Ti_(40)Zr_(22)V_(24)Cr_(8)Mn_(6)非蒸散型吸气剂低温激活性能研究

Low-Temperature Activation Performance of Ti-Based Non-Evaporable Getter

使用电弧熔炼法制备了Ti_(40)Zr_(22)V_(24)Cr_(8)Mn_(6)合金,并通过机械破碎和模压成型法获得了多孔块状吸气剂。X射线衍射(XRD)结果表明Ti_(40)Zr_(22)V_(24)Cr_(8)Mn_(6)合金是由体心立方(bcc)相和C15 Laves相组成的双相结构,扫描电镜(SEM)图像显示其中的C15 Laves相呈簇晶状弥散分布于具有bcc相的Ti基固溶体中。使用原位X射线光电子能谱(XPS)分析了吸气剂表面活性元素在150~450℃的价态变化,结果发现Ti_(40)Zr_(22)V_(24)Cr_(8)Mn_(6)吸气剂表面钝化层中的Ti,V,Cr,Mn元素可在350℃时被完全还原为金属态;当激活温度升至450℃后,样品表面氧化物含量低至1.16%,具有较高的低温激活效率。在相同条件下,使用定压法对Ti_(40)Zr_(22)V_(24)Cr_(8)Mn_(6)和Zr_(56)V_(37)Fe_(7)吸气剂的室温吸氢性能进行测试,结果显示在250℃烘烤3 h条件下,前者的吸气速率是后者的约1.4倍;接着在400℃保温30 min的条件下对吸气剂进行再激活,此时前者的吸气速率是后者的约1.2倍。可见Ti_(40)Zr_(22)V_(24)Cr_(8)Mn_(6)吸气剂具有优良的室温吸氢性能,这种Ti基吸气材料体系的突破为发展新一代低温激活材料提供了有效参考。

With the development of vacuum technology,non-evaporable getters have been widely used in sealed-off devices.In many of these devices,the getter is required to work or activate under relatively low temperature conditions,to reduce risk of damaging heat sensitive components surrounding the getter,and to reduce outgassing from the components or walls nearby the getter.For these devices,Zr_(56)V_(37)Fe_(7) nonevaporable getters can be activated at 450℃for 10 min or at 300℃for 90 min,the degree of this activation is suitable for applications that do not need high gettering rate.On the other hand,Zr_(56)V_(37)Fe_(7) getter have been developed by the European Nuclear Center (CERN) for the project of the Large Hadron Collider (LHC).These kinds of Ti-based getters have high hydrogen adhesion coefficient and low activation temperature,which can be fully activated at only 180℃for 24 h,and are often used in vacuum envelopes with space and shape restrictions.Although this kind of getter has outstanding advantages,the shortcomings of its small sorption quantity and high production cost restrict its application in many directions.This study is expected to provide valuable information for the better development of Ti-based bulk getters,and Ti_(40)Zr_(22)V_(24)Cr_8Mn_(6) pill-shaped getter was prepared.X-ray diffraction analysis(XRD),microscope analysis,scanning electron microscope (SEM) and energy dispersive analysis (EDS) were used to characterize the phase structure,surface morphology and surface composition of the alloy.From XRD pattern,it was clear that two distinct crystallographic phases coexisted in the alloy,namely Ti-based solid solution phase with body-centered cubic(bcc) structure and C15 Laves phase with AB_(2) type cubic structure.Using Rietveld analysis,the weight fraction of bcc and Cl5 phases were determined to be 55.1%and 44.9%,respectively.SEM image showed that there were three different parts in the alloy,namely black colonies (A),gray matrix(B) and white precipitates (C).In this alloy,micron-sized white precipitates were scattered throughout the matrix,and black colonies presented a broken fishbone structure,forming three-dimensional (3D) framework.It was reported that the microstructure of“Laves phase related bcc solid solution”displayed as a kind of dendritic phase distributed in an interpenetrating matrix.Furthermore,it was pointed out that 3-D interpenetrating Laves phase worked as a catalyst for bcc phase which had a high absorption hydrogen capacity.Insitu X-ray photoelectron spectroscopy (in-situ XPS) was used to investigate the temperature dependence of Ti_(40)Zr_(22)V_(24)Cr_8Mn_(6) non-evaporable getter material,and the results showed that the reduction of Ti,V,Cr,Mn could be completed,while Zr still contained a small amount of oxidation state at 350℃,which meant that the reduction rate of Zr in this temperature range as relatively slow.After activation at 450℃,a small amount of zirconia still existed on the surface.Therefore,to complete the activation of the getter,methods of appropriately extending the holding time or slightly increasing the activation temperature could be used.Dynamic sorption method was used to test the H_(2) sorption performance of the getter,and the room temperature hydrogen absorption performance of Ti_(40)Zr_(22)V_(24)Cr_8Mn_(6getter) was compared with Zr_(56)V_(37)Fe_(7) getter under the same preparation process and test conditions.The results showed that the hydrogen pumping speed of the former was about 1.4 times that of the latter under the condition of baking activation (250℃,3 h).Further reactivated the getter at 400℃for 30 min,the hydrogen pumping speed of the former was about 1.2 times that of the latter,which could be seen that Ti_(40)Zr_(22)V_(24)Cr_8Mn_(6) getter had excellent low-temperature activation characteristics.This breakthrough in Ti-based getter material system provided effective information for the development of a new generation of low-temperature activation materials.