Structure and aging characteristics of H2-permselective SiO2-Vycor membranes
Structure and aging characteristics of H2-permselective SiO2-Vycor membranes
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H2选择性渗透SiO2-Vycor膜的结构和老化特性
DOI：
10.1016/0376-7388(94)87034-9
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发表时间：
1994
影响因子：
9.5
通讯作者：
G. Gavalas
中科院分区：
文献类型：
--
作者：
M. Tsapatsis;G. Gavalas
采用常压化学气相沉积（APCVD）法制备了多孔Vycor管中sio2层的氢透选膜。沉积是通过将反应物sicl4和H2O在600 ~ 800℃的温度下通过支撑管孔进行的。采用透射电镜（TEM）、扫描电镜（SEM）和电子能谱（EPMA）对沉积层进行了表征。当沉积物被限制在Vycor衬底的孔隙中时，膜在机械上是稳定的，但当沉积物延伸到多孔基体之外时，热循环引起的应力导致裂纹的形成和扩展。电镜观察发现，在孔表面附近约0.5 μm厚的区域sio2沉积密度最大，在距孔表面约10 μm深的区域sio2沉积密度逐渐降至零。最大沉积密度的薄区域负责过电选择性，因为它基本上阻止了氮和大分子的渗透，而允许大量的氢渗透。根据渗流理论，该区域含有≈10%体积的孔隙，因此具有相对较高的渗透率。高温退火导致沉积材料致密化，氢渗透活化能增加，渗透率相应降低。水蒸气的存在加速了致密化过程。在500℃下，致密膜的H2透过率高达0.1 cm3(STP)/min-atm-cm2， H2/ n2透过率高于500。
Hydrogen-permselective membranes were prepared by atmospheric pressure chemical vapor deposition (APCVD) of SiO2layers in porous Vycor tubes. The deposition was carried out by passing the reactants SiCl4and H2O through the bore of the support tubes at temperatures ranging from 600 to 800°C. The deposit layers were examined by TEM, SEM, and EPMA. When the deposit was confined inside the pores of the Vycor substrate, the membranes were mechanically stable but when it extended substantially outside of the porous matrix the stresses induced by thermal cycling led to crack formation and propagation. Electron microscopy revealed that the SiO2deposit density is maximum in a region ≈0.5 μm thick adjacent to the bore surface and gradually declines to zero within a depth of ≈10 μm from the surface. The thin region of maximum deposit density is responsible for permselectivity, for it essentially blocks the permeation of nitrogen and larger molecules while allowing substantial permeation of hydrogen. This region contains ≈10% by volume trapped voids and as a result has relatively high permeability as suggested by the percolation theory. Annealing at high temperatures causes densification of the deposited material as evidenced by increased activation energy for H2permeation and correspondingly reduced permeance. The presence of H2O vapor accelerates the densification process. The densified membranes had a H2permeance as high as 0.1 cm3(STP)/min-atm-cm2at 500°C and a H2/N2permeance ratio above 500.