Ball milling and sintering of neutron absorber Mo-based Tb2O3-Dy2O3 composite and its characterization

The key to gray control rods controlling and adjusting nuclear reactivity to safely operate a nuclear reactor was in their internal neutron absorbers. New types of Mo-based Tb2O3-Dy2O3 composites used as neutron absorbers were designed and then synthesized by ball milling, cold isostatic pressing and sintering. The microstructure of ball-milled powders and sintered bulks were analyzed. Ball milling induced terbium oxide and dysprosium oxide to be first fined, nano-crystallized, amorphized and finally dissolved into Mo crystal to form Mo (Tb, Dy, O) supersaturated nanocrystalline solid solution, which was driven by mechanical work, not by negative heat of mixing after thermodynamic analysis of a ternary Mo-Tb-Dy systems and the dynamic discussion of ball milling. Sintering caused Tb, Dy and 0 atoms precipitated from Mo crystal and then formed Tb2O3 and Dy2O3 precipitates that uniformly distributed in Mo matrix. The microhardness, compression strength, coefficient of thermal expansion of sintered bulks were measured, and the corresponding mechanism was also discussed. (C) 2018 Elsevier B.V. All rights reserved.