The Isotope Effect Of Erbium Hydride Research

In order to develop metal hydride technology for storing and processing deuterium and tritium, H/D/T isotope effects on the thermodynamics and kinetics of erbium hydrides are under investigation.A special designed Sievert intrument with high tempeartue sample chamber for measuring gas sorption and desorption properties of metarials, especially for pressure-composition-temperature (PCT) charactertics of metal tritide materials are developed. The temperature limitation problem of commercial intrument was solved successfully. And with the using of this instrument and some experimental method, such as the Pressure Dependence Method (PDM), Thermal Desorption Spectroscopy (TDS), and X Ray Diffraction (XRD), the thermodynamics and kinetics of erbium reacts with protium, deuterium and tritium are determined.The pressure-composition-temperature (PCT) and activation characteristics of deuterium and tritium from erbium at different temperature are measured. The isotherms show a wide and straight plateau, and there was no significant hysteresis effect. Based on the measured PCT relations, the change of enthalpy and entropy for Er-D and Er-T reaction were calculated from the Van’t Hoff plots. In the region of atomic ratio H/Er from0.6up to1.6, the enthalpy and entropy decreases with the increasing of the hydrogen concentration. It can be seen that the enthalpy and entropy of ditritide is under the dideuteride with the same atomic ratio, shows a slight thermodynamic isotope effects. The calculated value of enthalpy and entropy during the formation of the ErD1phase are equal to-199.7±7.3(kJ·mol-1D2) and-143.4±7.2(J·mol-1·K-1D2), and the value of ErT1phase are equal to-209.3±3.3(kJ·mol-1T2) and-152.9±3.2(J·mol-1·K-1T2), respectively. The enthalpy and entropy of ErD1phase was computed from the kinetics curve of dihydride phase, and the value are equal to-187.9±15.0(kJ·mol-1H2) and-134.2±11.5(J·mol-1K-1H2), respectively. It’s shows that thermodynamics parameters of ditritide are the largest. This means that the erbium dihydride of larger mass number hydrogen isotopes with a little better stability according to the thermodynamics charactertics.Utilizing the pressure dependence method (PDM), the pressure changes during the process of erbium absorbing and desorbing protium, deuterium and tritium were investigated at673K up to1123K, and then the pressure-time curve was ploted. The calculated results shown that the reaction of erbium with hydride can be described by the first-order rate law. Some normalized models ware used for kinetics characteritics analysis, and the rate constant of each reaction is derived, and then the activation energy of each conditons is derived with Arrhenius equation. It’s show that the larger mass number hydrogen isotopes having a higher activation energy in the absorption reaction of solid-solution phase up to dihydride phase. On the contrary, the desorption activation energy of erbium dihydride is under the dideuteride slightly. This means that the dideuteride with a little better thermal stability in compared with dihydride, but the difference is negligible.In order to compare the thermal stability of erbium hydrides, deuterated and tritide more accurately, their thermal desorption spectroscopy (TDS) are measured with the using linear temperature programmed experimental method. The results show that the peak position of hydrogen increased with raising the heating rate. However, there was no significant diffence in the TDS peak position of erbium hydride, deuteride and tritide. In other words, the thermal stability difference of erbium hydrides is negligible. The results are not difficult to understand. It’s can be explined by interplay of the slinght isotope effects in the thermodynamics and kinetics at the beginning.The peak position of TDS reflects the difference of activation energy, and each phase of metal hydride had difference desorption activation energy. Therefore, the relations of TDS peak position and erbium hydride phase was established successfully by multispectralanalysis method, and then the activation energy of α+β、βTet、βOct、β+γ phase for trihydride and trideuteried powder, and ditritide film are calculated with the using Redhead’s kinetic model. It’s shows than the results deriving from TDS and PDM have good coincidence in kinetics isotope effects. The erbium tritide film shows good thermal stability with high activation energy.From what has been discussed above we may safely draw a conclusion that the erbium dihydride powder had slight isotopes effects and good thermal stability. For the purpose of well understand the properties of erbium hydride film, a number of molybdenum-supported erbium thin films grown by electron beam evaporation were loaded simultaneously in a PCT apparatus at different temperature, and the impact of outgassing and hydriding temperature on the hydriding rate, hydride phase, crystal structure and texture are under investigation. It’s shows that the outgassing temperature have serious impact on reacting rate, but the impact of hydriding temperature is not very obvious. X Ray Diffraction shows that all the hydride film had higher preferred orientation of (111), and the proportion of (111) increased with rasing hydriding temperature. Furthermore, the experment shows that the impact of gas evacuating temperature are notable, when the gas evacuating temperature lower than trihydride thermodynamic equilibrium, trihydride phase formation and the thermal stability of decreased, and the film itself can decompose along with the formation of erbium oxides in atmosphere, and this transferable charactertics is a new application property of erbium hydride needs to be developed.A major significance of this study is that kinetic and thermodynamic parameters were determined for erbium dihydride thoroughly. The results Presented in this paper provide the basis for fundamental understanding and further application of erbium hydride.