Effect of sample diameter on primary and secondary dendrite arm spacings during directional solidification of Pb-26wt.%Bi hypo-peritectic alloy

The microstructure scales of dendrites, such as primary and secondary dendrite arm spacings, control the segregation profiles and the formation of secondary phases within interdendritic regions, which determine the properties of solidified structures. Investigations on primary and secondary dendrite arm spacings of primary a-phase during directionally solidified Pb-26wt%Bi hypo-peritectic alloy were carried out in this research, and systematic studies were conducted using cylindrical samples with different diameters （Ф = 1.8 and 7.0 mm） in order to analyze the effects of sample diameter on the primary and secondary dendrite arm spacings. In this work, the dependence of dendrite arm spacings on growth velocity was established. In addition, the experimental data concerning the primary and secondary dendrite ann spacings were compared with the main predictive dendritic models from the literatures. A comparison between experimental results for dendrite arm spacings of the 1.8-mm-diameter sample and 7.0-ram-diameter sample was also conducted.

Experimental Research of Electronic Devices Thermal Control Using Metallic Phase Change Materials

A Phase-change thermal control unit( PTCU) filled with metallic phase change material( PCM) Bismuth alloy for electric devices thermal protection was developed and investigated experimentally. The PTCU filled with PCM was designed and manufactured. Resistance heating components( RCHs) produced 1 W,3 W, 5 W,7W,and 10 W for simulating heat generation of electronic devices. At various heating power levels,the performance of PTCU were tested during heating period and one duty cycle period. The experimental results show that the PTCU delays RCH reaching the maximum operating temperature. Also,a numerical model was developed to enable interpretation of experimental results and to perform parametric studies. The results confirmed that the PTCU is suitable for electric devices thermal control.

J_c-B Characteristics and Microstructure Dependence of J_c of High J_c Bi-based Superconducting Oxide Tapes

Bi-based 2223 superconducting tapes with high critical current densities were prepared by silver-sheathing method. The relationship between processing, microstructure and property was discussed. The results of critical current density measurement at 77.7K with different applied magnetic field are as follows: Jc=2.87×104A/cm2 (OT) and Jc=4100A/cm2. Jc and Jc-B characteristics were obviously improved with temperature decreasing form 77K to 4.2K. Microstructure observations indicate that intermediate pressing with subsequent heat-treating can lower the porosity of superconductor inside the silver sheath. and reduce the amount and size of non-superconducting phases, leading to the formation of a strong c-axis-oriented texture and the emergence of high dislocation density within the 2223 grains, and consequently the Jc and Jc-B characteristics were improved.

Effect of Pb Addition on Melting Behavior ofBi-Sr-CuO System 2201 Phase

The effect of Pb on the melting of the 2201 phase was studied by DTA and XRD. The results indicate that as the mole ratio of Pb/(Pb+Bi) is up to 20%, the tetragonal 2201 phase will transform into the orthorhombic 2201 and that the melting point Tm of the tetragonal 2201 decreases with increasing Pb-content, however, Tm of the orthorhombic 2201 remains 883°C.

New Asymmetric Model for Predicting Ternary Thermodynamic Properties

The prediction of the thermodynamic properties of ternary systems from the properties of their sub-binary systems is of great importance to phase diagram calculations. In the present study, a new asymmetric model which has more clear physical significance has been developed for evaluating the ternary thermodynamic properties from its three binary components. The model is considered to be rigorous in the case where the pseudobinary systems of fixed X2/X3 are regular are regular solution. The application of new model to the prediction of ternary enthalpies of mixing for Bi-Ga-Sn, Au-Ag-Sn and NaCl-KCl-CaCl2 systems shows that the calculated results by new model are closer to experimental data than those by Toop's model.