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At least 1,027 records · Page 57
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Alkali-activated slag (AAS) and OPC-based composites containing crumb rubber aggregate: Physico-mechanical properties, durability and oxidation of rubber upon NaOH treatment

Value-added utilization of waste tires in cementitious materials has been studied for decades, whereas the synergy between rubber and alkali-activated cements deserves more investigations. To this end, we compared physico-mechanical and durability properties of alkali-activated slag (AAS) and OPC-based composites containing NaOH-pretreated/as-received crumb rubber (CR). It was found that the incorporation of CR had both positive and negative effects on specimens due to its special attributes. CR reduced electrical conductivity which was associated with the ion transport ability, since it worked as an electrical insulator and increased hydrophobicity of pore walls. The sulfate expansion decreased with CR content because the flow of sulfate ions was demobilized, and the flexibility of CR relieved the internal stress. CR also improved the freeze-thaw durability of composites if the total CR content was less than 30% in specimens. However, the low Young's modulus of CR impaired the compressive strength and failed to effectively control the total shrinkage upon drying. The composites with CR must avoid high temperature exposure which resulted in the pyrolysis of rubber. In addition, the NaOH pretreatment enhanced adhesion between CR and hydrated cement and improved overall performances of composites. The FTIR spectra confirmed the NaOH-induced accelerated oxidation of CR surface and the generation of polar functional groups including carbonyl and carboxyl groups, increasing the total surface energy of rubber. More importantly, the alkali-activation process for AAS could treat the CR aggregate in the meantime, which means the use of CR in alkali-activated cements does not require the pretreatment of CR before blending.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Monitoring of helium gas leakage from canister storing spent nuclear fuel: Radiological consequences and management

Chloride-induced stress corrosion cracking (CISCC) of canisters has been identified as a potential degradation mechanism requiring ageing management — especially in a marine air environment. Methods for monitoring helium gas leakage from canisters have been developed on the basis of a phenomenon that the bottom temperature of the canister increases as the top temperature of the canister decreases when helium gas leaks during storage. In this paper, we consider the radiological consequences of CISCC based on two scenarios of helium gas leakage and propose effective management that includes a timeline for monitoring and mitigation. Monitoring helium gas leakage by measuring the difference in temperature between canister surfaces in the dry cask storage of spent fuel (SF) can detect leakage before SF undergoes oxidation as a result of air ingress and before country-specific regulatory limits of off-site doses are exceeded, thereby enabling mitigatory action.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2023

Photoluminescence of Cr 3+ in β-Ga 2 O 3 and (Al 0.1 Ga 0.9 ) 2 O 3 under pressure

The effects of pressure on single crystals of Cr-doped gallium oxide (β-Ga 2 O 3 :Cr 3+ ) and aluminum gallium oxide [(Al 0.1 Ga 0.9 ) 2 O 3 ] were examined by measuring the wavelength shift in the spectral R lines. Photoluminescence (PL) spectra of these materials were collected from samples in diamond anvil cells at pressures up to 9 GPa. The β-Ga 2 O 3 :Cr 3+ R lines were found to shift linearly under hydrostatic pressure. The (Al 0.1 Ga 0.9 ) 2 O 3 R lines also show a linear shift but the R 1 line shifted less than for β-Ga 2 O 3 :Cr 3+ . The ratio of R 2 to R 1 peak areas vs pressure is dominated by nonradiative recombination. X-ray diffraction measurements of (Al 0.1 Ga 0.9 ) 2 O 3 indicate that its equation of state is similar to that of β-Ga 2 O 3 . β-Ga 2 O 3 :Cr 3+ was examined under non-hydrostatic conditions by using mineral oil as a pressure transmitting medium. Similar to the case in ruby, the R 1 line is much more sensitive to non-hydrostatic stress than R 2 . Spatially resolved PL of a sample at 8 GPa in mineral oil showed significant variations in the R 1 emission wavelength. Furthermore, these results suggest that the R 1 line can serve as a sensitive probe of alloy composition and non-hydrostatic stress, while the R 2 line is insensitive to these perturbations.

36 MATERIALS SCIENCE↗
NASA NTRS1974

Coatings for directional eutectics

Coating compositions were evaluated for oxidation protection of directionally solidified composite alloy NiTaC-13. These coatings included three NiCrAlY compositions (30-5-1, 25-10-1 and 20-15-1), two FeCrAlY compositions (30-5-1 and 25-10-1), a CoCrAlY composition (25-10-1), and one duplex coating, Ni-35Cr + Al. Duplicate pin samples of each composition were evaluated using two cyclic furnace oxidation tests of 100 hours at 871 C and 500 hours at 1093 C. The two best coatings were Ni-20Cr-15Al-lY and Ni-35Cr + Al. The two preferred coatings were deposited on pins and were evaluated in detail in .05 Mach cyclic burner rig oxidation to 1093 C. The NiCrAlY coating was protective after 830 hours of cycling, while the duplex coating withstood 630 hours. Test bars were coated and cycled for up to 500 hours. Tensile tests indicated no effect of coatings on strength. In 871 C air stress rupture, a degradation was observed for coated relative to bare material. The cycled NiCrAlY coating offered excellent protection with properties superior to the bare cycled NiTaC-13 in 1093 C air stress rupture.

Jackson, M. R.↗
NASA NTRS1983

Long life nickel electrodes for a nickel-hydrogen cell. I Initial performance

In order to develop a long life nickel electrode for a Ni/H2 cell, an investigation was begun to study the effects of sinter structure and active material loading level on the long life performance of nickel electrodes. This paper is a report on the initial performance of these electrodes as a part of an accelerated life test program. Seven different types of nickel plaques were made which included three levels of both their mechanical strength and median pore size. These plaques were impregnated with three levels of active material loading. The resultant electrodes were tested by a 200-cycle stress test which was conducted in flooded electrolyte, and also for initial performance in a Ni/H2 boiler plate cell. An interesting and unexpected observation was that an increased initial utilization of the active material was due more to its complete discharge to the lower average oxidation state than its increased charge acceptance in the charged state.

Lim, H. S.↗
NASA NTRS1996

Fluid flow stimulates rapid and continuous release of nitric oxide in osteoblasts

Interstitial fluid flow may mediate skeletal remodeling in response to mechanical loading. Because nitric oxide (NO) has been shown to be an osteoblast mitogen and inhibitor of osteoclastic resorption, we investigated and characterized the role of fluid shear on the release of NO in osteoblasts. Rat calvarial cells in a stationary culture produced undetectable levels of NO. Fluid shear stress (6 dyn/cm2) rapidly increased NO release rate to 9.8 nmol.h-1.mg protein-1 and sustained this production for 12 h of exposure to flow. Cytokine treatment also induced NO synthesis after a 12-h lag phase of zero production, followed by a production rate of 0.6 nmol.h-1.mg protein-1. Flow-induced NO production was blocked by the NO synthase (NOS) inhibitor NG-amino-L-arginine, but not by dexamethasone, which suggests that the flow stimulated a constitutive NOS isoform. This is the first time that a functional constitutively present NOS isoform has been identified in osteoblasts. Moreover, fluid flow represents the most potent stimulus of NO release in osteoblasts reported to date. Fluid flow-induced NO production may therefore play a primary role in bone maintenance and remodeling.

NASA Discipline Cell Biology↗
NASA NTRS2002

Tensile Behavior of As-Fabricated and Burner-Rig Exposed SiC/SiC Composites with Hi-Nicalon Type-S Fibers

Tensile stress-strain curves were measured at room temperature and 1315 C for 2D-woven SiC/BN/SiC ceramic matrix composites (CMC) reinforced by two variations of Hi-Nicalon Type-S SiC fibers. These fibers, which contained a thin continuous carbon-rich layer on their as-produced surface, provided the as-fabricated CMC with good composite behavior and an ultimate strength and strain of -350 MPa and -0.5%, respectively. However, after un-stressed burner-rig exposure at 815 C for -100 hrs, CMC tensile specimens with cut edges and exposed interphases showed a significant decrease in ultimate properties with effectively no composite behavior. Microstructural observations show that the degradation was caused by internal fiber-fiber oxide bonding after removal of the carbon-rich fiber surface layer by the high-velocity combustion gases. On the other hand, SiC/BN/SiC CMC with Sylramic-iBN fibers without carbon-rich surfaces showed higher as-fabricated strength and no loss in strength after the same burner rig exposure. Based on the strong role of the carbon layer in these observations, a process method was developed and demonstrated for achieving better strength retention of Hi-Nicalon Type-S CMC during burner rig exposure. Other general approaches for minimizing this current deficiency with as-produced Type-S fibers are discussed.

Yun, H. M.↗
NASA NTRS1974

Strengthening of oxidation resistant materials for gas turbine applications

Silicon nitride and silicon carbide ceramics were treated to form compressive surface layers. On the silicon carbide, quenching and thermal exposure treatments were used, and on the silicon nitride, quenching, carburizing, and a combination of quenching and carburizing were used. In some cases substantial improvements in impact resistance and/or flexural strength were observed. The presence of compressive surface stresses was demonstrated by slotted rod tests.

Kirchner, H. P.↗
NASA NTRS1989

Properties of oxide dispersion strengthened alloys

A contrast is drawn between the behavior of ODS alloys' matrix compositions and that of more conventional alloys. Mechanical property enhancements associated with ODS alloys are accounted for by both the presence of the dispersoids and, in some cases, the smaller size and number of secondary phases. Data obtained for ODS materials to date indicate the presence of three different threshold stresses, due to dislocation-particle interactions, diffusional creep/grain boundary sliding, and, in the case of the MA 956 ODS alloy, crack nucleation and growth processes. It is critical to establish which threshold stress is in effect, since the latter two stresses can result in failure by cracking.

Whittenberger, J. Daniel↗
DOE OSTI2026

Investigation of nonlinear mechanical behavior of two superfine-grained graphites with DIC assisted disc splitting test

Using standardized uniaxial tensile test specimens is not practical due to the limited volumes in irradiation capsules, molten salt degradation facilities, or oxidation apparatus. The ASTM International Standard Test Method for Tensile Strength Estimate by Disc Compression of Manufactured Graphite (ASTM D8289) was developed to provide a convenient way for estimating tensile strength. Unlike the traditional uniaxial tensile test in ASTM C749 (International Standard Test Method for Tensile Stress–Strain of Carbon and Graphite), which uses dog-bone shaped specimens larger than 12.95 mm × 120.65 mm, the ASTM D8289 standard uses smaller discs with diameters of 6–12.7 mm. A digital image correlation (DIC) system, which uses a full-field noncontact surface displacement measurement technique, was applied along with the ASTM D8289 disc splitting test on IG-110 samples and compared with previous measurements from Mersen 2114 samples. Results confirmed that the DIC technique can measure the surface displacement/strain on these small (Ø6 mm × 3 mm) graphite specimens with good repeatability. However, Mersen 2114 and IG-110 samples exhibited strain discrepancies when DIC measurements were compared with analytical and finite element simulation values. The loading history and strain results also indicated different mechanical behaviors between Mersen 2114 and IG-110, particularly the nonlinear behavior of the IG-110 samples. Good agreement was observed by comparing the splitting tensile strengths of two superfine-grained grades with results from other work. The specimen size effect is discussed when comparing the splitting tensile strength with corresponding uniaxial tensile strength of these two graphite grades.

Lin, Lianshan [ORNL] (ORCID:0000000203399219)↗
DOE OSTI2020

Techniques to characterize dynamics in biomaterials microenvironments: XPCS and microrheology of alginate/PEO–PPO–PEO hydrogels

Many recent studies have highlighted the timescale for stress relaxation of biomaterials on the microscale as an important factor in regulating a number of cell-material interactions, including cell spreading, proliferation, and differentiation. Relevant timescales on the order of 0.1–100 s have been suggested by several studies. While such timescales are accessible through conventional mechanical rheology, several biomaterials have heterogeneous structures, and stress relaxation mechanisms of the bulk material may not correspond to that experienced in the cellular microenvironment. Here we employ X-ray photon correlation spectroscopy (XPCS) to explore the temperature-dependent dynamics, relaxation time, and microrheology of multicomponent hydrogels comprising of commercial poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide) (PEO–PPO–PEO) triblock copolymer F127 and alginate. Previous studies on this system have shown thermoreversible behavior in the bulk oscillatory shear rheology. At physiological temperatures, bulk rheology of these samples shows behavior characteristic of a soft solid, with G' > G" and no crossover between G' and G" over the measurable frequency range, indicating a relaxation time >125 s. By contrast, XPCS-based microrheology shows viscoelastic behavior at low frequencies, and XPCS-derived correlation functions show relaxation times ranging from 10–45 s on smaller length scales. Finally, we are able to use XPCS to effectively probe the viscoelasticity and relaxation behavior within the material microenvironments.

36 MATERIALS SCIENCE↗
NASA NTRS1972

Metal-metal laminar composites for high-temperature applications.

The potentialities of composites consisting of multiple layers of tungsten alternated by layers of Nichrome V (a ductile, weaker than tungsten, but oxidation resistant alloy) at temperatures on the order of 2000 F are studied experimentally. The highest tensile strengths obtained for the composites were 600 MN/sq m (87,000 psi) at 1600 F and 448 MN/sq m (65,000 psi) at 2000 F. Highest 100-hr stress-rupture strengths at these temperatures were 387 MN/sq m (56,000 psi) and 121 MN/sq m (17,500 psi), respectively.

Hoffman, C. A.↗
NASA NTRS1999

Method for Forming Fiber Reinforced Composite Bodies with Graded Composition and Stress Zones

A near-net, complex shaped ceramic fiber reinforced silicon carbide based composite bodies with graded compositions and stress zones is disclosed. To provide the composite a fiber preform is first fabricated and an interphase is applied by chemical vapor infiltration, sol-gel or polymer processes. This first body is further infiltrated with a polymer mixture containing carbon, and/or silicon carbide, and additional oxide, carbide, or nitride phases forming a second body. One side of the second body is spray coated or infiltrated with slurries containing high thermal expansion and oxidation resistant. crack sealant phases and the other side of this second body is coated with low expansion phase materials to form a third body. This third body consisting of porous carbonaceous matrix surrounding the previously applied interphase materials, is then infiltrated with molten silicon or molten silicon-refractory metal alloys to form a fourth body. The resulting fourth body comprises dense composites consisting of fibers with the desired interphase which are surrounded by silicon carbide and other second phases materials at the outer and inner surfaces comprising material of silicon, germanium, refractory metal suicides, borides, carbides, oxides, and combinations thereof The resulting composite fourth body has different compositional patterns from one side to the other.

Singh, Mrityunjay↗
DOE OSTI2022

Strain-retardant coherent perovskite phase stabilized Ni-rich cathode

The use of state-of-the-art Ni-rich layered oxides (LiNi x Co y Mn 1-x-y O 2 , x > 0.5) as the cathode material for lithium-ion batteries can push the energy and power density to a higher level than is currently available. However, volume variation associated with anisotropic lattice strain and stress that is being developed during lithium (de) intercalation induces severe structural instability and electrochemical decay of the cathode materials, which is amplified further when the battery is operating at a high voltage (above 4.5 V), which is essential for unlocking its high energy. Even after much effort by the research community, an intrinsic strain-retardant method for directly alleviating the continuous accumulation of lattice strain remains elusive. By introducing a coherent perovskite phase into the layered structure functioning as a ‘rivet’, we significantly mitigate the pernicious structural evolutions by a pinning effect. The lattice strain evolution in every single cycle is markedly reduced by nearly 70% when compared with conventional materials, which significantly enhances morphological integrity leading to a notable improvement in battery cyclability. This strain-retardant approach broadens the perspective for lattice engineering to release the strain raised from lithium (de)intercalation and paves the way for the development of high-energy-density cathodes with long durability.

25 ENERGY STORAGE↗
DOE OSTI2020

Surface plasmon driven near- and midinfrared photoconductivity in ligand-free ITO nanocrystal films

Semiconductor nanocrystals (NCs) offer exciting opportunities to deploy infrared optoelectronic technology in a variety of applications that are off-limits to conventional single-crystalline materials. However, the performance and stability of state-of-the-art NC-based devices strongly depend on the details of the NC surface and its passivating ligands. Here, the authors use indium tin oxide NC films stripped of organic ligands and conformally coated with Al 2 O 3 to show that absorption enabled by infrared localized surface plasmon resonances permit infrared photoconduction. For Au electrodes, these metallic NC films exhibit stable photoconductive performance over months in ambient and under electrical stress.

36 MATERIALS SCIENCE↗
NASA NTRS1973

Deformation processes in forging ceramics

The deformation processes involved in the forging of refractory ceramic oxides were investigated. A combination of mechanical testing and forging was utilized to investigate both the flow and fracture processes involved. Deformation studies of very fine grain Al203 revealed an apparent transition in behavior, characterized by a shift in the strain rate sensitivity from 0.5 at low stresses to near unity at higher stresses. The behavior is indicative of a shift in control between two dependent mechanisms, one of which is indicated to be cation limited diffusional creep with significant boundary enhancement. The possible contributions of slip, indicated by crystallographic texture, interface control of the diffusional creep and inhomogeneous boundary sliding are also discussed. Additional experiments indicated an independence of deformation behavior on MgO doping and retained hot pressing impurities, at least for ultrafine grained material, and also an independence of test atmosphere.

Cannon, R. M.↗
NASA NTRS1977

Creep and tensile properties of several oxide-dispersion-strengthened nickel-base alloys at 1365 K

The tensile properties at room temperature and at 1365 K and the tensile creep properties at low strain rates at 1365 K were measured for several oxide-dispersion-strengthened (ODS) alloys. The alloys examined included ODS Ni, ODS Ni-20Cr, and ODS Ni-16Cr-Al. Metallography of creep tested, large grain size ODS alloys indicated that creep of these alloys is an inhomogeneous process. All alloys appear to possess a threshold stress for creep. This threshold stress is believed to be associated with diffusional creep in the large grain size ODS alloys and normal dislocation motion in perfect single crystal (without transverse low angle boundaries) ODS alloys. Threshold stresses for large grain size ODS Ni-20Cr and Ni-16Cr-Al type alloys are dependent on the grain aspect ratio. Because of the deleterious effect of prior creep on room temperature mechanical properties of large grain size ODS alloys, it is speculated that the threshold stress may be the design limiting creep strength property.

Wittenberger, J. D.↗
DOE OSTI2025

Hydride Reprecipitation in Prototypical 17x17 PWR Fuel Rods after Simulated Vacuum Drying Conditions

Light water reactor (LWR) fuel rod cladding picks up hydrogen as it oxidizes in reactor. Once the hydrogen concentration exceeds the solubility limit, zirconium hydride platelets precipitate, generally in the circumferential direction. In preparation for dry storage, elevated temperatures can dissolve some of the circumferential hydrides, which during cooling can then reprecipitate in a direction perpendicular to the hoop stress (radially). From 2019 to 2024, ORNL published a series of reports that included metallographic observations of cladding after a thermal transient to 400°C followed by slow cooling. The simulated dry storage process was performed on three full-length 17x17 PWR fuel rods at their as-discharged rod internal pressure. There were two important observations from the metallographic examinations of these heat-treated rods: (1) the propensity for hydride reorientation is strongly influenced by nearby as-discharged precipitated hydrides, (2) the radial hydrides observed near the cladding inner diameter were often associated with cracks in the pellet. Subsequent modeling using the BISON fuel performance code that considered the effects of pellet cracks and pellet-cladding bonding observed in high-burnup fuel support the conclusion that pellet cracks enhance the local hoop stress in the cladding creating preferential sites for hydride reorientation, and that the influence of the pellet cannot be ignored in accurate fuel rod performance predictions.

Montgomery, Rose [ORNL] (ORCID:0000000286038936)↗