烧结温度对铪块孔隙结构和成分的影响

Influence of Sintering Temperature on Microstructure and Composition of Hafnium Ingots

以纯铪粉为原料,采用真空烧结的方法,制备疏松、多孔且孔隙均匀的铪块,以能满足碘化的要求,防止铪粉在摩擦和碰撞的过程中易燃,不利于碘化装炉和出炉;同时高温烧结还可除去铪中的部分杂质,防止碘化过程发生中毒现象。利用SEM、电感耦合等离子体质谱分析法和EDS能谱分析等测试手段,主要研究了烧结温度对烧结后铪块的孔隙结构和成分变化的影响。实验结果表明:在真空度为6.7×10-3Pa、烧结温度1000℃(保温2 h)的条件下,所得试样的孔隙分布均匀,孔径大小基本一致,为150 nm,孔隙边缘光滑,形状由不规则倾向于圆形,且随温度的升高,粘结面不断扩大,逐渐形成烧结颈,颗粒边缘继续钝化,表面由粗糙变光滑,烧结颈由细变粗,大孔隙收缩,有的烧结颈出现熔化,小孔消失。烧结后的铪块中杂质元素W,Mo,Fe,O等含量不受温度的影响,H的含量随着烧结温度的升高而减少,由真空炉的压强分析知,氢含量的减少主要是由水分的蒸发和试样中的氢化铪高温分解产生氢气所造成的。

Loose and porous hafnium ingots with uniform pores were made of pure hafnium powder by the method of vacuum sintering to meet the requirements of iodination to prevent hafnium powder from flaming in friction and collision process which made it difficult to charging and discharging iodination furnace. At the same time, high temperature sintering could also remove part of impurities in hafni- um, to prevent hafnium from poisoning in iodinated process. The changes in the pore structure of the sintered samples and the contents of impurity elements were studied according to the component changes of the samples before and after sintering and combining with SEM, the ICPMS analytical methods and EDS analytical methods. Research showed that the vacuum sintered samples at 1000 ℃ and 2 h of heat preservation with vacuum degree of 6.7× 10^-3 Pa had even pore distribution, the pore size of about 150 nm and smooth pore edge, and the shape of the sample hole changed from irregular to the circular. The results showed that with temperature increas- ing, the bonding surface was constantly expanding, gradually forming sintering neck, and the particle edge began to passivate. With the surface changed from rough to polish, the sintering neck changed from fine to coarsening, then big pore contraction, some sintering necks began to melt, and some pores disappeared. It was found that the impurity elements （W, Mo, Fe, O） content in the vacuum sintered samples was not affected significantly by the reaction temperature, while the content of hydrogen decreased with the sintering temperature increasing. It could be seen from vacuum furnace pressure analysis that hydrogen content reduction was mainly due to water evaporation and hydrogen produced by the hydrogenated hafnium of sample decomposing at high temperature.