原位热压合成Ti3AlC2/Al2O3复合材料的研究

以Ti,Al,TiC,TiO2粉末为原料,采用原位热压合成法制备了Ti3AlC2/Al2O3复合材料。主要考察不同Al2O3含量对复合材料性能的影响。在1400℃,30MPa压力,保温2h条件下烧结制得致密的Ti3AlC2/Al2O3块体材料。采用XRD分析了不同Al2O3含量的复合材料的相组成。用SEM观察组织结构特征。测量了维氏硬度和电导率同Al2O3含量的关系曲线。研究结果表明,Al2O3的加入可大幅度提高复合材的硬度。Ti3AlC2/25%Al2O3的维氏硬度可达8.7GPa。虽然添加Al2O3后复合材料的电导率有所下降,但Al2O3对复合材料强度和硬度的增加有显著的贡献。Ti3Al2C2/Al2O3乃不失为一种性能良好的高温结材材料。     

A new strain Acidithiobacillus albertensis BY-05 for bioleaching of metal sulfides ores

An acidophilic,rod-shaped Gram-negative sulfur oxidizing strain BY-05 was isolated from an acid mine drainage of copper ore in Baiyin area,Gansu Province,China.Ultrastructural studies show that the isolate has a tuft of polar flagella and possesses sulfur granules with clear membrane adhering to the cell innermembrane.Physiological study shows that this isolate grows autotrophically and aerobically by oxidizing S0and reduced inorganic sulfur compounds(SO, 2 23-SO, 2 24- S2 -and ZnS)with the optimum growth at pH 3.5-4.0 and at the temperature range of 25-30℃.The 16S rRNA gene sequence(DQ 423683)of strain BY-05 has 100%sequence similarity to that of Acidithiobacillus albertensis(DSM 14366).So it is identified and named as A. albertensis BY-05.Bioleaching experiments with this new strain show that it can play an important role in recovery of metals from chalcopyrite and sphalerite.     

Substitutional diffusion and Kirkendall effect in binary crystalline solids containing discrete vacancy sources and sinks

We investigate vacancy-mediated diffusion in a binary substitutional alloy by explicitly accounting for discrete vacancy sources and sinks. The regions between sources and sinks are treated as binary crystals with a perfect lattice structure containing a dilute concentration of vacancies. The sources and sinks are assumed ideal, maintaining an equilibrium vacancy concentration in their immediate vicinity. Diffusion within the perfect lattice is described with a diffusion-coefficient matrix determined by kinetic Monte Carlo simulations for a binary, thermodynamically ideal alloy in which the components have different vacancy-exchange frequencies. Continuum simulations are performed for diffusion couples with discrete grain boundaries acting as vacancy sources and sinks. Effective grain coarsening due to the Kirkendall effect is observed even in the absence of Gibbs-Thomson driving forces. As in standard ternary systems, uphill diffusion is observed. We also find that the drift of the lattice frame of reference as a result of the Kirkendall effect increases with the source/sink density. Upon increasing the density of vacancy sources and sinks, we recover the conventional treatment of substitutional diffusion, which assumes a dense and uniform distribution of vacancy sources and sinks that maintain an equilibrium vacancy concentration throughout the solid. The inverse Kirkendall effect, where the slower component segregates at grain boundaries acting as vacancy sinks, is also observed in the simulations.     

Electron hydration energy: Nonempirical estimate

Based on the results of quantum chemical calculations, the energies of vertical (photoionization) electron removal from superficial and bulk water layers are estimated as 2.9 and 4.4 eV respectively. For the first time, a nonempirical estimate of the electron hydration energy is obtained, 2.6 eV, which characterizes the electron state both at the superficial and bulk hydration. To find these value, molecular cluster systems modeling the Bjerrum defects of the hydrogen-bond network of water localizing the additional electron were calculated. Typical ways of the reorganization of defects upon the electron removal are identified. Conditions under which the relaxation of defects is reversible upon the re-addition of the charge are determined. The pre-existence of defects is shown not to be an indispensable condition of the effective localization of excess electrons by water. Small distortions, as well as breakage, of the continuity of the hydrogen-bond network are sufficient. Original Russian Text ? Yu.V. Novakovskaya, 2007, published in Zashchita Metallov, 2007, Vol. 43, No. 2, pp. 139–151.     

Decomposition of the supersaturated solid solutions at the stage of coalescence under conditions of passage from dislocation-controlled to volume diffusion

The microstructure and thermal stability of multilayered Co/Zr amorphous films differing in the composition and thickness of individual layers have been studied. The range of the amorphous-phase existence was shown to be determined by both the chemical composition of films and thicknesses of individual layers. The critical thickness of cobalt layers which corresponds to the nucleation of a crystalline phase is 22–24 Å. A model of an island layered structure of multilayered Co/Zr amorphous films is suggested. Changes in the structure and phase composition of multilayered Co/Zr amorphous films caused by isothermal annealing have been studied. The temperature of the onset of crystallization (T _x) is shown to decrease from 460 to 380°C as the thickness of Co layers increases from 12 to 18 Å. The effect of annealing in the course of continuous heating on the specific saturation magnetization of the multilayered Co/Zr amorphous films has been studied. The effect of irreversible increase in the specific saturation magnetization was found for the first time at temperatures below the temperature of the onset of crystallization. A conception of a diffusion character of the structural relaxation and crystallization processes is used to interpret the results obtained.     

To the Tafel slopes at the anodic dissolution of iron in sulfuric electrolytes

Based on the hypothesis of the reversibility of an iron electrode, one can relatively easily explain the experimentally obtained Tafel slopes without multistage complex schemes involving hypothetic intermediate iron hydroxo compounds. On the other hand, the coincidence of the experimental slope with the slope following from the relation derived may be considered as a proof of the reversibility of the iron electrode. The Tafel slope is reproducible both on the clean and partially passivated iron surface. Original Russian Text ? Yu.P. Vishnevskaya, D.A. Tkalenko, M.V. Byk, V.A. Rupp, 2007, published in Zashchita Metallov, 2007, Vol. 43, No. 5, pp. 540–542.     

Effect of alloying and heat treatment on the structure and tribological properties of nitrogen-bearing stainless austenitic steels under abrasive and adhesive wear

The effect of nitrogen, silicon, and aging modes on the structure, resistance to abrasive and adhesive wear, friction factor, and mechanical properties of nitrogen-bearing (0.27–0.83% N) chromium-manganese austenitic steels is studied. It is shown that it is possible to ensure a favorable combination of mechanical and tribological properties in such steels by choosing the appropriate chemical composition and aging mode. __________ Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 5, pp. 9–18, May, 2007.     

Conditions and mechanism of the ionization and dissociation of water. Predictions based on nonempirical calculations

Based on the results of quantum chemical modeling of neutral and charged water clusters, mechanisms of the ionization and dissociation of water explaining the regularities discovered in experiments are proposed. There are two possible ways of the water and ice ionization, namely, (i) directly from the ground electronic state of the neutral system provided that the high-frequency stretching vibrations of molecules, which determine the formation of H₃O⁺ and OH⁻ ionic fragments, are sufficiently excited, and (ii) via the intermediate transfer to the excited electronic state where hydronium radicals may appear at a certain excess energy. The formation of atomic hydrogen may also take place in the processes of two kinds, namely, (i) the dissociation of the electronically excited water clusters and (ii) the recombination of an electron, appeared upon ionization, with a hydronium cation that leads to the spontaneous detachment of a hydrogen atom. The processes may proceed either successively or simultaneously in a time period compared to the characteristic or even resolution time of the experiment, which may result in incorrect estimation of the quantum yields of hydrated electrons and hydrogen atoms in terms of standard procedures. Original Russian Text ? Yu.V. Novakovskaya, 2007, published in Zashchita Metallov, 2007, Vol. 43, No. 3, pp. 235–243.     

热丝化学气相沉积法原位制备的MgB2超导薄膜

用热丝化学气相沉积法(HFCVD)在蓝宝石基片上原位制备了MgB2超导薄膜,并用XRD、SEM和dc SQUIDs研究了基片温度和时间对薄膜相组成、表面形貌和超导临界转变温度Tc的影响.结果表明,HFCVD原位生长MgB2薄膜可以抑制MgO杂质的生成.基片温度在500℃以下,MgB4杂相容易出现;在500℃以上时,可以消除MgB4杂相;在600℃时,获得了纯单相的MgB2薄膜,其超导临界转变温度达到36 K.随基片温度升高,薄膜结晶性、致密度和超导临界转变温度提高.