EFFECT OF CHROMIUM DOPING ON THE CRYSTAL STRUCTURE, ELECTRICAL CONDUCTIVITY AND THERMAL EXPANSION OF MANGANESE COBALT SPINEL OXIDES

摘要

Metallic interconnects have reduced the cost of solid oxide fuel cells, however their oxidation during operation and chromium volatilization can cause serious problems, such as chromium poisoning and cell degradation, so ceramic coatings have been developed as barriers to chromium and oxygen diffusion. Among them, Mn_(1.5)Co_(1.5)O_4 spinel has shown promising performance. To evaluate the long-term stability of the coating the properties of the reaction layer formed between the spinel coating and the Cr_2O_3 scale on the alloy surface need to be characterized. In this work, the crystal structure, electrical conductivity and thermal expansion of several manganese cobalt spinel samples, (Mn,Co)_(3-x)Cr_xO_4 (0≤x≤2) were determined. The crystal structure was determined using x-ray diffraction, electrical conductivity was measured by the 4-probe DC method and thermal expansion was tested from room temperature to 1000 ℃. With increasing Cr content the cubic crystal structure was stabilized, the electrical conductivity decreased and thermal expansion coefficient decreased. The decrease in electrical conductivity indicates that formation of the reaction layer, (Mn,Co)_(3-x)Cr_xO_4, may lead to an increase in electrical resistance of the spinel coating, which will increase the overall cell resistance.