Development of alumina coating on a ceramic monolith

Abstract

The objective of this study is to find the suitable condition for acid surface treatment of ceramic monolith and for coating alumina washcoat on monolith surface. It is found that the appropriate condition for acid surface pretreatment is dipping monolith in 2.5% by weight acetic acid for 2 min. It is also found that the suitable alumina content in washcoat slurry (alumina in 2.5 wt% acetic acid) is 40% by weight. The preferred calcination temperature and holding time in calcination for the washcoated monolith are 500 ํC and 2 hr., respectively. The thermalshock temperature at 600 ํC showed small washcoat grainsize, whereas the thermalshock temperature at 800 ํC showed large washcoat grainsize and some of washcoat grains released from the monolith surface. The results of the abrasive strength of the washcoated monolith showed that the monolith with small washcoat grainsize lost its coated alumina less than the monolith with larger washcoat grainsize. In conclusion, the suitable procedure for preparing the alumina washcoated monolith is dipping the monolith in alumina washcoat slurry for three times, each 2 min., and calcined at 500 ํC for 2 hr.