Experimental Determination of Emissivity and Resistivity of Yttria Stabilized Zirconia at High Temperatures

The emissivity and resistivity of yttria stabilized zirconia (YsZ), Y₂O₃-ZrO₂, a ceramic material that has been specially fabricated for use as an electrically powered high temperature air heater are determined for temperatures above 2000 K. Published results of measurements of emissivity and resistivity of yttria, zirconia, and their alloys at temperatures above 2000 K are rare in the technical literature. A survey of literature describing the properties of YsZ, particularly literature concerning the ionic conduction process at high temperatures, is assembled to provide a theoretical basis for the formulation of a temperature and resistivity relationship.

A specialized test apparatus, instrumentation, and control system which acquires data while controlling the YsZ temperature over the range of interest is described. A unique feature of this test apparatus is the use of joule heating of the material itself to produce the high temperature environment for obtaining the measurements. Radiative properties of the test configuration are analyzed and a methodology is established for determining emissivity and temperature. A method for determining electrical power input to the material and its resistivity are derived from an analysis of the heat transfer properties of the YsZ material and test apparatus. Data from a test that was conducted over the range of temperatures from 2000 K to 2300 K is analyzed to provide the final measured values of emissivity and resistivity. The results of this study provide material property data that can be used in the design of a YsZ air heater for aerospace testing applications.