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Mechanical Strength and Microstructure of Zinc Oxide Varistor Ceramics
Author(s) -
Balzer Beate,
Hagemeister Michael,
Kocher Peter,
Gauckler Ludwig J.
Publication year - 2004
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/j.1151-2916.2004.tb06343.x
Subject(s) - sintering , materials science , microstructure , ceramic , varistor , composite material , fracture toughness , zinc , mechanical strength , flexural strength , grain size , metallurgy , physics , quantum mechanics , voltage
ZnO‐based varistor ceramics were sintered under various conditions to optimize their mechanical strength. For highest strength, the optimum sintering temperature was 1070°C or below. At higher maximum temperature, the strength decreased because of grain coarsening and the increasingly inhomogeneous distribution of secondary phases thereby induced. Fracture typically started from holes associated with hollow or poorly compacted sprayed granules. All series contained the same type of critical flaws, but, depending on the sintering temperature, the fracture toughness changed, which led to different strengths. At sintering temperatures above 1050°C, the density started to decrease slightly because of swelling attributed to the pressure of gas entrapped in closed pores.