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4694 |
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Tubular asymmetric La0.6Sr0.4Co0.8Fe0.2O3 oxygen transport membranes prepared by low pressure plasma spraying and supersonic air-gas plasma spraying |
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Shaopeng Niu* / The department of material science and technology, South China University of Technology, China Kesong Zhou / Guangzhou Research Institute of Non-Ferrous Metals, China Liping Xu/ Guangzhou Research Institute of Non-Ferrous Metals, China Changguang Deng/ Guangzhou Research Institute of Non-Ferrous Metals, China Min Liu/ Guangzhou Research Institute of Non-Ferrous Metals, China Jie Mao/ Guangzhou Research Institute of Non-Ferrous Metals, China |
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It is already known that some types of oxides with perovskite structure provide a mixed conductivity behavior of electronic and oxygen ionic. Dense membranes made from such mixed conduction oxides can transfer oxygen ions through vacancies in the oxygen site of crystal lattice and thus can be used to separate theoretically pure oxygen from air at elevated temperatures (especially above 700). Owning to the oxygen transport feature, it is quite remarkable that the dense membranes are exhibiting a promising future in some oxygen-related catalytic processes, such as natural gas partial oxidation in producing syngas, carbon dioxide and nitric oxide decomposition, as well as hydrolysis hydrogen production. Despite those potentials, the practical application of oxygen transport membrane (OTM) is proceeding slowly due to the difficulty of meeting some performance requirements, chief among these are high oxygen permeability and thermal stability while the two are always incompatible in one oxygen transport material. Besides, brittleness, low mechanical strength, and high temperature joining and sealing problem are also critical factors that limit the application of membranes. In view of this, recent studies suggest that preparing asymmetric membranes with porous metallic supports can effectively improve the mechanical properties of the membranes. The thickness of membranes can thus be largely reduced, so it is helpful for increasing oxygen permeation due to oxygen bulk diffusion. Furthermore, metal supports also have an advantage to join and seal under high temperature. However, since the sintering atmospheres of metal supports and perovskites differ wildly (metal should be performed in reducing atmosphere in order to avoid oxidation, while perovskites must be sintered in air due to their reducibility), the commonly used wet chemical methods, such as tape casting and screen printing, are no longer suitable for preparing metal supported OTMs. Newly developed plasma spraying-physical vapor deposition (PS-PVD) technique provides an effective and more efficient avenue for preparation without sintering. By means of high-powered plasma gun and operating pressures down to 200Pa and below, the process leads to the formation of a laminar plasma plume with extended dimensions and produces a hot supersonic gas stream, so that a thin, dense and well-adherent ceramic coating can be deposited rapidly. And successful preparation has already been reported by researchers not long before. Another method, high energy supersonic air-gas plasma spraying (SAPS) technique is also a good candidate for preparation. Due to the special three-electrode spray gun with enhanced capacity of arc compression and fire gas explosion effect, an ultrahigh temperature and supersonic plasma jet can also be achieved. Especially, the process does not require a vacuum or expensive plasma gas (only use compressed air plus minor fire gas additions), so if practical, SAPS might be more promising for actual application because of its equivalent ability to produce rapidly dense ceramic coatings but cost less. |