Calculation of the thermal expansion coefficient for Bi2Sr2CaCu2O8

An estimation method of thermal expansion coefficient in term of lattice energy which was developed earlier for simple materials is extended to a complex material of Bi2Sr2CaCu2O8 (Bi-2212). The calculation of the chemical bond property and thermal expansion coefficient of Bi-2212 has been carried out and the theoretical values were in good agreement with the corresponding experimental results. The dependence of the thermal expansion coefficient on the different structures and on the flexible oxidation states of Bi and Cu are investigated. The results indicate that the thermal expansion coefficients of Bi-2212 are insensitive to the low lattice distortion of the average structure and the changes of formal valences of Bi and Cu ions.

Y-Ba-Cu-O mixed oxides for production of diphenols in liquid-solid phase

Superconductor mixed oxides were often used as catalysts at higher temperature in gas phase oxidations, and considered not suitable for lower temperature reactions in the liquid-solid phase; here the catalysis of YBa2Cu3O7+/-x and Y2BaCuO5+/-x in the phenol hydroxylation at lower temperature with H2O2 as oxygen donor was studied, and found that the superconductor YBa2Cu3O7+/-x, has no catalytic activity for phenol hydroxylation, but Y2BaCuO5+/-x does, even has better catalytic activity and stability than most previously reported ones. With the studies of catalysis of other simple metal oxides and perovskite-like mixed oxides, a radical substitution mechanism is proposed and the experimental facts are explained clearly, and draw a conclusion that the perovskite-like mixed oxides with (AO)(ABO(3)) and (AO)2(ABO(3)) structure have better catalytic activity than the simple perovskite oxides with (ABO(3))(3) structure alone, and (AO) structure unit is the key for the mixed oxides to have the phenol hydroxylation activity. No pollution of this process is very important for its further industrial application.

Investigation of Catalysis of Y-Ba-Cu-O Mixed Oxides in Phenol Hydroxylation

Superconductor Y-Ba-Cu-O mixed oxides were synthesized and their catalysis in phenol hydroxylation was studied too. Results show that, Y2BaCuO5 has better activity than that of YBa2Cu3O7-x, With the catalysis study of another mixed oxide La2CuO4 a conclusion that AO structure unit is the key for mixed oxides to have high activity in phyenol hydroxylation was drawn. Meanwhile, the effects of reaction temperature, medium and medium (water) pH on phenol hydroxylation catalyzed by Y2BaCuO5 and the stability of the mixed oxides were also studied.

THE CHARGE-DISTRIBUTION AND THE ELECTRIC-FIELD GRADIENT IN THE HIGH-TEMPERATURE SUPERCONDUCTOR TLBA2CAN-1CUNO2N+3 (N = 1 TO 3)

The net charges at atoms in the high-temperature superconductor TlBa2Can-1CunO2n+3 (n = 1 to 3) are calculated by means of the tight-binding approximation based on the EHMO method. The results indicate that the charge distribution in this kind of compounds possesses a specially layered arrangement. An insulating Ba-Ba layer is inserted between the Cu-O layer and the Tl-O layer. There may exist a weak coupling between the Cu-O layer and the Tl-O layer through the interaction of the same O(2) atom with both the Cu atom and the Tl atom. The existence of the Ca in the compounds can cause the valence fluctuation at the Cu atom. The calculated electric field gradients at atoms implies that the conducting electron or hole may move in the Cu-O layer, which is closest to the Tl-O layer, along the a-b plane.

SIMULATION OF THE OXYGEN-ATOM VACANCY IN THE HIGH-TEMPERATURE SUPERCONDUCTOR TIBA2CAN-1CUNO2N+2.5(N = 1)

These simulation calculations for the oxygen-atom vacancy in the high temperature superconductor TlBa2Ca(n-1)Cu(n)O2n+2.5(n = 1) have been performed by means of the tight-binding approximation based on the EHMO method. The results indicate that the effect of the oxygen-atom vacancy on the charge distributions at the Tl-, Ba-, Cu- and O-atom sites is appreciably different and that there may exist two kinds of Cu cation with different net charges (approximately + 3.0 or approximately + 1.0) due to the oxygen-atom vacancy in the lattice. The electric field gradient at the site of the oxygen-atom vacancy has been calculated. The position of the oxygen-atom vacancy which favours the high temperature superconductivity of TlBa2Ca(n-1)Cu(n)O2n+2.5(n = 1) has been discussed.

Formation, Thermal Stability and Deformation Behavior of Graphite-Flakes Reinforced Cu-based Bulk Metallic Glass Matrix Composites

Graphite-flake reinforced Cu47Ti34Zr11 Ni-8 bulk metallic glass matrix composite was fabricated by water-cooled copper mould cast. Most of the graphite flakes still keep unreacted and distribute uniformly in the amorphous matrix except that some reactive wetting occurs by the formation of TiC particles around the flakes. It reveals that the presence of graphite flakes does not affect the onset of the glass transition temperature, crystallization reaction and liquidus of the metallic glass. The resulting material shows obvious serrated flow and higher fracture strength under room temperature compressive load, comparing with the monolithic bulk metallic glass (BMG). Three types of interaction between the shear bands and graphite flakes, namely, shear band termination, shear bands branching and new shear bands formation near the graphite flakes can be observed by quasi-static uniaxial compression test and bonded interface technique through Vickers indentation.

Effect of Nb Content on the Microstructure and Mechanical Properties of Zr-Cu-Ni-Al-Nb Glass Forming Alloys

(Zr65Al10Ni10Cu15)(100-x) Nb-x glass forming alloys with Nb contents ranging from 0 to 15 at.% were prepared by water-cooled copper mould cast. The alloys with different Nb contents exhibited different microstructures and mechanical properties. Unlike the monolithic Zr65Al10Ni10Cu15 bulk metallic glass, only a few primary bee beta-Ti phase dendrites were found to distribute in the glassy matrix of the alloys with x = 5. For alloys with x = 10, more beta-phase dendrites forms, together with quasicrystalline particles densely distributed in the matrix of the alloys. For alloys with x = 15, the microstructure of the alloy is dominated by a high density of fully developed P-phase dendrites and the volume fraction of quasicrystalline particles significantly decreases. Room temperature compression tests showed that the alloys with x = 5 failed at 1793 MPa and exhibited an obvious plastic strain of 3.05%, while the other samples all failed in a brittle manner. The ultimate fracture strengths are 1793, 1975 and 1572 MPa for the alloys with x = 0, 10 and 15 at.% Nb, respectively.

Metallographic Analysis of Cu-Zr-Al Bulk Amorphous Alloys with Yttrium Addition

Minor yttrium addition can improve the glass-forming ability of Cu-Zr-Al ternary alloys via suppression of the growth of eutectic clusters. Yttrium addition also makes the room temperature ductility of the alloys decrease, and both the compressive strength and elastic strain limits increase slightly.

Kinetics of Glass Transition and Crystallization in Carbon Nanotube Reinforced Mg-Cu-Gd Bulk Metallic Glass

Mg65 Cu25 Gdlo bulk metallic glass and its carbon nanotube reinforced composite were prepared. Differential scanning calorimeter (DSC) was used to investigate the kinetics of glass transition and crystallization processes. The influence of CNTs addition to the glass matrix on the glass transition and crystallization kinetics was studied. It is shown that the kinetic effect on glass transition and crystallization are preserved for both the monothetic glass and its glass composite. Adding CNTs in to the glass matrix reduces the influence of the heating rate on the crystallization process. In addition, the CNTs increase the energetic barrier for the glass transition. This results in the decrease of GFA . The mechanism of the GFA decrease was also discussed.

Cu原子簇触发形核下的深过冷Ag-Ge合金组织演变研究

采用玻璃包覆的方法获得具有较大过冷度的亚共晶、共晶以及过共晶Ag-Ge合金熔体,并通过高能离子束轰击Cu箔产生Cu原子团簇溅射到过冷合金熔体中来触发非均质形核过程.凝固后合金显微组织的分析结果表明:在深过冷合金熔体中引入Cu原子团簇,它对亚共晶、共晶以及过共晶Ag-Ge合金的显微组织演变有着不同的影响效果,分析了显微组织的演变规律与形成机制. The Ag-Ge alloy melts with deeply undercooled hypoeutectic, eutectic and hypereutectic were obtained via glass fluxing technique. The nucleation of the deeply undercooled alloy melts were triggered by atoms cluster sputtering on the surface of the melts. The atoms clusters were generated by an ion beam bombarding on the Cu foil fixed above the alloy melts. The resultant microstructure reveals that the induced atom clusters exert great influence on the microstructural evolution of the highly undercooled eutectic and hypereutectic Ag-Ge alloys, but no obvious influence on the highly undercooled hypoeutectic alloy. The microstructural evolution and formation mechanism were analyzed and discussed.

Mechanism of nucleation and precipitation in Li containing Al-Zn-Mg-Cu alloys

Investigations on the aging hardening behavior of four Al-Li-Zn-Mg-Cu alloys were carried out using differential scanning calorimetry, transmission electron microscopy and hardness measurement. It is shown that the addition of Li inhibits the formation of Zn-rich G.P. zones in Al-Zn-Mg-Cu alloys. The dominant aging hardening precipitates is delta'(Al3Li) phase. Coarse T ((AlZn)(49)Mg-32) phase, instead of MgZn2, precipitates primarily on grain boundaries, and provides little strengthening. The multi-stop aging involving plastic deformation introduces in the matrix a high concentration of structural defects. These defects play different role on the nucleation of Zn-rich G.P. zones in different alloys. For the Li free alloy, structural defects act as vacancy sinks and tend to suppress the homogeneous precipitation of G.P. zones, while for the Li containing alloys, these defects promote the heterogeneous nucleation of G.P. zones and metastable MgZn2. A significant aging hardening effect is attained in deformed Li containing alloys due to the extra precipitation of fine MgZn2 in the matrix combined with deformation hardening.

Cu原子簇触发形核下的深过冷Ag-Ge合金组织演变研究

采用玻璃包覆的方法获得具有较大过冷度的亚共晶、共晶以及过共晶Ag-Ge合金熔体，并通过高能离子束轰击Cu箔产生Cu原子团簇溅射到过冷合金熔体中来触发非均质形核过程。凝固后合金显微组织的分析结果表明：在深过冷合金熔体中引入Cu原子团簇，它对亚共晶、共晶以及过共晶Ag-Ge合金的显微组织演变有着不同的影响效果，分析了显微组织的演变规律与形成机制。

Temperature Dependence of the Tribological Properties of Laser Re-Melted Al-Cu-Fe Quasicrystalline Plasma Sprayed Coatings

The aim of this study was to investigate the effect of temperature on tribological properties of plasma-sprayed Al-Cu-Fe quasicrystal (QC) coating after laser re-melting treatment. The laser treatment resulted in a more uniform, denser and harder microstructure than that of the as-sprayed coatings. Tribological experiments on the coatings were conducted under reciprocating motion at high frequency in the temperature range from 25 to 650 degreesC. Remarkable influence of temperature on the friction behavior of the coating was recorded and analyzed. Microstructural analysis indicated that the wear mechanisms of the re-melted QC coatings changed from abrasive wear at room temperature, to adhesive wear at 400 degreesC and severe adhesive wear at 650 degreesC owing to the material transfer of the counterpart ball. It was also observed that the ratio of the icosahedral (i)-phase to beta-Al-50(Fe,CU)(50) phase in the coating was higher after test at 400 'C than that at 650 'C. The variation of the ratio UP of coating and of the property of the counterpart ball and coating with the temperature are the two main factors influencing the wear mechanisms and value of the friction coefficient.

氮化铝基板与Cu和Al的接合及其表面改质效果

对AlN陶瓷基板进行了减压直流等离子体喷涂镀Al，在基板表面形成厚度约２μｍ的金属Al薄层，实现了Al与AlN中的良好接合。

Grain Boundary Effects On Plastic Deformation And Fracture Mechanisms In Cu Nanowires: Molecular Dynamics Simulations

Metallic nanowires have many attractive properties such as ultra-high yield strength and large tensile elongation. However, recent experiments show that metallic nanowires often contain grain boundaries, which are expected to significantly affect mechanical properties. By using molecular dynamics simulations, here, we demonstrate that polycrystalline Cu nanowires exhibit tensile deformation behavior distinctly different from their single-crystal counterparts. A significantly lowered yield strength was observed as a result of dislocation emission from grain boundaries rather than from free surfaces, despite of the very high surface to volume ratio. Necking starts from the grain boundary followed by fracture, resulting in reduced tensile ductility. The high stresses found in the grain boundary region clearly play a dominant role in controlling both inelastic deformation and fracture processes in nanoscale objects. These findings have implications for designing stronger and more ductile structures and devices on nanoscale.