Titanium And Hafnium Alloy Absorption And Desorption Of Deuterium Behavior And Phase Transitions

Based on adulteration alloying on Ti, TiHfx (x=0.13,0.26,0.52,1.03) were designed and prepared on electromagnetic levitation melting system for improving the capacity of hydrogen storage in the titanium metal by expanding the lattice parameters. Then, the thermodynamics, structural changing during desorbing and dynamics of TiHfx-D system were studied, a thermodynamic model was established and the mechanism of the alloys absorbing deuterium dynamic was deduced.The homogeneity of the alloys was proven by ICP-AES analysis. The cell volume of the alloys expands with the doping hafnium, however, the a-phase of the titanium basement is reserved in the alloys without any other phase. The dependence of the lattice parameter on the component of the alloys doesn't obey linearity, the deviation increasing with a larger Hf/Ti.The P-C-T curves of TiHfx-D system markedly differ from H-Ti or H-Zr system though they belong to the same group. The P-C-T curves of TiHfx-D system have a sharp starting but a smooth end, so slopes display. From the P-C isotherms, it could be found that equilibrium pressure of the deuterides at room temperature rise when Hf/Ti ratios enlarge in Ti-Hf alloys. The thermodynamic characteristics of Ti-Hf alloys deuterides are closer to those of H-Hf system than H-Ti system, which means that it's the Hf metal that dominates the thermodynamic feature of Ti-Hf alloys.Titanium deuterides have the f.c.c. lattice structures while Hafnium deuterides have the f.c.t. ones at the room temperature. The TiHfx-D systems all are f.c.t. structures when x equal 0.13,0.26,0.52 or 1, which means Hf adulteration in Ti stabilized the f.c.t. structure at the room temperature. Hf adulteration in Ti has remarkably reduced the lattice expansion, which will maybe ease the embrittlement of H-Ti system.According the higher-order multiplateau model of metal-hydrogen system, the occurrence of many plateaus is a consequence of progressive disorder of the interstitial hydrogen. A collective parameter, which involves the same number of degrees of freedom as the interstitial hydrogen, is introduced into the equation of state as a measure of the degree of disorder. The calculated curves are in good agreement with experimental results measured in the temperature 873 K.The high temperature in situ XRD technology (HTXRD) was used to research the structural evolvement during deuterium desorbing. A metastableγ'-phase was found when heating TiHfx deuterides. Theγ'-phase becomes stabler when Hf content raised. However, theγ'-phase will transfer toα-phase after it cooled to the ambient temperature. Theε-phase rises at the room temperature when Hf contents of TiHfx-D were lifted to 21 at.% and the temperature region ofε-phase occurring will extend with Hf contents ascend. When Hf/Ti rises, the emergence temperature ofδ-phase moves up simultaneously, but its discomposing temperature is hardly effected, between 773 and 813 K all the time. Noα-phase appears during the deuterides decomposed except the TiHf0.13-D. When deuterium in TiHfx-D mostly released at higher temperatures, Oxides were observed and the TiHfx with a greater Hf/Ti were easily oxidized. At the most heating temperature 1123 K only the oxide diffraction peaks were found in the XRD patterns. The reason is powder reunited at the high temperature and an oxide layer coats the surface of powder. The crystallinity ofα-phase and oxides after cooling to the ambient temperature proportions with the Hf/Ti ratios of TiHfx. Hafnium deuterides take onδ+εdouble phases, but theε-phase dominates. Between 723 and 773 K theε-phase hafnium deuteride transform to 8-phase completely. It is worth noting thatγ'-phase doesn't appear during degassing.The constant volume-changing pressure technology was used to study the kinetics of TiHfx absorbing deuterium gas. The common properties of TiHfx deuteration kinetics include that the initial velocity has a maximum, then decreases with time. The equation pressure of the deuterides move up when the temperature rises up. The difference of their kinetic behaviors is remarkable. The temperature 673 K is a boundary to separate the otherness. Over the 673 K, aα→β→δtwo times phase transformation takes place. But, onlyα→δphase transformation occurs below 673 K. This phenomena confirm that the eutectoid phase transformation of TiHfx-D system takes place around 673 K. The deuteration dynamic curves of hafnium have a different form from TiHfx. No inflexion was found near the 673 K because all the test temperatures are under the eutectoid temperature of H-Hf system.The temperature and Hf/Ti simultaneously influence the rate constants of TiHfx and Hf absorbing deuterium gas. The deuteration rate constants of TiHf0.13 and TiHf0.26 decrease at first and then increase during the temperature raised. However, the deuteration rate constants of TiHf0.52 and Hf descend when heating, no inflexion appears. The deuteration rate constants have a watershed at the 673 K.According the para-linear model, the deuteration kinetics of TiHfx was presumed as the diffusion-controlled mechanism.