Test for Electrical Resistance of Ceramics at Elevated Temperatures ASTM D1829

Scope:

ASTM D1829 covers two procedures to determine electrical resistance—insulation resistance and volume resistivity—of ceramic insulating materials at elevated temperatures between 100 and 500 °C. Insulation resistance and volume resistivity can indicate contamination in the insulator and provide data required in designing insulating devices for high temperatures. In electrical systems, insulators provide mechanical support to the components and isolate one conductor from the other, confining the flow of current to wires or other conducting paths. Materials with high resistances are considered to be better insulators.

Volume resistivity is calculated from resistance and dimensional data for designing an insulator for a specific application. Studies have shown that resistivity changes with temperature change. These changes in resistivity must be known when designing for conditions in which the insulator would actually be working in. Volume resistivity is used to check the uniformity of an insulating material, uniformity with regards to processing or to detect conductive impurities that affect the quality of the material.

Test Procedure:

Procedure A is suitable for a single sample over a wide range of temperatures. Whereas, procedure B is suitable for rapid testing of large numbers of samples at a single fixed temperature. Resistance is a measure of the opposition to the flow of the current. The resistance of a ceramic sample at elevated temperature is calculated by measuring the current or voltage at temperatures between 100 to 500°C. If the current drops as the temperature increases, it means that the resistivity is increasing with the increase in temperature but if the current increases, it means the resistivity is decreasing with the increase in temperature. Generally, we want the resistivity to increase or remain the same with the increase in temperature.

 Specimen size:

Most commonly used specimens are in the form of flat plates, tapes, rods, and tubes.

Data:

The change in the resistance of electrical insulating materials with temperature change can be represented by a function of the form:

R = Be_^m/T

Where:
B = proportionality constant.
m = activation constant, and
T = absolute temperature in kelvin (K).