交流磁场对Sn-20%Pb合金电阻的影响

EFFECT OF AC MAGNETIC FIELD ON ELECTRIC RESISTANCE OF Sn-20%Pb ALLOY

在不同温度测量Sn-20%Pb合金直流电阻时,沿纵向施加交流磁场.结果发现:对固态样品,无论是在室温还是在接近固相线的温度,磁场都没有引起电阻增加.对液态样品,施加磁场后,电阻开始逐渐增大,停止施加磁场,增大的电阻维持一段时间不变后,才缓慢恢复到施加磁场前的初始值.金相显微镜和扫描电镜结果表明,交流磁场不仅使初生β-Sn的晶粒明显细化,还使Pb在初生β-Sn的晶粒内的含量增加,且Pb的分布更均匀.利用无序理论,对实验结果进行定性讨论,认为交流磁场的电磁搅拌作用破坏了Sn-20%Pb熔体的短程有序,增大了系统的无序度,使部分扩展态电子转变成局域态电子,从而使熔体的电阻增大.

The electric resistance of Sn-20%Pb alloy was measured at different temperatures when the AC magnetic field was applied. The results showed that the AC magnetic field had no effect on the electric resistance of solid Sn-20%Pb alloy, but when it was applied on the liquid Sn-20%Pb alloy, the electric resistance of alloy increased gradually. After the AC magnetic field was stopped, the electric resistance remained at a constant value for a long time, and then slowly decreased to the value before applying the AC magnetic field. The results of metallographic microscope and SEM showed that the AC magnetic field not only refined the primary/^-Sn grain, but also increased the Pb content in primary ^-Sn grain, so that the distribution of Pb was more uniform than that in the sample without magnetic field. The Anderson＇s theory of disorder has been used to explain the experimental results. It was considered that the electromagnetic stirring caused by AC magnetic field destroyed the short range order of the Sn-20%Pb melt, improved the disorder degree of the system, transformed some extended states electrons into localized states electrons, consequently increased the electric resistance of the melts.