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At least 1,171 records · Page 65
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Mechanical properties of aluminosilicate fiber heat-treated from 800 °C to 1400 °C: Effects of phase transition, grain growth and defects

Highlights: • As reaction between amorphous SiO{sub 2} and γ-Al{sub 2}O{sub 3}, phase transition was triggered at ≈1150 °C in AS fiber, thus forming mullite. • Grain size of formed mullite phase was evidently increased as the heat-treated temperature increased from 1200 °C to 1400 °C. • Higher density flaws were formed at higher temperatures, which led to significant degradation of strength of the AS fiber. - Abstract: Thermal stability of oxide fiber is a key property for high temperature structural applications of typical oxide fiber reinforced oxide matrix composites. This work contributes to provide insight into the mechanical properties of a typical aluminosilicate (AS) fiber heat-treated from 800 °C to 1400 °C in air, with the emphasis on the effects of phase transition, grain growth and defect formations. The results showed a phase reaction occurring at 1150 °C, which formed an orthorhombic structured mullite phase. The grain size of the newly formed mullite was observed increased significantly at higher temperatures. Both the phase transition and grain size led to more flaw formations in the microstructure, which influenced significantly the mechanical property of the AS fiber. Specifically, the Young's modulus and tensile strength were both degraded remarkably from ≈145 GPa to ≈110 GPa, and from ≈1.03 GPa to ≈0.52 GPa, respectively, as the heat-treatment temperature increased from 1200 °C to 1400 °C. Finally, the formations of more flaws yielded a higher dispersion of tensile strength of AS fiber, due to the volume dependent flaw distributions, as revealed by the Weibull statistical analysis.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Simultaneously improving mechanical properties and corrosion resistance of pure Ti by continuous ECAP plus short-duration annealing

Highlights: • Additional short-time annealing led to enhanced strength of UFG Ti due to texture strengthening. • UFG Ti showed improved corrosion resistance in artificial seawater compared with initial CG Ti. • Short-duration annealing enhanced corrosion resistance of UFG Ti due to stronger basal texture. - Abstract: This work investigated the effect of short-duration annealing on mechanical properties and corrosion behavior of bulk ultrafine-grained (UFG) pure Ti (grade 2) produced by high-efficiency equal-channel angular pressing (ECAP), serving the fast developing of marine industries. The initial coarse-grained (CG) Ti achieved higher strength after continuous ECAP at 420 °C for 4 passes, while additional short-duration annealing at 300 °C for 15 min of UFG Ti further led to extraordinary improvement of strength, which was associated with texture strengthening. The yield strength was increased from 362 MPa in as-received state to 561 MPa in post-ECAP annealed condition, and ultimate tensile strength from 450 MPa to 663 MPa. The ECAP-processed UFG Ti had better corrosion resistance in artificial seawater than the initial CG Ti. Short-duration annealing further improved the corrosion resistance of UFG Ti, which was related to stronger basal texture. The corrosion current density decreased from 68.37 nA cm{sup −2} for CG Ti in as-received condition to 41.77 nA cm{sup −2} for UFG Ti processed by ECAP plus short-duration annealing. The fraction of TiO{sub 2} within the surface oxide film for the post-ECAP annealed sample was increased. The bulk UFG Ti after post-ECAP short-duration annealing revealed an excellent combination of high strength, good ductility and superior corrosion resistance for marine applications.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Beam current effect as a potential challenge in SEM-EBSD in situ tensile testing

Highlights: • In situ SEM-EBSD tensile tests were conducted using 304L steels with 8 and 10.4% Ni. • KAM and GROD evolution, twinning, and phase instability were investigated. • Phase transformation in 8% Ni-steel was sensitive to the electron beam current. In situ mechanical tensile tests coupled with electron backscatter diffraction (EBSD) analysis were conducted using specimens of two 304L steels with ~8 and 10.4% Ni content, respectively. Twinning was observed in steel with 10.4% Ni content, whereas steel with 8% Ni content demonstrated martensitic transformation. Testing showed that the kinetics of martensitic transformation in steel with 8% Ni content was influenced by the electron beam current used during EBSD scans. Continuous scanning using 32 nA nominal beam current led to suppression of the phase instability in the near-surface layer, but acceptable comparable-to-the-bulk results were obtained using 8 nA beam current. The exact mechanism of the beam current role is unclear, but it appears to be neutral regarding Kernel Average Misorientation behavior and deformation-induced twinning.

36 MATERIALS SCIENCE↗
DOE OSTI2012

A new green phosphor of SrAl{sub 2}O{sub 4}:Eu{sup 2+},Ce{sup 3+},Li{sup +} for alternating current driven light-emitting diodes

Graphical abstract: Display Omitted Highlights: ► This work focuses on exploring new phosphors of SrAl{sub 2}O{sub 4}:Eu{sup 2+},Ce{sup 3+},Li{sup +} for AC LEDs. ► The work provides a new route to synthesize the pure phase of SrAl{sub 2}O{sub 4}. ► The formation of the impurity phase of Sr{sub 4}Al{sub 14}O{sub 25} was suppressed by using Ce{sup 3+}. ► Charger defects were compensated by using Li{sup +}. ► The luminescence intensity was enhanced significantly by co-doping Ce{sup 3+} and Li{sup +}. -- Abstract: New phosphors are desired to overcoming the flickering luminescence of alternating current light-emitting diodes (AC-LEDs) by compensating dark duration with appropriately persistent luminescence. Here, the phosphor of SrAl{sub 2}O{sub 4}:Eu{sup 2+},Ce{sup 3+},Li{sup +} was developed for this application. The phosphor was synthesized with solid-state reaction method by using H{sub 3}BO{sub 3} as flux. The XRD patterns show that the impurity phase of Sr{sub 4}Al{sub 14}O{sub 25} which always formed together with SrAl{sub 2}O{sub 4} during reaction was suppressed by using Ce. The charger defects caused by the non-equivalent substitution of Sr{sup 2+} with Ce{sup 3+} were compensated with Li{sup +}. Thus, the luminescence intensity of SrAl{sub 2}O{sub 4}:Eu{sup 2+} was enhanced significantly by co-doping Ce{sup 3+} and Li{sup +}. The fluorescence lifetime of the phosphor is about 36.5 ms. The energy dispersive spectra (EDS) assisted with scanning electron microscope (SEM) pictures reveal that Ce ions mainly distribute along grain boundary.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Preparation of novel Sb{sub 2}O{sub 3}/WO{sub 3} photocatalysts and their activities under visible light irradiation

Highlights: ► Visible-light-driven Sb{sub 2}O{sub 3}/WO{sub 3} photocatalysts were synthesized. ► Results showed that RhB can be decomposed using a 4 W LED lamp as visible light. ► The coupling of Sb{sub 2}O{sub 3} and WO{sub 3} enhanced the photocatalytic activity of WO{sub 3}. - Abstract: Novel visible-light-driven Sb{sub 2}O{sub 3}/WO{sub 3} photocatalysts were prepared by a hydrothermal synthesis followed by heat treatment, and characterized by transmission electron microscopy (TEM), scanning electron microscope (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), BET surface area, Fourier transform infrared spectroscopy (FT-IR) and photoluminescence spectra (PL). The photocatalytic activities of Sb{sub 2}O{sub 3}/WO{sub 3} photocatalysts were evaluated by the rhodamine B degradation using a LED lamp as visible light irradiation. Compared with pure WO{sub 3} and Sb{sub 2}O{sub 3}, the significantly enhanced photocatalytic activities of the Sb{sub 2}O{sub 3}/WO{sub 3} composite particles are attributed to the decrease of the recombination rate of photoinduced electron–hole pairs due to the coupling of Sb{sub 2}O{sub 3} and WO{sub 3} within the composite nanoparticles. Studies of Sb{sub 2}O{sub 3}/WO{sub 3} composites indicate that one approach to design composite materials with enhanced photocatalytic performance is through coupling Sb{sub 2}O{sub 3} with WO{sub 3}, which the lowest energy states for electrons and holes are in different semiconductors.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Synthesis and luminescent properties of a white light phosphor KBa{sub 2}Nb{sub 5}O{sub 15}:Na{sup +}, Dy{sup 3+} for light-emitting-devices

Graphical abstract: - Highlights: • A novel red phosphor KBa{sub 2}Nb{sub 5}O{sub 15}:Dy{sup 3+} was synthesized and investigated firstly. • Crystal structure and characteristic luminescence properties are discussed. • The charge compensation mechanism is also investigated. • It has low color tolerance and better CIE chromaticity coordinates. - Abstract: The white light emission phosphor KBa{sub 2}Nb{sub 5}O{sub 15}:Dy{sup 3+} was synthesized by solid-state method. X-ray diffraction (XRD) study reveals that all the Dy{sup 3+} doped phosphors are single phase. Strong excitation peaks of KBa{sub 2}Nb{sub 5}O{sub 15}:Dy{sup 3+} were found around 380–400 nm, matched well with the NUV LED chip. Under 388 nm excitation, the phosphor exhibited intense white emission by combining the two emission peaks at 477 nm and 572 nm, attributed to the characteristic {sup 4}F{sub 9/2}–{sup 6}H{sub 15/2} and {sup 4}F{sub 9/2}–{sup 6}H{sub 13/2} transition of Dy{sup 3+}. The optimum doping concentration of Dy{sup 3+} is found to be 3%, whose Commission International de l’ Eclairage (CIE) chromaticity coordinates and correlated color temperature are (0.395, 0.422) and 3925 K, respectively. The results indicate that the KBa{sub 2}Nb{sub 5}O{sub 15}:Dy{sup 3+} phosphor could be considered as a potential candidate for white-LEDs.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Phase transition and multicolor luminescence of Eu{sup 2+}/Mn{sup 2+}-activated Ca{sub 3}(PO{sub 4}){sub 2} phosphors

Graphical abstract: We have synthesized Eu{sup 2+} doped and Eu{sup 2+}/Mn{sup 2+} co-doped Ca{sub 3}(PO{sub 4}){sub 2} phosphors. The emitting color varies from blue to green with increasing of Eu{sup 2+} content for the Eu{sup 2+}-doped phosphor, and the quantum yield of the 0.05Eu{sup 2+}: Ca{sub 2.95}(PO{sub 4}){sub 2} sample reaches 56.7%. Interestingly, Mn{sup 2+} co-doping into Eu{sup 2+}: Ca{sub 3}(PO{sub 4}){sub 2} leads to its phase transition from orthorhombic to rhombohedral, and subsequently generates tunable multi-color luminescence from green to red via Eu{sup 2+} → Mn{sup 2+} energy transfer. - Highlights: • A series of novel Eu{sup 2+}: Ca{sub 3}(PO{sub 4}){sub 2} phosphors were successfully synthesized. • Phase transition of Ca{sub 3}(PO{sub 4}){sub 2} from orthorhombic to rhombohedral occurred when Mn{sup 2+} ions were doped. • The phosphors exhibited tunable multi-color luminescence. • The quantum yield of 0.05Eu{sup 2+}: Ca{sub 2.95}(PO{sub 4}){sub 2} phosphor can reach 56.7%. • The analyses of phosphors were carried out by many measurements. - Abstract: Intense blue-green-emitting Eu{sup 2+}: Ca{sub 3}(PO{sub 4}){sub 2} and tunable multicolor-emitting Eu{sup 2+}/Mn{sup 2+}: Ca{sub 3}(PO{sub 4}){sub 2} phosphors are prepared via a solid-state reaction route. Eu{sup 2+}-doped orthorhombic Ca{sub 3}(PO{sub 4}){sub 2} phosphor exhibits a broad emission band in the wavelength range of 400–700 nm with a maximum quantum yield of 56.7%, and the emission peak red-shifts gradually from 479 to 520 nm with increase of Eu{sup 2+} doping content. Broad excitation spectrum (250–420 nm) of Eu{sup 2+}: Ca{sub 3}(PO{sub 4}){sub 2} matches well with the near-ultraviolet LED chip, indicating its potential applications as tri-color phosphors in white LEDs. Interestingly, Mn{sup 2+} co-doping into Eu{sup 2+}: Ca{sub 3}(PO{sub 4}){sub 2} leads to its phase transition from orthorhombic to rhombohedral, and subsequently generates tunable multi-color luminescence from green to red via Eu{sup 2+} → Mn{sup 2+} energy transfer, under 365 nm UV lamp excitation.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Temperature dependence of the luminescence of calcium-magnesium phosphate Ca{sub 3}Mg{sub 3}(PO{sub 4}){sub 4}:Eu{sup 2+}, a blue-emitting material for white light-emitting diodes

Graphical abstract: - Highlights: • Emission spectrum at 20 K confirms that Eu{sup 2+} ions occupy three sites. • Decay curves of three types of Eu{sup 2+} reflect the characteristics of energy transfer. • The Eu(I) emission is thermally quenched at 323 K. • Ca{sub 3}Mg{sub 3}(PO{sub 4}){sub 4}:Eu{sup 2+} has good thermal stability. • Ca{sub 3}Mg{sub 3}(PO{sub 4}){sub 4}:Eu{sup 2+} is a promising phosphor for near UV excited white LEDs. - Abstract: A blue-emitting phosphor Ca{sub 3}Mg{sub 3}(PO{sub 4}){sub 4}:Eu{sup 2+} peaking at 450 nm was synthesized by a solid state reaction. The XRD patterns, luminescence properties, decay curves of samples as well as their thermal quenching and comparing the luminescence properties with that of commercial material were investigated. At 20 K, the emission spectrum exhibiting two distinct bands peaking at 437 and 473 nm with a shoulder peak at 510 nm can be attributed to the overlap of Eu(I), Eu(II) and Eu(III) emission bands. At 423 K the PL intensity decreases to 80% of the value at room temperature, and the emission wavelength shifts toward high energy. The derived activation energy indicates that the lowest energy level of the Eu{sup 2+} 4f{sup 6}5d{sup 1} state is well isolated from the host lattice conduction band. The PL spectra and chromaticity coordinates are close to those of BAM. Ca{sub 3}Mg{sub 3}(PO{sub 4}){sub 4}:Eu{sup 2+} could be a potential candidate for near-UV excited white LEDs.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Synthesis and photoluminescence properties of Ca{sub 19}Mg{sub 2}(PO{sub 4}){sub 14}:Sm{sup 3+} red phosphor for white light emitting diodes

Highlights: • A novel red phosphor Ca{sub 19}Mg{sub 2}(PO{sub 4}){sub 14}:Sm{sup 3+} was synthesized and investigated firstly. • The structure and characteristic luminescence properties are discussed. • The excellent thermal stability was found and investigated. • It has good color saturation, the CIE is close to that of commercial Y{sub 2}O{sub 3}:Eu{sup 3+}. - Abstract: A series of Sm{sup 3+} doped Ca{sub 19}Mg{sub 2}(PO{sub 4}){sub 14} red phosphors were successfully synthesized. X-ray diffraction analysis indicates that all the samples are single phased. The luminescence property is investigated in detail by measuring their photoluminescence excitation and emission spectra. Ca{sub 19}Mg{sub 2}(PO{sub 4}){sub 14}:Sm{sup 3+} phosphors show strong absorption in 400–410 nm region, which is suitable for application in LEDs. When excited at 403 nm, Ca{sub 19}Mg{sub 2}(PO{sub 4}){sub 14}:Sm{sup 3+} phosphor can emit red emission with CIE chromaticity coordinates (0.615, 0.384). The optimal doping concentration of Sm{sup 3+} doped Ca{sub 19}Mg{sub 2}(PO{sub 4}){sub 14} is measured to be 0.02. The thermal quenching property is also measured and compared with the commercial red phosphor Y{sub 2}O{sub 3}:Eu{sup 3+} (Topstar, TXC-RIA). The results indicate Ca{sub 19}Mg{sub 2}(PO{sub 4}){sub 14}:Sm{sup 3+} phosphors have potential to serve as a red phosphor for white LEDs.

36 MATERIALS SCIENCE↗
DOE OSTI2014

The site occupation and valence of Mn ions in the crystal lattice of Sr{sub 4}Al{sub 14}O{sub 25} and its deep red emission for high color-rendering white light-emitting diodes

Highlights: • Different valences of Mn ions in Sr{sub 4}Al{sub 14}O{sub 25} were identified using XANES and EPR. • Red luminescence was attributed to Mn{sup 4+} occupying the center of AlO{sub 6} octahedron. • The Mn{sup 3+} incorporated in the center of AlO{sub 4} tetrahedron was non-luminescent. • The bond-valence theory was used to analyze the effective valences of cations. • A white LED device with CRI up to Ra 93.23 was packaged by using the red phosphor. - Abstract: The synthesis and component of red phosphor, Sr{sub 4}Al{sub 14}O{sub 25}: Mn, were optimized for application in white light-emitting diodes. The microstructure and morphology were investigated by the X-ray diffraction and scanning electron microscopy. Different valences of Mn ions in Sr{sub 4}Al{sub 14}O{sub 25} were discriminated using the electron paramagnetic resonance and X-ray absorption near-edge structure spectroscopy techniques. The bond-valence theory was used to analyze the effective valences of Sr{sup 2+} and Al{sup 3+} in Sr{sub 4}Al{sub 14}O{sub 25}. As a result, the strong covalence of Al{sup 3+} in the AlO{sub 4} tetrahedron other than in the AlO{sub 6} octahedron is disclosed. The deep red emission is attributed to Mn{sup 4+} occupying the center of AlO{sub 6} octahedron. The mechanism of energy transfer is mainly through dipole–dipole interaction, revealed by the analyses of critical distance and concentration quench. A high color rendering white LED prototype with color-rendering index up to Ra 93.23 packaged by using the red phosphor demonstrates its applicability.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Li doping effect on the photoluminescence behaviors of KSrPO{sub 4}:Dy{sup 3+} phosphors for WLED light

Highlights: • The luminescence intensity of KSrPO{sub 4}:Dy{sup 3+} can be increased with Li{sup +} ions co-doping. • The mechanisms for the emitting enhancement with Li{sup +} ions co-doping were investigated. • The thermal stability demonstrated that KSrPO{sub 4}:0.01Dy{sup 3+}, 0.06Li{sup +} is suitable for WLEDs. • The chromaticity coordinates of KSrPO{sub 4}:Dy{sup 3+}, Li{sup +} can be tuned with Li{sup +} ions increasing. - Abstract: A novel warm-white phosphor KSrPO{sub 4} co-doped with Dy{sup 3+} and Li{sup +} ions was prepared by solid state reaction. A strategy of Li{sup +} doping was used with the aim of enhancing the luminescence of 475 nm and 570 nm emission bands under NUV excitation. Compared to lithium-free KSrPO{sub 4}:Dy{sup 3+}, the intensities of the 570 nm emission peaks were increased by 4.32 times and 2.84 times excited by 351 nm and 388 nm with 6 mol% Li{sup +} ions co-doping, respectively. The mechanism of the enhancement was discussed, that is due to the improvement of the phosphors’ crystallinity and charge compensation when the Li{sup +} ions were introduced. Furthermore, the thermal stability of KSrPO{sub 4}:0.01Dy{sup 3+}, 0.06Li{sup +} was measured and discussed, demonstrating it can be applied for high-powered LED. And the chromaticity coordinates of KSrPO{sub 4}:0.01Dy{sup 3+}, xLi{sup +} can be tuned efficiently from the cold-white region to warm-white region with Li{sup +} ions increasing, presenting its potential applied value as a new warm-white LED phosphor.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Enhancement of photoluminescence properties and modification of crystal structures of Si{sub 3}N{sub 4} doping Li{sub 2}Sr{sub 0.995}SiO{sub 4}:0.005Eu{sup 2+} phosphors

Highlights: • Si{sub 3}N{sub 4} modified Li{sub 2}Sr{sub 0.995}SiO{sub 4}:0.005Eu{sup 2+} phosphors were prepared. • The luminescence intensity of Li{sub 2}Sr{sub 0.995}SiO{sub 4}:Eu{sup 2+} was enhanced by doping Si{sub 3}N{sub 4}. • The fluorescence decay times and thermal stability were enhanced by doping Si{sub 3}N{sub 4}. - Abstract: Si{sub 3}N{sub 4} modified Li{sub 2}Sr{sub 0.995}SiO{sub 4}:0.005Eu{sup 2+} (Li{sub 2}Sr{sub 0.995}SiO{sub 4−3x/2}N{sub x}:0.005Eu{sup 2+}) phosphors were synthesized with the conventional solid-state reaction in the reduced atmosphere. The crystal structure and vibrational modes were analyzed by X-ray diffraction, Raman scattering spectroscopy and Rietveld crystal structure refinement. Photoluminescence (PL) and photoluminescence excitation (PLE) spectra showed that Li{sub 2}Sr{sub 0.995}SiO{sub 4−3x/2}N{sub x}:0.005Eu{sup 2+} powder exhibited a broad yellow emission band centered at 560 nm under the excitation of 460 nm visible light, due to the 4f{sup 6}5d{sup 1} → 4f{sup 7} transition of Eu{sup 2+}. The partial nitridation of Li{sub 2}Sr{sub 0.995}SiO{sub 4−3x/2}N{sub x}:0.005Eu{sup 2+} (x = 0.01) phosphors led to a large enhancement in the luminescence intensity, as much as 190%. At the same time, the fluorescence decay behavior curves further showed that the photoluminescence efficiencies of Li{sub 2}Sr{sub 0.995}SiO{sub 4−3x/2}N{sub x}:0.005Eu{sup 2+} phosphors were enhanced by addition of Si{sub 3}N{sub 4}. The temperature quenching characteristics confirmed that the oxynitride based Li{sub 2}Sr{sub 0.995}SiO{sub 4−3x/2}N{sub x}:0.005Eu{sup 2+} showed slightly higher stability. It is implied that Li{sub 2}Sr{sub 0.995}SiO{sub 4−3x/2}N{sub x}:0.005Eu{sup 2+} phosphors had a possible potential application on white LEDs to match blue light chips.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Luminescence properties of Eu2+-activated NaCaBeSi2O6F for white light-emitting diode applications

Highlights: • A novel blue-emitting garnet NaCaBeSi{sub 2}O{sub 6}F:Eu{sup 2+} phosphor was synthesized. • The broad NUV excitation band (300–400 nm) gives blue emission. • The LED made with NaCaBeSi{sub 2}O{sub 6}F:Eu{sup 2+} and green and red-emitting phosphors gives white-light emission. - Abstract: A series of blue-emitting NaCaBeSi{sub 2}O{sub 6}F:Eu{sup 2+} phosphors were obtained via a solid state reaction. NaCaBeSi{sub 2}O{sub 6}F:Eu{sup 2+} exhibit a broad absorption from 250 to 450 nm when monitored at 467 nm and display a broad emission band from 400 to 600 nm when excited at 397 nm. The concentration quenching was obtained when the concentration of Eu{sup 2+} was increased to 0.8 mol%. Energy transfer interactions between Eu{sup 2+} in host is due to dipole-dipole mechanisms and the critical distance was calculated to be 31.96 Å. The results obtained in this study highly indicates that NaCaBeSi{sub 2}O{sub 6}F:Eu{sup 2+} can be a potential blue-emitting phosphor for light quality improvement in white-LED applications.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Room-temperature synthesis and characterization of carbon-encapsulated molybdenum nanoparticles

Highlights: • Carbon-encapsulated molybdenum nanoparticles were synthesized at room temperature. • Different hydrocarbons were used as carbon source for shell formation. • Increase of hydrocarbon mole ratio resulted in decrease of Mo-based nanoparticle cores. • Increase of laser pulses number resulted in increase of Mo content in CEMNPs. • Carbon shells prevented Mo nanoparticles from aggregation. - Abstract: Carbon-encapsulated molybdenum nanoparticles were synthesized by laser-assisted photolysis of gaseous precursors. In the proposed method, gas mixtures containing various hydrocarbons and molybdenum hexacarbonyl vapor diluted in argon were irradiated with a nanosecond pulsed UV laser at room temperature. Particle samples were analyzed by transmission electron microscopy (TEM), electron microdiffraction (EMD), energy-dispersive X-ray spectroscopy (EDS), and high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) techniques to observe the morphology and composition of the Mo/C nanoparticles. The influence of the type of hydrocarbon, its mole fraction, and the number of UV laser pulses on the resulting nanoparticles was investigated. The nanoparticles were heavily aggregated and consisted of Mo-based cores surrounded by carbon. The type of hydrocarbon did not have any visible effects on the nanoparticle structure and the size of the Mo-based cores or aggregates. Increasing the hydrocarbon mole fraction in the precursor mixture led to an increase in the carbon content and decrease of the Mo-based core size. Increasing the number of UV laser pulses led to larger Mo cores.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2018

Two-step synthesis of a novel red-emitting Ba2ZrF8:Mn4+ phosphor for warm white light-emitting diodes

Highlights: • A novel red-emitting Ba{sub 2}ZrF{sub 8}:Mn{sup 4+} was prepared by two-step method at low temperature. • The phosphor shows an intense red emission under 460 nm excitation matching well with blue LED chip. • The energy transfer between Mn{sup 4+} was confirmed to be electric dipole-quadrupole interaction. - Abstract: A novel red-emitting Ba{sub 2}ZrF{sub 8}: Mn{sup 4+} phosphor was prepared by two-step method at low temperature, where critical precursor K{sub 2}MnF{sub 6} was prepared first by the reduction of KMnO{sub 4} using H{sub 2}O2 as reducer. The crystal structure and morphology of the phosphor was characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) equipped with energy-dispersive X-ray spectroscopy (EDS), showing single phase product. Luminescent properties of the phosphor were investigated by photoluminescence spectroscopy (PL) and decay curves. The molar ratio of KMnO{sub 4}: KHF{sub 2} was confirmed to play the key role in improving the luminous efficiency. More importantly, the phosphor exhibits a broadband excitation from 300 to 520 nm due to {sup 4}A{sub 2g}→{sup 4}T{sub 1g} and {sup 4}A{sub 2g}→{sup 4}T{sub 2g} transition of Mn{sup 4+}, matching well with blue LED chips. Under 465 nm excitation, intense red emission at around 630 nm with high color purity is achieved, suggesting the red-emitting phosphor has great potential for white light-emitting diodes (wLEDs).

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Tuning the activity of Cu-containing rare earth oxide catalysts for CO oxidation reaction: Cooling while heating paradigm in microwave-assisted synthesis

Highlights: • Organic chemistry synthesis concepts have been smartly tailored to catalysts’ development. • Enhanced microwave synthesis of (Ce-La-10Cu)O{sub 2} led to an one phase system. • CO{sub 2}-philicity, and oxygen vacancies can be tuned by synthesis. • Coupling microwave with air cooling led to T{sub 50} decrease by 32% in the CO oxidation reaction. - Abstract: (Ce-La-xCu)O{sub 2} catalysts with low (3 at.%) and high (10 at.%) Cu content were prepared by conventional microwave (MW) and enhanced microwave methods where air cooling (AC), while heating, was applied. The catalysts were tested for the CO oxidation reaction in the 25–500 °C range using 4%CO/20%O{sub 2}/He feed gas. Varying spectroscopic, microscopic and catalytic studies were used to probe the effect of synthesis on the nanostructure and the CO oxidation performance. It was found that the synthesis method adopted impacts on the extent of the Cu doping into the (Ce-La)O{sub 2} fluorite lattice, hence leading to one and two phases system in the case of catalyst prepared through enhanced (AC) and conventional (MW) microwave methods, respectively. Furthermore, only Ce{sup 4+} species were found on the surface of the (Ce-La-10Cu)O{sub 2} catalysts synthesized using MW and AC (XPS studies), whereas oxygen vacant sites which are associated with Ce{sup 3+} ions were indicated in the sub-surface/bulk (Raman studies). Ultimately, the catalysts with the low and high Cu loading, prepared under the AC-promoted microwave method, presented a superior performance against CO oxidation, exhibiting an overall improvement of the catalytic activity by 16% and 32%, respectively.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2024

From solid surfactants to micromotors: An overview of the synthesis and applications of heterogeneous particles

Colloid science has classically concerned itself with the investigation of the properties of dispersed phases in a bulk medium. This has led to the development of a rich amount of chemistry, physics, and engineering that have facilitated the evolution and maturation of this field. One of the many developments made over the last 30 years is the introduction of particles that are heterogeneous in chemistry and shape. These heterogeneities can introduce behaviors that are not achievable in homogeneous systems and that are specific to the type and class of nonuniformity. This has led to the development of numerous technologies, two of which are Janus micromotors and solid surfactants. Here, this review aims to familiarize the reader with the field of heterogeneous particles. We begin with an overview of various synthetic methods to produce colloidal particles that are heterogeneous in chemistry and shape. We then discuss their use as solid surfactants and autonomous micromotors. We then close by summarizing and providing a future perspective on the field.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Effects of surface treatments on ABS mechanical properties from fused filament fabrication

This paper examines the influence of surface treatments on the mechanical properties of acrylonitrile butadiene styrene (ABS) samples printed by fused filament fabrication (FFF). Prior efforts have applied brushing, painting, solvent dipping, infiltration, and vapor smoothing as post-processing surface treatments to improve the mechanical properties of FFF components. Additionally, because FFF can produce components with undesirable surface roughness, mechanical abrasion, epoxy coating, and acetone treatment may increase tensile strength by decreasing stress concentrations. Ridged surface texture may provide desirable tribological or handling properties. Based on these opportunities, this paper investigates abrasive media blasting, epoxy coating, acetone immersion, and ridged texturing surface treatments on the tensile strength and other mechanical properties of FFF ABS samples. ASTM D638-14 Type-I samples were printed, treated on all sample sides, and tested. From tensile tests, the elastic modulus, tensile strength, and fracture strain for both the untreated and treated ABS samples were calculated. For each sample, the surface finish and fracture macromorphology were observed with optical microscopy and the roughness values for the surface finish were calculated from profilometer data. Furthermore, samples were submerged in water and weighed periodically to measure mass changes due to water absorption. From surface profilometry and optical miscopy data, mechanical media blasting, epoxy coating, and immersion in all concentrations of acetone decreased surface roughness. Overall, on average, grit blasting with large beads and epoxy coating led to 2.6% and 1.2% increases in tensile strength, respectively; immersion in 40% acetone led to a 1.9% increase in tensile strength while treatment in 60% and 80% acetone decreased tensile strength by 4.9% and 1.9%, respectively. The study concludes that only grit blasting with large beads, immersion in 60% acetone, and the ridged texture significantly affected the tensile strength.

36 MATERIALS SCIENCE↗