外部吸收法脱除金属钛、锆中的氧

Solid State Deoxidation of Metal Ti and Zr using External Gettering

金属钛、锆具有较强的氧亲和力,在冶炼、加工过程中易增氧导致材料性能下降。本研究采用了一种简单、易行的固态脱氧方法——外部吸收法,对金属钛、锆进行脱氧,并考察了脱氧过程中各种因素对脱氧效果的影响。研究结果表明,在Ca-CaCl_(2)脱氧体系下,脱氧温度为900℃,脱氧时间24 h,CaCl_(2)和金属Ti,Zr的质量之比为8∶1,金属Ca加入量为其在CaCl_(2)熔盐中溶解度的200%,并添加CaCl_(2)质量5%的KCl作为助熔剂,脱氧方式为金属样品、金属Ca,CaCl_(2)直接混合的条件下,金属Ti,Zr的氧含量分别由起始的670×10^(-6)和800×10^(-6)降至脱氧后的120×10^(-6)和70×10^(-6)。在Ca-CaCl_(2)脱氧体系中,氧会在熔盐中不断积累使氧的活度提高,脱氧效果产生波动。本文提出通过引入比Ca更亲氧的金属Y,来降低熔盐中氧的活度,改善Ca-CaCl_(2)体系脱氧效果不稳定的问题。实验结果表明,Y在脱氧过程中会生成Y_(2)O_(3)并和过量金属Y组成Y-Y_(2)O_(3)平衡,Y-Y_(2)O_(3)平衡可以将熔盐中氧的活度“锚定”在较低水平,从而将Ti,Zr样品的氧含量稳定控制在100×10^(-6)以下,改善了Ca-CaCl_(2)体系的脱氧效果。

Low oxygen content and high purity Ti and Zr were the key materials in laser components,large-scale integrated circuits,hydrogen isotope treatment,high temperature alloys and other fields.The physical and chemical properties of Zr and Ti were very sen-sitive to the interstitial oxygen.Because high oxygen content can easily lead to many problems or even safety risks,such as embrittle-ment and hardening of materials,defects of evaporative coating and deterioration of hydrogen absorption and discharge properties.However,both of Zr and Ti had strong oxygen affinity and high solubility of oxygen.During smelt,hot working and working condition,the oxygen concentration will inevitably increase which will degrade the material performance.Currently used high purity metal prepa-ration technology,such as vacuum EB-melting,vacuum arc melting,electrolytic refining cannot achieve the in-depth deoxidation of ti-tanium and zirconium.Therefore,high oxygen content had always been a difficult problem in the process of producing high purity tita-nium zirconium.To solve the problem,a simple solid state deoxidation method—“external gettering process”was employed to deoxi-dize Ti and Zr.The Ca-CaCl_(2)system a typical external gettering system was employed.Because it had strong deoxidation ability,good kinetic conditions and stable physical and chemical properties,which was suitable to the deoxidation of Ti and Zr.The influence of var-ious factors on deoxidation effect,such as temperature,deoxidation time,the mass ratio of CaCl_(2)to metal specimens,deoxidation mode during the deoxidation process were investigated systematically by chemical equilibrium technique.In addition,the effect of ad-ditives on deoxidation capacity of the Ca-CaCl_(2)system was also discussed.It was shown that the thermodynamic and kinetic conditions of external gettering deoxidation were opposite to each other.Therefore,the selection of actual deoxidation temperature needed to take into account the thermodynamic conditions and dynamics,find a balance point that can ensure strong deoxidation capacity and relative-ly short deoxidation time.The single factor experimental results showed that under the condition of that,in the Ca-CaCl_(2)deoxidation system,the deoxidation temperature was 900℃,the deoxidation time was 24 h,the mass ratio of CaCl_(2)to metal Ti and Zr specimens was 8∶1,the amount of Ca added was 200%of its solubility in CaCl_(2)molten salt,the amount of KCl added was 5%of CaCl_(2)molten salt,all the reagents were directly mixed,the oxygen concentration of Ti and Zr could be reduced from 670×10^(-6)and 800×10^(-6)to 120×10^(-6)and 70×10^(-6),respectively.However,in Ca-CaCl_(2)deoxidation system,oxygen would accumulate in molten salt to increase the oxy-gen activity.When the CaO saturated the CaCl_(2)molten salt,the deoxidation ability of Ca-CaCl_(2)system decreased significantly so the deoxidation effect of Ca-CaCl_(2)system fluctuates obviously.To improve the deoxidation ability of Ca-CaCl_(2)system further,the element which had stronger oxygen affinity was introduced into the system to reduce the activity of deoxidation product CaO.Thermodynamic af-finity for oxygen of Ca,Ga,Dy,Er,Y and other rare earth metals was compared and analyzed.The results showed that metallic Y had the strongest oxygen affinity and could form Y-O solid solution easily which was benefit to reduce the oxygen potential.Meanwhile Ycould coexist with Ca and CaCl_(2)stably under the deoxidation temperature.So metallic Y was employed to construct a Ca-Y-CaCl_(2)combined deoxidation system to regulate the oxygen activity in molten salt and achieve ultimate deoxidation of Zr and Ti.The experi-mental results showed that without the addition of metallic Y,the oxygen content of Ti,Zr was positively correlated with the added amount of CaO and finally reached or even exceeded the theoretical value of Ca-CaO equilibrium.When metallic Y was added and the mass of Y was 40%of the sum of the mass of Ti and Zr specimens,this trend was evidently suppressed.Even the added amount of CaO was 1.25 g,100%of its solubility in CaCl_(2)molten salt,the oxygen content of Zr and Ti was stabilized around the theoretical value of Y-Y_(2)O_(3)equilibrium.This verified that metallic Y did have the“anchoring effect”on oxygen activity in molten salt and could maintain the oxygen activity at a low level.X-ray diffraction(XRD)analysis of the film and substrate of reacted Y showed that Y_(2)O_(3)generated dur-ing deoxidation process and grew inward to formed Y-Y_(2)O_(3)equilibrium with residual Y.The Y-Y_(2)O_(3)equilibrium could“anchor”the ox-ygen potential of the system at an extremely low level of 1×10-40~1×10-45Pa,and the oxygen content of Ti and Zr specimens would be stabilized less than 100×10^(-6)and with the minimum of about 30×10^(-6).Thus,the deoxidation capacity of Ca-CaCl_(2)system was stabilized and improved.The deoxidized metallic Zr and Ti could satisfy the use requirements of optical coating materials,high K gate dielectric materials,hydrogen isotope treatment materials,high temperature alloys and other fields.