Investigation On Characteristics Of Composite Metal Hydrogen Separation Membranes With Discrete Structure Surface

Hydrogen is one of the most promising clean energy carriers in this century. Therefore, how to obtain the high purity hydrogen is one of the major problems to solve urgently in hydrogen technology. Membrane separation technology is a viable solution. The existing results show that the hydrogen separation composite membrane, in which non-noble metals are adopted as substrates, is most likely to become the important energy material during large-scale hydrogen separation process. However, the present dense structure composite metal membrane with high consumption of covering precious metal still suffers high cost and short life because of the protective film burst and separated from substrate, or even failure. In order to solve the above problems, a special discrete structure composite metal membrane for hydrogen separation was utilized as sustitute. Various advantages of discrete structure composite metal membranes in comparison to the dense structure are studied by combining the simulation and experimental methods at the macroscopical and microscopic scale.First of all, based on the heat transfer enhancement mechanism, the general formula of equivalent hydrogen permeability coefficients was deduced by introducing the shape factor and volume fraction, and calculated the equivalent hydrogen permeability coefficients of different structure palladium composite membranes. Compared to dense structure composite metal membrane, the discrete structure composite metal film not only has a high hydrogen permeation performance but also reduced effectively the usage of palladium materials. Then, thermal stability of different composite membranes was analyzed by the finite element analysis method, the thermal stress distribution of different embedded shapes, embedded depth, particle spacing was studied to verify the discrete structure composite membrane at high temperatures maintain the structure stability and had a longer service life. Furthermore, the discrete structure composite metal membrane was prepared by the high pressure cold spraying technology developed by our laboratory. The membrane surface morphologies and deformation characteristics were observed by electronic scanning electron microscopy(SEM) when the particles impacted on substrate surfaces. The feasibility of preparing discrete metal composite membranes by cold spraying was proved. Finally, by the molecular dynamics simulation method, the microscopic process and characteristics of larger and oversize palladium clusters deposited on tantalum substrates were studied, the influences of different factors on the clusters deposition process, the interface structure and clusters structure reforming were analyzed. At the same time, interface alloys formation and the change laws of clusters structure reconstruction during the deposition process were found.When the initial substrate temperature and the cluster impact speed were increased to a certain value, the whole cluster was embedded inside the substrate with an ellipsoid or cone structure by molecular dynamics simulations. During the collision process, atomic migration, mixed, diffusion and replacement emerged which resulted in the alloy compound formation on the the interface of the cluster and substrate. In the cold spray experiments, the elements of particle and substrate coexisted in the interface and impacted edge zone through the EDS analysis. The MD simulation results are consistent with the experimental results. Meanwhile, there are some cluster atoms aggregating around the interface, which is similar to the metal jet phenomenon occurring in the experiments.The discrete structure surface composite metal membrane with high hydrogen permeability and thermostability was studied by the theoretical analysis, macroscopical numerical simulation, respectively, in the thesis. Moreover, the discrete structure composite metal membrane can be prepared successfully by the cold spray. The microscopic deposition process, surface properties and structure evolution of the palladium particles collision on the tantalum substrates were further analyzed by molecular dynamics simulations, the simulation results and the experimental observations were valided each other. The superiority of the discrete structure surface composite metal membrane was proved from various angles, the cold spraying preparation parameters of discrete palladium metal composite membranes with superior hydrogen permeability performance and stable thermal structure can be searched, and which provides more realistic guid for preparing discrete palladium metal composite membranes.