A Basic Study of Developing Refractory Metals for Waste Burner

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High temperature corrosion behaviors of various metals were examined in an atmosphere including HCI by a thermogravimetric apparatus.For pure Fe, the corrosion rate at 700ﾟC in the atmosphere including HCI was higher than that in pure O_2. However, the corrosion rate above 900ﾟC was lower in the atmosphere including HCI in spite of the formation of a volatile FeCl_2. These phenomena were due to the simulaneous progress of oxidation and chlorination of Fe.For pure Cr. the formation of Cr_2O_3 was tremendously accelerated in the temperature region from 750ﾟC to 850ﾟC in the atmosphere including HCI.However, in the other temperature region the corrosion rate was almost the same as that in pure O_2. These were thought to be attributed to the fact that the formation of CrCl_2 playd an important role on the corrosion behavior.For pure Ni, the corrosion proceeded with a decrease in mass of the specimen due to the fotmation of a volatile NiCl_2 at the temperatures from 700ﾟC to 1000ﾟC in the atmosphere including HCl. A thin NiO scale layr was observed on the specimen after the test. The corrosion rate in an 1%HCl atmosphere was higher than in pure O_2. These suggested that the corrosion in the atmosphere including HCI was attributable to both oxidation and chlorination of Ni.For Fe-Cr alloys, the corrosion rate in an 1%HCl atmosphere was decreased with an increase in Cr content. For the alloys containing several percent Cr, however, the corrosion rates were higher than those in pure O_2. It was revealed that elemental Cr was concentrated in the scale around the metal/scale interface. Therefor, such higher oxidation resistance for the Fe-Cr alloys was due to the formation of Cr_2O_3 film at the metal/scale interface.