Sintering schedule and sample geometry effects on the electrical and physical properties of high field varistor materials
Abstract
The sample size scale-up required for the preparation of large (production-size) varistor slugs was found to produce material which did not meet both the electrical and physical property specifications when sintered using the standard schedule. As a result, the effects of sintering schedule variables (heating rate, soak temperature, and soak time) on the electrical and physical properties of high field varistor materials were investigated. One sintering schedule was found to be particularly effective in generating large, thick varistor slugs with reproducible electrical properties within specifications, but the physical characteristics did not meet program goals. Empirical relationships between the electrical and physical properties of sintered high field varistors showed that it was not possible to meet program goals with production-size (greater than or equal to 1.5 inch diameter, 0.6 to 0.7 inch thick) varistor parts. The sample thickness was found to play a significant role in determining the electrical properties of varistors sintered using a standard sintering schedule (732A). Significant decreases in electric field (E) and nonlinearity coefficient (alpha) were noted with corresponding increases in sample thickness. A new sample geometry was identified which produced sintered varistor material meeting both electrical and physical property specifications. Sintered varistor microstructures were evaluated and correlated with the electrical and physical properties.
- Publication:
-
NASA STI/Recon Technical Report N
- Pub Date:
- February 1989
- Bibcode:
- 1989STIN...8925384G
- Keywords:
-
- Electrical Properties;
- Fabrication;
- Geometry;
- Microstructure;
- Porosity;
- Sintering;
- Varistors;
- Bismuth Oxides;
- Cobalt Oxides;
- Manganese Oxides;
- Zinc Oxides;
- Electronics and Electrical Engineering