflectivity. For low molecular grafts, i.e., grafts with a molecular weight below the entanglement limit, the interdiffusion kinetics revealed both a sub- and Fickian diffusion regime. The former was attributed to the local dynamics that was constrained by the slow-moving cores of neighboring brush particles that acted as long-lived physical cross-links. No transition to Fickian diffusion was observed for entangled systems, even at prolonged annealing times. This suggested a higher level of kinetic restraint in entangled brush particle melts as compared to, for example, star polymers with a comparable chain length for which Fickian diffusion has been reported under similar conditions.

Diffusion, Polymer Grafted Nanoparticles, Neutron ↗
DOE OSTI2021

Anion Exchange of Ruddlesden–Popper Lead Halide Perovskites Produces Stable Lateral Heterostructures

Heterostructures of three-dimensional (3D) halide perovskites are unstable because of facile anion interdiffusion at halide interfaces. Two-dimensional (2D) Ruddlesden–Popper halide perovskites (RPPs) show suppressed and anisotropic ion diffu-sion that could enable stable RPP heterostructures, yet the direct and general growth of lateral RPP heterostructures remains challenging. Here we show that halide miscibility in RPPs decreases with perovskite layer thickness (n), enabling the for-mation of sharp halide lateral heterostructures from n = 1 and 2 RP lead iodide microplates via anion exchange with hydro-gen bromide vapor. In contrast, RPPs with n = 3 form more diffuse lateral heterojunctions, more similar to those in 3D perov-skites. The anion exchange behaviors are further modulated by the spacer and A-site cations in the RPP structures. These new insights, and kinetic studies of the exchange reactions, enable the preparation of lateral heterostructures from various n = 2 RPPs that are more stable against anion interdiffusion and degradation for potential device applications.

Roy, Chris R.↗
DOE OSTI2022

Post-irradiation Examination Status for the BSU-269 Project

High-density uranium inter-metallic uranium silicide (U 3 Si 2 ) was initially considered as a potential advanced nuclear fuel for light water reactor (LWR) systems due to several advantages it demonstrated in thermophysical properties, chemical, and irradiation stability. In addition to understanding the basic thermophysical and mechanical properties of U 3 Si 2 under LWR irradiation conditions, it is important to assess its performance with advanced claddings such as FeCrAl, SiC, or conventional Zr-based claddings. Several aspects of the fuel cycle and fuel performance are being evaluated for U 3 Si 2 coupled with different types of claddings. To thoroughly characterize the U 3 Si 2 -cladding system, their chemical compatibilities and the potential for fuel-cladding chemical interaction (FCCI) must be addressed. Interdiffusion studies have been performed between U 3 Si 2 /Zry-4 and U 3 Si 2 /FeCrAl using diffusion couples. For the U 3 Si 2 /Zry-4 system, ZrSi 2 was the primary interdiffusion product observed at 800°C in addition to other secondary phases from the Zr alloying elements such as Fe and Cr. Low melting point U 6 Fe was also observed at 1000°C. For the U 3 Si 2 /FeCrAl system, at temperatures above 500°C, chemical diffusion Fe-U and Fe-U-Si was observed, increasing with rising temperatures. Although information from these non-irradiated tests is a fundamental first assessment, follow-up with focused irradiation tests is necessary. Irradiation can significantly alter the structure and evolution of the FCCI layers compared to the non-irradiated conditions.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗