Rafailov Gennady, Dahan Isaac, Meshi Louisa
Materials Department, Nuclear Research Center of Negev (NRCN), PO Box 9001, Beer-Sheva, Israel.
Department of Materials Engineering, Ben-Gurion University of the Negev, Beer-Sheva 84105, Israel.
Acta Crystallogr B Struct Sci Cryst Eng Mater. 2014 Jun;70(Pt 3):580-5. doi: 10.1107/S2052520614003801. Epub 2014 May 24.
The industrial importance of the U-Al-Si system stems from the fact that during processing the Al-based alloy (containing Si as impurity), used for the cladding of U (fuel in nuclear reactors), undergoes heat treatment which stimulates diffusion between the fuel and the cladding. One of the possible ways to represent the ternary U-Al-Si phase diagram is the construction of an UAl3-USi3 quasi-binary phase diagram. On the one hand, since the UAl3 and USi3 phases are isostructural, an isomorphous phase diagram is expected; on the other hand, some researchers observed a miscibility gap at lower temperatures. During our study of the UAl3-USi3 quasi-binary phase diagram, a new stable U(Alx,Si1 - x)3 phase was identified. The structure of this phase was determined, using a combination of electron crystallography and powder X-ray diffraction methods, as tetragonal [I4/mmm (No.139) space group], with lattice parameters a = b = 8.347 (1), c = 16.808 (96) Å. Its unit cell has 64 atoms and it can be described as an ordered variant of the U(Al,Si)3 solid solution. A Bärnighausen tree was constructed using the original U(Al,Si)3 structure as an aristotype.
U-Al-Si体系在工业上的重要性源于这样一个事实：在加工用于包覆U（核反应堆中的燃料）的铝基合金（含Si作为杂质）时，会进行热处理，这会促进燃料与包覆层之间的扩散。表示三元U-Al-Si相图的一种可能方法是构建UAl3-USi3准二元相图。一方面，由于UAl3和USi3相是同构的，预计会得到一个同构相图；另一方面，一些研究人员在较低温度下观察到了混溶间隙。在我们对UAl3-USi3准二元相图的研究中，确定了一种新的稳定U(Alx,Si1 - x)3相。利用电子晶体学和粉末X射线衍射方法相结合，确定该相的结构为四方晶系[I4/mmm (No.139)空间群]，晶格参数a = b = 8.347 (1)，c = 16.808 (96) Å。其晶胞含有64个原子，可以描述为U(Al,Si)3固溶体的一种有序变体。以原始的U(Al,Si)3结构为原型构建了一个贝恩豪森树。
