As-prepared Research Articles

Effect of Ni substitution and annealing temperature on structural and magnetic properties of MnZn-Ferrites: Cytotoxicity study of ZnO and SiO2 coated core shell structures

Magnetic spinel ferrite nanoparticles (NPs) have a broad scope of applications based on their structural properties, including in lithium-ion batteries, catalysts, electrochemical energy storage, drug delivery, magnetic hyperthermia, and photothermia. In this study, we investigated the structure, crystallographic phase formations, and magnetic properties of Ni-substituted MnZn ferrites (MZFs), Mn(0.6-x)Zn(0.4-y)Ni(x+y)Fe2O4 (x = 0–0.6, y = 0; y = 0–0.4, x = 0) compositions of as-prepared (AP) and air annealed (350–1200 °C) samples. All AP NPs exhibited a pure spinel structure. Ni-MZF compositions annealed at 600 °C had high α-Fe2O3 secondary phase content in Ni-MZFs (Ni substituted for Zn), whereas Ni-MZFs with x = 0.4 (Ni substituted for Mn) had no impurities, and its magnetization (50 emu/g) was enhanced compared with that of the other samples. X-ray photoelectron spectroscopy revealed that Fe3+ cations were present in tetrahedral and octahedral sites. The single spinel phase reappeared with improved crystallinity in all Ni-MZFs by annealing at 1200 °C and exhibited superior magnetization (60–73 emu/g) compared with that of MZF (35 emu/g). Additionally, the spinel phase was stabilized in the ZnO- and SiO2-coated Ni-MZF core shell structures annealed at 700 °C with higher magnetization than MZF. Moreover, Ni-MZF core shell structures exhibited biocompatibility and may have biomedical applications.

Effect of Structural Relaxation on the Indentation Size Effect and Deformation Behavior of Cu–Zr–Based Nanoglasses

In this work, the deformation behavior of as-prepared (AP) and structurally relaxed (SR) Cu–Zr–based nanoglasses (NGs) are investigated using nano- and micro-indentation. The NGs are subjected to structural relaxation by annealing them close to the glass transition temperature without altering their amorphous nature. The indentation load, p, vs. displacement, h, curves of SR samples are characterized by discrete displacement bursts, while the AP samples do not show any of them, suggesting that annealing has caused a local change in the amorphous structure. In both the samples, hardness (at nano- and micro-indentation) decreases with increasing p, demonstrating the indentation size effect. The micro-indentation imprints of SR NGs show evidence of shear bands at the periphery, indicating a heterogeneous plastic flow, while AP NG does not display any shear bands. Interestingly, the shear band density decreases with p, highlighting the fact that plastic strain is accommodated entirely by the shear bands in the subsurface deformation zone. The results are explained by the differences in the amorphous structure of the two NGs.

Coexistence of large negative and positive magnetodielectric response in Bi1−xCaxFe1−yTiyO3−δ nanoparticle ceramics

Magnetodielectric (MD) properties of as-prepared (AP) and air-annealed ${\mathrm{Bi}}_{1\ensuremath{-}x}{\mathrm{Ca}}_{x}{\mathrm{Fe}}_{1\ensuremath{-}y}{\mathrm{Ti}}_{y}{\mathrm{O}}_{3\ensuremath{-}\ensuremath{\delta}}$ nanoparticle ceramics made by spark plasma sintering process are investigated as a function of temperature. Aliovalent ${\mathrm{Ca}}^{2+}$ substitution at ${\mathrm{Bi}}^{3+}$ site creates oxygen vacancies (${\mathrm{V}}_{\mathrm{O}}$) in the lattice disrupting the intrinsic spin cycloid of ${\mathrm{BiFeO}}_{3}$, which are suppressed when the charge compensating ${\mathrm{Ti}}^{4+}$ is co-substituted. In addition, cation substitution reduces the grain size and increases surface oxygen vacancies. These lattice and surface ${\mathrm{V}}_{\mathrm{O}}$ defects play a significant role in enhancing the magnetic properties. Zero-field-cooled magnetization curves of all AP samples show a sharp Verwey-like transition at \ensuremath{\sim}120 K, which weakens on air-annealing. A coexistence of positive and negative MD [MD = $\frac{\mathrm{\ensuremath{\Delta}}\ensuremath{\varepsilon}(H)}{\ensuremath{\varepsilon}(H=0)}$; $\mathrm{\ensuremath{\Delta}}\ensuremath{\varepsilon}(H)=\ensuremath{\varepsilon}(H)\ensuremath{-}\ensuremath{\varepsilon}(H=0)$] response is observed, with the former dominating at 300 K and the latter at 10 K. As-prepared 5 at.% (10 at.%) Ca and Ca-Ti substituted ${\mathrm{BiFeO}}_{3}$ ceramics exhibit a maximum MD response of --10% (\ensuremath{\sim}+3%) at 10 K (300 K). Negative MD response diminishes for air-annealed ${\mathrm{Bi}}_{1\ensuremath{-}x}{\mathrm{Ca}}_{x}{\mathrm{Fe}}_{1\ensuremath{-}y}{\mathrm{Ti}}_{y}{\mathrm{O}}_{3\ensuremath{-}\ensuremath{\delta}}$ ceramics due to the reduction in ${\mathrm{V}}_{\mathrm{O}}$ concentration. Samples exhibiting dominant positive MD response show a similar trend for MD $vs$ H and ${M}^{2}$ vs H plots. This agreement between ${M}^{2}$ and $\mathrm{\ensuremath{\Delta}}\ensuremath{\varepsilon}(H)$ demonstrates a strong inherent MD coupling. On the contrary, negative MD does not follow this trend yet shows a linear relationship of MD vs ${M}^{2}$, suggesting a strong coupling between the magnetic and dielectric properties. Temperature-dependent MD studies carried out at 5 T show a gradual change from negative to positive values. Negative MD at low temperatures could be activated by the spin-lattice coupling, which dominates even at high frequency (1 MHz) under the applied field. Other contributions, including Verwey-like transition, magnetoresistance, and Maxwell-Wagner effects, do not influence the observed MD response. A prominent role of oxygen vacancies in altering the MD behavior of ${\mathrm{BiFeO}}_{3}$ is discussed in detail.

Synthesis and electromagnetic properties of porous MnFeCoO4 structures by a facile sol-gel auto combustion method

We report the correlation between the microstructure, magnetic, and high-frequency electromagnetic properties of porous MnFeCoO4 structures synthesized by the simple sol-gel auto combustion method. The as-prepared (AP) samples were annealed in the temperature range of 350–1200 °C in air to perceive the temperature's influence on the morphology and properties. The field emission scanning electron microscopy (FESEM) analysis revealed the porous structures with the pore size varies from 100 to 350 nm. The number of pores decreased significantly with the increase of annealing temperature due to the rise of pore and particle size of the agglomerated nanoparticles. Interestingly, the annealing temperature leads to the development of hexagonal planes extended on the particles' surfaces. The X-ray diffraction (XRD), Raman, and X-ray photoelectron spectroscopy (XPS) studies confirm the cubic spinel phase formation. The magnetization (coercivity) of the AP NPs is 27. 9 emu/g (632 Oe), which increases (decreases) with the rise of annealing temperature and finally reached a value of 50.6 emu/g (39.5 Oe) for the sample annealed at 1200 °C. Moreover, the dielectric loss of AP sample is enhanced compared to the annealed samples, which originates from the porous structure, large surface area, and dipole/interfacial polarization.

Evolution of structure and magnetic properties in MnZn ferrite-silica nanocomposites fabricated by sol–gel method

We explore the influence of the silica matrix on size, spinel phase stability, and magnetic properties of MnZn ferrite. For this purpose, Mn0.6Zn0.4Fe2O4 (MZF) nanoparticles (NPs) dispersed in silica (SiO2) matrix [MZF1−x/(SiO2)x x = 0, 10, 30%] synthesized by one-pot sol–gel process. The evolution of a pure spinel phase is apparent from the as-prepared (AP) MZF/SiO2 (30%) amorphous state on annealing in the temperature range 600–900 °C in air, whereas the AP free-standing MZF NPs exhibit a secondary phase of α-Fe2O3 along with spinel structure in this temperature range. The crystallite size is 5 ± 1 nm for a 600 °C annealed sample and increases to 10 ± 1 nm for a 900 °C annealed sample. From the detailed analysis of the temperature and magnetic field-dependent magnetization data, it is found that the AP sample exhibits weak magnetic behavior. However, annealed samples exhibit a maximum in zero-field-cooled magnetization at a certain temperature (TP), which increases with the increase of annealing temperature. The M–H curves above TP indicate the presence of superparamagnetic (SPM)-like behavior. From the present study, we show that the phase stability and magnetic properties of MZF/SiO2 composites have improved compared to bare MZF NPs.

Band engineering via grain boundary defect states for large scale tuning of photoconductivity in Bi1−xCaxFe1−yTiyO3−δ

Spark plasma sintered Bi1−xCaxFe1−yTiyO3−δ (BCFTO) (x = y = 0.05 and 0.1) nanoparticle ceramics are studied for photoconductivity properties. As-prepared (AP) BCFTO hosts a large concentration of grain boundary (GB) oxygen vacancies (OV), whereas air annealed (AA) BCFTO have significantly suppressed GB OV. X-ray absorption near edge spectroscopy study confirms that Fe and Ti remain in 3+ and 4+ oxidation states, respectively. Thus, lattice OV created when only Ca2+ is substituted in BiFeO3 are charge compensated in Ca and Ti codoped BiFeO3. This ascertains that BCFTO is devoid of lattice OV. Photoconductivity studies show four orders of more photocurrent arising from GB OV contributions in BCFTO-AP compared to that in BCFTO-AA samples. A large increase in the activation energy for the AA samples (0.4 eV to 1.6 eV) compared to that for the AP samples (0.06 eV to 0.5 eV) is obtained from ln ω vs 1/T Arrhenius plots. This further substantiates the suppression of GB OV resulting in poor photoconductivity. Diffuse band edges observed in Kubelka-Munk plots of BCFTO-AP samples are a consequence of OV defect states occupying the bulk bandgap. In the absence of OV defect states, band edge becomes sharper. Density functional theory (DFT) calculations further support the experimental observations. DFT study shows that the presence of Ca and Ti does not enhance the photocurrent as these codopants do not produce mid-bandgap states. The mid-bandgap defect states are attributed only to the unsaturated bonds and OV at the GB in BCFTO. These studies manifest a critical role of OV residing at the GB in tuning the photoconductivity and, hence, the photoresponse of BCFTO.

Highly Sensitive and Stable NO2 Gas Sensors Based on SWNTs With Exceptional Recovery Time

Room temperature operable and highly sensitive NO2 gas sensors are fabricated based on (i) random and (ii) aligned networks of single-walled carbon nanotubes (SWNTs). The fabricated sensors are very sensitive, stable, and show shorter recovery time in the presence of UV light. Also, the variation of the response and recovery with network density is analyzed. The thin film resistor (TFR) of random network is fabricated by a reliable, cost-effective, and reproducible vacuum filtration method. The aligned network is fabricated using AC di-electrophoresis (DEP) technique. Electrodes spacing is optimized to avoid the chaining effect of aligned and bridged SWNTs between the gold electrode pair to enhance the stability and sensitivity of the sensor. Both the sensors based on random and aligned networks of SWNTs is tested with NO2 at room temperature. It is found that the sensor made of the aligned network shows ~3.5 times more sensitivity as compared to the random networks gas sensor but recovery time increases. It is also observed that sensors fabricated by TFR and aligned network techniques are stable and having less than 0.02 % and 0.15 % change in resistance with baseline, respectively. The TFR gas sensors fabricated using as prepared (AP) and purified and low functionality (P2) SWNTs show higher stability but less sensitive compared to the aligned network. The measured complete recovery time of sensors based on random and aligned SWNTs are 50 sec and 124 sec, respectively, for 0.5 ppm NO2. It is also observed that as the network density decreases response improves but the recovery time increases.

Oxygen vacancy induced photoconductivity enhancement in Bi1-xCaxFeO3-δ nanoparticle ceramics: A combined experimental and theoretical study

Based on experimental and density functional studies, we show that tailoring of oxygen vacancies (OV) leads to large scale enhancement of photoconductivity in BiFeO3 (BFO). The OV concentration is increased by substituting an aliovalent cation Ca2+ at Bi3+ sites in the BFO structure. Furthermore, the OV concentration at the disordered grain boundaries can be increased by reducing the particle size. Photoconductivity studies carried out on spark plasma sintered Bi1-xCaxFeO3-δ ceramics show four orders of enhancement for x = 0.1. Temperature dependent Nyquist plots depict a clear decrease in impedance with increasing Ca2+ concentration which signifies the role of OV. A significant reduction in photoconductivity by 2 to 4 orders and a large increase in impedance of the air-annealed (AA) nanocrystalline ceramics suggest that OV at the grain boundaries primarily control the photocurrent. In fact, activation energy for AA samples (0.5 to 1.4 eV) is larger than the as-prepared (AP) samples (0.1 to 0.5 eV). Therefore, the room temperature J-V characteristics under 1 sun illumination show 2–4 orders more current density for AP samples. Density-functional calculations reveal that, while the defect states due to bulk OV are nearly flat, degenerate, and discrete, the defect states due to surface OV are non-degenerate and interact with the surface dangling states to become dispersive. With large vacancy concentration, they form a defect band that enables a continuous transition of charge carriers leading to significant enhancement in the photoconductivity. These studies reveal the importance of tailoring the microstructural features as well as the composition-tailored properties to achieve large short circuit current in perovskite oxide based solar cells.

Structural and photoluminescence properties of thermally stable Eu3+activated CaWO4 nanophosphor via Li+ incorporation

In the present paper, we have reported the variation of CaWO4:Eu3+ nano phosphors with different compositions of Li+, (LEC) (Li+ = 2, 5, 7 and 10 at%). The as-prepared (ASP) samples are annealed at 900 °C to eliminate unwanted organic moieties present in the sample and to improve crystallinity. These nanoparticles are characterized by X-ray diffraction (XRD), Thermogravimetric Analysis (TGA), X-ray photoelectron spectroscopy (XPS), Fourier transform IR spectroscopy (FTIR), Raman spectroscopy, photoluminescence studies. FTIR gives the absorption band at ~832 cm−1, which corresponds to antisymmetric vibrations due to O-W-O band in the WO42- tetrahedron. This is also confirmed by the Raman Spectroscopy. CaWO4 has a crystal of the Scheelite type having C4 h point group symmetry and I41/a space group symmetry. The surface/ particle morphology of 900 °C annealed samples studied using Transmission Electron Microscopy (TEM) and Scanning Electron Microscopy (SEM) and show the formation of nanosheet like structure. Annealed samples of lithium co-doped CaWO4:Eu3+nanoparticles have shown the red luminescence which is attributed due to the strong host contribution and different energy transfers from Li+ ions to host matrix under 392 nm excitations. Li+ ion improves the crystallinity and radiative transition rate and these materials may be potential candidates for white light emitting diodes and may be widely used as optoelectronic materials.

The GdF3 phosphors with enhanced multicolor luminescence via multi-channel excitation and energy migration procedure

A collection of GdF3 core-shell structured (CSS) phosphors were synthesized by hydrothermal method. The as-prepared (AP) phosphors were coated with SiO2 layers to avoid aggregation and sintering during thermal annealing at 800 °C, after which the SiO2 layers were etched off and the annealed phosphors became highly dispersible. The annealed CSS phosphor aGdF3:Eu3+@GdF3:Ce3+,Dy3+ shows excellent multicolor luminescence performance with the aid of dual-channel excitation and energy migration (EM) procedure of Gd3+ ions. By inserting pyromellitic acid (PMA) organic ligands into the interfaces between annealed core and AP shell layer regions, the so-called antenna effect of organic ligands of PMA forms a new excitation channel, which makes the CSS phosphor aGdF3:Eu3+@PMA@GdF3:Ce3+,Dy3+ exhibit significantly enhanced multicolor luminescence via multi-channel excitation and EM process. The prepared CSS phosphors in this work are excellent candidates for applications in solid-state lighting.

Thermal stability and magnetic properties of MgFe2O4@ZnO nanoparticles

Magnesium ferrite, MgFe2O4, (MgFO) nanoparticles (NPs) have been synthesized through sol-gel process. Subsequently, as prepared particles were coated with Zinc-oxide (ZnO) layer(s) through ultrasonication process. Thermal stability, structure and magnetic properties of as-prepared (AP) and annealed samples in the temperature range of 350 °C-1200 °C have been investigated. Structural data suggests that AP MgFO NPs and samples annealed below 500 °C in air exhibit stable ferrite phase. However, α-Fe2O3 and a small fraction of MgO secondary phases appear along with ferrite phase on annealing in the temperatures range 500 °C- 1000 °C. This results in significant changes in magnetic moment for AP NPs 0.77 μB increases to 0.92 μB for 1200 °C air annealed sample. The magnetic properties decreased at intermediate temperatures due to the presence of secondary phases. On the other hand, pure ferrite phase could be stabilized with an optimum amount of ZnO coated MgFO NPs for samples annealed in the temperature range 500 °C-1000 °C with improvement in magnetic behavior compared to that of MgFO samples.

Influence of surface disorder, oxygen defects and bandgap in TiO2 nanostructures on the photovoltaic properties of dye sensitized solar cells

We present a detailed study on the microstructural, structural and optical properties of hydrogen treated (HT) diverse TiO2 nanostructures (TNS) in comparison to the as-prepared (AP) samples. The effect of oxygen vacancies (VO), introduced in the anatase TiO2 by hydrogenation, on the photovoltaic (PV) characteristics is discussed. Raman spectroscopy shows A1g second order scattering modes due to VO-influenced surface structural changes. EELS confirm the presence of Ti4+/Ti3+ mixed states and oxygen deficiency in all TNS-HT. Bandgap (Eg) of TNS can be tuned by controlling the temperature and/or duration of annealing. The indirect bandgap is found to be larger (~3.2–3.4eV) for TNS derived from Ti-foil, whereas TNS prepared using wet-chemical methods exhibit Eg in the range of 3.1–3.3eV. The introduction of VO red-shifts the band-edge by ~0.25eV. Hydrogenation decreases the PV efficiency (η) by 2–4 times compared to η=6–7% observed in DSSCs of diverse nanostructures. Despite the reduction in interfacial resistance enhancing electron generation and transport in TNS-HT samples, EIS studies indicate that the drop in η (%) is mainly due to the recapture of conduction band electrons via defect states shortening the electron lifetime.

Use of a pro-fibrogenic mechanism-based predictive toxicological approach for tiered testing and decision analysis of carbonaceous nanomaterials.

Engineered carbonaceous nanomaterials (ECNs), including single-wall carbon nanotubes (SWCNTs), multiwall carbon nanotubes (MWCNTs), graphene, and graphene oxide (GO), are potentially hazardous to the lung. With incremental experience in the use of predictive toxicological approaches, seeking to relate ECN physicochemical properties to adverse outcome pathways (AOPs), it is logical to explore the existence of a common AOP that allows comparative analysis of broad ECN categories. We established an ECN library comprising three different types of SWCNTs, graphene, and graphene oxide (two sizes) for comparative analysis according to a cell-based AOP that also plays a role in the pathogenesis of pulmonary fibrosis. SWCNTs synthesized by Hipco, arc discharge and Co-Mo catalyst (CoMoCAT) methods were obtained in their as-prepared (AP) state, following which they were further purified (PD) or coated with Pluronic F108 (PF108) or bovine serum albumin (BSA) to improve dispersal and colloidal stability. GO was prepared as two sizes, GO-small (S) and GO-large (L), while the graphene samples were coated with BSA and PF108 to enable dispersion in aqueous solution. In vitro screening showed that AP- and PD-SWCNTs, irrespective of the method of synthesis, as well as graphene (BSA) and GO (S and L) could trigger interleukin-1β (IL-1β) and transforming growth factor-β1 (TGF-β1) production in myeloid (THP-1) and epithelial (BEAS-2B) cell lines, respectively. Oropharyngeal aspiration in mice confirmed that AP-Hipco tubes, graphene (BSA-dispersed), GO-S and GO-L could induce IL-1β and TGF-β1 production in the lung in parallel with lung fibrosis. Notably, GO-L was the most pro-fibrogenic material based on rapid kinetics of pulmonary injury. In contrast, PF108-dispersed SWCNTs and -graphene failed to exert fibrogenic effects. Collectively, these data indicate that the dispersal state and surface reactivity of ECNs play key roles in triggering a pro-fibrogenic AOP, which could prove helpful for hazard ranking and a proposed tiered testing approach for large ECN categories.

Oxidation induced superconductivity and Mo/Cu charge equilibrium in Mo0.3Cu0.7Sr2ErCu2Oy

A detailed study of the structure-composition-properties correlation is reported for the as-prepared (AP) and two oxygenated (oxygenation carried out at ambient pressure and under high pressure) Mo0.3Cu0.7Sr2ErCu2Oy samples. Their crystal structures were characterized by combining the x-ray/neutron powder diffraction (NPD) and electron diffraction techniques. All the samples show tetragonal symmetry, crystallizing in the P4/mmm space group. The influence of oxygenation in the electronic states for the Mo0.3Cu0.7Sr2ErCu2Oy system associated with an oxidation reaction leading from a non-superconducting to a superconducting state has also been investigated by means of x-ray photoelectron spectroscopy (XPS). XPS measurements show the predominance of the MoV oxidation state over the MoVI one in the AP sample; annealing under flowing oxygen enhances both the MoVI and CuII amounts. The AP sample shows the existence of ferromagnetic clusters originated from the short-range magnetic correlations of the paramagnetic MoV cations. On the other hand, all the oxygenated samples are not magnetic but superconducting. The high-pressure oxygenated sample shows the highest superconducting transition temperature of TC = 84 K. A partial oxygen ordering in the (Mo/Cu)O1+δ chain and a decrease in the charge transfer energy after oxygenation induces superconductivity in the oxygenated samples.

Thermal-annealing effects on the structural and magnetic properties of 10% Fe-doped SnO2 nanoparticles synthetized by a polymer precursor method

Abstract In this work, we present the experimental results of Sn0.9Fe0.1O2 nanoparticles synthesized by a polymer precursor method. Studies were performed in the as-prepared (AP) and thermally-annealed (TA) samples. The X-ray diffraction (XRD) data analysis carried out using the Rietveld refinement method shows the formation of only the rutile-type structure in the AP sample and this phase remains stable for the TA sample. Additionally, the mean crystallite size shows an increase from ~4 nm to ~17 nm after the annealing and a clear reduction of the residual strain has also been determined. Micro-Raman spectroscopy measurements show the formation of an iron oxide phase (likely α-Fe2O3) after the thermal treatment. Magnetic measurements show a paramagnetic behavior for the AP sample and the coexistence of a weak ferromagnetism and paramagnetism for the TA sample. The magnetically-ordered contribution of the TA sample has been assigned to the formation of the hematite phase. DC and AC magnetic features of the TA sample are consistent with a cluster-glass behavior which seems to be related to the magnetic disorder of spins located at the particle surface. Those spins clusters seem to be formed due to the diffusion of iron ions from the core of the particle to the surface caused by the annealing process.

Luminescence properties of Eu3+ -activated SrWO4 nanophosphors- Concentration and Annealing effect.

Eu3+ (2, 5, 7 and 10 at.%) activated SrWO4 phosphors were prepared via a polyol synthesis route at low temperature (∼150 °C) under urea hydrolysis. X-ray diffraction studies of all Eu3+ doped samples corroborate good crystallinity with a tetragonal scheelite-type structure of the SrWO4 phase. The value of strain was obtained in the range ∼0.003 to 0.004 for as-prepared (ASP) and samples annealed at 900 °C. Vibrational modes were studied using IR and Raman Spectroscopy. Photoluminescence studies of Eu3+ doped SrWO4 samples were carried out under 266, 394 and 464 nm excitations. An intense red emission was observed with a strong peak at ∼613 nm due to 5D0 → 7F2 transition under 266 nm. Effect of annealing at 900 °C on the photoluminescence properties of samples has been studied and it was found that luminescence intensity increases up to ∼9 times (for 10 at.% Eu3+-doped SrWO4) on annealing as compared to the corresponding as-prepared sample. High asymmetric ratios (A21) ∼ 6–13 were observed demonstrating it to be a red emitter. Calculated CIE co-ordinates of these Eu3+ doped samples under 266 nm excitation for ASP and annealed at 900 °C are x = 0.65 & y = 0.34, which are closer to the standard of NTSC (x = 0.67 & y = 0.33). These studies reveal that SrWO4:Eu3+ nano-phosphors can be used as potential red emitting phosphors for the development of white LEDs.

1212-Molybdo-Cuprates; effect of oxygenation in the structure, properties and electronic states

ABSTRACTThe influence of oxygenation in the magnetism, superconductivity and electronic states for the Mo0.3Cu0.7Sr2RECu2Oy (RE = Y, Er and Tm) compounds are discussed here. The magnetic measurements on the as-prepared (AP) samples suggest the existence of short-range magnetic correlations due to the presence of the paramagnetic MoV cations in the copper chain site. On the other hand, all the oxygenated samples are not magnetic but superconducting. The high pressure oxygenated sample shows the highest superconducting transition temperature of TC = 84 K. The influence of oxygenation in the electronic states for the Mo0.3Cu0.7Sr2YCu2Oy system associated with an oxidation reaction leading from a non-superconducting to a superconducting state has also been investigated by means of X-ray photoelectron spectroscopy (XPS). XPS measurements show the predominance of the MoV oxidation state over the MoVI one in the AP material; annealing under flowing oxygen enhances both the MoVI and CuII amounts. A detailed study of the electronic states for the Mo0.3Cu0.7Sr2YCu2Oy samples has been performed and is also discussed.

Dispersal State of Multiwalled Carbon Nanotubes Elicits Profibrogenic Cellular Responses That Correlate with Fibrogenesis Biomarkers and Fibrosis in the Murine Lung

We developed a dispersal method for multiwalled carbon nanotubes (MWCNTs) that allows quantitative assessment of dispersion on profibrogenic responses in tissue culture cells and in mouse lung. We demonstrate that the dispersal of as-prepared (AP), purified (PD), and carboxylated (COOH) MWCNTs by bovine serum albumin (BSA) and dipalmitoylphosphatidylcholine (DPPC) influences TGF-β1, PDGF-AA, and IL-1β production in vitro and in vivo. These biomarkers were chosen based on their synergy in promoting fibrogenesis and cellular communication in the epithelial-mesenchymal cell trophic unit in the lung. The effect of dispersal was most noticeable in AP- and PD-MWCNTs, which are more hydrophobic and unstable in aqueous buffers than hydrophilic COOH-MWCNTs. Well-dispersed AP- and PD-MWCNTs were readily taken up by BEAS-2B, THP-1 cells, and alveolar macrophages (AM) and induced more prominent TGF-β1 and IL-1β production in vitro and TGF-β1, IL-1β, and PDGF-AA production in vivo than nondispersed tubes. Moreover, there was good agreement between the profibrogenic responses in vitro and in vivo as well as the ability of dispersed tubes to generate granulomatous inflammation and fibrosis in airways. Tube dispersal also elicited more robust IL-1β production in THP-1 cells. While COOH-MWCNTs were poorly taken up in BEAS-2B and induced little TGF-β1 production, they were bioprocessed by AM and induced less prominent collagen deposition at sites of nongranulomatous inflammation in the alveolar region. Taken together, these results indicate that the dispersal state of MWCNTs affects profibrogenic cellular responses that correlate with the extent of pulmonary fibrosis and are of potential use to predict pulmonary toxicity.

Quantitative Techniques for Assessing and Controlling the Dispersion and Biological Effects of Multiwalled Carbon Nanotubes in Mammalian Tissue Culture Cells

In vivo studies have demonstrated that the state of dispersion of carbon nanotubes (CNTs) plays an important role in generating adverse pulmonary effects. However, little has been done to develop reproducible and quantifiable dispersion techniques to conduct mechanistic studies in vitro. This study was to evaluate the dispersion of multiwalled carbon nanotubes (MWCNTs) in tissue culture media, with particular emphasis on understanding the forces that govern agglomeration and how to modify these forces. Quantitative techniques such as hydrophobicity index, suspension stability index, attachment efficiency, and dynamic light scattering were used to assess the effects of agglomeration and dispersion of as-prepared (AP), purified (PD), or carboxylated (COOH) MWCNTs on bronchial epithelial and fibroblast cell lines. We found that hydrophobicity is the major factor determining AP- and PD-MWCNT agglomeration in tissue culture media but that the ionic strength is the main factor determining COOH-MWCNT suspendability. Bovine serum albumin (BSA) was an effective dispersant for MWCNTs, providing steric and electrosteric hindrances that are capable of overcoming hydrophobic attachment and the electrostatic screening of double layer formation in ionic media. Thus, BSA was capable of stabilizing all tube versions. Dipalmitoylphosphatidylcholine (DPPC) provided additional stability for AP-MWCNTs in epithelial growth medium (BEGM). While the dispersion state did not affect cytotoxicity, improved dispersion of AP- and PD-MWCNTs increased TGF-β1 production in epithelial cells and fibroblast proliferation. In summary, we demonstrate how quantitative techniques can be used to assess the agglomeration state of MWCNTs when conducting mechanistic studies on the effects of dispersion on tissue culture cells.

加工熱処理を適用した W-Mo 系高速度工具鋼の疲労挙動

Application of a thermomechanical treatment to W-Mo type high-speed steel specimens enhanced the fatigue strength of the specimens. The fracture origin of as-prepared (AP) and thermomechanically-treated (TMT) specimens was large aggregates of about 12 μm, consisting of two or three M6C•MC carbides. Voids were produced by decohesion of the M6C/MC interfaces in M6C•MC carbides and a crack propagated between two voids in adjacent large M6C•MC carbides. The voids in the large carbides in the TMT specimens are less easily formed than in the AP specimens. This is attributable to greater stress concentration due to more inhomogeneous deformation around the carbides in the AP specimens than in the TMT specimens. A high density of tangled dislocations around the carbide brings about the inhomogeneous deformation around the carbide. The fatigue life of the TMT specimens is longer than that of the AP specimens because the nucleation of cracks in large M6C•MC carbide aggregates in the TMT specimens occurs less easily.