The volatilization of molten salt is one of the factors that control the performance of molten carbonate fuel cells (MCFC). Volatilization of molten salt promotes the cross-leakage and corrosion of metallic components. Moreover, pipe blockage is caused by the solidification of volatile matter. Especially, because reforming catalysts filling the anode channel are polluted by molten salt volatile matter in direct internal reforming molten carbonate fuel cells (DIR-MCFC), volatilizing of the molten salt is a weighty subject. However, neither the behaviour nor the volatilization volume of molten salt volatile matter has been elucidated, because molten salt volatile matter that has strong alkalinity cannot be supplied directly to an analyzer, its volatilization volume is small, and the analytical accuracy is poor. Therefore, an attempt was made to elucidate the behaviour of vaporized alkali hydroxide by using a non-contact image measurement technique. The DIR-MCFC electrolyte is generally 62Li(2)CO(3)/38K(2)CO(3). Consideration was given to the DIR-MCFC catalyst pollution mechanism as follows. Molten salt volatile matter is KOH generated as water generated in the cell reacts with the electrolyte. The generated KOH returns to K2CO3 again in high CO2 concentration regions, and catalyst pollution is caused by the adherence of the K2CO3 to the catalyst. Moreover, the K2CO3 particles mutually cohere when the generated water assists bonding and blocks the piping. The present report experimentally evaluates the volatilization volume of KOH, the change from KOH to K2CO3, and the particulate growth of KCO3, using the image measurement technique. In measuring the KOH volatilization volume, K2CO3 is generated as KOH volatilized by heating it in a crucible in an electric furnace reacts with CO2, and is then injected into a reaction tube. The amount of KCO3 is measured by measuring the image of the KCO3 particle with a YAG laser and a CCD camera, thereby obtaining the KOH volatilization volume from the calculation of the stoichiometry of the amount of K2CO3. In order to study the change from KOH to K2CO3, the particulate growth of K2CO3 can be monitored by taking a picture of a K2CO3 particle generated with KOH and CO, for an extended period. As a result, a conglomerate is generated by the mutual adhesion small particles, causing piping blockage. (c) 2005 Elsevier B.V. All rights reserved.