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

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At least 775 records · Page 43
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Study of the structure, dielectric and ferroelectric behavior of BaBi{sub 4+δ}Ti{sub 4}O{sub 15} ceramics

The structure and ferroelectric properties of excess bismuth doped barium bismuth titanate BaBi{sub 4+δ}Ti{sub 4}O{sub 15} (δ = 2 - 10 wt.%)) ceramics prepared by solid-state reaction method have been investigated. X-ray diffraction (XRD) confirms the formation of a single phase material with a change in the orthorhombic distortion with varying excess of bismuth content. There is no change in the phase transition temperature (T{sub m}) while the relaxor behaviour has been modified significantly with excess of bismuth doping. Saturated hysteresis loops with high remnant polarization (P{sub r} ~ 12.5 µC/cm{sup 2}), low coercive fields (E{sub c} ~ 26 kV/cm) are measured and a high piezoelectric coefficient (d{sub 33} ~ 29 pC/N) is achieved in poled BaBi{sub 4}Ti{sub 4}O{sub 15} ceramics prepared with up to 8 wt.% of excess bismuth oxide. The improvement in the ferroelectric properties with increase in the excess bismuth content in BaBi{sub 4}Ti{sub 4}O{sub 15} ceramics has been explained in terms of changing oxygen vacancy concentration and structural relaxation. Tunable ferroelectric materials can be obtained by manipulating the doping amount of excess bismuth.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Structure and electrical properties of 0.80 Na{sub 0.5} Bi{sub 0.5} TiO{sub 3}-0.16 K{sub 0.5} Bi{sub 0.5} TiO{sub 3}-0.04 BaTiO{sub 3} lead-free piezoelectric ceramics

Lead free pervoskite 0.80 Na{sub 0.5} Bi{sub 0.5} TiO{sub 3}-0.16 K{sub 0.5} Bi{sub 0.5} TiO{sub 3}-0.04 BaTiO{sub 3} (NKBBT) ceramics were fabricated via conventional solid state processing technique sintered at 1200 °C and their crystal structures and electrical properties were systematically studied. Structure of the prepared NKBBT ceramics was confirmed by Powder X-ray diffraction analysis. The dependence of dielectric constant on temperature for various frequencies (100 Hz-100 KHz) has been determined. The diffuse transition is observed in the variation of dielectric constant and it provides evidence for the relaxor characteristics. The ferroelectric response of the NKBBT ceramics with different frequency was studied. Polarisation electric field hysteresis loops revealed that the remnant polarization is 6.88 µC/cm{sup 2} and coercive electric field is 66.42 kV/cm.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Microstructure evolution and electrical characterization of Lanthanum doped Barium Titanate (BaTiO{sub 3}) ceramics

In the current work, we investigated the structural and dielectric properties of Lanthanum oxide (La{sub 2}O{sub 3}) doped Barium Titanate (BaTiO{sub 3}) ceramics and established a correlation between them. Solid state sintering method was used to dope BaTiO{sub 3} with 0.3, 0.5 and 0.7 mole% La{sub 2}O{sub 3} under different sintering parameters. The raw materials used were La{sub 2}O{sub 3} nano powder of ~80 nm grain size and 99.995% purity and BaTiO{sub 3} nano powder of 100 nm grain size and 99.99% purity. Grain size distribution and morphology of fracture surface of sintered pellets were examined by Field Emission Scanning Electron Microscope and X-Ray Diffraction analysis was conducted to confirm the formation of desired crystal structure. The research result reveal that grain size and electrical properties of BaTiO{sub 3} ceramic significantly enhanced for small amount of doping (up to 0.5 mole% La{sub 2}O{sub 3}) and then decreased with increasing doping concentration. Desired grain growth (0.80-1.3 µm) and high densification (<90% theoretical density) were found by proper combination of temperature, sintering parameters and doping concentration. We found the resultant stable value of dielectric constant was 10000-12000 at 100-300 Hz in the temperature range of 30°-50° C for 0.5 mole% La{sub 2}O{sub 3} with corresponding shift of curie temperature around 30° C. So overall this research showed that proper La{sup 3+} concentration can control the grain size, increase density, lower curie temperature and hence significantly improve the electrical properties of BaTiO{sub 3} ceramics.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Metal-ceramic materials. Study and prediction of effective mechanical properties

Mechanical behavior of stochastic metal-ceramic composite materials was numerically simulated on mesoscopic scale level. Deformation of mesoscopic volumes of composites, whose structure consists of a metal matrix and randomly distributed ceramic inclusions, was numerically simulated. The results of the numerical simulation were used for evaluation of the effective elastic and strength properties of metal-ceramic materials with different parameters of the structure. The values of the effective mechanical properties of investigated materials were obtained, and the character of the dependence of the effective elastic and strength properties on the structure parameters of composites was determined.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Damage formation, fatigue behavior and strength properties of ZrO{sub 2}-based ceramics

It is suggested that a non-destructive testing technique using a three-dimensional X-ray tomography be applied to detecting internal structural defects and monitoring damage formation in a ceramic composite structure subjected to a bending load. Three-point bending tests are used to investigate the fatigue behavior and mechanical and physical properties of medical-grade ZrO{sub 2}-based ceramics. The bending strength and flexural modulus are derived under static conditions at a loading rate of 2 mm/min. The fatigue strength and fatigue limit under dynamic loading are investigated at a frequency of 10 Hz in three stress ranges: 0.91–0.98, 0.8–0.83, and 0.73–0.77 MPa of the static bending strength. The average values of the bending strength and flexural modulus of sintered specimens are 43 MPa and 22 GPa, respectively. The mechanical properties of the ceramics are found to be similar to those of bone tissues. The testing results lead us to conclude that the fatigue limit obtained from 10{sup 5} stress cycles is in the range 33–34 MPa, i.e. it accounts for about 75% of the static bending strength for the test material.

36 MATERIALS SCIENCE↗
DOE OSTI2016

High charge-discharge performance of Pb{sub 0.98}La{sub 0.02}(Zr{sub 0.35}Sn{sub 0.55}Ti{sub 0.10}){sub 0.995}O{sub 3} antiferroelectric ceramics

The energy storage performance and charge-discharge properties of Pb{sub 0.98}La{sub 0.02}(Zr{sub 0.35}Sn{sub 0.55}Ti{sub 0.10}){sub 0.995}O{sub 3} (PLZST) antiferroelectric ceramics were investigated through directly measuring the hysteresis loops and pulse discharge current-time curves. The energy density only varies 0.2% per degree from 25 °C to 85 °C, and the energy efficiency maintains at about 90%. Furthermore, an approximate calculating model of maximum power density p{sub max} was established for the discharge process. Under a relatively high working electric field (8.2 kV/mm), this ceramics possess a greatly enhanced power density of 18 MW/cm{sup 3}. Moreover, the pulse power properties did not show degradation until 1500 times of charge-discharge cycling. The large released energy density, high energy efficiency, good temperature stability, greatly enhanced power density, and excellent fatigue endurance combined together make this PLZST ceramics an ideal candidate for pulse power applications.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2013

Characteristics of yttrium oxide laser ceramics with additives

Neodymium- or ytterbium-doped laser ceramics with a disordered crystal-field structure formed by introduction of iso- and heterovalent elements into yttrium oxide are studied. It is shown that these additives broaden the spectral band of laser transitions, which makes it possible to use ceramics as active laser media emitting ultrashort pulses. Lasing was obtained in several samples of this ceramics. At the same time, it is shown that addition of zirconium and hafnium stimulates the Foerster quenching of upper laser levels and pump levels. (extreme light fields and their applications)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Spectral and lasing characteristics of 1% Ho:YAG ceramics under intracavity pumping

High-transparency 1% Ho:YAG ceramics with the transmission coefficient of 82% in the IR range at the sample thickness of 1 mm are synthesised from a mixture of the Ho:Y{sub 2}O{sub 3} and Al{sub 2}O{sub 3} nanopowders obtained by the laser method. Results of investigations of spectral and lasing characteristics of 1 % Ho:YAG ceramics under intracavity pumping by radiation of a 5% Tm:KLuW disk element are presented. Based on spectral intensity analysis of generation in the 1.8 – 2.1 mm range and on cavity parameters, the estimated lasing slope efficiency for 1% Ho:YAG ceramics is about 40%. (lasers)

36 MATERIALS SCIENCE↗
DOE OSTI2015

Effect of microstructural features on the laser efficiency of Nd{sup 3+}:Y{sub 3}Al{sub 5}O{sub 12} ceramics

The optical properties and microstructure of transparent Nd{sup 3+}:Y{sub 3}Al{sub 5}O{sub 12} ceramics synthesised by different reactive sintering routes are studied. It is found that the residual porosity of optical ceramics is directly related to the homogeneity of the microstructure of initial compacts, which can be estimated by the existence of particle agglomerates larger than 1 mm in initial nanopowders. A qualitative correlation is established between the residual porosity, the optical losses and the lasing slope efficiency of Nd{sup 3+}:Y{sub 3}Al{sub 5}O{sub 12} ceramics. The maximum laser efficiency (η = 49%) was observed in the samples with the lowest porosity (2.3 × 10{sup -3} vol %). (lasers)

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2019

Synthesis and study of Fe{sup 2+} : MgAl{sub 2}O{sub 4} ceramics for active elements of solid-state lasers

The results of pioneering studies on preparation of highly transparent Fe{sup 2+} : MgAl{sub 2}O{sub 4} ceramics from powders synthesised in a laser torch are presented. This ceramics with a high transparency in the near-IR spectral region is synthesised for the first time at a low temperature (1300°C) and a short (1 h) sintering time. It is found that, as the iron oxide concentration increases from 0.1 to 5 wt %, the concentration of Fe{sup 3+} ions in samples decreases to zero. It is shown that the samples of Fe{sup 2+} : MgAl{sub 2}O{sub 4} ceramics contain the second phase (MgO){sub 0.91}(FeO){sub 0.09} with a concentration of several percent, which considerably decreases transmission coefficient T in the visible region. At the same time, the T coefficient increases with increasing wavelength λ due to a decrease in Rayleigh scattering and almost reaches the theoretical value 85.6 % for λ = 4 μm. The absorption cross section σ for Fe{sup 2+} ions at λ = 2 μm is determined to be (1.66 ± 0.14) × 10{sup −20} cm{sup 2}. (paper)

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2025

Additive manufacturing of high‐density silicon carbide ceramics through post‐processing spark plasma sintering

This research advances the field of additive manufacturing (AM) of silicon carbide (SiC) ceramics by integrating spark plasma sintering (SPS) to enhance material density, mechanical strength, and thermal properties. Traditional AM techniques struggle to achieve the high‐density SiC required for demanding applications, such as aerospace engineering, where high thermal conductivity and mechanical strength are paramount. Here, our study addresses these challenges by incorporating SPS as a post‐processing step, achieving near‐theoretical maximum densities and significantly reducing porosity, thereby resulting in outstanding thermal conductivity in SiC ceramics. We developed a specialized SiC ink optimized for 3D printing, ensuring structural integrity after deposition through tailored rheological properties. The application of SPS facilitates rapid, uniform sintering, essential for attaining superior density, mechanical properties, and thermal performance. Our experimental results, confirmed through scanning electron microscopy analysis, demonstrate significant microstructural properties, mechanical strength, and thermal conductivity, showcasing the effectiveness of integrating SPS in AM processes. This innovative approach not only expands the capabilities of AM in producing complex, high‐density ceramic structures but also broadens the potential applications of SiC in demanding environments.

36 MATERIALS SCIENCE↗
DOE OSTI2018

The Nature of the Nonsingularity of Inner Interfaces in Hydroxyapatite Ceramics

The morphology of inner interfaces in hydroxyapatite (HA) based calcium phosphate ceramics has been studied by transmission electron microscopy. Grain boundaries in the ceramics have been shown to have a vicinal character, which is related to the mechanism of secondary recrystallization in the material: layer growth of grains via sequential motion of elementary steps on planes corresponding to the {11̄00} HA prism faces, which grow through transitions of atoms from adjacent grains that are in contact through their planes with large Miller indices. The recrystallization process may be accompanied by a “collision” of vicinal growth surfaces of grains with relatively large misalignment angles and the formation of grain boundaries nanofaceted by prism planes of adjacent grains. The recrystallization process in such a case should be expected to continue in the grain with a smaller nonsingularity of the growth front. Grain boundaries may allow for a match between planes differing in Miller indices, nd{sub h1k1l1} ≈ md{sub h2k2l2}, and the formation of grain-boundary Pumphrey dislocations, which compensate for the size mismatch between interplanar spacings and/or misalignment of the planes. The observed characteristic grain match configurations are typical of both ceramics produced by sintering HA powders and HA films produced by ion sputtering.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Nd{sup 3+}:Y{sub 3}Al{sub 5}O{sub 12} laser ceramics: Influence of the size of yttrium oxide particles on sintering

The influence of the size of Y{sub 2}O{sub 3} powder particles on the structure formation and densification of Nd{sup 3+}:Y{sub 3}Al{sub 5}O{sub 12} laser ceramics has been studied. It is shown that the use of 50- and 100-nm yttrium oxide particles makes it possible to synthesize single-phase yttrium aluminum garnet at temperatures of 1200 and 1500°C, respectively, whereas in the case of 5000-nm yttrium oxide particles 2-h exposure at a temperature of 1500°C yields only 80 wt % of the Nd{sup 3+}:Y{sub 3}Al{sub 5}O{sub 12} phase. Bulk swelling of pressed samples during sintering of 2.94Y{sub 2}O{sub 3}-0.06Nd{sub 2}O{sub 3}-5Al{sub 2}O{sub 3} powders with the size ratio of the initial particles R(Al{sub 2}O{sub 3}/Y{sub 2}O{sub 3}) ∼ 5 is observed. The application of different-sized powders (R ∼ 2.5) provides quantitative ratios between phases in the 3Y{sub 2}O{sub 3}-5Al{sub 2}O{sub 3} system at which shrinkage in a temperature range of 20–1500°C is dominant. Laser ceramics 0–2 at % Nd{sup 3+}:Y{sub 3}Al{sub 5}O{sub 12} have been obtained by the solid-phase sintering of oxide powders (R ∼ 2.5). The slope efficiency for 1 at % Nd{sup 3+}:Y{sub 3}Al{sub 5}O{sub 12} laser ceramics is found to be 33%.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Thermodynamic Properties and Phase Transitions of Microcrystalline and Nanostructured SmFeO{sub 3} Ceramics

The heat capacity and dielectric properties of microcrystalline and nanostructured SmFeO{sub 3} ceramics obtained by solid phase synthesis are studied. The ceramics is synthesized by the treatment of the batch at room temperature in Bridgman anvils by forceful action combined with shear deformation followed by sintering. It is established that the mechanoactivation results in noticeable broadening antiferromagnetic–ferroelectric transition and shifting the temperature of phase transition in the low-temperature area. The phase transition having typical for relaxation oscillator frequency dependent character is found at 558 K. It is shown that the defect structure can take a dominant place in the formation of the physical properties of ceramics.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Superhard Nanostructured Ceramic–Metal Coatings with a Low Macrostress Level

The macrostressed state of (Ti,Al)N–Cu and (Ti,Al)N–Ni ceramic–metal coatings obtained by the arc-PVD method has been studied using X-ray diffraction and by measuring the radius of curvature of a coating–base composite sample (Stoney’s method). It is established that the presence of a tough metal phase favors significant reduction in the level of macrostresses in these structures as compared to those in (Ti,Al)N ceramic coatings, the absolute values of which decrease from 4.7–4.3 to 0.17–0.32 GPa. At the same time, both Ti–Al–Cu–N and Ti–Al–Ni–N coatings retain high hardness of 43 and 51 GPa, respectively, versus 29 GPa for Ti–Al–N coatings. The obtained results give grounds to suppose that the high hardness of the ceramic–metal coatings studied is determined by their nanocrystalline structure rather than by compressive macrostresses.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2019

Spark Plasma Sintering of SmS-Based Ceramic Targets for the Magnetron Sputtering

The results of studying the electric-spark plasma sintering of samarium monosulfide ceramics are presented. The dependence of the microstructure and phase composition of ceramics on the temperature of spark plasma sintering is studied on the basis of the data of scanning electron microscopy, energy dispersion X-ray microanalysis, and powder X-ray diffraction of synthesized samples. It is shown that a dense, nonporous ceramics, the phase composition of which is close to the composition of the initial powder, is formed at a sintering temperature of 1200°C.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

A uranium bed with ceramic body for tritium storage

It is widely recognized that ceramic coatings provide an attractive solution to lower tritium permeation in structural materials. Alumina based ceramic coatings have the highest permeation reduction factor for hydrogen. For this reason an attempt was made to apply crack-free low porous ceramics as a structural material of a bed body for tritium storage in a setup used for hydrogenating neutron tube targets at VNIIA. The present article introduces the design of the bed. This bed possesses essentially a lower hydrogen permeation factor than traditionally beds with stainless steel body. Bed heating in order to recover hydrogen from the bed is suggested to be implemented by high frequency induction means. Inductive heating allows decreasing the time necessary for tritium release from the bed as well as power consumption. Both of these factors mean less thermal power release into glove box where a setup for tritium handling is installed and thus causes fewer problems with pressure regulations inside the glove box. Inductive heating allows raising tritium sorbent material temperature up to melting point. The latter allows achieving nearly full tritium recovery.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Ceramic composites: A review of toughening mechanisms and demonstration of micropillar compression for interface property extraction

We present that ceramic fiber–matrix composites (CFMCs) are exciting materials for engineering applications in extreme environments. By integrating ceramic fibers within a ceramic matrix, CFMCs allow an intrinsically brittle material to exhibit sufficient structural toughness for use in gas turbines and nuclear reactors. Chemical stability under high temperature and irradiation coupled with high specific strength make these materials unique and increasingly popular in extreme settings. This paper first offers a review of the importance and growing body of research on fiber–matrix interfaces as they relate to composite toughening mechanisms. Second, micropillar compression is explored experimentally as a high-fidelity method for extracting interface properties compared with traditional fiber push-out testing. Three significant interface properties that govern composite toughening were extracted. For a 50-nm-pyrolytic carbon interface, the following were observed: a fracture energy release rate of ~2.5 J/m 2 , an internal friction coefficient of 0.25 ± 0.04, and a debond shear strength of 266 ± 24 MPa. Lastly, this research supports micromechanical evaluations as a unique bridge between theoretical physics models for microcrack propagation and empirically driven finite element models for bulk CFMCs.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗