Air Oxidation of Binary Ni-Dy Alloys at 923-1023K and Lithiation in Molten (0.62Li, 0.38K)_2CO_3at 923K

摘要

In order to decrease the solubility of NiO cathode of molten carbonate fuel cell (MCFC) and develop materials and coatings for separators in the cathode side of MCFC, dysprosium was introduced to modify nickel. In present paper, binary Ni-Dy alloys containing 1, 3 and 5 mass percent Dy respectively were prepared. The alloys are two-phase composed of a nickel solid solution and an intermetallic phase Ni_(17)Dy_2. The oxidation behavior of the alloys at 923-1023K in air was evaluated by thermogravimetric tests coupled with some physical analysis techniques. The samples pre-oxidized at 923K for 100h were then immersed in molten (0.62Li, 0.38K)_2CO_3 at 923K to examine the effect of Dy on the lithiation of NiO in the melt. The results indicated that the addition of dysprosium to nickel increased its oxidation rate, except for Ni-1Dy at 1023K. The scales formed on the alloys were composed of NiO with a trace of Dy_2O_3. The lithiation of NiO in molten (Li, K)_2O_3 could be favored by the addition of dysprosium. For comparison, binary Ni-Y alloys were also examined. The effect of yttrium on the air oxidation and molten (Li,K)_2O_3 corrosion of nickel was similar to dysprosium, except that the Y-containing precipitates in Ni-Y alloys underwent very fast preferential corrosion while the Dy-containing intermetallic phases in Ni-Dy alloys not.