High-Voltage Screening on Titania Ceramics with Differently Finished Surfaces.

Abstract

A screening field at or below which 30% of the titania samples broke electrically was applied to titania ceramics with differently finished surfaces. After high-voltage screening, the survived samples were subjected to three-point bending strength measurement, and the resultant strength distribution was compared to the original distribution. After screening, the Weibull plots of the samples placed rough face down became a convex curve, while plots in the high strength region remained unchanged, indicating that weak samples were selectively eliminated by the high-voltage screening. On the other hand, the apparent screening effect on samples placed with the rough face up was very small. There was a correlation between the mechanical and dielectric strengths, with a correlation coefficient of 0.62 in the former case and 0.3 in the latter case. Surface cracks induced by grinding are thought to act both as fracture origins and as a cause of dielectric breakdown when located on the tensile side. However, surface flaws located on the compression side do not act as fracture origins, but are the starting point of dielectric breakdown.