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At least 1,783 records · Page 99

All sources NASA NTRS DOE OSTI

DOE OSTI2015

Raman spectroscopy, dielectric properties and phase transitions of Ag{sub 0.96}Li{sub 0.04}NbO{sub 3} ceramics

Highlights: • First Raman scattering studies of Ag{sub 0.96}Li{sub 0.04}NbO{sub 3}, allowed us to correlate temperature evolution of relaxational frequency γ{sub R}(T) with the Nb-ion dynamics and showed its changes at freezing temperature and ferrielectric transition. - Abstract: Silver lithium niobates Ag{sub 1−x}Li{sub x}NbO{sub 3} are promising lead free piezoelectrics. Good quality Ag{sub 0.96}Li{sub 0.04}NbO{sub 3} ceramics were obtained. Dielectric and DSC studies showed that, in comparison to AgNbO{sub 3,} temperatures of phase transitions slightly decrease. Dielectric studies pointed to enhancement of polar properties. Remnant polarisations achieves value of 0.6 μC/cm{sup 2}. Maximum of ϵ(T) dependences related to the relaxor-like ferroelectric/ferrielectric M{sub 1}–M{sub 2} transition becomes higher and more frequency dependent. Analysis of Raman spectra showed that two modes at 50 and 194 cm{sup −1} exhibit significant softening. Low frequency part of the Raman spectra which involve central peak and soft mode were analysed using two models. CP was assumed as relaxational vibration and described by Debye function. The slope of temperature dependences of relaxational frequency γ{sub R}(T) changes at approximately 470 and 330 K, indicating that slowing down process of relaxational vibrations changes in the vicinity of partial freezing of Nb-ion dynamics T{sub f} and further freezing at ferroelectric/ferrielectric phase transition.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2023

Material Plasma Exposure eXperiment High Heat Flux Microwave Absorber Design, Manufacture, and Articles Test

The Material Plasma Exposure eXperiment (MPEX) at Oak Ridge National Laboratory is in the final design phase. MPEX will be capable of exposing neutron-irradiated materials to plasmas for the study of plasma-material interaction. This facility will provide information about the complex effects of plasmas on materials and contribute to examining new materials that can withstand high heat fluxes and high ion fluences for future fusion devices. MPEX plasma is heated by 70-GHz or 105-GHz electron Bernstein wave/electron cyclotron heating (ECH), and the high-frequency microwaves are prone to scattering microwave power, which can have detrimental effects, especially on diagnostic components. A large portion of the injected ECH power is expected to be absorbed by plasma, but the remainder requires that microwave absorbers be placed immediately upstream and downstream of the ECH launcher to minimize stray microwaves leaving the ECH region. These microwaves can inadvertently heat components that cannot be shielded or otherwise protected. The microwave absorber design is based on an array of pyramid-shaped ceramic tiles brazed to a water-cooled explosion-bonded heat sink and a stainless steel plate to produce one tile module. Computational fluid dynamics and structural analyses were performed to optimize and validate the design. Multiple test coupons were produced to validate the process for brazing the two different tile materials to the Glidcop AL-15 baseplate. The articles were tested to evaluate the reliability and thermal performance through exposure to an electron beam with a heat flux of up to 1.5 MW/m2. Nondestructive testing was performed before and after testing to identify voids or separations that may have been introduced by the high heat flux. This paper discusses the details of high heat flux microwave absorber design, manufacturing details and associated challenges, and test results, demonstrating the effectiveness of the proposed design.

Hussain, Aftab↗

DOE OSTI2019

Additive Manufacturing of Bi-Continuous Piezocomposites With Triply Periodic Phase Interfaces for Combined Flexibility and Piezoelectricity

An additive manufacturing-enabled bi-continuous piezocomposite architecture is presented to achieve mechanical flexibility and piezoelectricity simultaneously in piezoelectric materials. This architecture comprises an active ferroelectric ceramic phase and a passive flexible polymer phase, which are separated by a tailorable phase interface. Here, triply periodic minimal surfaces were used to define the phase interface, due to their excellent elastic properties and load transfer efficiency. A suspension-enclosing projection-stereolithography process was used to additively manufacture this material. Postprocesses including polymer infiltration, electroding, and poling are introduced. Piezoelectric properties of the piezocomposites are numerically and experimentally studied. The results highlight the role of tailorable triply periodic phase interfaces in promoting mechanical flexibility and piezoelectricity of bi-continuous piezocomposites.

42 ENGINEERING↗

DOE OSTI2015

Advanced Hydrogen Transport Membrane for Coal Gasification

A pilot-scale hydrogen transport membrane (HTM) separator was built that incorporated 98 membranes that were each 24 inches long. This separator used an advanced design to minimize the impact of concentration polarization and separated over 1000 scfh of hydrogen from a hydrogen-nitrogen feed of 5000 scfh that contained 30% hydrogen. This mixture was chosen because it was representative of the hydrogen concentration expected in coal gasification. When tested with an operating gasifier, the hydrogen concentration was lower and contaminants in the syngas adversely impacted membrane performance. All 98 membranes survived the test, but flux was lower than expected. Improved ceramic substrates were produced that have small surface pores to enable membrane production and large pores in the bulk of the substrate to allow high flux. Pd-Au was chosen as the membrane alloy because of its resistance to sulfur contamination and good flux. Processes were developed to produce a large quantity of long membranes for use in the demonstration test.

08 HYDROGEN↗

DOE OSTI2022

Complex Oxide Nanoparticle Synthesis: Where to Begin to Do It Right?

Synthesis of advanced ceramics requires a high degree of control over the particle size and stoichiometry of the material. When choosing a synthesis method for complex oxides it is important to begin with the correct precursors and solvents to achieve high purity nanoparticles. Here, we detail the selection process for precursors and solvents for liquid-phase precipitation synthesis. Data for metal nitrate, chloride, acetate, and oxalate precursors has been compiled to assist future synthesis. The role of hydration within the precursors is discussed as it affects the final stoichiometry of the material. Melting temperatures are also compiled for these compounds to assist in material selection. The solubility of the precursors in different solvents is examined to determine the correct solvent during synthesis. As an example, using the methodology presented here, two different materials are synthesized based on commonly available precursors. A catalyst based on a quaternary perovskite and an advanced ionic conductor based on a high entropy fluorite oxide are synthesized using precipitation methods and their characterization is detailed.

Gager, Elizabeth (ORCID:0000000306046571)↗

NASA NTRS1976

Durability of zirconia thermal-barrier ceramic coatings on air-cooled turbine blades in cyclic jet engine operation

Thermal barrier ceramic coatings of stabilized zirconia over a bond coat of Ni Cr Al Y were tested for durability on air cooled turbine rotor blades in a research turbojet engine. Zirconia stabilized with either yttria, magnesia, or calcia was investigated. On the basis of durability and processing cost, the yttria stabilized zirconia was considered the best of the three coatings investigated.

Liebert, C. H.↗

NASA NTRS1990

Kinetics and transport at AMTEC electrodes. I - The interfacial impedance model

Mixed mass-transport and kinetic control of sodium ion reduction at porous inert electrodes on sodium beta-double-prime alumina solid electrolyte (BASE) ceramic in a high-temperature electrochemical cell has been observed and modeled. The high ionic conductivity of BASE and the reversibility of the liquid sodium/BASE anodic half-cell led to assignment of potential-dependent (nonohmic) resistances to kinetic and mass-transport processes associated with the porous electrode. The morphology of these electrodes and typical sodium gas pressures are consistent with Knudsen, or free-molecular, flow through the electrode.

Williams, R. M.↗

NASA NTRS1998

An Investigation of Reliability Models for Ceramic Matrix Composites and their Implementation into Finite Element Codes

The development of modeling approaches for the failure analysis of ceramic-based material systems used in high temperature environments was the primary objective of this research effort. These materials have the potential to support many key engineering technologies related to the design of aeropropulsion systems. Monolithic ceramics exhibit a number of useful properties such as retention of strength at high temperatures, chemical inertness, and low density. However, the use of monolithic ceramics has been limited by their inherent brittleness and a large variation in strength. This behavior has motivated material scientists to reinforce the monolithic material with a ceramic fiber. The addition of a second ceramic phase with an optimized interface increases toughness and marginally increases strength. The primary purpose of the fiber is to arrest crack growth, not to increase strength. The material systems of interest in this research effort were laminated ceramic matrix composites, as well as two- and three- dimensional fabric reinforced ceramic composites. These emerging composite systems can compete with metals in many demanding applications. However, the ongoing metamorphosis of ceramic composite material systems, and the lack of standardized design data has in the past tended to minimize research efforts related to structural analysis. Many structural components fabricated from ceramic matrix composites (CMC) have been designed by "trial and error." The justification for this approach lies in the fact that during the initial developmental phases for a material system fabrication issues are paramount. Emphasis is placed on demonstrating feasibility rather than fully understanding the processes controlling mechanical behavior. This is understandable during periods of rapid improvements in material properties for any composite system. But to avoid the ad hoc approach, the analytical methods developed under this effort can be used to develop rational structural design protocols.

Duffy, Stephen F.↗

NASA NTRS2008

Development and Characterization of the Bonding and Integration Technologies Needed for Fabricating Silicon Carbide Based Injector Components

Advanced ceramic bonding and integration technologies play a critical role in the fabrication and application of silicon carbide based components for a number of aerospace and ground based applications. One such application is a lean direct injector for a turbine engine to achieve low NOx emissions. Ceramic to ceramic diffusion bonding and ceramic to metal brazing technologies are being developed for this injector application. For the diffusion bonding technology, titanium interlayers (coatings and foils) were used to aid in the joining of silicon carbide (SiC) substrates. The influence of such variables as surface finish, interlayer thickness, and processing time were investigated. Electron microprobe analysis was used to identify the reaction formed phases. In the diffusion bonds, an intermediate phase, Ti5Si3Cx, formed that is thermally incompatible in its thermal expansion and caused thermal stresses and cracking during the processing cool-down. Thinner interlayers of pure titanium and/or longer processing times resulted in an optimized microstructure. Tensile tests on the joined materials resulted in strengths of 13-28 MPa depending on the SiC substrate material. Nondestructive evaluation using ultrasonic immersion showed well formed bonds. For the joining technology of brazing Kovar fuel tubes to silicon carbide, preliminary development of the joining approach has begun. Various technical issues and requirements for the injector application are addressed.

Halbig,Michael C.↗

NASA NTRS2018

Signatures of the Impact Histories of Comets and Asteroids within Shocked Phyllosilicates, Enstatite, and Forsterite Minerals

Throughout the lifetime of the solar system, collisions between small bodies and impacts on the surfaces of small bodies in the Kuiper Belt have occured at speeds of 1.5 - 3 km s-1 (Stern, Astron J 124, 2002), typically at 1-10 km s-1 between Trojan asteroids (Marzari et al. Icarus 119, 1996), and at ~4-8 km s-1 in the asteroid belt (Farinella and Davis, Icarus 97, 1992). Shock effects recorded by minerals composing these bodies are one observable legacy of this evolutionary process, whether they were generated through large collisions, micrometeoroid impacts, or processing during the formation of the solar system. Shock metamorphism has been observed in cometary samples such as those from Comet Wild 2 (Keller et al. Geochim. Cosmochim. Acta 72, 2008; Tomeoka et al. MAPS 43, 2008; Jacobs et al. MAPS 44, 2009) as well as in forsterites and enstatites found in meteorites (McCausland et al. AGU, 2010). To investigate the observable signatures of these processes, we have conducted a suite of impact experiments at NASA Johnson Space Center's Experimental Impact Laboratory (EIL). Target materials included Mg-rich forsterite (olivine), Mg-rich enstatite (orthopyroxene), and antigorite and lizardite (both in the serpentine group of phyllosilicates). Alumina-ceramic spheres were launched at speeds ranging from ~2.0 - 2.6 km s-1 into targets at temperatures from 25degC to -100degC. Recent advancements have been made in cooling targets in the EIL's vertical gun. Liquid nitrogen (LN2) is fed through a unique jacket surrounding the metallic sample container to chill the samples. Real-time values from temperature sensors attached to the sample holder are converted to target temperature through predetermined regression relationships, providing the target temperature at the time of impact with sub-degree accuracy. Fourier Transform Infrared Spectrometer (FTIR) data in the near to mid-IR will be presented, along with trends relating temperature and velocity with impact speeds, and thereby peak shock stresses experienced by the impacted minerals.

Lederer, Susan M.↗

DOE OSTI2020

Dehalogenation of electrochemical processing salt simulants with ammonium phosphates and immobilization of salt cations in an iron phosphate glass waste form

This study demonstrates the conversion of simulated pyroprocessing salt wastes [i.e., ER(SF) and ERV2] into chemically durable iron phosphate glass waste forms through reactions with ammonium hydrogen phosphate precursors [i.e., NH4H2PO4 and (NH4)2HPO4] and added Fe2O3. The reaction of the salt simulants with the phosphate precursors resulted in dehalogenation of the salt through the production of NH4Cl and NH4I (along with water), of which the NH4Cl can be used to produce UCl3 oxidant for use in the electrorefiner during pyroprocessing. These iron phosphate glasses contain a notably higher waste loading than the baseline glass-bonded sodalite ceramic waste form, which requires about 70 vol% sodalite to accommodate Cl from the salt, because they are dehalogenated prior to vitrification. The high waste loadings coupled with higher bulk densities (~3×103 kg/m3) than glass-bonded sodalite (~2.3×103 kg/m3) mean that these glasses have a higher storage volume, i.e., the volume required to immobilize a given mass of waste. The iron phosphate glass waste forms were characterized using a variety of techniques including physical property measurements and chemical durability testing. Following initial testing, a proof-of-concept demonstration was conducted to show that the NH4Cl generated from this process could be used to produce UCl3 using depleted uranium dendrites as a feedstock.

phosphate glass, pyroprocessing, waste forms, salt↗

NASA NTRSDate not supplied

Pt/HTCC Alumina based Electronic Packaging System and Integration Processes for High Temperature Harsh Environment Applications

Electronic devices capable of operation at 500°C are required for long term Venus surface missions, as well as for in situ monitoring and control of next generation aeronautical engines. High temperature sensors and electronics can also find many applications in military, and energy and automobile industries. Various silicon carbide (SiC) sensors and electronic devices have been developed for operation at 500 °C, and a compatible packaging system is needed for long term test and deployment of these high temperature devices. High temperature co-fired ceramics (HTCC) alumina with platinum (Pt) conductor was proposed for high temperature electronic packaging. A prototype Pt/HTCC alumina packaging system including chip-level package and circuit board has been briefly reported previously for long-term electrical testing of SiC integrated circuits at 500 °C, and brief testing at much higher temperatures. HTCC alumina is an excellent dielectric material with acceptable dielectric constant and low dielectric loss over wide temperature and frequency ranges. Pt is chemically noble and can be co-fired with HTCC alumina in air ambient producing a viable electronic packaging material system for high temperature applications. This paper presents a more detailed description of this packaging system including prototype low power packages and circuit boards based on HTCC alumina and Pt metallization for 500°C and other harsh environment applications. The key technical considerations for chip-level packaging and circuit board assembly, including materials and processes for 500 °C durable wire-bonding and SiC die attach, and integration of multi-chip circuit boards, are presented. Experimental test results of this packaging approach applied to SiC integrated circuits at 500 °C and 700°C are discussed as well.

High temperature↗

NASA NTRSDate not supplied

Pt/HTCC Alumina based Electronic Packaging System and Integration Processes for High Temperature Harsh Environment Applications

electronic packaging↗

DOE OSTI2024

Solar Thermochemical Carbon Dioxide Splitting Using Ceria and Iron Aluminate Foam Devices and Simulation of a Plant System for Demonstration

An international research project has been undertaken to integrate a unique solar thermal processing reactor system with ceria and iron aluminate as active redox materials for CO2 splitting. Experimental investigations for CO2 splitting were conducted using a solar simulator and tube furnace at Niigata University, followed by demonstrations using a high-flux solar furnace (HFSF) at the National Renewable Energy Laboratory (NREL) in Golden, CO. Each experimental setup consisted of foam devices composed of reticulated porous ceramic (RPC). The RPC has a full ceria or iron aluminate body. It fabricated using the replica method and subjected to a two-step redox reaction, which iteratively separated a stream of CO2 into O2 and CO. Reactivity was evaluated using CO production per mass of the reactive material. The tubular furnace yielded a CO production of 6.41 mL/g at a reduction temperature of 1600degrees C, showcasing a higher CO production rate and total amount than those obtained from experiments conducted with solar simulators and solar furnace setups. For iron aluminate RPC, the productivity was measured as 3.57 mL/g using HFSF at a reduction temperature of 1450degrees C. These results are somewhat higher than those of the previous experiment at lower reduction temperatures of 1400degrees C-1500degrees C. Additionally, the production of CO in the case of ceria RPC was compared with the steady flow model simulation, which assumed chemical equilibrium at various levels of oxygen partial pressure during the reduction process. On the basis of these results, this study proposes a solar fuel system with an open receiver that uses a high-temperature heat transfer fluid.

carbon dioxide thermochemical splitting↗

NASA NTRS1999

Monte Carlo Simulation of Nanoparticle Encapsulation in Flames

Two critical challenges facing the application of flames for synthesis of nanopowder materials are: (1) overcoming formation of agglomerates and (2) ensuring that the highly reactive nanopowders that are synthesized in flames can be produced in such a manner that their purity is maintained during subsequent processing. Agglomerates are produced in flames because particle formation occurs in a high temperature and high number density environment. They are undesirable in most advanced applications of powders. For example, agglomerates have a deleterious effect on compaction density, leading to voids when nanopowders are consolidated. Efforts to avoid agglomeration in flames without substantially reducing particle number density and, consequently, production rate, have had limited success. Powder purity must also be maintained during subsequent handling of nanopowders and this poses a significant challenge for any synthesis route because nanopowders, particularly metals and non-oxide ceramic powders, are inherently reactive. Impurities acquired during handling of nanopowders have slowed the advancement of the nanostructured materials industry. One promising approach that has been proposed to address these problems is nano-encapsulation. In this approach, the core particles are encapsulated in a removable material while they are within the flame but before excessive agglomeration has occurred. Condensation can be very rapid so that core particles are trapped within the condensed material and agglomeration is limited. Nano-encapsulation also addresses the handling concerns for post-synthesis processing. Results have shown that when nano-encapsulated powders are exposed to atmosphere the core particles are protected from oxidation and/or hydrolysis. Thus, handling of the powders does not require extreme care. If, for example, at the time of consolidation the encapsulation material is removed by vacuum annealing, the resulting powder remains unagglomerated and free of impurities. In this work, we described a novel aerosol model that has been developed to simulate particle encapsulation in flames. The model will ultimately be coupled to a one-dimensional spherical flame code and compared to results from microgravity flame experiments.

Sun, Z.↗

DOE OSTI2019

Infiltration studies of additive manufacture of WC with Co using binder jetting and pressureless melt method

Additive manufacturing (AM) of tungsten carbide-cobalt (WC-Co) is explored starting with WC preforms shaped with binder jet additive manufacturing (BJAM) followed by melt infiltration of Co. The research objective is to demonstrate the ability to net-shape WC-Co composites through BJAM of a WC preform followed by backfilling with cobalt via pressureless infiltration. This method also has the potential to minimize shrinkage and grain growth compared to other AM techniques. The effects of sintering, Co content, and infiltration time on the net shaping and properties of processed composites are shown. The best shaped material had an average grain size of 5.1 μm, 32 vol.% Co, density of 98.54% theoretical, fracture toughness of 23.2 MPa m 1/2 , and hardness of 9.0 GPa. Data presented illustrates that the proposed approach results in favorable ceramic-metal (cermet) properties and is viable for fabricating cermets of other material combinations. Furthermore successful AM of cermets provides complex geometries, high throughout, and low costs.

36 MATERIALS SCIENCE↗

DOE OSTI2018

In situ observations of cracking in constrained sintering

Here in this article, we examine the long-standing problem of cracking during constrained sintering of a powder aggregate. Using binder jet 3D printing, we prepare ceramic green bodies in the form of center-notched panels, then use in situ imaging to observe how cracks nucleate and grow from the notch as the material sinters under restraint. Quantitative image analysis allows us to identify important characteristics of the sinter-cracking process, indicating a framework for analyzing the problem and developing methods for avoiding it, including representation of sinter-cracking as a creep crack growth process, use of fracture mechanics parameters to design specimen geometries that do not exceed critical stress intensities, and the possibility of exploiting the inherently ductile nature of sinter-cracking to mitigate damage.

36 MATERIALS SCIENCE↗

DOE OSTI2013

Theory and modeling of active brazing.

Active brazes have been used for many years to produce bonds between metal and ceramic objects. By including a relatively small of a reactive additive to the braze one seeks to improve the wetting and spreading behavior of the braze. The additive modifies the substrate, either by a chemical surface reaction or possibly by alloying. By its nature, the joining process with active brazes is a complex nonequilibrium non-steady state process that couples chemical reaction, reactant and product diffusion to the rheology and wetting behavior of the braze. Most of the these subprocesses are taking place in the interfacial region, most are difficult to access by experiment. To improve the control over the brazing process, one requires a better understanding of the melting of the active braze, rate of the chemical reaction, reactant and product diffusion rates, nonequilibrium composition-dependent surface tension as well as the viscosity. This report identifies ways in which modeling and theory can assist in improving our understanding.

van Swol, Frank B.↗