Electrochemical studies on cerium(III) in molten fluoride mixtures

This study aims to determine the principal electrochemical characteristics of the electrodeposition of cerium metal from molten fluoride systems. The cathodic process of Ce³⁺ ions in LiF-NaF and LiF-NaF-CaF₂ molten salts was studied using electrochemical techniques as steady state and cyclic voltammetry methods. The decomposition potential (E_d) and the overvoltage(η) were determined for NaCeF₄ using current-potential curves under galvanostatic conditions. The E_d was found to be 2.025 V in LiF-NaF and 2.045 V in LiF-NaF-CaF₂. It was also found that the ohmic drop potential (EΩ) was not dependent on NaCeF₄ concentration and it rose as the current intensity increased. The overvoltage (η) was determined from the polarization curves and the Tafel coefficients and kinetic parameters were calculated on the assumption that the process constitutes of direct discharge of Ce³⁺, with no solvent-solute interaction. In order to elucidate the cathodic process the investigation by cyclic voltammetry technique was finally used. From the evolution of the voltammograms we concluded that the electrochemical reduction of Ce³⁺ ion was actually a reversible process on the molybdenum electrode and cathodic reduction of Ce³⁺ took place in one single step involving three electron exchanges.     

Substituent effects on novel lanthanide(III) hydrazides complexes

New lanthanide (Eu³⁺ and Gd³⁺) complexes were successfully synthesized and the effect of the p-phenyl substituent on the Eu³⁺ luminescent properties was evaluated. In this sense, benzhydrazide, p-toluic hydrazide, 4-hydroxybenzhydrazide and 4-aminobenzoic hydrazide were used as ligands and the complexes were obtained by mixing the lanthanide salts with hydrazides in ethanol at room temperature and keeping the reaction for 2 h under mechanical stirring. Crystal of Gd-amino was obtained and its structure was elucidated by single-crystal X-ray diffraction, revealing that Gd³⁺ centered in a distorted tricapped trigonal-prismatic molecular geometry. IR spectroscopy and the elucidated structure confirm hydrazides acting as bidentate ligands binding to Ln³⁺ ions through the oxygen of carbonyl group and the nitrogen of terminal amine, forming a five-membered ring. CHN analyses confirm the molecular formulas [Gd(amino)₄(H₂O)](NO₃)₃·(C₂H₅OH) and [Eu(toluic)₃(H₂O)₃](NO₃)₃. Lower T₁ state energies are observed for ligands p-substituted with higher electron donating capacity groups, such as p-NH₂ and p-OH. In contrast, higher lifetimes and quantum efficiencies are obtained for Eu³⁺ complexes with ligands p-H and p-CH₃ substituted, which are not deactivator groups.     

Solid phases of the Mn-C system

The Mn-C system between 700° and 1110°C was reexamined by microscopic and X-ray diffraction methods. The results summarized in a phase diagram show cubic α-, β- γ-Mn, and hexagonal ∈ existing over appreciable ranges of composition, and cubic Mn₂₃C₆, hexagonal Mn₁₅C₄, orthorhombic Mn₃C, monoclinic Mn₅C₂, and hexagonal (or trigonal) Mn₇C₃ as essentially line compounds. Room temperature lattice parameters of the quenched hexagonal ∈?Mn₄C₁₊ X phase were found to increase froma _h=2.685 (268.5) andc _h=4.412¶ (441.2 pm) withX=?0.30 toa _h=2.709 (270.9) andc _h=4.429±0.001 ¶ (442.9 pm) withX=+0.06.     

Effect of carbon coating on electrochemical properties of AB3.5-type La–Y–Ni-based hydrogen storage alloys

The superlattice La–Y–Ni-based hydrogen storage alloys have high discharge capacity and are easy to prepare. However, there is still a gap in commercial applications because of the severe corrosion of the alloys in electrolyte and poor high-rate dischargeability (HRD). Therefore, (LaSmY) (NiMnAl)_3.5 alloy was prepared by magnetic levitation induction melting, and then the alloy was coated with different contents (0.1 wt%–1.0 wt%) of nano-carbons by low-temperature sintering with sucrose as the carbon source in this work. The results show that the cyclic stability and HRD of the alloy first increase and then decrease with the increase of carbon contents. The kinetic results show that the electrocatalytic activity and conductivity of the alloy electrodes can be enhanced by carbon coating. The electrochemical properties of the alloy are the best when the carbon coating content is 0.3 wt%. Compared with the uncoated alloy, the maximum discharge capacity (C_max) improves from 354.5 to 359.0 mAh/g, the capacity retention rate after 300 cycles (S₃₀₀) enhances from 73.15% to 80.01%, and the HRD₁₂₀₀ of the alloy enhances from 74.39% to 74.39%.     

Molten salt synthesis of Z-scheme CeO2/C3N4 photocatalysts with excellent properties for removal of organic pollutants: Characterization,kinetics and mechanisms

In this work,we firstly synthesized a CeO₂/C₃N₄ photocatalyst with Z-scheme heterojunction by a facile LiC-KCI molten salt method.The synthesized catalyst has an excellent quality for removing organic pollution of dyes and antibiotics in wastewater.As an example,the CeCN-1:5 prepared with a mass ratio of Ce₂(CO₃)₃·xH₂O:C₃H₃N₆=1:5 exhibits a methylene blue(MB) removal capacity of 100%with...     

Manganese Capacity and Optical Basicity of Metallurgical Slag

In practice, the concept of slag capacity is used to assess the distribution of elements between condensed phases. In particular, researchers determine the sulfide, phosphate, chromate, and nitride capacity of slags. In the present work, a mathematical model of the manganese capacity is derived. To that end, two equivalent forms of the manganese capacity are derived from the equilibrium constants of the redox reaction of manganese [Mn] + (1/2)O₂ = (MnO). These indices reflect the manganese distribution between the metal and the slag and do not depend on the composition of the metal and the gas phase. One version takes the form C^Mn = K_Mn/γ_(MnO). If we take logarithms and use the known equilibrium constant K_Mn of the redox reaction, we may write logC^Mn = 21122/T–logγ_(MnO)–4.5509. To find the activity coefficient of manganese oxide, equilibrium between hot metal, cast iron, ferrosilicon, ferromanganese, and the corresponding slags is studied experimentally at various temperatures, on circulatory apparatus permitting the study of heterogeneous equilibria involving the gas phase. Using the apparatus, the change in gas volume in the reactions is monitored and automatically recorded and constant pressure is automatically maintained in the system. The attainment of equilibrium is also judged from the constancy of chemical composition of the condensed phases over time. If numerical values of γ_(MnO) are available, they may be used to calculate the manganese capacity of all the slags from the equation already given. For the sake of practical convenience, the manganese capacity is written in terms of the temperature and the optical basicity λ_ed calculated from the electron density known for elements in the periodic table: logC^Mn =–1.866λ_ed + 21049/T–3.131 (R² = 0.997). According to this equation, the manganese capacity depends only on λ_ed and the temperature and may be used for metals and slags of practically any composition.     

Thermophysics characteristics and densification of powder metallurgy composites

Abstract

An analytical densification model describing the final stages of hot pressing and sintering has been developed and found to be consistent with empirical findings. The behaviour of composite powders for the matrices of diamond tools has been studied under hot pressing conditions. Differential scanning calorimetry was used to determine the heat capacity at constant pressure C _p of pure Co, 663Cu, and composite iron- and cobalt based powders (also containing WC, Ni and 663Cu). The relationship between C _p and composite densification has been analysed, and it has been found that optimised rare earth additions to the iron based composite powders can produce C _p characteristics close or equivalent to that of pure Co powders. This modified composite powder has been used to hot press diamond drill and saw bits that show good properties. Employing a densification regime guided by the dynamic model has been found radically to improve stability in service (bend strength, hardness, impact, ductility and porosity).     

Characterization of carbonitrided layers formed on stainless steel by conversion electron Mössbauer spectrometry

Austenitic stainless steel was carbonitrided by the tufftride process, and the hardened layers formed on the surface were investigated by conversion electron Mössbauer spectrometry (CEMS) and grazing angle X-ray diffractometry (GXRD). It was found that carbides such as M₇C₃ (M = Fe, Cr), chromium nitride (CrN),ε-nitride (M₂N, M = Fe, Cr), andε-carbonitride º_2+x (C,N), M = Fe, Ni} were precipitated on the outermost surface at the initial stages of carbonitriding. By the increase of treatment time up to 20 and 30 minutes,∈ M_2+x (C,N) became a main component, while M₇C₃ and CrN disappeared in the outermost surface. After 60 minutes, M₇C₃ and CrN were observed again, and theγ nitride, the oxide of iron and chromium (FeCr₂O₄), was formed on the outermost surface for the first time. Cross-sectional micrographs of surface layers using a scanning electron microscope (SEM) after etching the hardened layers with Marble reagent revealed the presence of black and white layers. The former layer mainly consisted of∈ M_2+x (C,N),∈ M₂N, CrN, and M₇C₃, and the latter layer did not contain nitrogen, although carbon was detected in both layers. The Vickers hardnesses of the black and white layers were HmV(0.l) 1000 to 1200 and HmV(0.l) 500 to 600, respectively. It was said that both layers were harder compared with HmV(0.1)200 of bulk. The white layer was far superior to the black one in the corrosion resistance proved by anodic polarization curve measurements in 5 vol pct H₂SO₄ solution. The white layer formed on carbonitrided stainless steel beneath the black layer has possibilities as an excellent corrosion and wear resistive layer.     

The Use of Oxalic Acid as a Chelating Agent in the Dissolution Reaction of Calcium Molybdate

In this study, the dissolution behavior of calcium molybdate (CaMoO₄) was investigated in oxalic acid (H₂C₂O₄) solution. The effects of stirring speed, temperature, H₂C₂O₄ concentration, and particle size on the dissolution reaction of CaMoO₄ were determined. The dissolved quantities of molybdenum and calcium were analyzed quantitatively by ICP-OES. Fractional conversion of CaMoO₄ vs time and concentration of calcium vs time diagrams were plotted. It was observed that at constant temperatures and lower H₂C₂O₄ concentrations, the dissolution increased by increasing H₂C₂O₄ concentration, but at higher H₂C₂O₄ concentrations, the effect of H₂C₂O₄ concentrations was negligible. The dissolution reaction of CaMoO₄ in H₂C₂O₄ solution was performed in two steps as series–parallel type reaction. In the first step, CaMoO₄ reacted with H₂C₂O₄ to form the water-soluble calcium aqua oxalato molybdate (Ca[MoO₃(C₂O₄)(H₂O)]) intermediate chelate product. In the second step, the intermediate chelate, Ca[MoO₃(C₂O₄)(H₂O)], reacted with the reactant, H₂C₂O₄, to yield water-soluble hydrogen oxalato dimolybdate chelate (H₂[(MoO₃)₂(C₂O₄)]) and insoluble CaC₂O₄H₂O as final products. It was found that 500 rpm was enough to eliminate the resistance of liquid film layer that surrounds the solid particles. It was concluded that the optimum temperature was 313 K (40 °C) and the optimum concentration of H₂C₂O₄ was 1 kmol m^?3 to obtain high conversion during the dissolution of CaMoO₄.     

The anomalous behavior of Schottky barrier diodes made on lightly doped GaAs

When Schottky barrier diodes are used to evaluate lightly dopedn type (n～10¹⁵ per cu cm) epitaxial GaAs onn ⁺ substrates, the diodes do not always have the expected varactor characteristics. The capacitance variation with bias is sometimes too small, and the voltage intercept on the 1/C ² vsV plot too high. This behavior has been attributed either to a thin intrinsic semiinsulating layer between substrate and epi layer,¹ or to deep trap impurities in the epi layer.² The effects seen in this work are shown to be due to traps by the dependence of diode characteristics on heat, light, and frequency. These diodes also have conductances which decrease with reverse bias. The model of Sah and Reddi³ leads to a reduction in high frequency junction capacity and capacitance-bias variation range. The large, bias dependence conductance observed in our diodes must also be explained, however. A schematic model is proposed in which a series resistancer, due to the resistance of the undepleted epi layer at high frequency, is shunted by a capacitanceC _u, also due to the undepleted layer. A junction conductance 1/R is in parallel with the junction capacitanceC. The equivalent circuit seen by the capacitance bridge, used for obtaining data, is a measured capacitanceC _m in parallel with the measured shunt resistanceR _m. Much of the observed diminution of capacity and varactor action can be accounted for in terms of this model. The series resistancer seems to be large only at high frequencies, and is associated with the traps in the epi layer.     

Anomalous small-angle X-ray scattering determination of the partial structure factors of an aged Fe-Ni-W alloy: A synchrotron radiation study

The phase transformation at 480°C of a Fe-0.17 Ni-0.027 W (at.%) alloy was studied by anomalous small-angle X-ray scattering (ASAXS). Partial structure factors (PSF) were extracted from ASAXS data obtained in the neighbourhood of K Fe and L_IIIW absorption edges. The PSF were decomposed into two contributions: a pseudobinary one and a complementary one. This latter was shown to be very low ( ∼- 3%). From these PSF, it has then been concluded that the precipitation occurs according to a two-phase system. Such a result agrees well with TEM observations which have revealed two phases having different crystalline structures: precipitates of hexagonal symmetry embedded in a b.c.c. depleted ex-martensitic matrix. The composition of both phases does not change during isothermal ageing, being for the precipitate C_Fe = 0.956, C_W = 0.044, C_Ni∼-0 and for the matrix C_Fe = 0.696, C_Ni = 0.291, C_w = 0.013 with a volume fraction of precipitates of about 45%.     

Table-like magnetocaloric effect and large refrigerant capacity of composite magnetic refrigerants based on LaFe11.6Si1.4Hy alloys

Composite magnetic refrigerants were prepared by physical mixing LaFe_(11.6)Si_(1.4)H_y alloys with different Curie temperatures(Tc). The phase structures of these LaFe_(11.6)Si_(1.4)H_y alloys were analyzed by X-ray diffraction(XRD) and the magnetocaloric effect(MCE) and refrigerant capacity(RC) of these composite magnetic refrigerants were investigated by experiment and calculation in this paper. The magnetocaloric effect(MCE) and refrigerant capacity(RC) of these composite magnetic refrigerants were investigated by experiment and calculation in this paper. The results indicate the experimental magnetic entropy change(-△S_M)-Tcurve corresponds reasonably with the(-△S_M)-Tcurve calculated by the linear combination of(-△S_M)-T curves of the single material. An optimal mixing ratio can make the composite magnetic refrigerant possess a table-like(-△S_M)-Tcurve which is beneficial to magnetic Ericsson cycle. When three LaFe_(11.6)Si_(1.4)H_y alloys with different T_c are mixed, the full width at half maximum(△T_(FWHM)) of(-△S_M)-T curves is about 48.7 K and the RC is about 177.76 J/kg under a magnetic field change of 2 T. The composite magnetic refrigerants based on LaFe_(11.6)Si_(1.4)H_y alloys can be promising candidates for near room temperature magnetic refrigeration and the work will be helpful to develop novel composite magnetic refrigerants with table-like MCE and large RC.     

Magnetic and specific heat studies of the frustrated Er2Mn2O7 compound

A new Er2Mn2O7 compound was synthesized by the ceramic method and its crystal structure was characterized using powder X-ray diffraction (XRD) and observed by scanning electron microscopy (SEM). The magnetic properties were investigated using a BS2 magnetometer and the heat capacity was studied using a quantum design (PPMS). The structural study revealed that this compound was monophasic and crystallized in the monoclinic system with the P2/M space group. Magnetization measurements were carried out in the temperature range of 1.8-200 K under an applied magnetic field of 0.05 T. A crossover from a room temperature paramagnetic phase to an antiferromagnetic one at low temperature was detected from the magnetic study. The magnetic susceptibility, in the paramagnetic region above 40 K, was found to present a simple Curie-Weiss type behavior. From the specific heat (CP) measurements in magnetic fields up to 5 T, we noted the presence of a wide peak characteristic of a second order mag-neto-structural transition.     

Electrochemical behavior of cerium（IV） in a RTIL and its mixture with ethanol

A systematic study was carried out to explore the electrochemical behavior of Ce in room temperature ionic liquid（CnmimBr, where n=6, 8, 10） and mixture of C6 mimBr and ethanol by cyclic voltammetry. With increase in the number of carbon atoms on the alkyl substituent on methyl imidazolium cation, the electrochemical window of the ionic liquids was found to extend towards more negative potential value, as a result there was a possibility of reduction of Ce to lower oxidation states. The diffusion coefficient and activation energy for the diffusion were calculated in all the ionic liquids and one of their mixtures with ethanol. With increase in n value, the diffusion coefficient of Ce decreased due to increase in viscosity of the medium while the activation energy for the diffusion followed a reverse trend for C6 mimBr, C8 mimBr and C10 mimBr, respectively. The observations indicated that the nature of species of Ce might be different in room temperature ionic liquids（RTILs） from that present in their mixtures with ethanol.     

Hybrid DFT study of structural,electronic,magnetic and elastic properties of laves phase binary intermetallics RFe2(R=La,Ce,Pr and Nd)

Hybrid density functional theory was used to investigate the structural,electronic,magnetic and elastic properties of the Laves phase binary intermetallics RFe₂(R=La,Ce,Pr and Nd) in C₁₅ crystal structure.The calculated lattice constants of these materials are found in good agreement with the experiments.The band structures and density of states distribution confirm the metallic nature of all these intermetallics.The optimized energies in different magnetic phases and magne...     

Refining by fractional solidification

A new process is described for purifying metals by fractional solidification. The process comprises isothermal compression of solute-rich interdendritic liquid from semi-solid starting material. Purification is measured by “refining ratio”, ˉC_c/C_o (where ˉC_c is wt pct solute of the refined “cake” and C_o is initial pct solute). Refining ratio depends on partition ratio,K, initial fraction solid, amount of liquid retained in the “cake”, and extent of diffusion in the solid. For intermediate fractions solid and low retained liquid, ˉC_c/C_o ≈ k. Refining experiments were conducted on Sn-Pb alloys. Semi-solid samples were isothermally compressed against a filter under controlled strain to pressures up to 21 MPa (2900 psi). The pct solute of the liquid squeezed from the sample was that given by the liquidus curve of the phase diagram. The amount of liquid removed depended on fraction liquid initially present and applied pressure, and not on plunger speed in the range of 10⁻³ to 10⁻¹f cmJ.s. At 21 MPa (2900 psi) and fractions solid up to 0.7, over 95 pct of the interdendritic liquid present was removed so that fraction liquid in the final “cake” (“cake wetness”) was reduced to about 0.04. Refining ratios within 80 pct of the theoretical minimum were obtained. Refining ratios obtained ranged from 0.1 at 0.08 to 0.4 at 0.8 fraction solid. This paper is based on doctoral thesis work of A. L. Lux.     

Influence of Al4C3 Particles on Grain Refinement of Mg–3Al Alloys

Al?CSi/Al₄C₃ master alloy has been developed by reacting the SiC particles in Al melt. The extent of SiC conversion to Al₄C₃ in the Al?CSi/Al₄C₃ master alloy has been calculated using optical emission spectroscopy. Experimental results indicated that only 70?% of SiC particles have been converted into Al₄C₃ after the reaction between Al and SiC in Al/5?wt% SiC_p composites at 900?°C. The grain refining efficiency of Al?CSi/Al₄C₃ master alloy has been assessed by adding this into the Mg?C3Al alloy. Grain size of Mg?C3Al alloy has been significantly refined from 480 to 220???m by the addition of 0.07?wt% of Al₄C₃ particles in the form of Al?CSi/Al₄C₃ master alloy.     

Effect of C on Phase Evolution,Microstructure, and Magnetic Properties of Pr2Fe14B-Type Nanocomposites

The phase evolution, microstructure and magnetic properties of melt-spun Pr-rich Pr₁₁Fe_bal.B_8-yC_y (y = 0–8) and Pr-lean Pr₉Fe_bal.Ti_xB_11–yC_y (x = 0, 2.5 and 4; y = 0–11) ribbons have been investigated intensively. A slight substitution of C for B (y=2) was proven to be effective in improving the magnetic properties of Pr-rich Pr₁₁Fe_bal.B_8–yC_y nanocomposites. C atoms prefers to enter 2:14:1 phase in forming Pr₂Fe₁₄(B, C). But the volume fraction of Pr₂Fe₁₇C_z, α-Fe and 1:2 carbide increases, due to the dissociation of 2:14:1 phase and the suppression of Fe₃B phase, with further increase of carbon content. The optimal magnetic properties of B_r = 9.4 kG, _iH_c = 9.3 kOe, and (BH)_max = 17.3 MGOe were obtained for Pr₁₁Fe_bal.B₆C₂. In contrast, the increase of C substitution in Pr₉Fe_bal.Ti_2.5B_11–yC_y (y=0–11) ribbons degrades the B_r, _iH_c, and (BH)_max monotonically, which is arisen from the increase of vol % of Pr₂Fe₁₇C_z and α-Fe phases, and the rapid decrease of 2:14:1 phase. In comparison with those of Pr₉Fe_bal.B_11–yC_y (y=0–5.5) ribbons, improved magnetic properties of (BH)_max=15.3–17.8 MGOe with higher coercivity of _iH_c=9.7–10.8 kOe have been obtained in Ti-containing Pr₉Fe_bal.Ti_2.5B_11–yC_y (y=0–5.5) ribbons. However, in higher Ti concentration Pr₉Fe_bal.Ti₄B_11–yC_y, ribbons, a slight substitution of C for B (y = 0.5–1) is beneficial in improving the coercivity and magnetic energy product, simultaneously. The optimal properties of B_r = 9.4 kG, _iH_c = 11.1 kOe, (BH)_max = 18.0 MGOe and α = −0.146 %/°C, β = −0.576 %/°C were achieved in Pr₉Fe_bal.Ti₄B_10.5C_0.5 nanocomposites.     

Elastic Properties,Thermal Expansion Coefficients,and Electronic Structures of Mg and Mg-Based Alloys

Ab-initio density functional theory (DFT) calculations were performed to study alloying effects on hcp Mg. The alloy solid solution strengthening represented by bond strength enhancement in alloys, elastic properties, thermal expansion coefficients, and electronic structures of Mg-based alloys was investigated. Results show that alloying additions with sp-metal Al and rare earth (RE) Y are capable of increasing the bond strength, with the addition of Y achieving a better effect. The bond strength enhancement due to an RE Y addition is associated with a hybridization between the d-orbital of Y and the p-orbital of the Mg atoms near the Fermi energy, and this was consistent with the electron localized function (ELF) evaluations showing that more localized and stronger covalent bonds are formed between Y and Mg atoms. It is also found that alloying additions of Al, Zn, and Y are not capable of increasing elastic coefficients and moduli, indicating that bond strength enhancement could play a major role in alloy solid solution strengthening in Mg-based alloys. Possible reasons for the elastic properties accompanying the alloying addition are given from the electronic point of view. Furthermore, from the calculated negative Cauchy pressure (C ₁₃ – C ₄₄ < 0), it is concluded that the chemical bonds between Y and Mg atoms show angular characteristics.     

Hydrogen detrapping from grain boundaries and dislocations in high purity iron

Hydrogen detrapping in high purity iron was studied by measuring evolution rates of quenched-in hydrogen from 80 to 800 K using a quadrupole mass spectrometer in an ultra high vacuum system. The peak of the evolution rate was observed at 395 K in single crystal specimens and 415 K in polycrystalline specimens with a heating rate of 1 K min⁻¹. Effects of grain size and deformation on the evolution rate was also studied. It was shown that the results are consistent with the evolution rates calculated with the binding energy B = 0.51 ± 0.02 eV and the trap density term γC_{T = (4 ∼ 15) × 10⁻⁵} in polycrystalline iron, and B = 0.47 ± 0.02 eVand γC_T = (2 ∼ 13) × 10⁻⁵ in single crystal iron. The dominant traps are considered to be grain boundaries in polycrystalline specimens and dislocations in single crystal specimens.