Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “Solid”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,621 records · Page 90
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Deep eutectic solvent-based polymer electrolyte for solid-state lithium metal batteries

Poly(ethylene) oxide (PEO)-based electrolytes have been widely studied for solid-state lithium batteries while their ionic conductivity and lithium-ion transference number still need to be further improved. Herein, using the combined experimental and theoretical approach, we demonstrate a novel, solid-state PEO-deep eutectic solvent (DES) electrolyte for the first time. We found that the in situ formation of DES can reduce the crystallinity of PEO matrix and more Li + ions can move freely owing to the weakened coordination between ether oxygens and Li-ions. Besides, we show that more Li + ions can be dissociated from Li salts in PEO-DES electrolyte using the molecular dynamics simulations. Such liquid-free PEO-DES electrolytes showed good ionic conductivity (2.1 × 10 −4 S cm −1 ) which is 160% higher than that of conventional PEO-LiTFSI (8.1 × 10 −5 S cm −1 ) electrolyte at 60 °C. Additionally, the PEO-DES electrolyte showed 136% increase of Li-ion transference number (0.33) compared with ionic liquid-doped PEO-LiTFSI (0.14) at 60 °C. Moreover, the PEO-DES exhibited good compatibility with Li metal and stable Li plating/stripping behavior with little morphology change of Li metal. In conclusion, this research also provides new insights into the enhancement mechanisms of novel polymer electrolytes, improving our fundamental understanding of critical challenges that have impeded the adoption of solid-state lithium metal batteries.

Deep eutectic solvent↗
DOE OSTI2020

Tailoring grain growth and solid solution strengthening of single-phase CrCoNi medium-entropy alloys by solute selection

In the present study, we selected solutes to be added to the CrCoNi medium-entropy alloy (MEA) based on the mismatch of self-diffusion activation energy (SDQ) between the alloying elements and constituent elements of the matrix, and then investigated their grain growth behavior and mechanical properties. Mo and Al were selected as the solutes for investigation primarily because they have higher and lower SDQ, respectively, than those of the matrix elements; a secondary factor was their higher and lower shear modulus. Their concentrations were fixed at 3 at.% each because previous work had shown these compositions to be single-phase solid solutions with the face-centered cubic structure. Three alloys were produced by arc melting, casting, homogenizing, cold rolling and annealing at various temperatures and times to produce samples with different grain sizes. They were (a) the base alloy CrCoNi, (b) the base alloy plus 3 at.% Mo, and (c) the base alloy plus 3 at.% Al. The activation energies for grain growth of the CrCoNi, CrCoNi-3Mo and CrCoNi-3Al MEAs were found to be ~251, ~368 and ~219 kJ/mol, respectively, consistent with the notion that elements with higher SDQ (in this study Mo) retard grain growth (likely by a solute-drag effect), whereas those with lower values (Al) accelerate grain growth. The room-temperature tensile properties show that Mo increases the yield strength by ~40% but Al addition has a smaller strengthening effect consistent with their relative shear moduli. The yield strength as a function of grain size for the three singlephase MEAs follows the classical Hall-Petch relationship with much higher slopes (> 600 MPa μm -0.5 ) than traditional solid solutions. Furthermore, this work shows that the grain growth kinetics and solid solution strengthening of the CrCoNi MEA can be tuned by selecting solute elements that have appropriate diffusion and physical properties.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Manufacturing scalability implications of materials choice in inorganic solid-state batteries

The pursuit of scalable and manufacturable all-solid-state batteries continues to intensify, motivated by the rapidly increasing demand for safe, dense electrical energy storage. Here, we describe the numerous, often conflicting implications of materials choices that have been made in the search for effective mitigations to the interfacial instabilities plaguing solid-state batteries. Specifically, we show that the manufacturing scalability of solid-state batteries can be governed by at least three principal consequences of materials selection: (1) the availability, scaling capacity, and price volatility of the chosen materials’ constituents, (2) the manufacturing processes needed to integrate the chosen materials into full cells, and (3) the cell performance that may be practically achieved with the chosen materials and processes. While each of these factors is, in isolation, a pivotal determinant of manufacturing scalability, we show that consideration and optimization of their collective effects and trade-offs is necessary to more completely chart a scalable pathway to manufacturing.

25 ENERGY STORAGE↗
DOE OSTI2022

Zero carbon solid-state rechargeable redox fuel for long duration and seasonal storage

Here, this work presents a unique thermochemical process for charging magnesium-manganese-oxide-based solid-state rechargeable redox fuel. High-temperature heating of the processing furnace can be driven by either renewable electricity or concentrated solar power. The simple recyclable fuel charging concept is based on a tubular falling bed reactor with countercurrent oxygen-depleted gas flow for complete heat recuperation. The main focus of this work is achieving solid flowability at high temperatures (1,450°C) and extracting chemically charged solid at ambient temperature with minimal energy loss. The operation strategies described in this work have enabled consistent magnesium-manganese-oxide particle flow up to 1,450°C. The measured extent of the thermal reduction reaction after cooling the particles is more than 90% of the fully reduced state at equilibrium. The thermal-to-chemical efficiency and overall system efficiency are 96% and 35% respectively, which are the highest reported for thermochemical fuels to date.

25 ENERGY STORAGE↗
DOE OSTI2022

Effect of Gd-doped ceria infiltration into Ni-YSZ on reversible solid oxide cell operation

Gadolinium doped ceria (GDC) infiltration into Ni-(Y 2 O 3 ) 0•08 (ZrO 2 ) 0.92 (Ni-YSZ) fuel electrodes has been shown to significantly improve solid oxide electrolysis cell performance and stability. However, the effects of GDC infiltration on cells operated reversibly between fuel cell and electrolysis modes have not been reported previously. Here we present reversible solid oxide cell life test results for different GDC infiltration loadings into Ni-YSZ electrodes in two types of fuel-electrode-supported solid oxide cells. Electrochemical impedance spectroscopy reveals that GDC infiltrant lowers the initial cell area specific resistance (ASR) and limits the degradation – for example, the GDC-infiltrated electrode ASR increased by 0.1 Ω cm 2 over 1000 h of reversible operation at ±0.5 A cm –2 and 800 °C, compared to 0.19 Ω cm 2 for non-infiltrated cells. Cell voltage degradation rates were reduced by infiltration during operation at a current density of ±0.5 A cm –2 at 800 °C, and during at 700 °C at ±0.75 A cm –2 . Furthermore, scanning electron microscopy observations show that the infiltrated GDC nanoparticles mitigate Ni particle coarsening in the Ni-YSZ electrode, possibly explaining the enhanced cell stability.

25 ENERGY STORAGE↗
DOE OSTI2025

Mapping of fracture and ionic conductivity changes in ion implanted solid electrolytes: Insights from molecular dynamics

Ion implantation emerges as a promising technique to address the persistent challenge of lithium (Li) filament growth in solid-state electrolytes as it can induce compressive stresses inhibiting crack growth and deflect dendrites, de facto mitigating early electrolyte failure. In this study, we examine the potential paradox of ion implantation: while aiming to enhance electrolyte performance, the radiation damage associated with implantation might inadvertently compromise both the ionic conductivity and the intrinsic fracture toughness of the material, rendering the material unsuitable for battery applications. Specifically, we employed molecular dynamics simulations to examine the scope of the downsides of ion implantation, specifically: (i) reduced ionic conductivity (due to radiation-induced amorphization) and (ii) mechanical stability (due to radiation-induced embrittlement) in ion-implanted Li 7 La 3 Zr 2 O 12 (LLZO) solid-state electrolytes. We explore how radiation damage impacts LLZO’s crystalline structure, Li-ion diffusion, and fracture properties at various temperatures and radiation damage levels. The study aims to provide insights into the competing effects of ion implantation and suggest potential engineering strategies for developing more robust solid-state electrolytes with improved conductivity and dendrite resistance.

Conductivity↗
DOE OSTI2024

A method for generating quantitative vapor-phase infrared spectra of solids: results for phenol, camphor, menthol, syringol, dicyclopentadiene and naphthalene

Here, a method is presented to generate quantitative vapor-phase infrared spectra from substances that naturally occur as solids with moderate volatility. The solid is gravimetrically dissolved into a solvent that has few infrared spectral features, typically CS 2 and CCl 4 separately. The solution is flowed at a constant rate from a linearly pumped syringe into a metered stream of nitrogen carrier gas regulated by a mass flow controller. The analyte/solvent mix is flash vaporized by volatilizing the solution across a heated stainless-steel surface as it emanates from the syringe tip. The N 2 gas-solution mixture is flowed into a long-path White cell thermostatted at a desired temperature, the long optical path compensating for the modest analyte mixing ratio. A composite spectrum is generated from typically ten or more 760-Torr pressure-broadened spectra over the 600 to 6500 cm -1 spectral range at 0.1 cm -1 spectral resolution. The solid analytes reported here using this novel technique include dicyclopentadiene, menthol, syringol, phenol, camphor, and naphthalene.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2013

Intermolecular interactions between imidazole derivatives intercalated in layered solids. Substituent group effect

This study sheds light on the intermolecular interactions between imidazole derive molecules (2-methyl-imidazole, 2-ethyl-imidazole and benzimidazole) intercalated in T[Ni(CN){sub 4}] layers to form a solid of formula unit T(ImD){sub 2}[Ni(CN){sub 4}]. These hybrid inorganic–organic solids were prepared by soft chemical routes and their crystal structures solved and refined from X-ray powder diffraction data. The involved imidazole derivative molecules were found coordinated through the pyridinic N atom to the axial positions for the metal T in the T[Ni(CN){sub 4}] layer. In the interlayers region ligand molecules from neighboring layers remain stacked in a face-to-face configuration through dipole–dipole and quadrupole–quadrupole interactions. These intermolecular interactions show a pronounced dependence on the substituent group and are responsible for an ImD-pillaring concatenation of adjacent layers. This is supported by the structural information and the recorded magnetic data in the 2–300 K temperature range. The samples containing Co and Ni are characterized by presence of spin–orbit coupling and pronounced temperature dependence for the effective magnetic moment except for 2-ethyl-imidazole related to the local distortion for the metal coordination environment. For this last one ligand a weak ferromagnetic ordering ascribed to a super-exchange interaction between T metals from neighboring layers through the ligands π–π interaction was detected. - Graphical abstract: In the interlayers region imidazole derivative molecules are oriented according to their dipolar and quadrupolar interactions and minimizing the steric impediment. Highlights: • Imidazole derivatives intercalation compounds. • Intermolecular interaction between intercalated imidazole derivatives. • Hybrid inorganic–organic solids. • Pi–pi interactions and ferromagnetic coupling. • Dipolar and quadrupolar interactions between intercalated imidazole derivatives.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Solid-state synthesis, structure and properties of a novel open-framework cadmium selenite bromide: [Cd{sub 10}(SeO{sub 3}){sub 8}Br{sub 4}]·HBr·H{sub 2}O

A novel open-framework cadmium selenite bromide, [Cd{sub 10}(SeO{sub 3}){sub 8}Br{sub 4}]·HBr·H{sub 2}O (1), has been obtained by a solid-state reaction at 450 °C, and the structure has been determined by single-crystal X-ray diffraction analysis. Compound 1 crystallizes in Pbcm of the orthorhombic system: a=10.882(3), b=16.275(5), c=18.728(6) Å, V=3317(2) Å{sup 3}, R1/wR2=0.0411/0.0659. Compound 1 is characteristic of a novel 3-D open-framework structure, composing {sub ∞}{sup 2}[CdSeO{sub 3}] layers and the pillars of edge-shared CdO{sub 3}Br{sub 2} square pyramids. The lattice water molecules and the HBr molecules locate in the voids of the framework. Optical absorption spectrum of 1 reveals the presence of an optical gap of 1.65 eV. Solid-state photoluminescent study indicates that compound 1 exhibits strong violet emission. TG–DSC measurement shows that compound 1 is thermally stable up to 200 °C. - Graphical abstract: A metal selenite halide has been synthesized and features a 3-D open-framework structure, composing edge-shared CdO{sub 8} decahedra and pillars of edge-sharing pentahedra. UV–vis, TG–DSC and luminescent measurements are also reported. Highlights: • This paper reports a novel cadmium selenite bromide obtained by an intermediate-temperature solid-state reaction. • The title compound is characteristic of a novel 3-D open-framework structure, composing {sub ∞}{sup 2}[CdSeO{sub 3}] layers and the pillars of edge-shared CdO{sub 3}Br{sub 2} square pyramids. • The title compound is thermally stable up to 200 °C. • The title compound has an optical gap of 1.65 eV and exhibits strong violet emission.

36 MATERIALS SCIENCE↗
DOE OSTI2013

A green synthesis of a layered titanate, potassium lithium titanate; lower temperature solid-state reaction and improved materials performance

A layered titanate, potassium lithium titanate, with the size range from 0.1 to 30 µm was prepared to show the effects of the particle size on the materials performance. The potassium lithium titanate was prepared by solid-state reaction as reported previously, where the reaction temperature was varied. The reported temperature for the titanate preparation was higher than 800 °C, though 600 °C is good enough to obtain single-phase potassium lithium titanate. The lower temperature synthesis is cost effective and the product exhibit better performance as photocatalysts due to surface reactivity. - Graphical abstract: Finite particle of a layered titanate, potassium lithium titanate, was prepared by solid-state reaction at lower temperature to show modified materials performance. Display Omitted - Highlights: • Potassium lithium titanate was prepared by solid-state reaction. • Lower temperature reaction resulted in smaller sized particles of titanate. • 600 °C was good enough to obtain single phased potassium lithium titanate. • The product exhibited better performance as photocatalyst.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2013

A high-pressure route to thermoelectrics with low thermal conductivity: The solid solution series AgIn{sub x}Sb{sub 1−x}Te{sub 2} (x=0.1–0.6)

Metastable rocksalt-type phases of the solid solution series AgIn{sub x}Sb{sub 1−x}Te{sub 2} (x=0.1, 0.2, 0.4, 0.5 and 0.6) were prepared by high-pressure synthesis at 2.5 GPa and 400 °C. In these structures, the coordination number of In{sup 3+} is six, in contrast to chalcopyrite ambient-pressure AgInTe{sub 2} with fourfold In{sup 3+} coordination. Transmission electron microscopy shows that real-structure phenomena and a certain degree of short-range order are present, yet not very pronounced. All three cations are statistically disordered. The high degree of disorder is probably the reason why AgIn{sub x}Sb{sub 1−x}Te{sub 2} samples with 0.4<x<0.6 exhibit very low thermal conductivities with a total κ<0.5 W/K m and a lattice contribution of κ{sub ph} ∼0.3 W/K m at room temperature. These are lower than those of other rocksalt-type tellurides at room temperature; e.g. the well-known thermoelectric AgSbTe{sub 2} (κ ∼0.6 W/K m). The highest ZT value (0.15 at 300 K) is observed for AgIn{sub 0.5}Sb{sub 0.5}Te{sub 2}, mainly due to its high Seebeck coefficient of 160 µV/K. Temperature-dependent X-ray powder patterns indicate that the solid solutions are metastable at ambient pressure. At 150 °C, the quaternary compounds decompose into chalcopyrite-type AgInTe{sub 2} and rocksalt-type AgSbTe{sub 2}. - Graphical abstract: Reaction scheme, temperature characteristics of the ZT value and a selected-area electron diffraction pattern (background) of AgIn{sub 0.5}Sb{sub 0.5}Te{sub 2}, which crystallizes in a rocksalt-type structure with statistical cation disorder. Display Omitted - Highlights: • High-pressure synthesis yields the novel solid solution series AgIn{sub x}Sb{sub 1−x}Te{sub 2}. • In contrast to AgInTe{sub 2}, the compounds are inert at ambient pressure. • HRTEM shows no pronounced short-range order in the disordered NaCl-type structure. • The metastable phases exhibit very low total thermal conductivities <0.5 W/K m. • ZT values of 0.15 at room temperature were measured for AgIn{sub 0.5}Sb{sub 0.5}Te{sub 2}.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Investigation of the hydrothermal crystallisation of the perovskite solid solution NaCe{sub 1−x}La{sub x}Ti{sub 2}O{sub 6} and its defect chemistry

Perovskites of nominal composition NaCe{sub 1−x}La{sub x}Ti{sub 2}O{sub 6} (0≤x≤1) crystallise directly under hydrothermal conditions at 240 °C. Raman spectroscopy shows distortion from the ideal cubic structure and Rietveld analysis of powder X-ray and neutron diffraction reveals that the materials represent a continuous series in rhombohedral space group R3-bar c. Ce L{sub III}-edge X-ray absorption near edge structure spectroscopy shows that while the majority of cerium is present as Ce{sup 3+} there is evidence for Ce{sup 4+}. The paramagnetic Ce{sup 3+} affects the chemical shift and line width of {sup 23}Na MAS NMR spectra, which also show with no evidence for A-site ordering. {sup 2}H MAS NMR of samples prepared in D{sub 2}O shows the inclusion of deuterium, which IR spectroscopy shows is most likely to be as D{sub 2}O. The deuterium content is highest for the cerium-rich materials, consistent with oxidation of some cerium to Ce{sup 4+} to provide charge balance of A-site water. - Graphical abstract: A multi-element A-site perovskite crystallises directly from aqueous, basic solutions at 240 °C; while the paramagnetic effect of Ce{sup 3+} on the {sup 23}Na NMR shows a homogeneous solid-solution, the incorporation of A-site water is also found from {sup 2}H NMR and IR, with oxidation of some cerium to charge balance proved by XANES spectroscopy. Display Omitted - Highlights: • Direct hydrothermal synthesis allows crystallisation of a perovskite solid-solution. • XANES spectroscopy shows some oxidation of Ce{sup 3+} to Ce{sup 4+}. • The paramagnetism of Ce{sup 3+} shifts and broadens the {sup 23}Na solid-state NMR. • The perovskite materials incorporate water as an A-site defect.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Origin of the solid solution in the LiInSe{sub 2}–In{sub 2}Se{sub 3} system

Techniques of bulk and local analyses were used to characterize the melt-grown single crystals of LiInSe{sub 2}, where yellow matrix coexists together with extended red areas distributed irregularly. Bulk chemical analysis showed that the average stoichiometry of yellow matrix is close to ideal 1:1:2, but red areas are enriched with In{sub 2}Se{sub 3}. An excess In{sub 2}Se{sub 3} is incorporated coherently into the crystal lattice of LiInSe{sub 2}, forming the substitution solid solution with the general formula (Li{sub 1−3x}In{sub x}⎕{sub 2})InSe{sub 2} and changing the color from yellow to red. The test crystals with the 50–55% content of In{sub 2}Se{sub 3} were found by the X-ray analysis to be single phase. The differential dissolution technique, measuring the spatial variation of the composition with high resolution, demonstrated that the single phase crystals in the LiInSe{sub 2}–In{sub 2}Se{sub 3} system might be grown only in a very narrow range close to stoichiometric. Being supersaturated, the heterovalent solid solution phases decompose in the course of cooling, and the concentration micro-heterogeneity occurs in the matrix as the coherent (or incoherent) inclusions of two different types, practically pure selenides of lithium and indium. The origin and scale of the micro-heterogeneity determining the physical properties of LiInSe{sub 2} are discussed as a starting point for the development of physicochemical foundations for growing high quality optical crystals. - Graphical abstract: Differential dissolution technique applied for detection of dispersive precipitates in as-grown LiInSe{sub 2} single crystals: kinetic curves of the phase dissolution: F is the main phase Li{sub 0.96}In{sub 1.01}Se{sub 2} (98.9%), secondary minor phases Li{sub 2}Se (0.1%), In{sub 2}Se{sub 3} (0.9%). - Highlights: • Phase purity of crystals Li{sub 1−3x}In{sub 1+x}Se{sub 2} was examined by a new stoichiographic method. • Breakup of the metastable solid solution with temperature drop was detected. • Dispersive precipitates Li–Se and In–Se of low content result from the breakup. • A crucial role of the precipitates in optical properties of the crystals is shown. • Conditions are given how to grow stoichiometric and single-phase crystals.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Controlling polymorphic structures and investigating electric properties of Ca-doped zirconia using solid state ceramic method

Structural study of Zr{sub 1−x}Ca{sub x}O{sub 2−x} samples with x=0.01–0.15 were prepared using solid state ceramic method. X-ray diffraction analysis revealed a mixture of the high temperature phase and the monoclinic one for the samples with x≤0.05. On the other hand, the formation of a single high temperature cubic phase was observed within a concentration range of x=0.06–0.10. At concentrations higher than 0.10 the calcium zirconate phase was observed besides the dominant high temperature one. Rietveld refinement of the single phase data clearly revealed, that substitution of zirconium by calcium increases both the lattice parameters as well as the tetrahedral bond length. Ionic to electronic conductivity ratio enhanced considerably as Ca-doping level ascends. The dielectric constant shows strong temperature dependence at lower frequencies. The dielectric loss factor increases rapidly with the increase in temperature at lower frequencies, while decreases with the increase in frequency at higher temperatures. The ionic conduction is considered as the dominant process at higher temperatures. - Graphical abstract: Forming a high temperature cubic zirconia phase at 1200 °C using ceramic solid state method and aliovalent cation. - Highlights: • Formation the high temperature cubic polymorph of zirconia using Ca-doping. • Solid state ceramic method was used for preparing the cubic Ca-doped zirconia. • Substitution of zirconium by calcium increases the lattice parameters and the bond length. • Ionic to electronic conductivity ratio enhanced considerably as Ca-doping level increases.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

Structural, magnetic, and dielectric properties of solid solutions between BiMnO{sub 3} and YMnO{sub 3}

Bi{sub 1−x}Y{sub x}MnO{sub 3} (0.1≤x≤0.9) solid solutions were prepared by the high-pressure high-temperature method at 6 GPa and 1573 K. They crystallize in the GdFeO{sub 3}-type perovskite structure with the Pnma symmetry. Crystal structures of Bi{sub 0.9}Y{sub 0.1}MnO{sub 3} and Bi{sub 0.5}Y{sub 0.5}MnO{sub 3} are studied by synchrotron X-ray powder diffraction at room temperature. Only one Néel temperature, T{sub N}, is found in samples with 0.1≤x≤0.9 in comparison with two Néel temperatures observed in YMnO{sub 3} (T{sub N}=29 and 39 K). Samples with 0.5≤x≤0.9 have almost constant T{sub N}=44 K, while T{sub N} starts to increase linearly for other compositions: T{sub N}=46 K for x=0.3, T{sub N}=58 K for x=0.2, and T{sub N}=68 K for x=0.1. Field-induced transitions from canted-antiferromagnetic states to antiferromagnetic states are detected at about 30 kOe for x=0.2 and 70 kOe for x=0.1. Dielectric constant increases below T{sub N} in samples with 0.5≤x≤1, while it decreases below T{sub N} in samples with 0.1≤x≤0.3. Our data suggest that a magnetic structure changes near x=0.4. By extrapolation, we could estimate lattice parameters (a=5.9221 Å, b=7.5738 Å, and c=5.4157 Å) and T{sub N}=79 K for a hypothetical Pnma modification of BiMnO{sub 3}. - Graphical abstract: Bi{sub 1−x}Y{sub x}MnO{sub 3} solid solutions were prepared in the whole compositional range by the high-pressure method. Magnetic and dielectric data suggest that a magnetic structure changes near x=0.4. No ferroelectric properties were found. - Highlights: • Orthorhombic Bi{sub 1−x}Y{sub x}MnO{sub 3} solid solutions are prepared by the high-pressure method. • Structural, magnetic, and dielectric properties are studied. • One Néel temperature is found in all the samples. • T{sub N}=44 K for x=0.5–0.9, 46 K for x=0.3, 58 K for x=0.2, and 68 K for x=0.1. • No ferroelectricity is observed.

36 MATERIALS SCIENCE↗
DOE OSTI2018

In-situ microstructural observation of Ti-Cu alloys for semi-solid processing

The semi-solid processing of metallic alloys strongly depends on the microstructural features exhibited by the raw material. Consequently, many characterization techniques have been used to elucidate semi-solid microstructures. In the present work, high-temperature laser-scanning confocal microscopy (HT-LSCM) was used to characterize Ti-Cu alloys intended for thixoforming. During the reheating stage, this in-situ technique enabled us to observe the Ti-β grains formed through the reverse eutectoid transformation. Furthermore, the results showed that thermomechanical treatment was primarily responsible for breaking up the dendritic microstructure. The liquid formation and peritectic temperature were easily determined via the HT-LSCM investigation. Prior to the reverse peritectic reaction, which corresponds to the onset of equilibrium melting, we obtained experimental evidence of the melting of non-equilibrium phases that originated via segregation during solidification. Finally, it was possible to qualitatively study the coarsening mechanisms that occurred in the semi-solid state. Irrespective of the alloy composition (liquid fraction), both Ostwald ripening and coalescence occurred during the isothermal heat treatments. Based on the obtained results, HT-LCSM can be considered a valuable technique for the characterization of thixotropic alloys.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Fabrication of platinum nanoparticles in aqueous solution and solid phase using amphiphilic PB-b-PEO copolymer nanoreactors

Graphical abstract: TEM image of Pt nanoparticles produced by reducing by NaBH{sub 4} within PB-b-PEO micelles in aqueous media (scale bar 1 nm). - Highlights: • Pt nanoparticles were synthesized within amphiphilic diblock copolymer micelles. • The effects of reducing agents and precursor dose on Pt np size were investigated. • The effect on fabrication of Pt np by reducing in aqueous and solid phases was compared. • The size of nanoparticles was about 1.4 nm for all doses and reducing agents types. - Abstract: Fabrication of Pt nanoparticles using an amphiphilic copolymer template in aqueous solution was achieved via polybutadiene-block-polyethyleneoxide copolymer micelles, which acted as nanoreactors. In addition, Pt nanoparticles were synthesized using hydrogen gas as the reducing agent in solid state for the first time to compare against solution synthesis. The influences of loaded precursor salt amount to micelles and the type of reducing agent on the size of nanoparticles were investigated through transmission electron microscopy. It was found that increasing the ratio of precursor salt to copolymer and using different type of reducing agent, even in solid phase reduction, did not affect the nanoparticle size. The average size of Pt nanoparticles was estimated to be 1.4 ± 0.1 nm. The reason for getting same sized nanoparticles was discussed in the light of nucleation, growth process, stabilization and diffusion of nanoparticles within micelles.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Lithium stoichiometry of solid electrolytes based on tetragonal Li{sub 7}La{sub 3}Zr{sub 2}O{sub 12}

Graphical abstract: - Highlights: • We prepared Li{sub x}La{sub 3}Zr{sub 2}O{sub 8.5+0.5x} (x = 6, 7, 8, 9, 10) by the citrate–nitrate method. • We studied phase composition and conductivity of Li{sub x}La{sub 3}Zr{sub 2}O{sub 8.5+0.5x}. • We proposed a simple method to determine the carbonate impurity content in the solid electrolytes. • The synthesized solid electrolytes Li{sub x}La{sub 3}Zr{sub 2}O{sub 8.5+0.5x} (x = 7–9) have 1.32–3.49 wt.% Li{sub 2}CO{sub 3}. • The composition with x = 9 has high total conductivity, 7.5 × 10{sup −6} S cm{sup −1}, at room temperature. - Abstract: Samples of Li{sub x}La{sub 3}Zr{sub 2}O{sub 8.5+0.5x} (x = 6, 7, 8, 9, 10) were synthesized with the citrate–nitrate method. Neutron diffraction studies have shown the presence of lithium carbonate impurities in the synthesized compounds. We propose a simple and effective method to determine the carbonate impurity content in the solid electrolytes. The technique is based on the measurement of the carbon dioxide volume produced from the interaction of the investigated material with acid. Determined in this way, the content of Li{sub 2}CO{sub 3} in the synthesized electrolytes Li{sub 7}La{sub 3}Zr{sub 2}O{sub 12}, Li{sub 8}La{sub 3}Zr{sub 2}O{sub 12.5} and Li{sub 9}La{sub 3}Zr{sub 2}O{sub 13} are 1.32 ± 0.04, 1.95 ± 0.06 and 3.49 ± 0.10 wt.%, respectively. From the obtained data, the actual lithium content per formula unit of complex oxide was calculated for the synthesized compounds. The composition with x = 9 had the highest total conductivity, σ = 7.5 × 10{sup −6} S cm{sup −1}, at room temperature. All the investigated electrolytes have an activation energy of approximately 50 kJ mol{sup −1}.

36 MATERIALS SCIENCE↗