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DOE OSTI2024

Boron nitride: Novel ceramic reductant for low‐activity waste vitrification

Abstract During vitrification of radioactive wastes, excessive foaming reduces processing rates within melters by hindering heat transfer from the molten glass pool to the reacting melter feed. Formulations of low‐activity waste (LAW) melter feeds, for vitrification at the Waste Treatment and Immobilization Plant at the Hanford Site, conventionally include the addition of sucrose to mitigate excessive foaming by hastening the denitration process. However, incomplete combustion of sucrose produces organics such as acetonitrile (C 2 H 3 N) that may exceed bounding limits of downstream effluent treatment facilities. Using boron nitride (BN) as an alternate reductant to sucrose, in a representative LAW melter feed reduced C 2 H 3 N production by 90% by preventing the low‐temperature sucrose–nitrate reactions. Furthermore, foaming was suppressed due to the higher decomposition temperature of BN than H 3 BO 3 meaning a delayed reaction of a large fraction of boron with the transient glass‐forming melt until above the foam onset temperature, thus reducing the quantity and viscosity of the connected melt and trapping less gas in the foam layer.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗

NASA NTRS2004

Processing Techniques Developed to Fabricate Lanthanum Titanate Piezoceramic Material for High-Temperature Smart Structures

Piezoelectric ceramic materials are potential candidates for use as actuators and sensors in intelligent gas turbine engines. For piezoceramics to be applied in gas turbine engines, they will have to be able to function in temperatures ranging from 1000 to 2500 F. However, the maximum use temperature for state-of-the-art piezoceramic materials is on the order of 300 to 400 F. Research activities have been initiated to develop high-temperature piezoceramic materials for gas turbine engine applications. Lanthanum titanate has been shown to have high-temperature piezoelectric properties with Curie temperatures of T(sub c) = 1500 C and use temperatures greater than 1000 C. However, the fabrication of lanthanum titanate poses serious challenges because of the very high sintering temperatures required for densification. Two different techniques have been developed at the NASA Glenn Research Center to fabricate dense lanthanum titanate piezoceramic material. In one approach, lower sintering temperatures were achieved by adding yttrium oxide to commercially available lanthanum titanate powder. Addition of only 0.1 mol% yttrium oxide lowered the sintering temperature by as much as 300 C, to just 1100 C, and dense lanthanum titanate was produced by pressure-assisted sintering. The second approach utilized the same commercially available powders but used an innovative sintering approach called differential sintering, which did not require any additive.

Goldsby, Jon C.↗

NASA NTRS1989

Rapid fabrication of lightweight ceramic mirrors via chemical vapor deposition

Lightweight Si/SiC mirrors of nominal diameter 7.5 cm have been fabricated via a scalable and rapid CVD process to demonstrate the CVD mirror fabrication technology. These mirrors consist of a faceplate of either Si or Si-coated SiC and a lightweight backstructure made of either Si or SiC. The mirrors were polished to a figure better than 1/5th of a wave at 0.6328 A and a finish of better than 10 A rms. A procedure for fabricating these mirrors is described. The CVD fabrication process is fast and has the potential to yield several mirrors in a few weeks time from a single reactor. The CVD mirror fabrication technology is quite general and can be extended to include mirrors of other ceramic materials such as TiB2 and B4C.

Goela, Jitendra S.↗

NASA NTRS1993

Near net shape processing: A necessity for advanced materials applications

High quality discrete parts are the backbones for successful operation of equipment used in transportation, communication, construction, manufacturing, and appliances. Traditional shapemaking for discrete parts is carried out predominantly by machining, or removing unwanted material to produce the desired shape. As the cost and complexity of modern materials escalates, coupled with the expense and environmental hazards associated with handling of scrap, it is increasingly important to develop near net shape processes for these materials. Such processes involve casting of liquid materials, consolidation of powder materials, or deformation processing of simple solid shapes into the desired shape. Frequently, several of these operations may be used in sequence to produce a finished part. The processes for near net shape forming may be applied to any type of material, including metals, polymers, ceramics, and their composites. The ability to produce shapes is the key to implementation of laboratory developments in materials science into real world applications. This seminar presents an overview of near net shapemaking processes, some application examples, current developments, and future research opportunities.

Kuhn, Howard A.↗

DOE OSTI2018

Microwave sintering of complex shapes: From multiphysics simulation to improvements of process scalability

The microwave sintering homogeneity of large and complex shape specimens is analyzed. A new approach enabling the fabrication of complex shapes ceramics via 3D printing and microwave sintering is presented. The use of a dental microwave cavity is shown to enable a substantial level of densification of complex shape components while restricting the grain growth. The homogeneity of the processed samples during microwave sintering is studied by an electromagnetic-thermal-mechanical simulation. The realistic densification behavior, that phenomenologically takes into account the microwave effect, is included in the modeling framework. We observe that the simulation indicates the sharp correlation between the microwave field distribution in the cavity, the temperature profile, and the specimen's shape distortion.

36 MATERIALS SCIENCE↗

DOE OSTI2019

A three-dimensional interconnected polymer/ceramic composite as a thin film solid electrolyte

In this work we introduce an approach to fabricate a solid composite electrolyte film that is thin, ionically conductive, and mechanically robust with good potential for manufacturability, in the application of lithium metal batteries. First a doped-lithium aluminum titanium phosphate ceramic thin film with thickness of ~25 μm is formed by aqueous spray coating, a scalable process. The film is partially sintered to form a three-dimensionally interconnected structure with a dense backbone. It is then backfilled with a crosslinkable poly(ethylene oxide) (PEO)-based polymer electrolyte. We report the composite has very high ceramic loading of 77 wt% (61 vol%) and an ionic conductivity of 3.5 × 10 -5 S/cm at 20 °C with an activation energy of 0.43 eV. The main ion transport pathway is through the ceramic network, predicted by modelling and verified by experiments. Owing to the interconnected structure of the ceramic, the composite electrolyte exhibits much improved mechanical strength.

25 ENERGY STORAGE↗

DOE OSTI2018

Numerical Modeling of Fiber-Reinforced Metal Matrix Composite Processing by the Liquid Route: Literature Contribution

One of the technologies used to produce metal matrix composites (MMCs) is liquid route processing. One solution is to inject a liquid metal under pressure or at constant rate through a fibrous preform. This foundry technique overcomes the problem of the wettability of ceramic fibers by liquid metal. The liquid route can also be used to produce semiproducts by coating a filament with a molten metal. These processes involve physical phenomena combined with mass and heat transfer and phase change. The phase change phenomena related to solidification and also to the melting of the metal during the process notably result in modifications to the permeability of porous media, in gaps in impregnation, in the appearance of defects (porosities), and in segregation in the final product. In this article, we provide a state-of-the-art review of numerical models and simulation developed to study these physical phenomena involved in MMC processing by the liquid route.

36 MATERIALS SCIENCE↗

DOE OSTI2015

Mechanism of photochromic effect in Pb(Zr,Ti)O{sub 3} and (Pb,La)(Zr,Ti)O{sub 3} ceramics under violet/infrared light illumination

Obvious photochromic effects were observed in Pb(Zr,Ti)O{sub 3} and (Pb,La)(Zr,Ti)O{sub 3} (PLZT) ceramics, along with exponential responses to illumination power in both darkening and bleaching processes. An interesting anomalous dispersion in the transparent PLZT was observed and discussed. A tentative physical picture based on photoinduced electron stimulated processes and on structural change was proposed to explain all the interesting observations. Rate equations were established and solved in verifying the validity of the proposed model. This work may serve as guidance in designing tunable achromatic lenses, UV and IR light detectors and sensors.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

NASA NTRS1999

Design Tool Developed for Probabilistic Modeling of Ceramic Matrix Composite Strength

Ceramic matrix composites are being evaluated as candidate materials for many high temperature applications such as engine combustor liners for the High-Speed Civil Transport (HSCT). They are required to have an assured life of several thousand hours. Estimating the reliability of these components is quite a complex process and requires knowledge of the uncertainties that occur at various scales. The properties of ceramic matrix composites (CMC) are known to display a considerable amount of scatter due to variations in fiber/matrix properties, interphase/coating properties, bonding, amount of matrix voids, and many geometry- and fabrication-related parameters such as ply thickness and ply orientations. The objective of this research effort is to account for these uncertainties in a formal way by probabilistically analyzing both the stiffness- and strength related properties of CMC's. In current deterministic approaches, uncertainties are usually accounted for by safety factors. This approach often yields overly conservative designs, thereby reducing the potential of many advanced composite materials.

Murthy, Pappu L. N.↗

DOE OSTI2023

Development of New Magnetron Sputter Deposition Processes for Laser Target Fabrication

Magnetron sputter deposition is an enabling technology for laser target fabrication. Solutions are readily available for the deposition of most sub-micron-thick elemental films on planar substrates. However, major challenges still remain for the development of robust deposition processes in regimes of ultrathick (over ~10 μm) coatings and nonplanar substrates. These challenging deposition regimes are directly relevant to laser target applications, including both sphero-cylindrical hohlraums and spherical ablators for inertial confinement fusion (ICF) targets. Understanding underlying physical mechanisms for a specific material system is crucial for process development, given the overall complexity of the deposition process, its nonlinear dependence on deposition parameters, and a very large process space, often precluding conventional process optimization approaches. Here, we describe our approach to developing new deposition processes and give practical advice with examples of new results from our ongoing studies of glassy boron carbide ceramics for next-generation ICF ablators and nonequilibrium gold-tantalum alloys for hohlraums for magnetized ICF schemes. Emphasis is given to two major challenges of ultrathick coatings related to achieving process stability and reducing residual stress.

36 MATERIALS SCIENCE↗

NASA NTRS1989

Properties of Pb(1-x)Bi(x)/Ba2YCu3O(x) composites - Reaction of Ba2YCu3O(x) with Pb and Bi

This paper describes experiments conducted with a purpose of fabricating superconducting composites from Pb, Bi, and Ba2YCu3O(x), together the results of SEM examinations and energy dispersive spectroscopy performed on products. Results showed a limited utility of Pb and Pb(1-x)Bi(x) as matrices for ceramic superconductors. It was found that cold pressing followed by sintering at 200 C resulted in a composite which excluded flux below 90 K but did not show zero electrical resistance until the metal superconducting transition. Processing at 400 or 950 C resulted in oxygen depleted perovskite and/or metal oxides; these materials displayed greatly degraded superconducting properties. Finally, processing at 800 C resulted in high Tc only for composites containing more than 90 wt pct ceramic.

Hepp, A. F.↗

DOE OSTI2018

Research on the interfacial structure and property improvement of the Cfiber/2Si-B-3C-N ceramic matrix composite

Highlights: • The C{sub fiber}/2Si-B-3C-N composite with nice properties was successfully prepared. • ZrO{sub 2} promotes the densification process, homogeneous nucleation and grain growth. • The interface reaction in the composite was well controlled by the addition of ZrO{sub 2}. • The damage to carbon fiber was largely avoided by the addition of ZrO{sub 2}. - Abstract: A mixture of the mechanically alloyed 2Si-B-3C-N powder and short carbon fiber was hot pressed at 1800 °C for 30 mins in nitrogen. Careful investigation to the prepared C{sub fiber}/2Si-B-3C-N ceramic matrix composite revealed that the composite was very difficult to be densified. Heterogeneous nucleation, abnormal grain growth and severe interface reaction occurred on the fiber surface or between the fiber and the ceramic matrix, leading to a small density and weak mechanical properties of the composite. For the prepared composite without any additive, the relative density, flexural strength, elastic modulus and fracture toughness is 71.7%, 64.6 MPa, 14.7 GPa and 1.47 MPa·m{sup 1/2}, respectively. The average size of the SiC grains close to and far away from the carbon fiber is 249.10 nm and 50.45 nm, respectively. However, with the addition of ZrO{sub 2} (7.5 mol%), the above mentioned phenomenons are changed noticeably, and those properties are significantly increased to 88.5%, 112.4 MPa, 111.1 GPa and 2.94 MPa·m{sup 1/2}, respectively. At the same time, the SiC grains close to or far away from the carbon fiber almost have the same average size of about 448.21 nm, and almost no interface reaction occurs. It shows that the addition of ZrO{sub 2} not only facilitates the sintering and densification process, but also depresses the interface reaction, promotes the homogeneous nucleation and grain growth, and hence significantly improves the mechanical properties of the C{sub fiber}/2Si-B-3C-N composite. This interesting finding is favorable for the preparation of carbon fiber reinforced ceramic matrix composite, which requires both a large relative density and well controlled interface reaction.

36 MATERIALS SCIENCE↗

DOE OSTI2017

Sealing glass-ceramics with near-linear thermal strain, part III: Stress modeling of strain and strain rate matched glass-ceramic to metal seals

Thermal mechanical stresses of glass-ceramic to stainless steel (GCtSS) seals are analyzed using finite element modeling over a temperature cycle from a set temperature (T set ) 500°C to -55°C, and then back to 600°C. There are two glass-ceramics that have an identical coefficient of thermal expansion (CTE) at ~16 ppm/°C but have very different linearity of thermal strains, designated as near-linear NL16 and step-like SL16, and were formed from the same parent glass using different crystallization processes. Stress modeling reveals much higher plastic strain in the stainless steel using SL16 glass-ceramic when the GCtSS seal cools from T set . Upon heating tensile stresses start to develop at the GC-SS interface before the temperature reaches T set . On the other hand, the much lower plastic deformation in stainless steel accumulated during cooling using NL16 glass-ceramic allows for radially compressive stress at the GC-SS interface to remain present when the seal is heated back to T set . Finally, the qualitative stress comparison suggests that with a better match of thermal strain rate to that of stainless steel, the NL16 glass-ceramic not only improves the hermeticity of the GCtSS seals, but would also improve the reliability of the seals exposed to high-temperature and/or high-pressure abnormal environments.

36 MATERIALS SCIENCE↗

NASA NTRS2014

A Fully Non-metallic Gas Turbine Engine Enabled by Additive Manufacturing

The Non-Metallic Gas Turbine Engine project, funded by NASA Aeronautics Research Institute (NARI), represents the first comprehensive evaluation of emerging materials and manufacturing technologies that will enable fully nonmetallic gas turbine engines. This will be achieved by assessing the feasibility of using additive manufacturing technologies for fabricating polymer matrix composite (PMC) and ceramic matrix composite (CMC) gas turbine engine components. The benefits of the proposed effort include: 50 weight reduction compared to metallic parts, reduced manufacturing costs due to less machining and no tooling requirements, reduced part count due to net shape single component fabrication, and rapid design change and production iterations. Two high payoff metallic components have been identified for replacement with PMCs and will be fabricated using fused deposition modeling (FDM) with high temperature capable polymer filaments. The first component is an acoustic panel treatment with a honeycomb structure with an integrated back sheet and perforated front sheet. The second component is a compressor inlet guide vane. The CMC effort, which is starting at a lower technology readiness level, will use a binder jet process to fabricate silicon carbide test coupons and demonstration articles. The polymer and ceramic additive manufacturing efforts will advance from monolithic materials toward silicon carbide and carbon fiber reinforced composites for improved properties. Microstructural analysis and mechanical testing will be conducted on the PMC and CMC materials. System studies will assess the benefits of fully nonmetallic gas turbine engine in terms of fuel burn, emissions, reduction of part count, and cost. The proposed effort will be focused on a small 7000 lbf gas turbine engine. However, the concepts are equally applicable to large gas turbine engines. The proposed effort includes a multidisciplinary, multiorganization NASA - industry team that includes experts in ceramic materials and CMCs, polymers and PMCs, structural engineering, additive manufacturing, engine design and analysis, and system analysis.

manufacturing↗

NASA NTRS2002

Life Prediction/Reliability Data of Glass-Ceramic Material Determined for Radome Applications

Brittle materials, ceramics, are candidate materials for a variety of structural applications for a wide range of temperatures. However, the process of slow crack growth, occurring in any loading configuration, limits the service life of structural components. Therefore, it is important to accurately determine the slow crack growth parameters required for component life prediction using an appropriate test methodology. This test methodology also should be useful in determining the influence of component processing and composition variables on the slow crack growth behavior of newly developed or existing materials, thereby allowing the component processing and composition to be tailored and optimized to specific needs. Through the American Society for Testing and Materials (ASTM), the authors recently developed two test methods to determine the life prediction parameters of ceramics. The two test standards, ASTM 1368 for room temperature and ASTM C 1465 for elevated temperatures, were published in the 2001 Annual Book of ASTM Standards, Vol. 15.01. Briefly, the test method employs constant stress-rate (or dynamic fatigue) testing to determine flexural strengths as a function of the applied stress rate. The merit of this test method lies in its simplicity: strengths are measured in a routine manner in flexure at four or more applied stress rates with an appropriate number of test specimens at each applied stress rate. The slow crack growth parameters necessary for life prediction are then determined from a simple relationship between the strength and the applied stress rate. Extensive life prediction testing was conducted at the NASA Glenn Research Center using the developed ASTM C 1368 test method to determine the life prediction parameters of a glass-ceramic material that the Navy will use for radome applications.

Choi, Sung R.↗

NASA NTRS1986

Ceramics for turbine engines

The Ceramics for Turbine Engines Project is comprised of three main research programs with major elements as indicated: materials and processing (monolithics and fiber reinforcement), design methodology (design code and tribology), and life prediction (environmental effects, nondestructive evaluation, fracture and fatigue, and time dependent behavior). From the NASA perspective an enhanced ceramics technology base directly supports aeronautics initiatives in small engine technology, high-performance turbine engine technology, and hypersonics. An overview of the program, which includes the technical objectives and content of each program, is provided.

Levine, Stanley R.↗

DOE OSTI2022

In Situ Nanoscale Dynamics Imaging in a Proton‐Conducting Solid Oxide for Protonic Ceramic Fuel Cells

Abstract Hydrogen fuel cells and electrolyzers operating below 600 °C, ideally below 400 °C, are essential components in the clean energy transition. Yttrium‐doped barium zirconate BaZr 0.8 Y 0.2 O 3‐d (BZY) has attracted a lot of attention as a proton‐conducting solid oxide for electrochemical devices due to its high chemical stability and proton conductivity in the desired temperature range. Grain interfaces and topological defects modulate bulk proton conductivity and hydration, especially at low temperatures. Therefore, understanding the nanoscale crystal structure dynamics in situ is crucial to achieving high proton transport, material stability, and extending the operating range of proton‐conducting solid oxides. Here, Bragg coherent X‐ray diffractive imaging is applied to investigate in situ and in 3D nanoscale dynamics in BZY during hydration over 40 h at 200 °C, in the low‐temperature range. An unexpected activity of topological defects and subsequent cracking is found on a nanoscale covered by the macroscale stability. The rearrangements in structure correlate with emergent regions of different lattice constants, suggesting heterogeneous hydration. The results highlight the extent and impact of nanoscale processes in proton‐conducting solid oxides, informing future development of low‐temperature protonic ceramic electrochemical cells.

25 ENERGY STORAGE↗

DOE OSTI2016

The Consolidation of Glass-Ceramic Waste forms by Hot Isostatic Pressing: Sample Optimisation - 16581

Zirconolite based glass-ceramics were developed for the disposition of plutonium residues at the UK's Sellafield site. Glass-ceramics act as double barrier systems, separating Pu into a durable ceramic phase and retaining miscellaneous material in the amorphous phase. Here we discuss the optimisation of processing parameters and formulations of these alternative waste-forms. All samples were HIPed at 1250 deg. C, 100 MPa for 4 hrs. By investigating the effects of different pre-HIP heat treatments on sample quality and throughput, and glass phase compositions on the crystalline phase assemblage, an optimised method and wasteform composition were achieved. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗