The Anti-hydrogen Isotope Effect Of Ti-V-Cr Alloy

Usually, the isotope effects of metal-hydrogen systems indicate the different stabilities among the protide, deuteride and tritide of metals. They can be used in many fields such as hydrogen isotope recovery, enrichment, purification, and separation, etc. Therefore, they have been widely and deeply investigated for many years. However, the investigations were mostly related to normal isotope effects of Pd. In order to substitute for the expensive Pd and broaden the investigating fields of isotope effects, the investigation of inverse isotope effects are necessary.In this paper, the inverse isotope effects in Ti-V-Cr alloys were investigated systematically using protiume (H) and deuterium (D). The separation factor (aH_D) was used for characterizing the isotope effects quantitatively. The research contents and results were listed below.1) Kinds of Ti-V-Cr alloys were prepared by arc melting under argon atmosphere. Then the dependence of aH_D on e/? and the lattice constants were investigated. It was found that the structures of the alloys are BCC in a wide range of constitution. aH_D is dependent on e/? as parabolic for V 40 at%. Moreover, there are outstanding inverse isotope effects for e/?=4.6-5.2 (?H_D>1.3), and the maximum aH_D emerges at e/?=5.0 (?H-D=1.47). By the adjustment of vanadium content at e/?=5.0, ?H-D dependent on the lattice constants are separately investigated. The results indicated that ?H-D linearly decreased with the increase of lattice constants. On the other hand, the change of lattice constants caused by vanadium content is very tiny compared with that by e/?, but the change of ?H-D caused by vanadium content is larger than that by e/?. This means that the increase of e/? will lead to the decrease of ?H-D if the lattice constant is not considered. Based on the results above, we propose that e/? and the lattice constant can be used to appraise the practical Ti-V-Cr alloys for the handling of hydrogen isotopes.2) Ti30V4oCr3o alloy (e/?=5.0) was selected for further investigation, since it is typical in terms of the isotope effects according to the results above. The difference between the phase equilibria of H2 absorption and D2 absorption was investigated at different temperatures. The difference was characterized by the pressure-composition isotherms (p-c-T) intuitively, and it was quantified by the ratio of equilibrium pressures of H2 and D2, i.e. RP=PHzeq/PD2eq-It was found that the plateaus are inclined both for H2 and D2, and RP is changed with pressure. According to the unhomogenous constitution of Ti3oV4oCr3o alloy, and combined with the results of p-c-T, XRD, and DSC-TG, the calculation model of ?H-D was derived from RP, i. dn.It was found that the calculating ?H0-D agree with theexperiments. Moreover, according to this model, aH0-D will be constant approximately in a wide range of pressure, although RP is changed with pressure.3) The hydrogen isotope effects of Ti3oV4oCr3o and Ti1.0Cr 1.5V 1.7 alloys were investigated under different pressures, deuterium concentrations and temperatures. It was found that the dependence of ?h-D on pressure is insensitive in the pressure range between 0.1 MPa and 5 MPa. This result is accorded with the model above. Moreover, the increase of deuterium concentration led to the decrease of ?H-D, and the relationships between them can be quantitatively characterized aHD= 1.41 for Ti1.0Cr1.5V1.7. Usually, the dependence of ?H-D on temperature can be characterized by the harmonic oscillator model (HOM), and it can be simplified as lnaH-D= A+B/T. However, the dependence of ?H -D on temperature was complicated in this experiment. In 773-373K, the experiments agreed with HOM, but did not agree with the linear behavior. In 373-213K, the experiments agreed with HOM and the linear behavior well, and A=-0.733,B=333 for Ti3oV4oCr3o; A=-0.74,B=335, for Ti1.0Cr1.5V1.7. In 213-77K, there were great differences between the experimental ?H-D and calculated value of HOM. On the other hand, the results of DSC measurement indicated that the phase transitions are not related to the abnormal change of ?H-D at low temperature. It is needed to point out that ?H-D of Ti3oV4oCr3o and Ti1.0Cr1.5V17 alloy is equal to 2.31 and 2.29 at 213 K, respectively. Then the two alloys may be the hopeful candidates for hydrogen isotope separation, and even a potential replacer of Pd.4) The dependences of thermal desorbing properties of the hydrides and cycle absorbing behavior of the alloys on e/a and lattice constants were investigated, using SEM, EDS, XRD, and DSC-TG analysis. For this purpose, several alloys with different e/a and vanadium content were selected, i.e. Ti6oV4o, Ti4.5V40Cr15, Ti3oV4oCr3o, Ti50Cr50, Ti40V20Cr40, and Ti10V80Cr10. It was found that the unhomogenous constitution of the alloys may be caused by the addition of Cr according to the analysis of SEM and EDS, and it was also supported by the results of derivative TG. The results of XRD analysis for the hydrides showed that the lattices were expanded and the crystallinities were decreased with absorbing. The results of DSC-TG analysis for the hydrides showed that the desorbing peaks of H and D were moved to the lower temperature with the increase of e/? or the original absorbing amount, but not significantly influenced by the vanadium content and the type of hydrogen isotopes. The residual hydrogen amounts in the alloys were decreased with the increase of e/a, vanadium content and the original hydrogen amount at a certain temperature. The results of cycle experiments indicated that the decline of hydrogen storage amounts were mostly ascribed to the first three cycles, then the hydrogen storage amounts did not change obviously with cycling.