Surface Modification And Anti-toxicity Of ZrNi-based Hydrogen Storage Alloys

Ti0.1Zr0.9Ni0.6Co0.4 alloy is considered to be a promising hydrogen isotope gas treatment material with its characteristics of large hydrogen absorption capacity at room temperature,low hydrogen absorption equilibrium pressure,moderate hydrogen release pressure,and can realize hydrogen isotope gas efficient extraction and recovery.However,in the hydrogen isotope treatment process,the material is easily poisoned by the impurity gas contained in the system and fails.Therefore,in order to meet the practical application requirements of hydrogen isotope gas treatment,it is necessary to improve the anti-poisoning performance of the alloy.In this thesis,the anti-impurity gas poisoning performance of the alloy is improved by coating the surface of Ti0.1Zr0.9Ni0.6Co0.4 alloy with a hydrogen selective PdCu alloy film.The PdCu film preparation method was studied.The morphology of the PdCu film was systematically analyzed by SEM,EDS,XRD,ICP-AES and other methods.The effect of the coating parameters on the film morphology was studied,and the optimal coating process was obtained.The anti-toxicity properties of the alloy material after anti-poisoning treatment were studied.The specific conclusions are as follows:(1)Pd film and Cu film were sequentially plated on the surface of the alloy by electroless plating to form a PdCu composite film,and the preparation process of the composite film was studied to finally optimize the preparation process of the composite film.The optimum process conditions for the Pd film on the surface of the sheet-like TiZrNiCo alloy are as follows:sensitizating and activating three times,forming an active layer that adheres firmly and uniformly;based on this catalytic substrate,1.0 g/L PdCl2 is the main salt,and the reducing agent N2H4·H2O is 0.0122 mol/L.The palladium plating reaction is carried out by means of slow dropping.The plating time should not be less than 40 minutes to ensure a dense uniform Pd layer.The most important experimental control parameter of the Cu-plated film on the surface of TiZrNiCo alloy is the pH value of the bath.The main salt is 5.24g/L CuSO4·5H2O,and the reducing agent is CHOCOOH0.0256mol/L.The proper amount of NaOH(40%)is required to adjust the plating.The pH of the solution is 12.5 to ensure that the bath is stable and that Cu is uniformly deposited on the surface of the substrate at an appropriate rate.The study found that the deposition method of the film is closely related to the morphology of the alloy substrate.The deposition process of Pd and Cu on the surface of the sheet alloy conforms to the kinetic model of "self-catalytic deposition on hemispherical surface".(2)the alloying heat treatment process of PdCu composite coating coated by electroless plating was optimized.The phase structure of the PdCu alloy film was affected by the heat treatment time and the initial Pd and Cu element ratio of the film.A Pd-Cu bimetallic film was deposited on the surface of the alloy particles in a ratio of Pd:Cu=60:40,and heat treatment at 673K for 8 hours allowed the Pd-Cu alloy to be a bcc phase layer..It was found that the elements of the film layer interact with the substrate during heat treatment.EDS analysis showed that the main element of the diffusion layer was Pd and Zr.(3)The TiZrNiCo alloy particles before and after surface coating with PdCu film were tested for anti-poisoning performance,and it was found that the anti-toxic properties of the coated materials are obviously improved and the uncoated 0.58wt.%is increased to 1.7wt.%when hydrogen absorption in the H2 standard gas containing impurity gas.The results showed that the PdCu film coating obviously improved the toxicity resistance of the alloy.After repeated desorption of hydrogen in the H2 standard gas containing 3 different concentrations of impurity gases,the hydrogen absorption capacity of the coated PdCu film decreased,but the capacity could basically be stable after 6 cycles.Through the SEM analysis of the alloy after the absorption and discharge of hydrogen,it was found that the decrease of the alloy properties is due to the cracking and falling off of the PdCu film caused by the pulverization of the alloy during the process of hydrogen absorption and discharge.By comparing the performance of the anti toxic material to the absorption and discharge of hydrogen with different concentration of impurity gas,it was found that the toxic effect of O2 on the alloy material is prominent.With the increase of the content of O,the attenuation of hydrogen absorption of the material increases and the attenuation amount after repeated cycles is more significant.