超导射频腔用铌材的表面化学抛光技术

Chemical Polishing of Niobium for Superconducting Radio Frequency Cavity

通过分析化学抛光过程中铌材的抛光速率、表面形貌和氧化状态等参数,确定了超导腔用铌材的表面化学抛光工艺:混合酸(HNO_3:HF:H_3PO_4=1:1:2,体积比)为适合的抛光试剂,抛光速率方程为h=29.359t 0.9247,抛光6~15 min可移除厚度154~360μm,表面粗糙度Ra小于0.65μm,表面Nb_2O_5层厚度小于10 nm。同时,利用电子背散射衍射技术(EBSD)结合表面形貌讨论了化学抛光机制,发现机加纹路消除后继续延长抛光时间,晶粒内高指数晶面(原子疏排面)会被优先抛光,从而在晶界处形成较深的沟槽,在晶粒内出现尖锐突起。

The polishing rate, surface topography, chemical composition and grain orientation of the chemical polishing process for niobium metal were analyzed to optimize process parameters. The mixed solution （hydrofluoric acid： nitric acid： phosphoric acid=1：1：2, volume ratio） was proposed as appropriate polishing reagents with rate equation h=29.359t^0.9247. Polishing for 6-15 rain can remove 154-360 μm of material using this solution, and roughness Ra and Nb205 layer thickness of polished surface is less than 0.65 μm and 10 nm, respectively. Meanwhile, the polishing mechanism was discussed using electron back scatter diffraction （EBSD） and laser scanning confocal microscope （LSCM）. We find that the outmost surface of over-polishing sample consists of many fine high-index planes which intersect each other to form sharp edges in grains or at boundaries.