High strength Ni based composite reinforced by solid solution W(Al) obtained by powder metallurgy

The solid-solution-particle reinforced W(Al)-Ni composites were successfully fabricated by using mechanical alloying (MA) and hot-pressing (HP) technique when the content of Ni is between 45 wt% and 55 wt%. Besides, samples of various original component ratio of Al50W50 to Ni have been fabricated, and the corresponding microcomponents and mechanical properties such as microhardness, ultimate tensile strength and elongation were characterized and discussed. The optimum ultimate tensile strength under the experiment conditions is 1868 MPa with elongation of 10.21 % and hardness of 6.62 GPa. X-ray diffraction (XRD), FE-SEM and energy dispersive analysis of X-rays (EDS) were given to analysis the components and morphology of the composite bulk specimens.

快速凝固/粉末冶金高阻尼铝合金挤压成形过程的数值模拟

采用有限元分析软件ANSYS,分析了快速凝固/粉末冶金(Rapidly Solidified/Powder Metallurgy,RS/PM)高阻尼铝合金FMS0714/10(Zn-30Al)的挤压成形过程,研究了模具与坯料间的摩擦条件和挤压比对阻尼铝合金成形过程的影响,探讨了挤压过程材料表面产生裂纹的机理,进行了成形工艺优化.研究结果表明:挤压过程中FMS0714/10(Zn-30Al)阻尼铝合金材料的流动与变形不均匀,导致了应力应变分布的不均匀:材料表面应力应变较大,芯部应力应变较小;表面过大的应变和轴向拉应力是表面裂纹的诱因;减小模具和坯料间的摩擦,增大挤压比,可以减小材料表面应力,使应变分布趋于均匀,从而减少材料表面损伤,优化材料表面质量,提高成品合格率.数值模拟的研究结果将为FMS0714/10(Zn-30Al)阻尼铝合金材料挤压工艺的制订以及新材料的设计和研制提供有益的参考.

Electrolytic Deposition and Diffusion of Lithium onto Magnesium-9 Wt Pct Yttrium Bulk Alloy in Low-Temperature Molten Salt of Lithium Chloride and Potassium Chloride

The electrolytic deposition and diffusion of lithium onto bulk magnesium-9 wt pct yttrium alloy cathode in molten salt of 47 wt pct lithium chloride and 53 wt pct potassium chloride at 693 K were investigated. Results show that magnesium-yttrium-lithium ternary alloys are formed on the surface of the cathodes, and a penetration depth of 642 mu m is acquired after 2 hours of electrolysis at the cathodic current density of 0.06 A center dot cm(-2). The diffusion of lithium results in a great amount of precipitates in the lithium containing layer. These precipitates are the compound of Mg41Y5, which arrange along the grain boundaries and hinder the diffusion of lithium, and solid solution of yttrium in magnesium. The grain boundaries and the twins of the magnesium-9 wt pct yttrium substrate also have negative effects on the diffusion of lithium.

Surface characterization study on SnO2 powder modified by thiourea

The SnO2 material prepared by sol-gel method was modified by thiourea solution in different concentrations (0.05, 0.1 and 0.2 mol dm(-3)). Then the structure and the average grain size of the SnO2 material were investigated by X-ray power diffraction. In order to understand the nature of the species on the SnO2 surfaces, the thermal gravimetric and differential thermal analyzer (TG-DTA) and IR spectra of these modified and unmodified sample were taken. The result indicates that the stability of oxygen adsorbed on thiourea-modified surface was improved and the amount of surface hydroxyl groups adsorbed on this grain surface was decreased. The thiourea adsorbed on SnO2 grain surface is translated to SO42- after sintered at 600 degrees C. SO42- species stabilize the resistance of the SnO2 sensor. (c) 2005 Elsevier B.V. All rights reserved.

Investigation of thermodynamic properties of Co2O3 powder

The isobaric molar heat capacities of powder of Co2O3 were determined by an adiabatic calorimeter in the temperature range from 78 to 350 K. No phase transition takes place in this temperature range. The relationship of C-p,C-m with thermodynamic temperature T was established as C-p,C-m = -5 x 10(-6)T(3) + 0.0026T(2) + 0.0325T + 4.2592 (J K-1 mol(-1)), fitting coefficient R-2 = 0.9996. According to this relationship and the relationships between thermodynamic functions, the thermodynamic functions of powder of C2O3 were derived with 298.15 K as reference temperature. Thermal decomposition of Co2O3 powder was studied through thermogravimetry (TG). The possible mechanism of the thermal decomposition reaction was suggested according to the TG result. (C) 2003 Elsevier Science B.V. All rights reserved.

Local similarity in organic crystals and the non-uniqueness of X-ray powder patterns

Two new concepts for molecular solids, 'local similarity' and 'boundary-preserving isometry', are defined mathematically and a theorem which relates these concepts is formulated. 'Locally similar' solids possess an identical short-range structure and a 'boundary-preserving isometry' is a new mathematical operation on a finite region of a solid that transforms mathematically a given solid to a locally similar one. It is shown further that the existence of such a 'boundary-preserving isometry' in a given solid has infinitely many 'locally similar' solids as a consequence. Chemical implications, referring to the similarity of X-ray powder patterns and patent registration, are discussed as well. These theoretical concepts, which are first introduced in a schematic manner, are proved to exist in nature by the elucidation of the crystal structure of some diketopyrrolopyrrole (DPP) derivatives with surprisingly similar powder patterns. Although the available powder patterns were not indexable, the underlying crystals could be elucidated by using the new technique of ab initio prediction of possible polymorphs and a subsequent Rietveld refinement. Further ab initio packing calculations on other molecules reveal that 'local crystal similarity' is not restricted to DPP derivatives and should also be exhibited by other molecules such as quinacridones. The 'boundary-preserving isometry' is presented as a predictive tool for crystal engineering purposes and attempts to detect it in crystals of the Cambridge Structural Database (CSD) are reported.

Study on thermodynamic properties of polypyromellitimide molding powder

Polypyromellitimide molding powder has been prepared. In the 78-370 K range, the dependence of the specific heat capacity (c(p)) on the temperature (T) is given by the polynomial: c(p)=0.8163+0.4592X+0.02468X(2)+0.1192X(3)+0.05659X(4) (J K-1 g(-1)) where X=(T-225.5)/144.5. Thermal decomposition in air starts at 716 K, and is complete at 1034 K. The standard combustion enthalpy is Delta(c)H=-26.442 kJ g(-1). (C) 2000 Elsevier Science B.V. All rights reserved.