CVD Preparation of Hydrogen Semipermeable Metallic-Ceramic Membrane Composites

本研究试图开发一种膜，用于高 从气体混合物中分离氢气的温度。为 在高温应用中， 必要的，钯和钯银合金金属 膜对氢表现出最高的选择性。 的 这些金属膜的问题是温度或 压力循环会导致它们破裂， 会被气体中的含硫分子所毒害 混合物. 为了避免破裂，通常使用金属膜。 制造成大的厚度，这赋予结构 刚度 然而，较大的膜厚度降低了通量 以至于厚膜的使用 经济上没有吸引力。 为了开发具有高通量和选择性的膜， 该研究表明，形成膜，其中金属Pd和 Pd/Ag膜被放置在大孔多孔膜的孔内， 陶瓷基板 两种类型的多孔陶瓷膜 被利用 第一个是一层。多孔氧化铝圆盘 直径在0.2 - 0.7 μ m的范围内。 第二个是两个 由薄（5 μ m）、小孔（5 nm）层组成的层盘 氧化镧改性的γ Al 2 O3层，其顶部厚（1-2 mm），大 孔隙（0.2 - 0.7 μ m）。氧化铝载体 金属将被放置在 在陶瓷载体中通过使用CVD反扩散工艺 其中PdCl 2或PdCl 2和AgBr混合物将扩散 从陶瓷载体的一面通过孔， 将从对面扩散。 当气体相遇时 在膜内的某个地方，还原反应： PdCl2（g）+ H2（g）- Pd（s）+ 2HCl（g） AgBr（g）+ 1/2 H2（g）- Ag（s）+ HBr（g） 将生产金属（或金属合金），将跨越 孔隙的间隙空间并形成气密层。 由陶瓷膜支撑的层应该更多， 耐用且不易受化学侵蚀。

This study attempts to develop a membrane for use in the high temperature separation of hydrogen from a gaseous mixture. For high temperature applications, inorganic membranes are necessary, and palladium and palladium silver alloy metal membranes exhibit the highest selectivity for hydrogen. The problems with these metallic membranes are that temperature or pressure cycles can cause them to crack, and their surfaces can be poisoned by sulfur containing molecules in the gaseous mixture. To avoid cracking, metallic membranes are usually fabricated to large thicknesses which imparts a structural rigidity. However large membrane thicknesses lower the flux to the point where the use of thick membranes becomes economically unattractive. In order to develop a membrane with high flux and selectivity, the study suggests forming membranes in which metallic Pd and Pd/Ag films have been placed inside the pores of a macroporous ceramic substrate. Two types of porous ceramic membranes will be used. The first is a one layer . alumina disk with a pore diameter in the range of .2 - .7 >m. The second is a two layer disk consisting of a thin (5>m), small pore (5 nm) layer lanthana modified y Al2O3 layer atop a thick (1-2 mm), large pore (.2 - .7 >m) . alumina support. The metal will be placed in the ceramic support by using a CVD counterdiffusion process in which PdCl2 or a mixture of PdCl2 and AgBr will diffuse through the pores from one face of the ceramic support and H2 will diffuse from the opposite face. When the gases meet somewhere inside the membrane, the reduction reactions: PdCl2(g) + H2(g) --- Pd(s) + 2HCl(g) AgBr(g) + 1/2 H2(g) --- Ag(s) + HBr(g) will produce the metal (or metal alloy) which will span the interstitial space of the pore and form a gas tight layer. The layers, supported by the ceramic membrane, should be more durable and less susceptible to chemical attack.