This work reports on the degradation of pure YSZ and YSZ+10 wt% alumina composite electrolytes by exposure to the atmosphere of a heat recovery chamber of an industrial glass furnace at a temperature of around 1300 deg C. Microstructural observations and impedance spectroscopy measurements were used to evaluate the corrosion effects. YSZ samples directly placed in the sidewalls and intimately exposed to the dusts and atmosphere show strong corrosion effects after short periods. These samples present large amounts of a glassy phase in the intergrannular region, containing the same elements as the common batch with inclusion of volatile species from the fuel. At the same time, the average composition of YSZ grains remains almost unchanged.