Electrolysis of molten fluorides is one of the promising methods for the recovery and recycling of rare earth metals from used magnets. Due to the dearth of phase equilibria data for molten fluoride systems, thermodynamic modelling of LiF-DyF3-NdF3 system using the CALPHAD approach was carried out. Gibbs energy modelling for LiF-NdF3 and LiF-DyF3 systems was performed using the constitutional data from literature. Ab initio calculations were used to obtain enthalpy of reaction of LiDyF4, an intermediate phase that is found to exist in the LiF-DyF3 system. Differential thermal analysis was carried out for selected compositions in the NdF3-DyF3 system, in order to determine liquidus and solidus temperatures. The Gibbs energy parameters for the limiting binaries determined in this work is used for modelling the Gibbs energy functions of equilibrium phases in the ternary system. Selected compositions of LiF-NdF3-DyF3 were subjected to DTA in order to validate the calculated phase temperatures involving melt.
Uniform, high quality, CuFe2O4 nanorods with high aspect ratios were synthesized by a surfactant-free single step polyol process at 220 degrees C. The structure of the product was characterized by XRD and FT-IR, and the morphology of the product was analyzed by SEM. The results showed that the as-prepared nanorods have a uniform cross-section and with average diameter of similar to 100 nm and aspect ratio in the range of 13-52. X-ray line profile fitting resulted in crystallite size of 15 nm, which reveals the polycrystalline nature of these nanorods. Magnetic characterization of product was performed by EPR and VSM techniques and the results show that the CuFe2O4 nanorods are ferromagnetic. The line width of the resonance lines in FMR is about 1.8 kOe which may originate from different resonance fields of randomly distributed nanocrystals which have different orientation of magnetic easy axes.
A thermodynamic description of the Fe-Te system needs to be developed in order to model internal corrosion by fission products in fuel pins of Generation IV nuclear reactors. In preparation for a thermodynamic assessment of the system, an experimental study has been performed in order to clarify some unknown or conflicting phase diagram data. New phase diagram data have been obtained using Differential Thermal Analysis and isothermal heat treatments followed by electron microscopy with EDS and WDS analysis. The DTA analysis revealed new phase boundary data, and confirmed a very steep Fe-rich liquidus, supporting the possibility of a liquid miscibility gap in the Fe-FeTe region. The analyses also confirmed the probable eutectoid reaction δ→β+δ’ at 523 °C. The invariant arrests of the unknown γ phase were consistent with information available in literature, but the phase was not identified via XRD of samples at its postulated composition. However, metallography of the samples revealed an unexpected microstructure pertaining to the δ phase, which might be the γ phase, and is discussed in this paper. The monoclinic space group C2/m is proposed for the δ phase based on XRD. The collected data will be used together with that available in literature to perform a thermodynamic Calphad assessment in a subsequent paper Part II: Thermodynamic modeling.
A thermodynamic description of the Fe-Te system modeled via the Calphad method is proposed, based on data published in a preceding publication Part I: Experimental study, and that available in literature. End-member formation energies for the phases beta, beta', delta, delta' and epsilon, as well as lattice stabilities of FCC and BCC tellurium, have been evaluated via DFT and used in the numerical optimization. The final Gibbs energy models fit thermodynamic and phase diagram data well, and inconsistencies are discussed. The thermodynamic description is then used to evaluate Gibbs energy of formation for selected Fe-Te compounds of interest for the modeling of internal corrosion of stainless steel fuel pin cladding during operation of Liquid Metal-cooled Fast Reactors (LMFR).
Knowledge about solid fraction versus temperature during solidification is crucial for the control of solidification processes. In the present paper solidification sequence and path of Al-Mg binary alloys containing 6.7 and 10.2 wt.% Mg was investigated by a series of DTA and quenching experiments and numerical modeling in 0.5 and 5 K min(-1) cooling rates. Experimental results show that at both cooling rates, Al-6.7 wt.% Mg solidifies with a single phase structure, but Al-10.2 wt.% Mg solidifies with a two phase structure. According to the results of numerical modeling, good agreement between calculated solidification curves and experimental solid fractions, but poor correlation with concentration profiles. The source of discrepancies is discussed according to different theories of microsegregation.
Poly(2-thiophen-3-yl-malonic acid)/Fe(3)O(4) nanocomposite was synthesized by the precipitation of Fe(3)O(4) in the presence of poly(2-thiophen-3-yl-malonic acid) (PT3MA). Characterizations of the nanocomposite were performed by XRD, FT-IR, TEM, TGA, AC/DC conductivity and dielectric measurements. The capping of PT3MA around Fe(3)O(4) nanoparticles was confirmed by FTIR spectroscopy, the interaction being between bridging oxygen of the carboxylate and the nanoparticle surface through bidentate binding. The crystallite particle sizes of 6 +/- 3 nm and 7 +/- 3 nm were obtained from XRD line profile fitting and from TEM image analysis respectively, and they are in good agreement with each other. Magnetization measurements revealed that PT3MA coated magnetite particles do not saturate at higher fields. The material showed superparamagnetic character as revealed by the absence of coercivity and remnant magnetization. Magnetic particle size was calculated as 7.3 +/- 1.0 nm from the mean magnetization term in the Langevin function which is also in conformity with the values determined from TEM micrographs and XRD line profile fitting. The TEM particle size analysis of the nanoparticles revealed the presence of a slightly modified magnetically dead nanoparticle surface. AC and DC conductivity measurements were performed to elucidate the electrical conduction characteristics of the product.
We report on the synthesis of (polyvinylpyrrolidone) PVP-Mn3O4 nanocomposite via a polyol route. Crystalline phase was identified as Mn3O4 and the crystallite size was obtained as 6 +/- 1 nm from X-ray line profile fitting. Average particle size of 6.1 +/- 0.1 nm obtained from TEM analysis reveals nearly single crystalline nature of these nanoparticles in the composite. The capping of PVP around Mn3O4 nanoparticles was confirmed by FT-IR spectroscopy, the interaction being via bridging oxygens of the carbonyl (C=O) and the nanoparticle surface. T-C and T-B for PVP-Mn3O4 nanocomposite were observed at 42K and 28.5 K, respectively. The sample has hysteresis with small coercivity and remanent magnetization at 40K, resembling the superparamagnetic state. ac conductivity measurements on PVP-Mn3O4 nanocomposite revealed a conductivity in the order of 10(-7) S cm(-1) at lower frequencies. The conductivity change with respect to frequency can be explained by electronic exchange occurring between Mr(+2) and Mn+3 existing in sublattice of spinel lattice.
The present study reports the synthesis and physico-chemical characterization of Mn1−xZnxFe2O4 (x = 0.5, 0.4, 0.3, 0.2, 0.1) nanoparticles-based magnetic fluids with reference to magnetic fluid hyperthermia. The properties of these fluids are studied using XRD, FTIR, TGA, VSM and the induction heating equipment operated at 330 kHz. The heating response of the fluids is investigated within the safety limit of H·f (4.8 *108 A/m-s). The study is also extended to simulate it for the agarose gel phantom system. The power absorption by these samples in distilled water and in agarose gel is calculated to compare with the experimentally observed value. To the best of the author's knowledge, no study of temperature sensitive magnetic fluid is reported on agarose gel, which simulates or phantom an in vivo condition. Results analysis show that the control of hyperthermia temperature is possible at lower fields and frequencies for the A91 sample with the smallest possible concentration, which can be acceptable for in vitro study.
Polypyrrole-BaFe12O19 nanocomposite was successfully synthesized by an in situ polymerization of pyyrole in the presence of synthesized BaFe12O19 nanoparticles. Structural, morphological, electrical and magnetic properties of the nanocomposite were performed by XRD, FT-IR, TEM, TGA, VSM and ac conductivity measurements respectively. XRD analysis reveals the inorganic phase as bariumhexaferrite and TGA shows about 22 wt% loading of hexaferrite in the nanocomposite. FT-IR analysis indicates a successful conjugation of hexaferrite particles with polypyrrole. Magnetization measurements show that polypyrrole coating decreases the saturation magnetization of BaFe12O19 significantly. This reduction has been explained by the pinning of the surface spins by the possible adsorption of non-magnetic ions during the polymerization process. Interactions between the hard and impurity phases, determined using the Stoner-Wohlfarth theory, reveal that particles' single domain character and the coating destabilizes the remanence state of the polypyrrole-BaFe12O19 nanocomposite.
Accurate values needed for the most commonly used indicators of good Glass Forming Ability (GFA) in alloys, i.e. the liquidus (T-l), crystallization (T-x) and glass transition (T-g) temperatures, are only available after successful production of the metallic glass of interest. This has traditionally made discovery of new metallic glasses an expensive and tedious procedure, based on trial-and-error methodology. The present study aims at testing the CALPHAD (Computer Coupling of Phase Diagrams and Thermochemistry) approach for predicting GFA in the Fe-Nb-B system by the use of the Thermo-Calc software and the thermodynamic database TCFE7. The melting temperatures and phase stabilities were calculated and combined with data for an atomic size mismatch factor, lambda, in order to identify and map potential high-GFA regions. Selected compositions in the identified regions were later produced by suction casting and melt spinning, and the potential success verified using X-Ray Diffraction (XRD). Differential Scanning Calorimetry (DSC) was also used to compare thermodynamic calculations for the model predictions, and evaluate standard GFA indicators. The model is found to fit well with literature data, as well as predict new bulk glassy compositions at and around Fe70.5Nb7B22.5. These results show promise in further predictive use of the model.
48.28 at.%Ti-51.72 at.%Ni thin films were prepared by magnetron sputtering and post-annealed at 450, 500, 550 and 600 degrees C, respectively. The evolution of structure, phase transformation and nanoscale indentation behavior of Ti-Ni thin film annealed at different temperature were investigated by X-ray diffractometer (XRD), differential scanning calorimetry (DSC) and nanoindention test, respectively. The results showed that the as-deposited Ti-Ni thin films were amorphous and crystallized after post-annealing. As the annealing temperature increased from 450 to 600 degrees C, both the content of parent phase (B2) and that of the precipitate phase (Ni4Ti3) increased. Both the phase transformation temperature and the micro-hardness of the annealed Ti-Ni thin films increased as well. Meanwhile, the pseudo-elasticity energy recovery ratio 77 first increased to the maximum value and then decreased with the increasing annealing temperature. It revealed that the annealed Ti-Ni thin film specimens exhibited the highest pseudo-elasticity degree with the largest 71 values under the load of 10 mN.
The crystal and magnetic structures of AlFe2B2 have been studied with a combination of X-ray and neutron diffraction and electronic structure calculations. The magnetic and magnetocaloric properties have been investigated by magnetisation measurements. The samples have been produced using high temperature synthesis and subsequent heat treatments. The compound crystallises in the orthorhombic crystal system Cmmm and it orders ferromagnetically at 285 K through a second order phase transition. At temperatures below the magnetic transition the magnetic moments align along the crystallographic a-axis. The magnetic entropy change from 0 to 800 kA/m was found to be - 1.3 J/K kg at the magnetic transition temperature.
The microstructural features required to optimize both the strength and ductility of copper are investigated by examining the as-cast pure Cu and Cu-(1.0e3.0)Fe-0.5Co and Cu-1.5Fe-0.1Sn (wt %) alloys. Uniaxial tensile tests show that (Fe, Co)- or (Fe, Sn)-doping improves both the strength and ductility of pure copper. The microstructure evolution with Fe, Co, or Sn doping is characterized by using optical and scanning and transmission electron microscopies. The effects of Fe, Co, and Sn doping on the microstructure clearly show that (i) iron-rich nanoparticles are dispersed inside the grains. The spherical nanoparticles grow in size with increasing Fe content, and when the Fe content exceeds 2.0 wt %, the particles transition into a petal-like morphology. (ii) The microstructure of the alloys (grain size and morphology) is notably influenced by the Fe and Co contents, and the grain size is reduced from an average of 603 mu m in pure Cu to an average of 26 mm in the Cu-3.0Fe-0.5Co alloy. (iii) The addition of 1.5wt % Fe and 0.1wt % Sn dramatically reduces the grain size to an average of 42 mu m, and this reduction is correlated with the appearance of smaller spherical iron-rich nanoparticles. The evolution mechanisms of the iron-rich nanoparticles and grain structure under the alloying effect are discussed.
The microstructure evolution in the as-cast pure Cu and Cu-(1.0–3.0)Fe-0.5Co and Cu-1.5Fe-0.1Sn (wt. %) alloys was characterised in the previous work. Herein, the plastic deformation characteristics were examined by uniaxial tensile tests at room temperature. Along with the microstructure evolution, the yield strength increased with increasing Fe content and reached a peak value at 1.5 wt % Fe, but thereafter decreased with the further addition of Fe in the Cu–Fe–Co alloys. Nevertheless, the tensile strength and elongation synchronously improve with increasing Fe content. In particular, the Cu-1.5Fe-0.1Sn alloy achieved the optimal strength–ductility combination. In terms of the strengthening mechanism, the (Fe, Co)- or (Fe, Sn)-doped copper encouraged impediment, trapping, and storage of dislocations by the iron-rich nanoparticles and grain boundaries, which enhanced the strength and sustained the work hardening and elongation. The evolution of mechanical properties under an alloying effect was quantitatively described by the strengthening models. The results indicate that the optimum balance between strength and ductility was achieved by designing a microstructure containing fine grains, intragranular smaller spherical nanoparticles, and a minor solute element with higher misfit and higher growth restriction effect. The necessities for engineering a microstructure to achieve simultaneously strong and ductile bulk metals were discussed.
Microstructure evolution in the as-cast pure Cu, Cu-(1.0, 2.0, 3.0)Fe-0.5Co (wt. %) alloys were characterized in the former work. The aim of the present study is to investigate the slow strain rate tensile (SSRT) performance and fracture behavior of the Cu–Fe–Co alloys reinforced with fined grains (FG) and iron-rich nanoparticles (NP), referred as NPFG structure. The plastic deformation and fracture characteristics were examined by multiaxial SSRT tests at 75 and 125 °C on notched specimens. The addition of Fe and Co enhanced the ultimate tensile strength and yield strength almost by double to triple times the properties compare to pure Cu, along with an acceptable reduction in ductility, both at 75 and 125 °C. The SSRT properties of the copper samples varied as a function of temperature and alloying content. The analysis of fracture surface indicates the effect of iron-rich nanoparticles and grain boundaries on the deformation and fracture processes. The Kocks-Mecking model was applied to describe the SSRT experimental results with fitting parameters. The model predicted the dynamic recovery ability of the copper samples with different Fe, Co content and temperature. The evolution mechanism of SSRT properties upon alloying content and temperature was discussed in terms of the microstructure characterization, fractographic observation, deformation modeling, strengthening models as well as the analysis of strain-hardening curves. The results indicate through further microstructural engineering the NPFG Cu–Fe–Co alloy is promising in utilization as the canister for the storage of the nuclear waste.
Optimization of the deposition parameters was conducted by the response surface methodology to synthesize high-quality ZnO rod arrays with a high texture coefficient, a large aspect ratio and a narrow bandgap. In addition, mathematical models based on statistical analysis were also developed to predict the texture coefficient, aspect ratio and bandgap of the ZnO rod arrays. With the optimized parameters, all of the three involved responses obtained the desired optimum values. The results show that the texture coefficient can be elevated up to a value of 0.998, which represents an almost perfect value. Moreover, wide range of aspect ratios was obtained for various applications and the obtained maximum value of 21.3 is relatively high value by wet chemical method, especially when no capping agent and no refreshing growth solution in a nearly neutral solution is used.
The growth of zinc oxide (ZnO) microrods on porous ceramic substrates by mild hydrothermal process was studied. One-dimensional ZnO microrods were grown on ZnO nanoparticle seeded substrates by using equimolar concentration of zinc nitrate and hexamethylenetetramine at temperatures lower than 100 degrees C. We found that the growth of ZnO microrods on alumina and diatomite substrates were affected due to hydrolysis of substrate surfaces. Stunted ZnO microrod growth on gamma-alumina and diatomite substrates were attributed to arise due to the degradation of hexamine molecules in the growth solution. Adjusting the pH prior to the growth of ZnO microrods on both alumina and diatomite lead to the growth of ZnO microrods similar to what is observed on flat glass substrates. Cordierite does not hydrolyze easily and hence ZnO microrods with aspect ratio as high as 24, were obtained without any pH control of the growth solution. Copper nanoparticles deposited on ZnO microrods were utilized as a catalyst for methanol steam reforming and about 14% hydrogen yield was obtained with almost 90% methanol conversion at reforming temperature of 350 degrees C.
The present work investigates how the substitution of Ni for Fe in the amorphous precursor of the high flux density Fe–Si–B–P–Cu (Nanomet®) alloy avoids the creation of detrimental pre-existing nuclei in the amorphous precursor as a step forward for improved amorphization capability, retains homogenous nanocrystalline structure with excellent soft magnetic properties, and affects the mechanical properties in terms of reduced hardness and Young's modulus. This has been achieved by adding Ni of various concentrations (0–8 atomic %). The investigation includes structural characterization, calorimetry, optimization of annealing temperature, extensive magnetic characterization and nanoindentation to assess the mechanical properties. The excellent soft magnetic properties demonstrate a strategy to deploy the nanocrystalline ribbons where freedom of device design is a limiting factor for electrodynamic energy conversion applications.
The present study aimed to quantify the anomalous crystallization and soft magnetic properties of Fe-Si-B-P-Cu (Nanomet) alloy by isothermal calorimetry. The isothermal crystallization had slow kinetics at temperatures below the peak temperature of the exothermic event. The inhomogeneous distribution of pre-existing nuclei in the amorphous structure led to the anomalous crystallization, and hence, to a nonlinear Avrami plot with lowered localized Avrami exponents, attributed to temperature dependent crystallization kinetics. To the best of our knowledge, the presence of pre-existing magnetic nuclei was experimentally confirmed for the first time using ultra-high sensitive magneto-thermo-gravimetry (MTG). This is otherwise challenging, if not impossible, with conventional structural diffraction techniques. The incremental saturation magnetization (Ms) revealed how the volume fraction of the nanocrystallites intrinsically depends on both the annealing temperature and dwell time, and the significant change in the coercivity (He) confirmed the vital role the homogenous nucleation growth process has in order to achieve excellent soft magnetic properties.
We have conducted an in-depth study of the magnetic phase due to a spinodal decomposition of the BCC phase of a CrFe-rich composition. This magnetic phase is present after casting (arc melting) or water quenching after annealing at 1250 degrees C for 24 h but is entirely absent after annealing in the interval 900-1100 degrees C for 24 h. Its formation is favored in the temperature interval ca 450-550 degrees C and loses magnetization above 640 degrees C. This ferromagnetic-paramagnetic transition is due to a structural transformation from ferromagnetic BCC into paramagnetic sigma and FCC phases. The conclusion from measurements at different heating rates is that both the transformation leading to the increase of the magnetization due to the spinodal decomposition of the parent phase and the vanishing magnetization at 640 degrees C are diffusion controlled.
This study investigates the magnetocaloric potential of the Al50Cr21-xMn17+xCo12 (x=0, 4, 8 at%) high-entropy alloy (HEA) series using integrated experimental and theoretical approaches. Structural analysis by X-ray diffraction and scanning electron microscopy indicate a dual phase containing B2 and body-centered cubic (BCC) structures. Magnetic characterization shows an approximately linear decrease in saturation magnetization and Curie temperature with increasing Cr content. Curie temperatures calculated by Monte Carlo simulations suggest that the measured magnetic properties originate from the B2 phase rather than the BCC phase. The enhanced magnetocaloric effect with decreasing Cr content highlights the attractiveness of HEAs in magnetocaloric applications.
Effects of small additions of Si to Cu60Zn40 on the properties, microstructure and phase transformation were investigated. It was found that Si promotes the formation of beta' phase and the microstructure of the alloys was changed from duplex alpha + beta' to single phase beta' brass. Electron to atom ratio was calculated and it was concluded that increment in this ratio led to a decrease in stacking fault energy which had an important role in reduction of the grain size as well microstructural variations in this study. The dilatomeric analysis showed that Si increased the ordering temperature of Cu60Zn40 alloy. Finally, based on the properties, the Cu-Zn-40-Si alloys are predicted to have the potential of being an alternative for free cutting leaded brass.
The present study provides a benchmark of a sustainable solution utilizing ferroalloys to prepare ultra-clean CoCrFeMnNi high-entropy alloy (HEA). The designed CaO-MgO-Al2O3 slags saturated with CaAl2O4-MgAl2O4 (CA-MA, Slag A) and CaO-MgO (C-M, Slag M) were used to refine the HEA in Al2O3 and MgO refractory in an induction furnace under high-purity Ar atmosphere at 1773 K. The characteristics of non-metallic inclusions in the sampled HEA at different time intervals were quantitatively investigated. The results showed that three types of inclusions, i.e., sulfide (MnS), oxide, and complex type (oxide+sulfide), were found in the HEA regardless of refractory and slag types. The oxide inclusions such as MnAl2O4 and MgAl2O4 spinel particles can exist stably in the HEA melted in Al2O3 and MgO refractories with slag A and slag M, respectively. This fact is also confirmed not only by the electrolytic extraction method with elimination of the alloy matrix affection but also by the thermodynamic stability diagram for the HEA. For the structure of the complex inclusions, the core of oxide inclusions usually can act as the subsequent nucleation site for MnS since the precipitation temperature of the oxide inclusions (above the liquidus temperature of the HEA, TL approximately equal to 1623 K) is higher than that of MnS (below the solidus temperature of the HEA, TS approximately equal to 1573 K). The HEA melted in the MgO refractory with slag M had a higher cleanliness compared with that melted in the Al2O3 refractory with slag A, indicating that the MgO refractory with C-M saturated CaO-MgO-Al2O3 slag is suitable for producing an ultra-clean CoCrFeMnNi HEA prepared by the ferroalloys feedstock as the raw materials.
Commercial ferroalloys are used in the manufacturing of a CoCrFeMnNi high-entropy alloy (HEA) due to their price advantage and the productivity of the manufacturing process. However, elemental impurities such as sulfur in ferroalloys can undermine the mechanical properties of HEAs. Therefore, the desulfurization behavior of a CoCrFeMnNi HEA using the CaO-MgO-Al2O3 (CAM) slagging method with alumina or magnesia refractories and ferroalloys raw material feedstock was investigated in an induction melting furnace at 1773 K to determine how to control the cleanness of the HEA. The resulting desulfurization ratios of the alloy were approx. 47% when refined by the CaAl2O4-MgAl2O4(CA-MA)-saturated slag in an Al2O3 refractory, whereas 94% when refined by the CaO-MgO(C-M)-saturated slag in a MgO refractory. The overall mass transfer coefficients of sulfur for the HEA refined by the CA-MA- and C-M-saturated slags at 1773 K were ko = 1.4 x 10 6 m/s and ko = 2.0 x 10 6 m/s, respectively, which are lower than the coefficients of iron- and nickel-based alloys at the same experimental conditions. The MnS inclusion particles can precipitate in the mushy zone rather than the liquid region when the solid fraction is close to 1.0, i.e., at the final stage of the solidification. The theoretical radius of MnS increases from 0 to 1.6 mu m when the sulfur content rises from 3 ppm to 60 ppm, according to the hypothesis that the mass transfer of sulfur in the HEA is the rate-controlling step.
L-Carnosine coated iron oxide nanoparticles (CCIO NPs) have been prepared via co-precipitation of iron oxide in the presence of L-carnosine. Crystalline phase was identified as magnetite with an average crystallite size of 8 nm as estimated from X-ray line profile fitting. Particle size estimated from TEM by log-normal fitting was similar to 11 nm. FTIR analysis showed that the binding of carnosine onto the surface of iron oxide is through unidentate linkage of carboxyl group. CCIO NPs showed superparamagnetic charactersitic at room temperature. The magnetic core size of superparamagnetic CCIO NPs was found slightly smaller than the size obtained from TEM, due to the presence of magnetically dead layer. Magnetization measurements revealed that L-carnosine iron oxide composite has immeasurable coercivity and remanence with absence of hysteritic behavior, which implies superparamagnetic behavior at room temperature. The low value of saturation magnetization compared to the bulk magnetite has been explained by spin canting. LDH activity tests showed slight cytotoxicity of high dose of CCIO NPs. The ac conductivity of CCIO NPs was found to be greater than that of carnosine and the effective conduction mechanism was found as correlated barrier hopping (CBH). dc activation energy of the product at around room temperature was measured as 0.312 eV which was in good agreement with the earlier reports.
L-lysine coated iron oxide (LCIO) nanoparticles were synthesized by a co-precipitation method in the presence of amino acid. XRD analysis confirmed the presence of cubic magnetite phase with an average crystallite size of 8 +/- 4 nm. Particle size estimated from TEM, by log-normal fitting, is similar to 114 nm. The difference between the crystallite size from XRD and particle size from TEM indicates polycrystalline nature of synthesized particles. FT-IR show that the binding Of L-lysine on the surface of iron oxide through carboxyl groups is via unidentate linkage. The presence of L-lysine on iron oxide is also confirmed by zeta potential measurements on LCIO nanoparticles, revealing a partial coverage of iron oxide with L-lysine. In order to obtain chemically stable, well-dispersed and uniform sized nanoparticles, amino acids are suitable because they play a very important role in the body. Conductivity measurements were performed to investigate the influence of the coating on the conduction characteristics of iron oxide and results show the existence of a hopping conduction mechanism. Magnetic transition is observed at similar to 70 degrees C for uncoated iron oxide and LCIO samples. Frequency (1 Hz to 3 MHz) and temperature (290-420 K) dependant AC conductivity measurements have resulted in AC activation energies between 0.048 and 0.041 eV for uncoated and 0.050-0.044 eV for LCIO nanoparticles. Temperature-dependant DC resistivity measurements of iron oxide and LCIO at high temperatures resulted in the DC activation energies of 0.22 and 0.43 eV respectively. The higher activation energy value for LCIO is the result of coating by insulating L-lysine layer.
Nanocrystalline LiBxMn(2-x)O(4) (x = 0.1-0.4) particles are prepared by ultrasonic spray pyrolysis using lithium nitrate, manganese nitrate and boric acid at 800 degrees C in an air atmosphere. The materials properties are characterized by X-ray diffraction, scanning electron microscopy, and atomic absorption spectroscopy. The electrochemical behaviors are investigated with cyclic voltammetry and galvanostatic techniques. The particle characterization studies show that nanocrystalline particles have spinel structure of submicron size with spherical morphology. All boron substituted lithium manganese oxide spinels show improved cycling performance. Among them, LiB0.3Mn1.7O4 particles exhibit 92 mAh g(-1) discharge capacity and 82% capacity retention after 50 cycles at a 0.5 C rate. The higher degree of atomic ordering and the avoidance of the formation of a glass phase in LiBxMn2-xO4 materials are responsible for the better electrochemical performance.
Conjugated polymers have been widely used as hole transport materials (HTM) in the preparation of mesoscopic perovskite solar cells (PSCs). In this work, we employed p-type doped conducting polymer known as poly(9,9-dioctylfluorene-co-bis-N,N-(-4-butyl phenyl)-bis-N,N-phenyl-1,4-phenylenediamine) (PFB) as a hole transport material (HTM) in perovskite based solar cell. The effect of dopant concentration on the optical and electrical properties of PEB was investigated to optimize the electrical properties of the material for the best function of the solar cell. The highest power conversion efficiency of mesoscopic perovskite solar cells (PSCs), fabricated in this investigation, was found to be 14.04% which is 57% higher than that of pristine PFB hole transport layer. The UV–Vis absorption and Raman spectroscopy measurements confirm the occurrence of oxidation in a p-type doped PFB hole transport layer. This is attributed to the transfer of electrons from the highest occupied molecular orbital (HOMO) of PEB to the lowest unoccupied molecular orbital (LUMO) of F4TCNQ. The solar cells produced using p-type doped PFB:F4TCNQ composite not only improves device performances but also shows superior long-term stability. The optical, morphological and electrical properties of the doped composite PFB: F4TCNQ and newly fabricated devices are presented and discussed in this paper.
The electronic structure of U-diluted in an Ag matrix has been studied in situ by ultraviolet and X-ray photoelectron spectroscopy (UPS and XPS, respectively). UxAg100-x thin films (x = 0-100 at.%) were produced by sputter co-deposition in an Ar atmosphere. UPS spectra of the Ag-4d line indicate formation of a homogeneous mixture despite the fact that U and Ag do not form stable alloys. A major goal of this work was to find out whether the dilution of U atoms in an inert matrix with no bonding states induces the localisation of the U-5f states. Both U-4f core level spectra and the U-5f spectra indicate U-5f delocalisation, down to 5 at.% of uranium in UxAg100-x films.
A facile synthesis of three-dimensional (3D) network of copper confined nitrogen-doped graphene (NG)/carbon nanotube (CNT) with high atomic percentage of nitrogen (10.1 at.%) has been reported. The homogenous intercalation of the CNT network in-between the graphene layers decorated with copper nanoparticles take place which inhibits the self-agglomeration within the lattice and enhance the volumetric storage capability. The composite electrode demonstrates exceptionally high specific capacitance of 1250 mA h/g obtained at a current density of 0.1 A/g which is 3.4 times greater than the theoretical capacity of graphite (372 mA h/g). The discharge-charge profiles (from 0.002 to 3 V) with reversible battery capacity exhibit a stable state of the lithium-ion batteries which were observed at high rate capability of 420 mA h/g at a current density of 1 A/g even after 500 cycles. The enhancement of the electrochemical performance could be attributed to the 3D electrically conductive networks of copper confined nitrogen-doped graphene/carbon nanotubes (Cu@[N-Gr/CNT]).
In this work, four different methods, including polyvinyl alcohol (PVA)-assisted sol-gel process, polyethylene glycol (PEG)-assisted sol-gel process, citrate sol-gel process and oxalate coprecipitation process (OCP) are employed to synthesize the Sm and Nd co-doped ceria electrolyte with the composition of Ce(0.85)Sm(0.075)Nd(0.075)O(2-delta) (SNDC). The phase structure of the powders can be well indexed with the fluorite-type CeO(2) structure. The morphology of sintered samples indicates that the ceramics can be highly densified. The relative density and the average grain size vary with the synthesis processes and the sintering temperatures. The bulk conductivities are quite close and the OCP-SNDC yields highest grain-boundary conductivities and total conductivities. The results indicate that the OCP process for the powder synthesis results in higher relative density and conductivities, lower grain-boundary resistance and activation energy. Grain-boundary space charge potentials for different specimens are calculated based on the Mott-Schottky model. The synthesis process and sintering temperature have significant effect on the space charge potential and the specific grain-boundary conductivity. (C) 2011 Elsevier B.V. All rights reserved.
A four-component equimolar high-entropy alloy (HEA) with the composition of HfNbTiZr and body-centered cubic (bcc) structure was processed by HPT at RT. The evolution of the dislocation density, the grain size and the hardness was monitored along the HPT-processed disk radius for different numbers of turns between ¼ and 20. It was found that most of the increase of the dislocation density and the refinement of the grain structure occurred up to the shear strain of ∼40. Between the strains of ∼40 and ∼700, only a slight grain size reduction was observed. The saturated dislocation density and grain size were ∼2.1 × 10 16 m −2 and ∼30 nm, respectively. The saturation in hardness was obtained at ∼4450 MPa. These values were similar to the parameters determined in the literature for five-component HEAs processed by HPT. The analysis confirmed that the main component in the strength was given by the friction stress in the HPT-processed bcc HfNbTiZr HEA. It was also revealed that the contribution of the high dislocation density to the strength was significantly higher than the effect of the small grain size.
The changing role of the 5f electrons across the actinide series has been of prime interest for many years. The remarkable behavior of americium's 5f electrons under pressure was determined experimentally a few years ago and it precipitated a strong interest in the heavy element community. Theoretical treatments of americium's behavior under pressure followed and continue today. Experimental and theoretical findings regarding curium's behavior under pressure have shown that the pressure behavior of curium was not a mirror image of that for americium. Rather, one of the five crystallographic phases observed with curium (versus four for americium) was a unique monoclinic structure whose existence is due to a spin stabilization effect by curium's 5f(7) electronic configuration and its half-filled 5f-shell. We review briefly the behavior of pure curium under pressure but focus on the pressure behaviors of three curium alloys with the intent of comparing them with pure curium. An important experimental finding confirmed by theoretical computations, is that dilution of curium with its near neighbors is sufficient to prevent the formation of the unique C2/c phase that appears in pure Cm metal under pressure. As this unique C2/c phase is very sensitive to having a 5f7 configuration to maximize the magnetic spin polarization, dilution of this state with adjacent actinide neighbors reduces its stability.
Point defects in B2 compounds are described with a model based on the formula (A,B,Va),(B,A,Va), and results are compared with previous results from two models based on combined defects and using the formulae (A,B), (B,A), and (A,Va)(1) (B,A)(1) The comparison is straight-forward close to the stoichiometric composition but not closer to the pure elements. Using the more general model, it is demonstrated that the fact that vacancies are the predominant defect in some B2 compounds with a small excess of B atoms depends primarily on interactions between next-nearest neighbours rather than on a high enthalpy of formation of the compound, as proposed earlier.
The compound energy formalism for solution phases with sublattices is very flexible and thermodynamic models for a large variety of phases have been constructed within this formalism. The range of applications is reviewed and the methods of handling various problems are examined. Recent developments including treatments of short range order within the compound energy formalism are reviewed.
The effect of Zn/Gd ratio on dynamic recrystallization (DRX) of Mg-2Gd-xZn (x = 0, 1, 2 and 3 wt%) alloys was investigated by shear punch tests in the temperature range of 623-723 K and shear strain rate range of 1.0 x 10(-2)-1.2 x 10(-1) s(-1). It was observed that at low Zn/Gd ratio, excessive co-segregation of Gd and Zn solute atoms retards recrystallization and provides higher strength. At high Zn/Gd ratios, precipitation reduces the co-segregation, so that the alloy with Zn/Gd = 1.5, experienced the fastest DRX and the lowest strength. In addition, segregation resulted in a weaker texture, by elimination of nucleation and growth of the preferred orientations. rights reserved.
In the present work, the oxidation kinetics of AlN powder was investigated by using thermogravimetric analysis, X-ray diffraction (XRD) and scanning electron microscopy (SEM). The experiments were carried out both in isothermal as well as non-isothermal modes under two different oxidizing atmospheres. The results showed that the oxidation reaction started at around 1100 K and the rate increased significantly beyond 1273 K forming porous aluminum oxide as the reaction product. The oxidation rate was affected by temperature and oxygen partial pressure. A distinct change in the oxidation mechanism was noticed in the temperature range 1533-1543 K which is attributed to the phase transformation in oxidation product, viz. alumina. Diffusion is the controlling step during the oxidation process. Based on the experimental data, a new model for predicting the oxidation process of AlN powder had been developed, which offered an analytic form expressing the oxidation weight increment as a function of time, temperature and oxygen partial pressure. The application of this new model to this system demonstrated that this model could be used to describe the oxidation behavior of AlN powder.
In lanthanide-doped upconversion nanoparticles (UCNPs), the concentration of emitter ions, also known as activator ions, is usually limited to 1 - 5 mol% due to concentration quenching effects. This circumstance limits the luminescent efficiency of UCNPs' and their use in a variety of application areas. Earlier studies have attributed the activator concentration quenching to migration of energy to the nanoparticle surface, while indicating that cross-relaxation between activator ions had a minor role therein. In this work, we carried out comparative studies on Er3+-doped and Yb3+-Er3+ codoped UCNPs and could, in contrast to this notion, prove a general adverse effect of cross-relaxation between activator ions, here Er3+ ions, on up -conversion luminescence (UCL). The direct result of the cross-relaxation is that the energy of the excitation light is accumulated into a low-lying excited state of Er3+ in the infrared region, so forming a "low-lying excited state energy trap ". As a result, the excitation energy is used for generating down-conversion lu-minescence or for indirectly facilitating UCL channels that are directly related to the low-lying excited state energy trap. The identified effect can be used to regulate UCL channels to achieve a concentrated UCL band that is more favorable for certain applications, e.g., biological imaging.
Developing highly effective catalysts for oxygen reduction reaction (ORR) is crucial to enable the low-temperature operation of solid oxide fuel cells (SOFCs). Recent studies have proposed a promising O2-/H+/e- conducting oxide, LiNi0.8Co0.15Al0.05O2-delta (LNCA) with good ORR catalytic activity for SOFC cathode uses. Herein, to further optimize the cathode functionality of LNCA, a fluorine anion (F-) doping strategy is ap-plied to develop highly active LNCAF0.1 and LNCAF0.2 cathodes for Sm-doped ceria (SDC) electrolyte-based SOFCs. It is found the successful doping of F- in the oxygen site of LNCA leads to improved oxygen ionic conductivity and facilitated surface exchange and bulk diffusion of oxygen in LNCAF0.1 and LNCAF0.2, which thus gain distinctly promoted ORR catalytic activity at 450-550 degrees C, as confirmed by the decreased area specific resistances (ASR) and activation energy on symmetrical cells. The as-fabricated two SDC-based SOFCs with LNCAF0.1 and LNCAF0.2 cathodes exhibit peak power densities of 497 and 591 mW cm-2 at 550 degrees C, respectively, which are higher than that of the cell with LNCA cathode. Furthermore, the single cell with the best-performing LNCAF0.2 cathode demonstrates a good stability for 110 h at 550 degrees C. The present study thus provides a feasible strategy of F anion doping to promote the ORR catalytic activity of LNCA cathode for developing low-temperature SOFCs.
The 5f elements, actinides, show many properties which have direct correspondence to the 4f transition metals, the lanthanides. The remarkable similarity between the solid state properties of compressed Ce and the actinide metals is pointed out in the present paper. The alpha-gamma transition in Ce is considered as a Mott transition, namely, from delocalized to localized 4f states. An analogous behavior is also found for the actinide series, where the sudden volume increase from Pu to Am can be viewed upon as a Mott transition within the 5f shell as a function of the atomic number Z. On the itinerant side of the Mott transition, the earlier actinides (Pa-Pu) show low symmetry structures at ambient conditions; while across the border, the heavier elements (Am-Cf) present the dhcp structure, an atomic arrangement typical for the trivalent lanthanide elements with localized 4f magnetic moments. The reason for an isostructural Mott transition of the f electron in Ce, as opposed to the much more complicated cases in the actinides, is identified. The strange appearance of the delta-phase (fcc) in the phase diagram of Pu is another consequence of the border line behavior of the 5f electrons. The path leading from delta-Pu to alpha-Pu is identified.
Poly(3-pyrrol-1-ylpropanoic acid) (PPyAA)-Fe(3)O(4) nanocomposite was successfully synthesized by an in situ polymerization of 1-(2-carboxyethyl) pyrrole in the presence of synthesized Fe(3)O(4) nanoparticles. Evaluation of structural, morphological, electrical and magnetic properties of the nanocomposite was performed by XRD, FT-IR, TEM, TGA, magnetization and conductivity measurements, respectively. XRD analysis reveals the inorganic phase as Fe(3)O(4) and TGA shows about 90 wt% loading of Fe(3)O(4) in the nanocomposite. FT-IR analysis indicates a successful conjugation of Fe(3)O(4) particles with polypyrrole acetic acid. Magnetization measurements show that polypyrrole acetic acid coating decreases the saturation magnetization of Fe(3)O(4) significantly. This reduction has been explained by the pinning of the surface spins by the possible adsorption of non-magnetic ions during the polymerization process. The conductivity and dielectric permittivity measurements strongly depend on the thermally activated polarization mechanism and thermal transition of PPyAA in the nanocomposite structure. Large value of dielectric permittivity (epsilon') of the nanocomposite at lower frequency is attributed to the predominance of species like Fe(2+) ions and grain boundary defects (interfacial polarization).
Nanosize ZnxNi1-xFe2O4 spinel composites with x = 0, 0.2, 0.4, 0.6, 0.8 and I were synthesized by using surfactant (polyethylene glycol (PEG)) assisted hydrothermal route and characterized by TEM, XRD and VSM techniques. The crystallite size was calculated from different characterization methods, and magnetic core size was found to be in the range of 9-20 nm from VSM. All particles showed superparamagnetic character at room temperature and M, decreased with increasing concentration of Zn2+. Due to the bigger ionic radius of Zn2+ with respect to Ni2+, the unit cell parameter 'a' increased linearly with increasing x, likewise, the oxygen positional parameter 'u' increased theoretically and experimentally as observed in the literature. Particle size was observed to decrease by substitution of Zn. The cation distribution has been calculated analytically by using X-ray diffraction data and Fe3+ cations were found to occupy mostly tetrahedral sites revealing almost an inverse-spinel structure. These results are proved to be consistent with the results of magnetic measurements. The site preference of Fe3+ cations on tetra sublattice is attributed to the synthesis conditions utilizing surfactant and low temperature.
Nanostructured powders of thermoelectric (TE) CoSb3 compounds were synthesized using a chemical alloying method. This method involved co-precipitation of oxalate precursors in aqueous solution with controlled pH, followed by thermochemical treatments including calcination and reduction to produce stoichiometric nanostructured CoSb3. Moreover, CoSb3 nanoparticles were consolidated by spark plasma sintering (SPS) with a very brief processing time. Very high compaction densities (>95%) were achieved and the grain growth was almost negligible during consolidation. An iterative procedure was developed to maintain pre-consolidation particle size and to compensate Sb evaporation during reduction. Significant changes in particle size and morphology were observed, and the post-reduction cooling was found to be an important stage in the process. The spark plasma sintering (SPS) parameters were optimized to minimize the grain growth while achieving sufficient densification. Grain sizes in the range of 500 nm to 1 mu m, with compaction density of 95-98% were obtained. Preliminary measurements of thermal diffusivity and conductivity showed the dependence on grain size as well as on porosity. TE transport properties were measured in the temperature range of 300-650 K. Sample showed p-type behavior with a positive Seebeck coefficient, which increases with increasing temperature. Electrical conductivity measurements indicate metallic behavior and it decreases with increasing temperature. Thermal conductivity also decreases with increasing temperature and major contribution is due to the lattice component. A TE figure of merit of 0.15 was achieved for high purity CoSb3 nanostructured TE material at 650 K and these results are comparable with the values reported for the best unfilled/undoped CoSb3 in the literature.
Raney nickel and its alloys with the transition metals were prepared and investigated as gas diffusion electrodes for the hydrogen oxidation reaction (HOR) in 6 M KOH and at 60degreesC. The spongy Raney nickel prepared by a mixture of Ni and Al with a weight ratio of 1: 1 was compared for the catalytic activity as hydrogen electrodes with other alloy formations containing 2 wt.% of Cu, Fe, Cr, Ti and La. Depending on the composition of the active layer, the electrocatalytic activity of the Raney nickel was found to decrease in a descending order of the doped metals: Cr>La>Ti>Cu>Fe and with no admixture. The catalytic response of the electrodes, especially for the Cr and Ti-based Raney Ni showed high enrichment and aggregation on the surface and hence affects the activity and stability. Surface area, particle size. average pore diameter, particle morphology and surface elements of the various alloy combinations, have been analyzed and assessed using BET-specific surface areas, SEM and EDXS.
The C-Cr-Fe-Ni-O and Fe-Mn-O systems have been studied earlier with the intention to thermodynamically describe the influence of oxygen on high alloyed steels. In this study the ternary Cr-Mn-O system is assessed. The liquid phase is assessed using the ionic two-sublattice model. Good agreement between calculated and experimental values is achieved.
The pressure dependence of the lattice parameters of the ternary layered carbide, Ti2SC, was measured by using synchrotron radiation X-ray diffraction and a diamond anvil cell setup. The experiment was conducted at room temperature and no phase transformation was observed up to the maximum pressure of 47 GPa. The a and c lattice parameters at room condition are 3.216 (A) over circle and 11.22 (A) over circle, respectively. The bulk modulus, calculated using the Birch-Murnaghan equation of state, is 191 +/- 3 GPa, with a pressure derivative of 4.0 +/- 0.3 and that obtained by our ab initio calculations is 183 GPa, with a pressure derivative of 4.1. L Like the majority of the ternary layered carbides (MAX phases), compressibility along the c-axis was higher than that along the a-axis.
First-principles methods are employed to study the ground-state atomic volumes of alpha-Pu-Ga(Al) alloys. It is shown that a random distribution of Ga(Al) atoms in the monoclinic lattice of alpha-Pu results in a maximum expansion of this lattice and creation of the so-called alpha'-Pu phase. Any kind of ordering of Ga(Al) atoms on the monoclinic lattice results in a shrinking of the lattice constant while the ordered alpha(8)-(Pu-Ga(Al)) configuration yields the smallest lattice constant which is very close to that of pure alpha-Pu. In addition, energetics of the ordered (unrelaxed and relaxed) and disordered configurations is discussed.