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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 289 records · Page 16
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

A supported liquid membrane system for the selective recovery of rare earth elements from neodymium-based permanent magnets

We present that the rare earth elements (REEs) play a vital role in the development of green energy and high-tech industries. In order to meet the fast-growing demand and to ensure sufficient supply of the REEs, it is essential to develop an efficient REE recovery process from post-consumer REE-containing products. In this research effort, we have developed a supported liquid membrane system utilizing polymeric hollow fiber modules to extract REEs from neodymium-based magnets with neutral extractants such as tetraoctyl digylcol amide (TODGA). The effect of process variables such as REE concentration, molar concentration of acid, and membrane area on REE recovery was investigated. We have demonstrated the selective extraction and recovery of REEs such as Nd, Pr, and Dy without co-extraction of non-REEs from permanent NdFeB magnets through the supported liquid membrane system. The extracted REEs were then recovered by precipitation followed by the annealing step to obtain crystalline REE powders in nearly pure form. Finally, the recovered REE oxides were characterized by X-ray diffraction, scanning electron microscope coupled with energy-dispersive X-ray spectroscopy, and inductively coupled plasma–optical emission spectroscopy.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Permeability and Mineral Composition Evolution of Primary Seal and Reservoir Rocks in Geologic Carbon Storage Conditions

It has been reported that deep saline aquifers represent the largest geologic CO 2 storage resource. To better predict containment effectiveness and long-term reservoir behavior of these formations, it is important to understand the potential geochemically induced changes to the porosity and permeability of both the primary sealing formation and CO 2 storage formation rocks. To investigate these potential changes, an experimental study to probe the geochemical interactions of CO 2 /brine/rock system under geologic CO 2 storage conditions was conducted in a static reaction system. Marine shale (primary sealing formation) and Lower Tuscaloosa sandstone (CO 2 storage formation) core samples taken from the Plant Daniel CO 2 storage test site (Jackson County, Mississippi) were exposed to CO 2 -saturated brine in a batch reactor at relevant geologic storage conditions (85°C and 23.8 MPa CO 2 pressure) for 6 months. X-ray diffraction, scanning electron microscopy, computed tomography, and brine chemistry analyses were performed before and after the exposure. Permeability measurements from the marine shale and sandstone core samples before and after CO 2 /brine exposure indicated a significant effective permeability change. Sealing marine shale permeability increased following exposure while the permeability of the sandstone from the storage formation was observed to decrease. Analysis results of the primary sealing formation sample (marine shale) at the Plant Daniel CO 2 storage test site have not been reported before. In conclusion, the permeability decrease of the Lower Tuscaloosa sandstone sample reported in this study verifies the results reported in a previous study. These results have implications for the integrity of the primary seal in a CO 2 storage setting.

01 COAL, LIGNITE, AND PEAT↗
DOE OSTI2014

Structure and dynamics of C60 molecules on Au(111)

Earlier studies of C60 adsorption on Au(111) reported many interesting and complex features. We have performed coordinated low-energy electron diffraction, scanning tunneling microscopy (STM), and density functional theory studies to elucidate some of the details of the monolayer commensurate (2√3 × 2√3)R30° phase. We have identified the adsorption geometries of the two states that image as dim and bright in STM. These consist of a C60 molecule with a hexagon side down in a vacancy (hex-vac) and a C60 molecule with a carbon-carbon 6:6 bond down on a top site (6:6-top), respectively. We have studied the detailed geometries of these states and find that there is little distortion of the C60 molecules, but there is a rearrangement of the substrate near the C60 molecules. The two types of molecules differ in height, by about 0.7 Å, which accounts for most of the difference in their contrast in the STM images. The monolayer displays dynamical behavior, in which the molecules flip from bright to dim, and vice versa. We interpret this flipping as the result of the diffusion of vacancies in the surface layers of the substrate. Our measurements of the dynamics of this flipping from one state to the other indicate that the activation energy is 0.66 ± 0.03 eV for flips that involve nearest-neighbor C60 molecules, and 0.93 ± 0.03 for more distant flips. Based on calculated activation energies for vacancies diffusing in Au, we interpret these to be a result of surface vacancy diffusion and bulk vacancy diffusion. These results are compared to the similar system of Ag(111)-(2√3 × 2√3)R30°-C60. In both systems, the formation of the commensurate C60 monolayer produces a large number of vacancies in the top substrate layer that are highly mobile, effectively melting the interfacial metal layer at temperatures well below their normal melting temperatures.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Tunable magnetic ordering through cation selection in entropic spinel oxides

Twelve multicomponent spinels, comprised of (Mg, Cr, Mn, Co, Fe, Ni, Cu, and/or Zn)(Cr,Fe,orAl) 2 O 4 , were prepared using solid state synthesis methods, resulting in nine homogenous, single phase samples with a Fm-3m structure, and three samples with multiple phases. Using dc magnetometry in conjunction with x-ray diffraction, scanning electron microscopy with energy dispersive x-ray spectroscopy, and x-ray absorption spectroscopy, the effects of multicomponent material design on the structural, magnetic, and chemical properties are explored. The ferritic spinel high-entropy oxide (HEO) samples show high-temperature ferrimagnetic transitions and both ferritic and chromium-based HEO spinel samples show evidence of low-temperature antiferromagnetic ordering. Blocking temperatures are evident in some samples and magnetic transition temperatures are reported. Constituent valence states and temperature dependent valence is described for the example case of (Mg 0.2 Fe 0.2 Co 0.2 Ni 0.2 Cu 0.2 )Cr 2 O 4 , including the unexpected presence of Cr 4+ , indicating a 2–4 type spinel configuration. Valence trends for two ferritic HEO spinels are also discussed. Some of these compositions are synthesized for the first time and this work provides an investigation into the magnetic properties of the novel class of cubic spinel multicomponent oxides showing interesting behavior that warrants further investigation.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Microstructural and Superconducting Radiofrequency Properties of Multilayer Sequentially Sputtered Nb 3 Sn films

Nb 3 Sn is considered as a potential candidate for superconducting radiofrequency cavities for particle acceleration due to its higher transition temperature of 18.3 K and higher superheating field of 400 mT. Nb 3 Sn films can be grown inside the surface of a Nb cavity by sequentially sputtering multiple layers of Nb and Sn thin films followed by annealing at 950 °C for 3 h. We report on the properties of Nb 3 Sn films grown on Nb substrates by magnetron sputtering. The films’ crystal structure, surface morphology, and composition were characterized by X-ray diffraction, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. The films had a polycrystalline Nb 3 Sn structure with a fine-grain surface and an atomic Sn composition of ~23%. The RF surface resistance of the films was measured for different temperatures at 7.4 GHz to understand the feasibility of this method for the SRF application. The RF surface resistance of the films was 5 mΩ at 12 K, which is about 2 orders of magnitude higher than 60 μΩ previously measured in Nb 3 Sn films grown by Sn vapor diffusion. Finally, the sputtered film had a superconducting transition at 17.2 K, which is also lower than 17.9 K observed in Nb 3 Sn film prepared by vapor diffusion.

43 PARTICLE ACCELERATORS↗
DOE OSTI2013

Crystallization of rhenium salts in a simulated low-activity waste borosilicate glass

This study presents a new method for looking at the solubility of volatile species in simulated low-activity waste glass. The present study looking at rhenium salts is also applicable to real applications involving radioactive technetium salts. In this synthesis method, oxide glass powder is mixed with the volatiles species, vacuum-sealed in a fused quartz ampoule, and then heat-treated under vacuum in a furnace. This technique restricts the volatile species to the headspace above the melt but still within the sealed ampoule, thus maximizing the volatile concentration in contact with the glass. Various techniques were used to measure the solubility of rhenium in glass and include energy dispersive spectroscopy, wavelength dispersive spectroscopy, laser ablation inductively-coupled plasma mass spectroscopy, and inductively-coupled plasma optical emission spectroscopy. The Re-solubility in this glass was determined to be ~3004 parts per million Re atoms. Above this concentration, the salts separated out of the melt as inclusions and as a low viscosity molten salt phase on top of the melt observed during and after cooling. This salt phase was analyzed with X-ray diffraction, scanning electron microscopy as well as some of the other aforementioned techniques and identified to be composed of alkali perrhenate and alkali sulfate.

ampoule↗
DOE OSTI2016

Investigation of Nd x Y 0.25-x Zr 0.75 O 1.88 inert matrix fuel materials made by a co-precipitation synthetic route

Yttria-stabilized zirconia (YSZ) is a material that we are considering in our inert matrix fuel nuclear reactors, but a complete characterization of these materials is required for them to be licensed for use. A series of NdxY0.25–xZr0.75O1.88 materials have been synthesized using a co-precipitation method, and the thermal stability of these materials has been studied by annealing them at 1400 and 1500 °C. (Nd was used as surrogate for Am.) The long-range and local structures of the materials were characterized via powder X-ray diffraction, scanning electron microscopy, wavelength dispersive spectroscopy, and X-ray absorption spectroscopy at the Zr K- and Y K-edges. These results were compared with the previous characterization of Nd-YSZ materials synthesized using a ceramic method. Moreover, the results indicated that the ordering in the local metal–oxygen polyhedral remains relatively unaffected by the synthetic method, but there was increased long-range disorder in the materials prepared by the co-precipitation method. Further, it was found that the materials produced by the co-precipitation method were unexpectedly unstable when annealed at high temperature. This study highlights the importance of determining the effect of synthetic method on material properties and demonstrates how the co-precipitation route could be used to produce inert matrix fuels.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2015

Effect of deposition pressure on the microstructure and thermoelectric properties of epitaxial ScN(001) thin films sputtered onto MgO(001) substrates

Four epitaxial ScN(001) thin films were successfully deposited on MgO(001) substrates by dc reactive magnetron sputtering at 2, 5, 10, and 20 mTorr in an Ar/N2 ambient atmosphere at 650 °C. The microstructure of the resultant films was analyzed by x-ray diffraction, scanning electron microscopy, and transmission electron microscopy. Electrical resistivity, electron mobility and concentration were measured using the room temperature Hall technique, and temperature dependent in-plain measurements of the thermoelectric properties of the ScN thin films were performed. The surface morphology and film crystallinity significantly degrade with increasing deposition pressure. The ScN thin film deposited at 20 mTorr exhibits the presence of <221> oriented secondary grains resulting in decreased electric properties and a low thermoelectric power factor of 0.5 W/m-K² at 800 K. ScN thin films grown at 5 and 10 mTorr are single crystalline, yielding the power factor of approximately 2.5 W/m-K² at 800 K. The deposition performed at 2 mTorr produces the highest quality ScN thin film with the electron mobility of 98 cm² V⁻¹ s⁻¹ and the power factor of 3.3 W/m-K² at 800 K.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Collaboration for the Advancement of Indirect 3D Printing Technology

Amorphous powders often possess high hardness values and other useful mechanical properties. However, densifying these powders into complex shapes while retaining their unique properties is a challenge with standard processing routes. Pressureless sintering, for example, can densify intricate green parts composed of rapidly-solidified powders. But this process typically involves long exposures to elevated temperatures, during which the non-equilibrium microstructure of the powder can evolve towards lower energy configurations with inferior properties. Pressure-assisted compaction techniques, by contrast, can consolidate green parts with simple shapes while preserving the microstructure and properties of the powder feedstock. But parts made with these processes generally require additional post-processing, including machining, which introduces new challenges due to the high hardness of these materials. One processing route that can potentially avoid these issues is Indirect 3D Printing (I-3DP; aka Binder Jetting) followed by melt infiltration. In I-3DP, an organic binder is used to join powder feedstock, layer-by-layer, into a green part. In melt infiltration, this green preform is densified by placing it in contact with a molten alloy that wets the preform and wicks into the pores as a result of capillary forces. When these processes are paired together, they offer two key advantages for the densification of rapidly-solidified powders. The first advantage is that the timescale associated with melt infiltration is on the order of seconds for parts with cm-scale dimensions. So in many instances, infiltration requires only a brief thermal excursion that does not degrade the feedstock’s microstructure. The second advantage is that the combination of binder-jet 3D printing and melt infiltration gives fully-dense net shape objects, minimizing the need for subsequent post-processing. In this work, fully-dense, net shape objects have been fabricated from an amorphous powder using I-3DP and molten bronze infiltration while maintaining the amorphous microstructure. X-ray diffraction, scanning electron microscopy, and differential thermal analysis were used to characterize the structural evolution of the powder feedstock during an infiltration heating cycle. Microindentation and bend tests were performed on the infiltrated material to evaluate its mechanical properties. It was found that infiltration improved both the ductility and strength of the sintered preforms by eliminating the stress concentration at the interparticle necks. The infiltrated material had an 11 GPa Vickers hardness and moderate damage tolerance, making it well-suited for applications requiring hard, net shape parts.

42 ENGINEERING↗
DOE OSTI2018

Fabrication and Thermoelectric Characterization of Transition Metal Silicide-Based Composite Thermocouples

Metal silicide-based thermocouples were fabricated by screen printing thick films of the powder compositions onto alumina tapes followed by lamination and sintering processes. The legs of the embedded thermocouples were composed of composite compositions consisting of MoSi2, WSi2, ZrSi2, or TaSi2 with an additional 10 vol % Al2O3 to form a silicide–oxide composite. The structural and high-temperature thermoelectric properties of the composite thermocouples were examined using X-ray diffraction, scanning electron microscopy and a typical hot–cold junction measurement technique. MoSi2-Al2O3 and WSi2-Al2O3 composites exhibited higher intrinsic Seebeck coefficients (22.2–30.0 µV/K) at high-temperature gradients, which were calculated from the thermoelectric data of composite//Pt thermocouples. The composite thermocouples generated a thermoelectric voltage up to 16.0 mV at high-temperature gradients. The MoSi2-Al2O3//TaSi2-Al2O3 thermocouple displayed a better performance at high temperatures. The Seebeck coefficients of composite thermocouples were found to range between 20.9 and 73.0 µV/K at a temperature gradient of 1000 °C. There was a significant difference between the calculated and measured Seebeck coefficients of these thermocouples, which indicated the significant influence of secondary silicide phases (e.g., Mo5Si3, Ta5Si3) and possible local compositional changes on the overall thermoelectric response. The thermoelectric performance, high sensitivity, and cost efficiency of metal silicide–alumina ceramic composite thermocouples showed promise for high-temperature and harsh-environment sensing applications.

47 OTHER INSTRUMENTATION↗
DOE OSTI2025

In-Pile Irradiation Induced Defects and the Effect on Thermal Diffusivity of MgO

The effects of neutron irradiation temperature and dose on thermal diffusivity are compared between non-irradiated and in-pile irradiated MgO samples. MgO pellets were irradiated in-pile of the Advanced Test Reactor at Idaho National Laboratory. Samples were irradiated at 623 and 973 K to fast neutron fluences of 1 x 1025 (1.5 dpa) and 2 x 1025 n/m2 (3 dpa). Post irradiation examination included X-ray diffraction, scanning electron microscopy, laser flash thermal diffusivity, and transmission electron microscopy. The radiation induced thermophysical and structural evolution of MgO is reported

T. Moorea, Donald↗
DOE OSTI2016

Earth Abundant High Temperature Materials for Radioisotope Power Conversion System

Advances in high temperature thermoelectric materials were made and published. Two major developments are out lined in this final report. Alkaline earth Zintl phases represent the starting point of a series of compounds selected for development due to their high abundance as the supply chain and as the availability of certain rare earths (i.e. Yb) are limited and can be difficult to obtain. A new Zintl phase, Ca 14 MnSb 11-x Sn x , where Sb is replaced by Sn resulting in changes to the band structure and properties. The structures are investigated by powder diffraction and samples consolidated into fully dense pellets for thermoelectric measurements. The band structure of a reasonable structure, Ca 14 MgSb 7 Sn 4 , is calculated in order to better understand the properties. These Sn containing phases show improved thermoelectric properties over Ca 14 MgSb 11 by increasing the Seebeck while decreasing resistivity without significant impact to the already low thermal conductivity. In addition, a composite phase of Yb 14 MgSb 11 was investigated. Composite phases have been shown to improve both the thermoelectric efficiency and mechanical properties of materials. Here we demonstrate an improved thermoelectric figure of merit, power factor, and mechanical properties for the high-temperature p-type Zintl phase Yb 14 MgSb 11 . Composites with 0, 1, 2, 3, 4, 6, 8 volume % 6 – 10 µm reduced Fe powder were prepared via a fast, scalable mechanical milling and spark plasma sintering procedure. Powder X-ray diffraction, scanning electron microscopy, and transmission electron microscopy show that Fe is not incorporated into the Yb 14 MgSb 11 structure. First order reversal curves and scanning electron microscopy images show that the Fe inclusions are larger and closer together with increasing Fe content. Thermogravimetric and differential scanning calorimetry show that the composites are stable up to 1273 K. The elastic constants of the 8 volume % Fe composite were measured by resonant ultrasound spectroscopy and show that Yb 14 MgSb 11 becomes stiffer with increasing Fe volume % and SEM after indentations show crack arresting occurs at the Fe interface. Thermoelectric properties on dense pellets are measured from 300 K – 1273 K. The thermoelectric power factor (PF= $\frac{S^2}{ρ}$) increases with increasing Fe content, with the 8 volume % Fe resulting in 40% higher PF than pristine Yb 14 MgSb 11 . The increase in PF is attributed to a systematic reduction in electrical resistivity. Peak thermoelectric figure of merit (zT= ($\frac{S^2T}{κρ}$) is observed at 3 volume % Fe, an 11% improvement in zT compared to Yb 14 MgSb 11 . Yb 14 MgSb 11 composites with Fe are compatible with Ce 0.9 Fe 3.5 Co 0.5 Sb 12 for thermoelectric generator couple segmentation.

30 DIRECT ENERGY CONVERSION↗
DOE OSTI2021

Effect of substrate temperature on the growth of Nb$_3$Sn film on Nb by multilayer sputtering

Nb3Sn films were fabricated by multilayer sequential sputtering on Nb substrates at substrate temperatures ranging from room temperature to 250 °C. The film material properties were characterized by X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, atomic force microscopy, and transmission electron microscopy. The films’ superconducting properties were studied by four-point probe resistivity measurements from room temperature to below the superconducting critical temperature Tc. The highest Tc was17.76 K, when the multilayers were deposited at room temperature. A superconducting Nb3Sn thin film with a smoother surface morphology but a lower Tc of 17.58 K was obtained on the film deposited at a substrate temperature of 250 °C.

Sayeed, Md. Nizam↗
DOE OSTI2021

Fast Grain Mapping with Sub-Nanometer Resolution Using 4D-STEM with Grain Classification by Principal Component Analysis and Non-Negative Matrix Factorization

High-throughput grain mapping with sub-nanometer spatial resolution is demonstrated using scanning nanobeam electron diffraction (also known as 4D scanning transmission electron microscopy, or 4D-STEM) combined with high-speed direct-electron detection. An electron probe size down to 0.5 nm in diameter is used and the sample investigated is a gold–palladium nanoparticle catalyst. Computational analysis of the 4D-STEM data sets is performed using a disk registration algorithm to identify the diffraction peaks followed by feature learning to map the individual grains. Two unsupervised feature learning techniques are compared: principal component analysis (PCA) and non-negative matrix factorization (NNMF). The characteristics of the PCA versus NNMF output are compared and the potential of the 4D-STEM approach for statistical analysis of grain orientations at high spatial resolution is discussed.

47 OTHER INSTRUMENTATION↗
DOE OSTI2021

A Fast Algorithm for Scanning Transmission Electron Microscopy Imaging and 4D-STEM Diffraction Simulations

Scanning transmission electron microscopy (STEM) is an extremely versatile method for studying materials on the atomic scale. Many STEM experiments are supported or validated with electron scattering simulations. However, using the conventional multislice algorithm to perform these simulations can require extremely large calculation times, particularly for experiments with millions of probe positions as each probe position must be simulated independently. Recently, the plane-wave reciprocal-space interpolated scattering matrix (PRISM) algorithm was developed to reduce calculation times for large STEM simulations. Here, we introduce a new method for STEM simulation: partitioning of the STEM probe into “beamlets,” given by a natural neighbor interpolation of the parent beams. This idea is compatible with PRISM simulations and can lead to even larger improvements in simulation time, as well requiring significantly less computer random access memory (RAM). We have performed various simulations to demonstrate the advantages and disadvantages of partitioned PRISM STEM simulations. We find that this new algorithm is particularly useful for 4D-STEM simulations of large fields of view. We also provide a reference implementation of the multislice, PRISM, and partitioned PRISM algorithms.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2018

Hardness and modulus of Fe2B, Fe3(C,B), and Fe23(C,B)6 borides and carboborides in the Fe-C-B system

Highlights: • Hardness and modulus of the Fe{sub 2}B, Fe{sub 3}(C,B), Fe{sub 23}(C,B){sub 6} and M{sub 7}C{sub 3} phases are analyzed. • Hardness and modulus of the Fe{sub 3}(C,B) phase are increasing with its B content. • Size effects are apparent for hardness of Fe{sub 2}B, Fe{sub 3}(C,B), Fe{sub 23}(C,B){sub 6} and M{sub 7}C{sub 3}. • The model of Nix and Gao was used to evaluate the load-independent hardness H{sub 0}. • Hardness ranking is Fe{sub 2}B > M{sub 7}C{sub 3} > Fe{sub 3}(C,B) > Fe{sub 23}(C,B){sub 6} - Abstract: This work provides a comparative and comprehensive study of the indentation hardness and indentation modulus of iron-rich borides and carboborides of types Fe{sub 2}B, Fe{sub 3}(C,B), and Fe{sub 23}(C,B){sub 6}. In addition, the hardness and elastic modulus of Cr-rich M{sub 7}C are investigated for comparative purposes. We investigated the impact of increasing B content and indentation size effect (ISE). The phases of interest were stabilized in cast Fe-C-B alloys that varied with respect to the B / (B + C) ratio and heat treatment. The resulting microstructures were characterized by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), and wavelength X-ray spectroscopy (WDS). Dynamic in-situ nanoindentation experiments based on the method of continuous stiffness measurement (CSM) were coupled to SEM and EBSD investigations to determine the mechanical properties of the individual borides and carboborides as a function of the indentation depth. The results were compared to values obtained for the Cr-rich M{sub 7}C{sub 3} carbide. It was found that the hardness of the B-rich Fe{sub 3}(C{sub ,}B) phase is considerably higher than pure Fe{sub 3}C and increases with increasing B content. The ISE was present in all investigated phases, and the hardness decreased as a function of indentation depth. The hardness at infinite indentation depth H{sub 0} was estimated according to the model of Nix and Gao. The Fe{sub 2}B phase was found to be the hardest phase (H{sub 0} = 19.04 GPa), followed by M{sub 7}C{sub 3} (H{sub 0} = 16.43 GPa), Fe{sub 3}(C,B) (H{sub 0} = 11.18 to 12.24 GPa), and Fe{sub 23}(C,B){sub 6} (H{sub 0} = 10.39 GPa).

36 MATERIALS SCIENCE↗
DOE OSTI2018

Study of the scale formed on super 304H boiler tube steels after long-term steam oxidation at high temperatures

Highlights: • Steam oxidation tests were performed on the conventional and shot-peened Super304H boiler tube. • A continuous amorphous SiO{sub 2} layer separated the metal from the scale in shot-peened specimen. • The SiO{sub 2} layer enhanced the formation of dense Cr{sub 2}O{sub 3} and FeCr{sub 2}O{sub 4} layers. • The scale on shot-peened specimens is stable upon steam temperature and time increase. Steam oxidation of a Super 304H boiler tube was performed at steam temperatures of 650 °C and 700 °C for time durations up to 5000 h. The oxidation scale outcomes which formed on as-received untreated and shot-peened (SP) tubes were studied using X-ray diffraction (XRD), scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), and transmission electron microscopy (TEM). γ-Grain nanocrystallization on the surface of the SP specimen generated an abundant fraction of grain boundary that guaranteed the formation of a continuous amorphous SiO{sub 2} layer at the metal-scale interface that enhanced the formation of dense Cr{sub 2}O{sub 3} and FeCr{sub 2}O{sub 4} in the scale. Scale breakaway along defects in the outer layer of the scale was accelerated by the steam temperature in the untreated specimens, whereas the scale that formed on the SP specimens appeared to be stable.

36 MATERIALS SCIENCE↗