Preparation And Investigation Of Mg-Ni Composite Films

Mg-Ni based films prepared by sputtering, thermal evaporation and other methods exhibit advantages in hydrogen storage for being easy to control the micro structure. In addition, Mg-Ni films covered with PdAg layer show improved property in the industry of hydrogen isotopes separation. Mg-Ni-PdAg composite films and Mg-Ni multilayer films were prepared by pulsed laser deposition and DC magnetron sputtering. The microstructure, surface and cross-sectional morphologies of the films were investigated by X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), infrared spectra, atomic force microscopy (AFM) and scanning electron microscopy (SEM). The relationship between the microstructure and property of the films has been studied in this work.The synthesis method of Mg-Ni-PdAg composite films was studied by using different processes by pulsed laser deposition. It has been found that the Mg-Ni-PdAg composite film could be synthesized by alternately deposition of stitching target. The film is smooth, and the element composition is 64.87%(Mg),25.79%(Ni),3.93% (Pd).5.41%(Ag).Mg-Ni-PdAg sandwiched film and multilayer film were prepared by DC magnetron sputtering. The main phase of the composite film is Mg2Ni, however, there is a little MgNi2 phase in the Mg-Ni-PdAg multilayer films. The hydrogen coefficient was tested by electrochemical methods. It has been found that the diffusion coefficient in the Mg-Ni-PdAg multilayer film is much larger than that in the sandwiched film. It may attribute to the existence of quantities of boundries. The diffusion coefficient of hydrogen is 2.71x10-16 cm2/s in the sandwiched film, and 1.26×10-14 cm2/s in multilayer film.Mg-Ni multilayer films were deposited by sputtering Mg and Ni targets alternately. The substrate temperature influences the microstructure of the films greatly. The film deposited at 298 K exhibits multilayered structure, while the film shows nanocrystalline/amorphous composite structure at the deposition temperature of 473 K. The optical properties between hydrogenation/dehydrogenation states of the films were performed using spectrophotometer in visible light region. The film deposited at 473 K can switch from mirror-like metallic state towards brownish yellow transparent state under 0.6 MPa H2 at 298 K, and the optical transmittance modulation reaches up to 20% both at a wavelength of 770 nm and IR region, while the film deposited at 298 K exhibits low optical change, and the optical switching behavior can hardly be found.The bilayer period has an influence on the microstructure and property of the nanostructured Mg-Ni multilayer films. The results show that the adjacent Mg and Ni layers inter-diffuse completely and form amorphous Mg-Ni phase at the alternate sputtering time of 5 s. The degree of diffusion alloying decreases with the increase of the bilayer period. The composite film and the multilayer film with the bilayer period of 52 nm exhibit optical switching properties between hydrogenation and dehydrogenation states. The optical transmittance of the hydrogenated films also decreases with the bilayer period.