Predictions of high-pressure structural, electronic and thermodynamic properties of α-Si3N4

The plane-wave pseudo-potential method within the framework of first-principles technique is used to investigate the fundamental structural properties of Si3N4 . The calculated ground-state parameters agree quite well with the experimental data. Our calculation reveals that α-Si3N4 can retain its stability to at least 45 GPa when compressed below 300 K. No phase transition can be seen in the pressure range of 0-45 GPa and the temperature range of 0-300 K. Actually, the α→β transition occurs at 1600 K and 7.98 GPa. Many thermodynamic properties, such as bulk modulus, heat capacity, thermal expansion, Gru¨neisen parameter and Debye temperature of α-Si3N4 were determined at various temperatures and pressures. Significant differences in these properties were observed at high temperature and high pressure. The calculated results are in good agreement with the available experimental data and previous theoretical values. Therefore, our results may provide useful information for theoretical and experimental investigations of the N-based hard materials like α-Si3N4.     

Modeling of thermodynamic properties of multi-component electrolyte solutions

1　ＩＮＴＲＯＤＵＣＴＩＯＮＴｈｅｅｌｅｃｔｒｏｌｙｔｅｓｏｌｕｔｉｏｎｓｏｆＣｕＣｌ2 ,ＮｉＣｌ2 ,Ｃｏ Ｃｌ2 ,ＺｎＣｌ2 ,ＣｄＣｌ2 ,ＦｅＣｌ2 ,ＨＣｌ,ＮａＣｌ,ＫＣｌ,ＣａＣｌ2 ,ＭｇＣｌ2 ,ＢａＣｌ2 ,ｅｔａｌ,ｗｅｒｅｏｆｔｅｎｉｎｖｏｌｖｅｄｉｎｔｈｅｈｙ ｄｒｏｍｅｔａｌｌｕｒｇｉｃａｌｐｒｏｃｅｓｓｅｓ .Ｔｈｅｔｈｅｒｍｏｄｙｎａｍｉｃｐｒｏｐ ｅｒｔｉｅｓｏｆａｑｕｅｏｕｓｓｏｌｕｔｉｏｎｓｏｆｔｈｅｅｌｅｃｔｒｏｌｙｔｅｓａｒｅｖｅｒｙｉｍｐｏｒｔａｎｔｔｏｅｘｔｒａｃｔｉｖｅｍｅｔａｌ…     

Phase stability and structural distortion of NiO under high pressure

The phase stability and structural distortion of NiO under high pressure were investigated using first-principles calculations based on density-functional theory. Different forms of exchange-correlation functional including LDA, GGA and GGA＋U were used in the present calculations. All of the three methods predict NiO to be AFM II ordering with the cell slightly compressed along [111] direction and also indicate that there is no structural phase transition of NiO under pressure up to 140 GPa, which are in agreement with the experiment. However, both LDA and GGA incorrectly predict the structural distortion under pressure especially above 60 GPa. Only when strong correlations are included in form of GGA＋U, structural distortion under high pressure can qualitatively agree with the experiment. The related mechanism was also analyzed and discussed. These results suggest that the strong electronic correlations still play a very important role in the properties of NiO under high pressure.     

Thermodynamic properties and mixing thermodynamic parameters of binary homogeneous metallic melts

After the investigation on the thermodynamic properties and mixing thermodynamic parameters of binary homogeneous metallic melts involving compound, peritectic as well as solid solution, it was found that the equations of mixing free energy △Gm and excess free energy △Cxs of them can be expressed by the following equations: and △GxS =△Gm -RT(alna + blnb), respectively.     

Synthesis of Ti2AlC by hot pressing and its mechanical and electrical properties

Ti2AlC bulk material was synthesized by hot pressing of mixture powders of TiC, Ti, Al and active carbon. The phase compositions of resultant product at different temperature were detected by X-ray diffractometer. The microstructures of the samples were observed by SEM. Finally, the mechanical properties and thermal properties of the sample at 1 400 ℃ were measured. The results show that high purity Ti2AlC material with little Ti3AlC2 can be synthesized by hot pressing 0.5TIC/1.5Ti/1.0A1/0.5C at 1 400 ℃. Ti2AlC exhibits high mechanical properties and metallic electrical properties. Its fractm＇e toughness is 7.0 MPa·m^1/2, its flexural strength is 384 MPa at room temperature, and its electrical conductivity is 2.56 × 10^6 Ω^-1·m^-1 at room temperature.     

Magnetic properties of α-Fe_2O_3 nanopallets

It is the result of a systemic study about uniform hematite nanopallets with length of about 100 nm, width of about 30 nm, and thickness of less than 10 nm. The sample has superparamagnetic(SPM) properties above the blocking temperature of ～16 K. The temperature dependence of magnetization was well fitted by Bloch T~(3/2) law considering the dipolar interaction of the particles. The field dependence of magnetization was fitted with revised Langevin equation.The magnetization of the weak ferromagnetic(WF) canted spins contributes to the linear portion in the high field region;the surface uncompensated spins and the parasitic ferromagnetic moments due to the canted spins both contribute to the particle moments and the superparamagnetic behavior.     

First-principle calculations of structural,elastic and thermodynamic properties of Fe–B compounds

The structural, elastic and thermodynamic properties of FeB, Fe₂B, orthorhombic and tetrahedral Fe₃B, FeB₂ and FeB₄ iron borides are investigated by first-principle calculations. The elastic constants and polycrystalline elastic moduli of Fe–B compounds are usually large especially for FeB₂ and FeB₄, whose maximum elastic constant exceeds 700 GPa. All of the six compounds are mechanically stable. The Vickers hardness of FeB₂ is estimated to be 31.4 GPa. Fe₂B and FeB₂ are almost isotropic, while the other four compounds have certain degree of anisotropy. Thermodynamic properties of Fe–B compounds can be accurately predicted through quasi-harmonic approximation by taking the vibrational and electronic contributions into account. Orthorhombic Fe₃B is more stable than tetrahedral one and the phase transition pressure is estimated to be 8.3 GPa.     

Investigation of the microstructure and properties of Al–Si–Mg/SiC composite materials produced by solidification under pressure

Composite materials based on alloys of the Al–Si–Mg system have been obtained via the introduction of 5, 10, and 15 wt % of SiC particles into the alloy melt and the solidification under a pressure. As a result of solidification under pressure, the porosity of the composite materials decreased substantially. An increase in the content of SiC particles in the composites enabled a smaller size of dendritic cells to be obtained. It has been shown by the X-ray diffraction method that, in the process of solidification under pressure, an interaction occurred between the matrix and reinforcing SiC particles. The presence of SiC particles in the structure of composites led to the acceleration of the aging process and to an increase in the peak hardness in comparison with the matrix alloy.     

Kinetic process of oxidative leaching of chalcopyrite under low oxygen pressure and low temperature

Kinetic process of oxidative leaching of chalcopyrite in chloride acid hydroxide medium under oxygen pressure and low temperature was investigated. The effect on leaching rate of chalcopyrite caused by these factors such as ore granularity, vitriol concentration, sodium chloride concentration, oxygen pressure and temperature was discussed. The results show that the leaching rate of chalcopyrite increases with decreasing the ore granularity. At the early stage of oxidative reaction, the copper leaching rate increases with increasing the oxygen pressure and dosage of vitriol concentration, while oxygen pressure affects leaching less at the later stage. At low temperature, the earlier oxidative leaching process of chalcopyrite is controlled by chemical reactions while the later one by diffusion. The chalcopyrite oxidative leaching rate has close relation with ion concentration in the leaching solution. The higher ion concentration is propitious for chalcopyrite leaching.     

Structure and magnetic properties of amorphous and polycrystalline Fe3O4 thin films

Half-metallic Fe3O4 films prepared by-DC magnetron reactive sputtering with a tantalum（Ta） buffer layer was investigated. Primary emphasis is placed on the structural impact on its magnetic properties. The experimental results show that the amorphous Fe3O4 films exhibit a superparamagnetic response at a large-scale from 20 nm to 150 nm, and the magnetoresistance （MR） isn＇t detected. By contrast, the polycrystalline Fe3O4 films possess large saturation magnetization Ms of 420 A/（kg.cm） and a clear magnetoresistance with a field of 40 kA/m. The unusual properties for the amorphous Fe3O4 film are attributed to the existing large density of the similar structure as anti-phase boundaries in the film.     

Furan- and pyrrole-containing analogs of α-quinquethiophene: spectroscopic and electrochemical properties

A series of pentacyclic analogs of α-quinquethiophene containing one or two furan or pyrrole units has been synthesized. The synthesis is based on the cyanide-catalyzed Stetter reaction, providing the ketonic precursors to the pentacycles. Spectral and electrochemical investigations show that the redox-stable mixed pentacycles display hypsochromic shifts in their absorption maxima, as well as a greater ease of oxidation, in comparison to α-quinquethiophene.     

The formation,structure, and properties of the Au–Co alloys produced by severe plastic deformation under pressure

The mechanical alloying of Au–Co mixtures, which are systems with high positive mixing enthalpy, is studied following high-pressure torsion deformation at room and cryogenic temperatures. X-ray diffractometry in synchrotron radiation and scanning microscopy are used to investigate the sequence of structural changes in the course of deforming the mixtures up to the end state of the fcc substitutional solid solution based on gold. The mechanical properties of the alloys are measured both during mixture processing and after mechanical alloying. Microfractographic studies are performed. Factors that facilitate the solubility of Co in Au, namely, increased processing pressure, cobalt concentration in a charge mixture, true strain, and temperature decreased to cryogenic level have been identified.     

Thermodynamic properties and mixing thermodynamic parameters of Ba-Al, Mg-Al, Sr-Al and Cu-Al metallic melts

Application of equations of mixing thermodynamic parameters formulated on the basis of the coexistence theory of metallic melts in Ba-Al, Mg-Al, Sr-Al and Cu-Al melts leads to fruitful results that not only the evaluated mass action concentrations agree well with the measured activities, but also the calculated mixing thermodynamic parameters are quite coincident with the experimental values. Moreover, the calculated mass action concentrations strictly obey the mass action law. The evaluated mixing thermodynamic parameters have very fine regularity: the mixing free energy is composed of standard free formation energies of all compounds and chemical potentials of all structural units at equilibrium; the mixing enthalpy consists of standard formation enthalpies of all compounds; the mixing entropy is composed of standard entropies of all compounds and configuration entropies of all structural units at equilibrium. As the equations of mixing thermodynamic parameters formulated are widely applicable to metallic melts involving compound formation, they can be used as the second practical criterion to determine whether thermodynamic models of metallic melts are correctly formulated.     

Microstructures and properties of Si_3N_4/TiN ceramic nano-multilayer films

1INTR0DUCTIONInrecentyears,ceramicsuperhardnesscompositionallymodulatedmultilayerfilmshavebeenactivelyinvestigated.Theresultsshowedthatmultilayerscanc0mbinethepropertiesoftheconstituentmaterialsandhavemoreexcellentpropertiesthanthesingle-layerfilm.Multilayerswithoptimizedinterfaceareasseemt0bem0stpromisingwithrespecttoan0ptimumhardness-to-toughness..ti.[1~5].Especiallyinceramicnano-multilayerfilms,ithasbeenattractingat-tentionbecausethehardnessoffilmsexhibitsmaximumvalue,thatis,so-calledsu…     

Preparation and microwave dielectric properties of Csf/Si3N4 composites

The CJSi3N4 composites were prepared by hot-press sintering method using α-Si3N4 power, short carbon fibers and La2O3-Y2O3 sintering additives. The mechanical and microwave dielectric properties of CjSi3N4 composites were studied and discussed. The results show that the addition of the short carbon fibers can not destroy the relative density of the sintered samples, but it deteriorates the flexural strength of the sintered samples, so the flexural strength of the silicon nitride matrix is the highest among the samples. The real part （ε3 and the imaginary part （ε＇3 of the permittivity of CsfCSi3N4 composites greatly increase with increasing voltmae fraction of the short carbon fibers, achieve the maximum 73.1 and 101.5, respectively. A strong frequency dependence of the imaginary part （ε″） of the permittivity is observed.     

Experimentation and thermodynamic modelling on SrZrO3

Experimental data for the perovskite phase SrZrO3 were subjected to a critical thermodynamic assessment using the CALPHAD approach. Special attention was paid to the structural behavior of SrZrO3 to illustrate, how to select an appropriate thermodynamic model based on crystal structure and chemistry information, how to identify and resolve the inconsistency between various kinds of experimental data, and how to use thermodynamic modeling as a basic tool in the development and optimization of materials and process. Our assessment results in a Gibbs energy function covering the temperature range between 300 K and the melting point, which explains the experimental data within the experimental uncertainty.     

Effect of pressure on microstructures and mechanical properties of Al-Cu-based alloy prepared by squeeze casting

A new high-strength aluminum alloy with better fluidity than that of ZL205A was developed. The effect of applied pressure during squeeze casting on microstructures and properties of the alloy was studied. The results show that the fluidity of the alloy is 16% and 21% higher than that of ZL205A at the pouring temperature of 993 K and 1 013 K, respectively. Compared with permanent-mold casting, mechanical properties of the alloy prepared by squeeze casting are much higher. The tensile strength and elongation of the alloy are 520 MPa and 7.9% in squeeze casting under an applied pressure of 75 MPa, followed by solution treatment at 763 K for 1 h and at 773 K for 8 h, quenching in water at normal temperature and aging at 463 K for 5 h. The improvement of mechanical properties is attributed to the remarkable decreasing of the secondary dendrite arm spacing(SDAS) and eliminating of micro-porosity in the alloy caused by applied pressure.     

Application of the annexation principle to the study of thermodynamic properties of ternary metallic melts In-Pb-Ag and In-Bi-Sb

Based on the phase diagrams, measured activities and the annexation principle, the calculating models of mass action concentrations for In-Pb-Ag and In-Bi-Sb ternary metallic melts have been formulated. The results of calculation both agree with practice, and obey the law of mass action, showing that the models formulated can reflect the structural reality of the corresponding melts and the annexation principle is applicable to the them.