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DOE OSTI2022

Nanoporous Titanium (Oxy)nitride Films as Broadband Solar Absorbers

Broadband absorption of solar light is a key aspect in many applications that involve an efficient conversion of solar energy to heat. Titanium nitride (TiN)-based materials, in the form of periodic arrays of nanostructures or multilayers, can promote significant heat generation upon illumination thanks to their efficient light absorption and refractory character. In this work, pulsed laser deposition was chosen as a synthesis technique to shift metallic bulk-like TiN to nanoparticle-assembled hierarchical oxynitride (TiO x N y ) films by increasing the background gas deposition pressure. The nanoporous hierarchical films exhibit a tree-like morphology, a strong broadband solar absorption (~90% from the UV to the near-infrared range), and could generate temperatures of ~475 °C under moderate light concentration (17 Suns). The high heat generation achieved by treelike films is ascribed to their porous morphology, nanocrystalline structure, and oxynitride composition, which overall contribute to a superior light trapping and dissipation to heat. These properties pave the way for the implementation of such films as solar absorber structures.

14 SOLAR ENERGY↗

DOE OSTI2022

Comparison of ablators for the polar direct drive exploding pusher platform

We examine the performance of pure boron, boron carbide, high density carbon, and boron nitride ablators in the polar direct drive exploding pusher (PDXP) platform. The platform uses the polar direct drive conguration at the National Ignition Facility to drive high ion temperatures in a room temperature capsule and has potential applications for plasma physics studies and as a neutron source. The higher tensile strength of these materials compared to plastic enables a thinner ablator to support higher gas pressures, which could help optimize its performance for plasma physics experiments, while ablators containing boron enable the possiblity of collecting addtional data to constrain models of the platform. Applying recently developed and experimentally validated equation of state models for the boron materials, we examine the performance of these materials as ablators in 2D simulations, with particular focus on changes to the ablator and gas areal density, as well as the predicted symmetry of the inherently 2D implosion.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2020

Band alignments and polarization properties of the Zn-IV-nitrides

Zn-IV-nitrides have a range of potential applications in electronic and optoelectronic devices and can be integrated with currently used III-nitride semiconductors and their alloys. Using hybrid density functional theory, we examine band gaps, band offsets, and polarization properties of the Zn-IV-nitrides and the ramifications of these properties on heterointerfaces formed between the Zn-IV-nitrides and III-nitrides. Here, we find a type-II band alignment between ZnGeN 2 and GaN, where the valence band of GaN is 0.28 eV above the valence band of ZnGeN 2 . Heterostructures between Zn-IV-nitrides and III-nitrides result in interface charges that allow for novel heterostructures and increased control over polarization fields. We find that an interface between In x Ga 1-x N and ZnGeN 2 can lead to zero interfacial polarization charge; however, the band alignments are unfavorable for carrier confinement in light-emitting devices. At the interface between AlN and ZnSiN 2 , we predict a large two-dimensional electron gas to form, confined to the ZnSiN 2 layer.

36 MATERIALS SCIENCE↗

DOE OSTI2026

Improvements in the Sample Space for the Backscattering Silicon Spectrometer (BASIS)

The increase in neutron flux at the Oak Ridge National Laboratory (ORNL) Spallation Neutron Source (SNS), currently operating at 2.0 MW proton beam power, has created new opportunities for higher-throughput neutron scattering experiments while also increasing the importance of minimizing background scattering and optimizing sample-environment operations. To address these challenges on the Backscattering Silicon Spectrometer (BA-SIS), several upgrades were developed and evaluated, including boron carbide (B₄C) masking for flat-plate sample containers, multi-cell sample holders used with a vertically translating sample stick, and an automated helium pump and purge (HPP) system for closed-cycle refrigerators. Neutron diffraction measurements demonstrate that B₄C masks reduce background scattering by 49–67%, outperforming both borated aluminum and boron nitride masks while introducing no additional Bragg reflections within the instrument’s accessible Q-range. Commissioning tests of a double-cell flat-plate sample contain-er showed no measurable crosstalk between adjacent sample compartments and con-firmed stable thermal performance, enabling multiple samples to be measured without re-peated temperature cycling. In addition, the automated HPP system provided reproducible sample-space gas handling with approximately ±1 mbar precision while reducing the need for operator intervention and supporting remote operation. Together, these developments improve signal-to-noise performance, increase experimental throughput, and enhance operational efficiency at BASIS, supporting the instrument’s continued operation under higher neutron flux conditions.

Jalarvo, Niina [ORNL] (ORCID:0000000306446866)↗

NASA NTRS1973

Volatile element chemistry of selected lunar, meteoritic, and terrestrial samples

Using vacuum pyrolysis and high resolution mass spectrometry, a study is made of the gas release patterns of representative lunar samples, meteorites, terrestrial samples, and synthetic samples doped with various sources of carbon and nitrogen. The pyrolytic gas evolution patterns were intercorrelated, allowing an assessment of the possible sources of the volatilizable material in the lunar samples to be made. Lightly surface adsorbed species and more strongly chemisorbed species are released from ambient to 300 C and from 300 to 500 C, respectively. The low-temperature volatiles (less than 500 C) derived from various chondrites correlate well with the gas evolution patterns of volatile-rich samples, as for example 74220 and 61221. Solar wind entrapped species and molecules derived from reactions probably in the grain surfaces are evolved from about 500 to 700 C, respectively. Solar wind implanted C, N, and S species are generated from 750 to 1150 C, probably by reaction with the mineral matrix during the annealing process. Possible indigenous and/or refractory carbide, nitride, and sulfide C, N, and S are released in the region from 1200 C to fusion.

Simoneit, B. R.↗

DOE OSTI2023

Heavy ion irradiation induced failure of gallium nitride high electron mobility transistors: effects of in-situ biasing

Abstract While radiation is known to degrade AlGaN/GaN high-electron-mobility transistors (HEMTs), the question remains on the extent of damage governed by the presence of an electrical field in the device. In this study, we induced displacement damage in HEMTs in both ON and OFF states by irradiating with 2.8 MeV Au 4+ ion to fluence levels ranging from 1.72 × 10 10 to 3.745 × 10 13 ions cm −2 , or 0.001–2 displacement per atom (dpa). Electrical measurement is done in situ , and high-resolution transmission electron microscopy (HRTEM), energy dispersive x-ray (EDX), geometrical phase analysis (GPA), and micro-Raman are performed on the highest fluence of Au 4+ irradiated devices. The selected heavy ion irradiation causes cascade damage in the passivation, AlGaN, and GaN layers and at all associated interfaces. After just 0.1 dpa, the current density in the ON-mode device deteriorates by two orders of magnitude, whereas the OFF-mode device totally ceases to operate. Moreover, six orders of magnitude increase in leakage current and loss of gate control over the 2-dimensional electron gas channel are observed. GPA and Raman analysis reveal strain relaxation after a 2 dpa damage level in devices. Significant defects and intermixing of atoms near AlGaN/GaN interfaces and GaN layer are found from HRTEM and EDX analyses, which can substantially alter device characteristics and result in complete failure.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗

NASA NTRS1991

Advanced Turbine Technology Applications Project (ATTAP)

This report summarizes work performed in support of the development and demonstration of a structural ceramic technology for automotive gas turbine engines. The AGT101 regenerated gas turbine engine developed under the previous DOE/NASA Advanced Gas Turbine (AGT) program is being utilized for verification testing of the durability of next-generation ceramic components and their suitability for service at reference powertrain design conditions. Topics covered in this report include ceramic processing definition and refinement, design improvements to the test bed engine and test rigs, and design methodologies related to ceramic impact and fracture mechanisms. Appendices include reports by ATTAP subcontractors addressing the development of silicon nitride and silicon carbide families of materials and processes.

Source record↗

NASA NTRS1979

Development of silicon nitride of improved toughness

The application of reaction sintered Si2N4 energy absorbing surface layers to hot-pressed Si3N4 was investigated. The surface layer was formed by in-place nitridation of silicon powder. It was found that reaction sintered Si3N4 layers of 1 mm thickness, fabricated from either -100, +200, -200, or -325 mesh Si powder and nitrided in 96% N2/4% H2 so that approximately 20-25 vol % unnitrided Si remained in the layer, resulted in a sevenfold increase in ballistic impact resistance of a 0.64 cm thick hot-pressed SI3N4 substrate from RT 1370 C. Both NC-132 SI3N4, with MgO additive, and NCX-34 Si3N4, with Y2O3 additive, were evaluated as substrate material. The finer grain size -200 and -325 mesh nitrided Si layers were for their smoothness and relatively high density. It was found that nitriding in N2/H2 mixtures, rather than pure N2, resulted in a microstructure that did not substantially degrade the strength of the hot-pressed Si3N4 substrate. Thermal cycling tests on the RSSN/HPSN combinations from 200 C to 1370 C for 75 cycles in air did not degrade the impact resistance nor the interfacial bonding, although a large amount of internal silica formation occurred within the RSSN layer. Mach 0.8, 5 hr, hot gas erosion tests showed no surface recession of RSSN layers at 1200 C and slight surface recession at 1370 C.

Brennan, J. J.↗

NASA NTRS1978

Materials review for improved automotive gas turbine engine

The potential role of superalloys, refractory alloys, and ceramics in the hottest sections of engines operating with turbine inlet temperatures as high as 1370 C is examined. The convential superalloys, directionally solidified eutectics, oxide dispersion strenghened alloys, and tungsten fiber reinforced superalloys are reviewed and compared on the basis of maximum turbine blade temperature capability. Improved high temperature protective coatings and special fabrication techniques for these advanced alloys are discussed. Chromium, columbium, molybdenum, tantalum, and tungsten alloys are also reviewed. Molbdenum alloys are found to be the most suitable for mass produced turbine wheels. Various forms and fabrication processes for silicon nitride, silicon carbide, and SIALON's are investigated for use in highstress and medium stress high temperature environments.

Belleau, C.↗

NASA NTRS2009

Influence of Containment on Defects in GeSi Crystals

Crystals grown without being in contact with a container have superior quality to otherwise similar crystals grown in direct contact with a container, especially with respect to impurity incorporation, formation of dislocations, and residual stress in crystals. "Detached" or "dewetted" Bridgman growth is similar to regular Bridgman growth in that most of the melt is in contact with the crucible wall, but the crystal is separated from the wall by a small gap, typically of the order of 10(exp -5) m. A small meniscus bridges the gap between the top of the crystal and the wall. Key parameters involved in achieving detached growth are the contact angle between the melt and crucible and the pressure differential across the meniscus. Sessile drop measurements were used to determine the wetting angles of Ge(sub 1-x)Si(sub x) melts on a variety of substrates and found that the highest wetting angles were achieved with pyrolitic boron nitride (pBN). GeSi crystals have been repeatedly grown detached in pBN crucibles but only occasionally in crucibles with lower wetting angles. Experiments have been conducted to assess the effect of pressure differential across the meniscus in sealed crucibles. This was done by adjusting the temperature profile after partial melting of the starting material. In a separate set of experiments, the pressure was controlled by connecting the volume below the meniscus to a regulated gas supply. The experiments were in agreement with calculations which predicted that stable detachment will only occur in crucibles with a low wetting angle over a relatively narrow range of pressure differential. Detached-grown crystals exhibited superior structural quality as evidenced by measurements of etch pit density, synchrotron white beam X-ray topography and double axis X-ray diffraction.

Volz, M. P.↗

NASA NTRS1986

Fractographic and microstructural evaluation of 3500-hour durability specimens

Long term durability testing of candidate ceramic materials for advanced gas turbine applications was performed. Specimens of the materials were exposed to combustion atmospheres under temperature cyclic conditions for times up to 3500 hours and at peak temperatures of 1200 and 1370 C. The specimen strengths after exposure were measured at room temperature and at 1200 C. In addition, a number of physical measurements were taken; however, no microstructural examination of the specimens was performed. Materials examined include: sintered alpha silicon carbide, sintered silicon nitride, and reaction bonded silicon nitride. Sample preparation techniques were developed to provide high quality thin-section specimens which can be examined by transmitted light or thinned using an ion mill for subsequent transmission electron microscopic examination. Specimen preparation techniques and the results of optical and electron microscopic examination of the reaction interfaces of the selected specimens are presented.

Miller, A. D.↗

DOE OSTI2021

Wall conditioning and ELM mitigation with boron nitride powder injection in KSTAR

Results from KSTAR powder injection experiments, in which tens of milligrams of boron nitride (BN) were dropped into low-power H-mode plasmas, show an improvement in wall conditions in subsequent discharges and, in some cases, a reduction or elimination of edge-localized modes (ELMs). Injected powder is distributed by the plasma flow and is deposited on the wall and, over the course of several discharges, was observed to gradually reduce recycling by 33%, and decrease both the ELM amplitude and frequency. This is the first demonstration of the use of BN for ELM mitigation. In all of these experiments, an Impurity Powder Dropper (IPD) was used to introduce precise, controllable amounts of the materials into ELMy H-mode KSTAR discharges. The plasma duration was between 10 s and 15 s, I p = 500 kA, B T = 1 . 8 T, P NBI = 1 . 6 MW, and P ECH = 0 . 6 MW. Plasma densities were between 2 and 3 × 1 0 19 m -3 . In all cases, the pre-fill and startup gas-fueling was kept constant, suggesting that the decrease in baseline D α emission is in fact due to a reduction in recycling. The results presented herein highlight the viability of powder injection for intra-shot and between-shot wall conditioning

36 MATERIALS SCIENCE↗

NASA NTRS2013

Wear and Reactivity Studies of Melt infiltrated Ceramic Matrix Composite

As interest grows in the use of ceramic matrix composites (CMCs) for critical gas turbine engine components, the effects of the CMCs interaction with the adjoining structure needs to be understood. A series of CMC/material couples were wear tested in a custom elevated temperature test rig and tested as diffusion couples, to identify interactions. Specifically, melt infiltrated silicon carbide/silicon carbide (MI SiC/SiC) CMC was tested in combination with a nickel-based super alloy, Waspaloy, a thermal barrier coating, Yttria Stabilized Zirconia (YSZ), and a monolithic ceramic, silicon nitride (Si3N4). To make the tests more representative of actual hardware, the surface of the CMC was kept in the as-received state (not machined) with the full surface features/roughness present. Test results include: scanning electron microscope characterization of the surfaces, micro-structural characterization, and microprobe analysis.

Jarmon, David C.↗

NASA NTRS1982

Gas-phase hydrogen permeation through alpha-titanium - Surface film and dimensional effects

The process of hydrogen transport through alpha-Ti involves simultaneous diffusion and phase boundary reactions at both surfaces, with the relative effect on each surface depending on the extent of surface contamination as well as the physical dimensions of the titanium membrane used. It is shown by the present study that hydrogen permeation in commercially pure alpha-Ti increases exponentially with temperature and is dependent on the first power of the input pressure, whether the surface is as-polished, preoxidized or prenitrided. Permeation decreases in the case of the as-polished condition if nitride or oxide films are formed at the surface in contact with source hydrogen, while increasing slightly for the same condition if such films are formed at the hydrogen exit surface.

Shah, K. K.↗

NASA NTRS1987

Detection of interstellar PN - The first phosphorus-bearing species observed in molecular clouds

Phosphorus nitride (PN) has been detected in the interstellar medium. The J = 2-1, 3-2, 5-4, and 6-5 rotational lines of this species have been observed toward Orion-KL, and the J = 2-1 transition in Sgr B2 and W51. The PN line profiles in Orion indicate that the molecule's emission arises from the 'plateau' or 'doughnut' region associated with the outflow from IRc2. The species is thus primarily present in hot, dense gas. Column densities derived for PN toward Orion-KL are (3-4) x 10 to the 13th/sq cm, but may be as high as 10 to the 14th/sq cm, if the species is located in a 10-arcsec region. These column densities imply a fractional abundance for PN in the Orion 'plateau' of (1-4) x 10 to the -10th. Such a large abundance for PN is not predicted by quiescent cloud ion-molecule chemistry and suggests that high-temperature processes are responsible for the synthesis of PN in the KL outflow.

Ziurys, L. M.↗

NASA NTRS1997

The Development of Engineering Tomography for Monolithic and Composite Materials and Components

The research accomplishments under this grant were very extensive in the areas of the development of engineering tomography for monolithic and composite materials and components. Computed tomography was used on graphite composite pins and bushings to find porosity, cracks, and delaminations. It supported the following two programs: Reusable Launch Vehicle (RLV) and Southern Research institute (SRI). Did research using CT and radiography on Nickel based Superalloy dogbones and found density variations and gas shrinkage porosity. Did extensive radiography and CT of PMC composite flywheels and found delamination and non-uniform fiber distribution. This grant supported the Attitude Control Energy Storage Experiment (ACESE) program. Found broken fibers and cracks of outer stainless steel fibers using both radiographic and CT techniques on Pratt and Whitney fuel lines; Supported the Pratt & Whitney and Aging Aircraft engines program. Grant research helped identify and corroborate thickness variations and density differences in a silicon nitride "ROTH" tube using computed tomography.

Hemann, John↗

NASA NTRS1990

Role of the interfacial thermal barrier in the effective thermal diffusivity/conductivity of SiC-fiber-reinforced reaction-bonded silicon nitride

Experimental thermal diffusivity data transverse to the fiber direction for composites composed of a reaction bonded silicon nitride matrix reinforced with uniaxially aligned carbon-coated silicon carbide fibers indicate the existence of a significant thermal barrier at the matrix-fiber interface. Calculations of the interfacial thermal conductances indicate that at 300 C and 1-atm N2, more than 90 percent of the heat conduction across the interface occurs by gaseous conduction. Good agreement is obtained between thermal conductance values for the oxidized composite at 1 atm calculated from the thermal conductivity of the N2 gas and those inferred from the data for the effective composite thermal conductivity.

Bhatt, Hemanshu↗

DOE OSTI2022

Metal Oxynitrides for the Electrocatalytic Reduction of Nitrogen to Ammonia

The successful deployment of technologies for the electrocatalytic nitrogen reduction reaction (e-NRR) to synthesize ammonia would enable distributed ammonia production with lower greenhouse gas emissions compared to the Haber–Bosch process. However, electrocatalysts that can readily activate N 2 , promote selective ammonia formation over the competing hydrogen evolution reaction, and maintain stability under reaction conditions are needed to enable this technology. Herein, we give our perspective on metal oxynitrides (A x B y O w N z ) as an emerging and underexplored materials class for e-NRR. Furthermore, we contrast the activity, selectivity, and stability of metal oxynitrides with those of their metal nitride and metal oxide counterparts. We discuss the different possible e-NRR reaction mechanisms on metal oxynitrides, emphasize challenges related to using metal oxynitrides for e-NRR, and provide an outlook for future research. Ultimately, the huge design space of metal oxynitrides is ripe for exploration to find catalyst formulations that overcome some of the limitations of traditional metal oxides and metal nitrides for e-NRR.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗