钠在320GPa高压下的电子结构和光学性质的第一性原理研究

利用基于密度泛函理论（DFT）的广义梯度近似（GGA）研究了320GPa高压下钠的电子结构和光学性质．给出了其沿布里渊区高对称轴的能带结构、态密度（DOS）和分态密度（PDOS）。并计算了介电函数ε（ω）,反射率R（ω）,能量损失函数L（ω）,光吸收系数I（ω）,光导率σ（ω）,折射率n（ω）,以及消光系数k（ω）,用以讨论高压下钠的光学性质。     

Grain refining potency of LaB6 on aluminum alloy

Al-LaB6 alloy was successfully prepared by aluminum melt reaction method.Microstructure analysis of this alloy was carried out by field emission scanning electron microscopy(FESEM),Raman spectroscopy and transmission electron microscopy(TEM).It was found that cubic LaB6 particles were highly dispersed in aluminum matrix with a uniform edge length of about 4.5 μm.Grain refining potency of LaB6 on commercial pure aluminum was also investigated.It was shown that LaB6 could act as an effective and stable nucleation substrate for α-Al during solidification process,due to their crystallographic similarity.The coarse grains of commercial pure aluminum were obviously refined to small equiaxed ones by addition of 0.5% Al-5LaB6 alloy at 720℃.     

Effect of Terbium addition on the coercivity of the sintered NdFeB magnets

The effects of Tb addition on the microstructure and magnetic properties of the NdFeB magnets prepared by HD method were investigated by X-ray diffraction (XRD) and BH magnetometers. The results of the microstructure showed that both the Tb-doped and undoped permanent magnets were composed mostly of Tetragonal phase Nd₂Fe₁₄B (space group P42/mnm) and a trace amount of Nd-rich phase. Accordingly, addition of Tb led to a decrease of the pole density factor of (004), (006) and (008) crystal plane of the Nd₂Fe₁₄B phase calculated by Horta formula, but the coercivity of the magnets increased from 2038 kA/m up to 2302 kA/m as a consequence of Tb addition. The study of the H_c(T)/M_s(T) versus H^min_N/(M_s(T) behavior showed that the nucleation was the dominating mechanism for the magnetization reversal in both sintered magnets, and the microstructural parameters of α_k and N_eff were obtained also. The Kronmüller-plot showed an increase of the α_k responsible for an increase of the coercivity.     

Influence of Grain Coarsening on the Creep Parameters During the Superplastic Deformation of a Severely Friction Stir Processed Al-Zn-Mg-Cu Alloy

During grain boundary sliding in ultrafine-grain materials at intermediate temperatures and high strain rates (~10^?2 s^?1), apparent creep parameters usually deviate from the theoretical values, due to microstructural coarsening. An analysis has been carried out in a severely friction stir processed (FSP) 7075 alloy with three different ultra-fine grain sizes (L), obtaining explicit grain size dependence of the creep parameters n _ap = n _ap(L) and Q _ap = Q _ap(L), confirming the validity of the theoretical values of these parameters in the constitutive equation.     

Resonance character of polymorphic transformations for the phase transition α′<Subscript><Emphasis Type="Italic">L</Emphasis></Subscript> → β-Ca<Subscript>2</Subscript>SiO<Subscript>4</Subscript>

Experimental results are presented showing that rapid cooling of dicalcium silicate is accompanied by delay of structural processes, which leads to a decreasing in temperature of the phase transition α′ _L → β-Ca₂SiO₄. As starting materials, nepheline ore and limestone were used. In preparing the charge, the dosage of starting components was calculated for obtaining a molar ratio of CaO/SiO₂ = 2.0. From the charge, the series of samples was prepared. Each of the samples was sintered to t = 1250°C with subsequent keeping of the material at this temperature for 30 min. Then the samples were subjected to rapid cooling in air to t = 750, 650, 550, 450, 350, 250, 150, and 25°C. By means of quantitative X-ray powder diffraction analysis using a DRON-3 setup, the content of α′ _L and β-Ca₂SiO₄ was determined in the samples. The data allow us to suppose the occurring polymorphic transformations in dicalcium silicate have a resonance character.     

High-temperature dilatometry of Ti-46Al-8Nb refractory alloy

The temperature dependence of the linear thermal expansion coefficient K _L of the intermetallic Ti-46Al-8Nb (at %) alloy is experimentally determined for the first time within the temperature range from 373 to 1773 K (solidus point). The determined boundaries of phase fields are compared with the results of differential thermal analysis and the calculated phase diagram of the alloy. The high-temperature limit (1384 K) of the alloy structure thermostability is detected from signs of the α₂ + γ ? α + γ phase transition in dilatometric curves. The restructuring mechanism in the α + γ field is studied by scanning electron microscopy. It is shown that the α₂ + γ → α + γ phase transition is accompanied by selective structural degradation of single-crystalline α₂ lamellae and the related destruction of a fine lamellar α₂-Ti₃Al(Nb) + γ-TiAl(Nb) texture. The average values of K _L of the alloy are calculated within 100-K ranges in the low-temperature α₂ + γ phase field, which is of interest from a practical viewpoint, according to the State Standard GOST 8.018-2007.     

Effect of Refractory Boride Particles on Crystallization of the Amorphous Alloy Fe85B15

We have studied the characteristic features of the process of transition from the amorphous to the crystalline state in the presence of refractory boride particles of different crystallographic types (zirconium diboride ZrB₂ and lanthanum hexaboride LaB₆), introduced into ribbons of Fe₈₅B₁₅ amorphous alloy directly during ribbon formation. ZrB₂ particles in the base alloy have practically no effect on its thermal stability, defined by the temperature of onset of formation of primary α-Fe crystals, while in the presence of LaB₆ particles the thermal stability is considerably reduced. This qualitatively correlates with the Dankov principle of structural and dimensional correspondence considered in the theory of heterogeneous nucleation. We have shown that the major factor determining the high catalytic activity of LaB₆ particles with respect to nucleation of α-Fe crystallization centers is rapid chemical reaction within the zone where they come in contact with the Fe₈₅B₁₅ melt. The ZrB₂ particles which do not enter into such a reaction, do not affect the course of crystallization processes and the thermal stability of the base amorphous alloy.     

Model of temperature field for the preparation process of melt-spun NdFeB powders

Melt-spun ribbons which are the important raw material for hot-deformed magnets can be prepared by single-roller melt-spinning. In order to prepare well-structured ribbons, the model of temperature field for single-roller melt-spinning process was constructed in this work. The heat conduction in this process was simplified as one dimensional heat conduction problem. It was shown by modeling that, the temperature field in the melt-spinning before solidification in this model could be described as this equation T(x,t)=Tmoexp[–k(x–x0)–k2αt]+T0. The temperature T(x,t) of the alloy melts decreased with increased position x and cooling time t exponentially from the wheel-free surface to the wheel-side surface. The constant k determined the decrease speed of alloy temperature T(x,t), which was proportional to the interfacial heat transfer coefficient h and the interfacial area of heat conduction A0, but inversely proportional to the thermal conductivity K. x0 was the thickness of the alloy melt. With increased x0, the temperature difference between wheel-free surface and the wheel-side surface became larger, which would lead to larger difference in grain size. In experiments, the influence of melt-spinning process parameters on the temperature field model was discussed, such as cooling roller materials, wheel speed, and so on. Melt-spun ribbons prepared by single-roller melt spinning at different wheel speed were investigated and magnetic properties of die-upset magnets from melt-spun ribbons on different cooling roller were analyzed. The variation of grain size in the depth direction consisted with temperature field model. This model provided directions for the preparation of melt-spun ribbons with uniformly distributed fine grains, which were very necessary for producing hot-deformed magnets with high magnetic performance.     

Subgrain strengthening of aluminum conductor wires

The influence of wire processing variables on the formation of subgrain structures and strengthening in three aluminum conductor materials is described. Electrical conductor grade aluminum, an Al-Fe-Mg alloy and an Al-Fe-Co alloy each develop subgrain structures with mean linear intercepts (•L) in the range of 0.4 to 1.5 μm with several sequences of wiredrawing and partial annealing. The yield strengths of these wires were found to obey a a = σ₀ +k(•L) ^m relationship, with an exponentm = -1 independent of the processing sequence used to arrive at the structure. The role of precipitate particles in the alloys is to raisek above that for EC-A1 while Mg in solid solution increases σ₀. The precipitates also affect the development of the substructure during the wiredrawing and annealing.     

Temperature dependent behaviors of electro-elastic properties of NdCa4O(BO3)3 crystal with monoclinic symmetry

Rare-earth calcium oxyborate crystals (RECa₄O(BO₃)₃, RECOB, RE: rare-earth elements) are a kind of multifunctional crystal materials. In this work, the temperature dependent behaviors of the electro-elastic constants of NdCOB crystal were investigated over the temperature range of –80–200 ℃, and their temperature coefficients were evaluated. It is found that NdCOB crystal possesses minimal variation of relative dielectric permittivities (<3%). The temperature coefficient of frequency for ZY cut with width shear vibration mode is in the order of 0.07 × 10^?4/℃. The temperature coefficients of the elastic compliances are obtained to be in the range of ?33.0 × 10^?4/℃–32.2 × 10^?4/℃. Particularly, the s₄₄ and s₆₆ were found to show low temperature coefficients of the elastic compliances, i.e. 1.0 × 10^?4/℃ and ?0.4 × 10^?4/℃, respectively, indicating the existence of zero temperature coefficient of frequency crystal cut. Furthermore, the electromechanical coupling factors and piezoelectric coefficients as a function of temperature were studied. The electromechanical coupling factor k₂₆ and piezoelectric coefficient d₂₆ are determined to be ～30.8% and ～15.2 pC/N at room temperature, respectively. The large piezoelectric response and zero temperature coefficient of frequency indicate the potential usage of NdCOB crystal for piezoelectric frequency devices over a wide temperature range.     

Liquid-liquid extraction of divalent manganese,cobalt, copper,zinc and cadmium from aqueous chloride solutions by tricaprylmethylammonium chloride

The distribution of divalent manganese, cobalt, copper, zinc and cadmium between aqueous solutions of hydrochloric acid and/or lithium chloride and the solutions of tricaprylmethylammonium chloride (Aliquat-336, R₃R′NCl) in benzene has been investigated under different conditions. It is found that the extraction of these metals by Aliquat-336 proceeds as MCl₄^2?(aq) + 2 R₃R′NCI(org) ? (R₃R′N)₂MCI₄ (org) + 2 Cl^?(aq). The extraction curves have been examined utilizing a modified chemical model on the basis of this equilibrium equation. In addition, the electronic, electron spin resonance and infrared spectral results suggest that all the complexes formed in the organic phases are in a tetrahedral arrangement.     

Electrophysical properties of resistive thick films based on powdered Sn0.9Sb0.1O2 and glasses with additions of LaB6

The electrophisical properties (temperature dependence of electrical resistance, activation energy, thermoelectric power, current-voltage characteristics) of highly resistive thick films containing powders of solid solution Sn_0.9Sb_0.1O₂, amorphous glass, and lanthanum hexaboride have been studied. The ohmic contact was shown to form at the LaB₆-glass interface. Due to the contact potential difference the electrons are injected from lanthanum hexaboride particles into the glass interlayers. These electrons are assumed to increase the carrier concentration taking part in the electrical conduction of the film. Institute for Problems of Materials Science, Ukraine National Academy of Sciences, Kiev. Translated from Poroshkovaya Metallurgiya, Nos. 7–8(402), pp. 108–112, July–August, 1998.     

Kinetics of removal of bismuth and lead from molten copper alloys in vacuum induction melting

An investigation was made of the rates of removal of bismuth and lead from molten copper alloys stirred differently under vacuum at 1403 K. The heating conditions, which corresponded to highest, intermediate, and lowest stirring, were referred to as HC-A, HC-B, and HC-C, respectively. The rates of removal were described by a first-order rate equation involving the final concentration of the impurity. The overall mass-transfer coefficient for bismuth or lead (i),K _i, was determined, and it was found that K_i(HC-A) > K_i(HC-B) but K_i(HC-B) < K_i(HC-C) in Cu-Bi, Cu-Pb, and Cu-Bi-Pb alloys. In general, it was found that K_i(Cu-Bi-Pb) > K_i(Cu-Bi) or K_i(Cu-Pb). Oxygen reducedK _i more than sulfur. The reducing effect of oxygen and sulfur was weakened when stirring rate increased. In vacuum melting of Cu-Bi-Pb-O and Cu-Bi-Pb-S alloys under HC-C,K _i tended to decrease with increasing oxygen and sulfur concentrations. The loss of copper indicated that the rates were determined by liquid-phase mass-transfer and evaporation. The liquid-phase mass-transfer coefficient,K _L, was calculated, and it was found thatK _L(UC- A) > K_L(HC-B) but K_L(HC-B) < K_L(HC-C). The last relation was contrary to current theoretical prediction. A new model was assumed to account for this fact. The observed relative volatility coefficients of bismuth and lead were much smaller than their respective theoretical coefficients. Oxygen and sulfur adsorbed on the surface of the melt were considered to be close to equilibrium with their respective bulk concentrations, and their effects on the evaporation mass-transfer coefficients for bismuth and lead were estimated to be fairly small. This result means that the observed reduction ofK _i is due mostly to the decrease inK _L and made possible the calculation ofK _L. Oxygen decreasedK _L more than sulfur. In vacuum melting of Cu-Bi-Pb-O and Cu-Bi-Pb-S alloys under HC-C,K _L decreased linearly with increasing oxygen or sulfur concentration. The final concentrations of bismuth and lead in these alloys under HC-C tended to increase with increasing oxygen and sulfur concentrations and tended to decrease with increasingK _i andK _L.     

Synthesis and characterization of rare earth metal doped tungsten trioxide photocatalyst for degradation of Rhodamine B dye

Nowadays,it is concern for researchers that due to high recombination rate of photogenerated charge carriers in tungsten trioxide(WO₃) nanoparticles,the future applications are limited in the field of photocatalysis.Herein we attempt to synthesize tungsten trioxide nanoparticles with different doping concentrations of lanthanum i.e.2 wt%,4 wt%,6 wt% and 8 wt%.The synthesized samples were characterized by using various characterization techniques:X-ray diffraction(XRD),Raman spectrosco...     

Fracture toughness and the extents of primary void growth

It is generally believed that, for an otherwise constant microstructure, the crack tip opening displacement at fracture(δ, _IC) will scale with the primary particle spacing,X _o. However, fracture toughness is also influenced by the microstructure as well as by particle spacing and volume fraction. It has been proposed that the extents of primary void growth could be used as a measure of the influence of microstructure on toughness. Two approaches to using the extents of primary void growth have been suggested. In one, it was proposed that δ,_IC would scale asX _o(R_v/R_I), whereR _v is the radius of the void as viewed normal to the fracture surface andR, is the radius of the particle nucleating the void. In the second, it has been proposed that a measure of the true local strain would be Inh/2R ₁), whereh is the depth of the void, and that δ_IC would scale asL Inh/2R ₁), whereL is some microstructural distance, taken here to beX _o. These two approaches have been tested for materials for which δ_IC ranges from about 7 to over 150 μm. The results suggest that the two proposed scalings hold only for high-strength microstructures of low constrained ductility containing primary particles of small spacings and which blunt smoothly and not to vertices. Formerly Graduate Student, Carnegie Mellon University Formerly Graduate Student, Carnegie Mellon University     

Interaction in the LaB6-HfB2 system

Conclusions The data of metallographic and x-ray diffraction analyses, determination of the melting point, and measurement of the microhardness of individual phases served as the basis for constructing the phase diagram of the quasibinary eutectic type LaB₆-HfB₂ system with a eutectic composition of 70% LaB₆ 30% HfB₂ and t_eut= 2750°K. Up to the eutectic temperature in the LaB₆-HfB₃ system the components are practically insoluble.The established compatibility of LaB₆ with HfB₂ is an indication of the possibility of the development of sintered compositions with controlled physicomechanical properties.Translated from Poroshkovaya Metallurgiya, No. 2(254), pp. 79–81, February, 1984.     

Electrochemical behavior of cerium ion in molten LiCI-KCI

The electrode process of cerium(Ⅲ) on the Mo electrode in eutectic LiCl-KCl melt was investigated by electrochemical transient techniques in the temperature range of 673-783 K,respectively.These results unanimously indicated that the reduction process of cerium(Ⅲ) to cerium metal was a single step exchanging three electrons which was controlled by diffusion of cerium(Ⅲ).Diffusion coefficients(D Ce(Ⅲ)) in eutectic LiCl-KCl melt were determined by cyclic voltammetry,chronopotentiometry and square wave voltammetry.An empirical diffusion coefficient function depending on temperature was proposed:lnD Ce(Ⅲ) =-2.129-5704/T.The formal potentials(Eθ’ Ce(Ⅲ)/Ce(0) versus Ag/AgCl reference electrode) at different temperatures were obtained from chronopotentiometry,which were-2.10 V(673 K) and-2.07 V(733 K),respectively.     

Thermal expansion in the Ni−Cr−Al and Co−Cr−Al systems to 1200°C determined by high-temperature X-ray diffraction

The effect of temperature on the lattice parameters of phases in twelve nickel-chromium-aluminum (Ni?Cr?Al) alloys and nine cobalt-chromium-aluminum (Co?Cr?Al) alloys was determined using high temperature diffraction (HTXRD). The temperature range was from 25 to 1200°C. The data for each phase of each alloy were computer fit to an empirical thermal expansion equation developed in this study: \(LP_T = LP_{25^\circ C} (1 + R)^{(1 + T/273)^{1.5} } \) and a value forR was derived for each. Excellent fits were obtained for nearly all cases. A comparison ofR values revealed that for a given phase (ψ/ψ′, β and α in Ni?Cr?Al and αCo and β in Co?Cr?Al),R was independent of alloy composition. In the Ni?Cr?Al systemR for γ/γ′ was 19.2×10^?4,R for β was 19.9×10^?4 andR for αCr was 13.4×10^?4. In the Co?Cr?Al system theR value for αCo was 20.9×10^?4 and theR for β was 17.8×10^?4. Of all of the phases only the αCr in the Ni?Cr?Al system had anR sufficiently low to reduce to an unimportant level the stress generated from thermal expansion mismatch between Al₂O₃ and substrate or coating and substrate with either Ni?Al or Co?Al coatings on a γ/γ′-δ substrate.     

Emissive electric-spark coatings based on lanthanum hexaboride

Conclusions The electric-spark alloying of metals and steels with lanthanum hexaboride and its alloys results in the formation of heterophase coatings whose principal phase constituent is a lower boride of the basis metal. The coatings contain also a small amount of a LaB₆-base phase, whose presence ensures that their level of emission is close to that of LaB₆ itself. By varying the composition of the alloy and using different basis materials, it is possible to exercise control over the efficiency of deposition of coatings and their thermionic emission properties.Translated from Poroshkovaya Metallurgiya, No. 2(254), pp. 50–53, February, 1984.     

A New Grain Refiner for Ferritic Steels

A new grain refiner, LaB₆, was identified for ferritic steels based on the crystallographic calculation using the edge-to-edge matching model. Addition of 0.5 wt pct LaB₆ led to a reduction of the average grain size from 765 to 92 μm and the proportion of the columnar structure from 35 to 8 pct in an as-cast Fe-4Si ferritic alloy. Although LaB₆ was supposed to act as an active inoculant for δ-ferrite, thermodynamic calculation indicated that LaB₆ is not thermodynamically stable in the melt of the Fe-4Si alloy. It was subject to decompose into La and B solutes. Consequently, both La and B reacted with Fe, O and S, forming different compounds. Microstructural examination at room temperature observed La₂SO₂ and La₂O₃ particles within the ferrite grains and Fe₂B along the grain boundaries in the samples. Through EBSD analysis, a reproducible orientation relationship between ferrite and La₂SO₂ was identified. In addition, the edge-to-edge matching calculation also predicted the high potency for La₂SO₂ to be an effective nucleant for δ-ferrite. It was considered that the grain refinement of LaB₆ was attributed to the enhanced heterogeneous nucleation of δ-ferrite by La₂SO₂, and the solute effect of B due to the high Q-value in ferrite.