Abstract
To develop the new electrically heated catalyst supported by anodized alumina layers for preparing high heat-resistance and quickly start-up catalyst systems, we have used a commercial aluminum /NiCrAlloy/ aluminum clad as a raw material and anodized them in oxalic acid then, activating these anodized layers according to the former method for preparation of alumite catalysts. However, the problem is the detachment of alumina layers from Ni-Cr alloy when they were burned at high temperature (650°C and over) and suddenly cooled them down to low temperature, because of the difference in thermal expansion. Therefore, our objective is to develop a way for reducing the difference in thermal expansion rate of anodized alumina layers and Ni-Cr alloy to prevent the detachment of alumina layers from base metal. A preparation method was proposed according to a three-steps procedure involving: pre-heating, anodizing and subdivision of alumina layers. An aluminum clad was calcined at 500°C for forming a diffusion layer of Al, Ni and Cr between aluminum layers and Ni-Cr Alloy. Then, It was anodized into oxalic acid solution to obtain about 50µm of alumina layers. And, the plate was soaked into oxalic acid, then, soaked into deionized water, sequentially; it was calcined at 500°C for 3 h in air. The experimental results showed that the alumina layers have not detached from the base metal even if they were calcined at 1000°C. Moreover, the detachment of alumina layers had not occurred during the electrically heating test at about 800°C for over 5000 times of ON-OFF repeating test. We present herein data concerning the effects of major steps on the detachment of alumina layers from Ni-Cr alloy and results of thermal-shock tests as well as the thermal-electro characters, physical characters of the new electrically heated catalyst support.
