不锈钢基材上a-轴取向ZSM-5分子筛涂层的制备及其形成机理

Preparation of a-Oriented ZSM-5Coatings on the Stainless Steel Substrate and Its Mechanism of Formation

采用原位水热法研究了在不锈钢基材上a-轴取向ZSM-5分子筛涂层的形成过程及其机理,讨论了若干因素对分子筛涂层中晶体择优取向性的影响。结果表明,在斜放基材的正面,可得到a-轴取向的ZSM-5分子筛涂层,但反面得不到致密的分子筛涂层;在相同的水热条件下,平放基材表面得到的是晶体无序排列的分子筛涂层,但通过超声波处理后也能得到a-轴取向的分子筛涂层;若在反应液中添加少量乙醇,在平放基材上可直接得到致密的、a-轴取向的ZSM-5分子筛涂层。a-轴取向ZSM-5分子筛涂层是由基材上无定型涂层转变而来,无定型涂层首先转化为b-轴取向的分子筛晶体,然后在这些晶体的(010)晶面上生长出a-轴取向的分子筛晶体,最终形成a-轴取向的分子筛涂层。在平放基材上首先形成的也是a-轴取向的分子筛涂层,但随后被溶液中形成的晶体所覆盖,得到无序排列的分子筛涂层。

The formation process and mechanism of ZSM-5 coating on stainless steel substrate prepared by using in-situ hydrothermal synthesis were studied. The influences of several factors on the preferential orientation of the crystals in the coating were discussed. The results showed that α-oriented ZSM-5 coating was formed on the upward side, while no continuous coating formed on the downward side of stainless steel substrate, when it rested in the autoclave at an angle. Under the same hydrothermal conditions, randomly oriented crystals were formed on the substrate which was positioned horizontally at the bottom of the autoclave, and after ultrasonic washing in deionized water for 20 min, however, some α-oriented crystals also appeared. Continuous α-oriented ZSM-5 coating was successfully obtained on the horizontally positioned substrate, when a reaction mixture with a small amount of ethanol was employed, α-Oriented ZSM-5 coating was shown to be transformed from an amorphous coating on the substrate in two steps, in which b-oriented crystals were first formed from the amorphous coating, followed by the formation of α-oriented crystals on the （010） face of these b-oriented crystals. On the horizontally positioned substrate, α-oriented ZSM-5 coating was also formed first, and then was covered subsequently with randomly oriented crystals which were formed in the solution.