Yuanzineng kexue jishu (Jul 2024)
Research on Densification Process of Al Based Metal Oxide Dispersed Pellet by Spark Plasma Sintering
Abstract
The preparation of high-density Al transuranic oxide dispersed pellets is a vital step of the californium-252 producing. High density dispersed pellets can not only improve the thermal conductivity of pellets, but also enhance the irradiation safety of target materials, thereby increasing the nuclide loading capacity of irradiated target materials and improving the economic efficiency of irradiation nuclide production. Thanks for the advantages of fast heating rate, short sintering time and effective suppression of grain growth of spark plasma sintering (SPS) process. This paper successfully developed a new routine for preparation of Al based mental oxide dispersed pellets. By using Nd2O3 as nonradioactive surrogate of Am/Cm oxides, the densification behavior of Al based metal oxide dispersed pellets during SPS process was studied. Firstly, a planetary ball mill was employed to homogenize Al and Nd2O3 composite powder in an Ar atmosphere, then the homogenized Al-Nd2O3 composite powder was vacuum sintered in the range of 500-600 ℃ using an SPS device to prepare uniformly dispersed high-density pellets. By analyzing the shrinkage curve, change rate, density, microstructure, and phase characterization of Al-Nd2O3 dispersed pellets during SPS, the densification process of Al transuranium nuclide oxide dispersed pellets was simulated and studied. The research results indicate that SPS can achieve rapid and efficient densification of Al transuranium nuclide oxide dispersed pellets. When the density of Al-Nd2O3 dispersed pellets is less than 95%, water in the air is prone to enter the dispersed pellets and react with Nd2O3 to form Nd(OH)3, which increase in volume by 1.8 times. The significant volume change may lead to the re-pulverization of Al-Nd2O3 dispersed pellets. As a result, when the density of Al-Nd2O3 dispersed pellets exceeds 95%, the dispersed pellets can exist stably. In practical applications, it is necessary to extend the sintering time appropriately to fully transform from Nd(OH)3 to Nd2O3. Under sintering pressure of 50 MPa, holding time of 5 minutes, and 580 ℃ conditions, the relative density of Al-Nd2O3 dispersed pellets can reach 98.5%, and the powders achieve atomic level tight bonding, with no other phases generated between the interfaces. Al and O elements exhibit certain diffusion behavior between the micro interfaces of Al and Nd2O3, while Nd is difficult to diffuse due to its large atomic number and radius. The O element has a certain solubility in the Al matrix, which to some extent hinders the formation of the intermediate phase of Al and Nd2O3 and improves the stability of the interface between Al-Nd2O3 dispersed pellets.
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