贵金属与稀土金属的相互作用:(Ⅱ)Ag-RE系

Interaction between Precious Metals and Rare-Earth Metals (Ⅱ)Ag-RE Systems

评述了Ag与RE金属相互作用与合金化行为。随着镧系元素原子序数增大 ,RE在Ag中固溶度增大 ;RE与Ag原子半径差 (Δr/rAg)是影响RE在Ag中固溶度的主要因素 :当Δr/rAg>2 6 %时 ,Cmax很小或为零 ;当Δr/rAg<2 6 %时 ,Cmax=A -B(logΔr/rAg-1)。在Ag-RE系中出现 (RE∶Ag) 1∶5、 2∶9、 1∶4、 14∶5 1、 2∶7、 1∶3、 1∶2、 1∶1、 3∶2和 5∶2十种化学计量化合物和 19种晶体结构 ,4个共晶系 10种共晶反应和 8种包晶反应。根据简约温度图 ,评述了简约共晶温度和中间相简约转变温度与RE原子序数的关系 :随着RE原子序数增大 ,简约温度有规律下降 ,但在Ce、Eu和Yb上出现反常高值。简约共晶温度(Teu/TAg)与RE原子半径的关系符合由Au -RE系建立的判据 :Teu/TAg随RE原子半径增大而线性降低 ,但当rRE大于 0 175nm (原子半径差大于 2 1% )后Teu/TAg基本保持不变。在Ag-RE系中 ,Eu和Yb取 2价态 ,其它RE取

The interaction and alloying behavior between Ag and RE metals were reviewed in present paper.Along with the increase of atomic numbers of lanthanide,the solid solubilities of RE in Ag increased.The difference of atomic radii between RE and Ag,Δr/r Ag ,is the main factor influencing the maximumsolid solubility (C max )of RE in Ag.The C max values are very small or negligible when Δr/r Ag >26%;and C max =A-B(logΔr/r Ag -1) when Δr/r Ag <26%.There occure 10 stoichiometrical compounds with RE∶Ag=1∶5,2∶9,1∶4,14∶51,2∶7,1∶3,1∶2,1∶1,3∶2 5∶2 and 19 crystal structures,4 eutectic systems with 10 eutectic reactions,and 8 peritectic reactions in Ag-RE systems.According to the reduced temperature plots ,the dependences of the reduced eutectic temperatures and the reduced transition temperatures of intermediate phases on the atomic numbers of RE metals were reviewed.The reduced temperatures decreased regularly along with increase of atomic numbers of RE except anomalous high values for Ce,Eu and Yb.The dependence of reduced eutectic temperatures (T eu /T Ag ) on the atomic radii (r RE ) of RE conform the criterion established for Au-RE systems:T eu /T Ag values decline linearly with the increase of r RE and then keep essentially a constant when r RE values are larger than 0 175nm.In Ag-RE systems,Eu and Yb take 2 valence,other RE metals take 3 valence.