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High temperature fusion behavior of mixtures of ash exhibiting a wide range of melting temperature and additive has been investigated under reducing (CO/CO2) at mospheres. Six additives were used: limestone, two iron ores, red mud, CaO obtained by calcin-ing CaCO3 reagent, and Fe2O3 reagent. Characteristic ash fusion temperatures were measured in an electric furnace in conformity to the JIS M8801 method. A microscope equipped with a high temperature heating stage was also used to perform in-situ observation of the reaction and fu-sion behavior between the ash and the additive. The mixtures, treated in several temperature ranges from 900 V to the fluid temperature, were quenched rapidly and identified by the X-ray diffraction.(1) It was found that fusion behavior of ash-iron are mixtures and ash-imestone mix-tures approximately coincided with that of the ash-reagent mixtures. The minimum value of hemispherical temperature was 100°C to 500DC f-fect of red mud was lower than that of Fe2O3 reagent.(2) Partially fused phases were observed at temperatures 100°C to 200°C below the softening temperature. From X-ray analysis FeO was found to be the principal fluxing element that controls partial ash melting(3) At softening temperature a shift from the local solid-solid reaction mode to the liquid-solid slurry reaction mode was observed. Above the hemispherical temperature volatiles and CO2 gas were released in the form of bubbles and the shape of molten ash was changed into a sphere in a graphite crucible. This melting behavior was observed in all ashes irrespective of the presence of additives.

High temperature behavior of mixtures of ash exhibiting a wide range of melting temperature and CaO additive under both oxidizing (Air) and reducing (CO/CO2) atmospheres has been investigated by RS M 8801 and by X-ray diffraction method.(1) Hemispherical temperature of ash with CaO decreased with the increased addition of CaO until CaO content reached about 30wt% and the minimum value of hemispherical temperature was ranged of 1250 to 1350°C under oxidizing atmospheres. Above 40wt% of CaO, the hemispherical temperature went above that of original ash.(2) The U shaped trend of the hemispherical temperature was also observed under reducing atmospheres. The minimum hemispherical temperature under reducing atmospheres was about loot lower than that under oxidizing atmospheres. The percent of CaO corres-ponding to the minimum hemispherical temperature was as low as 10wt%. All the hemispherical temperatures obtained at about 30wt% addition of CaO are found in a range of 1200 to 1350°C.(3) Depending on CaO content, the principal compounds detected were anorthite, gehle-nite, pseudowolla stonite, and rankinite. The minimum hemispherical temperatures of the mixtures of ash and CaO additive were almost equal to the lowest temperature eutectic points in the Ca0-Al2O3-SiO2 phase diagram.