Modeling of γ/γ′ phase equilibrium in the nickel-aluminum system

A theoretical model is proposed for the determination of phase equilibrium in alloys taking into consideration dissimilar lattice parameters. Volume dependent pair interactions are introduced by means of phenomenological Lennard-Jones potentials and the configurational entropy of the system is treated in the tetrahedron approximation of the cluster variation method. The model is applied to the superalloy relevant nickel-rich, γ/γ′ phase region of the Ni-Al phase diagram. The model predicts reasonable values for the lattice parameters and the enthalpy of formation as a function of composition, and the calculated phase diagram closely approximates the experimental diagram.     

Phase changes in the niobium-hydrogen system—III. Acoustic studies of hydride phase transitions at H/Nb = 0.78

Ultrasonic techniques were used to measure the moduli and attenuation of single crystals of NbH_0.78 composition over the temperature range 77–525 K. Sufficient acoustic modes were measured to allow determination of all of the cubic moduli for the α′ (b.c.c.) phase and the orthorhombic moduli for the β and ε phases. Significant softening of the moduli and increases of the attenuation were observed near the α′-β transition. Discussion of these results is based on a Zener relaxation mechanism and on a Landau model for a second-order phase transition. The moduli and attenuation near the β-ε transition did not exhibit any precursor behavior. Relaxations were seen above the β-ε transition and these are interpreted on the basis of H density fluctuations in the β phase.     

Fe(III)–As(V) precipitates obtained from a sulphate system and their leach stability

Fe(III)–As(V) precipitates were synthesised from the Fe(II)-As(V)-SO₄^2--H₂O system at a temperature of 90°C and a constant pH maintained at 1.5?±?0.05. The precipitates obtained were characterised by X-ray diffraction (XRD), chemical composition analysis, scanning electron microscope (SEM) and Raman spectrum, thermogravimetric analyzer (TGA) and electron probe micro-analyzer (EPMA). The precipitates were in irregular aggregation of about 1–4?μm in size. The precipitates consisted of scorodite, ferric arsenate and an amorphous ferric hydroxide sulphate formulated as Fe(OH)_x(SO₄)_y. The precipitates were stable in modified Toxicity Characteristic Leaching Procedure (TCLP) tests at pH 4.93 for 60?h. Arsenic concentrations in the leaching solutions of 0.27?mg?L^?1 and 0.59?mg?L^?1 were obtained for the precipitates prepared initial Fe(II)/As(V) molar ratios of 4.0 and 5.0, respectively. Significantly more iron than arsenic was dissolved with up to 280?mg?L^?1 of iron reporting to solution. Long-term stability tests of the precipitates were carried out by leaching them for 40 days at 25°C under various media of pH between 9.50 and 10.57. The results showed that the precipitates tested in this study were more stable than those by previous researchers owing to a preferential dissolution of the amorphous ferric hydroxide sulphate.     

Phase relations,microstructure, and valence transition studies on CaZr_(1-x)Ce_xTi_2O_7(0.0≤x≤1.0) system

In this study, Ce-doped zirconolite was synthesized through high-temperature solid-state reaction at 1250 ℃ in air for 96 h. The crystal phase.microstructure and valence transition were studied by X-ray diffraction(XRD), scanning electron microscopy(SEM), and X-ray photoelectron spectroscopy(XPS).Phase relations of CaZr_(1-x)Ce_xTi_2O_7 systems were determined by XRD analyses and Rietveld refinements.Four different phases are identified, namely zirconolite, perovskite, pyrochlore, and cerianite. The phase transformation(2M-zirconolite → 4M-zirconolite → Ce-pyrochlore) is caused by cations rearrangement as cerium content increases. The solubility limit of cerium ions in CaZr_(1-x)Ce_xTi_2O_7 system is estimated to be approximately 0.80. Under sintering air atmosphere, partial reduction of Ce~(4+) in Ce~(3+) is detected in Ce 3d XPS spectra, and the ratio of Ce~(3+) and Ce~(4+) significantly decreases as cerium content increases.     

Report on the First International Conference on f-Elements (ICFE)

The First ICFE was held September 4～7, 1990 in Katholieke Universiteit Leuven, Belgium. The generalconference chairperson was C. Gorller-Walrand. The conference was sponsored by the Commission of theEuropean Communities. This conference has brought together chemists, physicists and other scientists in-volved in the fundamental and application research of f-elements from many countries. It was an importantinternational conference in series, held parallelly and alternatively with the northern american Rare EarthResearch Conference. In fact it was the third conference in Europe, inherited the International Rare EarthConference held in Zurich(1985)and International Conference on Lanthanides and Actinides held in Lisbon(1987). The international advisory committee of this conference included almost all the famous scientists of     

Electrochemical co-reduction of Y(III) and Al(III) in a fluoride molten salt system and electrolytic preparation of Y–Al intermediate alloys

In this study, a molten salt co-reduction method was proposed for preparing Y–Al intermediate alloys and the electrochemical co-reduction behaviors of Y(III) and Al(III) and the reaction mechanism of intermetallic compound formation were investigated by transient electrochemical techniques. The results show that the reduction of Y(III) at the Mo electrode is a reversible electrochemical process with a single-step transfer of three electrons, which is controlled by the mass transfer rate. The diffusion coefficient of Y(III) in the fluoride salt at a temperature of 1323 K is 5.0238 × 10^?3 cm²/s. Moreover, the thermodynamic properties associated with the formation of Y–Al intermetallic compounds were estimated using a steady-state electrochemical method. Y–Al intermediate alloy containing 92 wt% yttrium was prepared by constant current electrolysis at 1323 K in the LiF–YF₃–AlF₃–Y₂O₃ (6 wt%)–Al₂O₃ (1 wt%) system at a cathodic current density of 8 A/cm² for 2 h. The Y–Al intermediate alloy is mainly composed of α-Y₂Al and Y phases. The development and application of this innovative technology have solved major technical problems, such as a long production process, high energy consumption, and serious segregation of alloy elements at this stage.     

Luminescence study of europium(III) tris(β-diketonato)/phosphonate complexes in chloroform

The extraction of Eu(III) with β-diketone, HA, and monodentate or bidentate Lewis bases, B, into chloroform and the luminescence properties of the extracted species were studied. Pivaloyltrifluoroacetone, Hpta, and 2-thenoyltrifluoroacetone, Htta, were used as the β-diketones. The Lewis bases, B, were tetraethyl methylene diphosphonate, POPO, which was bidentate, and diethyl benzylphosphonate, PhPO which was monodentate. Based on the extraction data, the stability constants, log β of the first complexes between tris(β-diketonato)Eu(III) and the phosphonate, EuA3B, were determined to be 6.0 for the POPO complex and 3.40 for the PhPO complex. The Eu(III) luminescence intensity in the EuA3POPO was larger than EuA3 where A was either pta or tta at similar concentrations of Eu(III), while that in Eu(pta)3PhPO was stronger than EuA3; however, in Eu(tta)3PhPO, it was weaker than Eu(tta)3. The POPO functions as a sensitizer, and the PhPO functions as a quencher for the tta chelate and as a sensitizer for the pta chelate. From the lifetime and quantum yield, φ, of the Eu(III) luminescence in the complexes as well as the observation of the extractability of Eu(III) with the Hpta and the phosphonates and of the luminescence spectra of the complexes, it was confirmed that the extraction of Eu(III) was remarkably enhanced with a β-diketonate and a strong Lewis base, and also the ternary complex that was formed as the extracted species, showed luminescence enhancement. This phenomenon may be due the formation of a strong bond between the Eu(III) and the strong Lewis base leading to more hydrophobicity in the extracted species and also to more effective energy transfer from the Lewis base to the Eu(III). It was not significant whether the donor atoms were N or O.     

Price Indicators on the Local Markets(The period of 28 August-8 September,2000)

Unit:RMB yuanlmetrie ton┌──┬─────┬───┬───┬────┬───┬───┬────┬───┬────┬───┬───┐│ │而pertlng │即 │Sh6n │Tianjin │WUh自n│Chang │Shang │Cheng │日.iyin │L目n │Guang ││ │ period │J Ing │yang │ │ │ Sha │ hai │ dU │ │ZhOU │Zh0U │├──┼─────┼───┼───┼────┼───┼───┼────┼───┼────┼───┼───┤│CU │28 AUg │18800 │18200 │18800 │18900 │18500 │18900 │ │18500 │18600 │1…     

Diffusion coefficients of the uranium(III) and (IV) ions in the LiCl–KCl–CsCl eutectic melt

Diffusion coefficients of the uranium(III) and (IV) ions in the eutectic melt of the lithium, potassium, and cesium chlorides in the temperature range of 573–1073 K have been determined using two independent methods: cyclic voltammetry and chronopotentiometry.     

Influence of alkaline earth metal cations on the charge transfer kinetics for the redox couple Ti(IV)/Ti(III) in a chloride–fluoride melt

The influence of strongly polarizing cations Mg²⁺, Ca²⁺, Sr²⁺, and Ba²⁺ on the charge transfer kinetics of the redox couple Ti(IV)/Ti(III) is studied. The standard rate constants of charge transfer (k _s) for the Ti(IV)/Ti(III) redox couple in the (NaCl–KCl)_eq–NaF (10 wt %)–K₂TiF₆ melt upon the addition of the strongly polarizing cations into the starting melt are determined. The dependence of the charge transfer rate constants on the ionic potential of the cations is established. The activation energies of the charge transfer process are calculated for the fluoride complexes of the Ti(IV)/Ti(III) redox couple with the outer-sphere cations Mg²⁺, Ca²⁺, Sr²⁺, and Ba²⁺.     

Fe(III)-SCN-体系薄层树脂相光度法测定矿石中铁

提出了利用薄层树脂相通过光度法测定痕量铁的新方法.铁离子与硫氰酸钾形成红色络合物,将其富集在H+型732#阳离子交换树脂上,通过制作成薄层直接测定.本法选择性好,精密度高(RSD%＝1.22%～4 .2%),回收率97.4%～99%,用于矿石中铁的测定,结果满意.     

Solvent extraction and separation of light rare earth elements (La,Pr and Nd) in the presence of lactic acid as a complexing agent by Cyanex 272 in kerosene and the effect of citric acid,acetic acid and Titriplex III as auxiliary agents

At present, the use of rare earth elements (REEs) has become an inevitable necessity in many modern industries. In general, liquid extraction is the best commercial method for extracting REEs due to its ability to control high volumes of liquids with electrical load. With the aim of improving a separation technology that would be superior to the existing extraction systems, the extraction behaviors of La(III), Pr(III), and Nd(III) from an HCl medium with Cyanex 272 in the presence of the complexing agent lactic acid (HLac) and auxiliary agents citric acid (H₃Cit), acetic acid (HAc), and Titriplex III have been reported. The effect of pH and lactic acid concentration has been examined. The use of lactic acid as a complexing agent leading to a high extraction of REEs with Cyanex 272 at pH = 5 was compared with systems without lactic acid. The results show that the use of acetic acid along with lactic acid leads to an increase in the extraction percentage of LREEs. While use of citric acid and Titriplex III reduces the extraction percentage of LREEs. Finally, the presence of Titriplex III together with lactic acid could lead to an increase in the separation factor of Pr and Nd.     

SETC on the 10~(th) five-year plan for the nonferrous metals industry

4.The key tasksThe key tasks for the development of China'snonferrous metals industry include further re-form of the enterprises,speeding up of thestructure adjustments,setting up large enter-prise groups and promoting large-scale busi-ness operations with specialized distribution ofmanufacture.It is also essential to increase the supply of themuch-needed raw materials on the domesticmarket with the rational development and use     

Anisotropic Magnetoresistance of Perovskite La_(2/3)Ca_(1/3)MnO_3/YBa_2Cu_4O_8/La_(2/3)Ca_(1/3)MnO_3 Trilayer Films

Magneticanisotropyhasbeenfoundinmanyex oticmaterials,suchasmetallicsuperlatticeswithgi antmagnetoresistanceeffectsandthehightempera turesuperconductingoxideYBa2Cu3O7 δ[1～4].The anisotropycouldfindnovelusesinnewdeviceappli cations.Agoodexampleisthehig…     

Comparative studies on Y(Ⅲ)and Dy(Ⅲ)extraction from hydrochloric and nitric acids by Cyanex 572 as a novel extractant

Extraction of Y(III) and Dy(III) from hydrochloric and nitric acids by Cy-572 in kerosene was studied. The factors affecting the extraction were separately investigated. The stoichiometry of the extracted species was deduced on the basis of slope analysis method. Evaluation of extraction equilibrium and stripping investigation was studied as well as saponification effect of Cy-572. The composition of the extracted metal species in the organic phase was found to be [MA_3·(HA)_3] for Y(III) or Dy(III) in both media.1.0 mol/L HCI is the best stripping agent for each metal ion from the studied acidic media in one step.Saponified Cy-572 does not exhibit any selectivity towards the extraction of Y(III) or Dy(III) from both HCI and HNO_3 solutions. Based on the obtained results, the data were compared and the separation feasibility between lanthanides and Y(III) in the two media was discussed.     

低合金高强钢焊接t_(8/5)测定实验研究

t_(8/5)的选择对低合金高强钢焊接性能的影响非常重要,但目前的经验公式均具有一定的适用范围,难以做到与每个钢种均能很好吻合。为此,本文在MMS-200热力模拟试验机上进行了焊接热模拟试验,对960高强钢的SH-CCT曲线进行了测定。并采用多个经验公式对不同热输入条件下的t_(8/5)进行计算,同时采用实测的方式得到了实际的t_(8/5)值,根据实测值对经验公式进行了修正,建立了960钢焊接线能量与t_(8/5)的关系公式。在对比实验中发现,t_(8/5)=30s时热模拟粗晶区和实际焊接接头(E=1.3KJ/mm)粗晶区组织和硬度是一致的。     

低合金高强钢焊接t_(8/5)测定实验研究

t_(8/5)的选择对低合金高强钢焊接性能的影响非常重要,但目前的经验公式均具有一定的适用范围,难以做到与每个钢种均能很好吻合。为此,在MMS-200热力模拟试验机上进行了焊接热模拟试验,对960高强钢的SHCCT曲线进行了测定。采用多个经验公式对不同热输入条件下的t_(8/5)进行计算,同时以实测方式得到t_(8/5)值,根据实测值对经验公式进行修正,建立了960钢焊接线能量与t_(8/5)的关系公式。在对比实验中发现,t_(8/5)为30s时热模拟粗晶区和实际焊接接头(E=1.3kJ/mm)粗晶区组织及硬度是一致的。