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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 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Optimization of Interlayer/CrWN Bilayer Films Fabricated and Monitored under Shewhart Control

Chromium tungsten nitride (CrWN) films were deposited onto SUS 304 stainless steel, cutter inserts and glass substrates using direct current reactive magnetron sputtering, with pure W and Cr metal targets. The deposition parameters for the interlayer (W and WN) with multiple qualities were optimized using the gray Taguchi method. The microstructure of these coatings was determined using x-ray diffraction, scanning electron microscopy, energy dispersive spectroscopy and transmission electron microscopy. The results showed that the mechanical properties of bilayer samples with an interlayer of WN nitride film are superior to those with a W metal interlayer. Moreover, increasing the N{sub 2}/(N{sub 2} + Ar) flow ratio and working pressure enhanced the microhardness and the elastic recovery for coatings with an interlayer/CrWN bilayer. Dry milling tests also showed that bilayer film coatings have better mechanical performance. This increase in multiple performance characteristics is attributed to a bilayer that is manufactured using the gray Taguchi method. Control charts, which are powerful tools and widely used, were employed to monitor and ensure high-quality fabrication of the interlayer/CrWN bilayer and to show the coating processes to be stable and well regulated.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Solid-state synthesis of Mg{sub 2}Si via short-duration ball-milling and low-temperature annealing

In this work, a short duration ball-milling of elemental Mg and Si followed by a thermal treatment is suggested in order to synthesize magnesium silicide via solid-state reaction. The formation of magnesium silicide was studied in terms of its structure and thermal characteristics by powder X-ray diffraction, scanning electron microscopy, energy dispersive spectroscopy and differential scanning calorimetry. Pure Mg{sub 2}Si was formed after short milling and heating at temperatures as low as 280 Degree-Sign C. Differential scanning calorimetry analysis was performed to study the kinetics of the reaction. The activation energy of the reaction was calculated using the Ozawa-Flynn-Wall and Friedman methods. The thermoelectric properties suggested semiconducting behavior whereas thermal conductivity values of highly dense hot-pressed pellets are consistent with the literature. - Graphical abstract: Thermographs of ball-milled Mg and Si powders (1 and 2) show exothermic areas suggesting Mg{sub 2}Si formation at low temperatures. Unmilled Mg and Si mixture (3) forms Mg{sub 2}Si at higher temperatures. Highlights: Black-Right-Pointing-Pointer Ball-milling process is crucial for the formation of pure Mg{sub 2}Si at low temperatures. Black-Right-Pointing-Pointer Synthesis profiles based on different temperature settings and duration are suggested. Black-Right-Pointing-Pointer Thermal analysis confirms the shift of the Mg{sub 2}Si formation at low temperatures.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Utilizing maleic acid as a novel fuel for synthesis of PbFe{sub 12}O{sub 19} nanoceramics via sol–gel auto-combustion route

PbFe{sub 12}O{sub 19} nanostructures were prepared in an aqueous solution by the sol–gel auto-combustion method using Pb(NO{sub 3}){sub 2} and Fe(NO{sub 3}){sub 3} as starting materials and various carboxylic acids, including oxalic acid, malonic acid, succinic acid and maleic acid as fuel and reducing and capping agents. The as-synthesized products were characterized by X- ray diffraction, scanning electron microscopy, and X-ray energy dispersive spectroscopy. The effect of carboxylic acid type, Pb{sup +} {sup 2} to carboxylic acid molar ratio, and calcination temperature was investigated on the morphology of the products and several experiments were carried out to obtain the optimal reaction conditions. It was found that the phase and the morphology of the products are influenced by the investigated parameters. Furthermore, vibrating sample magnetometer (VSM) was used to study the magnetic properties of PbFe{sub 12}O{sub 19} samples. - Graphical abstract: Display Omitted - Highlights: • PbFe{sub 12}O{sub 19} nanoceramics were synthesized from Fe(NO{sub 3}){sub 3} and Pb(NO{sub 3}){sub 2} via the sol–gel auto combustion method. • The maleic acid can be instead of common capping agent and fuel in auto-combustion sol–gel. • The synthesized PbFe{sub 12}O{sub 19} is a hard magnetic material. • The specific saturation magnetization and coercivity are 27 emu/g and 1900 Oe, respectively.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2012

Flower-like and hollow sphere-like WO{sub 3} porous nanostructures: Selective synthesis and their photocatalysis property

Graphical abstract: -- Abstract: Nanoflake-based flower-like and hollow microsphere-like hydrated tungsten oxide architectures were selectively synthesized by acidic precipitation of sodium tungstate solution at mild temperature. Several techniques, such as X-ray diffraction, scanning electron microscopy, thermogravimetric-differential thermalgravimetric analysis, transmission electron microscopy, and Brunauer–Emmett–Teller N{sub 2} adsorption–desorption analyses, were used to characterize the structure and morphology of the products. The experimental results show that the nanoflake-based flower-like and hollow sphere-like WO{sub 3}·H{sub 2}O architectures can be obtained by changing the concentration of sodium tungstate solution. The possible formation process based on the aggregation–recrystallization mechanism is proposed. The corresponding tungsten oxide three-dimensional architectures were obtained after calcination at 450 °C. Finally, the obtained WO{sub 3} three-dimensional architectures were used as photocatalyst in the experiments. Compared with WO{sub 3} microflowers, the as-prepared WO{sub 3} hollow microspheres exhibit superior photocatalytic property on photocatalytic decomposition of Rhodamine B due to their hollow porous hierarchical structures.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Catalytic activities of two different morphological nano-MnO2 on the thermal decomposition of ammonium perchlorate

Highlights: • Nano-MnO{sub 2} was produced easily. • Nano-MnO{sub 2} can promote the decomposition of AP. • Sea-urchin nano-MnO{sub 2} is a superior catalyst. - Abstract: In order to investigate the catalytic activity of nano-MnO{sub 2} on the thermal decomposition of ammonium perchlorate, two different shapes of nano-MnO{sub 2} (sea-urchin and linear) were prepared by the hydrothermal method with MnSO{sub 4}·H{sub 2}O and Na{sub 2}S{sub 2}O{sub 8}, MnSO{sub 4}·H{sub 2}O and (NH{sub 4}){sub 2}S{sub 2}O{sub 8}, respectively. X-ray diffraction, scanning electron microscopy and the nitrogen adsorption/desorption analysis were used to characterize the structure of the nanocomposites. The sea-urchin nano-MnO{sub 2} possesses a greater specific surface area than the linear nano-MnO{sub 2}. The catalytic properties of nano-MnO{sub 2} on the thermal decomposition of ammonium perchlorate (AP) were demonstrated by differential scanning calorimeter (DSC). As show in the DSC carves, the addition of the sea-urchin nano-MnO{sub 2} got the thermal decomposition peak temperature of AP reduced much more than the addition of the linear nano-MnO{sub 2}, the low-temperature decomposition process even disappeared, and the high-temperature pyrolysis peak temperature decreased by 94.6 °C. All evidences indicated that the sea-urchin nano-MnO{sub 2} is a better catalytic than the linear one.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2014

Origin of spin-glass and exchange bias in La{sub 1∕3}Sr{sub 2∕3}FeO{sub 3−γ} nanoparticles

The structure and the magnetic properties of nanopowdered samples of La{sub 1∕3}Sr{sub 2∕3}FeO{sub 3−γ} with average particles size d in the range of 67-367 nm prepared by a sol-gel method were investigated in detail. The samples were characterized by X-ray diffraction, scanning electron microscopy, specific heat, Mössbauer spectroscopy, ac susceptibility, and magnetization measurements. Exchange bias with vertical magnetization shift was found in all samples. Charge ordering and antiferromagnetism were observed close to 200 K for large particles (d ≥ 304 nm) samples, while for particles with intermediated and smaller values (d ≤ 156 nm) a cluster-glass like behaviour and a short range charge ordering were seen near 115 K and 200 K, respectively. The spin-glass like and exchange bias behaviour in nanopowdered samples of La{sub 1∕3}Sr{sub 2∕3}FeO{sub 3−γ} are associated to compact Fe{sup 3+} antiferromagnetic (AF) clusters caused by an oxygen deficiency, which was found to be higher in the samples with the smallest average particles sizes. The effect of exchange bias and vertical magnetization shifts are explained by a simple model involving the interaction of one AF phase with a canted AF phase.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Improvement of the Magnetization and Coercivity of La{sub 0.67}Ca{sub 0.33}MnO{sub 3} Induced by Substitution of Nickel for Manganese

La{sub 0.67}Ca{sub 0.33}Mn{sub 1−x}Ni{sub x}O{sub 3} (0 ≤x ≤ 0.3) is synthesized by solid-state reaction at low temperatures, followed by calcination in air. The precursor and its calcined products are characterized by thermogravimetry and differential scanning calorimetry, x-ray powder diffraction, scanning electron microscopy, and vibrating sample magnetometer. A high-crystallized La{sub 0.67}Ca{sub 0.33}Mn{sub 1−x}Ni{sub x}O{sub 3} with an orthorhombic structure is obtained when the precursor is calcined at 900{sup ∘}C in air for 3 h. Crystallite size of La{sub 0.67}Ca{sub 0.33}Mn{sub 1−x}Ni{sub x}O{sub 3} increases with the increase of Ni content, attributed to the decrease of lattice strains of the La{sub 0.67}Ca{sub 0.33}Mn{sub 1−x}Ni{sub x}O{sub 3} with the increase in Ni content. Nickel substitution can markedly improve coercivity and specific magnetization of La{sub 0.67}Ca{sub 0.33}Mn{sub 1−x}Ni{sub x}O{sub 3}. The coercive field (9 Oe) of La{sub 0.67}Ca{sub 0.33}Mn{sub 0.7}Ni{sub 0.3}O{sub 3} is higher, even at 293 K, indicating that La{sub 0.67}Ca{sub 0.33}Mn{sub 0.7}Ni{sub 0.3}O{sub 3} continues being ferromagnetic above 260 K (Curie temperature for LCMO).

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Solid Phase Equilibrium Relations in the CaO-SiO{sub 2}-Nb{sub 2}O{sub 5}-La{sub 2}O{sub 3} System at 1273 K

Silicate slag system with additions Nb and RE formed in the utilization of REE-Nb-Fe ore deposit resources in China has industrial uses as a metallurgical slag system. The lack of a phase diagram, theoretical, and thermodynamic information for the multi-component system restrict the comprehensive utilization process. In the current work, solid phase equilibrium relations in the CaO-SiO{sub 2}-Nb{sub 2}O{sub 5}-La{sub 2}O{sub 3} quaternary system at 1273 K (1000 °C) were investigated experimentally by the high-temperature equilibrium experiment followed by X-ray diffraction, scanning electron microscope, and energy dispersive spectrometer. Six spatial independent tetrahedron fields in the CaO-SiO{sub 2}-Nb{sub 2}O{sub 5}-La{sub 2}O{sub 3} system phase diagram were determined by the Gibbs Phase Rule. The current work combines the mass fraction of equilibrium phase and corresponding geometric relation. A determinant method was deduced to calculate the mass fraction of equilibrium phase in quaternary system according to the Mass Conservation Law, the Gibbs Phase Rule, the Lever’s Rule, and the Cramer Law.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Crystal structure and characterization of a novel layered copper-lithium phosphonate with antiferromagnetic intrachain Cu(II)···Cu(II) interactions

Novel metal phosphonate [CuLi(PPA)] [H{sub 3}PPA=3-phosphonopropionic acid] was synthesized hydrothermally and characterized by single-crystal X-ray diffraction, powder X-ray diffraction, scanning electron microscopy, infrared spectroscopy, and thermogravimetric analysis. It crystallizes in the space group C2/c, with cell parameters a=21.617(2) Å, b=4.9269(2) Å, c=14.342(1) Å, β=132.3(2)°, and Z=8. Its framework is built up from a main trimer, acting as a secondary building unit (SBU), which is formed by vertex-shared between two (LiO{sub 4}) and one (Cu(1)O{sub 4}) polyhedra. These units repeat along b-axis forming infinite inorganic chains, these chains are in turn cross-linked by corner sharing with (Cu(2)O{sub 4}) polyhedra to produce inorganic layers lying in the bc-plane. The neighboring layers are connected through the PPA ligand, leading to a 3D pillared-layered structure. The topological analysis reveals that the compound exhibits 3,4,10-c net. Finally, magnetic susceptibility measurement of this compound over the temperature range of 2–300 K reveals the occurrence of weak antiferromagnetic intrachain interactions. - Graphical abstract: Hydrothermal synthesis and structural characterization of a novel lithium-copper phosphonate, formulated as [CuLi(PPA)] (H{sub 3}PPA=3-phosphonopropionic acid), have been reported. This compound has a 3D pillared-layered structure with 3,4,10-c net topology. The magnetic susceptibility data over the temperature range of 2–300 K reveals the occurrence of weak antiferromagnetic interactions. - Highlights: • Novel metal phosphonate, [CuLi(PPA)] (1), has been synthesized and characterized. • Compound 1 has a 3D pillared-layered structure with 3,4,10-c net topology. • Magnetic susceptibility data reveals the occurrence of weak antiferromagnetic interactions.

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

Corrosion behavior of magnetic ferrite coating prepared by plasma spraying

Graphical abstract: The saturation magnetization (M{sub s}) of the ferrite coating is 34.417 emu/g while the M{sub s} value of the ferrite powder is 71.916 emu/g. It can be seen that plasma spray process causes deterioration of the room temperature soft magnetic properties. - Highlights: • Spinel ferrite coatings have been prepared by plasma spraying. • The coating consists of nanocrystalline grains. • The saturation magnetization of the ferrite coating is 34.417 emu/g. • Corrosion behavior of the ferrite coating was examined in NaCl solution. - Abstract: In this study, spray dried spinel ferrite powders were deposited on the surface of mild steel substrate through plasma spraying. The structure and morphological studies on the ferrite coatings were carried out using X-ray diffraction, scanning electron microscope and Raman spectroscopy. It was showed that spray dried process was an effective method to prepare thermal spraying powders. The coating showed spinel structure with a second phase of LaFeO{sub 3}. The magnetic property of the ferrite samples were measured by vibrating sample magnetometer. The saturation magnetization (M{sub s}) of the ferrite coating was 34.417 emu/g. The corrosion behavior of coating samples was examined by electrochemical impedance spectroscopy. EIS diagrams showed three corrosion processes as the coating immersed in 3.5 wt.% NaCl solution. The results suggested that plasma spraying was a promising technology for the production of magnetic ferrite coatings.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Synthesis and photocatlytic performance of nano-sized TiO{sub 2} materials prepared by dealloying Ti–Cu–Pd amorphous alloys

Highlights: • TiO{sub 2} nanospindles were synthesized by dealloying Ti–Cu–Pd amorphous alloy. • Pd significantly enhanced the exposure of high-energy (0 0 1) facet of TiO{sub 2}. • TiO{sub 2} with high-energy (0 0 1) facet showed good photocatalytic activity. - Abstract: TiO{sub 2} nanospindles with exposed (0 0 1) facet were synthesized through a simple dealloying reaction. The rutile photocatalysts were characterized by X-ray diffraction, scanning electron microscope and transmission electron microscope, inductively coupled plasma optical emission spectrometry and ultraviolet–visible spectrophotometer. A Rhodamine B dye (RhB) was used to detect the photocatalytic activity of TiO{sub 2} under full light irradiation. The presence of Pd in the original amorphous alloy reduced the surface free energy of TiO{sub 2}, stabilized the (0 0 1) facet. The Pd8-TiO{sub 2} sample exhibited the largest crystal size along the direction which is perpendicular to the (0 0 1) facet. The photocatalytic degradation rate of RhB was improved due to the Pd addition in the original amorphous alloy. This indicated that the exposure of (0 0 1) facets could enhance the activity of TiO{sub 2} photocatalyst. In addition, the presence of isolated Pd atoms on the surface of TiO{sub 2} would be another probable reason for the improvement of photocatalytic activity.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Room temperature magnetocaloric effect and refrigerant capacitance in La{sub 0.7}Sr{sub 0.3}MnO{sub 3} nanotube arrays

High aspect ratio La{sub 0.7}Sr{sub 0.3}MnO{sub 3} nanotube (NT) arrays have been synthesized using nitrates based sol-gel precursor by nanoporous anodized aluminum oxide template assisted method. Their phase purity and microstructures were analyzed by X-ray diffraction, scanning electron microscopy, and energy-dispersive x-ray spectroscopy. Magnetocaloric effect (MCE) of as prepared NTs was investigated by means of field dependence magnetization measurements. Significant magnetic entropy change, −△S{sub M} = 1.6 J/kg K, and the refrigerant capacitance, RC = 69 J/kg, were achieved near the transition temperature at 315 K for 5 T. For comparison, a bulk sample was also prepared using the same precursor solution which gives a value of −△S{sub M} = 4.2 J/kg K and a RC = 165 J/kg. Though the bulk sample exhibits higher △S{sub M} value, the NTs present an expanded temperature dependence of −△S{sub M} curves that spread over a broad temperature range and assured to be appropriate for active magnetic refrigeration. The diminutive MCE observed in manganite NTs is explained by the increased influence of surface sites of nanograins which affect the structural phase transition occurred by external magnetic field due to the coupling between magnetism and the lattice in manganese perovskites. Our report paves the way for further investigation in 1D manganite nanostructured materials towards applications in such magnetic refrigeration technology or even on hyperthermia/drug delivery.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2016

Cation distribution in CuFe{sub 2}O{sub 4} nanoparticles: Effects of Ni doping on magnetic properties

The Cu{sub 1−x}Ni{sub x}Fe{sub 2}O{sub 4} nanoparticles (with x = 0, 0.3, 0.5, 0.7, and 1) were synthesized by using spray co-precipitation method at annealing temperature T{sub a} = 900 °C in air for 5 h. The crystal structure, microstructure, oxidation state, and magnetic properties of the samples were characterized by using X-ray diffraction, synchrotron X-ray diffraction, scanning electron microscopy, X-ray absorption spectroscopy, and vibrating sample magnetometer. It was shown that all the samples have cubic structure. Lattice constant and grain size decrease, while the Curie temperature T{sub C} increases with increasing of Ni{sup 2+} content. A small amount of Fe{sup 2+} was found in all the samples. Cation distribution was determined by using a combination of magnetization measurements, extended X-ray absorption fine structure analysis, and Rietveld refinement from synchrotron X-ray diffraction data. It was indicated that Ni{sup 2+} ions occupy in octahedral site only, while Cu{sup 2+} ions distribute in both tetrahedral and octahedral sites. The variation of magnetic parameters is discussed based on Ni{sup 2+} concentration, grain size, the cation distribution, surface effect, and the presence of Fe{sup 2+} ion in the samples.

36 MATERIALS SCIENCE↗
DOE OSTI2018

One-step reduction synthesis of Ag/Ag3PO4/AgBr sub-micron composites for enhanced visible photocatalytic degradation of methyl orange

Highlights: • Ag/Ag{sub 3}PO{sub 4}/AgBr photocatalysts were synthesized by a one-step reduction method. • The conditions affecting performances of the photocatalysts were optimized. • The main radicals responsible for degrading MO were investigated. • The Ag/Ag{sub 3}PO{sub 4}/AgBr photocatalyst presented excellent stability and recyclability. - Abstract: An efficient semiconductor composite, silver/silver orthophosphate/silver bromide, was successfully synthesized by a facile one-step reduction and ion exchange process. Its crystal structure, morphology, optical property, surface element composition were characterized by X-ray diffraction, scanning electron microscopy, ultraviolet-visible diffuse reflectance spectrometer and X-ray photoelectron spectrometer. The effects of composite proportion and synthesis duration on performances of as-prepared photocatalysts were investigated, and the results showed that Br/P molar ratio of 3 and the synthesis duration of 4 h were the optimum conditions. The radical scavenging experiments indicated that the hole and superoxide radical were the main active species in this reaction system. The Ag/Ag{sub 3}PO{sub 4}/AgBr-3 presented excellent stability and recyclability, maintaining 92% of degradation efficiency after 5 cycles. The good photocatalysis performance could be attributed to the formation of the heterojunction between Ag and Ag{sub 3}PO{sub 4}/AgBr.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Unusual Changes in Electronic Band-Edge Energies of the Nanostructured Transparent n-Type Semiconductor Zr-Doped Anatase TiO 2 (Ti 1– x Zr x O 2 ; x < 0.3)

By the establishment of highly controllable synthetic routes, electronic band-edge energies of the n-type transparent semiconductor Zr-doped anatase TiO 2 have been researched holistically for the first time up to 30 atom % Zr, employing powder X-ray diffraction, scanning electron microscopy, transmission electron microscopy, nitrogen gas sorption measurements, UV/vis spectroscopies, and Mott–Schottky measurements. The materials were produced through a sol–gel synthetic procedure that ensures good compositional homogeneity of the materials, while introducing nanoporosity in the structure, by achieving a mild calcination condition. Vegard’s law was discovered among the homogeneous samples, and correlations were established between the chemical compositions and optical and electronic properties of the materials. Up to 20% Zr doping, the optical energy gap increases to 3.29 eV (vs 3.19 eV for TiO 2 ), and the absolute conduction band-edge energy increases to -3.90 eV (vs -4.14 eV). Furthermore, the energy changes of the conduction band edge are more drastic than what is expected from the average electronegativities of the compounds, which may be due to the unnatural coordination environment around Zr in the anatase phase.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Formation Mechanisms and Leachability of Hexavalent Chromium in Cr{sub 2}O{sub 3}-Containing Refractory Castables of Electric Arc Furnace Cover

Cr (III)-containing refractories are widely used as electric-arc furnace cover because of their excellent corrosion resistance properties. However, the formation of hexavalent chromium [Cr(VI)] remains a matter of concern during the service and subsequent disposal of the spent refractories. Moreover, the Cr(VI) formation mechanism and total amount of Cr(VI) generated are not clearly understood. In this study, samples from different parts of a spent electric arc furnace cover were collected from a local integrated steel plant. The phase composition, microstructure, formation and leachability of Cr(VI) were investigated using X-ray photoelectron spectroscopy, X-ray diffraction, scanning electron microscopy with energy dispersive X-ray spectroscopy, and TRGS 613 leaching test (Technische Regeln für Gefahrstoffe-TRGS 613-October 2002)/multiple leaching tests. A Cr(VI)-containing phase namely CaCrO{sub 4} existed in the sample at a medium temperature range, while another Cr(VI)-containing phase namely hauyne (Ca{sub 4}Al{sub 6}CrO{sub 16}) and a Cr(III)-containing phase (Al{sub 2}O{sub 3}–Cr{sub 2}O{sub 3} solid solution) formed in the high temperature region. Concentrations of Cr(VI) in the leachates (as in the TRGS 613 procedure) exceeded the European permissible limit. During the leaching tests in an acid condition, Cr(VI) was reduced by Fe{sup 2+}, which was primarily derived from the dissolution of FeO in the samples, while more Cr(VI) leached out with distilled water. Formation of an Al{sub 2}O{sub 3}–Cr{sub 2}O{sub 3} solid solution can inhibit Cr(VI) generation.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Preparation, characterization and CO{sub 2} gas sensitivity of Polyaniline doped with Sodium Superoxide (NaO{sub 2})

Highlights: • NaO{sub 2} prepared in single step method from NaNO{sub 3} in oxygen rich environment. • The sensors show better performance towards the CO{sub 2}. • A significant sensitivity and fast response toward of CO{sub 2} is observed. • Sensing response assign to transition from n-type to p-type behavior of samples. - Abstract: The sodium superoxide was prepared in single step method by heating sodium nitrate (NaNO{sub 3}) in oxygen rich environment. The PANi/NaO{sub 2} composites were prepared using Ex-situ technique range from 5–20 wt.%. The crystallinity and structure morphology of the PANi/ NaO{sub 2} composite films were characterized by X-ray diffraction, Scanning electron microscopy and Fourier transform infrared spectroscopy respectively. The sensor response was estimated by the change in electrical resistance of sensor in presence of CO{sub 2} gas. The sensor response and selectivity for pure PANi and doped PANi/NaO{sub 2} sensors as a function of concentration of CO{sub 2} at room temperature has been systematically studied. The sensors show better performance towards the CO{sub 2}. A significant sensitivity and fast response toward CO{sub 2} observed for the 20 wt.% PANi/NaO{sub 2} composite film. The sensing response curve assign to transition from n-type to p-type behavior of samples.

36 MATERIALS SCIENCE↗
DOE OSTI2015

A study of thermal properties of sodium titanate nanotubes synthesized by microwave-assisted hydrothermal method

Highlights: • The microwave-assisted hydrothermal route was used for titanate nanotubes synthesis. • Conversion to single-phase nanotube morphology completes after 8 h reaction time. • The nanotube morphology is stable up to 600 °C, as determined by in-situ XRD and SEM. • Sodium ions migrate to the surface due to thermal motion and structure condensation. - Abstract: Sodium titanate nanotubes (NaTiNTs) were synthesized by microwave-assisted hydrothermal treatment of commercial TiO{sub 2}, at constant temperature (135 °C) and different irradiation times (15 min, 1, 4, 8 and 16 h). The products were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, differential scanning calorimetry and specific surface area measurements. The irradiation time turned out to be the key parameter for morphological control of the material. Nanotubes were observed already after 15 min of microwave irradiation. The analyses of the products irradiated for 8 and 16 h confirm the complete transformation of the starting TiO{sub 2} powder to NaTiNTs. The nanotubes are open ended with multi-wall structures, with the average outer diameter of 8 nm and specific surface area up to 210 m{sup 2}/g. The morphology, surface area and crystal structure of the sodium titanate nanotubes synthesized by microwave-assisted hydrothermal method were similar to those obtained by conventional hydrothermal method.

77 NANOSCIENCE AND NANOTECHNOLOGY↗