CNTs辅助球磨对Zr粉形貌和氧化性能的影响（英文）

Effect of CNTs-Assisted Ball Milling on Morphology and Oxidation Behavior of Zr Powders

研究了不同球磨时间条件下CNTs辅助球磨对Zr粉形貌和氧化性能的影响。采用XRD和SEM分析了球磨过程中Zr粉的物相组成和形貌演变,采用热重(TG)法评估了Zr粉的氧化性能。结果表明:添加CNTs辅助球磨对Zr粉的物相组成没有影响,但是会影响Zr粉的形貌和氧化性能。不添加CNTs时,随着球磨时间的增加(1~3 h),Zr粉粒径持续减小,球磨3 h后,Zr粉粒径由十几微米减小到2~3μm。添加CNTs辅助球磨后,Zr粉的颗粒细化过程滞后,球磨初期(1~2 h),Zr粉粒径没有显著变化,直到球磨时间延长到3h时,Zr粉粒径才开始明显减小。这是因为CNTs在Zr颗粒表面的黏附和CNTs在Zr粉中的团聚阻碍了磨球对Zr颗粒的机械冲击和破碎作用。与直接球磨Zr粉相比,当所得Zr粉粒径相差不大时,添加CNTs辅助球磨使Zr粉的起始氧化温度和峰值氧化温度降低了11~37℃,这是因为CNTs的良好导热性促进了Zr粉氧化过程中的传热。另一方面,球磨时间少于2 h时,Zr/CNTs混合物中Zr粉的氧化增重量比纯Zr粉的增重量略有降低,但球磨时间超过2 h时,这种趋势出现反转。前者是因为短时间球磨时,CNTs引起Zr粉的局部团聚,阻碍了团聚体中Zr粉与氧气的接触,并且混合物中的Zr粉颗粒还没有被明显细化,这都降低了Zr粉的氧化程度;随后的反转趋势是因为球磨时间增加后,混合物中的Zr粉开始明显细化,促进了其氧化反应的进行,但是纯Zr粉由于颗粒尺寸提前细化而发生了显著的自发氧化,降低了活性Zr的含量。

Morphology evolution and oxidation behavior of Zr powders milled with and without CNTs for different time were compared. XRD and SEM were used to determine the phase composition and morphology of obtained Zr and Zr/CNTs powders. Thermogravity（TG） analysis was applied to evaluate the thermal oxidation behavior of Zr and Zr/CNTs. Results show that the phase composition of Zr after milling is not influenced by adding CNTs,but the morphology and oxidation behavior of Zr are influenced. In case of milling without CNTs,particle size of Zr continues to reduce from more than 10 μm to about 2~3 μm when milling time increases from 1 h to 3 h. In case of CNTs-assisted milling,the particle size reduction of Zr is not obvious until milling time is prolonged to 3 h. This is because those CNTs adhered on the surface of Zr or CNTs-induced agglomerations among Zr prohibit the mechanical impact and fracturing effects of milling balls on Zr particles. Compared with direct milling of Zr,when the obtained Zr has similar particle size,adding CNTs lowers the onset oxidation temperature and peak exothermic temperature of Zr powders by 11~37 °C,depending on milling time. This is ascribed to the high heat conductivity of CNTs which favors heat transfer between Zr particles. At the same time,oxidative mass gain of Zr/CNTs is slightly lower than that of the corresponding pure Zr when milling time is less than 2 h and then this trend reverses. The initial decrease in mass gain of Zr in Zr/CNTs mixtures under shorter milling time is related to two factors： one is CNTs-induced agglomerations of Zr,which prohibits the contact of Zr with oxygen and thus decreases the degree of oxidation,and the other is the delayed particle size reduction of Zr in Zr/CNTs mixtures. The subsequent reversal in mass gain for pure Zr and Zr/CNTs is due to the positive effect of particle size reduction of Zr in Zr/CNTs on its thermal oxidation just began,while the spontaneous oxidation-induced negative effect for well-refined pure Zr has become very obvious.