Materials Science Forum Vols. 610-613

Abstract: Mg2+ doped LiFePO4 was synthesized from Li3PO4, FeSO4 and MgSO4 by a hydrothermal synthesis at 150 °C（Li1-xMgxPO4, x=0.00, 0.01,0.02,0.04,0.06）. The samples were characterized with X-ray diffraction (XRD), scanning electron microscopy (SEM) and charge-discharge test. The results showed that Mg2+ dissolved in the LiFePO4 lattice. When the content is in the range of 0 to 6 mol%, Mg2+ caused the shrinkage of LiFePO4 cell volume. The capacity of doped and undoped samples at low discharging rate was similar, about 145mAhg-1 for 0.2C. But the sample doped with 2-4 mol% Mg2+ has higher capacity and longer cycle lifetime than the undoped one at 5C.

Abstract: In this paper, the CNT was used as the reinforcing material to overcome the PPy swelling and shrinkage during the doping-undoping process. The electrochemical capacitance is about 25 F/g in organic electrolyte. The PPy/CNT composite (2:1, m/m) was prepared by depositing the polypyrrole onto functionalized multi-walled CNT in aqueous-methanol solution via chemical polymerization. The obtained composite material was characterized by scanning electron microscopy and infrared spectrum. And the electrochemical performance of the composite material was tested by cyclic voltammetry and galvanostatic charging–discharging cycling. The results showed that the obtained polymer was the PPy and sheet; moreover, the PPy was coated on surface of the CNT. The electrochemical capacitance was about 154.5 F/g (organic electrolyte), which was about 6 times that of pure PPy (about 25 F/g).

Abstract: Sn-based anode materials have poor cycling performance due to mechanical fatigue caused by volume expansion during lithium insertion and extraction processes. In this work, the mechanism of lithium insertion/extraction in the Ni3Sn4 alloy electrode is investigated using the first-principle plane-wave pseudopotential and experimnetal method. The calculated results indicate that the Ni3Sn4 alloy phase has relatively minor expansion ratio and fluctuating electrochemical potential, which the tendency is consistent with the experimental result. On the other hand, the Sn-Ni alloy thin films with different tin content are prepared by electrodepostion on copper as an anode for lithium-ion batteries. The structural and electrochemical characteristics of Sn-Ni alloy are examined using X-ray diffraction (XRD) and repeated constant current charge/discharge (CC). The results show Tthheat Ni3Sn4 alloy phase has best cyclic stability during the lithium insertion and extraction processes.

Abstract: With eEmploying dichloromethane as solvent, sodium dodecanesulphonate as surface active agent, ammonium persulphate as oxidizer, PAn was introduced into PVDF and co-polymer with high relative permittivity reaching to 280 was obtained by emulsion polymerization. By detecting the structural information and electrical property through FT-IR, XRD, SEM, informations about the co-polymers were presented and in this paper. By adjusting the quantity of aniline in polymerization and the concentrations of protonic acid in the post processing, polymers with different electric properties could bewere compared and analyzed. It was The SEM images and XRD patterns showed the crystallization and microstructure information of the co-polymers in comparison. Particularly, the SEM images showed that the PVDF-PAn co-polymers had homogeneous properties in certain constitute range and as a result of emulsion, spherical PAn-PVDF media was fabricated. After robber mixing procedure at certain temperature, the PAn had a relatively average-fine dissolving in the PVDF, which overcame the difficulty of dissolving PAn oin other substrateance. This ensured the fine property for the matrix material in composites. The XRD pattern showed, wWith the increasing of the introduction quantity of PAn, the crystallization of the entire material complex had been raised greatly.

Abstract: Metallic interconnection electromigration is a common phenomenon in integral circuit, and it influences circuit reliability seriously as rapid miniaturization of circuit size. Resistance is a traditional electromigration characterization parameter, but it requires strict testing condition, and it is not sensitive to vacancies accumulation at early stage of electromigration. Some recent researches show that noise is very sensitive to metallic thin film electromigration, it can be used as an effective inspect method for electromigration. So noise wais used to characterize damage degree of Al thin film electromigration in this paper., Tthe results showeds both noise amplitude and frequency exponent increased during electromigration process, and when void nucleation occuredhappens, frequency exponent increased sharply. noise can also reflect electromigration degree under different environment temperature. Through comparing with resistance, noise can be proved a better characterization parameter for electromigration

Abstract: Based on the available thermodynamic and phase equilibria data, the thermodynamic criteria for oxidation in tin-based lead-free solders under soldering condition was deduced. The dependence of Gibbs free energy on temperature in Pb-free solder oxidation reaction was calculated by applying MATLAB program. The characteristics of oxidation reaction of a varity of solder alloy systems such as Sn-Ag, Sn-Cu, Sn-Sb, Sn-Zn, Sn-Ag-Cu and Sn-Pb eutectic alloys at elevated temperature were analyzed. The results suggested that zinc preferentially oxidized in Sn-Zn solder alloys in the elevated temperature state, while tin preferentially oxidized in the other alloys. The oxidation potential of the Sn-Zn eutectic alloys was higher than that of the pure tin at elevated temperature, whereas the oxidation potentials of Sn-Ag, Sn-Cu, Sn-Sb and Sn-Ag-Cu eutectic alloys were approxiately equal to that of the pure tin. All tin-based Pb-free solder alloys more easily oxidized than the Sn-Pb solder alloys. Oxidizability of these alloys followed in a decreasing order: Sn-Zn＞Sn-Sb＞Sn-Cu＞Sn-Ag＞Sn-Ag-Cu＞Sn-Pb.

Abstract: Based on Miedema’s model, the enthalpy of formation, excess free-energy and partial molar excess free-energy of Sn-Pb binary alloy solders were calculated. The model of the activity coefficient for each component in the solders was established. The diagrams of enthalpy of formation, free energy versus composition and activity versus composition and temperature as well as activity coefficients as a function of composition and/or temperature were drawn. And then the relationship between the activity coefficients of elements Sn/Pb in the solders and temperature was obtained. The approaches to reduction in the volatilization of lead at high temperature were proposed from the point of views that the lead pollution to environment results from its chemical activity in the solder alloys.

Abstract: It is a difficult subject to develop the high temperature solder with thewhose melting point is within 250～450°C in solder field. Bi5Sb solder alloy whosewith the melting point of about is about 280°C is limited for itshas bad solderability and mechanical properties. In the present work, the new BiSbCu ternary alloy wasis preparformed by adding different contents of Cu to Bi5Sb solder alloy to improve its solderability and mechanical properties. Results showed that the effect of adding 0.5～5.0％Cu into Bi-5Sb on the melting point of Bi5Sb solder alloy wais not distinct , but its solderability and mechanical properties weare markedly improved. Compared to the matrix of Bi5Sb, the spreading area of solder alloy wais about 57.8% largbigger and the tensile strength wais about 212.4% highbigger when the content of Cu wais 1.5wt.%. Analysis of tThe microstructure showeds that the needle-like Cu2Sb gradually becaomes shorter and dense along with the increasing of the content of Cu, which can effectaffected the properties of the solder alloy.

Abstract: The high silicon content Si-Al alloy is a typical heat dissipation material that used in the electrical packaging field. A spray forming process wais used to produce a 90%Si-Al alloy specimen as a heat dissipation material in the present study. Then the spray formed 90%Si-Al specimens weare hot pressed at 1000°C with different pressure ranged from 2MPa to 10MPa to increase their density. The physical properties of the experimental alloy specimen weare measured. And the microstructure wass are observed by using optical microscopy and scanning electronic microscopy. The results showed that the Spray forming wais suitable forto producinge a 90%Si-Al alloy. With hot pressure of 10MPa, the relative density value of 90%Si-Al reachedcan obtain 94%. The typical physical properties such as the thermal conductivity, coefficient of thermal expansion and electrical conductivity of 90%Si-Al alloy are acceptable as a heat dissipation material for many electronic packaging applications.

Abstract: SiCp/Al composites based on different matrix elements Mg and Si content were fabricated by pressureless infiltration. Through microscope investigation by SEM and TEM, density examination, coefficient of thermal expansion (CTE) and thermal conductivity measuring by Netzsch DIL 402EP and Netzsch LFA 447 Nanoflash, the effects of Mg and Si in the aluminum on the thermo-physical properties of SiCp/Al composites was studied and analysed. The results showed that , adding Mg element in matrix enhaced the densification and thermal conductivity of composites, but meanwhile increased the CTE of SiCp/Al composites. When Mg element content was in higher than 6.3wt%, CTE of SiCp/Al composites increased obviously. Adding Si element in matrix markedly reduced the CTE of composites , but meanwhile decreased thermal conductivity of composites. When Si element content was higher than 5-9wt%,thermal conductivity of composites declined obviously. Adding Mg element in matrix improved the interface wet ability between molten aluminum and SiC particles, and adding Si element in matrix could control the formation of A14C3 which is a detrimental interface reaction product during the pressureless infiltration processing. Therefore, adding appropriate Mg in company with Si in matrix will be more benefit to enhance the integer properties of SiCp/Al composites.