放电等离子烧结Al基金属氧化物弥散芯块致密化过程研究

Research on Densification Process of Al Based Metal Oxide Dispersed Pellet by Spark Plasma Sintering

高密度Al-超铀核素氧化物弥散芯块制备是实现锎-252生产的重要环节。通过对Al-Nd_(2)O_(3)弥散芯块在放电等离子烧结过程中的收缩曲线及其变化率、密度、微观组织、物相表征分析,模拟研究了放电等离子烧结Al-超铀核素氧化物弥散芯块的致密化过程。研究结果表明,放电等离子烧结能够实现Al-超铀核素氧化物弥散芯块快速、高效致密化,在烧结压力为50 MPa、保温时间为5 min、温度为580℃的条件下,Al-Nd_(2)O_(3)弥散芯块相对密度可达到98.5%,粉体之间达到原子级别紧密结合,且界面之间无其他相产生。Al、O元素在Al-Nd_(2)O_(3)微观界面间发生了一定的扩散行为,而Nd元素由于其原子序数、原子半径较大,扩散较为困难。O元素在Al基体中有一定的溶解度,在一定程度上阻碍了Al-Nd_(2)O_(3)中间相的形成,提高了Al-Nd_(2)O_(3)弥散芯块界面间的稳定性。

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 Nd_(2)O_(3) 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 Nd_(2)O_(3) composite powder in an Ar atmosphere,then the homogenized Al-Nd_(2)O_(3) 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-Nd_(2)O_(3) 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-Nd_(2)O_(3) dispersed pellets is less than 95%,water in the air is prone to enter the dispersed pellets and react with Nd_(2)O_(3) 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-Nd_(2)O_(3) dispersed pellets.As a result,when the density of Al-Nd_(2)O_(3) 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 Nd_(2)O_(3).Under sintering pressure of 50 MPa,holding time of 5 minutes,and 580℃conditions,the relative density of Al-Nd_(2)O_(3) 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 Nd_(2)O_(3),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 Nd_(2)O_(3) and improves the stability of the interface between Al-Nd_(2)O_(3) dispersed pellets.